Alcatel BSS System Description

Alcatel BSS

BSS System Description

Descriptive Documentation

BSS Concepts

3BK 20572 AAAA TQZZA Ed.04

Status RELEASED

Short title System Description

All rights reserved. Passing on and copying of this document, useand communication of its contents not permitted without writtenauthorization from Alcatel/Evolium.

BLANK PAGE BREAK

2 / 250 3BK 20572 AAAA TQZZA Ed.04

Contents

Contents

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141.2 BSS Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

1.2.1 Call Set Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161.2.2 Call Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171.2.3 Call Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171.2.4 Operations & Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

1.3 BSS Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181.3.1 Base Station Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181.3.2 Base Transceiver Station . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191.3.3 Transcoder And Transmission Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221.3.4 The Multi-BSS Fast Packet Server . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231.3.5 Multi-GPU per BSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

1.4 Extended GSM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261.5 External Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

1.5.1 Network Subsystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291.5.2 Mobile Stations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301.5.3 Phase 2 Mobile Support in a Phase 1 Infrastructure . . . . . . . . . . . . . . . . . . . . . . . 331.5.4 Operations and Maintenance Center-Radio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

1.6 Network Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341.6.1 Telecommunications Management Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341.6.2 Q3 Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

1.7 BSS Telecommunications Layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361.7.1 Call Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361.7.2 Mobility Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361.7.3 Radio Resource Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371.7.4 The A Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381.7.5 The Abis Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391.7.6 Satellite Links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391.7.7 The Air Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

2 GPRS in the BSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 472.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

2.1.1 Packet Switching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482.1.2 GPRS Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

2.2 GPRS Channels and System Information Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 522.2.1 Master Channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 522.2.2 Static Allocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 522.2.3 Dynamic Allocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532.2.4 Multiple PCCCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 542.2.5 Logical Channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 562.2.6 Virtual Channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 562.2.7 System Information Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

2.3 GPRS Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 592.3.1 The Gb Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 592.3.2 The BSCGP Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 602.3.3 The GCH Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

2.4 GPRS Network Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 622.4.1 Mobility Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 632.4.2 Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 642.4.3 Radio Power Control and Radio Link Measurement . . . . . . . . . . . . . . . . . . . . . . . . 64

2.5 Resource Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 652.5.1 Time Slot Allocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

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2.5.2 Frequency Hopping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 662.5.3 PCM Link Sharing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 662.5.4 Resource Reallocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

2.6 Traffic Load Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 682.6.1 Congestion Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 692.6.2 Smooth PDCH Traffic Adaption to Cell Load Variation . . . . . . . . . . . . . . . . . . . . . . 702.6.3 GPRS Overload Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702.6.4 Delayed Downlink TBF Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

2.7 Data Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 722.7.1 GPRS Attach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 722.7.2 Packet Data Protocol Context Activation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 742.7.3 Data Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 762.7.4 Packet Data Protocol Context De-activation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 782.7.5 GPRS Suspend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 812.7.6 GPRS Resume . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 822.7.7 GPRS Detach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

3 Call Set Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

3.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 883.2 Mobile Originated Call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

3.2.1 Radio and Link Establishment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 903.2.2 Authentication and Ciphering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 963.2.3 Normal Assignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

3.3 Mobile Terminated Call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1023.3.1 Radio and Link Establishment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1033.3.2 Authentication and Ciphering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1033.3.3 Normal Assignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1043.3.4 IMSI Attach-Detach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

3.4 Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1063.4.1 Paging Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1083.4.2 Discontinuous Reception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

3.5 Congestion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1113.5.1 Queueing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1113.5.2 In-queue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1123.5.3 Pre-emption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

3.6 Classmark Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1173.6.1 Classmark IE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1173.6.2 Classmark Updating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1193.6.3 Location Updating with Classmark Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120

3.7 Authentication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1223.8 Ciphering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

3.8.1 Ciphering Keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1253.8.2 Ciphering Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

3.9 Tandem Free Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1283.9.1 TFO Functional Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1303.9.2 TFO Optimization and Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

4 Call Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1334.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1344.2 In-Call Modification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134

4.2.1 In-Call Modification Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1354.2.2 Circuit-switched Group 3 Fax Data Rate Change . . . . . . . . . . . . . . . . . . . . . . . . . 1364.2.3 Error Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136

4.3 Frequency Hopping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1374.3.1 Baseband Frequency Hopping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1384.3.2 Synthesized Frequency Hopping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139

4.4 Discontinuous Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1404.4.1 Speech Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140

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4.4.2 BSS Discontinuous Transmission Towards Mobile Station . . . . . . . . . . . . . . . . . 1414.4.3 Mobile Station Discontinuous Transmission Towards BSS . . . . . . . . . . . . . . . . . 142

4.5 Radio Power Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1444.5.1 BTS Radio Power Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1444.5.2 Mobile Station Radio Power Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1444.5.3 Radio Link Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1454.5.4 Power Control Decision and Handover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1464.5.5 Change Power Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148

4.6 Handover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1494.6.1 Radio Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1514.6.2 Handover Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1524.6.3 Target Cell Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1594.6.4 Synchronous and Asynchronous Handover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160

4.7 Overload Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1674.7.1 BTS Overload . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1674.7.2 BSC Overload . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168

4.8 Call Re-establishment by the Mobile Station . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170

5 Call Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1715.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1725.2 Call Release Procedures in Normal Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173

5.2.1 Normal Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1735.2.2 Calls Terminated Following a Channel Change . . . . . . . . . . . . . . . . . . . . . . . . . . . 178

5.3 Call Release - Special Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1795.3.1 Call Release Following Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1795.3.2 BSC-Initiated Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1805.3.3 BSC-Initiated SCCP Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1825.3.4 BTS-Initiated Call Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1835.3.5 Mobile Station-Initiated Call Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1855.3.6 Remote Transcoder Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186

6 Handling User Traffic Across the BSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1876.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1886.2 Speech . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188

6.2.1 Enhanced Full-Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1906.2.2 Half-Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1916.2.3 Adaptive Multiple Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1926.2.4 Channel Mode Adaption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194

6.3 Circuit-Switched Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1956.3.1 Transparent Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1966.3.2 Non-Transparent Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197

6.4 Short Message Service - Cell Broadcast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1986.5 Support of Localized Service Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2006.6 PLMNs Interworking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200

7 Cell Environments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2037.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2047.2 Concentric Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2067.3 Sectored Site . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2077.4 Extended Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2087.5 Umbrella Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210

7.5.1 Mini Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2107.5.2 Microcell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211

7.6 Cell Shared by Two BTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215

8 Operations & Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2178.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2188.2 O&M Architecture and Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218

8.2.1 O&M Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219

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8.2.2 O&M Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2208.3 O&M Control - The OMC-R . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221

8.3.1 Multiple Human-Machine Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2228.3.2 ACO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2238.3.3 Secured X.25 Connection From BSC to OMC-R . . . . . . . . . . . . . . . . . . . . . . . . . . 2248.3.4 Electronic Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226

8.4 Configuration Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2278.4.1 Hardware Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2288.4.2 Logical Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2288.4.3 Software Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2288.4.4 Auto Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2298.4.5 OML Auto-detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2308.4.6 NE Provisioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231

8.5 Fault Management - Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2328.5.1 Alarm Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2348.5.2 Alarm Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2348.5.3 BSC Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2358.5.4 BTS Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2388.5.5 Alarms Detected by the TSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2408.5.6 MFS Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2408.5.7 Recovery Example: Carrier Unit Failures with BCCH . . . . . . . . . . . . . . . . . . . . . . 2418.5.8 Automatic Power-Down . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2438.5.9 BSC Alerter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243

8.6 Performance Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2448.6.1 Traces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2448.6.2 Performance Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2458.6.3 Radio Measurements Statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2468.6.4 Results Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247

8.7 Audits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2488.8 Remote Inventory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250

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Figures

FiguresFigure 1: BSS in the PLMN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Figure 2: Antenna Diversity on G1 and G2 BTSs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Figure 3: Antenna Diversity on the BTS A9100 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Figure 4: Transmission Components in the BSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Figure 5: Cell Mapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Figure 6: Logical Position of External Components Associated with BSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Figure 7: Location Update . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Figure 8: TMN System Hierarchy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Figure 9: General Telecommunication Layers within GSM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Figure 10: BSS Application, Transmission Layers and Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Figure 11: Time Slot 4 of a Time Division Multiple Access Frame Supporting Access Grant Channels . . . 41

Figure 12: Model LLC Packet Data Unit used in GPRS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Figure 13: The Alcatel GPRS solution in the PLMN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Figure 14: GPRS Traffic Load Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

Figure 15: GPRS Attach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

Figure 16: Mobile Station-Originating Packet Data Protocol Context Activation . . . . . . . . . . . . . . . . . . . . . . . . 74

Figure 17: GGSN-Originating Packet Data Protocol Context Activation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

Figure 18: Mobile-Originated Data Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

Figure 19: Mobile-Terminated Data Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

Figure 20: Mobile Station Originating Packet Data Protocol Context De-activation . . . . . . . . . . . . . . . . . . . . . 78

Figure 21: Network-Originating Packet Data Protocol Context De-activation Processes . . . . . . . . . . . . . . . . 79

Figure 22: GPRS Suspend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

Figure 23: GPRS Resume . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

Figure 24: Mobile Station-Originating GPRS Detach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

Figure 25: Network-Originating GPRS Detach Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

Figure 26: Radio and Link Establishment for Mobile Originated Call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

Figure 27: SDCCH Channel Activation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

Figure 28: Immediate Assignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

Figure 29: Connection for Mobile Originated Call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

Figure 30: Normal Assignment for Mobile Originated Call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

Figure 31: Channel Activation Process for the Traffic Channel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

Figure 32: Channel Assignment Process for the Traffic Channel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

Figure 33: Call Connection for Mobile Originated Call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

Figure 34: Radio and Link Establishment for Mobile Terminated Call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

Figure 35: Normal Assignment for Mobile Terminated Call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

Figure 36: CCCH with Three Blocks Reserved for AGCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

Figure 37: Four TDMA Frame Cycles Providing 24 Paging Sub-channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

Figure 38: Paging Message Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

Figure 39: Location Update with Classmark Update . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120

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Figures

Figure 40: Location Update with Mobile Station Sending Location Area Identity of Previous VLR . . . . . . . 122

Figure 41: Ciphering Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

Figure 42: Example of TFO Establishment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

Figure 43: Frequency Hopping within an FHS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138

Figure 44: Different Forms of Discontinuous Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143

Figure 45: Power Control Flow of Measurement and Decision Action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146

Figure 46: Power Output Balancing Based on Received Quality and Signal Levels . . . . . . . . . . . . . . . . . . . . 147

Figure 47: Quality and Level Handover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

Figure 48: Better Zone Handover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154

Figure 49: Better Cell Handover (Power Budget) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155

Figure 50: Distance Handover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156

Figure 51: Umbrella Cell Load in Mobile Velocity Dependent Handover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157

Figure 52: Synchronous Internal Handover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161

Figure 53: Asynchronous External Handover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164

Figure 54: Mobile Station Disconnecting a Call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173

Figure 55: Normal Call Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174

Figure 56: Initiation of Normal Release by MSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

Figure 57: BSC/BTS/Mobile Station interactions in Normal Call Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176

Figure 58: Normal Release Final Steps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177

Figure 59: Call Release Following a Channel Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178

Figure 60: Call Release Following Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180

Figure 61: BSC-initiated Call Release toward the MSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181

Figure 62: BTS-initiated Call Release following LAPD failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184

Figure 63: Call Release due to Mobile Station initiated Radio Link Failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185

Figure 64: Call Release due to Communication Failure detected by Transcoder . . . . . . . . . . . . . . . . . . . . . . 186

Figure 65: Encoded Speech Transmission Across the BSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188

Figure 66: Multiplexed Ater Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189

Figure 67: Data Transmission Across the BSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195

Figure 68: Short Message Service - Cell Broadcast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198

Figure 69: Example: Cell Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205

Figure 70: Sectored site configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207

Figure 71: Example of Extended Cell Topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208

Figure 72: Umbrella Cell with Mini Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210

Figure 73: Example: Handovers due to Threshold Triggering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212

Figure 74: Indoor cell example network hierarchy with three layers and two bands . . . . . . . . . . . . . . . . . . . . 213

Figure 75: Multiple HMI Access to OMC-Rs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222

Figure 76: ACO Links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223

Figure 77: X.25 Without Redundancy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224

Figure 78: X.25 With Redundancy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225

Figure 79: RSL Correlation on the Abis Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236

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Figures

Figure 80: Example: Alarm Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237

Figure 81: Example: Loss of Carrier Unit Holding BCCH. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242

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Tables

TablesTable 1: System Information Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Table 2: GPRS System Information Message . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Table 3: GPRS System Information Messages Used with MPDCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Table 4: Gb Interface Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Table 5: BSCGP Interface Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

Table 6: Network Operation Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

Table 7: Time Slot Allocation Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

Table 8: PDCH Traffic Load States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

Table 9: Types of Calls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

Table 10: Call Set Up Phases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

Table 11: Cell List Identifier and Paging Performed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

Table 12: Paging Request Message and Mobile Station Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

Table 13: Classmark Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

Table 14: Classmark Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

Table 15: Mobile Station Ciphering Capabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

Table 16: Downlink Discontinuous Transmission Status in Channel_activation . . . . . . . . . . . . . . . . . . . . . . . . 141

Table 17: Operator Discontinuous Transmission Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142

Table 18: Radio Link Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

Table 19: Mobile Station Maximum and Minimum Power Ranges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148

Table 20: Circuit-Switched Data Rate Conversions Across the Air Interface . . . . . . . . . . . . . . . . . . . . . . . . . . 196

Table 21: Configuration Management Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227

Table 22: Fault Management Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233

Table 23: BTS Alarm Hardware Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238

Table 24: BTS Alarms Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238

Table 25: Performance Management Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244

Table 26: Audit Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248

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Preface

Preface

Purpose This document provides detailed descriptions of the functions and featuresof the Alcatel BSS. Some functions and features may not be available onthe system installed at your location.

The technical information in this document covers:

Mobile Communications SupportThese areas describe how the BSS handles communications between amobile station and the NSS. It follows a call through the Alcatel BSS, anddescribes how each element in the system functions individually and withother elements. This shows how the BSS and its units react as a system.

Operations and MaintenanceThese areas describe the O&M functions within the system. It describesboth local and distributed O&M functions in a BSS.

Audience This manual is for people requiring an in-depth understanding of the functionsof the Alcatel BSS:

Network decision makers who require an understanding of the underlyingfunctions of the system, including:

Network planners

Technical design staff

Trainers.

Operations and support staff who need to know how the system operates innormal conditions, including:

Operators

Support engineers

Maintenance staff

Client Help Desk personnel.

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Preface

Assumed Knowledge The document assumes that the reader has an understanding of:

GSM

GPRS

Mobile Telecommunications

Network Management concepts and terminology.

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1 Introduction

1 Introduction

This chapter gives a brief overview of the Alcatel BSS, its functions andfeatures. It describes:

Overview

BSS functions

Internal and external components and interfaces

BSS Network Management

The distribution of telecommunications software in the BSS.

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1 Introduction

1.1 OverviewThe BSS provides radio coverage for GSM subscribers in a defined area. Itsprincipal role is to provide and support signalling and traffic channels betweenmobile stations and the NSS.

The following figure shows the BSS within the PLMN, and its links to the PSTNand the PSDN in a fixed network.

Base Station Subsystem

Mobile Stations

NetworkSubsystem

FixedNetwork

PLMN

OMC−R

NMC

MFS

BTS

SGSN

MSC PSTN

TC

BSC

PSDN

GGSN : Gateway GRPS Support Node

HLR : Home Location Register

MFS : Multi-BSS Fast Packet Server

NMC : Network Management Center

PSDN : Packet Switched Data Network

PSTN : Public Switched Telephone Network

SGSN : Serving GRPS Support Node

Figure 1: BSS in the PLMN

EVOLIUM™ RadioSolutions

To respond to the swiftly evolving needs in BSSs, Alcatel offers the EVOLIUM™Radio Solutions.

The Alcatel EVOLIUM™ Radio Solutions includes the following BSS equipmentdescribed in this document:

G2 BSC

G2 Transcoder

G2.5 Transcoder

BTS A9100

BTS A910

A935 MFS.

Note: BTS G1 and BTS G2 are still supported by EVOLIUM.

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1 Introduction

Extended GSM Band(E-GSM)

The Alcatel BSS supports the E-GSM band. E-GSM consists of:

The 900 MHz primary band, called the P-GSM band. This uses 890-915

MHz for uplink, and 935-960 MHz for downlink.

The 900 MHz extended band, called the G1 band. This uses 880-890 MHzfor uplink, and 925-935 MHz for downlink.

This corresponds to a total number of 174 addressable frequencies.

GSM 850 The GSM 850 MHz band has been introduced in the Release 1999 of the 3GPPStandard in 1999 to allow operators to replace progressively the D-AMPS andCDMA technologies that were using these frequencies. Besides certain Asiancountries, the GSM 850 MHz band concerns in particular the Latin Americancountries where many operators already use in their network the GSM systemwith the GSM 1900 MHz to extend or replace their D-AMPS existing network.The term GSM 850 is used for any GSM system which operates in 824 MHz to849 MHz band for the uplink direction and in the 869 MHz to 894 MHz band forthe downlink direction. The GSM 850 band is defined by 124 absolute radiofrequency channel numbers (ARFCN) among the 1024 ARFCNs available inthe GSM standard.

Frequency BandConfigurations

The Alcatel BSS supports the following multiband network configurations:

BSS with a mix of GSM 850 and GSM 1900 cells

BSS with a mix of GSM 850 and GSM 1800 cells

BSS with a mix of GSM 900 and GSM 1800 cells.

Refer also to Basic GSM System Specifications.

GPRS GPRS, the solution chosen by European Telecommunication StandardsInstitute to answer the demand for increased data transmission rates, is nowavailable in the Alcatel BSS. This means there are now two parallel systemsin the PLMN: circuit-switched transmission for voice, and packet-switchedtransmission for data. For information on how GPRS functions within the BSS,see GPRS in the BSS (Chapter 2).

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1 Introduction

1.2 BSS FunctionsFunctions are defined by the International Telecommunications Union andEuropean Telecommunication Standards Institute recommendations.

This section describes the BSS functions with a system-wide view; that is, howthe BSS functions work together within the system. Network elements andfunctional units are indicated where applicable, but are not described. For moreinformation, refer to the specific network element description manuals, suchas the BTS Functional Description.

The BSS provides signalling and traffic channels between the mobile stationand the NSS. To ensure a high level of service to the subscribers, the BSSoffers the following functions:

Call Set Up

Call Handling

Call Release

Operations & Maintenance.

1.2.1 Call Set Up

The Call Setup function is used for speech and data calls. The three basictypes of call are:

Mobility Management

Supplementary service

User traffic.

Mobility ManagementCalls

Mobility Management calls, such as location update, are used by the systemto gather mobile station information. The exchanges are protocol messagesonly. Therefore, only a signalling channel is used.

Supplementary ServiceCalls

Supplementary service calls, such as SMS, allows the mobile station to sendand receive messages to and from the BTS. These calls pass small amounts ofinformation. Therefore, only a signalling channel is used.

User Traffic Calls User traffic calls, such as speech or data calls to a correspondent, can passlarge amounts of information. Therefore, they require greater bandwidth than asignalling channel. These calls use traffic channels.

Call set up processes include:

Radio and Link Establishment to assign a signalling channel betweenthe mobile station and the NSS

Classmark handling to manage different mobile station power and ciphering

capabilities

Ciphering to ensure data security on the Air Interface

The normal assignment process to assign a traffic channel between the

mobile station and the NSS.

See Call Set Up (Chapter 3) for more information.

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1 Introduction

1.2.2 Call Handling

The call handling function is used to supervise and maintain calls which arein progress. Call handling involves:

In-call channel modification during a call

Maintenance of call integrity and quality through features such as Frequency

Hopping, Discontinuous Transmission or Radio Power Control

Handover to change channels when a mobile station moves from onecell to another

Handover when the quality of the current channel drops below an acceptable

level

Ciphering to ensure data security on the Air Interface

Overload control to manage the call load on the system.

See Call Handling (Chapter 4) for more information.

1.2.3 Call Release

The call release function ensures that resources allocated to a call are free forreuse when they are no longer required by the current call.

Specifically the Call Release function includes:

Call Release in normal service:

Calls terminated by call management

Calls terminated following a channel change.

Special Cases:

Call release following a reset

BSC-initiated release

BTS-initiated release

Mobile station-initiated release.

See Call Release (Chapter 5) for more information.

1.2.4 Operations & Maintenance

O&M provides the operator interface for the management and control of theBSS, and its interconnection to the NSS. O&M is divided into three principalareas:

Configuration Management

Fault Management

Performance Management.

See Operations & Maintenance (Chapter 8) for more information.

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1 Introduction

1.3 BSS ComponentsThere are three main units in the BSS:

The BTS, which provides the radio transmission and reception functions

for a cell

The BSC, which acts as the controller of the BSS. The BSC providescontrol of the BTSs and their resources, and performs switching functions

within the BSS

The Transcoder, which performs rate adaptation and encoding/decoding ofspeech and data between the MSC and the BSC.

The BSS shown in Figure 1 is supervised by the OMC-R. In a large network,one or more high-level supervisors, such as NMCs, can exist to centralizenetwork management activities. The NMC has the authority to send directivesto the OMC-R.

For more information about the NMC, refer to documentation supplied withthe NMC.

1.3.1 Base Station Controller

The BSC provides control of the BTSs and manages radio resources and radioparameters. From a transmission point of view, the BSC also performs aconcentration function if more radio traffic channels than terrestrial channels areconnected to the MSC. A single BSC can control a large number of BTSs. Theexact number is a function of the BSC equipment and the configurations used.

The BSC provides:

Resource management

Database management

Radio measurement processing

Channel management

Operations and maintenance functions within the BSS

Communication with the OMC-R

Switching between the Air Interface channels (and their associated Abis

channels), and the A Interface channels. Further information concerningthese interfaces can be found in The A Interface (Section 1.7.4), The AbisInterface (Section 1.7.5) and The Air Interface (Section 1.7.7).

The BSC also incorporates the following transmission equipment:

The Base Station Interface Equipment, which performs signalling andsubmultiplexing on the Abis Interface

The Transcoder Submultiplexer Controller, which collects and processes

transmission data. It also provides an operator interface to certaintransmission functions via a Local Maintenance Terminal.

For a more detailed description of the BSC, refer to the EVOLIUM BSC/TCOverall Description document.

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1 Introduction

1.3.2 Base Transceiver Station

The BTS provides radio transmission, control and baseband functions for acell. The BTS also supports the Air Interface with the mobile stations. Alcatelfurnishes two families of BTS:

BTS G1 or G2 (includes Micro-BTS M1M and M2M)

BTS A9100 or BTS A910.

These families of BTS have different architectures, and are not functionallyidentical, (e.g. only the BTS A9100 or BTS A910 can support GPRS).

The BTS performs the following functions under the control of the BSC:

Transmit and receive functions

Antenna diversity

Frequency hopping

Radio channel measurements

Radio frequency testing.

The BTS also includes BIEs which enable it to communicate with the BSC overthe Abis interface. In the BTS A9100 and BTS A910, the BIE is integratedinto the SUM.

For a more detailed description of the BTS, refer to the BTS FunctionalDescription or the EVOLIUM BTS A9100/A910 Functional Descriptiondocuments.

1.3.2.1 Antenna DiversityAntenna Diversity is a BTS feature that protects against multipath fading. Thisis achieved by duplicating the receive antenna and receive path up to the FrameUnit of the BTS (or the TRE for a BTS A9100 or BTS A910). The Frame Unit(or TRE) uses the data burst which has the fewest errors. This increases thelow-power mobile station range, thereby allowing larger cells.

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1 Introduction

1.3.2.2 G1 and G2 BTS Antenna DiversityAntenna diversity on G1 and G2 BTSs duplicates the receive antenna andreceive path up to the Frame Unit. The Frame Unit uses the data burst whichhas the fewest errors. This increases low-power mobile station range, thusallowing larger cells and lowering infrastructure investment.

The following figure shows the antenna diversity path through the G1 andG2 BTS.

BASEBANDCONTROL

CONTROL

BASEBAND RADIO COUPLING

OMU

BIE

FHU

OTHER ANTENNAS

TX

CUFU

aaa

b bb

abbest of a&b

COUPLING

UNIT

aRX

RX

(option)b

BIE : Base Station Interface Equipment

CU : Carrier Unit

FHU : Frequency Hopping Unit

FU : Frame Unit

OMU : Operations and Maintenance Unit

RX : Receiver

TX : Transmitter

Figure 2: Antenna Diversity on G1 and G2 BTSs

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1 Introduction

1.3.2.3 BTS A9100/A910 Antenna DiversityAntenna diversity on the BTS A9100 or BTS A910 follows the same principle asin the G1 and G2 BTSs. The antennas are used for both transmit and receive,and the receive path is duplicated up to the TRE, providing the same gain inefficiency and low-power mobile station range.

The following figure shows the antenna diversity path through the BTS A9100.

TRE 1

TRE 2

TRE 3

TRE 4

BASEBAND

CONTROL

RADIO

SUM

ANy ANx

RADIO

COMBINING DUPLEXING

ANT a

ANT b

ab

Tx / Rx

Tx / Rx

b

b

b

a

a

a

best of a&b

best of a&b

best of a&b

best of a&b

b

a

b

a

b

a

b

a

ab

ab

ab

ab

BASEBAND

ANC

ANT : Antenna

ANx : Antenna Network Type x

ANy : Antenna Network Type y

SUM : Station Unit Module

TRE : Transmitter/Receiver Equipment

Figure 3: Antenna Diversity on the BTS A9100

Note: The configuration shown above (1 Sector, 3X4 Transceivers) is one exampleonly. Other combinations of Antennas and TREs are possible. There is noantenna network y in the BTS A910, and the antenna network y is not needed ifthe sector has two TREs.

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1 Introduction

1.3.3 Transcoder And Transmission Function

The Transcoder is the key component for the transmission function, whichprovides efficient use of the terrestrial links between the equipment of the BSS.

The Transcoder provides:

Conversion between A-law and Radio Test Equipment-Long Term Predictionencoded traffic (speech)

Conversion between A-law and Algebraic Code Excited Linear Prediction

encoded traffic (speech)

Rate adaptation (data)

O&M control of the transmission function.

The Transcoder is normally located next to the MSC.

Submultiplexers The Submultiplexer performs submultiplexing on the Ater Interface, betweenthe MSC and the BSC. When submultiplexing is used, a Submultiplexer islocated at each end of the link.

The following figure shows how transmission components are distributed inthe BSS.

BTS BSC

MSC

BSC

TC

TCBTS

BTSTSC

BIE

BIE

BIE SM SM

TSC

BIE

OMC−R


SM : Submultiplexer

TSC : Transcoder Submultiplexer Controller

TC : Transcoder

Figure 4: Transmission Components in the BSS

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1 Introduction

1.3.4 The Multi-BSS Fast Packet Server

The MFS is preferably located at the Transcoder/MSC site. It is internal to theBSS and provides the following functions:

PCU functions:

PAD function

Scheduling of packet data channels

Automatic Retransmission Request functions

Channel access control functions

Radio channel management functions.

The Gb interface protocol stack.

The MFS converts GPRS frames, carried on multiple 16 kb/s links from multipleBTSs, to one or more frame relay channels connected to the SGSN on the Gbinterface. See The Gb Interface (Section 2.3.1) for details of the Gb interface.

The set-up of Packet Data Channels is controlled by the MFS. It also negotiatesresources with the BSC and routes GPRS packets. When an additional channelis required on a BTS, the MFS asks the BSC to allocate a channel and toconnect it to an Ater channel which the MFS controls.

The Alcatel solution also supplies two dedicated GPRS interfaces between theMFS and the BSS:

The BSCGP interface supplies routing of GPRS messages and resource

negotiation between the BSC and the MFS

The GCH interface routes user data traffic and signaling between the MFS

and the BTS transparently (to the BSC).

Hardware and software management of the MFS is provided using the IMT.

The MFS is divided in GPRS processing units (GPU) which are inter-connectedvia an Ethernet bus and controlled a control station. The GPU handles theO&M and telecom functions of several cells, but a cell cannot be sharedbetween several GPUs.

A GPU cannot be connected to more than one BSC, which means that eachGPU cannot manage simultaneously several BSSs. However, the use of severalGPUs per BSS is required for traffic capacity reasons. The MFS is in charge ofassociating each cell to a GPU. This later operation is called GPU cell mapping.

The GPU is in charge of:

O&M functions:

Initialization of the MFS

Software download

Software configuration

Performance monitoring.

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1 Introduction

Telecom functions:

Radio and transmission resources control

Radiolink control of packet connections

Common control channels management

MS radio resource control

Logical Link Control (LLC)

Protocol Data Unit (PDU) transfer

Multiframe management

Congestion control

Gb interface management

Signalling management on the GSL interface.

The GPU is split into two sub-units, the Packet Management Unit (PMU)and the Packet Traffic Unit (PTU).

The protocols handled by a GPU are split in the following manner:

Protocols handled by the PTU:

Radio interface protocols (RLC and MAC)

GCH interface protocols (L2-GCH and L1-GCH).

The PTU manages the corresponding GCH interface (see The GCHInterface (Section 2.3.3) for more information).

Protocols handled by the PMU:

Gb interface protocols (BSSGP, Network Service, and FR)

BSC interface protocols (BSCGP, L2-GSL, and L1-GSL)

RRM protocol.

The PMU manages the corresponding Gb and GSL interfaces.

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1.3.5 Multi-GPU per BSS

To increase the GPRS capacity of the BSS in terms of number of PDCH,several GPU boards can be connected to the BSC to support the PCU function.This feature is applied regardless of the BTS type. Four GPU boards canbe connected in each BSC.

Cell Mapping Mapping a cell means that a cell is associated to a GPU. Remapping a cellmeans that a cell, already linked to a GPU, is moved to another GPU. Themapping of cells onto GPUs is performed by the MFS, which actually definesthe mapping of cells onto LXPUs (logical GPU). An LXPU is either the primaryGPU, or the spare GPU in the case of switch-over. All the GPRS traffic of onecell is handled by only one GPU. The following figure shows an example ofcell mapping.

MFS

GPU1

GPU2

GPU3

GPU4

BSC

Cell 1

Cell 2Cell 4

Cell 3

Cell 8

Cell 9Cell 12

Cell 11

Cell 5

Cell 6

Cell 7

Cell 14

Cell 13

Cell 10

GPU : GPRS Processing Unit

Figure 5: Cell Mapping

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1.4 Extended GSMTwo 10 MHz extended bands for GSM 900 in the range 880-890 MHz/925-935MHz have been specified as an option on a national basis. The reason forthis is mainly due to the lack of primary band frequencies in countries outsideEurope. The term “G1” is used for the extended band. The term “P-GSM” isused for the primary band. The term “E-GSM” is used for the whole GSM-900frequency band, i.e. the primary band (890-915 MHz/935-960 MHz) plusthe extended band (880-890 MHz/925-935 MHz). This corresponds to 174addressable carrier frequencies and leads to an increase of 40% against the124 frequencies in the primary band.

All BCCH frequencies and SDCCH channels are entirely supported on theGSM primary band. This allows for the support of both primary and extendedband mobiles in the same network.

E-GSM Mobile StationRecognition

From messages sent by the mobile station, the BSS determines if a mobilesupports the E-GSM band.

The mobile station is determined to be E-GSM if:

The FC bit of the Classmark 2 is set to 1 (regardless of the value of theBand 2 bit of the Classmark 3) or

The FC bit of the Classmark 2 is set to 0, and the Band 2 bit of the

Classmark 3 is set to 1.

If the information is not available, the mobile station is considered as notsupporting the G1 band. The BSS never triggers a Classmark Interrogationprocedure to obtain the E-GSM ability of a mobile station.

E-GSM ManagementAfter Initial

Determination

Once the E-GSM ability has been initially determined as described above, itmay happen that the mobile station radio characteristics change during atransaction. If the BSC receives a classmark change message, it takes thisinto account and updates the E-GSM ability according to the content of thereceived message.

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E-GSM Determinationat Handover

In the case of internal handover, the E-GSM ability of a mobile station isstored in the BSC memory. In the case of external incoming Handover, thehandover request message includes either Classmark 1 or Classmark 2 IE,and optionally Classmark 3 IE. If Classmark 1 is present and Classmark 3 isnot present or Classmark 3 is present but does not contain the Band 2 bit,the mobile station is not considered as E-GSM. If both Classmark 1 andClassmark 3 are present, and Classmark 3 contains the Band 2 bit, the BSCgets the E-GSM ability of the mobile station from the Classmark 3. If Classmark2 is present and Classmark 3 is not present, or Classmark 3 is present butdoes not contain the Band 2 bit, the BSC gets the E-GSM ability of the mobilestation from the Classmark 2 ("FC" bit). If both Classmark 2 and Classmark 3are present, the mobile station is seen as E-GSM:

If the FC bit of the Classmark 2 is set to 1 (whatever the value of the band

2 bit of the Classmark 3)

If the FC bit of the Classmark 2 is set to 0 and the band 2 bit of theClassmark 3 is set to 1.

After an incoming external handover, if a classmark change message hasbeen received from the mobile station, the BSC ignores any subsequentclassmark update message received from the MSC.

TCH Allocation The allocation of G1 band channels can be done for Normal Assignment(NASS), Internal Channel Change (ICC), or External Channel Change (ECC).Each TRE has the capability to support the P-GSM or the E-GSM band. EachTRX is configured as a P-GSM TRX or a G1 TRX. When a TCH is needed, if itis for an E-GSM mobile station then a TCH belonging to the G1 TRX subsetis preferably chosen. If no resource is available in the G1 TRX subset, themobile station is allocated to the P-GSM TRX subset.

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1.5 External ComponentsThe BSS communicates with three external components:

The NSS on the A Interface

The mobile station on the Air Interface

The OMC-R on the BSS/OMC-R Interface.

The following figure shows the logical position of the External Components.

Base Station Subsystem

MobileStations

NetworkSubsystem

FixedNetwork

PLMN

OMC−R

NMC

MFS

MSCTranscoder

PSDN

HLR

AbisInterface

Ater Interface

Gb Interface

AInterfaceBTS

BTS

BTS

BSC

PSTN

GGSNSGSN





PSDN : Packet Switched Data Network



Figure 6: Logical Position of External Components Associated with BSS

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1.5.1 Network Subsystem

Managing communication within the PLMN and external networks is theprimary role of the NSS. The NSS manages the subscriber administrationdatabases. It contains the following components:

MSC

Home Location Register

Visitor Location Register

Authentication Center

Equipment Identity Register.

The Alcatel BSS shall support several own PLMN (up to four, at least one); anOMC-R may thus manage at least one (own) PLMN and up to eight PLMN(four own + four foreign). Both cell reselections and handovers shall be allowedbetween two cells belonging to different own PLMN.

MSC Performs and coordinates the outgoing and incoming Call Set Up function.The MSC is a large capacity switch used for passing mobile traffic to mobilesubscribers, or to subscribers of external networks. This part of the NSSinterfaces with the BSS.

Home Location Register The HLR is the central database within a given network for mobile subscriberspecific data. It contains static data such as access authorization, informationabout subscribers and supplementary services. It also controls the dynamicdata about the cell in which the mobile station is located.

Visitor Location Register The VLR temporarily stores information about mobile stations entering itscoverage area. Linked to one or more MSCs, the VLR transmits data to a newVLR when a mobile station changes areas.

Authentication Center The AuC manages the security data used for subscriber authentication.

Equipment IdentityRegister

The EIR contains the lists of mobile station equipment identities.

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1.5.2 Mobile Stations

Mobile stations provide radio and processing functions which allow subscribersto access the mobile network via the Air Interface. Subscriber relatedinformation is stored on a specific device called a SIM.

The SIM is a removable smart-card that conforms to internationally recognizedstandards specified by the ISO. It contains the IMSI. This is used by theNetwork Operator to identify the subscriber in the network and to providesecurity and protection against misuse.

Each mobile station has its own IMEI. The IMEI is used by the NetworkOperator to prevent stolen, or non-type approved mobile stations, fromaccessing the network.

There are three types of mobile station in GSM:

Phase 1

Phase 1 extended

Phase 2.

For information on GPRS mobile stations, refer to GPRS Elements (Section2.1.2).

Mobile stations have different capabilities according to the class of mobilestation and the purpose for which the mobile station was designed. Thesedifferences include power output and ciphering.

Only phase 2 mobile stations can turn off ciphering, or change the cipheringmode, during a channel change procedure such as a handover. The cipheringcapability of a mobile station is signalled to the BSS in the mobile stationclassmark.

Ciphering is used to protect information transmitted on the Air Interface. Thisis performed between the BTS and the mobile station (i.e. Air Interface).Transmission ciphering does not depend on the type of data to be transmitted(i.e. speech, user data, signalling), but to normal transmission bursts. SeeCiphering (Section 3.8) for further information concerning mobile stationciphering capabilities.

Mobile Station Idle Mode A mobile station is in idle mode when it is switched on, but not communicatingwith the network on an SDCCH or a traffic channel. The BSS supports threeidle mode functions:

Cell selection and cell reselection

Location updating

Overload control.

Mobile StationCell Selection and

Reselection

A mobile station monitors the broadcast messages from the BTS. This includesmonitoring the FCCH and SCH.

The mobile station chooses the best cell on which to camp. If this cell is in alocation area other than that stored in the mobile station memory, then themobile station initiates a location update procedure. For a mobile station tocamp on a cell, it has to synchronize with the cell.

The BTS broadcasts an FCCH and an SCH at a defined time in the BCCHcycle. These channels are used as reference points for the mobile station tosynchronize with the BCCH. Once synchronized, the mobile station continuesto monitor these channels to stay synchronized.

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This type of synchronization, along with cell configuration and channelfrequency information, enables the mobile station to calculate where channelsoccur in the multiframe sequences.

Timing advance information is sent to the mobile station when an SDCCH isassigned. The mobile station uses the channel configuration informationto calculate which part of the CCCH contains its paging message, andtherefore which time slot to monitor for paging messages. When the mobilestation is camped on a cell, it continues to monitor the BCCH transmissionsfrom neighboring cells. The BCCH frequencies of the neighboring cells aretransmitted on the BCCH of the home cell (sys_info 2 ). It can decide to campon a new cell if it receives a better signal from an adjacent cell.

Reasons for moving to a new cell include:

A problem in the existing cell

The mobile station moving.If the mobile station moves to a new cell which is in the same location areaas the one currently in its memory, it does not initiate a location update. Itrecalculates its paging group and monitors the new paging channel. Pagingmessages are broadcast from all cells in a particular location area.

GSM/GPRS to UMTSCell Reselection

The reselection of a UTRAN cell is triggered by a multi-RAT mobile stationin circuit-switched idle mode, packet-switched idle mode, or packet-switchedtransfer mode. In NC0 mode, a multi-RAT mobile station can reselect aUTRAN cell in any GMM state. In dedicated mode, the multi-RAT mobilestation follows the GSM handover procedures. The BSS then broadcasts theset of UTRAN cell parameters which allows the multi-RAT mobile station toreselect a UTRAN cell on its own.

Location Updating The location update procedure is always initiated by the mobile station.Location update is performed after the call has finished (cell reselection).Reasons for location updates include:

A periodic updatePeriodic location update is performed by the mobile station after a lack ofsignalling activity for a specific time. If the timer expires, the mobile stationinitiates a location update, even if it has not changed Location Area. Theduration of the mobile station timer is defined by the network and sent to themobile station as system information messages on the BCCH. The time canbe between six minutes and 25 hours.

A handover to a cell in a new location area.When a mobile station is handed over to a cell in a new location area, thereis no automatic location update in the network. A new Location AreaIdentity in the BCCH (sys_info 3 and sys_info 4 ) is detected by the mobilestation when the current call has finished, and initiates the location updateprocedure. This saves the system performing several location updates if themobile station is handed over several times during a call.

The mobile station camps on a cell with a different location area code to the onein the mobile station memory. The mobile station initiates the location updateprocedure by sending a channel_request message indicating that the call isfor a location update. The BSS assigns a dedicated signalling channel andestablishes a signalling path between the mobile station and MSC. See MobileOriginated Call (Section 3.2) for more information.

When a signalling path is established, the mobile station sends the LocationArea Identity of the old cell on which it was camped to the MSC. The new VLR

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interrogates the old VLR for authentication and subscriber information. Forfurther information see Location Updating with Classmark Procedure (Section3.6.3) and Authentication (Section 3.7).

The Location Area Identity is made up of:

Mobile Country Code

Mobile Network Code

Location Area Code.

The BSS adds the cell identity of the mobile station current location to themessage sent to the MSC. This information is sent in a Mobility Managementsub-layer message and is transparent to the BSS. The NSS stores thisinformation in either its HLR or its VLR. Following a location update procedure,the VLR can assign a new Temporary Mobile Subscriber Identity to the mobilestation. See Authentication (Section 3.7) for more information about the TMSI.The following figure shows a mobile station as it moves to a new location area.

MSC

MSCBSCBTS

BSC

Mobile Station connectingin a new location area

VLR

VLR

MobileStation

MobileStation BTS

BSC

BSCProtocol Messages

VLR : Visitor Location Register

Figure 7: Location Update

Overload Control To protect the system against overload, the system can bar access to mobilestations, by changing the RACH control information in the system informationmessages described in Table 1. For further information, see GPRS OverloadControl (Section 2.6.3) and Overload Control (Section 4.7).

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1.5.3 Phase 2 Mobile Support in a Phase 1 Infrastructure

When a phase 2 mobile station is used in a phase 1 infrastructure network,the BSS functions as phase 2 on the Air Interface and has the capability offunctioning as phase 1 or phase 2, depending on the MSC capabilities. Theinfrastructure (BSS and MSC) remains phase 1. This conforms to updatedGSM recommendations for phase 1.

The problems of using phase 2 mobile stations on a phase 1 network are:

The implementation rules for phase 1 are not strictly defined. Therefore

some implementations cannot function with phase 2 mobiles.For example, some of the spare bits in phase 1 are now used by the phase2 protocol. However, some phase 1 infrastructures reject the message asspare bits are used

Some protocol changes in phase 2 changed or replaced a phase 1 protocolFor example, power and quality measurements sent by phase 2 mobilestations have a finer range of power control, which the phase 1 infrastructuremust process

Phase 2 mobile stations send some phase 2 messages even though they

are in a phase 1 environment.For example, phase 2 mobile stations send either new messages or newelements in messages, which the phase 1 infrastructure could reject. Thisblacklists the mobile station due to an invalid protocol message for phase1. Depending on what these messages are, the updates to the phase 1infrastructure would accept these messages/elements. The messagescan be either ignored or only partly treated. This is based on informationcontained within the messages or elements.

1.5.4 Operations and Maintenance Center-Radio

The OMC-R supervises one or more BSSs. It performs the following functions:

Manages the BSS software versions

Acts as the central repository for configurations

Manages fault and performance measurement reports

Handles supervision of alarms and events

Manages the MFS.

The reported data is available to the operator from the OMC-R’s centraldatabase. The OMC-R only performs O&M activities. It does not perform usertraffic processing or call establishment and control activities. Refer to theOperations & Maintenance Principles for more information.

Operator actions via the terminal interface trigger commands throughout theBSS. The OMC-R provides object-oriented management information, andsupports a Manager/Agent scheme to perform and control managementactivities. The terminal interface supports different user profiles with differentaccess rights.

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1.6 Network ManagementNormally the OMC-R provides all the network management and controlfunctions required by the BSS. However, the management and controlfunctions are proprietary to the system supplier. In keeping with InternationalTelecommunications Union and European Telecommunication StandardsInstitute recommendations, the Telecommunications Management Networkstructure has been developed to standardize the Network Managementfunction. Network Management is compatible with all equipment, even thatof different manufacturers. Network Management is controlled from one orseveral NMCs.

1.6.1 Telecommunications Management Network

The ability to transfer management information across the TelecommunicationsManagement Network environment is defined by a protocol suite, the QInterfaces. The following figure shows the hierarchical structure of theTelecommunications Management Network. It graphically defines therespective management responsibilities in the three main levels of theManagement Information Tree.

Telecommunications Management Network is more fully discussed in theBSS/MFS and TMN Functions section of the Operations & MaintenancePrinciples document.

NMC

OMC−R

BSC

BTS BTSBTS

Q3

BSS

OSS

NMC Operator (Resource Management)

OMC−R Operator (Resource and Equipment

Management)

Security Block (SBL) Management

Network Management

&Network Element

Management

Mediation Function

Network ElementMFS

OSS : Operation Support System



Figure 8: TMN System Hierarchy

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1.6.2 Q3 Interface

Communication between the NMC and the OMC-R takes place across the Q3Interface (see Figure 8). The Q3 protocols can be divided into the followingmain areas:

Association connection and disconnection mechanisms

Message format and structure

Command types.

For further information on Network Management and the Q3 Interface see theOperations & Maintenance Principles document.

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1.7 BSS Telecommunications LayersThe telecommunications functions of a GSM network are split into layers.These layers are split into two basic categories:

The Application layer is split into sub-layers, to control:

Call Management

Mobility Management

Radio Resource Management.

The transmission layers which provide transmission between the variouscomponents.

Note: These transmission layers relate to the OSI layers, that is, the Physical Layer(i.e. Layer 1) and the Data Layer (i.e. Layer 2). The protocols used for theselayers are standard.

The following figure shows the general distribution of the telecommunicationfunctions within a GSM network.

MS BTS BSC NSS

CM

MM

RRM

GSM Application Layers

TRANSMISSION

CM : Call Management

MM : Mobility Management

MS : Mobile Station

RRM : Radio Resource Management

Figure 9: General Telecommunication Layers within GSM

1.7.1 Call Management

The Call Management sub-layer performs Call Control to establish, maintainand release calls. SMS within Call Management allows the mobile station tosend and receive messages of up to 160 characters. The SupplementaryService functions are also provided to the mobile stations as part of CallManagement.

1.7.2 Mobility Management

The Mobility Management sub-layer is used by the NSS to manage thesubscriber database, including information on subscriber location andauthentication. It is also used by the mobile stations to send location updateswhen they move to new location areas.

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1.7.3 Radio Resource Management

The Radio Resources Management sub-layer establishes, maintains andreleases stable connections between the mobile station and the MSC for theduration of a call. This includes functions such as managing the limited radioresources, to ensure high service availability. It also performs handoverswhen a mobile station moves during a call, or the channel quality falls belowan acceptable level. RRM functions occur mainly between the mobile stationand the BSC.

The following figure shows the application layers, transmission layers andInterfaces of the BSS.

MS BTS BSC MSC

MM

RRM

GSMApplicationLayers

Layer 2

Air Interface Abis Interface A Interface

Layer 1 Layer 1

TC08.60

CM

LAPDm LAPD LAPD SCCP

SS7

SCCP

SS7

LAPDm

BSSAP BSSAP BSSAP

Layer 1Layer 1Layer 1Layer 1

BSSAP : BSS Application Part

CM : Call Management

LAPD : Link Access Protocol on the D Channel

LAPDm : Link Access Protocol on the Dm Channel

MM : Mobility Management

RRM : Radio Resource Management

SCCP : Signal Connection Control Part

SS7 : Signaling System No. 7

TC : Transcoder

Figure 10: BSS Application, Transmission Layers and Interfaces

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1.7.4 The A Interface

The A Interface is used for communication between the BSC and the MSC. Theconnection between the BSC and MSC can be via one of the following:

Terrestrial lines

Satellite link.

The A Interface comprises the:

Physical layer 1

Data Link layer 2

RRM sub-layer 3 of the application layer.

Physical Layer 1 The physical layer provides a physical connection to transport the signals. Itsupports a 2 Mbit/s link divided into 32 x 64 kbit/s channels by Time DivisionMultiplex. The actual physical link used depends on Network Operatorimplementation.

Data Link Layer 2 Layer 2 provides the frame handling functions for the interface. It is also used topass signalling messages using the International Telecommunications Unionsignalling System No. 7 protocol. This comprises:

Message Transfer Part, which provides the mechanism for reliable transfer

of the signalling messages

Signalling Connection Control Part, which provides the mechanism toidentify transactions relating to a specific communication.

Application Sub-layerRRM

To transfer layer 3 messages relating to a transaction, the SCCP uses the BSSApplication Part. This is divided into two parts:

Direct Transfer Application Part, which transfers messages directly between

the MSC and the mobile station. These messages are not interpretedby the BSS. The BSS must read and recognize the initial message as

a DTAP message

BSS Management Application Part which supports procedures between theMSC and the BSC, such as resource management and handover control.On the A Interface, the process is terminated at the BSC. Messages for theBSS, passed by the BSSMAP, are interpreted by the BSC layer 3.

Ater Interface The part of the A Interface between the Transcoder and BSC is known as theAter Mux Interface. The Ater Mux Interface is the result of multiplexing four AterInterfaces. Transcoding is a layer 1 process, therefore the difference betweenthe two interfaces is at the physical level.

Optimized Ater InterfaceMapping

This feature improves efficiency on the Ater Mux PCM connection betweenthe G2 BSC and the G2 Transcoder.

Four Ater Interfaces are submultiplexed onto the Ater Mux connection. Thisinterconnects four Digital Trunk Controllers and four Transcoder Rate AdaptionUnits, achieving a 4:1 mapping.

The 4:1 mapping of the G2 BSC and G2 Transcoder allows up to 116 trafficchannels.

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1.7.5 The Abis Interface

The Abis Interface is used for communication between the BSC and the BTS.

The Abis Interface comprises:

Physical layer 1

Data Link layer 2

BTS management sub-layer 3 of the application layer.

Physical Layer 1 The physical layer provides a physical connection to transport the signals. Itsupports a 2 Mbit/s link divided into 32 x 64 kbit/s channels by TDM.

The physical link used depends on the Network Operator implementing theinterface.

Data Link Layer 2 The data link layer provides frame handling and signalling functions usingthe LAPD.

This layer supports three types of signalling links:

The Radio Signalling Link for signalling to the mobile station (including SMS)

The O&M Link for O&M informationThe OML Auto-detection feature (see OML Auto-detection (Section 8.4.5))allows the time slot reserved for the O&M Link to be used for signalling(if there are no G1/G2 BTS on the Abis interface). This provides for anincrease in the amount of telecom traffic on the Abis interface.

The Layer 2 Management Link for the layer 2 management functions such

as frame checking and error correction.

Application Sub-layerBTS

The BTS management layer is used for layer 3 messages between the BSCand the BTS. Some of these messages are transparent to the BTS. These arepassed directly to the mobile station using the BTS RR management sub-layer3 on the Air Interface. Non-transparent messages include messages for radiolink layer control and channel management.

1.7.6 Satellite Links

The Abis and Ater interfaces were designed to use terrestrial transmission links.However, in developing countries the terrestrial transmission infrastructure doesnot exist and in many cases is difficult and costly to provide. There is also aneed in the developed world to provide temporary GSM coverage for transientmobile population density increases, for example at sporting events. Usinggeostationary earth orbiting satellites is a simple and relatively low cost solutionto these problems. Unfortunately, there is one major drawback, transmissiondelay. The Geostationary orbit is located at an altitude of 35,786 km abovethe equator, therefore propagation delay of radio signals can vary between119 ms at the equator to a maximum delay of 139 ms. The delay for one hop(the path from one point on earth to another point, via one satellite link) variesbetween 238 and 278 ms. This delay degrades speech quality, but although thedegradation is worse than experienced in the PSTN, it is usable. The delay alsohas an effect on signaling messages.

Satellite links can be used on the Abis interface or on the Ater interface (butnot both).

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Modification of parameters is done from the OMC and propagated to the BSCand the concerned BTSs. A new connection type parameter is associated toeach Abis link. The operator can set the parameter at Abis creation time. Ifthe satellite link is to be made using the Ater interface, the new connectiontype parameter associated to Ater as a whole is used. Both Abis and Aterconnection types can be either terrestrial, or via satellite. The default value foreach is terrestrial.

Note: This is not a standard GSM feature and Alcatel cannot guarantee theperformance because there are so many unknown factors, such as error rateand mobile population variations, which have significant effects because ofthe delay.

1.7.6.1 Abis Interface Using Satellite LinksThis feature is available only for EVOLIUM™ BTSs and later. When the link isinstalled on the Abis interface, for those BTS where the satellite link is installed,the following features are not available:

Closed multidrop

PCM synchronization (the BTS must be configured as free running)

GPRS not supported. GPRS connections are not supported for:

All BTS if the satellite is between MFS and BSC

Some BTS if the satellite is between BSC and BTS.

GPRS timers are generally shorter than GSM timers and the establishmentof the connection may fail due to the round trip delay induced by the satellitelink. The coding of the parameter BS_CV_Max, which defines the round tripdelay on the radio interface cannot be extended for satellite usage.

Synchronous handovers, fax and data (in circuit-switched mode, transparentand not transparent), are supported.

1.7.6.2 Ater Interface Using Satellite LinksOn the Ater interface, the satellite link can be installed either on the Ater(between the BSC and the Transcoder), or on the A interface (between theTranscoder and the MSC). Because this latter case is rare, the wording Ateris used for both cases. When only some of the time slots are routed via thesatellite, at least the Qmux and the X.25 (if the satellite link is on the A interface)must be routed. Channels that are not routed must be blocked, either from theMSC or from the OMC-R. If only one link is forwarded, there will be no longerbe redundancy on the following: System No. 7, X.25, and Qmux.

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1.7.7 The Air Interface

The Air Interface is the radio interface between the BTS and the mobile station.

The Air Interface comprises:

Physical layer 1

Data Link layer 2

RRM sub-layer 3 of the application layer.

Physical Layer 1 The physical layer is a radio link where channels are divided by time andfrequency.

Data Link Layer 2 The data link layer provides frame handling and signalling functions, usinga modified version of the LAPDm.

Application Sub-LayerRadio Resources

Management

On the Air Interface, most of the layer 3 messages are transparent to the BTS.The BTS uses layer 3 to extract certain information from some messagesbefore passing on the equivalent message.

For example, when the BTS receives an encryption_command message fromthe BSC, it reads the Ki value and the algorithm to be used, before passingon the cipher_mode_command message. This procedure is explainedin detail in Ciphering (Section 3.8).

Air Interface Channels The Air Interface is divided by frequency and time, using Frequency-DivisionMultiplex Access and Time Division Multiple Access. This provides frames ofeight time slots for each frequency supported by the cell. The channels of thecell are then assigned to specific time slots within the Time Division MultipleAccess frames.

GPRS traffic uses the same radio resources as circuit-switched traffic, andis carried on the same type of physical channel. Refer to GPRS in the BSS(Chapter 2) for information on GPRS channels.

However, not all channels require the full capacity of a time slot at eachoccurrence of a frame. Channels are configured to share time slots by onlyusing certain occurrences of the frame. The cycle of frame occurrences isknown as a multiframe. A multiframe can be 26 or 51 occurrences of a frame,depending on the channels configured within it. Within a multiframe, the samephysical channel can support more than one logical channel.

The following figure shows time slot four of a TDMA frame supporting AccessGrant Channels.

AGCH

AGCH

AGCH

AGCH

AGCH

Frame 1 Frame 2 Frame 3 Frame 4 Frame 5

AGCH : Access Grant Channel

Figure 11: Time Slot 4 of a Time Division Multiple Access Frame Supporting Access Grant Channels

Channels can be divided into traffic channels and control channels.

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Traffic Channels A traffic channel can be used for speech or data. The Alcatel BSS supports thefollowing types of traffic channels:

Speech:

Full-rate speech traffic channel

Enhanced full-rate speech traffic channel

Half-rate speech traffic channel.

Data:

Full-rate data traffic channel (9.6 Kbit/s)

Full-rate data traffic channel (4.8 Kbit/s)

Half-rate data traffic channel (4.8 Kbit/s)

Full-rate data traffic channel (<2.4 Kbit/s)

Half-rate data traffic channel (<2.4 Kbit/s).

Control Channels CCHs control communications between the BSS and the mobile stations.There are three types of CCH:

The BCCH broadcast cell information to any mobile station in range. Three

channels use the BCCH time slot:

FCCH: used on the downlink for frequency correction of the mobilestation with the BTS

SCH: used on the downlink for frame synchronization of the mobilestation with the BTS

BCCH: used to broadcast system information to the mobile stations on

the downlink, to give the cell configuration, and how to access the cell.

The CCCH communicate with mobile stations in the cell before a dedicated

signalling channel is established. Three channels use the CCCH time slot:

RACH: used on the uplink by the mobile station for initial access tothe network

PCH: used on the downlink for paging messages to the mobile station

AGCH: used on the downlink to give the mobile station accessinformation before a dedicated channel is assigned.

The DCCH and ACCH pass signalling information for a specific mobile

station transaction. Two channels use the DCCH time slot:

SDCCH: used for signalling and short message information

CBCH: uses an SDCCH channel for Short Message Service — Cell

Broadcasts.

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Two channels use the ACCH time slot:

FACCH: associated with a traffic channel, and can steal slots out of 24 or26 slots which are normally dedicated to the traffic channel for signalling

purposes as well as the SACCH slot

SACCH: associated with a traffic channel, which uses 1 out of 26 slots

for signalling purposes.

An ACCH channel is always associated with a traffic channel.

System InformationMessages

System information messages transmit information about the cell to the mobilestation. There are six system information messages. Four are sent on theBCCH as a general broadcast to any mobile stations in the cells, and two senton the SACCH to mobile stations in communication with the BSS. Systeminformation messages 2 and 5 have several variations to avoid compatibilityproblems with phase 1 mobile stations.

The following table shows the system information messages, the channel onwhich they are transmitted and the type of information in each.

Message Channel Information

Sys_info 1 BCCH Cell channel description.

RACH control information.

Sys_info 2 BCCH Neighbor cell BCCH frequency list

Indication of which Network Color Code it is allowed to monitor.


Sys_info 2bis(multibandsystems only)

BCCH Extended Neighbor cell BCCH frequency list in same band as servingcell. This message is only sent if Sys_info 2 is not sufficient to encodeall available frequencies.


Spare bits.

Sys_info 2ter(multibandsystems only)

BCCH Extended Neighbor cell BCCH frequency list in different band asserving cell.

The minimum number of cells, if available, to be reported in eachsupported band in measurement results.


Spare bits.

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Sys_info 3 BCCH Cell Identity

Location Area Identity

Control channel description

Cell options:

Power central information

Discontinuous Transmission (mechanism) information

Radio link timeout.

Cell selection parameters:

Cell reselect hysteresis for Location Area reselection

Maximum transmit power allowed in cell

Additional reselection parameter

Allows/forbids new establishment causes (phase 2 mobile stations)

Minimum receive level to access cell.

RACH control information

Spare bits setting flags and timers.

Sys_info 4 BCCH Location Area Identity

Cell selection parameters:

Cell reselect hysteresis for Location Area reselection

Maximum transmit power allowed in cell

Additional reselection parameter

Allows/forbids new establishment causes (phase 2 mobile stations)

Minimum receive level to access cell.

RACH control information

CBCH channel description

CBCH Mobile Allocation

Spare bits setting flags and timers.

Sys_info 5 SACCH Neighbor cell BCCH frequency list.

Sys_info 5bis(multibandsystems only)

SACCH Extended Neighbor cell BCCH frequency list. This message is onlysent if:

The serving cell is a GSM 1800 cell and Sys_info 5 is not sufficientto encode all GSM 1800 neighbor frequencies

The serving cell is a GSM 900 cell andThe mobile station is phase 2 andThere are neighboring GSM 1800 cells andSys_info 5ter is not sufficient to encode all of the GSM 1800 cells.

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Sys_info 5ter(multibandsystems andphase 2 mobilestations only)

SACCH Extended Neighbor cell BCCH frequency list in different band asserving cell.

The minimum number of cells, if available, to be reported in eachsupported band in measurement results.

Sys_info 6 SACCH CI

Location Area Identity

Cell options:

Power control information

Discontinuous Transmission information

Radio link timeout

Indication of which Network Color Code it is allowed to monitor.

Table 1: System Information Messages

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2 GPRS in the BSS

GPRS in the BSS, provides an introduction to GPRS and describes:

Overview

Packet Switching

GPRS Elements

GPRS Channels and Interfaces

GPRS Network Functions

GPRS Data Transmission.

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2.1 OverviewThe success of GSM has taken place in parallel with the explosion of interest inthe Internet and related data services. Presently, data transmission over the airinterface is limited to 9.6 kb/s, too slow for use of graphics-intensive servicessuch as the World Wide Web and personal video conferencing. In addition,the circuit-switched method used for data transmission makes inefficient useof radio resources, which are under increasing pressure from the growth inGSM subscribers and use.

The solution chosen by European Telecommunication Standards Institute forthe double challenge of increased demand for data service and pressureon radio resources is called General Packet Radio Service. The EuropeanTelecommunication Standards Institute recommendations establish a standardfor inserting an alternative transmission method for data in the PLMN: packetswitching instead of circuit switching.

The Alcatel GPRS solution follows the ETSI GSM phase 2+ recommendationsclosely.

2.1.1 Packet Switching

In circuit switching, a connection is established and maintained during the entirelength of the exchange, whether data is being transmitted or not. Resourcesare dedicated to a single end-to-end connection, and a radio channel in a cell,with its associated transmission channels, may be unavailable for use evenwhen little or no information is passing across it at a given moment.

In packet-switched systems, data is transmitted over virtual circuits, which existonly while data is actively being transmitted over them. This means that duringidle time, time slots can be used for carrying other data.

Packet-switching systems operate according to the following generalprocedures:

1. The PAD function disassembles data into “packets” of a predefined size.

2. The PAD encloses the packets in a data envelope (headers and footers).This data envelope includes information about origination and destinationpoints, and the order in which the packet’s contents are to be reassembledat the destination. The following figure shows a model of a GPRS PacketData Unit at the LLC layer.

3. Packets move from origination to destination point by different routes and canarrive at the destination in a different order than that in which they were sent.

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4. At the destination, another PAD reads the envelope information, strips it off,and reassembles the data in the proper order.

DATA Footer

ENVELOPE

Address Field Contains:Protocol discriminatorCommand/response SAPI (mobility management,QoS, SMS)

Control Field − 4 possible types:Confirmed information transferSupervisory functionsUnconfirmed information transferControl functions

HeaderAddress Field

Control Field FCSInformation Field

FCS : Frame Check Sequence

SAPI : Service Access Point Indicator

Figure 12: Model LLC Packet Data Unit used in GPRS

Examples of packet switching protocols include X.25 and Internet Protocol.Since GPRS is compatible with these widely used protocols, it is suitable foraccess to public or custom packet data services, or to the Internet. Mobiletelephones using packet data services must be connected to a portablecomputer or an electronic organizer.

2.1.2 GPRS Elements

The different elements shown in the figure below represent a parallel system tothe circuit-switched system used in GSM until now.

BTS

MS

BSC

To PSTN

BSS

GGSN

BTS

BSCGP

GCH

Ater

Gb

Packet

GCH

Abis

SGSN

To Public DataNetworks

GCH

Traffic

Switched

FRDN Gb

MSC/VLR

OMC−R

MFS

Circuit

Traffic

SwitchedTranscoder

BSCGP : BSC GPRS Protocol

FRDN : Frame Relay Data Network

GCH : GPRS Channel






Figure 13: The Alcatel GPRS solution in the PLMN

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In the Alcatel solution, the Multi-BSS Fast packet Server with its associatedinterfaces is the BSS element. All other components are external to the BSS.The following internal and external components are described in this chapter:

GPRS mobiles

The Serving GPRS Support Node

The Gateway GPRS Support Node

The Multi-BSS Fast packet Server.

GPRS Mobiles There are three classes of GPRS-capable mobile stations:

Class A

Class B

Class C.

Currently, only class B and C mobile stations are supported.

Class A Class A mobile stations can handle circuit-switched voice and GPRS trafficsimultaneously.

Class B Class B mobile stations can be IMSI attached and GPRS attached at the sametime, but use only one service (circuit-switched or GPRS) at a time. A GPRSattached class B mobile station can initiate an IMSI connection and suspend itsGPRS service in the following cases:

When the user is not engaged in any GPRS data transfer, and either:

A mobile station originated call is initiated

The mobile station receives a mobile termination call.

When the user is engaged in a GPRS session (e.g. an internet session),and either:

A mobile station originated call is initiated

The mobile station receives a mobile termination call.

The mobile station performs a LAU procedure in network mode II ornetwork mode III

Class C Class C mobile stations an be either IMSI attached or GPRS but not both, andcan use circuit-switched or GPRS services alternately.

The Serving GPRSSupport Node

The SGSN is a GPRS network entity at the same hierarchical level as theMSC. It is external to the BSS and communicates with it via Frame Relayover the Gb interface. The SGSN is involved in requesting specific networkresources for GPRS traffic. It performs GPRS paging, authentication, andcipher setting procedures based on the same algorithms, keys and criteriaas in circuit-switched GSM traffic.

When a mobile station wants to access GPRS services, it makes its presenceknown to the network by performing a GPRS Attach procedure. Thisestablishes a logical link between the mobile station and the SGSN. The mobilestation is then available for SMS over GPRS, paging from the SGSN, andnotification of incoming GPRS data.

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The SGSN also participates with other network elements in the routing andrelaying of packets from one node to another.

One SGSN can be connected to many MSCs and many MFSs.

The Gateway GPRSSupport Node

The GGSN is connected with SGSNs via an IP-based backbone. It providesinterworking between the GPRS network and external packet switchednetworks. It is external to the BSS.

When the mobile station sends or receives GPRS data, it activates the PacketData Protocol address that it wants to use. This has the effect of making themobile station known to the GGSN. User data is transferred transparently fromthe mobile station and external data systems by the GGSN using encapsulationand tunnelling. This allows data packets equipped with GPRS-specific protocolinformation to be transferred between the mobile station and GGSN. Thisreduces the requirement for the GPRS system to interpret external dataprotocols.

The GGSN also works with other network elements in the routing and relayingof packets from one node to another.

The Multi-BSS FastPacket Server

See The Multi-BSS Fast Packet Server (Section 1.3.4) for details of the MFS

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2.2 GPRS Channels and System Information MessagesGPRS traffic uses the same radio resources as circuit-switched traffic, andis carried on the same type of physical channel. When a physical channel isallocated to carry packet logical channels (using TDMA frames, as doescircuit-switched traffic), it is called a Packet Data Channel, or PDCH.

2.2.1 Master Channels

Master Channels are packet channels that carry Packet Broadcast ControlChannel (PBCCH) only on the primary MPDCH, the Packet Common ControlChannel (PCCCH), the Packet Data Traffic Channel (PDTCH) and the PacketAssociated Control Channel (PACCH). They allow:

More performance packet services to be offered through:

Enhanced cell reselection by using optimized cell reselection criteria

Optimized system information reception (the mobile station does not

interrupt its data transfer to acquire or refresh system information fromserving and neighbor cells)

Faster TBF establishment (through dedicated PCCCH channels and

multislot TBF allocation in one phase).

GPRS signalling traffic to be placed on dedicated PCCCH channels.To prevent CCCH channel congestion, and thus degradation of the qualityof the circuit-switched services, even at a low level of GPRS traffic (e.g.cells where the signalling induced by the circuit-switched services is alreadyhigh, or cells at the border of a Location Area). Multiple MPDCHs may berequired in case of an increase in the GPRS traffic in the cell.

There are two types of Master Channel:

GPRS Primary

GPRS Secondary

Primary Master Channels can be statically or dynamically allocated, secondaryMaster Channels can only be dynamically allocated.

2.2.2 Static Allocation

A dedicated O&M parameter allows the operator to configure the primaryMPDCH. Only a primary MPDCH can be configured for static allocation. Theprimary MPDCH is permanently established in the cell even if there is noGPRS traffic. This is of use if the operator wants the mobile station to performautonomous cell reselection based on the C31 and C32 parameters, or if thepaging load is high independent of the GPRS traffic.

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2.2.3 Dynamic Allocation

The number of MPDCHs needed in a cell may significantly change in a dayaccording to the GPRS traffic variation. Dynamic allocation of MPDCHs avoidsforcing the operator to permanently configure MPDCHs (and hence GPRSradio slots), even when the GPRS traffic decreases.

GPRS Primary MasterChannel

A primary Master Channel can be dynamically allocated as soon as there isGPRS traffic in a cell. This feature can be enabled on a per cell basis. If thereis no GPRS traffic, the primary Master Channel is released in this cell.

The GPRS Primary Master Channel is a Packet Data Channel (PDCH) carryingthe Packet Broadcast Control Channel (PBCCH) to broadcast GPRS systeminformation in the cell and the Packet Common Control Channel (PCCCH)providing GPRS specific control channels.

The Primary MPDCH is dynamically allocated by the BSS upon occurrenceof any GPRS traffic in the cell (receipt of either a downlink LLC PDU, or achannel request from a mobile station with any establishment cause). Theprimary MPDCH is dynamically de-allocated when no GPRS traffic is detectedduring a given period (typically a few minutes). This minimizes the TCU load(and also the CCCH load).

When there is a GPRS Primary Master Channel in a cell, the Alcatel BSSbroadcasts its channel description on the BCCH. Mobile stations can monitorthe broadcast and thus receive all GPRS specific system information pertainingto the cell. The Primary Master Channel is mandatory when the Optimizedaccess on CCCH feature is not used. There may be at most one PrimaryMaster Channel in a cell.

The Primary Master Channel feature allows the operator to set a primary MasterChannel and to benefit from the following advantages, on a per cell basis:

More complete GPRS system information to be broadcast which enhancesthe overall performance of the network. For example, the permanent

broadcast of C31 and C32 criteria enhances the cell reselection for all

GPRS attached mobile stations.

Better performance in a GPRS network by reducing the load on CCCH.

Shortened access time for multislot mobile stations.

A faster paging cycle.

A higher radio resource efficiency due to the flexibility in the mapping oflogical channels onto the physical channels.

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GPRS Secondary MasterChannel

The GPRS Secondary Master Channel is a Packet Data Channel (PDCH)carrying the Packet Common Control Channel (PCCCH) providing GPRSspecific control channels. In addition to the Primary Master Channel, oneor several Secondary Master Channels can be allocated in the cell. Thisfeature enables automatic dynamic allocation and release of secondary MasterChannels based on common signalling traffic load estimates. This dynamicallyadapts the GPRS signalling capacity of the cell to the traffic demand. Thesecondary master PDCH are always dynamically established or released inthe cell, regardless of whether the Primary Master Channel is statically ordynamically allocated. The feature provides the operator with the followingimprovements:

Increase the GPRS signalling capacity as the traffic load increases inthe cell.

Avoids the need to reserve static radio resources to match the maximum

traffic demand.

Configuration of the allocation and de-allocation algorithm thresholds is

performed automatically by the BSS.

2.2.4 Multiple PCCCH

To allow for an increase in GPRS traffic and its associated signaling, andadvanced servises (e.g. network controlled cell reselection, GPRS in multibandnetworks, traffic load management), more than one MPDCH is required. Asecondary MPDCH is required to handle the increase in signaling.

The following logical channels can be dynamically multiplexed on one MPDCH:

PBCCH

PCCCH

PDTCH

PACCH.

The MPDCH carrying the PBCCH is called the primary Master PDCH. ThePBCCH carrier is indicated on the BCCH (in the SI13 message). Up to16 MPDCH can be allocated in a cell (one primary MPCCH, 15 secondaryMPDCH). The additional MPDCH are called secondary Master PDCH.

When the primary MPDCH is activated, the BSC broadcasts the SI 13 messagewith the radio configuration of the PBCCH. When the primary MPDCH isdeactivated (always decided by the MFS even following a fault, e.g. TRXrecovery impacting the MPDCH), the SI 13 message no longer contains aPBCCH description. Paging and assignment messages are routed either onCCCH or PCCCH according to the presence or not of the MPDCH.

To summarize, if the primary MPDCH is on slots 0 to 3, the secondary MPDCHcan be located at any slot position. If primary MPDCH is on slot k (k = 4 to 7),secondary MPDCH shall be on slot n with n > k – 4; in such case, the lower k is,the highest flexibility is to allocate a secondary MPDCH.

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The following table describes the parameters that can be defined by theoperator.

Parameter Name Definition Type Mandatory Rules

BS_PBCCH_BLKS Coded on 2 bits:

00=BlockB0 used for

PBCCH

01=Block B0and B6 used

for PBCCH

10=BlockB0, B6, and

B3 used forPBCCH

11=Block B0,

B6, B3, andB9 used for

PBCCH

Number if:

BS_PBCCH_BLKS=1thenPSI_REPEAT_PERIOD >3.

if:

BS_PBCCH_BLKS > 1 thenPSI_REPEAT_PERIOD >4/BS_PBCC H_BLKS.

BS_PAG_BLKS

_RES

Number of blocksallocated tothe PAGCH orPDTCH or PACCHper 52 multiframe.

Number None.

BS_PRACH_

BLKS

Number of staticprach blocks.

Number BS_PRACH_BLKS <=BS_PRACH_BLKS_MAX

BS_PRACK_

BLKS_MAX

Number ofdynamic prachblocks.

Number BS_PRACH_BLKS_MAX>= BS_PRACH_BLKS

S/(16 * BS_PRACH_BLKS_ MAX) >round_trip_delay.

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2.2.5 Logical Channels

The types of logical channels which can be carried on a PDCH are:

Packet traffic channel

Packet Timing Advance Control Channel

Packet Traffic Channel This channel is analogous to a circuit-switched traffic channel, and is used foruser data transmission and its associated signaling. It has two sub-channels:

Packet Data Traffic Channel which contains the user data traffic

Packet Associated Control Channel (bi-directional) which contains thesignalling information.

If multiple PDTCHs are assigned to one mobile station, the PACCH is alwaysallocated on one of the PDCHs on which PDTCHs are allocated.

The function of these sub channels is analogous to their circuit-switchedcounterparts.

Packet Timing AdvanceControl Channel

This bi-directional channel is used for maintaining a continuous timing advanceupdate mechanism.

2.2.6 Virtual Channels

Packet switching is a mode of operation adapted to transmission of "bursty" data- that is, data which comes in intense "bursts" separated by periods of inactivity.The network establishes a connection during the transmission of such a "burst"of data. If there is no activity on this connection, the connection is taken down.

When the original user needs to send or receive another burst of data, a newtemporary connection is put up. This can be on another channel in the samecell, or in another cell if the mobile station is in motion. The routing of one burstof data may be different from the routing of another.

The establishment and dis-establishment of temporary connections istransparent to the user. The user sees an exchange of data that seems to bea continuous flow, unless the network is over congested. This semblance ofcontinuous flow is a Virtual Channel.

A virtual channel can be represented as the flow of data between two terminalsduring a user session. The user has the impression of a single continuousconnection, but in the network, this is not the case.

A single data transfer, either in the uplink or in the downlink direction, canpass between the MFS and the mobile station via one or more PDCH. APDCH is shared between multiple mobile stations and the network. It containsasymmetric and independent uplink and downlink channels.

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2.2.7 System Information Messages

GPRS system information messages, like their GSM counterparts, transmitinformation about the cell to the mobile station. GSM BCCH messages, shownin Table 1, are also used in GPRS. GPRS also uses the additional messageshown in the following table.


SI 13 BCCH The SI 13 message is sent on the BCCH andcontains all the necessary information requiredfor GPRS. It also indicates the presence andthe location of the PBCCH in the serving cell.The SI13 message is broadcast only if GPRSis supported in the cell.

Table 2: GPRS System Information Message

Also, when an MPDCH exists, the messages shown in the following tableare used.


PSI 1 PBCCH The PSI 1 message is sent on the PBCCH andgives information on:

Cell selection

Control of the PRACH

Description of the control channels

Description of power control parameters.

To reduce the possibility that a mobile stationinvolved in a data transfer has to reread thePBCCH, the PSI 1 message is also broadcast onPACCH/D of a MS in packet transfer mode:

When one of the packet system information

messages has been modified

Every T_PSI_PACCH seconds.

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PSI 2 PBCCH The PSI 2 message is sent on the PBCCHin several instances (up to 8) in order to giveinformation on:

Reference frequency lists

Cell allocation

GPRS mobile allocations

PCCCH channel description

Non GPRS cell options applicable to circuit

switched access

Cell identification.

If the PSI 2 message is modified, the new PSI2 message is also broadcast on PACCH/D of amobile station that is in packet transfer mode.

PSI 3/3bis PBCCH The PSI 3/3bis messages are sent on PBCCHin several instances (up to 16) in order to giveinformation on:

BCCH allocation in the neighbor cells: The

list of BCCH frequencies is then called theBA(GPRS) list.

Cell selection parameters for the serving cell

and the neighbor cells.

Localized Service Area (LSA) identification of

the serving cell and of the neighbor cells forthe SoLSA feature.

Up to 32 neighbor cells can be defined by thePSI 3/3bis messages. In order to reduce thenumber of PSI3/3bis instances, the codingof the PSI3/3bis messages is optimized bycompressing the redundant parameters.

PSI 8 PBCCH The PSI 8 message is optionally sent on thePBCCH to give information on the configurationof the cell broadcast channel (CBCH).

Table 3: GPRS System Information Messages Used with MPDCH

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2.3 GPRS InterfacesNew interfaces have been introduced for GPRS needs. These interfaces linkthe MFS and the SGSN, the BTS, and the BSC.

2.3.1 The Gb Interface

The Gb interface uses frame relay techniques to link the PCU function of theMFS and the SGSN. Physically, it can be routed in a variety of ways:

A direct connection between the MFS and the SGSN

Via a public Frame Relay Data Network

Via the MSC

Via the Ater Mux interface through the Transcoder to the MSC. In this caseit carries a combination of packet-switched and circuit-switched traffic

and signalling.

Combinations of these methods are also possible. See Figure 13 for theposition of the Gb interface in the system.

The Gb interface provides end-to-end signaling between the MFS and theSGSN, and serves as the BSS-GPRS backbone. Its principal functions areshown in the following table.

Function Description

Transfer of BSSGP-PDUs between BSS andSGSN

Allocation and load sharing of PDUs amongVirtual Channels

Network services

Access to intermediate Frame Relay Data Network

Radio resource information

Quality of Service Information

Routing information

Transfer of LLC-PDUs between the BSS and theSGSN

BSS-GPRS Protocolservices

Suspend and Resume procedures for class Bmobile stations

Table 4: Gb Interface Functions

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2.3.2 The BSCGP Interface

The BSCGP interface provides communication between the BSC and the MFS(see Figure 13). The BSC GPRS Protocol controls two LAPDs connections(for redundancy) using 64 kb/s time slots. The following information is carriedon the BSCGP Interface:

Function Description

Circuit-switched and packet-switched paging(MFS to BSC)

Channel Requests from BSC to MFS

Common radio signaling

Uplink and downlink channel assignment (MFSto BSC)

Allocation/de-allocation of resources (MFS toBSC)

Release indication (BSC to MFS)

GPRS radio resourcemanagement

Load indication: this limits the allocation for GPRStraffic (BSC to MFS)

Table 5: BSCGP Interface Functions

Note: The common radio signaling functions of the BSCGP are handled on the GPRSSignaling Link, which is carried inside the Ater interface.

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2.3.3 The GCH Interface

The GCH interface provides a synchronous connection between the MFS andthe BTS, using 16 kb/s time slots. The GCH links pass transparently throughthe BSC (see Figure 13). Its functions are as follows:

Transfer of PDUs between MFS and BTS (thus packet data is not directly

handled by the BSC but passes transparently through it on the GCHinterface)

Synchronization with the radio interface at GCH link establishment

Correction of clock drifts between Abis and BTS clocks.

The protocol for the GCH interface uses two layers:

L1-GCH layerL1-GCH is the physical layer based on ITU-T recommendations G.703.The L1-GCH layer utilizes digital transmission at a rate of 2048 kbit/s with aframe of 32 x 64 kbit/s time slots. An L1-GCH channel has a transmissionrate of 16 kbit/s.

L2-GCH layerL2-GCH is the data link layer which is an Alcatel proprietary protocol. Thislayer is in charge of the data transfer of the GCH frames between theMFS and the BTS.The L2-GCH layer offers a service of data transport for the RLC/MAC layerslocated in the MFS. Its main functions are:

GCH link establishment and release

Synchronization with the radio interface

RLC/MAC PDUs transfer.

For more information on GSM transmission, refer to Call Set Up (Chapter 3).

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2.4 GPRS Network FunctionsThis section describes various GPRS-specific network functions necessaryfor successful packet data transfer. This includes paging, cell reselection,error checking and reestablishment, as well as radio power control and linkmeasurement.

MAC and RLC Functions Since multiple mobile stations can be competing for the same physicalresource(s), an arbitration procedure is necessary. This is provided by theMedium Access Control function.

The MAC function operates between the MFS and the mobile station, andworks in conjunction with the Radio Link Control function. Radio Link Controldefines the procedures for retransmission of unsuccessfully delivered datablocks (error correction) and for the disassembly and reassembly of PDUs.

Temporary Block Flow When PDUs need to be transferred between the MFS and the mobile station,a temporary point-to-point physical connection is set up to support theunidirectional transfer of PDUs on one or more PDCHs. This connectionis called a Temporary Block Flow.

A Temporary Block Flow is maintained only for the duration of the data transfer.The Temporary Block Flow is allocated radio resources on one or more PDCHsand comprises a number of RLC/MAC blocks carrying one or more PDUs.

A typical user session in which data is exchanged bi-directionally requires theestablishment of one Temporary Block Flow in each direction, and the pathof each Temporary Block Flow can be different.

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2.4.1 Mobility Management

Since the integrity of the data transmitted is crucial, packet-switched networksemploy a method of error checking. This confirms that the data receivedcorrespond exactly to the data transmitted.

In GPRS, an LLC-PDU includes a Frame Check Sequence used to detect errorsin the header and information fields of the PDU (see Figure 12). The FrameCheck Sequence uses the Cyclic Redundancy Check method of error checking.

When an error is detected, retransmission of the LLC-PDU is requested. Thischaracteristic of packet-switched data transfer means that handovers, as theyare done in traditional circuit-switched GSM calls, are not necessary.

Mobility Management in GPRS can be accomplished by the combination ofautonomous cell reselection by the mobile station and packet error correction.The process is as follows:

1. The mobile station performs an autonomous cell reselection. The process isbased on average measurements of received signal strength on the PBCCHfrequencies of the serving cell and the neighbor cells as indicated in theGPRS neighbor cell list.

The cell reselection procedure is the same as for circuit-switched traffic, butbased on GPRS reselection parameters configurable by the operator.

If the cell does not have a PBCCH the mobile station applies existing circuitswitching parameters using the BCCH.

2. Once the mobile station is camped on the new cell, the data transfer isresumed If an LLC-PDU has not been correctly received, it is re-emitted.

This process produces a slight overhead on throughput but has the advantageof greatly simplifying the cell change process.

Re-establishment If the mobile station detects a radio link failure, it will re-establish the link withthe SGSN. The BSS transmits the reselection configuration parameters to beused by the mobile station. Mobile controlled re-selection is equivalent tocircuit-switched call re-establishment. Refer to Call Re-establishment by theMobile Station (Section 4.8) for more information.

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2.4.2 Paging

Paging is the procedure by which the network contacts a mobile station.The network can coordinate circuit-switched and packet-switched paging, ifthere is a Gs interface between the MSC and the SGSN. This means thatcircuit-switched paging messages can be sent on the channels used forpacket-switched paging messages, and vice-versa. Three modes are defined.

Mode Description

NetworkOperation Mode1

Circuit-switched paging messages are sent via the SGSNand MFS

The circuit-switched paging message for theGPRS-attached mobile station is sent on the PPCH orCCCH paging channel, or on the PACCH. This meansthat the mobile station only needs to monitor one pagingchannel. It receives circuit-switched paging messages onthe PACCH when the mobile station is in packet transfermode.


Circuit-switched paging messages are sent via the MSCand BSC, but not the MFS.

The circuit-switched paging message for theGPRS-attached mobile station is sent on the CCCHpaging channel. The channel is also used forpacket-switched paging messages. This means thatthe mobile station only needs to monitor the PCH.Circuit-switched paging continues on the PCH even if themobile station is assigned a PDCH.


Circuit-switched paging messages are sent via the MSCand BSC, but not the MFS.

The circuit-switched paging message for theGPRS-attached mobile station is sent on the CCCHpaging channel. The packet-switched paging message issent on either the PPCH (if allocated) or on the CCCHpaging channel

Table 6: Network Operation Modes

Packet-switched paging does not use the Local Area for paging, but a GPRSRouting Area . The RA is smaller, thus fewer cells are involved.

2.4.3 Radio Power Control and Radio Link Measurement

In order to decrease the level of interference in a network, the uplink anddownlink transmissions are constantly measured and a balance maintainedbetween transmission power and the actual quality of the link. In GPRS, powercontrol is implemented in open loop on the uplink path. This maintains speechquality in the network and keeps a low bit error rate for data transmission.

The BSS broadcasts the configuration parameters necessary for the mobilestation. When it first accesses a cell, the mobile station sets its output power asdefined in the system information. It then re-sets its power output according tothe parameters broadcast, and to an evaluation of the uplink path loss.

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2.5 Resource ManagementIn order to provide flexibility to the operator in managing the use of resourcesby circuit-switched and packet-switched traffic, resources are shared betweenthe MFS and the BSC. Use of these resources by one system or the other canbe controlled by a variety of parameters to meet operators’ needs. The MFSand BSC co-ordinate resource management over the BSCGP interface.

In GPRS, resource management refers principally to the allocation of PacketData Channels. PDCHs are dynamically allocated according to user-settablecriteria.

When a Temporary Block Flow request is made, resources are allocated onone or more PDCH for the transfer of PDUs. The allocation process takesplace as follows:

1. A TBF establishment request is received (through a (Packet) Channelrequest for the uplink, or through a downlink LLC PDU for the downlink)

2. The number of PDCHs is determined with the:

Mobile station multislot class. This is not always known in the uplink case.

O&M parameter (MAX_PDCH_PER_TBF). This defines the maximum

number of PDCHs which can be allocated per TBF.

3. If the requested number of PDCHs is not available, a request to establish aTBF is sent to the BSC.

4. PDCHs are allocated to the TBF

2.5.1 Time Slot Allocation

GPRS allows bandwidth to be shared between several mobiles. On a radiotime slot, bandwidth can be shared between up to nine users on the downlinkpath and six on the uplink path- or up to 16 GPRS requests within one time slot.Circuit-switched data services require at least one time slot per user.

The radio blocks on each time slot are equally distributed among the usersassigned to the channel. For example, on the uplink path when coding scheme2 is used, the minimum raw bit rate per user is 1.9 kbit/s (13.4/7) instead of 13.4kbit/s. The following table describes the parameters for time slot allocation.

This parameter: Is used to:

MAX_UL_TBF_

SPDCH

Define the maximum number of users (between one andsix) that share a PDCH in the uplink direction.

MAX_DL_TBF_

SPDCH

Define the maximum number of users (between one andnine) that share a PDCH in the downlink direction.

N_TBF_PER_

PDCH

Define the optimum number of shared users per directionand per PDCH. This ensures a good bit rate as long asthe GPRS load is normal.

Table 7: Time Slot Allocation Parameters

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Time Slot AllocationScenario

If MAX_UL_TBF_SPDCHis set to five, the minimum raw bit rate per user will beincreased from 1.9 kbit/s to 2.68 kbit/s (13.4/5). When the PDCH reaches five,it is declared full and will not accept a sixth shared user.

However, setting the N_TBF_PER_PDCHparameter will affect a compromisebetween resource efficiency and quality of service For example, ifN_TBF_PER_PDCH= 2and coding scheme 2 is used, the preferred raw bit rateper user will be 6.7 kbits/s (13.4/2). When the number of users on the PDCHreaches the N_TBF_PER_PDCHvalue (2), the PDCH is declared “busy” and willpreferably not accept a third user. But if the GPRS load is such that all PDCHsare busy, the BSS will override the number of users set in N_TBF_PER_PDCH

and increase the number of shared resources to the maximum, using theMAL_XL_TBF_SPDCHvalue.

2.5.2 Frequency Hopping

Frequency hopping improves the bit error rate and therefore contributes tooverall network quality. Frequency hopping, already provided for circuit-switchedchannels, has been extended to the packet-switched channels for GPRSimplementation. The BSS sends the hopping law when setting up a connection.All GPRS channels then use the same hopping law in a synchronized scheme.

For detailed information on frequency hopping, refer to Call Set Up (Chapter 3).

2.5.3 PCM Link Sharing

Resource allocation is facilitated by the use of a shared 2048 kb/s PCM link.GPRS signaling and traffic channels can be multiplexed with circuit-switchedtraffic channels on this link between the MFS and the BSC.

Traffic on the Ater Mux interface between the MFS and the Transcoder is eitherprocessed by the MFS as GPRS traffic, or passed transparently through thecross-connect in the MFS to the BSC as circuit-switched traffic.

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2.5.4 Resource Reallocation

This feature can be enabled using the EN_RES_REALLOCATIONparameter. Thefeature provides radio and transmission resources for a TBF following an uplinkrequest received from the mobile station, or one or more downlink LLC PDUsreceived from the SGSN, when there is no established TBF for the mobilestation. It is also now possible for more than one TRX allocated to GPRSservices in any given cell. Resource allocation needs to be prioiitized, soproirity is set on PDCH groups. The allocation is granted towards the PDCHgroup with the highest priority. The feature avoids PDCH groups is a congestedstate and PDCG groups that are dual-rate capable.

There can be one or more master PDCHs in a given cell (to support PBCCHand PCCCH channels). The primary master channel is allocated on time slots0-3. The MPDCH allocation is therefore done preferrably on the leftmostavailable PDCH on the preferred TRX. In order to avoid holes between theMPDCH(s) and the SPDCH(s), the SPDCH allocation is therefore also donepreferrably on the leftmost available PDCH.

The requested throughput is served on the:

Maximum number of slots allowed by the MS multislot class

GPRS service constraints (the operator gives the maximum number ofallowed slots for one GPRS connection)

Network constraints (resource availability).

Therefore the allocation strategy consists in maximising the usage of theallocated PDCH(s) and, if necessary, to request additional PDCH(s) fromthe BSC.

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2.6 Traffic Load ManagementTraffic load conditions affect PDCH allocation, as described in CongestionControl (Section 2.6.1). A PDCH can have one of four possible states, asshown in the following table.

State Explanation

Empty No established TBFs.

Active At least one established TBF and the total number ofestablished TBFs is smaller than a defined threshold(O&M Parameter N_TBF_PER_PDCH).

Busy The number of established TBFs is greater thanor equal to O&M Parameter N_TBF_PER_PDCHbutsmaller than the maximum allowed (O&M ParameterMAX_UL/DL_TBF_PDCH).

Full The number of established TBFs is equalto the maximum set by O&M ParameterMAX_UL/DL_TBF_PDCH.

Table 8: PDCH Traffic Load States

Additional O&M parameters are available to define a condition of "high load"traffic in the BSC. When traffic exceeds the threshold defining “high load”,the following occurs:

1. The maximum number of PDCHs allowed is lower than under normal loadconditions. This maximum is set by the parameter MAX_PDCH_HIGH_LOAD.This corresponds to the reception of a high load BSC notification. Thereare two phases involved:

A "soft pre-emption" where exceeding PDCHs are marked and cannotsupport new TBFs. The timer T_PDCH_Pre-emption is started.

A "fast pre-emption" phase is entered when the timer

T_PDCH_Pre-emption expires. When this occurs, the remaining TBFs onmarked PDCHs are released.

2. The MFS de-allocates PDCHs as soon as they become empty until thenew, lower threshold is reached.

3. When normal load conditions resume, the MFS can then reallocateadditional resources up to the limit defined for its PDCH group. This is set bythe parameter MAX_PDCH_GROUP.

This is the process that takes place during the phase marked “High BSC Load”,shown in the figure below. The figure shows a typical sequence illustrating thePDCH allocation procedure. Numbers in bold refer to the steps above.

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Allocated PDCHs

High BSC load Normal BSC loadNormal BSC load

Time

MAX_PDCH_GROUP

MIN_PDCH_GROUP

MAX_PDCH_HIGH_LOAD

Cell activated

GPRS MS requests time slots

Maximum number of PDCHs is reached

1

2

3

GPRS : General Packet Radio Service

MS : Mobile Station

PDCH : Packet Data Channel

Figure 14: GPRS Traffic Load Management

2.6.1 Congestion ControlCapacity on Demand Capacity on demand allows operators to both reserve a number of PDCH for

GPRS traffic and reserve other PDCH for shared traffic, according to the realtraffic load in the cell at any given moment. The actual GPRS traffic load isdynamically matched by allocating or de-allocating PDCH after negotiationbetween the MFS and the BSC.

The BSC is the master in the negotiation process, which means ifcircuit-switched traffic is heavy in a cell, there is no guarantee a GPRS mobilestation can establish a call. To ensure GPRS calls are possible at any time,the parameter MIN_PDCHcan be set at the OMC-R to define the number ofPDCH permanently allocated to GPRS in a cell. Using this parameter to set theminimum number of PDCH allocated to GPRS traffic also sets the maximumnumber of PDCH allocated to circuit-switched traffic.

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2.6.2 Smooth PDCH Traffic Adaption to Cell Load Variation

To avoid wasting GPRS traffic resources when entering a high load situation,(with the ability to allocate GPRS traffic on multiple TRXs the gap betweenMAX_PDCHand MAX_PDCH_HIGH_LOADcould be much bigger than in B6.2),the BSC evaluates the total (circuit and packet-switched) traffic per cell andindicates the amount of PDCHs that can be granted for GPRS traffic to the MFS.

The BSC notifies the MFS about any change in the number of available GPRSresources. Thus the GPRS traffic is constantly adapted to the actual trafficsituation in the cell.

Two parameters conrol smooth PDCH traffic adaption:

EN_DYN_PDCH_ADAPTATION. Enables smooth PDCH traffic adaption.

Load_EV_Period_GPRS . Calculates the number of load samples (calculated

every TCH_INFO_PERIOD) for the PDCH traffic adaption load averagingalgorithm.

2.6.3 GPRS Overload Control

To prevent traffic overload conditions, the SGSN and the BSS constantlyexchange traffic load information. This exchange of information, or flow control,regulates the downlink traffic between the SGSN and the BSS. The BSS sendsmobile station and BSSGP Virtual Connection radio status information to theSGSN, which then regulates the output traffic to the BSS when needed. Flowcontrol is thus applied at two levels: mobile station and BVC.

Because more than one Network Service Virtual Connection can be usedbetween the BSS and the SGSN, the traffic load can be shared and thussmoothly distributed over the Gb interface. At data transfer uplink initialization,an Network Service Virtual Connection is selected and the uplink bandwidthis reserved. If an Network Service Virtual Connection is unavailable, trafficis then put on another Network Service Virtual Connection. The reservedbandwidth on the Network Service Virtual Connection is released at the end ofthe transfer. Load sharing allows different data transfers within the same cell tobe carried by different Network Service Virtual Connection.

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2.6.4 Delayed Downlink TBF Release

Delaying the release of downlink TBFs allows enhancement of the datathroughput served to mobile station end users. It also significantly reducesthe GPRS signalling load. GPRS RLC/MAC procedures were designed fornonreal-time data transfer where the data arrives as one large block. However,the true nature of packet traffic is usually different from this assumption. Forexample, TCP based applications often send small packets between peerentities before the actual data transfer starts. This leads to a high number ofTBF establishments and releases. Consequently, the resource utilization is farfrom optimal and transmission delays unnecessary long. The problem canbe avoided by delaying TBF release for a short period (e.g. 0.5-2s) after thetransmission buffer becomes empty.

Delayed downlink TBF release can occure in the following two modes:

Acknowledged mode

Unacknowledged mode.

Two paramaters control delayed downlink TBF release:

EN_DELAYED_DL_TBF_REL, enables the delayed TBF release feature on thedownlink. The default value is OFF.

T_NETWORK_RESPONSE_TIME. This timer indicates the typical response time

of a network server as seen from this MFS. The timer range is 0-5000 ms(in 100 ms steps). The default value is 700 ms.

Acknowledged Mode When the network wishes to delay the release of the TBF, it sends the lastRLC data block but does not set the Final Block Indicator (FBI) bit. Thenetwork only sets the FBI bit when it wishes to permanently end the TBF.Once the network has sent the RLC data block containing the last octets ofthe most recent LLC frame to the MS, the network maintains the downlinkTBF by occasionally sending dummy downlink RLC data blocks to the MS,incrementing the BSN with each dummy data block sent. When the networkreceives a new LLC frame, it begins to transmit new RLC data blocks to the MS,beginning with the next available BSN.

When the network wishes to poll the MS for a Packet Downlink Ack/Nack when ithas no LLC data to send, the network sends a dummy downlink RLC data block.The dummy downlink RLC data block is formed by inserting an LLC DummyUI Command into a CS-1 downlink RLC data block. The LLC Dummy UICommand is an invalid LLC PDU and is discarded by the LLC entity in the MS.

Unacknowledged Mode In RLC unacknowledged mode the MS detects the end of the TBF by detectingthe Final Block Indicator (FBI) bit set to 1. The MS then transmits a PacketControl Acknowledgement, acknowledging the end of the TBF. The procedurefor delayed release of downlink TBF in RLC acknowledged mode appliesexcept that no retransmission of data blocks is done.

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2.7 Data TransmissionThis section describes the actual process for GPRS data transmission,and explains Attach/Detach procedures, Packet Data Protocol ContextActivation/De-activation, and mobile-originated and mobile-terminated datatransfer.

2.7.1 GPRS Attach

To access GPRS services, the mobile station performs a GPRS Attach orcombined GPRS/IMSI Attach to the SGSN. (For more information on IMSIAttach-Detach, a mobility feature, see IMSI Attach-Detach (Section 3.3.4)).This procedure establishes a logical link between the mobile station and theSGSN, and allows the mobile station to be available for paging from the SGSNand notification of incoming GPRS data.

This process is illustrated in the following figure.

MS BTS BSC MFS SGSN

Update Location

Subscriber

Data

SubscriberData ACK

Update

Location ACK

GPRS Attach Complete

HLR

GPRS Attach Request

Authentication

GPRS Attach Accept



MS : Mobile station

GPRS : General Packet Radio Service


Figure 15: GPRS Attach

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1. The mobile station sends a GPRS Attach Request to the SGSN. Thisrequest contains:

The mobile station identity (IMSI or P_TMSI)

The mobile station Routing Area Identity

The type of Attach procedure requested (GPRS Attach, or combinedGPRS/IMSI Attach)

The mobile station classmark

2. The SGSN verifies the mobile station identity, sends a location update tothe HLR, (if the attach requested is a combined GPRS/IMSI Attach, theMSC/VLR is also updated), and requests a subscriber data profile.

3. The HLR sends a location acknowledgment back to the SGSN with thesubscriber data inserted.

4. The SGSN then assigns a P_TMSI to the mobile station.

5. The mobile station acknowledges the P_TMSI, and the Attach procedureis complete.

Once the GPRS Attach procedure is performed, the mobile station is in Standbyand can activate Packet Data Protocol contexts.

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2.7.2 Packet Data Protocol Context Activation

A Point-To-Point GPRS subscription contains one or more Packet DataProtocol addresses. Each Packet Data Protocol address is defined by anindividual Packet Data Protocol context in the mobile station, the SGSN, andthe GGSN. Before a mobile station can send or receive data, a Packet DataProtocol context must be activated. Only the GGSN or a mobile station inStandby or Ready can activate Packet Data Protocol contexts. This processis illustrated in the following figure.

MS BTS BSC MFS SGSN

Activate PDP Context Request

Create PDP Context Request

Create PDP

Context Response

GGSN

Activate PDP Context Accept



MS : Mobile station

PDP : Packet Data Protocol


Figure 16: Mobile Station-Originating Packet Data Protocol Context Activation

MobileStation-Originating

Activation

1. The mobile station sends an Activation Request to the SGSN. This requestcontains:

Transaction Identifier

Packet Data Protocol type

Packet Data Protocol address

Access Point Name

Quality of Service requested

Packet Data Protocol configuration options.

2. The SGSN verifies the mobile station subscriber data, creates a TunnelIdentifier (TID — a logical bidirectional tunnel between the mobile stationand the GGSN), and sends the new Packet Data Protocol type and addressto the GGSN.

3. The GGSN creates a context, sends an acknowledgment to the SGSN,which sends an acknowledgment to the mobile station.

4. The GGSN can now send data through the SGSN, and billing can begin.

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GGSN-OriginatingActivation

The GGSN Packet Data Protocol context activation process is illustrated inthe following figure.

MS BTS BSC MFS SGSN

Routing InfoACK

PDP PDU

HLR

PDU Notification Request

GGSN

Routing Info

Request

PDU Notification Response

Request PDP Context Acitvation

PDP Context Activation




MS : Mobile station


PDU : Protocol Data Unit


Figure 17: GGSN-Originating Packet Data Protocol Context Activation

1. When the GGSN receives data, it sends a message to the HLR requestingthe mobile station location.

2. The HLR sends the GGSN location information and the current SGSN IPaddress.

3. The GGSN sends a PDU Notification Request to the SGSN, which indicatesa Packet Data Protocol context needs to be created.

4. The SGSN returns a PDU Notification Response to the GGSN, and sends aRequest Packet Data Protocol Context Activation message to the mobilestation. This message contains the Packet Data Protocol type and address

5. The mobile station then begins a Packet Data Protocol context activationprocedure as described above

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2.7.3 Data TransferMobile-Originated Data

TransferThe following figure illustrates the process.

MS BSS SGSN

Packet UL TBF

Assignment

Packet ChannelRequest

UL LLC PDU

RLC PDU

ACK/NACK

RLC PDU

RLC PDU

ACK/NACK

1

2

3

4

5

6

LLC : Logical Link Control

MS : Mobile station


RLC : Radio Link Control


TBF : Temporary Block Flow

UL : Uplink

Figure 18: Mobile-Originated Data Transfer

When the mobile station has data to send:

1. An Uplink Temporary Block Flow is requested (either on PRACH, if thereis a master PDCH, or on RACH).

2. An Uplink Temporary Block Flow is established.

3. Data is sent to the network through the Radio Link Control Protocol DataUnits.

4. Radio Link Control Protocol Data Units are acknowledged by the network.

5. Radio Link Control Protocol Data Units are re-assembled into Logical LinkControl Packet Data Units and sent to the SGSN.

6. On receipt of the last Radio Link Control Protocol Data Units, anacknowledgment is returned and the Uplink Temporary Block Flow isreleased.

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Mobile-Terminated DataTransfer

The following figure illustrates the process.

MS BSS SGSN

Paging PS

PPCH or PCH

Packet ChannelRequest

STAND BY

Packet UL TBF

Assignment

LLC PDU

UL − LLC PDU

READY

DL − LLC PDU

Packet DL TBF

Assignment

1

2

3

4

5

6

DL : Downlink

MS : Mobile station

LLC : Logical Link Control

PCH : Paging Channel


PPCH : Packet Paging Channel

PS : Packet Switched


TBF : Temporary Block Flow

UL : Uplink

Figure 19: Mobile-Terminated Data Transfer

When the network has data to send to the mobile:

1. The SGSN receives a downlink Packet Data Protocol PDU for a mobilestation, and sends a paging request to the BSS.

2. The BSS sends packet paging requests to all the cells in the routing area, onthe PPCH if there is a master PDCH in the cell, or on the PCH.

3. The mobile station requests the establishment of an UL TBF from the BSS.

4. The UL TBF is established, which allows the mobile station to send a LogicalLink Control PDU to the SGSN in order to acknowledge the paging message.

5. The SGSN sends the data LLC PDUs to the BSS.

6. The BSS establishes a Downlink TBF on receipt of the first LLC PDU, andreleases on receipt of the last LLC PDU.

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2.7.4 Packet Data Protocol Context De-activation

Before a GPRS Detach procedure can be initiated, the Packet Data Protocolcontext must be de-activated.


De-activation

The following figure illustrates this process.

MS BTS BSC MFS SGSN

De−Activate PDP Context Request

Delete PDPContext Request

Delete PDP

Context Response

GGSN

De−Activate PDP Context Accept



MS : Mobile station



Figure 20: Mobile Station Originating Packet Data Protocol Context De-activation

1. The mobile station sends a De-activate Packet Data Protocol ContextRequest to the SGSN.

2. The SGSN sends a Delete Packet Data Protocol Context Request to theGGSN, which contains the TID.

3. The GGSN deletes the Packet Data Protocol context, and sends a DeletePacket Data Protocol Context Response with the de-activated TID to theSGSN.

4. The SGSN sends a De-activate Packet Data Protocol Context Acceptmessage to the mobile station, confirming the de-activation.

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SGSN-OriginatingDe-activation

Network originated Packet Data Protocol context de-activation processesare shown in the following figure.

MS BTS BSC MFS SGSN


Delete PDP

Context Response

GGSN


SGSN−Originating


GGSN−OriginatingDelete PDP

Context Request



Delete PDPContext Response



MS : Mobile station



Figure 21: Network-Originating Packet Data Protocol Context De-activation Processes

1. The SGSN sends a Delete Packet Data Protocol Context Request to theGGSN, which contains the TID.

2. The GGSN de-activates the Packet Data Protocol context and sends aDelete Packet Data Protocol Context Response to the SGSN.

3. The SGSN sends a De-activate Packet Data Protocol Context Request tothe mobile station.

4. The mobile station de-activates the context, and returns a De-activatePacket Data Protocol Context Accept.

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GGSN-OriginatingDe-activation

1. The GGSN sends a Delete Packet Data Protocol Context request to theSGSN, which contains the TID.

2. The SGSN sends a De-activate Packet Data Protocol Context Request tothe mobile station.

3. The mobile station de-activates the context and returns a De-activatePacket Data Protocol Context Accept.

4. The SGSN sends a Delete Packet Data Protocol Context Response to theGGSN, which deletes the context.

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2.7.5 GPRS Suspend

GPRS suspend processes are shown in the following figure.

MS BTS BSC MFS SGSN

RR Suspend

Suspend

Suspend

Suspend Ack

Suspend Ack

T3



Figure 22: GPRS Suspend

1. The GPRS suspension procedure is initiated by the mobile station bysending an RR Suspend (TLLI, RAI, suspension cause) message to theBSC. This is sent as soon as possible, after entering the dedicated mode. Ifthe GPRS suspension procedure was initiated during a GPRS transfer, themobile station releases all its GPRS resources.

2. The BSC sends a Suspend (TLLI, RAI, suspension cause) message to theMFS, via the GSL link. The BSC stores TLLI and RAI in order to be able torequest the SGSN (via the MFS) to resume GPRS services when the mobilestation leaves the dedicated mode. A timer is not necessary to monitor theSuspend Ack reception. If this acknowledgment is not received (i.e. noSuspend Reference Number (SRN) reception, see step 4), the Resume willnot be sent at circuit-switched call completion.

3. The MFS sends a Suspend (TLLI, RAI) message to the SGSN.

4. The MFS receives a Suspend Ack from the SGSN, in which there is aSuspend Reference Number which is used in the GPRS resume process.The acknowledgment of the SGSN is supervised by a timer (T3).

5. The MFS sends a suspend acknowledgment to the BSC, with the SuspendReference Number information.

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2.7.6 GPRS Resume

GPRS resume processes are shown in the following figure.

Routing Area Update Request

MS BTS BSC MFS SGSN

Resume

Resume

Resume Ack

Resume Ack

T4

RR Channel Release

T_GPRS_Resume


MS : Mobile station

RR : Radio Resource


Figure 23: GPRS Resume

1. The BSC determines that the circuit-switched radio channel must bereleased (typically upon circuit-switched call completion). If the BSC is ableto request the SGSN to resume GPRS services (i.e. the suspend proceduresucceeded and the BSC received the Suspend Reference Number, and noexternal handover has occurred), the BSC sends a Resume (TLLI, RAI,Suspend Reference Number) message to the MFS. After sending theResume message, the BSC starts a guard timer (T_GPRS_Resume) andwaits for a Resume Ack message from the MFS. The guard timer is set asshort as possible, so as to be compatible with the usual RR connectionrelease procedure, and therefore not delay the procedure. However, thismessage is not sent in the case of successful completion of an externalhandover. In this case, the BSC deletes any stored data or suspend/resumecontext related to that mobile station.

2. On receipt of a Resume message from the BSC, the MFS sends a Resume(TLLI, RAI, Suspend Reference Number) message to the SGSN, starts aguard timer (T4) and waits for a Resume Ack message from the SGSN.

3. The MFS receives a Resume Ack from the SGSN.

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4. On receipt of the Resume Ack from the SGSN, the MFS stops the guardtimer (T4) and sends a Resume Ack message to the BSC. If no Resume Ackis received from the SGSN before expiry of the guard timer (T4), the MFSsends a Resume Nack to the BSC. On receipt of the Resume Ack or Nackmessage from the MFS, the BSC stops the guard timer (T_GPRS_Resume).

5. The BSC sends an RR Channel Release (GPRS Resumption) messageto the mobile station and deletes its suspend/resume context. GPRSResumption indicates whether the BSS has successfully requested theSGSN to resume GPRS services for the mobile station, (i.e., whetherResume Ack was received in the BSS before the RR Channel Releasemessage was transmitted). The mobile station then exits dedicated mode. Ifthe guard timer expired, or if a Resume Nack message was received bythe BSC, the Channel Release message includes the GPRS Resumptionindication equal to NOK.

6. The mobile station resumes GPRS services by sending a Routing AreaUpdate Request message in the following cases:

Reception of a Channel Release with GPRS Resumption = NOK

Reception of a Channel Release without GPRS Resumption IE

T3240 expiry.

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2.7.7 GPRS Detach

After the Packet Data Protocol Context has been de-activated, the mobilestation or the network can perform a GPRS Detach procedure. Whether thedetach is initiated by the mobile station or the network, the results are the same:

The mobile station leaves the Ready mode and enters the Idle mode

All Packet Data Protocol contexts are deleted

The mobile station returns to the circuit-switched system.


Detach

The following figure illustrates this process.

MS BTS BSC MFS SGSN


Delete PDP

Context Response

GGSN

GPRS Detach Accept

Detach Request



MS : Mobile station



Figure 24: Mobile Station-Originating GPRS Detach

1. The mobile station sends a GPRS Detach Request to the SGSN. Thismessage contains:

The type of Detach (GPRS or GPRS/IMSI)

An indication if the Detach is due to a mobile station Switch off.

2. The SGSN tells the GGSN to de-activate the Packet Data Protocol context,and sends a Detach Accept message to the mobile station.

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Network-OriginatingDetach

Network-originating GPRS Detach procedures are shown in the following figure.

MS BTS BSC MFS SGSN


GGSN HLR

GPRS Detach Request

Cancel Location

Delete PDP

Context Response

Detach Accept

Cancel Location ACK




MS : Mobile station



Figure 25: Network-Originating GPRS Detach Procedures

A GPRS Detach can be initiated by both the SGSN and the HLR.

An SGSN Detach is the most common network Detach. In this procedure:

1. The SGSN sends a Detach Request to the mobile station, which containsthe Detach type. The Detach type tells the mobile station if it needs tore-attach and re-activate the Packet Data Protocol context previously used.

2. The SGSN tells the GGSN to de-activate the Packet Data Protocol contexts,and the mobile station sends the Detach Accept message to the SGSN.

If the Detach is requested by the HLR:

1. The HLR sends a Cancel Location message to the SGSN, which initiatesthe above process.

2. The SGSN confirms the Packet Data Protocol context deletion by sending aCancel Location Acknowledgment to the HLR.

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3 Call Set Up

This chapter provides an overview of how a call is set up between the NSS andthe mobile station. It describes the various kinds of calls that can be set up.The type of teleservice and bearer service required are also described.

This chapter also describes the following parts of the Call Set Up procedure:

Overview

Mobile Originated Call

Mobile Terminated Call

Paging

Congestion

Classmark Handing

Authentication

Ciphering.

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3.1 OverviewCall set up is required to establish communication between a mobile stationand the NSS. The NSS is responsible for establishing the connection with thecorrespondent. Different types of calls require different teleservices. Theseteleservices are defined in the GSM specifications. The type of teleserviceand bearer service to be used is negotiated before the normal assignmentprocedure. See Normal Assignment (Section 3.2.3) for more information.

Call Types The following table shows the three basic types of call:

Type of Call Description

Mobility Management Calls These calls, e.g. location update, are used bythe system to gather mobile station information.The exchanges are protocol messages only;therefore, only a signalling channel is used.Figure 7 illustrates the location updateprocedure.

Service Calls These calls, e.g. SMS and SS calls, passsmall amounts of information. Therefore, onlya signalling channel is used.

User Traffic Calls These calls, e.g. speech or data calls to acorrespondent, can pass large amounts ofinformation. Therefore they require greaterbandwidth than a signalling channel. Thesecalls use traffic channels.

Table 9: Types of Calls

The channels used for calls are the SDCCH for signalling and the traffic channelfor user traffic (see The Air Interface (Section 1.7.7) for more information).These channels are associated with FACCH/SACCH. An SDCCH is alwaysassigned for call set up, even if a traffic channel is later required for the call.

The role of the BSS in call set up is to assign the correct channel for thecall, and to provide and manage a communications path between the mobilestation and the MSC.

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Call Set Up Phases The following table shows the phases involved in call set up:

Phase Composition

Radio and LinkEstablishment

Paging (for mobile terminated calls only) informsthe mobile station that it is being called.

If attach_detach_allowed is activated, themobile station IMSI_detach message caneliminate the need for paging. See IMSIAttach-Detach (Section 3.3.4).

Immediate assignment procedure allocates aresource to the mobile station and establishes aRadio signalling Linkbetween the BSS and themobile station.

A interface connection, to assign an SCCPsignalling channel between the BSC and MSC

Assignment of a switching path through the BSC.

Authentication andCiphering

Classmark handling

Authentication

Ciphering.

Normal assignment Teleservice/bearer service negotiation

Channel allocation

Physical context procedure

Assigning a traffic channel, if required

Connecting the call.

Table 10: Call Set Up Phases

The phases are described in Mobile Originated Call (Section 3.2) and MobileTerminated Call (Section 3.3).

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3.2 Mobile Originated CallA call initiated by a mobile station can either be a subscriber call, wherespeech and/or data is passed across the network, or a location update callfrom a mobile station in idle mode. Location update information is passedon the signalling connection. Therefore, the initial call set up procedure issimilar to a subscriber call. The location update does not require allocationof a traffic channel.

3.2.1 Radio and Link Establishment

When a connection with a mobile station is required, the following must happen:

A radio channel must be assigned to permit communication between the

mobile station and the BSS

A terrestrial link must be established in order to signal the presence of

the mobile station to the network.

The procedure of obtaining these initial connections is called radio and linkestablishment. The radio and link establishment procedure establishessignalling links between:

The BSS and the mobile station via the SDCCH channel

The BSS and the MSC via the SCCP link.

These links pass the information for call negotiation, and set up a trafficchannel, if required.

The figure below shows radio and link establishment for a mobile originated call.

Channel Request The mobile station initiates a call by sending a channel_request message,with an REF. The REF includes an establishment cause and a RAND (used forauthentication). It is transmitted on the RACH channel. The RACH channel isassociated with the CCCH channel which the mobile station is monitoring whilein idle mode. The establishment cause field of the REF specifies:

An emergency call

Call re-establishment

Response to paging

Mobile station originating speech call

Mobile station originating data call

Location update

Service call (SMS, etc.).

The mobile station notes the random number and frame number associatedwith each channel_request message. These are used by the mobile station torecognize the response sent from the BSS. This response is sent on the AGCH,which can be monitored by many mobile stations. The mobile station decodesall messages sent on this AGCH, and only accepts a message with a randomnumber and frame number matching one of the last three requests sent.

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MS BTS BSC MSC

SDCCHAllocation

Switch toSDCCH

REF stored in MS memory

Service Request must match original sent by MS in the SABM

MS compares message with REF in memory

Channel Request (RACH)

REF Channel RequiredREF+RFN+TA

Channel Activation

TA+SDCCH+power

Channel Activation Ack

Immediate assign command

TA+SDCCH+power+RFN+REF

Immediate assignment (AGCH)

REF+RFN+TA+SDCCH

SABM+ cm + Service Request

UA

Service Request

Establish Indicationcm + Service Request

SCCP Connection Requestcm + Service Request

SCCP Connection Confirm

cm : Classmark

ID : Mobile station identity

power : Mobile station power or BTS power

REF : Random access information value

RFN : Reduced frame number

SDCCH : Description of the allocated SDCCH (Stand-alone Dedicated Control Channel)

ServiceRequest

: Initial layer 3 message

TA : Timing advance

UA : Un-numbered acknowledgment

Figure 26: Radio and Link Establishment for Mobile Originated Call

The mobile station continues to transmit channel_request messages until itreceives a response. If no response is received before the mobile station hastransmitted a predefined number of retries, the mobile station:

Displays a network error message for all calls except location updates

Performs automatic reselection for location update calls. This means thatthe mobile station attempts random access on a different cell.

On receipt of the channel_request message from the mobile station, the BTSsends a channel_required message to the BSC. This message contains therandom number sent by the mobile station, and the timing advance measuredby the BTS.

Note: Under peak load conditions, resources may be over allocated due to thisprocess. See below for details on how the Immediate Assignment Extendedfeature works to alleviate this problem.

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SDCCH ChannelActivation

The BSC checks the channel_required message to ensure it can accept therequest. It allocates an SDCCH channel if one is available. The resourcemanagement software of the BSC allocates the SDCCH on the basis of whichtraffic channel has the most available SDCCHs. This ensures the load isspread between the traffic channels.

The BSC then sends a channel_activation message to the BTS. It also sets atimer to wait for an acknowledgment from the BTS, indicating that it is ready toactivate the channel. The channel_activation message contains:

A description of the SDCCH to be used

The timing advance

Mobile station and BTS power commands. The mobile station and BTSpower are set to the maximum allowed in the cell.

The BTS initiates the physical layer resources for the channel and sets theLAPDm contention resolution ready for the first mobile station message on theSDCCH. It then sends a channel_activation_acknowledgment message tothe BSC. The BSC stops its guard timer.

Note: Contention resolution prevents two mobile stations connecting to the sameSDCCH.

The following figure shows the Channel Activation procedure.

MS BTS BSC MSC

SDCCHAllocation

Channel Activation Ack

Channel Activation

TA+SDCCH+power

power : Mobile station power or BTS power


TA : Timing advance

Figure 27: SDCCH Channel Activation

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Immediate Assignment The BSC builds and sends an immediate_assign_command messagereiterating the information given in the channel_activation message. Thismessage also includes the random number and frame number of the originalmobile station request to which the BSC is replying. It also instructs the BTS toinform the mobile station of the SDCCH channel assignment. The BSC starts aguard timer for the mobile station to respond.

The following figure shows the Immediate Assignment procedure.

MS BTS BSC M

Switch toSDCCH

Immediate assignment (AGCH)

REF+RFN+TA+SDCCH

Immediate assign command

TA+SDCCH+power+REF+RFN




TA : Timing advance

Figure 28: Immediate Assignment

The BTS sends the immediate_assignment message to the mobile stationon the AGCH.

The mobile station checks the random number and frame number in theimmediate_assignment message. If it matches those from one of itslast three channel_request messages, the mobile station switches to theindicated SDCCH and sets its timing advance to the value indicated in theimmediate_assignment message.

Immediate AssignmentReject

When there is congestion on the SDCCH, the mobile station could retryrepeatedly without success to access a channel. This produces the followingundesired effects:

Undesirable messages on the mobile station screen

The subscriber has to restart his call attempt manually

Repeated futile attempts to connect overload the RACH and Abis interface

“Ping-pong” cell reselection by the mobile station.

Therefore, the system implements a special immediate_assignment_rejectmessage when the following conditions are met:

The BSC flag EN_IM_ASS_REJ is set to true. This flag is set on a BSC

basis, and can be viewed but not modified from the OMC-R.

All SDCCHs in the cell are busy.

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The BSC receives a channel_required message from the BTS with one ofthe following establishment causes:

Emergency call

Call re-establishment

Mobile station originating call

Location update

Service Calls.

The immediate_assignment_reject message is contained in the informationelement of the immediate_assign_command message. This message startsa timer in the mobile station which causes it to wait in idle mode until the timerexpires, before sending new channel_request messages. The length of thetimer is dependent upon the establishment cause, and is user setable.

If an immediate_assign_command message is received before expirationof the timer, it has priority and the mobile station will respond to it, thusconnecting the call.

Note: This message can not be used when the mobile station is responding topaging, i.e. in the case of a Mobile-terminated call.

Immediate AssignmentExtended

Under peak load conditions, it is likely that the mobile station will send severalchannel_request messages before receiving an immediate_assignmentmessage indicating that a channel has been allocated to it. At this stage,the BSC is unable to identify the mobile station which sent a givenchannel_request and so it will grant several SDCCHs to the same mobilestation, thus wasting resources and reducing throughput on the AGCH.

If several immediate_assignment messages are queued on the AGCH,the BTS will try to build an immediate_assignment_extended message,passed to the mobile station on the air interface, constructed from pieces oftwo immediate_assignment messages as follows:

The first immediate_assignment message in the queue (i.e. the oldest)

The first of the remaining immediate_assignment messages in the queue,

which are able to be merged according to one of the following criteria:

At least one of the two allocated channels is non-hopping

If both allocated channels are hopping, they share the same Mobile

Allocation (see Baseband Frequency Hopping (Section 4.3.1) for more

information about Mobile Allocation).

If there are several immediate_assignment messages in the AGCH queue,but the first one cannot be merged with any other in the queue (using the abovecriteria), a “classic” immediate_assignment message is sent on the airinterface.

Set AsynchronousBalanced Mode

The first layer 2 frame sent on the SDCCH is a standard LAPDm type frame,known as the Set Asynchronous Balanced Mode. This is equivalent to theSet Asynchronous Balanced Mode Extended frame in the LAPD. On the Airinterface, it establishes the LAPDm connection with the BTS. This framecan also contain layer 3 messages.

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Contention Resolution The mobile station starts its LAPDm connection and sends a layer 3 messagein its first frame. The BTS uses this message for contention resolution. TheBTS sends an acknowledgment to the mobile station containing the same layer3 message. Therefore, only the mobile station that sent the message canaccept the acknowledgment from the BTS and consider itself connected.

The following figure shows the establishment of the connection for a mobileoriginated call.

MS BTS BSC MSC

SABM+ cm + Service Request

UA

Service Request

Establish Indicationcm + Service Request

SCCP Connection Requestcm + Service Request

SCCP Connection Confirm

cm : Classmark

ServiceRequest

: Initial layer 3 message including the mobile station identity and classmark

UA : Un-numbered acknowledgment

Figure 29: Connection for Mobile Originated Call

For a mobile station originated call, the layer 3 message from the mobilestation contains:

An Information Element indicating:

CM service request (speech/data, SMS, emergency call)

Location updating request (location updating procedure)

CM re-establishment request (after a failure)

IMSI detach indication (mobile station power off - see IMSI Attach-Detach(Section 3.3.4) for more information).

The mobile station identity (see Authentication (Section 3.7) for moreinformation)

The mobile station classmark (see Classmark Handling (Section 3.6) for

more information).

The network uses this message to decide which call negotiation procedures arerequired and whether to assign a traffic channel.

Establish Indication The BTS sends an establish_indication message to the BSC to indicate thatthe mobile station has connected. The BSC stops the guard timer, extracts theclassmark information, and initiates an SCCP connection with the MSC.

SCCP Connection The BSC sends an SCCP_connection_request message to the MSC. TheMSC replies with an SCCP_connection_confirm message. This messagecan contain a classmark request or a cipher mode command.

The signalling link is established between the mobile station and the MSC.

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3.2.2 Authentication and CipheringClassmark Procedure The content of the classmark IE sent during radio and link establishment

depends on the type of mobile station. The classmark information is used formobile station power control and to set ciphering. The MSC can request aclassmark update to ensure that it has the correct information. Classmarkprocedures are described in Classmark Handling (Section 3.6).

Authentication The authentication procedure:

Authenticates the mobile station identity

Checks the mobile station has the correctIndividual Subscriber

Authentication Key value on the SIM for the ciphering procedure

Sends the Random Number for the ciphering and authentication procedures.

This procedure is described in Authentication (Section 3.7).

Ciphering Information passed on the Air interface must be protected. The MSC canrequest that the BSS set the ciphering mode before information is passed onthe SDCCH. Ciphering is described in Ciphering (Section 3.8).

3.2.3 Normal Assignment

The figure below shows the normal assignment process for a mobile originatedcall.

Once the Radio and Link Establishment procedure has been successfullycompleted, the mobile station has a signalling link with the network. If the callrequires a traffic channel to communicate with a called party, the mobile stationsends a setup message. This indicates the teleservice and bearer servicerequired, and the called party number. The information is sent transparentlythrough the BSS. This message can contain more than one bearer serviceelement, and a parameter indicating that the subscriber may request a changeof service (In-Call Modification) during the call. See In-Call Modification(Section 4.2) for information concerning In-Call Modification.

The MSC sends a call_proceeding message to the mobile station. Thisindicates that the call parameters have been received, and that attempts toestablish communication with the called party are under way.

Channel Request The MSC initiates the assignment of the traffic channel by sending theassignment_request message and sets a timer to supervise the responsefrom the BSC.

The BSC checks the message which must contain a channel type (for trafficchannel this is speech or data plus data rate ). This message also containsthe mobile station classmark which the BSC uses if it has not received theclassmark from the mobile station.

The assignment_request message may contain a codec list, giving, in order ofpreferences, the type of codec it prefers to use (for example, one that supportsenhanced full-rate speech). In this case, the BSC checks the list against thosesupported by the cell, and chooses the preferred codec type that can be usedby both the BTS and by the mobile station.

If the BSC finds an error in the assignment_request message, it sends anassignment_failure message. If no error is detected, it starts the normalassignment procedure towards the mobile station.

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MS BTS BSC MSC

Settranscoder

releaseSDCCH

TCHallocation

Set switchingpath

initiate SDCCHrelease

set up (SDCCH)

tele/bearer servicecalled party no.

layer 3 CC

layer 3 CC

layer 3 CC layer 3 CC call proceeding

assignment request

channel type+cm

physical context request

physical context confirmpower + TA

channel activation

TCH + TA + cipher

+ DTX + power

channel activation acknowledge

assignment command

assignment command (SDCCH)

establish indication

SABM (FACCH)

UA (FACCH)

assignment complete (FACCH)

assignment complete

connect acknowledgement

layer 3 CC

layer 3 CC

layer 3 CC

layer 3 CC

layer 3 CC

alerting

connect

(SACCH)

TA + power updates

+ sys info 5 e 6

cipher : Encryption algorithm + ciphering key

cm : Classmark

DTX : Discontinuous transmission flags

TA : Timing advance

Figure 30: Normal Assignment for Mobile Originated Call

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Traffic ChannelAllocation

The BSC ensures that it is not running any other procedures for the mobilestation and then allocates resources for the traffic channel. The resourcesallocated are calculated using an algorithm in the BSC. The BSC can receivean assignment_request message in various situations. Therefore, it has trafficchannel resource allocation algorithms for:

Normal assignment

In-call modification

Intercell handover

Intracell handover

Directed retry

Concentric cells

Microcells.

In normal conditions (mobile station originated call, normal assignment), thenormal assignment algorithm is used. The BSC keeps a table of idle channelsin which the channels are classified by their interference level (1 = low, 5 = high).

The interference level of all free channels is monitored by the BTS. Thisinformation is periodically sent to the BSC in the RF_resource_indicationmessage. The BSC does not automatically allocate a channel from the lowestinterference level, as a number of channels can be reserved for handover.After all reserved channels are accounted for, the channel allocated is fromthe lowest interference level. If the number of reserved channels exceedsthe number of free channels, then the BSC allocates a channel from thehighest interference level. If no channels are available, the BSC sends anassignment_failure message to the MSC indicating the cause of the failure.

Traffic ChannelActivation

The BSC sends a physical_context_request message to the BTS, to find outthe current power and timing advance being used by the mobile station onthe SDCCH. The BTS responds with a physical_context_confirm message,containing the relevant information. If no channel is available, and queuingis enabled, the call is placed in the queue. Refer to Congestion (Section3.5) for more about queuing.

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The following figure shows the channel activation process for the traffic channel.

MS BTS BSC MSC

TCHallocation

physical context confirm

power + TA


channel activation

TCH + TA + cipher

+ DTX + power(SACCH)

TA + power updates

+ sys info 5 & 6 channel activation acknowledge

assignment command

assignment command (SDCCH)

cipher : Encryption algorithm + ciphering key

DTX : Discontinuous transmission flags

MS : Mobile station

TA : Timing advance

TCH : Traffic Channel

Figure 31: Channel Activation Process for the Traffic Channel

The BSC sends a channel_activation message to the BTS. This contains:

A description of the traffic channel to be used

The mobile station timing advance to be applied

The encryption algorithm and ciphering key (same as for SDCCHassignment)

A Discontinuous Transmission indicator for uplink (not used) and downlink

(see Speech Transmission (Section 4.4.1) for more information)

The mobile station power to be used (see Radio Power Control (Section4.5) for more information)

The BTS power to be used.

The BSC starts a timer, and waits for the BTS to acknowledge that it hasactivated the channel.

The BTS initializes its resources for the traffic channel, sets the cipheringmode, sends timing advance and power information to the mobile stationon the SACCH associated to the traffic channel, which is constantlymonitored by the mobile station. At the same time, the BTS sends achannel_activation_acknowledgment message to the BSC. The BSC stopsits timer and sends an assignment_command message on the SDCCH to themobile station. This instructs the mobile station to change to the traffic channel.

When the mobile station receives the assignment_command message, itdisconnects the physical layer, and performs a local release to free the LAPDmconnection of the SDCCH.

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The following figure shows the channel assignment process for the trafficchannel.

MS BTS BSC MSC

Settranscoder

releaseSDCCH

Set switchingpath

SABM (FACCH)

UA (FACCH)

assignment complete (FACCH)


assignment complete

FACCH : Fast Associated Control Channel

MS : Mobile station

SABM : Set Asynchronous Balanced Mode

UA : Unnumbered Acknowledgment

Figure 32: Channel Assignment Process for the Traffic Channel

The mobile station then establishes the LAPDm connection (via the SABM onthe FACCH) for the traffic channel. The BTS sends an establish_indicationmessage to the BSC. It also sets the Transcoder and its radio link failuredetection algorithm. The BTS sends a layer 2 acknowledgment to the mobilestation. The mobile station sends an assignment_complete message tothe BSC.

When the BSC receives the establish_indication message, it establishesa switching path between the allocated Abis and A interface resources.When it receives the assignment_complete message, it sends anassignment_complete message to the MSC and initiates release of theSDCCH (see chapter 4 for more information).

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Connecting the Call Once communication with the called party is established (but before the call isanswered), the MSC sends an alerting message to the mobile station. Themobile station generates a ring tone.

When the called party answers, the MSC sends a connect message to themobile station. The mobile station responds with a connect_acknowledgmentmessage. The call is established.

The following figure shows the call connection process for a mobile originatedcall.

MS BTS BSC MSC

initiate SDCCHrelease

connect acknowledgement

layer 3 CC

layer 3 CC

layer 3 CC

layer 3 CC

layer 3 CC

alerting

connect

MS : Mobile station

SDCCH : Stand-alone Dedicated Control Channel

Figure 33: Call Connection for Mobile Originated Call

Off Air Call Set-Up OACSU is a method available in the BSS where the network assigns a trafficchannel only when the called party has answered the call. This improves theefficiency of traffic channel allocation as unsuccessful calls will not take up anytraffic channel resources. This feature is controlled by the MSC.

Practically speaking, the way this happens is the Layer 3 alerting messageis sent by the MSC just after the call_proceeding message. The mobilestation then enters the ringing phase. The assignment_request message isnot sent by the MSC until the called party answers. The rest of the Layer 3exchanges between MSC and BSC take place after the mobile station sendsthe assignment_complete message to the MSC.

When OACSU is in use the mobile station may provide internally generatedtones to the user (in a Mobile Originated call) during the ringing phase, as thetraffic channel is not yet available for tones or in-band announcements to besent.

This feature has the effect on the system of increasing the probability of aninternal (SDCCH to SDCCH) handover being initiated by the BSS while theNormal Assignment procedure is being initiated by the MSC.

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3.3 Mobile Terminated CallA call from the NSS to a mobile station can be either a call routed throughthe NSS from a calling party, or it can be initiated by the NSS for mobilitymanagement.

A mobile terminated call set up follows the same basic procedures as amobile originated call. This section describes only those procedures whichare different. The following figure shows radio and link establishment fora mobile-terminated call.

MS BTS BSC MSC

channel request (RACH)

paging request (PCH)

TMSI/IMSI

paging command

TMSI/IMSI paging group +

channel number

paging

TMSI/IMSI + cell list

channel required

IMSI : International Mobile Subscriber Identity

MS : Mobile station


RACH : Random Access Channel

TMSI : Temporary Mobile Subscriber Identity

Figure 34: Radio and Link Establishment for Mobile Terminated Call

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3.3.1 Radio and Link EstablishmentPaging Before the BSS sets up a signalling link, the mobile station has to be paged.

This procedure is initiated by the MSC. It sends a paging message to the BSCcontrolling the location area from which the mobile station last performed alocation update. This message is sent in connectionless mode and contains:

The mobile station identity (TMSI or IMSI of the mobile station to be paged)

A cell identifier list which identifies the cells where the paging request is to

be sent. This could be all cells or a group of cells.

The MSC sets a timer to wait for a paging_response message from themobile station.

The BSC checks the paging message and, if valid, calculates the mobilestation paging group and the CCCH time slot for the paging group.

The BSC sends a paging_command message to each BTS, indicating theTMSI or IMSI, the paging group and the channel number.

Each BTS formats the information and broadcasts a paging_request messageon the Paging Channel.

The mobile station listens to messages sent to its paging group. Whenit receives a paging message with its mobile station identity, it sends achannel_request message on the RACH to the BTS, indicating that therequest is in response to a paging_request message.

The BSS then performs the radio and link establishment procedure describedin Mobile Originated Call (Section 3.2).

Note: When the mobile station sends the SABM, it indicates that the connection isin response to a paging request. For more information about paging, seePaging (Section 3.4).

3.3.2 Authentication and Ciphering

The system handles authentication and ciphering for a mobile terminatedcall in the same manner as a mobile originated call. Refer to Authenticationand Ciphering (Section 3.2.2). Refer to Classmark Handling (Section 3.6)for more information about the classmark, Authentication (Section 3.7) formore information about authentication, and Ciphering (Section 3.8) for moreinformation about ciphering procedures.

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3.3.3 Normal Assignment

The normal assignment procedure for a mobile station terminated call isinitiated by the MSC. This is shown in the figure below.

The MSC sends a layer 3 Call Control set_up message to the mobile station,indicating the bearer service and teleservice to be used for the call. The MSCcan indicate more than one bearer service.

The mobile station checks this message. If it can accept the call, it sends acall_confirmation message which can contain a bearer capability parameterindicating which bearer service is preferred.

The BSS performs the physical context and channel assignment. This isdescribed in Normal Assignment (Section 3.2.3). Once the traffic channelis assigned, the mobile station alerts the user and sends an alertingmessage to the MSC. When the mobile station user answers, the mobilestation sends a connection message to the MSC. The MSC sends aconnection_acknowledgment message to the mobile station and connectsthe call.

All these messages are layer 3 Call Control messages, and are transparent tothe BSS.

MS BTS BSC MSC

ringtone

useranswer

call confirmed (SDCCH)

layer 3 CC

bearer service

layer 3 CC

set up

layer 3 CC

layer 3 CC

tele/bearer service

alerting

layer 3 CC

layer 3 CC

connect

layer 3 CC

layer 3 CC

layer 3 CC

layer 3 CC

connect acknowledge

MS : Mobile station


Figure 35: Normal Assignment for Mobile Terminated Call

Off Air Call Set-Up If OACSU is in use, it is possible that at one moment the called party may haveanswered the call, but the traffic channel is still not assigned by the network (forexample, the call is queued). In this case the mobile station may supply tonesto the answering user, so that the user does not hang up before the NormalAssignment procedure completes.

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3.3.4 IMSI Attach-Detach

IMSI Attach-Detach is a mobility feature which primarily concerns the MSCand the mobile station. Used together with the periodic location updateprocedure, IMSI Attach-Detach allows the network to provide more efficientcontrol and use of resources.

For example, if a mobile-terminated call arrives for a mobile station which is“detached”, the MSC knows that the mobile station is not active and does notneed to start a paging request. For the BSS, this can reduce load on the PCH.

Initiation of the IMSI Attach-Detach procedure is controlled by a parameterin the BSS, attach_detach_allowed . When this parameter is set, the BSSbroadcasts system information on all cells indicating that the network supportsIMSI Attach-Detach.

Mobile stations which have successfully connected and logged themselvesonto the network are then obliged to perform IMSI Attach-Detach procedures.

Refer to documentation supplied with mobile stations which support thisfunction.

For more information about the attach_detach_allowed parameter, seeA1353–RA Configuration Handbook.

IMSI Attach-Detach is also used for other functions at the MSC. Refer todocumentation for your network’s MSC equipment.

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3.4 PagingPaging is the procedure by which the network contacts a mobile station. Forexample, if the network needs to inform the mobile station of an incoming call, itpages the mobile station to prompt it to request a channel. After the immediateassign procedure, the service_request message from the mobile stationindicates that the connection is in response to a paging message.

Paging messages are sent on the CCCH. The downlink CCCH carries theAGCH and the PCH.

The PCH is divided into sub-channels, each corresponding to a paging group.To save the mobile station from monitoring every occurrence of the PCH,each mobile station is assigned a paging group calculated from the IMSI.Each mobile station calculates its paging group and monitors only that PCHsub-channel. This saves mobile station battery power.

The number of paging groups and the CCCH organization varies for eachconfiguration. The mobile station knows the CCCH organization from theinformation passed on the BCCH (sys_info 3 ).

The AGCH sends the immediate_assignment message to the mobile station.A number of blocks can be reserved for the AGCH using the BS_AG_BLKS_RES

parameter. If this parameter is set to 0, then the immediate_assignmentmessage is sent on the PCH. The following figure shows a TDMA frame withnine CCCH blocks, three of which are reserved for the AGCH and the rest are forthe PCH. The parameter to reserve these blocks is set to BS_AG_BLKS_RES= 3.

CCCH0 CCCH1 CCCH2 CCCH3 CCCH4 CCCH5 CCCH6 CCCH7 CCCH8

Reserved for AGCH Available for PCH channels

TDMA Frame Cycle


CCCH : Common Control Channel


TDMA : Time Division Multiple Access

Figure 36: CCCH with Three Blocks Reserved for AGCH

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In the example shown in the figure above, BS_AG_BLKS_RESis set to three.Every occurrence of the TDMA frame cycle carrying the CCCH has threeAGCHs and six PCHs. However, more than six paging groups can be definedby assigning a different group of six PCHs to a number of TDMA multiframecycles. This is specified using the parameter BS_PA_MFRMS, as shown inthe following figure.

AGCH AGCH AGCH PGR0 PGR1 PGR2 PGR3 PGR4 PGR5

First TDMA Frame cycle


Second TDMA Frame cycle


Third TDMA Frame cycle


Fourth/1 TDMA Frame cycle

These four TDMA frames represent 24 PCHs. The parameter to reserve these is BS_PA_MFRMS = 4


PGR : Paging Group


TDMA : Time Division Multiple Access

Figure 37: Four TDMA Frame Cycles Providing 24 Paging Sub-channels

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3.4.1 Paging Control

The MSC has to initiate the paging procedure, as it holds the information on thelast mobile station location update.

The MSC sends the paging message to the BSC(s) and sets a timer forthe paging_response from the mobile station, which is sent as part of theservice_request message after the immediate assign procedure.

The paging message from the MDC contains a cell list identifier IE, identifyingthe cells in which the paging message is to be transmitted.

The BSC checks the cell identifier list and builds a paging_command messagefor the relevant BTSs. The following table shows the different cell identificationlists and the paging performed by the BSC.

Cell List Identifier Paging Performance

No IE present Paging performed in all cells controlled by BSC

IE indicates all cells Paging performed in all cells controlled by BSC

Error in IE Paging performed in all cells controlled by BSC

IE indicated specificcell(s)

Paging performed in only those cells specified

IE indicates specificlocation area(s)

Paging performed in all cells of each location areaspecified

Table 11: Cell List Identifier and Paging Performed

The BSC calculates the paging group of the mobile station for each cell and theCCCH time slot. It then sends a paging_command message to each BTS,indicating the CCCH time slot number, mobile station paging group and themobile station identity (IMSI/TMSI).

The BTS builds a paging_request_type_x message to send to the mobilestation. There are three types of paging request messages, as the BTS canpage more than one mobile station at a time. The following table shows therelationship between the paging message type, the number of mobile stationsto be paged and the mobile station ID used.

Paging Request Message Mobile Station Identification

Type_1, identifying up to two mobilestations

IMSI or TMSI (for 1 mobile station)

IMSI, IMSI or TMSI, TMSI or IMSI,TMSI (for two mobile stations)

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Paging Request Message Mobile Station Identification

Type_2, identifying three mobilestations

TMSI, TMSI, TMSI or

TMSI, TMSI, IMSI

Type_3, identifying four mobile stations TMSI, TMSI, TMSI, TMSI

Table 12: Paging Request Message and Mobile Station Identification

By using a combination of paging message types, several mobile stations canbe simultaneously paged. This is done even if some mobile stations are pagedusing the IMSI and others are paged using the TMSI.

The paging_request messages are stored in a buffer, while waiting to besent on the relevant PCH subchannel. If this buffer becomes full, the nextpaging_command message is discarded.

When the mobile station receives the paging_request message, it sends achannel_request message to initiate the immediate assign procedure. Theservice request message following the immediate assign procedure indicatesthat the channel_request is in response to a paging request message. This isshown in the following figure.

MS BTS BSC MSC

channel request

paging request

TMSI/IMSI

paging command

+ CCCH timeslot + paging group

channel required

REF + RFN + TA

paging

+ cell list IE

SABM


+ service request (paging response)

CCCH : Common Control Channel

IE : Information Element


MS : Mobile station




TA : Timing advance


Figure 38: Paging Message Sequence

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3.4.2 Discontinuous Reception

Discontinuous Reception adds to the power saving abilities of the system,extending mobile station autonomy under battery operation.

The DRX feature implements a receiver off/on ratio of 98 to 2. When the mobilestation is in idle mode, DRX allows the mobile station to switch off its receiverand data processing. Instead of the mobile station listening continually on thePaging Channel sub-channel of the CCCH for a paging message, it only listensto that part of the PCH which corresponds to its paging group. The PCH issplit into a number of paging sub-channels, each of which serves the mobilestations of a particular paging group.

The mobile station calculates its paging group and the part of the PCH ithas to monitor. It gets the information from its IMSI, and from the ControlChannel description sent on the BCCH (sys_info 3 ). The paging information istransmitted at predefined regular intervals. The mobile station only turns onits receiver to listen to its paging group and then turns itself off again. Thisoccurs cyclically, between 0.95 seconds and 4.25 seconds, depending onthe configuration of the cell.

Apart from listening to the PCH, the mobile station monitors the home cell’sBCCH up to once every 30 seconds, and the top six neighboring cells up toonce every five minutes. For more information about Paging, refer to Paging(Section 3.4).

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3.5 CongestionTo prevent an assignment_request or an external handover_requestmessage being rejected, the BSS allows queueing of traffic channel requests.Congestion occurs when all traffic channels are busy for a particular celland the message arrives at the BSC. Queueing is allowed if indicated bythe MSC in the request message.

3.5.1 Queueing

Queueing is used to achieve a higher rate of successful call set up and externalhandover completion in cases of traffic channel congestion. This is achieved byqueueing the request for a defined period of time. During this time a trafficchannel can become available and the traffic channel assignment can thenbe completed.

When all traffic channels of a cell are busy, assignment and external handoverrequests for traffic channel allocation can be queued, if:

Requested by the MSCIf the MSC allows queueing, this information and the priority of the requestfor queueing are sent in the Priority Information Element of the request.

Configured in the BSCThe BTS can perform queueing if specified in the BSC configuration. BTSqueueing can be enabled/disabled by an operator command through theOMC-R. Setting the BTS_Q_LENGTHparameter to 0 disables the queueing.

If either the MSC or BSC does not allow the request to be queued, the request isimmediately rejected and an assignment_failure message is sent to the MSC.

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3.5.2 In-queue

If queueing is allowed, the request cannot be queued if one of the two queuelimits is exceeded. These limits are:

The maximum number of requests that can be queued per BTS if defined bythe O&M parameter BTS_Q_LENGTH. The range is from 1 to 64. This can

be individually set for each BTS.

The global limit of 64 queued requests in the BSS. The sum of all BTSqueue lengths cannot exceed 64.

When one of the queue limits is exceeded, the request may still be queued ifthere is a lower priority request in the queue. If the priority of the incomingrequest is higher than the lowest in the queue, the incoming request is queuedand the oldest lowest priority request is then rejected.

Once a request is queued, the BSC informs the MSC by sending aqueueing_indication message.

A timer is activated when the request is queued. If the timer expires or therequest is preempted by a higher priority request, the request is rejected.

Once in the queue, the request waits to be either accepted or rejected due toone of the following events:

Traffic channel availability

Forced Directed Retry.

Traffic ChannelAvailability

If another traffic channel disconnects within the cell, the request at the top ofthe queue is assigned to the newly available traffic channel. The request isremoved from the queue. An assignment_complete message is sent to theMSC notifying it of the successful assignment of a traffic channel.

Forced Directed Retry The BSC detects that the call can be supported on another cell, andimplements Forced Directed Retry.

If the BSC detects the possibility of a handover for the queued request, itgenerates an internal or external handover alarm and initiates the appropriatehandover procedure. A handover from an SDCCH in the serving cell to a trafficchannel in a target cell is known as directed retry.

On detection of the handover alarm, the BSC cancels the queued request,stops the timer, and selects a neighbor cell in the target cell list. The target cellmust be able to support the ciphering requirements of the call. Once a cell isselected, a traffic channel is chosen and a handover is attempted (SDCCH totraffic channel). If the handover fails, another cell is chosen from the target celllist. This procedure continues until a successful handover or the handover limit(number of handover attempts allowed) is exceeded.

The MSC is notified of a successful handover by an assignment_completemessage. The direct retry finishes if the number of handover attempts isexceeded, or there are no more cells left in the target cell list. Finally anassignment_failure message is sent to the MSC indicating that there are noradio resources available.

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Queue Preemption If a higher priority request arrives in the queue, Queue Preemption isimplemented.

If one of the queue limits is exceeded and the request is the oldest of the lowestpriority requests in the queue, the request is rejected. An assignment_rejectmessage is sent to the MSC indicating that there are no radio resourcesavailable.

Timer Expires If the timer expires, the request is de-queued and rejected. Anassignment_reject message is sent to the MSC indicating that there are noradio resources available.

Reshuffling Half-RateCalls

Half-rate calls use only a half time slot. If two half-rate calls are alone onseparate time slots they are gathered on to a single time slot. This frees awhole time slot to serve a queued full-rate request. Reshuffling half-rate callsis enabled on a per cell basis, by setting the EN_HR_RESHUFFLINGparameterto TRUE. Setting the EN_HR_RESHUFFLINGparameter to FALSE disablesreshuffling half-rate calls for that cell.

Fast traffic handover is enabled when all of the following conditions are met:

A request is queued at the top of the queue. The request is of full-ratetype for assignment or emergency external incoming handover, and is not

in the HOLD state

There are at least two half-rate resources in the half-rate pool

The parameter EN_HR_RESHUFFLINGis set to TRUE.

If the request is a half-rate request, it is not queued but served, because at leasttwo half-rate resources in the half-rate pool are required to trigger the algorithm.

If there is only one resource in the half-rate pool, it means there is an oddnumber of half-rate calls in the cell, so it is not possible to pair the last one. Thequeued request may be an assignment, or an incoming external emergencyhandover. If the algorithm has been triggered once and the queued requestserved (or rejected by expiry of the timer), if at least another request stillremains in the queue, and if the trigger condition is still fulfilled for the topqueued request (assignment or external emergency handover), then thealgorithm is triggered again. If a half-rate request is queued behind a full-raterequest, the half-rate request is served on a remaining half-rate resource of thehalf-rate pool (if any) without triggering the algorithm again.

Half-rate calls are paired using an intracell handover. In the case of concentriccells, mobile stations are queued in the outer zone only. The check for twofree half-rate resources applies to the outer zone only (to free a resource inthe outer zone). The mobile station selected will make its handover into theouter zone (i.e. this handover does not allow handover from the outer zoneto the inner zone).

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Fast Traffic Handover Another possibility to save resources in case of traffic peaks is to forcehandovers toward neighbor cells which have less traffic. The fast traffichandover searches in the whole cell for a mobile which can perform a handoverto a neighbor cell with less traffic if the received signal level of the BCCH isgood enough. It is much more efficient than the forced directed retry when theoverlap of adjacent cells is reduced, e.g., in the case of single layer networks,or for deep indoor coverage (if the umbrella cell does not overlap totally themicrocells). Fast traffic handover is enabled on a per cell basis, by setting theEN_FAST_TRAFFIC_HOparameter to TRUE. Setting the EN_FAST_TRAFFIC_HO

parameter to FALSE disables fast traffic handover for that cell.

Fast traffic handover is enabled when all of the following conditions are met:

A request is queued at the top of the queue. The request is of full-ratetype for assignment or emergency external incoming handover, and is not

in the HOLD state.

The parameter EN_FAST_TRAFFIC_HOis set to TRUE.

The queued request is an assignment. If it is an external incoming handover, itis an emergency handover to trigger the algorithm; otherwise the algorithmshall not be triggered.

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3.5.3 Pre-emption

Pre-emption is an optional feature and is initiated during congestion periods.The feature allows radio resources in a cell to be allocated to those calls whichare deemed to be the most important. The importance of the connectionis given by the MSC to the BSC via signalling on the A interface. Duringcongestion periods, the BSC ensures that high priority transactions obtain theresources they require. The BSC performs a release of radio resources in orderto obtain the radio resource for the higher priority call.

For Phase 1 & Phase 2 GSM the signalling for priority and pre-emption existson the A interface. The setting of this data on the A interface is controlled bythe MSC. The conditions under which the information is set is up to operatorchoices. For Phase 2+ GSM the priority and pre-emption information is basedon subscription data which is stored in the HLR and downloaded to the VLR viaMAP protocols. This information can also be used by the MSC when setting thepriority level and pre-emption attributes for the call.

The pre-emption attributes of a call are defined by three bits:

pci. The pre-emption capability indication indicates if the transaction can

pre-empt another transaction

pvi. The pre-emption vulnerability indication indicates if the transactioncan be pre-empted

prec. The pre-emption recommendation. This is needed in order that

pre-emption can be deferred while a suitable non-congested cell is found inthe preferred cell list. The pre-emption recommendation is used when the

old BSS recommends that another connection is to be pre-empted.

Pre-emption isapplied to TCH only. The pre-emption feature is optional andcontrolled by the O&M parameter (EN_TCH_PREEMPT) on a per-BSC basis.The BSC provides pre-emption of TCH radio resources. This takes into accountthe priority of the call. The lowest lower priority call with the pvi bit set ispre-empted and thus released. Directed retry and/or forced handover in orderto avoid pre-emption is not supported.

eMLPP Enhanced Multi Level Priority and Pre-emption (eMLPP) is a supplementaryservice that allows a subscriber in the fixed or mobile network to initiate callsthat have a priority and pre-emption attribute known to all the network elements.The eMLPP standardization provides the transportation of the subscriptioninformation for priority and pre-emption on MAP. This subscription information isstored in the HLR and the GCR and is transported to the VLR.

The informaton is used for the following procedures:

Paging

TCH Assignment

TCH Handover.

Only TCH pre-emption is supported (i.e. only for circuit-switched services).

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Pre-emption Rules An Assignment Request message with pci=1 and priority level=p1 willpre-empt an on-going call with pvi=1 and priority level=p2 (p2 is lower than p1).A Handover Request message with pci=1 and priority level=p1 will pre-emptan on-going call with pvi=1 and priority level=p2, except if the prec bit is presentand set to 0 (i.e. the old BSS does not recommend the pre-emption of anon-going call to be performed by the target BSS).

In both cases, the call with the lowest priority level=p2 value is selected first,and if several calls have the same lowest priority level=p2 value, one of themwith the pci bit set to 0 is preferred.

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3.6 Classmark HandlingThe mobile station classmark contains information about the mobile stationtype and capabilities. This information is used by the BSS when implementingprocedures that affect a mobile station, such as:

Handover

Power Control

Ciphering

Overload Control

Location Updating.

Mobile stations of different types have different capabilities within the network.It is essential that the network recognizes the mobile station classmark wheninitiating procedures for a specific mobile station.

There are three entities that provide classmark handling as shown in thefollowing table.

Entity Classmark Handling

BSS Performed by the BSC, which is responsible forcollecting the classmark data needed to performprocedures on the mobile station.

MSC Indicates the mobile station classmark data to theBSC for MSC-initiated procedures.

Mobile station The BSS is informed of any classmark changes andinformation is sent on request from the BSS.

Table 13: Classmark Handling

Note: The BSS can receive mobile station classmark information from both the MSCand the mobile station. The information from the mobile station overridesinformation from the MSC.

3.6.1 Classmark IE

The Alcatel 900/1800 BSS supports classmark 1, classmark 2 and classmark 3IEs. The classmark 1 IE is always sent to the BSS when the mobile stationtries to establish communication.

Classmark 1 The classmark 1 IE contains:

The revision Level

The RF Power Level

Support of A5/1 Encryption.

Classmark 2 The classmark 2 IE is defined in GSM to allow the coding of phase 2 capabilitiessuch as the A5/2 ciphering algorithm. The classmark contains the sameelements as the classmark 1 IE, plus support of A5/2 encryption.

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Classmark 3 The classmark 3 IE is defined in GSM to allow multiband mobile stationsto indicate their capabilities. The classmark specifies the supported bandsand the respective power classes.

Revision Level The revision level indicates either a phase 1 or phase 2 mobile station. It doesnot distinguish between phase 1 and phase 1 extended mobile stations. If thereis an error in this field, then a default phase 1 is assumed.

RF Power Level The RF Power Level indicates the mobile station power capability.

For Alcatel 900:

Class 1 = 20W

Class 2 = 8W

Class 3 = 5W

Class 4 = 2W

Class 5 = 0.8W.

For Alcatel 1800:

Class 1 = 1W

Class 2 = 0.25W.

The value is not permitted if there is an error in this field. The result of thisis that the mobile station power capability is assumed to be the same as themaximum transmit power allowed in the cell.

Support of A5/1Encryption

This field indicates whether the mobile station supports the A5/1 encryptionalgorithm. If the A5/1 encryption algorithm is not supported, there is noindication of other algorithms being supported.

Support of A5/2Encryption

This field indicates whether the mobile station supports the A5/2 encryptionalgorithm. If the A5/2 encryption algorithm is not supported, there is noindication of other algorithms being supported.

Impact on BSS and MSC The main difference between classmarks 1 and 2 for the BSS or MSC is thesupport of the encryption algorithm. For procedures that require ciphering,the BSS and MSC cannot recognize the mobile station ciphering capability ifonly the classmark 1 Information Element was received. Therefore, there isa classmark updating procedure.

Similarly, for classmark 3, the BSS and MSC do not recognize the mobilestations multiband capabilities if only classmark 1 Information Element wasreceived. Therefore, a classmark updating procedure is required.

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3.6.2 Classmark Updating

Further classmark information may be required by the BSS or MSC wheninitiating a procedure which needs to encrypt information. The mobile stationcan also send updated information if, for example, its power capability changes.This means that the updating of classmark information can be initiated from the:

Mobile station by sending a classmark_change message to the BSC whichsends a classmark_update message to the MSC.

BSC by sending a classmark_enquiry message through the BTS to the

mobile station. The mobile station responds with a classmark_changemessage.

MSC by sending a classmark_request message to the BSC. This prompts

the BSC to send a classmark_enquiry message to the mobile station whichresponds with a classmark_change message.

The classmark_change message from the mobile station is passed throughthe BTS to the BSC. The BSC stores the information for its own use andforwards the information to the MSC. Depending on the network type andconfiguration, the classmark update is not always required. Therefore, the BSShas a parameter in the BSC (Parameter: BSS_SEND_CM_ENQUIRY) which can beconfigured. The following table shows the possible configurations.

Parameter Value Action

0 The classmark_enquiry message is never initiated bythe BSC.

1 The BSC always initiates a classmark update when itreceives a location update request.

2 The BSC only initiates a classmark update on receptionof a location update request if A5/1 is not available. Thisis worked out from the classmark 1 IE.

Table 14: Classmark Configuration

If the system requests a classmark update to a phase 1 mobile station, themobile station is not able to respond. It considers the message an error andsends an RR_status message. This message is ignored by the BSS andis not passed to the MSC.

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3.6.3 Location Updating with Classmark Procedure

If the mobile station is a phase 1 extended or phase 2 mobile station, it can sendclassmark update information on request from the BSS or MSC. Because theBSS does not know the mobile station ciphering capability from the classmark 1Information Element, updating is required. This is received when the mobilestation establishes the LAPDm connection, as shown in the following figure.

MS BSC MSC

switch toSDCCH

channel request

(FACCH/SACCH)

power + TA + sys info 5 & 6

BTS

channel required

(RACH)


SABM + rn + fn + cm

SCCP connection

classmark enauiry

SCCP connection

confirm

classmark change

classmark 2IE

classmark update

classmark 2IElocation update

(SDCCH)

cm : Classmark


IE : Information Element

MS : Mobile station

RACH : Random Access Channel


SACCH : Slow Associated Control Channel



TA : Timing advance

Figure 39: Location Update with Classmark Update

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The mobile station initiates a location update procedure by sending achannel_request message on the RACH.

The BSS performs the immediate assign procedure, as described in MobileOriginated Call (Section 3.2).

The mobile station establishes the LAPDm link and sends the location updaterequest and classmark 1 IE. The BTS sends an establish_indication messageto the BSC, containing the location update request and classmark 1 IE.

The BSC uses the classmark to send mobile station power control informationto the BTS to start power control. It stores the classmark information andrequests an SCCP connection with the MSC.

When the BSC receives an SCCP_connection_confirm message, it sends aclassmark_enquiry message to the mobile station.

The mobile station responds with a classmark_change messagecontaining the classmark 2 IE. This information is passed to the MSC in aclassmark_updating message. If the mobile station is a phase 1 mobilestation, it responds with an RR_status message which is ignored by theBSS. In this case, the BSS sets ciphering with the information available fromthe classmark 1 IE.

The MSC initiates the authentication procedure and on receipt of theauthentication response message, initiates the ciphering procedure. Refer toCiphering (Section 3.8) for more information about ciphering.

When ciphering is set, the MSC can accept the location update.

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3.7 AuthenticationThe authentication procedure ensures that the subscriber identification (IMSI,TMSI) and the IMEI are valid. The system behavior for non-valid identificationsis at the discretion of the Network Operator. The procedure also validatesthe Ki value in the mobile station, and sends the RAND which is used tocalculate the ciphering key.

IMSI/TMSI When the subscriber accesses the network for the first time, the subscription isidentified by the IMSI sent in the location_updating_request message. Whenthe NSS has performed authentication and set the ciphering mode, the VLRassigns a TMSI, in an encrypted format over the Air interface.

The next time the subscriber connects to the system, it uses the TMSI as itsidentification. If the mobile station has changed location area, it includes theold Location Area Identity. The new VLR interrogates the old VLR for theauthentication information (IMSI and Ki value). The new VLR then assigns anew TMSI. This is shown in the figure below.

New TMSIs can be assigned by the serving VLR at any time. The subscriberidentity is secure because the TMSI is always ciphered and changed regularly.

service request + TMSI + old LAI

MSCBSCBTS

MSC

BSCBTS

Mobile Station moving and connectingin a new location area

MobileStation

new TMSI

info request

IMSI +Ki

VLR

VLR

MobileStation


Ki : Individual Subscriber Authentication Key

LAI : Location Area Identity



Figure 40: Location Update with Mobile Station Sending Location Area Identity of Previous VLR

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AuthenticationProcedure

The authentication procedure is initiated by the NSS. It sends anauthentication_request message to the mobile station and sets a guardtimer. This message contains:

Parameters for the mobile station to calculate the response

A ciphering key sequence number.

The ciphering key is calculated from the authentication Key value assigned tothe IMSI or TMSI and the value RAND.

The mobile station responds using the RAND and the value authenticationKey assigned to its TMSI or IMSI.

For mobile station originated calls, the mobile station uses:

The TMSI, if available

The IMSI, if no TMSI is assigned.

For mobile station terminated calls, the mobile station uses the TMSI or IMSI asrequested in the paging message from the network.

For emergency calls, the mobile station uses:

The TMSI, if available

The IMSI, if no TMSI is assigned

The IMEI, if there is no TMSI or IMSI. This can happen when there is no

SIM in the mobile station.

When the mobile station sends the authentication_response message, theNSS stops its guard timer and validates the response.

If the mobile station response is not valid, the network response depends onwhether the TMSI or IMSI was used:

If the TMSI was used, the network can request that the mobile stationsends its IMSI.

If this is a valid IMSI, but is different from the IMSI that the network

associated with the TMSI, the authentication procedure is restarted withthe correct parameters.

If the IMSI is invalid, the network sends an authentication_reject messageto the mobile station.

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3.8 CipheringCiphering is supported in the Alcatel 900/1800 BSS to protect informationtransmitted on the Air interface. This includes:

Subscriber information such as the IMSI

User data

SMS and SS data

Information such as called and calling party numbers.

Ciphering protects the information by using encryption. There are threedifferent ciphering modes, the use of which depends on the mobile stationclassmark and the capability of the BTS. These modes are:

Encryption using algorithm A5/1

Encryption using algorithm A5/2

No encryption.

The two encryption algorithms are defined in GSM. If either is to be used, boththe mobile station and BTS must have the same encryption capability.

Mobile Station Capability The mobile station ciphering capability depends on whether it is a phase 1mobile station, a phase 1 extended mobile station, or a phase 2 mobile station.The following table shows the different mobile station ciphering capabilities.

Mobile Station Type Capability

Phase 1 No encryption and A5/1

Phase 1 Extended No encryption and A5/1 and A5/2

Phase 2 No encryption

No encryption and A5/1

No encryption and A5/2

No encryption and A5/1 and A5/2

Table 15: Mobile Station Ciphering Capabilities

Only phase 2 mobile stations can turn off ciphering or change the cipheringmode during a channel change procedure such as a handover.

The ciphering capability of a mobile station is signalled to the BSS in themobile station classmark.

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BSS Capability The Alcatel 900/1800 BSS supports both uniform ciphering networkconfigurations and mixed ciphering network configurations.

A cell can be configured to support one of the following:

No encryption

No encryption and the A5/1 algorithm

No encryption and the A5/2 algorithm.

A uniform ciphering network configuration is where all cells have the sameciphering capability.

A mixed ciphering network configuration is where the cells have differentciphering capabilities.

3.8.1 Ciphering Keys

The encryption used on the Air interface is provided by the physical layerhardware. This means that it does not distinguish between signalling and usertraffic; therefore, the entire bit stream is encrypted.

The encryption pattern added to the bit stream is calculated by the algorithmA5/1 or A5/2, using a ciphering key.

For maximum security, the value of the Ciphering Key is not a fixed value. It iscalculated separately by the HLR, BSC and the mobile station for each call.This means that the value Kc is never transmitted on the Air interface.

The value Kc must be the same in the HLR, BSC and the mobile station. Itis calculated using:

A value Ki, which is assigned to the IMSI when the user subscribed

to the service

A RAND, sent from the MSC during the authentication procedure.

The resulting value Kc is used to decipher the encrypted bit stream on thedownlink, by the mobile station, and on the uplink, by the BTS.

3.8.2 Ciphering ProcedureChoosing the Ciphering

ModeThe ciphering chosen by the BSC for a call depends on:

The algorithms that the Network Operator allows in the network. This

information is sent in the permitted_algorithm message from the MSCduring ciphering or external handover procedures.

The ciphering capability of the mobile station. This information is sent to the

BSC in the mobile station classmark.

The ciphering capability of the BTS being used to set up the call.

If the mobile station capability is not compatible with that of the BTS or isnot allowed by the Network Operator, then the BSC sets ciphering withno encryption.

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Setting the CipheringMode

Ciphering is initiated by the MSC by sending a cipher_mode command to theBSC. This command contains the permitted_algorithms message.

The BSC compares the permitted algorithms with the mobile stationclassmark and the BTS capability. If they match, the BSC sends anencryption_command message to the BTS containing the value Kc and thealgorithm to be used. If there is no match and ’no encryption’ is permitted, theBSC sends the encryption_command to the BTS indicating ’no encryption’.

If the BTS and mobile station capabilities are not compatible and the MSC doesnot allow the ’no encryption’ option, then the BSC sends a cipher_mode_rejectmessage to the MSC.

The BTS sends the ciphering_mode command on the SDCCH to the mobilestation indicating the algorithm or ’no encryption’. If encryption is to be usedthe BTS sets its decryption mode ready to receive encrypted frames fromthe mobile station.

The mobile station either:

Starts the encryption and sends an encrypted layer 2 acknowledgment

message to the BTS. This prompts the BTS to start encryption mode forframes sent to the mobile station.

Sends an unencrypted level 2 acknowledgment to the BTS.

The mobile station sends a ciphering_mode_complete message tothe BTS which is passed transparently to the BSC. The BSC sends acipher_mode_complete message to the MSC.

This process is shown in the following figure.

MS BTS BSC MSC

algorithm orno encryption

ciphering mode command

(SDCCH)

ciphering mode complete

encryption command

algorithm + Kc or

no encryption

ciphering mode command

permitted algorithms + Kc

cipher mode complete

MS : Mobile station

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Figure 41: Ciphering Procedure

Ciphering DuringHandover

Only phase 2 mobile stations can change ciphering mode during a handover.If a phase 2 mobile station using the A5/1 algorithm is handed over to a cellwhich supports A5/2 and ’no encryption’, the BSC instructs the target BTS toset the new ciphering algorithm and sends the value Kc.

If a phase 1 mobile station using the A5/1 algorithm needs to be handed over,the target cell must support A5/1, as the phase 1 mobile station cannot changeciphering mode. For mixed ciphering networks, it is normal that the initialcipher_mode command from the MSC only allows a phase 1 mobile station touse the ’no encryption’ option, as this is supported by all cells.

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3.9 Tandem Free OperationTandem Free Operation (TFO) provides a better voice quality by avoidingunnecessary successive coding and decoding operations in the case ofmobile to mobile calls. The importance of TFO is always increasing, as thepercentage of mobile to mobile calls increases with the number of subscribers.Taking the example of a call involving two mobile stations, mobile station 1and mobile station 2:

With TFO feature, the same codec will be used on both BSS, this will improvethe speech quality of mobile-to-mobile calls, and particularly when usingthe half-rate codec.

Without TFOOne GSM coding and decoding scheme (codec), is used between mobilestation 1 and Transcoder 1, then A/µ law coding is used (at 64 kbit/s)between the two Transcoders and finally one GSM codec is used betweenTranscoder 2 and mobile station 2. This means a loss of quality for thespeech call.

With TFOThe intermediate transcoding realized by the two involved Transcoders isavoided. The same codec is used on both BSS. This improves the speechquality of mobile-to-mobile calls, particularly when using the half-rate codec.This allows the wide use of the half-rate codec, with a good level of speechquality, in order to save resources in BSS.

The TFO procedure can be applied whenever the two mobile stations use thesame codec. To satisfy this condition, after TCH allocation, the two BSSnegotiate at each side a common codec (full-rate, half-rate or enhancedfull-rate), by using an in-band protocol in the speech frame. The following figureshows an example of TFO call establishment.

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BTS A BSC A TC A TC B BSC B BTS B

Channel activationTFO enabled

Channel activationTFO enabled

CON_REQ CON_REQ

DL_ACKDL_ACK

TRAU frames

TFO_REQ

Codecs match

1

2

3

4

5TFO REPORT (TFO STATUS= ON)

TFO_ON TFO_ONTFO frames

TRAU frames

PCM samplesTRAU frames TRAU frames

TFO_ACK

TFO REPORT (TFO STATUS= ON)

TFO_ACK

TFO_REQ

PCM : Pulse Code Modulation

TC : Transcoder

TFO : Tandem Free Operation

TRAU : Transcoder Rate Adaptation Unit

Figure 42: Example of TFO Establishment

Referring to the figure above, the call establishment scenario is as follows:

1. At call establishment, the BSC sends to the BTS the channel activationmessage, containing information related to TFO.

2. TRAU frames are exchanged between the BTS and the Transcoder. PCMsamples are exchanged between TRAUs. One TRAU frame is stolen fromthe BTS by the Transcoder, to send TFO configuration information (inthe con_req message).

3. As soon as the TRAUs have received the information that the TFO is enabledin the con_req message, (and also the TFO configuration information), theysend the tfo_req message, within PCM speech samples, to indicate that theTRAUs are TFO-capable. Meanwhile, the TFAUs acknowledge the con_reqmessage to the BTS with the dl_ack indication.

4. The TRAUs acknowledge that the tfo_req message has been receivedby sending a tfo_ack indication.

5. The same codecs are then used on both sides. The TRAUs can exchangeTFO frames.

6. The BTS are made aware of the exchange of TFO frames with the tfo_onindication. The BSC is informed via a tfo_report message on the Abisinterface.

The Alcatel TFO implementation is fully compliant with the GSM standardand additionally provides:

As an operator s choice, the Alcatel BSS is able to force the distant BSS

(Alcatel or not) to overcome ETSI codec choice rules, in order to optimizevoice quality and load management. This mechanism is patented by Alcatel.

Codec optimization, to take into account that the two mobile stations may

use the same codec, but a better codec is available on both parts.

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3.9.1 TFO Functional Architecture

The TFO procedure is defined between two Transcoding and Rate AdaptationUnits (TRAU). When TFO is possible between two Mobile Stations, TFO frames(similar to TRAU frames) are transferred between the two TRAUs on the Ainterface. These frames contain coded speech streams, and may also containembedded TFO messages. They are supported by a 0.5 kbit/s signallingchannel between two Transcoders, emulated during the TFO negotiationphase. This channel uses one bit (Least Significant Bit) every 16 PCMsamples, regularly stolen on the 64 kbit/s circuit. Note that when TFO framesare transmitted, speech is nevertheless coded to G.711 law and sent to the Ainterface on the remaining MSB bits of the PCM samples. This allows a fasterreversion to normal operation mode if required. Moreover, lawful interception inMSCs is still possible. The Alcatel solution avoids any Ater supplementarylinks, because the BSC-Transcoder TFO messages are exchanged through theBTS and the Abis layer 3 protocol.

Same Codec Used onEach Side

As the same codec is used on both sides, there is no TFO negotiation neededbetween the TRAU.

Codec Mismatch,Negotiation Needed

In this case, TFO communication is possible between the two BSS, but theTRAUs do not use the same speech codec. TFO negotiation and resolution bythe BSS are needed. When detecting the mismatch, each TRAU sends to theother (using TFO messages) the codec locally used, and the list of possiblecodecs. At each side, the BSS determines the matching codec. On each BSS,the same algorithm is implemented, this algorithm attempts to find a matchingcodec using the information given by the TRAU. If a common codec can befound, an internal intra-cell handover is performed to change the speech codeclocally used, and TFO exchange of speech stream begins. A logical parameter,configurable at OMC-R level, allows the BSC to ignore the load in the celland to force the handover in order to solve codec mismatch situations. If nocommon codec can be found, or internal intra-cell handover is not possible,TFO mode is given up, and the system reverts to normal mode.

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3.9.2 TFO Optimization and Management

TFO is fully managed by the OMC-R operator, on a per cell basis. Severalfunctions have been introduced to provide full control of TFO optimization,regarding load regulation, speech quality, or Adaptive Multi-Rate (see AdaptiveMultiple Rate (Section 6.2.3)) codec support.

TFO Optimization For a better speech quality, TFO Optimization allows a new TFO negotiationon an on-going TFO mobile-to-mobile call, to find a better common codec, interms of speech quality. Therefore, enhanced full-rate coding is considered tobe better than full-rate coding which is considered to be better than half-ratecoding. The Enable TFO Optimization feature can be enabled or disabled, percell, at the OMC-R.

In some cases, both parts may use the same codec, but a better codec isavailable at each side and may be used (e.g., half-rate is used at both sides,but full-rate is possible). The procedure is then the same as the modification ofspeech codec in mismatch status, except that it takes place only when TFOframes are already exchanged. The TFO messages exchanged between bothTRAUs are then embedded in TFO frames.

TFO Negotiation Control For a better traffic load regulation Alcatel has defined the function "ForceTFO half-rate when loaded" to give control to the operator of load regulationprecedence over TFO. This function can be enabled or disabled, per cell, atthe OMC-R, and allows the BSC to take into account the load in the cell whilebuilding the list of supported codec types. If the cell is loaded, only half-rate (ifpossible) will be included in the list. If the distant BSS supports TFO but nothalf-rate, the function "Force TFO half-rate when loaded" allows the BSC inthis case to recompute the list of supported codec types by inserting full-rateand enhanced full-rate in the list. Therefore, the function Force TFO half-ratewhen loaded leads to three different behaviors, depending on three possiblevalues of corresponding flag:

TFO half-rate not forced. No filtering on the load is done. The load is not

tested and all the codec types supported by the call and by the cell are listedin the supported codec type list

TFO half-rate only. Filtering is done on the load, half-rate is forced if the cell

is loaded and the mobile station supports half-rate, and if this codec typeis authorized in the cell. The list of supported codec types is restricted to

the half-rate codec type. As a consequence, if the distant part supportshalf-rate, then the distant part will do an intra-cell handover to use half-rate,

and TFO will go on with half-rate. If the distant part does not supporthalf-rate, TFO will not be possible.

TFO half-rate preferred. Filtering is done on the load, but TFO is preferred

to half-rate. In the case of a load situation, only half-rate is sent in the list ofpreferred codecs. But if the distant BSS does not support half-rate, a new

list is computed, without taking into account the load in the cell.

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4 Call Handling

This chapter provides an overview of Call Handling and describes thesupervision of a call in progress. The following specific areas are described:

Overview

In-call modification

Frequency hopping

Discontinuous Transmission

Radio Power Control

Handover procedures

Overload conditions

Call re-establishment by the mobile station.

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4.1 OverviewAn obvious requirement for the effective management of calls in the BSSis to provide the following:

Maximum perceived signal quality with minimum perceived interference

Call continuity regardless of changes in propagation conditions or changeof location of the mobile station.

Given that spectrum is limited, this must be accomplished with maximumresource reuse. Another important factor for the customer (and the operator aswell) is power efficiency to reduce overall power consumption and prolong theautonomy of the mobile station under battery operation.

The supervision of calls in progress is provided by the Call Handling function.Call Handling, with associated features, implements needed changes in therequired teleservice to maintain call quality and continuity.

Call Handling functions and features include:

In-Call Modification

Frequency Hopping


Radio Power Control

Handover

Overload Control

Call re-establishment by the mobile station.

4.2 In-Call ModificationIn-call modification allows the teleservice to be changed during a call. Thismeans that a call does not have to be cleared, and a new call established, ifmore than one teleservice is to be used.

The different types of in-call modification are:

Alternate between speech and a transparent data service

Alternate between speech and a non-transparent data service

Change from speech to a transparent data service

Change from speech to a non-transparent data service

Alternate between speech and transparent fax group 3

Alternate between speech and non-transparent fax group 3

Data rate change for transparent fax group 3

Data rate change for non-transparent fax group 3.

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Calls requiring a change of service have to negotiate a ’dual-service’ before thenormal assignment procedure. This is indicated in the set_up message, whichis described in Call Set Up (Chapter 3).

Note: Changing the data rate of a fax call is not a true in-call modification procedure,as the teleservice is not changed (no dual-service negotiation).

The main difference between the in-call modification procedure and a changeof data rate for fax are as follows:

The in-call modification procedure is triggered by a message from themobile station

The data rate change for fax is triggered by in-band signalling from thefax machine to the MSC.

Both procedures use existing resources, therefore no new resources need tobe allocated. All full-rate traffic channels can be used for speech or data at anyof the defined data rates.

Both procedures use the mode ’modify procedure’ to change the transmissionmode. This is basically a normal assignment procedure but instead of a newchannel being assigned, a new mode is assigned.

4.2.1 In-Call Modification Procedure

In-call modification is initiated from a mobile station. This can occur during acall to a correspondent on the public telephone network or to a mobile station.

Mobile Station to MobileStation Call

For a mobile station to mobile station call, both mobile stations must negotiate adual service during call establishment.

The mobile station initiates the procedure by sending a layer 3 Call Controlmodify message to the MSC, indicating the new mode. If the data call directionis different to the original call set up, then this message contains an indicatorto reverse the call direction. The mobile station starts a guard timer for theprocedure.

The MSC checks the modify message. If it can accept the mode change, itstarts the normal assignment procedure by sending an assignment_requestmessage and starting a guard timer. This message contains a channel type(speech or data plus data rate ).

The BSS handles the normal assignment procedure as if assigning a trafficchannel during call set up (described in Call Set Up (Chapter 3)), with thefollowing exceptions:

When the BSC has checked and accepted the assignment_requestmessage, it does not assign a new traffic channel. This is because italready has a traffic channel assigned for the transaction. The transaction

is identified by the SCCP connection on which the assignment_requestmessage was received

The channel_activation and channel_activation_acknowledgemessages are replaced by the mode_modify and mode_modifyacknowledge messages.

When the MSC receives the assignment_complete message from the BSC, itsends a layer 3 CC modify_complete message to the mobile station. This

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informs the mobile station that the procedure is successfully completed, andthe mobile station can start transmitting in the new mode.

4.2.2 Circuit-switched Group 3 Fax Data Rate Change

Group 3 facsimile equipment can change the data transmission speed toreduce the error rate. Fax data rates can be:

9600 bit/s

4800 bit/s

2400 bit/s

1200 bit/s.

The Alcatel 900/1800 BSS supports both transparent and non-transparent faxtransmission. The BSS supports the Group 3 fax data rate change by:

In-band signalling for non-transparent fax

The mode modify procedure for transparent fax.

Non-Transparent Group3 Fax

For non-transparent fax transmission, the data rate change is handled withinthe BSS, using in-band signalling. This means that the frame size is signalledin the frame by a "frame delimiter" field. The Radio Link Protocol in the BTSuses this information to control the data flow on the Air interface. The BSS doesnot need to change the channel mode.

Transparent Group 3 Fax Transparent fax frames are passed transparently through the BSS. Therefore,in-band signalling cannot be used within the BSS. The Group 3 fax equipmentinforms the MSC of a data rate change using in-band signalling. The MSC theninitiates a mode modify procedure using the assignment_request message.

This procedure is the same as the mode modify procedure for in-callmodification, except that the MSC does not send a layer 3 Call Controlmode_modify_complete message. This is because the procedure was nottriggered by a layer 3 CC modify message from the mobile station. When theMSC receives the assignment_complete message from the BSC, it sets thenew data rate to the correspondent.

4.2.3 Error Handling

The Alcatel 900/1800 BSS tries to provide the highest level of service at alltimes. In general, if errors occur during an in-call modification, the BSS triesto revert to the old mode to keep the call active.

In-Call ModificationExample

For example, if the mobile station does not reply to the channel_mode_modifymessage from the BSC, it is assumed that it is still active but in the old mode.The BTS, however, has set the new mode. The BSC sends a mode_modifymessage to the BTS indicating the old mode. If the BTS acknowledges that ithas reverted to the old mode, the call is kept active.

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4.3 Frequency HoppingFrequency Hopping is a method to increase frequency reuse and improve thesystem’s ability to cope with adjacent channel interference.

The Frequency Hopping algorithm can be either random or cyclic. Associated(i.e. paired) uplink and downlink frequencies are always ±45 MHz.

There are two major types of frequency hopping:

Baseband Frequency Hopping

Synthesized Frequency Hopping.

Frequency Hopping improves BSS-mobile station performance by providingtwo types of diversity:

Frequency diversity

Interference diversity.

Frequency Diversity Frequency Diversity averages the effects of signal fading by using severalfrequencies to improve transmission performance. Obstacles such as buildingsproduce fading by reflecting the signal out of phase with the main signal. Eachfrequency is affected differently by fading.

After error correction information is added to the data, it is encoded so thatthe data is split into packets and the information is repeated. This createsredundant information which is transmitted in bursts on the Air Interface. WithFrequency Hopping, each redundant information burst is transmitted on adifferent frequency. This enables the original data to be reconstructed from thereceived flow, even if errors occur due to fading.

In this way Frequency Hopping improves transmission performance.

Interference Diversity Interference Diversity spreads the co-channel interference between severalmobile stations. In high traffic areas, the capacity of a cellular system is limitedby its own interference; that is, the interference caused by frequency re-use.Interference Diversity minimizes the time during which a given user on a givenmobile station will experience the effects of such interference.

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4.3.1 Baseband Frequency Hopping

A Mobile Allocation is a set of all the frequencies available for frequencyhopping. When the Frequency Hopping procedure is implemented a group ofmobile stations is assigned to a Mobile Allocation.

When a traffic channel is set up in a cell where Frequency Hopping is active,the traffic channel is assigned:

A particular time slot

An FHS. An FHS is defined as the subset of frequencies within the MA tobe used by a given cell for Frequency Hopping.

A MAIO. The MAIO indicates the initial hopping frequency of the traffic

channel within the FHS. Use of the MAIO ensures that each traffic channelis assigned a different frequency during hopping.

An HSN. The HSN supplies the identifying number of an algorithm which isused to calculate the next frequency in the FHS on which the traffic channel

transmits. There can be up to 63 different HSN algorithms, all of which are

pseudo random. Within a given FHS, only one algorithm is used to avoidcollisions. An HSN of zero means a cyclic use of the frequencies.

An example of Frequency Hopping is shown in the figure below. Because theHSN = 0, hopping occurs in a sequential manner. With a non-zero HSN, eachof the 3 traffic channels would hop in a random fashion determined by thealgorithm corresponding to the HSN.

TCH1 on TS1

TCH2 on TS2

TCH3 on TS3

MAIO=0

MAIO=1

MAIO=2

Assignmentfor TCH 1:TS=1MAIO=0HSN=0

Frame n

Frame n+1

Frame n+2

Frame n+3

f 1

f 2

f 3

Within this FHS the HSN=0

f 1f 2 f 3

f 1

f 3

f 3f 2

f 2f 1

f : Frequency

FHS : Frequency Hopping System


MAIO : Mobile Allocation Index Offset

HSN : Hopping Sequence Number

TS : Time slot

Figure 43: Frequency Hopping within an FHS

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4.3.2 Synthesized Frequency Hopping

Synthesized Frequency Hopping functions in a similar fashion to BasebandFrequency Hopping, but is performed at a different location. Instead ofswitching each time slot between traffic channels, the channel assigned to atime slot is assigned to a fixed Carrier Unit (or TRE).

The Carrier Unit/TRE changes frequency with each TDMA frame in accordancewith the HSN algorithm selected, in the same manner as above. Thus, insteadof the channel hopping from one fixed transceiver to another, the transceiveritself hops from one frequency to another, in both cases, according to thealgorithm and parameters selected.

Synthesized Frequency Hopping has the advantage of allowing an FHS tocontain one more frequency than the number of Carrier Units/TREs in thesystem. This is particularly useful in some microcellular applications where onlyone transceiver is available for Frequency Hopping.

Note: Normally, in both Frequency Hopping schemes (Baseband and Synthesized),time slot 0 (TS0) is not available for Frequency Hopping. This is becauseit carries the BCCH, which must always be at maximum power and on afrequency known to mobile stations in Idle mode in the cell.

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4.4 Discontinuous TransmissionDiscontinuous Transmission and VAD work together to decrease the averagetransmission time on a channel. By transmitting only when actual speech ispresent, the system reduces the interference level generated by the network inboth the uplink and downlink directions and saves power.

In tandem with Frequency Hopping, this improves spectrum efficiency withoutjeopardizing the quality of the telephony service.

4.4.1 Speech Transmission

Speech is transmitted over the air in the following ways:

Continuous transmission

Discontinuous transmission.

ContinuousTransmission

Sound is continuously encoded into digital information even when no oneis talking.

In normal conversation, only one participant at a time talks. This is used by thesystem to its advantage, by transmitting only when someone is speaking.

DiscontinuousTransmission

Only actual speech is digitally encoded and transmitted. During the non-speechphase (silent periods), noise/comfort mode information is sent once every 480ms instead of once every 20 ms for speech. In this way the system:

Improves spectral interference

Increases power savings.

By transmitting at a reduced rate of 1 in 24 during the silent phases, the powerautonomy of the mobile station improves.

Discontinuous Transmission does not occur during half-rate speech or datamodes. It can be activated for either the uplink or the downlink or both.

The receivers of Discontinuous Transmission information can automaticallydetect that the transmitter is in Discontinuous Transmission mode by thereception of Silence Indication messages.

During quiet periods SID messages are sent instead of speech bursts. SIDscarry noise information about background noise. This information is used to:

Let the receiver know that the link is still open

Provide comfort noise. Users of telephones prefer to hear background noise

rather than silence; complete silence disturbs the listener.

Provide measurements of the link quality and timing advance. If there areno bursts of data over the Air Interface for a particular channel, no power

level control and quality can be performed.

To eliminate the noise side effects generally known as banjo noise, the operatorcan ban Discontinuous Transmission on the downlink for all calls that areestablished on the BCCH TRX, without hopping, for all types of BTS. This isachieved using the FORBID_DTXD_NH_BCCHparameter. The parameter canbe set to one of two values:

0. This is the default value, and allows Discontinuous Transmission on the

downlink for all calls that are established on the BCCH TRX.

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1. This bans Discontinuous Transmission on the downlink for all calls thatare established on the BCCH TRX.

Voice Activity Detection VAD is used to detect when there is speech, silence or just background noise.The VAD device is located in the Transcoder. Once the VAD detects speech, itstarts transmitting speech bursts. After four bursts of detected silence, the VADgoes back into silent mode, and SID information frames are transmitted (i.e. thecomfort noise generation is activated).

4.4.2 BSS Discontinuous Transmission Towards Mobile Station

Downlink Discontinuous Transmission is activated on a per call basis bycombining information from the MSC and the OMC-R.

The MSC informs the BSC about its downlink Discontinuous Transmissionpreference. It does this via the Downlink Discontinuous Transmission flag in theassignment_request or handover_request messages on a per call basis.

The OMC-R can enable or disable the possibility of downlinkDiscontinuous Transmission per BSC via the Discontinuous

Transmission_DOWNLINK_ENABLE parameter. This is a static parameter whichcan be set via the CMISE command M_LOGICAL_PARAM_MODIFY. Theoverall system reaction is shown in the following table.

OMC-R DiscontinuousTransmission_DOWNLINK_ ENABLE(per BSC basis)

MSC Downlink_DiscontinuousTransmission flag (percall basis)

ResultDiscontinuousTransmissionflag

True Allowed ON

True Unavailable/not allowed OFF

False Allowed OFF

False Unavailable/not allowed OFF

Table 16: Downlink Discontinuous Transmission Status in Channel_activation

The MSC requests no downlink Discontinuous Transmission during mobilestation to mobile station calls, where double clipping can occur if both endsperform Discontinuous Transmission. This can have a staccato-like effecton speech.

The BTS tells the Transcoder to perform Discontinuous Transmission by settingthe Discontinuous Transmission bit in the speech frame.

In the BSS, the Transcoder is responsible for Discontinuous Transmissionoperation. In the BTS, the information is processed in the FU in the followingway:

1. When the Transcoder detects voice activity it informs the FU, using inbandsignalling. The speech signalling flag is set in the speech frame.

2. Every 20 ms the FU receives either speech frames or SID frames containingbackground noise characteristics.

3. At the end of the speech period (four bursts of detected silence) the FUsends a SID frame over the Air Interface.

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4. During speech inactivity, the last received SID frame is sent at regular 480ms intervals rather than at 20 ms. Otherwise dummy bursts are sent.These dummy bursts are:

Transmitted for traffic channels on the BCCH frequency, due to the needfor constant transmission on the BCCH frequency

Not transmitted for traffic channels on other frequencies.

Note: The BTS uses the measurement_result message to inform the BSCthat Discontinuous Transmission is operating. The BSC compensates forDiscontinuous Transmission when calculating power control and handover.

4.4.3 Mobile Station Discontinuous Transmission Towards BSS

The OMC-R operator controls whether a mobile station can performDiscontinuous Transmission towards the BSS per cell. This information is sentin cell options information (sys_info 3 , and sys_info 6 on the Air Interface).The following table shows the available operator options.

Option Description

Will performDiscontinuousTransmission

This forces the mobile station to use DiscontinuousTransmission. It reduces the call quality but alsoreduces interference in the cell and saves mobilestation battery power. During silent phases only1 in 24 bursts are sent, which greatly reducesinterference.

Can performDiscontinuousTransmission

This allows the mobile station to choose either qualityby not using uplink Discontinuous Transmission,or power-saving by using uplink DiscontinuousTransmission.

Cannot performDiscontinuousTransmission

The OMC-R operator has decided, due to lowinterference, to have improved speech andmeasurement control on the uplink side.

Table 17: Operator Discontinuous Transmission Options

The Transcoder detects that the mobile station is in Discontinuous Transmissionmode by the reception of SIDs.

Note: There is a small quality reduction due to the fact that VAD only starts sendingspeech when a user starts to talk. This can cut the start of each speech activity.Power control and handover are also affected, as the BTS has fewer incomingmessages with which to calculate power and interference.

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The following figure shows the different forms of transmission.

DTX during ’Silence’ in uplinkSound continuously encoded

DTX during ’Silence’ in downlink DTX during ’Silence’ in up and downlink

Continuous Transmission


DTX : Discontinuous Transmission

Figure 44: Different Forms of Discontinuous Transmission

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4.5 Radio Power ControlRadio Power Control operates independently, but in a coordinated manner withHandover to provide reliable service to the user.

Both directions of the radio link between the mobile station and the BTSare subject to continuous power adjustments. The power adjustment of theBTS and the mobile station are under the control of the BSC (see RadioMeasurements (Section 4.6.1)). RPC improves spectrum efficiency by limitingintra-system interference. It also increases the autonomy of the mobile stationby saving battery power.

The reasons for changing the mobile station power level are:

Uplink power level too high or too low

Uplink link quality too low, or using power resources beyond qualityrequirements of the call.

Similarly, the reasons for changing the BTS power control are:

Downlink power level too high or too low

Downlink link quality too low, or using power resources beyond qualityrequirements of the call.

4.5.1 BTS Radio Power Control

The mobile station performs power measurements of radio signals beingtransmitted by the BTS. The mobile station, via the SACCH, regularly sends ameasurement_report message to the BTS indicating the quality and strengthof the downlink plus measurements of neighboring cells. This information iscombined with uplink measurements taken by the BTS and sent to the BSC inthe measurement_result message.

The BSC then alters the BTS power, based on the measurement information itreceives from the mobile station. The maximum power level is limited by themaximum power of the BTS, and also by the maximum power allowed in the cell.

4.5.2 Mobile Station Radio Power Control

The BTS measures the signal power transmitted by the mobile station. Theresulting measurements are combined with the measurement_report messagefrom the mobile station and are sent to the BSC in the measurement_resultmessage. The BSC sends commands to change the power level of the mobilestation as needed. The maximum power level is limited by the maximum powerof the mobile station, and also by the maximum power allowed in the cell.

Power control can be applied to traffic channels and Stand-Alone DedicatedControl Channels.

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4.5.3 Radio Link Measurements

Due to interference and signal quality problems on the Air Interface, the uplinkand the downlink transmissions are constantly measured to maintain maximumefficiency of the air-waves. A balance is maintained between the transmissionpower, which can interfere with other cells using the same frequency, andthe quality of the actual link.

The following table shows the measurements used to achieve this balance.

Measurement Description

Signal strength Signal strength is calculated on both active andinactive channels.

On active channels, this measurement is used toprovide the actual strength of the signal receivedfrom the transmitter.

Inactive channel strength provides measurement ofinterference levels.

Signal quality The signal quality of a channel is calculated onthe average Bit Error Rate on a particular channel.BER is a standard quality calculation in radiotransmission.

Absolute mobilestation-BS distance

This is estimated by measuring the Time Of Arrival ofthe received burst at the BTS for each allocated timeslot. The TOA is based on transmission distanceand not the actual ground distance travelled. Thecalculation of one bit period (3.69 µs) correspondsto 550m.

Table 18: Radio Link Measurements

Reporting Period The statistical parameters of signal level and quality are obtained over ameasurement period. This period is called the ’Reporting Period’. The reportingperiod for a traffic channel is 104 TDMA frames (480 ms). The information istransmitted in the SACCH frames.

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4.5.4 Power Control Decision and Handover

At every measurement interval, the BSC receives:

Pre-processed power measurement information (uplink and downlink)

Timing advance (distance information)

Power level information about neighboring cells (only the best six aretransmitted).

The BSC uses this information to perform power control by:

Lowering the power level in the uplink or downlink, as this has little effect

on the quality of the link

Increasing the power on the uplink or downlink if the link quality/level is low

Producing a handover alarm (refer to Handover Detection (Section 4.6.2) for

more information)

Taking no action, if the quality/level balance is acceptable.

The following figure illustrates the measurements described previously, as wellas power-control flow. Figure 46 shows how power control tries and maintainsoptimum quality and power levels.

MS BTS BSC MSC

Interruption of SACCH frames

start counterconnection failure indication

cause value

RF channel release

clear request

MIE including cause valueclear command

MS : Mobile station

TX : Transmitter

Figure 45: Power Control Flow of Measurement and Decision Action

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Note: The signal and quality levels are converted into the ranges Received SignalLevel and Received Signal Quality respectively. Each range is classed from0-63 (Received Signal Level where 63 is high) and 7 -0 (Received SignalQuality where 7 is poor).

High Quality

Low QualityLow Signal Level

High Signal Level

RXQUAL

RXLEV

Quality badIncrease power output

Signal level too highDecrease power output

Signal level too highQuality badHandover desired

Signal level lowIncrease power output

Desired balance

no change

RXQUAL : Received Signal Quality

RXLEV : Received Signal Level

Figure 46: Power Output Balancing Based on Received Quality and SignalLevels

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4.5.5 Change Power Levels

The BSC controls the power levels of the BTS and the mobile station.

The BTS power level can be altered down from its maximum power. This is donein 2 dBm steps to a minimum of -30 dBm from the maximum level. The BSCinforms the BTS of the new power level via a BS_power_control message.

The mobile station power level can be altered in steps of 2 dBm. The followingtable shows the maximum and minimum power ranges of mobile stations.

Mobile Station PhaseGSM 850/900/1800/1900 Max Power Min Power

Mobile station phase 1,GSM 900

43 dBm (20 W) 13 dBm


30 dBm (1 W) 10 dBm

Mobile station GSM 850 39 dBm (8 W) 13 dBm


39 dBm (8 W) 13 dBm


30 dBm (1 W) 4 dBm

Mobile station GSM 1900 33 dBm (2 W) 0 dBm

Table 19: Mobile Station Maximum and Minimum Power Ranges

The maximum power setting of a mobile station is based on two factors: itsclassmark (its physical maximum power rating), and the maximum mobilestation power setting for the cell.

Each cell can limit the maximum power level for all mobile stations in the cell.For example, a 20 W mobile station can be limited to 5 W maximum power ifthat is the maximum mobile station power level allowed in the cell. However, a 1W mobile station can never exceed 1 W, and can therefore never reach the5 W maximum allowed in the cell.

The BSC informs the BTS of the new power levels via the BS_power_controlmessage. The BTS in turn transmits a power_command to the mobile stationover the SACCH.

Changing power from one power level to another happens gradually. The powerlevel changes by 2 dB every 60 milliseconds, until the desired level is reached.

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4.6 HandoverA handover changes an active call from one channel to another channel. Thenew channel can be in the same cell or another cell. The types of handover are:

Internal

External

Directed retry

Internal

External.

Incoming emergency

Fast traffic

UMTS to GSM

Handovers ensure a high level of call quality. They are performed when theBSS detects that the call quality has dropped below a defined level, and thecall can be better supported by a different channel.

The call quality can drop due to problems in the cell, such as an interface oran equipment problem. Call quality can also be affected simply because themobile station has moved to an area where the radio coverage from anothercell is better.

The BSS detects the need for a handover by:

Measuring the Air interface channel quality, mobile station and BTS power

outputs and the timing advance

Using an algorithm to see if the received information conforms to the criteria

for handover

Selecting a more suitable channel from a list of target cells and theiravailable channels.

If the BSS decides that a handover is required, the exact sequence of eventsdepends on the type of handover to be performed. In all cases:

A new channel is assigned, ready to support the call

The mobile station moves over to the new channel

On successful completion of the handover, the system clears the resources

for the old channel.

Internal Internal handovers take place between cells controlled by the same BSC. Thiscan include channel changes within the same cell. More details about thesehandover cases is given in Target Cell Evaluation (Section 4.6.3).

External External Handovers take place between cells controlled by different BSC’s.These can be under control of the same MSC or of different MSCs. See TargetCell Evaluation (Section 4.6.3) for more details about these handover cases.

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Directed Retry Handovers can also be performed when there is congestion in a cell. Ifcongestion exists, the traffic channel assignment can be queued. For moreinformation about congestion management, refer to Congestion (Section 3.5).

If there is no available traffic channel for the normal assignment procedure, aDirected Retry can be performed. A Directed Retry is an attempt to assign amobile station to a traffic channel in a cell other than the serving cell.

There are two types of Directed Retry:

An Internal Directed Retry without queueing attempts to handover the call toa traffic channel of a neighbor cell controlled by the same BSC.

An External Directed Retry attempts to handover the queued call to a trafficchannel of a neighbor cell which is controlled by a different BSC.

Secured Incoming The ability to keep free resources in a cell for incoming emergency and powerbudget handovers is provided on a cell basis. When the resource threshold isreached, assignments and other handover types are handled as if the cell wascompletely congested. Once such a request is queued, a directed retry can beperformed as usual. The free resources can also be accessed in the case of afull-rate to half-rate handover in the case of AMR calls, because it allows half aresource (full-rate to half-rate) to be freed from the cell point of view. The featureimproves the quality of service, as it helps to limit the number of lost calls.

Fast Traffic The fast traffic handover searches in the whole cell for a mobile which canperform a handover to a not loaded neighbor cell if the received signal level ofthe BCCH is good enough. It is much more efficient than the forced directedretry when the overlap of adjacent cells is reduced, e.g., in the case of singlelayer networks, or for deep indoor coverage (if the umbrella cell does notoverlap totally the microcells).

UMTS to GSM For circuit-switched services, the BSS supports handover from UMTS to GSM.The handover from GSM to UMTS is not supported in this release of the BSS.A hard handover is performed from the UTRAN to the GSM BSS between aUMTS core network and a 2G MSC. This handover is regarded by the BSS asa GSM inter-BSS hand over. The signalling procedures, from the BSS point ofview, rely almost on the normal GSM procedures.

For packet-switched services, the current 3GPP standard does not allowhandover with channel preparation. Therefore, the UMTS mobile stationreceives the 2G radio resource cell change order Information Element from theUTRAN in the Inter System handover message. The UMTS mobile station thenperforms an access request in the GPRS cell. Therefore, from a BSS pointof view, the UMTS mobile station is regarded as a 2G mobile station when itindicates that it has selected a GSM cell.

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4.6.1 Radio Measurements

The BTS constantly monitors the radio link by:

Measuring the received signal strength for active channels

Measuring the received signal quality for active and inactive channels

Measuring the received signal timing for active channels

Collecting signal strength and quality measurements from the mobile

station for the active channel

Collecting adjacent cell BCCH signal strength measurements from themobile station (adjacent cell BCCH frequencies are sent to the mobile

station in the sys_info 5 message on the SACCH).

The mobile station sends its measurements to the BTS in a layer 3RadioResource measurement_report message on the SACCH. The mobilestation and BTS measurements are passed to the BSC in a layer 3 RRmeasurement_result message. These messages are sent once permultiframe and are processed by the BSC. The BSC uses this information to:

Perform power control for the BTS and mobile station

Calculate whether a handover is needed

Make traffic channel quality tables

Make the target cell list

Make a handover decision.

Power Control BTS and mobile station power control is described in Power Control Decisionand Handover (Section 4.5.4). From a handover point of view, no handoverdecision is made due to signal quality until the power levels have been setto maximum.

Need for Handover The BSC calculates the need for a handover using an algorithm, the use ofwhich is described in Handover Detection (Section 4.6.2).

Traffic Channel QualityTables

The BSC uses the uplink idle channel measurements made by the BTS tomake a table of traffic channel channels, classified by interference levels. Thistable is used to select a channel for assignment.

Target Cell List A target cell list can be made by the BSC using the neighbor cell BCCHmeasurements sent by the mobile station. This is used to evaluate whether aneighbor cell can provide a better channel than the existing one.

Handover Decision Handover decision is based on averaged measurements and the results areaveraged over a period of time. For example, the BSC detects the need fora handover, based on one measurement that may have been caused byfreak conditions changing the signal propagation for a short period. Thismeasurement is averaged with other measurements and a handover decisionmay or may not result, depending on the other measurements.

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4.6.2 Handover Detection

Each time the BSC processes a set of Air interface measurements, it checkswhether a handover is needed. If the need for a handover is detected, ittriggers the target cell evaluation process. See Target Cell Evaluation (Section4.6.3) for more information.

If the handover algorithm in the BSC detects the need for a handover, itproduces a handover alarm. As the target cell evaluation is handled by theBSC, this alarm is also handled internally by the BSC. The alarm includes acause value used by the BSC to evaluate which type of handover is required.The basic types of handover are:

Quality and level

Better zone

Better cell (power budget)

Distance

Mobile velocity dependent

Preferred band.

4.6.2.1 Quality and Level HandoverThese handovers are used to keep an active call connected when the signalquality falls below a defined threshold. If a handover is not performed, a radiolink failure may be detected and the call cleared. This type of handover canbe caused by the following events:

Quality level too low on the uplink or downlink

Signal level too low on the uplink or downlink

Interference level too high on the uplink or downlink

Signal level too low on the uplink or downlink compared to low threshold

(microcells only)

Signal level too low on the uplink or downlink compared to high threshold(microcells only)

Several consecutive bad SACCH frames received (microcells only)

Signal level too low on the uplink or downlink inner cell (concentric cellsonly).

Microcell handovers are described in detail in Microcell (Section 7.5.2). Refer toConcentric Cell (Section 7.2) for more information on concentric cells.

If the received signal level or the received signal quality is too low, the BSCperforms BTS and mobile station power control to try and achieve the optimumlevel/quality ratio. This is described in Power Control Decision and Handover(Section 4.5.4).

The figure below shows a graph of received signal level and received signalquality. The hatched areas show where power control is successful. The solidgray shaded areas show where power control fails to achieve the desiredlevel/quality ratio. These areas are where the BSC detects the need for ahandover.

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123456123456123456123456123456123456123456123456123456123456123456123456123456123456123456123456

123456789123456789123456789123456789123456789123456789123456789123456789123456789123456789123456789123456789

1234567890123412345678901234123456789012341234567890123412345678901234

Power Increase to improve quality

Quality IntercellHandover

Quality IntracellHandover

High Quality

Level Intercell

HandoverReceived Signal Quality

Low Quality

Received Signal Level

High Level

Desired Quality

and Level Balance

(no action needed)

Power Decrease to

Conserve Resources

and Minimize Interference

PowerIncrease

to Improve

Level

Low Level

Figure 47: Quality and Level Handover

Level Intercell Handover The Level Intercell Handover area represents the range of measurementswhere the received signal quality is acceptable, but the received signal level istoo low. If the power output levels are already set to the maximum allowed inthe cell, the BSC generates a handover alarm with a cause value indicatingthe reason for handover. Although the quality of the signal is acceptable (andmay be very good), the call is in danger of being lost if the signal level dropsrapidly, causing a radio link failure.

The handover is an intercell handover, as the serving cell cannot support thecall at the required power level. The call is handed over to a channel in a cellwhich can support the call at the required level and quality.

Quality IntercellHandover

The Quality Intercell Handover area represents the range of measurementswhere both the receive signal quality and the received signal level are toolow. If the power output levels are already set to the maximum allowed inthe cell, the BSC generates a handover alarm with a cause value indicatingthe reason for the handover.

The handover is an intercell handover, as the serving cell cannot support thecall at the required quality and power level. The call is handed over to a channelin a cell which can support the call at the required quality and level.

Quality IntracellHandover

The Quality Intracell Handover area represents the range of measurementswhere the received signal quality is too low, but the received signal level isacceptable. This situation is caused by interference on the channel, so the callis handed over to another channel in the same cell.

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4.6.2.2 Better Zone HandoverThis is used in concentric cell configurations when the mobile station movesinto the inner zone. If the inner zone has a free channel, an interzone handoveris triggered. This enables the mobile station to be supported on a channelrequiring a lower power level, therefore creating less interference in the cell. Thedetection of this type of handover is performed on signal level measurementsonly (SACCH of serving cell, BCCH of adjacent cells). This is shown in thefollowing figure. This type of handover can be caused by the signal level beingtoo high on the uplink and downlink outer zone (concentric cells only).

High PowerOuter Zone

MS HandedOver toLow PowerZone

Low PowerInner Zone

MS : Mobile station

Figure 48: Better Zone Handover

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4.6.2.3 Better Cell HandoverThis feature is used to handover the mobile station to a cell that can support thecall using lower BTS and mobile station power levels. The algorithm in the BSCcalculates the power levels for the current cell, and the power levels required byadjacent cells from the adjacent cell information sent by the mobile station.This is shown in the figure below.

This type of handover is often referred to as a power budget handover, as ituses the Power Budget parameter to detect whether an adjacent cell can beused (see also Multiband Power Budget Handover in Multiband Handover(Section 4.6.2.6 )). If the power budget for an adjacent cell gives a ’better’reading for a certain amount of time (a defined number of SACCH frames),then a handover alarm is produced. This type of handover can be caused bythe following events:

Power budget is greater than handover margin threshold

High signal level in neighbor microcell (macrocell to microcell handover).

BSS 1 = Best Cell BSS 2 = Best Cell

Target CellBSS 2

Serving CellBSS 1

Zone for Power Budget Handoverfrom BSS 1 to BSS 2

Figure 49: Better Cell Handover (Power Budget)

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4.6.2.4 Distance HandoverThis handover occurs when the propagation delay between the BTS and themobile station is considered excessive. The mobile station is considered tobe too far from the BTS and needs to be served by a closer BTS. This isshown in the figure below.

Under normal circumstances, as the mobile station moves away from a BTS, aQuality and Level or Better Cell handover takes place. However, under certainconditions which change the propagation qualities of a signal, a cell canprovide a very high quality signal outside of the normal operating range of theserving cell. These propagation qualities are often due to climactic conditionswhich can change suddenly. If the high quality signal ’disappears’ due to achange in the weather, the call would be lost. The distance handover ensuresthat this does not happen by handing the mobile station over to a ’closer’ cellonce a distance limit is exceeded. This type of handover is caused by too greata distance between the mobile station and the Base Station .

123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890

Area of NormalCell Boundaries

Distance HandoverArea from BSS1 to BSS2

BSS 1 BSS 2

Figure 50: Distance Handover

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4.6.2.5 Mobile Velocity Dependent HandoverIn a hierarchical cell structure, where mini or microcells are overlaid byan umbrella cell (macrocell), fast moving mobile stations are handled bythe upper layer cell.

Discrimination of the speed of a mobile station is based on the dwell time ofthat mobile station in a lower layer cell. Depending on the time elapsed in theserving cell, the call is transferred to the lower layer cell or the umbrella cell.

If the dwell time in the serving cell is above the threshold, the mobile stationis considered slow moving and is sent to the lower layer cell that triggeredthe handover.

If the dwell time is below the threshold, the mobile station is considered fastmoving. To prevent a high number of handovers between the smaller lowerlayer cells, the call is sent to the umbrella cell.

Dwell time is only calculated if there has been a power budget handoverfrom another lower layer cell. This is to avoid sending a call to the umbrellacell in the following cases:

A call initiated at the limit of the lower layer cell

A call transferred from the umbrella cell to the lower layer cell, just beforereaching the limit of that cell

After an external handover, when there is no information on the preceding

cell and handover cause.

Whatever the dwell time, any emergency handover sends the call to theumbrella cell, which acts as the rescue cell.

The load on the umbrella cell is taken into consideration when determiningthe threshold at which handovers are performed. Saturation of the umbrellacell can cause the loss of calls, when a handover is required from anotherumbrella cell or a lower layer cell.

As the load on the umbrella cell increases, the dwell time threshold isincreased, keeping some mobile stations in the lower layer cells. When theload on the umbrella cell is very high, speed discrimination is disabled, andpriority is given to the load in the umbrella cell. The following figure shows agraph of umbrella cell load and minimum dwell time.

Load in Umbrella Cell

Minimum Dwell Time

Macrocell with little traffic

Macrocell saturated

Traffic regulation

High load

Low minimum dwell time

High minimum dwell time

Speed discrimination

disabled

Max speed discrimination

in force

Low load

Figure 51: Umbrella Cell Load in Mobile Velocity Dependent Handover

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4.6.2.6 Multiband HandoverThere are two types of multiband handover:

Preferred-band handover

Multiband Power Budget handover.

Preferred-BandHandover

Network capacity can be expanded by introducing multiband operation. Thismeans that an existing network (for example, GSM 900) is expanded by addingcells in a different band (for example, GSM 1800). In such a network, theoriginal band (GSM 900) is referred to as the first band. The new band (GSM1800) is referred to as the preferred band.

The existing monoband mobile stations, which use the first band, continue todo so. However, multiband mobile stations are handed over to the preferredband, where possible. This is done to free resources in the first band for useby monoband mobile stations. Normal handovers (for example, better cellhandover), hand over multiband mobile stations to the preferred band.

A new handover type, called preferred-band handover, hands over multibandmobile stations immediately when a first-band cell reaches a specifiedcongestion threshold. This frees up resources for the monoband mobilestations in the cell.

For a preferred-band handover to occur, the following conditions must be met:

The first band cell’s traffic load reaches a high threshold

Suitable neighboring cells in the preferred band are available

The preferred band handover facility is enabled.

Multiband Power BudgetHandover

In certain networks, two different frequency bands can exist, for example, onefrequency band uses the GSM frequencies, the other frequency band usesthe DCS frequencies. In this case, multiband power budget handovers can beenabled between the two frequency bands using the EN_MULTIBAND_PBGT_HO

parameter:

Setting the EN_MULTIBAND_PBGT_HOparameter to TRUE enables multibandpower budget handovers between two frequency bands.

Setting the EN_MULTIBAND_PBGT_HOparameter to FALSE disables multiband

power budget handovers between two frequency bands.

This parameter must be defined for each cell where multiband power budgethandovers are required.

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4.6.3 Target Cell Evaluation

Cell evaluation is performed by the BSC. Once a handover alarm is detectedwithin the BSC, it evaluates the neighbor cells and compiles a list of possibletarget cells. The serving cell can be on the target cell list.

The cells are evaluated and ranked by preference, calculated by one of thetwo algorithms, ORDER or GRADE. The Network Operator chooses whichalgorithm is to be used on a cell-by-cell basis.

The BSC tries to handover to the most suitable cell. If this cell is controlledby the BSC, the BSC handles the handover procedure. If the target cell iscontrolled by another BSC, the serving BSC sends a handover_requestmessage to the MSC.

Target Cell The exact calculation performed to choose the target cell depends on thealgorithm used and the cause of the handover alarm.

The target cell is chosen taking into account the following criteria:

Received signal level

Power budget

Number of free channels

Relative load on the traffic channel of the cell

Maximum power allowed in cell

HO_MARGINparameter

Mobile station distance from target BTS

Handover cause.

The HO_MARGINparameter is an O&M parameter set by the Network Operator.It is used to prevent a call being continually handed over between two cells. Forexample, following a power budget handover, the new cell immediately startspower budget calculations for its neighbor cells. It may find that the original cellis giving a better power budget reading and try to hand back immediately. Thiseffect can be caused by slight climactic changes which affect the propagation ofsignals. It is known as the ’ping-pong’ effect. The HO_MARGINparameter stops acall being handed back to a cell from which it has just been handed over.

There is also an O&M parameter, W_PBGT_HOwhich can be set by theOMC-R operator, to add a weighting for the power budget parameters of cellscontrolled by another BSC. Refer to A1353–RA Configuration Handbookfor more information.

The target cell chosen also depends on the mobile station classmark (seeClassmark Handling (Section 3.6)) and its compatibility with the BTS’s cipheringcapabilities (see Ciphering (Section 3.8)).

The procedures initiated to handover a call depend on which cell has beenchosen as the target cell.

Internal: Intracell If the target cell and the serving cell are the same, the call is handed over to achannel in the same cell. This is an intracell handover. This type of handover ismost commonly due to interference in the cell. It is controlled by the BSC.

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Internal (IntraBSS):Intercell

If the target cell is not the same as the serving cell but is controlled by the sameBSC, this is called an intercell intraBSS handover. This handover is normallycontrolled by the BSC. However, the Network Operator can specify that thistype of handover is controlled by the MSC.

External (InterBSS):IntraMSC

If the target cell and the serving cell are not controlled by the same BSC, but thetwo BSC are controlled by the same MSC, this is called an interBSS intraMSChandover. This handover is controlled by the MSC.

External (InterBSS):InterMSC

If the target cell and the serving cell are controlled by different BSCs and thetwo BSCs are controlled by different MSCs, this is called an interBSS interMSChandover. The control of this handover is shared between the MSCs.

Handovers controlled by the BSC are called internal handovers. Handoverscontrolled by the MSC are called external handovers.

4.6.4 Synchronous and Asynchronous Handover

The handover to the target cell can be synchronous or asynchronous. Asynchronous handover can be performed if the master clocks of the serving celland the target cell are synchronized. This is the case when:

The serving cell and the target cell are the same cell

The BTSs of the serving cell and the target cell are in a collocatedconfiguration.

BTSs in a collocated configuration take the clock pulse from one BTS in theconfiguration.

For a synchronous handover, the mobile station does not have to resynchronizewith the target BTS. Therefore, the physical context procedure for power levelsand timing advance does not have to be performed after the mobile stationaccesses the target cell.

For an asynchronous handover, the mobile station has to synchronize withthe target cell before transmitting any user traffic.

4.6.4.1 Synchronous Internal HandoverThis section describes the message flow for a synchronous internal handover.The example in the figure below is for a handover of a traffic channel betweentwo separate cells controlled by two BTSs in a collocated configuration.

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MS BTS BTS BSC MSCTarget Serving

release withserving BTS

HO detectHO alarmcell evaluation

measurement reports

handover command

HO ref + power + cell desc + TA + cipher + channel

(SACCH)

measurement results

physical contextconfirm TA + power

channel activation

TA + cipher + DTX + power + channel


channel activation ack

access burst (SACCH)

SABM

handover detection


handover complete

handover performed


HO : Handover

MS : Mobile station



TA : Timing advance

Figure 52: Synchronous Internal Handover

Measurement Reporting The mobile station and BTS take measurements on the Air interface asdescribed above. The mobile station sends measurement information to theBTS in a measurement_report message. The BTS sends mobile station andBTS measurements to the BSC in a measurement_results message.

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Handover Detection The BSC detects the need for a handover and creates a handover alarmindicating the reason for the handover. The BSC evaluates possible target cellsand creates a cell list. For this example, the first cell on the list (target cell)is a cell controlled by this BSC and the BTSs of both serving and target cellare collocated. Once this cell is chosen, the BSC initiates the synchronousinternal handover procedure.

The BSC sends a physical_context_request message to the serving BTS,requesting current timing advance and power level information. This informationis passed to the target BTS.

The serving BTS responds with a physical_context_confirm message.

Channel Activation When the BSC receives the physical context information, it sends achannel_activation message to the target BTS, indicating:

The channel to be used

The mobile station timing advance to be applied

The encryption algorithm and ciphering key

A Discontinuous Transmission indicator for uplink (not used) and downlink(see Speech Transmission (Section 4.4.1))

The mobile station power to be used

The BTS power to be used.

The target BTS sets its resources to support the channel. It then uses achannel_activation_acknowledgment message to reply to the BSC. Thislets the BSC know that the target BTS is ready. The target BTS also startstransmission of SACCH/FACCH frames so that when the mobile stationaccesses this BTS, it receives sys_info 5 and sys_info 6 messages. Themobile station also receives the timing advance and power control updates.

Handover Command The BSC sends the handover_command message transparently through theBTS to the mobile station. This message contains:

The new channel and its associated control channel

The target cell description

A power level indication for the mobile station initial access to the target cell

A handover reference

The timing advance to be used in the target cell

Any cipher mode information (phase 2 mobile stations can change cipher

mode during a handover procedure).

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The Handover The mobile station releases its connection with the serving BTS and sendsfour consecutive access bursts to the target BTS on the uplink SACCH. Thesebursts include the handover reference and use a timing advance of 0.

The BTS calculates the timing advance (it may have changed since the physicalcontext procedure). It sends a handover_detection message to the BSCindicating the timing advance measured for the access burst. If the mobilestation timing advance needs to be updated, the BSC sends this information inthe physical_information message on the FACCH channel associated withthe traffic channel.

The mobile station then sets ciphering (as required). It sends its firstframe, SABM, using the timing advance information either as sent in thehandover_command message, or as updated in the FACCH frames.

When the BTS receives the frame from the mobile station, it sends anacknowledgment frame to the mobile station and an establish_indicationmessage to the BSC. This informs the BSC that the radio link has beenestablished. The BSC starts BTS and mobile station power control.

On receipt of the acknowledgment frame, the mobile station sends ahandover_complete message to the BSC. The mobile station can now starttransmitting on the new channel.

The BSC informs the MSC of the handover in a handover_performedmessage and initiates the release of the old channel.

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4.6.4.2 Asynchronous External HandoverThis section describes the message flow for an asynchronous externalhandover. The example in the figure below is for a handover of a traffic channelbetween two separate cells controlled by two different BSCs.

MS BTSTarget

BTSServing

BSCTarget

BSCServing

MSC

release withserving BTS

HO detectHO alarm

set up switching path between Abis

& A interfaces

handover detect

measurement reports (SACCH)

handover command

ch+cell+HOref+cipher

measurement results

handover required

channel activation

SACCH/FACCH

channel activation ackhanover request ack

+ handover command

handover command

handover command

Synchronization(FCCH + SCH)

access burst (SACCH)handover detect

HO ref + TAhandover detect

physical info


physical info (FACCH)

ack

handover complete

(FACCH)

handover performed

clear command

handover request

channel type+cipher+cell IDs+DTX+cause+cm



HO : Handover

MS : Mobile station



TA : Timing advance

Figure 53: Asynchronous External Handover

Measurement Reporting The mobile station and BTS take measurements on the Air interface asdescribed above. The mobile station sends measurement information to theBTS in a measurement_report message. The BTS sends mobile station andBTS measurements to the BSC in a measurement_results message.

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Handover Detection The BSC detects the need for a handover and creates a handover alarmindicating the reason for the handover. The BSC evaluates possible targetcells and creates a candidate cell list.

To initiate the external handover procedure, the BSC sends ahandover_required message to the MSC including the candidate cell list. Italso starts a timer to prevent it sending the same cell list. It can only re-send thecell list when the timer times out, or if it receives a handover_request_rejectmessage from the MSC.

The MSC chooses the target cell from the cell list. It sends a handover_requestto the target BSC to inform it that a mobile station is going to be handedover. This message contains:

Channel type required

Cipher mode information

Mobile station classmark information

Serving cell identification

Target cell identification

Downlink Discontinuous Transmission flag

Handover cause.

Channel Activation The target BSC initiates the channel activation for the new channel with thechannel_activation message.

The target BTS sets its resources to support the new channel, starts sendingthe SACCH/FACCH and sends a channel_activation_acknowledgmentmessage to the target BSC.

Handover Command The target BSC builds a handover command. This command is sent to theMSC in the handover_request_acknowledgment message. The handovercommand contains:

The new channel and its associated control channel

The target cell description

A handover reference

Any cipher mode information (phase 2 mobile stations can change cipher

mode during a handover procedure).

The MSC forwards the handover_command message to the serving BSC.

The serving BSC sends the handover command message to the mobile station.

The Handover The mobile station releases its connection to the serving BTS. It synchronizeswith the target BTS using the FCCH and SCH information. Once synchronized,the mobile station continually sends access burst on the uplink SACCH until itreceives the physical_information message on the FACCH from the targetBSC.

When the target BTS receives an access burst, it checks the handoverreference and calculates the timing advance. This is sent to the target BSCin the handover_detect message.

The target BSC informs the MSC of the handover detection and establishes aswitching path between the allocated Abis and A interface resources.

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When the mobile station receives the physical_information message, itsends its first frame on the new channel using the timing advance sent in thephysical_information message.

The target BTS acknowledges the mobile station’s first frame and sends anestablish_indication message to the target BSC, and an acknowledgment tothe mobile station. On receipt of the acknowledgment, the mobile station sendsa handover_complete message on the uplink FACCH to the target BSC.

The target BSC informs the MSC that the handover has been performed.

The MSC initiates the call clearing procedure towards the serving BSC.

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4.7 Overload ControlA lot of telecommunications signalling is required for the BSS to supportcommunication between mobile stations in the cells under its control andthe MSC. Telecommunication processors in the BTS or BSC can becomeoverloaded. To avoid a sudden loss of communication when a processorbecomes saturated, the BSS controls the load on these processors in thefollowing steps:

1. Taking local action to reduce the load.

2. Taking global BSS action to further reduce the load.

Note: The telecommunications processors of the MSC can also become overloaded.However, MSC overload control is not the domain of the BSS.

4.7.1 BTS Overload

The BTS Frame Unit (TRE for a BTS A9100 or BTS A910) handles all thetelecommunications signalling on the Air interface. If the FU or TRE becomessaturated, this can result in the loss of calls. Therefore, the BTS monitors theload and takes action where appropriate. On initial detection of the overloadcondition, the BTS takes local action to reduce the load. If the BTS local actiondoes not reduce the load, the BTS sends overload messages to the BSC,which can decide to take global action.

The different stages of BTS overload, from detection to resolution, aredescribed below.

BTS Overload Detection The BTS monitors the load on the FU or TRE by measuring the free time onthe FU or TRE’s Signalling Control Processor and the free message space onthe associated buffers. If either of these passes a set threshold, a counter isincremented. If a threshold is not passed again within a given time, the counteris decremented. The counter has two thresholds. If the first of these is passed,the BTS takes local overload action. If the second of these is passed the BTSsends overload messages to the BSC.

BTS Overload Action When local action is triggered in the BTS, it discards low priority messagessuch as the establish_indication message to reduce the load on the SCP.

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4.7.2 BSC Overload

The BSC has two entities handling telecommunications signalling:

The TCU handles telecommunications signalling for the Abis interface

The DTC handles telecommunications signalling for the A interface.

The different stages of BSC overload, from detection to resolution, aredescribed below.

BSC Overload Detection For the BTS, overload is calculated on the processor free time and the freemessage space of the associated buffers. As the BSC handles more signallingtraffic than the BTS, the detection of an overload, and whether to trigger local orglobal defense actions, is more complicated. The BSC uses an algorithm thattakes into account which processors are affected, the level of overload, andwhich buffers are affected. Each processor has a local overload controller.The BSC’s centralized overload controller is responsible for global overloaddefence actions.

BSC Local OverloadAction

Local action in the BSC is taken by the local overload controller on eachprocessor. Local actions reduce the load on an individual board. The localactions are:

TCU ActionThe TCU discards a percentage of the measurement_result messagesreceived from the BTS. The percentage of discarded messages is increasedand decreased in steps, under the control of the local overload control. Thisonly affects the handover and power control algorithms which still functionbut with less information.

DTC ActionWhen the DTC detects an overload, its state is set to congested on theBSC database. This means that it cannot be selected by the resourcemanagement software to provide a new SCCP connection. Also, the DTCcannot send connectionless messages to the MSC.

BSC Global Overload ActionThe BSC controls global actions for the whole BSS. Global action reducesthe amount of telecommunications signalling traffic in the BSS by inhibitingnew calls. The BSC bars mobile station access classes either in one cellif the global action is requested by a BTS or TCU, or in several cells if aDTC MSC are overloaded.

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Mobile Station AccessClass Barring

When the BSC receives a request for global overload action from a BTS, fromthe MSC, or from one of its local overload control processors, it checks themessage for errors. If it can accept the request, it builds new system informationmessages (1 to 4). These messages are sent on the BCCH. They bar certainmobile station classes from sending channel_request messages on the RACH.

If the overload condition persists, the BSC can change the system informationmessages to bar more mobile station access classes from using the RACH.

When the BTS is barring access classes, its behavior can be modified fromthe OMC-R by modifying the following parameters:

AUT_BARenables/disables the automatic banning of cells after all accessclasses have been barred. This forces the mobile station to camp on

another cell.

EC_BARenables/disables the automatic barring of emergency calls.

EN_BSS_OVRL_CLASS_BARRenables/disables the ability of the BSC toperform global action for BTS to BSC overload conditions.

The number of access classes that can be barred and unbarred in one step canalso be configured from the OMC-R.

Mobile Station AccessClass Unbarring

When an overload message is received from the BTS or when an overload isdetected in the BSC, a timer is set. If no overload message is received from theBTS, or no overload detected in the BSC during the period of the timer, thetimer expires. When the timer expires, the BSC unbars some access classesaccording to a defined algorithm.

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4.8 Call Re-establishment by the Mobile StationThe mobile station initiates call re-establishment when there is already aspeech or data call in a stable state (traffic channel path connected) andthe mobile station detects a radio link failure. The mobile station waits apredetermined time for a response from the network. If there is no responsethe mobile station performs a cell reselection procedure.

If the new cell allows the re-establishment procedure to be performed, themobile station initiates the channel request procedure RACH and awaits theimmediate_assignment message. The mobile station then performs thecontention resolution procedure using the cm re-establishment requestmessage.

The radio and link establishment procedure continues as described in MobileOriginated Call (Section 3.2).

The network may not allow the mobile station to perform the channel requestprocedure, due to inhibition of the mobile station access class broadcast in thesys_info 1 to 4 messages. If this is the case the mobile station radio resourceentity reports the failure of the radio and link establishment procedure to thehigher layer entities in the mobile station.

When the MSC receives the cm re-establishment request message it initiatesthe procedures necessary to establish a new radio resource connection andcontinue the call management connection.

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5 Call Release

This chapter provides an overview of Call Release and describes theprocedures which ensure resource allocation to a call. It specifically describesCall Release procedures in normal service plus the following special cases:

Overview

Following Reset

BSC initiated

BTS initiated

Mobile station initiated

This chapter also describes Remote Transcoder Alarms, and the processesused to break a connection and disconnect the resources, depending on thenature of radio transmission.

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5.1 OverviewThe Call Release procedures ensure that resources allocated to a call are freefor reuse when they are no longer required by the current call.

Call Release procedures are required when:

A call is finished and either the called or calling party hang up

A mobile station is turned off

A call is handed over and the resources for the original call are released

A call is modified and the resources for the original channel are released

There is operator intervention, such as a channel being blocked

There is a failure

There is a radio link failure

The system detects an LAPDm failure.

If a call is terminated normally, the Call Release procedures are triggeredautomatically. If the call is terminated abnormally, the system has to detect thatthe resources are no longer required and release them.

For a complete Call Release, the following resources must be released:

A interface resources

Abis interface resources

Air interface resources

MSC resources:

Layer 3 for the A interface

SS7 signalling for the A interface

Layer 1 physical resources for the A interface.

BSC:

Layer 3 for the A, Abis and Air interface

Layer 2 SS7 for the A interface and LAPD for the Abis interface

Layer 1 physical resource for the A and Abis interface.

BTS:

Layer 3 for the A, Abis and Air interface

Layer 2 LAPD for the Abis interface and LAPDm for the Air interface

Layer 1 physical resources for the Abis and Air interface.

Mobile station:

Layer 3 for the Air interface

Layer 2 LAPDm for the Air interface

Layer 1 for the Air interface.

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5.2 Call Release Procedures in Normal ServiceThe Call Release procedures, and the order in which they are triggered,depend on the reason for the release. This section describes the following CallRelease scenarios, which occur during normal service:

Normal Release (Calls terminated by Call Management)

Calls terminated following a channel change.

Special cases, including detailed behavior of the MSC, BSC, BTS and mobilestation are described later in this chapter.

5.2.1 Normal Release

Call termination initiated by Call Management is considered to be a normalreason for Call Release. In this type of Call Release, the MSC initiates therelease. Before this can happen, the mobile station must inform the MSC thatit has disconnected the call. This is done with layer 3 messages passedtransparently through the BSS between the mobile station and MSC, as shownin the following figure.

MS BSS MSC

disconnect (layer 3 CC)

release complete (layer 3 CC)

release request (layer 3 CC)

MS : Mobile station

Figure 54: Mobile Station Disconnecting a Call

Once the MSC has confirmation that the mobile station wants to disconnect andno longer requires the connection, it initiates the release procedure towardsthe BSC. This procedure:

Releases the circuit (if applicable)

Releases the SCCP connection.

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The BSC responds to the MSC to clear the connection on the A interface, andinitiates the Call Release procedure toward the BTS and mobile station. Thisprocedure releases the radio resources.

This action triggers the mobile station to release the LAPDm connection (discmessage) and the BSC to release physical resources allocated to the call.

This is shown in the following figure.

MS BTS BSC MSC

release of A interface resources

Timer start (SCCP release)

Timer start (release indication)

Timer

Timer

disable remote TC alarm detect

disc

channel release

deactivate SACCH

clear command

MIE including cause value

(to release LAPDm)

UA

release indication



RF channel release

RF channel release ack

clear complete

SCCP release complete

SCCP released



MIE : Mandatory Information Element

MS : Mobile station



TC : Transcoder


Figure 55: Normal Call Release

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MSC actions The MSC initiates Call Release at the end of the mobile station transaction.The MSC can be informed of the end of the mobile station transaction:

By a level 3 disconnection message from the mobile station (Figure 54)

By a disconnection message from the Network Operator if thecorrespondent terminates the call

At the end of a service call (i.e., SMS or location updating).

The normal release procedure of the MSC releases both the A interfaceresources used for the call, if any, and the SCCP connection used for thesignalling which controls the connection.

The MSC initiates the release procedure by sending a clear_commandmessage to the BSC. This command can include a cause value in theMandatory Information Element.

The BSC accepts the command even if no cause value is included. Itimmediately releases the A interface resources for the call and replies to theMSC with a clear_complete message. This is shown in the following figure.

MS BTS BSC MSC



Timer start (release indication)

channel release

deactivate SACCH

clear command


clear complete


SCCP released


MS : Mobile station



Figure 56: Initiation of Normal Release by MSC

The BSC initiates the release of the Abis and Air interface resources. It alsosets a timer to ensure that the MSC releases the SCCP signalling resources.

On receipt of the clear_complete message from the BSC, the MSC releasesthe resources associated with the A interface and initiates the release of theSCCP signalling resources by sending the SCCP_released message tothe BSC.

The BSC stops its timer and sends the SCCP_release_complete message.The SCCP resources are now released and can be used for another call.

If the BSC timer expires before the SCCP_released message is received, thenthe BSC force releases the SCCP connection.

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BSC/BTS/Mobile StationInteractions

The normal Call Release procedure towards the mobile station/BTS releases:

The radio resources associated with the call

The Radio Frequency channel.

The BSC initiates the release of the radio resource by sending:

A channel_release message to the mobile station via the BTS

A deactivate_SACCH message to the BTS.

Thechannel_release message prompts the mobile station to send a discmessage to the BTS to release the LAPDm resource. When this is received,the BTS acknowledges this with a ua message to the mobile station and sendsa release_indication message to the BSC. This procedure is supervised bya timer in the BSC. The BSC considers the mobile station disconnected andstarts the RF channel release when:

The timer expires

The BSC receives the release_indication message and stops the timer.

When the BTS receives the deactivate_SACCH message, it stops sendingSACCH information and disables the remote Transcoder alarm detection. Thisstops the sending of Transcoder alarms to the BSC when the Transcoderdetects inactivity on the channel. This is shown in the figure below.

If the mobile station does not receive the channel_release message, itconsiders the stopping of SACCH information as a radio link failure andperforms a local release.

MS BTS BSC MSC



Timer start (release indication)disable remote TC alarm detectdisc

channel release

deactivate SACCH

clear command


(to release LAPDm)

UArelease indication

clear complete


SCCP released



MS : Mobile station



TC : Transcoder


Figure 57: BSC/BTS/Mobile Station interactions in Normal Call Release

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Once the BSC considers the mobile station disconnected, it initiates releaseof the RF channel from the BTS. In a normal call release procedure, thisoccurs following the release of the mobile station from the Air interface (asdescribed earlier in this section).

Before releasing the RF channel, the BSC sends a physical_context messageto the BTS and starts a timer to supervise the response. The response from theBTS is a physical_context_confirm message which contains the last LAPDmperformance measurements for the RF channel.

On receipt of the physical_context_confirm message, or after the timer hastimed out, the BSC sends an RF_channel_release message to the BTS andstarts a timer to supervise the release. The BTS releases the level 1 and 2resources for the channel and replies with an RF_channel_release_ackmessage.

On receipt of the acknowledgment, the BSC releases all resources for the RFchannel. This is shown in the following figure.

MS BTS BSC MSC

Timer

Timer


UArelease indication


RF channel release


MS : Mobile station


Figure 58: Normal Release Final Steps

If the timer supervising the release times out, the BSC sends theRF_channel_release message again and restarts the timer. If the timer timesout again, the BSC releases all resources locally. It also sends an O&Merror report to the OMC-R with a cause value indicating that the RF channelrelease procedure has failed.

Note: The RF channel can be released locally by the BTS and still be active. If theRF channel is still active, it is released when the BSC attempts to assign itto another call with a channel_activation message. The BTS replies with achannel_activation_nack and the BSC releases the channel (refer to chapter3 for more information).

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5.2.2 Calls Terminated Following a Channel Change

This section describes the Call Release procedure following a successfulchannel change procedure. The case presented is an external intercellhandover. For an internal channel change, the serving and target BSCs are thesame, and in some cases, the serving and target BTSs are the same.

The target BSC receives confirmation of the successful handover from themobile station when the mobile station sends the handover_completemessage. This message is passed transparently through the target BTS. SeeCall Handling (Chapter 4) for more information about handovers.

The target BSC informs the MSC of the handover and initiates the Call Releaseprocedure towards the serving BSC, by issuing a clear_command message.The serving BSC issues a channel_release message to the mobile stationand a deactivate_SACCH message to the serving BTS. The normal CallRelease procedure described in Normal Release (Section 5.2.1) continuesbetween the serving BSC, the serving BTS, the MSC and the mobile station.This is shown in the following figure.

MS BTSTarget

BTSServing

BSCTarget

BSCServing

MSC

handover complete

channel release

handover performed


deactivate SACCH

clear command

(FACCH)



MS : Mobile station


Figure 59: Call Release Following a Channel Change

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5 Call Release

5.3 Call Release - Special CasesCall Release can occur for reasons outside normal service. This section treatsthe following special cases in which Call Release happens:

Call Release following Reset

BSC-initiated Call Release

BTS-initiated Call Release

Mobile station-initiated Call Release

Remote Transcoder alarms.

5.3.1 Call Release Following Reset

Resets are used in software/hardware failure situations, or when the databaseis corrupted and recovery procedures have failed. The MSC can reset all callswithin a BSC or an individual circuit. For example, if the MSC loses dynamicinformation regarding calls (i.e. preventing it from providing such services asaccounting), it can send a reset or a reset_circuit message to the BSC.

Reset The MSC initiates Call Release when it has to release all calls associatedwith the BSS (Reset).

The MSC sends a reset message containing a cause value to the BSC.The BSC then:

Sends an alarm to the OMC-R

Sends a block message to the MSC to block circuits

Starts to clear all calls in the BSS. For each call, the procedure in NormalRelease (Section 5.2.1) is repeated.

For each SCCP connection on the A interface, the BSC can send anSCCP_release message and release any A interface resources associatedwith the SCCP.

A timer allocates a certain amount of time for the calls to clear. When the timerexpires, the BSC sends a reset_ack message to the MSC. The figure belowshows the Call Release process after a reset is initiated.

Reset Circuit The reset circuit procedure is initiated from the MSC. The procedure informsthe BSC that an individual circuit is no longer active in the MSC. This triggersthe call clearing procedure if the circuit has an active SCCP connection.

The MSC sends a reset_circuit message to the BSC for each circuit to bereset. Depending on the resources allocated, this can trigger the BSC to:

Release the A interface resources

Initiate the release of the SCCP

Initiate Call Release towards the BTS and mobile station.

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MS BTS BSC MSC

circuits blocked

timer

reset

channel release

send alarm to OMC−R block

SCCP release


SCCP release


reset ack

channel release

release indication

disc

to release LAPDm

discto release LAPDm



indication RF channel

release

release


context requestphysical


RF channel release



MS : Mobile station


Figure 60: Call Release Following Reset

Note: If this procedure is invoked due to SCCP problems, then messages on the Ainterface may not be passed. The MSC and BSC locally release resourcesfor the A interface connections. Refer to BSC-Initiated Release (Section5.3.2) for more details.

5.3.2 BSC-Initiated Release

The BSC is involved in Call Release for both the A interface and Abis/Airinterfaces.

The BSC initiates Call Release on the A interface when events internal to theBSS terminate communication with the mobile station.

The Call Release towards the mobile station may already be in progress orhave finished when the BSC initiates a release on the A interface. If themobile station is still connected when the BSC initiates a release on the A

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interface, the release towards the MSC is triggered by the clear messagefrom the MSC to the BSC.

Towards the MSC The BSC initiates the release towards the MSC by sending a clear_requestmessage. It also starts a timer to supervise the procedure. The MSC releasesresources for the A channel and sends the clear_command message tothe BSC. This command contains a cause value indicating that the BSCinitiated the release.

From this point, the Call Release follows the procedure described for normalCall Release (refer to Normal Release (Section 5.2.1)). The procedure startswith the BSC releasing A channel resources. It initiates the release proceduretowards the mobile station (if still attached), and returns a clear_completemessage to the MSC. This sequence is shown in the following figure.

MS BTS BSC MSC

clear request



MS : Mobile station

Figure 61: BSC-initiated Call Release toward the MSC

Towards the MobileStation/BTS

The Call Release procedure towards the mobile station/BTS releases:

The radio resources associated with the call

The RF channel.

The BSC initiates the release of the radio resource by sending:

A channel_release message to the mobile station via the BTS

A deactivate_SACCH message to the BTS.

This is the Normal Release procedure described in Normal Release (Section5.2.1).

Note: In this process, once the BSC considers the mobile station disconnected, itinitiates release of the RF channel from the BTS.

This can occur following:

The release of the mobile station from the Air interface (as in the NormalRelease procedure)

A handover, when the BSC is sure that the mobile station has successfullychanged to the new channel. Refer to Calls Terminated Following a ChannelChange (Section 5.2.2).

An immediate assign procedure failure. This ensures that the SDCCH isavailable for reuse as quickly as possible.

A normal assignment failure or handover failure. This ensures that the traffic

channel is available for reuse as quickly as possible.

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5.3.3 BSC-Initiated SCCP Release

The BSC initiates an SCCP release when:

A release procedure has failed

Inactivity is detected in the BSC SCCP entity.

Failed ReleaseProcedure

If there are no resources allocated to a call and the normal release of the SCCPconnection has failed, the BSC forces the release of the SCCP connection:

Internally by sending a level 3 command to its SCCP entity

Externally by sending an SCCP_released message to the MSC.

The BSC does not wait for a reply from the MSC before releasing the SCCPconnection.

If the original failure is due to a problem on the SCCP connection or in the BSCSCCP entity, the SCCP_released message may not be sent. If the messageis sent, the MSC replies with an SCCP_release_complete message andreleases any allocated resources.

Inactivity Procedure The BSC performs an inactivity procedure for each SCCP connection. Ifthe BSC detects inactivity, it assumes that the associated transaction is nolonger active and therefore:

Performs Call Release on the Air and Abis interfaces

Initiates a reset circuit procedure if an A channel is active

Initiates the release of the SCCP connection.

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5.3.4 BTS-Initiated Call Release

The BTS initiates a Call Release only if it detects an LAPD failure or whenO&M requests a restart of the BTS.

Otherwise the role of the BTS in Call Release is to:

Relay channel release messages to the mobile station

Deactivate the SACCH under control of the BSC

Send a release_indication message to the BSC when the mobile station

releases the LAPDm connection.

LAPD Failure When the BTS detects an LAPD failure on a link between one of its frame unitsand the BSC, it forces the release of all mobile stations on active channelsassociated with that Frame Unit (TRE for a BTS A9100 or BTS A910).

The BTS stops SACCH frames and sends a layer 2 disconnect message toeach affected mobile station. It also starts a timer to supervise each LAPDmdisconnection. The LAPD connection cannot be re-established until the BTSreceives an acknowledgment, or the timer expires for each LAPDm connection.

If a mobile station sends an acknowledgment, the BTS releases the RFresources.

If a mobile station does not respond, the BTS continues to send layer 2disconnect messages up to a predefined number. It then waits for the timer toexpire and the BTS releases the RF resources.

Note: If the maximum number of disconnect retries is reached, the BTS LAPDm entitysends an error report to the BSC. This does not stop the timer supervisingthe disconnection.

When all mobile stations are disconnected, the BTS attempts to re-establishthe LAPD connection. The BTS then sends an error report to the BSC witha cause value indicating O&M intervention. This cause value indicates thatthe FU or TRE has cleared all calls.

The BSC reinitializes the link with the frame unit and starts Call Release for theaffected calls with the MSC. This sequence is shown in the following figure.

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5 Call Release

MS BTS BSC MSC

Detection of LAPD failure. BTS stops

sending SACCH frames.

timer

timer

timer

release RF resources



Re−establish LAPD connection

Re−initialize FU or TRE link

disc

disc

disc

UA

UA

UA

error report

cause value

clear request


clear complete

FU : Frame Unit

LAPD : Link Access Protocol on the D Channel


MS : Mobile station


TRE : Transmitter/Receiver Equipment


Figure 62: BTS-initiated Call Release following LAPD failure

O&M Intervention The BTS initiates a Call Release if its O&M entity requests a restart of anFrame Unit (TRE for a BTS A9100 or BTS A910).

The FU or TRE’s response to a restart request is to stop sending frameson the Air interface. The BTS starts a timer to supervise the disconnectionof the mobile stations. The timer allows enough time for the mobile stationsto detect a radio link failure due to the lack of SACCH frames. The BTS RFperforms a local release.

The BTS resets the FU or TRE and waits for the timer to expire. When thetimer expires, the FU or TRE attempts to reestablish the LAPD link with theBSC. The BTS sends an error report to the BSC with a cause value indicatingO&M intervention.

The BSC releases the RF resources and initiates a Call Release with the MSC.

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5 Call Release

5.3.5 Mobile Station-Initiated Call Release

The mobile station can initiate a Call Release by:

Initiating a radio link failure

Disconnecting the LAPDm connection.

Mobile Station-InitiatedRadio Link Failure

If SACCH frames are no longer received from the mobile station, the BTS startsto count the number of missing frames. When the BTS has counted a certainnumber of missing SACCH frames, it considers that the radio link has failed.

This happens when the mobile station ’disappears’ from the Air interface(caused by adverse radio conditions, the mobile station is switched off, fatalerror, etc.).

Note: There is an optional feature where, after a number of missing SACCH frames,the BSC sets both mobile station and BTS power to maximum in an attempt toregain the Air Interface. If the BTS continues to register missing frames, theradio link fails as described below.

The BTS sends a connection_failure_indication message to the BSC with acause value indicating that the radio link has failed. The BSC initiates NormalCall Release procedures to the BTS by sending an RF_channel_releasemessage to the BTS and a clear_request message to the MSC. This isshown in the following figure.

MS BTS BSC MSC

Interruption of SACCH frames

start counterconnection failure indication

cause value

RF channel release

clear request



MS : Mobile station


Figure 63: Call Release due to Mobile Station initiated Radio Link Failure

Mobile Station-InitiatedLAPDm Disconnection

If the mobile station has an error which unexpectedly terminates the call,it sends a disconnect message to the BTS. The system reaction to thedisconnect message in this instance is the same as when the disconnectmessage from the mobile station is prompted by a channel_release messagefrom the BSC (as explained in BSC-Initiated Release (Section 5.3.2)).

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5 Call Release

5.3.6 Remote Transcoder Alarms

If the Transcoder detects a break in communication with the BTS, it sets atimer. This timer is defined by GSM standards. On expiration of this timer, theTranscoder sends an alarm to the BTS. If the BTS remote Transcoder alarmdetection is active, a connection_failure_indication message is sent to theBSC with a cause value indicating a remote Transcoder alarm.

If the BTS detects a break in communication with the Transcoder, it sends aconnection_failure_indication message to the BSC with a cause valueindicating a remote Transcoder alarm. See the figure below.

During an internal handover, this can cause remote Transcoder alarms to arriveat the BSC, as the connection is still active but the call has been handed over.The BSC ignores these alarms for a guard period on new and old channelsduring handover.

connection failure indicationcause value

RF channel release

clear request

clear command

MS BTS BSC MSC

TC detects a communication break and times out

Alarm



MS : Mobile station

TC : Transcoder

Figure 64: Call Release due to Communication Failure detected by Transcoder

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6 Handling User Traffic Across the BSS


This chapter describes the flow of speech and data traffic across the BSS. Itdescribes:

Overview

How speech is encoded and rate adapted throughout the BSS

What types of data can be transferred across the BSS

Where data error correction is performed

How the data rate is adapted.

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6.1 OverviewThe BSS performs traffic handling in the uplink and downlink directionsfor speech and data.

The BSS uses the BSC and BTS to perform the required radio transmission,control and baseband functions of a cell and to control the BTSs in its domain.

The TSS provides the efficient use of the terrestrial links between the BSScomponents.

Together these components perform the required encoding and rate adaptationprocedures.

6.2 SpeechSpeech is passed from the mobile station to the PSTN and from the PSTN tothe mobile station. This section describes how speech is encoded from themobile station to the PSTN, as shown in the following figure. Speech in theopposite direction follows the reverse process and so is not described.

BTS BIE BIE SMBSC MSCSM

A 13 kbit/s 64 kbit/s A/D13 kbit/sCIM

TC

MobileStation

Full Rate Speech TCH

Half Rate Speech TCH

A 6.5 kbit/s 64 kbit/s13 kbit/sCIM A/D6.5 kbit/s

PSTN

A : Analog

A/D : Analog/Digital


CIM : Channel Encoded, Interleaved, and Modulated


SM : Submultiplexer

TC : Transcoder


Figure 65: Encoded Speech Transmission Across the BSS

Analog The microphone converts speech to an analog signal. The analog signal isencoded into a digital signal depending on the type of traffic channel used:

13 kbit/s for a full-rate traffic channel (or enhanced full-rate)

6.5 kbit/s for a half-rate traffic channel.

It is then transmitted on a 16 kbit/s (8 kbit/s for half-rate) radio time slot. 3kbit/s and 1.5 kbit/s are used for signalling on full-rate and half-rate channelsrespectively.

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Interleaving and ForwardError Correction

To pass speech over the Air interface, error checking and redundancy areincluded to make sure speech information is correctly transmitted. This ensuresthat valid continuous speech is passed through the BSS.

Error correction is based on high redundancy with complicated parity and cyclicredundancy methods. This is done to ensure that many types of parasitic andsporadic errors are detected and to some degree, corrected. In the case ofspeech, there is cyclic coding, convolutional and parity error encoding of thedata. The speech data starts as 260 bits (112 bits) and, after forward errorchecking, is encoded as a 456 bit block (228 bit block).

These blocks are then split into eight (four for half-rate), and interleaved withadjacent blocks into TDMA frames to be transmitted as radio wave bursts.This means that if some of the blocks are lost during transmission, there isa high chance that the other blocks hold enough redundancy to still have avalid speech block.

Speech Data Bursts The interleaved blocks are transmitted over the Air interface and are thenreassembled in the BTS. As described above, when the interleaved blocks arereassembled and checked for parity errors, there is a high chance that the datacan be recovered. In speech data the most significant bits are heavily protectedand are always transmitted at the start of a TDMA frame. This ensures thateven if the speech block cannot be reassembled, at least the most significantspeech data can be used to provide a close approximation.

Digital Speech Speech bursts are returned to digital speech blocks in the BTS. They are sentto the Transcoder as 13 kbit/s digital speech, plus 3 kbit/s for in-band signallingif they are full-rate speech. The channels on the Abis and Ater interfaces are64 kbit/s. The speech blocks to be multiplexed on to these links. This isshown in the figure below.

Half-rate speech is sent to the BSC on the Abis interface as 6.5 kbit/s, plus1.5 kbit/s signalling. Two half-rate 8 kbit/s channels are associated togetherinto a 16 kbit/s channel. On the Ater interface a 16 kbit/s submultiplexingscheme is used for all types of traffic. The two mated 8 kbit/s Abis channels areindependently switched by the BSC onto two 16 kbit/s Ater channels.

SMSM

Ater Interface Ater−mux Interface

BSC

30 x 16 kbit/s user traffic channelsper link

90 x 16 kbit/s user traffic channelsper link

30 x 16 kbit/s user traffic channels per link

MSC

A Interface

30 x 64 kbit/s user traffic channels per link

Ater Interface

TC

SM : Submultiplexer

TC : Transcoder

Figure 66: Multiplexed Ater Interface

Digital 64 kbit/s A-lawEncoded Speech

The Transcoder converts the 13 kbit/s digital speech to the 64 kbit/s A-lawencoding. This is a standard digital speech interface for ISDN and PSTNexchanges. The information passes through the MSC and is sent to the PSTN.

The Transcoder performs rate adaptation in both directions.

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6.2.1 Enhanced Full-Rate

Enhanced full-rate provides advanced speech encoding on a full-rate trafficchannel, for improved voice quality and user comfort. The feature uses acodec with ACELP coding.

Enhanced Full-RateProcess

Enhanced full-rate is enabled in the BSC, on a cell-by-cell basis, by the O&Mparameter EFR_ENABLED. When an enhanced full-rate call is set up, thefollowing processes occur:

The mobile station makes a call requiring speech, in which it announces its

codec preferences to the MSC in the setup message.

The MSC passes appropriate assignment_request and handover_requestmessages to the BSC.

The BSC uses the codec list supplied by the MSC to choose the correctcodec, based on the support for the codec in the BTS and A Interface

TRAU equipment.

The BSC activates the selected channel in the BTS, giving the indicationof codec type.

The BTS configures itself to handle the correct channel coding, and starts

sending TRAU frames to the TRAU, in order to configure the TRAU.

The BSC builds either an assignment_command message or a

handover_command message, indicating to the mobile station whichcodec it should use when accessing the new channel.

Once the mobile station is attached, the BSC reports the selected codec

type to the MSC.

In the case of subsequent handover if the BSC has had to change the codecthe BSC informs the MSC of the change.

For further information concerning enhanced full-rate, refer to the A1353–RAConfiguration Handbook.

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6.2.2 Half-Rate

Half-rate speech channels allow the operator to save time slots on the airinterface when the number of available frequencies is very limited. Half-rateuses a different encoding algorithm than full-rate, in order to minimize anyperceived loss of comfort by the subscriber. Use of the half-rate feature doescreate extra overhead on the A interface.

Half-rate is activated on a per-cell basis. In effect, the cell is capable ofoperating in Dual Rate\mode, permitting either half-rate or full-rate trafficchannels to be allocated.

Half-rate can be applied to BSSs with the following equipment:

G2 BSC

G2 Transcoder

One of the following BTSs:

G1 BTS equipped with Dual Rate Frame Unit

EVOLIUM™ BTS.

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6.2.3 Adaptive Multiple Rate

AMR increases the quality of speech during conversations and also increasesthe offered capacity due to the provision of half-rate channels.

When looking at current GSM codecs (full-rate, half-rate, and enhancedfull-rate), each of them answers only one facet of capacity and qualityrequirements:

Enhanced full-rate brings a higher speech quality than full-rate but withno noticeable impact on capacity.

Half-rate provides an answer to capacity requirement, but suffers from poor

speech quality in bad radio conditions, or mobile station to mobile stationcalls when TFO (see Tandem Free Operation (Section 3.9)) cannot be used.

AMR is a new technology defined by ETSI which relies on two extensive sets ofcodec modes. One has been defined for full-rate and one for half-rate. Whenused in combined full-rate and half-rate mode, AMR brings new answers to thetrade-off between capacity and quality:

Speech quality is improved, both in full-rate and half-rate.

Offered capacity is increased due to the provision of half-rate channels.This allows the density of calls in the network to be increased, with only

a low impact on speech quality.

The AMR technology also provides the advantage of a consistent set ofcodecs, instead of the one by one introduction of new codecs. Alcatel offertwo versions of AMR:

Full-rate mode only, for operators who do not face capacity issues and want

to benefit from the optimized quality of speech.

Combined full-rate/half-rate mode, for operators who want to benefit from

the above defined trade-off between quality of speech and capacity.

Through these codec mode adaptations, AMR is able to adapt the sharing ofspeech information and speech protection to current radio conditions, whichcan vary in a large scale, depending on location, speed, and interference.Therefore, for any radio conditions, the Alcatel BSS is able to offer the bestexisting codec, thus the best existing voice quality.

AMR functionality can be activated by configuration of the cells and the BTSradio resources in all the network elements (OMC, BSC, BTS). The relevantalgorithms are activated on a call by call basis. On the radio interface, the AMRcan only be used with AMR mobiles. On the A interface , the AMR can onlybe used if the NSS implements it.

The AMR capability is available on a cell by cell basis.

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Normal Assignment AMR is controlled on a per call basis by the MSC. In the assignment requestmessage, the MSC gives the Channel type IE, which indicates the following:

In octet 4 if full-rate or half-rate is to be used and if the BSS is allowed to

change.

In octet 5 and following octets indicate that AMR is allowed in half-rate or

full-rate.

The BSC activates the channel in the BTS by sending a channel activationmessage, containing the IE Multirate configuration. It indicates the subsetof codecs used for full-rate (or half-rate, respectively) link adaptation, thethreshold and hysteresis sent to the mobile station for full-rate (or half-rate,respectively) link adaptation and, optionally, the start mode (i.e. the initial codecmode). If the initial codec mode is not given, the BTS chooses the default startmode depending on the number of codec modes contained in the subset. Oncethe channel is activated within the BTS, the BSC sends all AMR relevantparameters to the mobile station in the assignment command message.When the speech path is established and synchronization is performed betweenthe Transcoder and the BTS, the BTS checks if the Request or IndicationFlag (RIF) given in the TRAU frame is coherent with the type of CodecMode (Indication or Command) that should be sent on the radio interface. Ifnecessary, a CMI_CMR alignment command is sent to the Transcoder. Oncethe BTS detects that downlink CMI/CMR is synchronized between the TRAUframes and the radio interface, it starts codec mode adaptation.

O&M Management This section summarizes the main O&M configuration parameters that can bechanged by the operator from the OMC-R:

AMR_SUBSET_FRBitmap of 8 bits defining the codec subset for AMR full-rate

(1 to 4 codecs out of 8), on a per BSS basis.

AMR_SUBSET_HRBitmap of 6 bits defining the codec subset for AMR half-rate(1 to 4 codecs out of 6), on a per BSS basis.

EN_AMR_CHANNEL_ADAPTATIONFlag on a per cell basis, used only for AMRcalls, to enable or disable intra-cell handovers for channel adaptation.

EN_AMRFlag on a per cell basis to enable or disable AMR. This single flag is

used for AMR full-rate and AMR half-rate.

OFFSET_CA_NORMALOffset for the channel mode adaptation hysteresisunder normal load. It can take the value from 0.0 to 7.0 (step = 0.1) on a

per cell basis.

OFFSET_CA_HIGHOffset for the channel mode adaptation hysteresis underhigh load. It can take the value from 0.0 to 7.0 (step = 0.1) on a per cell basis.

RXQUAL_CA_NORMALThreshold for channel mode adaptation under normalload. It can take the value 0.0 to 7.0 (step = 0.1) on a per cell basis.

RXQUAL_CA_HIGHThreshold for channel mode adaptation under high load. It

can take the value from 0.0 to 7.0 (step = 0.1) on a per cell basis.

AMR_THR_3, AMR_THR_2, AMR_THR_1Definition of thresholds on a per BSSbasis.

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AMR_HYST_3, AMR_HYST_2, AMR_HYST_1. Definition of thresholds andhysteresis, on a per BSS basis.

6.2.4 Channel Mode Adaption

Channel mode adaptation is the change from one full-rate channel to anhalf-rate channel and vice-versa. This adaptation is independent from thecodec mode currently used. This feature is available when the AMR half-rateoption has been installed. The operator has direct operational control of itthrough the parameter EN_AMR_CHANNEL_ADAPTATIONused for both changesfrom full-rate to half-rate and from half-rate to full-rate.

Full-Rate ChannelAdaptation Due to High

Radio Quality

This channel adaptation involves ongoing AMR full-rate communications withincells where half-rate is enabled. During any AMR call, the downlink radio qualityis reported by the mobile station through the RX_QUAL. In the same time, theuplink radio quality is evaluated by the BTS through the RX_QUAL, and bothare compared to a load dependent threshold. Indeed, in a cell heavily loaded,a half-rate channel will be preferred even with a bad quality. Whenever bothuplink and downlink radio quality are higher than this threshold, then an intracellhandover takes place from full-rate to half-rate channel. To take into accountthe load, two different threshold values are used. The change will also only beperformed if the current channel type is dual rate and it authorizes changes.

Half-Rate ChannelAdaptation Due to Low

Radio Quality

This channel adaptation involves ongoing AMR half-rate communications,using a dual-rate channel type authorizing changes. During any such AMRcall, the downlink and uplink radio quality are evaluated with the samemetrics as stated for the full-rate channel adaption, and the same thresholdcomparison is performed. If either uplink or downlink radio quality are lowerthan this threshold, then an intracell handover takes place from half-rate tofull-rate channel. To take into account the load, two different thresholds arealso used but they differ from the ones used in full-rate adaptation by an offsetvalue which is also cell load dependent. This offset allows a hysteresis to beintroduced between full-rate and half-rate channels.

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6.3 Circuit-Switched DataThere are two types of circuit-switched data modes:

Transparent

Non-transparent.

Transparent The transparent data mode is based on the V.110 protocol.

V.110 is an ITU recommendation. It specifies how ISDN supports DTE. It alsospecifies the transport of synchronous/asynchronous data over a synchronouslink.

Data is packaged and sent to the Transcoder in the same way as speech. It isconverted to the 64 kbit/s ISDN format for data transmission. Error handling isdealt with by the Air interface.

Non-Transparent The non-transparent data mode is similar, although data is transmitted aspackets from the modem on the mobile station to the modem in PSTN. Errorhandling is handled end-to-end.

Refer to Transparent Mode (Section 6.3.1) for more information about thetransparent mode and to Non-Transparent Mode (Section 6.3.2) for moreinformation about the non-transparent mode.

The following figure illustrates data transmission across the BSS.

BTS BIE BIE SMBSC MSCSM

A 13 kbit/s 64 kbit/s A/D13 kbit/sCIM

TC

V.110 data blocks ISDN/Analog

MobileStation

PSTN

A : Analog

A/D : Analog/Digital


CIM : Channel Encoded, Interleaved, and Modulated


SM : Submultiplexer

TC : Transcoder

Figure 67: Data Transmission Across the BSS

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6.3.1 Transparent Mode

Transparent mode implies that the following functions are performed by theBSS:

Interleaving and Channel Coding

Rate adaptation.

Interleaving and ChannelCoding

Interleaving for data is more complicated than for speech. The data block is splitinto 22 parts for interleaving 9.6 kbit/s and 4.8 kbit/s data rates. For 2.4 kbit/s,the interleaving is the same as speech. The lower the data rate, the more spacecan be used for redundancy and error detection. This lowers the error rate.

The Air interface performs the error handling. The V.110 data packets aregrouped together and transmitted across the Air interface exactly like speech.The table below shows the data rate and error rate. A low data rate providesmore space for a better forward error correction scheme, in turn reducingthe number of errors.

Rate adaptation Data is packaged differently in V.110 for different data rates. The bandwidth isreduced and therefore the rate is lower. See the table below for the rateconversions. The Transcoder plays the final role in the rate adaptation whenthe data stream is adapted to 64 kbit/s packets.

There is a difference between data and speech rate adaptation. Speech isencoded to A-law, while data is transposed to the first bit, and if required thesecond bit of a Pulse Code Modulation byte. PCM transmission is at 8 000bytes (64 kbit/s). The 8 kbit/s and 16 kbit/s intermediate rates (before theTranscoder) are transposed as 1 or 2 bits per byte respectively.

User Rate Intermediate Rate Radio InterfaceError Rate (atFull-Rate)

9600 16 kbit/s 12 kbit/s 0.3%

4800 8 kbit/s 6 kbit/s 0.01%

<=2400 8 kbit/s 3.6 kbit/s 0.001%

Table 20: Circuit-Switched Data Rate Conversions Across the Air Interface

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6.3.2 Non-Transparent Mode

The non-transparent data mode is a data transmission protocol. It is based onsending RLP packets as four V.110 frames. This is the same process usedin transparent mode. Interleaving and channel coding are still used, as theyare in the transparent mode. The RLP adds extra protection and also allowsthe re-transmission. Packing RLPs in four V.110 frames ensures transparencyover the network. RLP packet size is the same as a radio block size, so itis transmitted as one radio block.

The non-transparent data mode uses a 12 kbit/s radio interface rate.Interleaving and channel coding are at 9.6 kbit/s (the same as in Transparentmode). The only difference between transparent and non-transparent modesfor the BSS is the processing of the four V.110 frames of an RLP packet.

Error Handling The non-transparent data mode has a better error rate as there is no forwarderror checking or interleaving. Therefore, the size of packets remains small andless prone to errors. There are however, some cyclic redundancy bytes andthe protocol is very similar in principle to (LAPD).

Rate Adaptation There is no rate adaptation in non-transparent mode. The rate can only beadapted by physically transmitting less than the full bandwidth available. Thedata rate is also limited by the number of errors, as packets have to beretransmitted. The difference between transparent and non-transparent modedata links is transparent to the Transcoder, but not to the BTS. The Transcoder,as described in transparent mode, puts the data in the first bits of a PCM byte.

The BTS must ensure that an RLP packet maps into four V.110 framesnumbered 0, 1, 2, 3. These must be sent in one block on the Air interface.

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6.4 Short Message Service - Cell BroadcastThere are two types of SMS:

Point-to-point SMS allows a short message to be sent to, or received

from, a mobile station

SMS-CB allows messages to be broadcast to the mobile stations (i.e.,one way).

SMS-CB can be used for a number of reasons, e.g. to transmit emergencyinformation, road traffic information, etc. An SMS-CB message can betransmitted to all the cells connected to the BSC, or to selected cells only, asrequired.

The following figure shows the SMS-CB components.

OMC−R

BSCBTS

Broadcast Message set up by OMC−R Operator

Broadcast Message to

Selected Cell(s)

Messagebroadcast to allMobile Stations

HMI

Transmission Request

SMS−CB commands

and signaling

CBC

SMS−CB commands

and signaling

Broadcast Message set up by CBC Operator

CBC : Cell Broadcast Center

HMI : Human Machine Interface

SMS-CB : Short Message Service - Cell Broadcast

Figure 68: Short Message Service - Cell Broadcast

The SMS-CB is managed and operated from a separate CBC. The CBC isconnected to the BSC and the data needed to connect the BSC to the CBC issent from the OMC-R.

The operator at the CBC inputs the cell broadcast message identifying thebroadcast text and the selected cell identities. Only one broadcast messageper cell, or cells, is allowed. Any subsequent message simply replaces themessage being broadcast.

The message is sent from CBC to the BSCs handling the selected cells. TheBSCs then send the message to the individual BTSs of the selected cells.

On receipt of the transmission request message from the BSC, the BTSbroadcasts the message to the mobile stations in the cell over the CellBroadcast Channel of the Air Interface.

For SMS-CB, the BSC supports only the connection to an external CBCplatform. The SMS-CB implements all of the improvements of the phase 2+recommendations.

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Phase 2+ Enhancements An external CBC can be connected directly to the BSC. This allows the BSC tosend information to the CBC, e.g., billing information. Two types of connectioncan be used to connect the CBC to the BSC:

CBC to BSC via PSDNThis is the default connection. A BSC can be connected to one CBC.

CBC to BSC via MSCThe CBC and OMC-R must be connected to the same MSC

In addition to the feature SMS-CB managed from CBC, the followingenhancements are defined in the phase 2+ GSM recommendation:

Greater throughput with a second CBCH channel (extended CBCH)

Better responsiveness when urgent data is to be broadcast due to the use

of high priority messages. Messages can be allocated a priority of high,normal, or background.

Better service availability through the restart with recovery indication feature.

The feature brings also better convenience with the support of multipagemessages.

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6.5 Support of Localized Service AreaThe aim of SoLSA is to link radio resources (cells) with services such asspecific billing or differentiated access rights. These services are associatedto LSAs (Localized Service Area). An LSA can be defined over several cells,and a cell can belong to several LSAs. One possible usage of this featureis to enable the efficient deployment of dedicated corporate applications.The following description uses this example. In order to manage efficientlycorporate LSAs, the Alcatel BSS SoLSA implementation:

Favors the camping of SoLSA mobiles on cells belonging to an LSA where

they have a subscription. These mobile stations will likely camp on thecorporate cells, even if they are not the best ones

Informs the end user that he is camping on a cell belonging to a subscribed

LSA and thus that he can benefit from the LSA services. This is achievedthrough the Localized Service Area Indication SoLSA service.

The localized service area concept gives the operator the basis to offersubscribers or groups of subscribers different service features, different tariffsand different access rights depending on the location of the subscriber.It is up to the operator to decide which services features are required fora specific service.

The LSA (Localized Service Area) can be considered as a logical subnetworkof the operator‘s PLMN. This subnetwork can be configured by the operator.A subscriber can have LSA‘s at several PLMN‘s. The following list showsexamples of different types of localized service area:

Office indoors. The office cells are those that are provided by indoor base

stations.

Home or office and its neighborhood. The localized service area can bebroadened outdoors. The neighborhood cells outdoors can be included

into the local service area.

Industry area. A company having several office buildings may want to have alocalized service area that covers all its buildings and outdoor environments.

A part of a city or several locations.

6.6 PLMNs InterworkingA foreign PLMN is a PLMN different from the own PLMN to which the cellsinternal to the OMC-R belongs. Only cells external to the OMC-R can belong toa foreign PLMN. All internal cells shall belong to the own PLMN.

Both OMC-R own cells and cells external to the OMC-R can belong to anown PLMN.

The Alcatel BSS supports:

Incoming inter-PLMN 2G to 2G handovers

Outgoing inter-PLMN 2G to 2G handovers, optional featureThe operators are allowed to define handover adjacency links towardsexternal cells belonging to a foreign PLMN, i.e. handovers from a servingcell belonging to the own PLMN towards a target cell belonging to aforeign PLMN.

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Inter-PLMN 2G to 2G cell reselectionsThe Alcatel BSS allows the operator to define cell reselection adjacencybetween two cells belonging to different own PLMN (which must thusbe owned by two different BSCs).

Multi PLMN optional featureThe “Multi-PLMN” feature allows operators to define several “own PLMN”in order to support network sharing (Tool Chain, OMC-R, MFS, Abistransmissions - and also BTS, via “rack sharing”). Inter-PLMN handoversand cell reselections between two different own PLMN are supported. TheBSC itself cannot be shared and thus remains mono-PLMN (i.e. all BSCown cells belong to the same own PLMN).The Alcatel BSS supports several own PLMN (up to four, at least one). AnOMC-R thus manage at least one (own) PLMN and up to eight PLMN (fourown + four foreign). Both cell reselections and handovers are allowedbetween two cells belonging to different own PLMN.The operator is allowed to define handover adjacency between two cellsbelonging to different own PLMN (which must thus be owned by twodifferent BSCs).

The OMC-R (and the Tool Chain) is by definition of the feature itself alwaysshared between the different own PLMN. On the other hand:

The MFS can be shared.

The BSC cannot be shared.

The BTS can be shared up to the “rack sharing” level (no radio partsharing).

The Abis transmission part can be shared.

The transcoder part can be shared.

The outgoing inter PLMN handovers feature is a prerequisite for multiPLMN feature.

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7 Cell Environments

7 Cell Environments

This chapter describes the cell environments available in the Alcatel 900/1800BSS. The following cell environments are described:

Overview

Single Cell

Concentric Cell

Sectored Site

Extended Cell

Umbrella Cell

Mini Cell

Microcell.

Indoor cell

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7 Cell Environments

7.1 OverviewThe Alcatel BSS provides coverage suited to the needs of urban, rural andcoastal areas by offering a variety of possible cell environments. The BSSsupports a set of cell configurations to optimize the reuse of frequencies. Theoperator may choose to deploy a network using both GSM 900 and DCS 1800bands. The parameters to define cells are grouped into five types:

Cell dimension. This consists of macro up to 35 Km (can be up to 70 kmwith extended cell), and micro up to 300 meters.

Cell Coverage. There are four types of coverage, single, lower, upper,

and indoor.

Cell Partition. Two types of frequency partition exist, normal or concentric.

Cell Range. The cell range can be normal or extended.

Cell Band Type. A cell belongs to either the GSM 900 or DCS 1800 bands,

or both in case of a multi-band cell.

Rural and CoastalCoverage

In the rural and coastal environment coverage is principally a function of cellplanning. Standard cell layouts provide coverage of up to 35 km. Extendedcells, which have two co-located antennae, provide options covering trafficdensity and ranges up to 70 km.

Urban Coverage In the urban environment the coverage is determined by the location of the BTSantennae. Two types of cells are normally used:

Macrocells - where the antenna is located above the roof tops and

propagation occurs in all directions. These cells can be sectored by usingspecific antenna patterns.

Microcells - where the antenna is located below roof top level, on building

facades or street lights. Propagation occurs mainly as line of sight along thestreet, with strong attenuation at street corners.

Indoor cells.

These three cell types can be used in a hierarchical cell environment wherecontinuous coverage is provided by the macrocell (umbrella cell) and locationsof increased traffic density are covered by dedicated microcells and indoorcells. See Umbrella Cell (Section 7.5) for more information.

The figure below shows various configurations of the normal GSM 900 or GSM1800 cell type. Each of the following sections explain the functional differencesbetween the cell described and the single cell configuration.

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Single Cell ConcentricCell

Umbrella Cell

Umbrella & Concentric

Cell

Microcell

Inner Zone

Outer Zone

Microcell

Microcell

MicrocellMicrocell

Microcell

Extended Cell

Inner Cell

Outer Cell

Inner Cell Outer Limit

Outer Cell Inner Limit

Overlap Zone

Sectored Site

Figure 69: Example: Cell Configurations

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7 Cell Environments

7.2 Concentric CellThe goal of concentric cells is to increase the frequency economy of thenetwork. This is done by reducing the interference levels of some BTS carriers.These carrier frequencies can be re-used for smaller distances.

The inner zone serves a high concentration of mobile station calls in a smallarea, with a reduced maximum power output limit. The outer zone performs callhandling for a greater radius with a normal maximum power output limit.

The BCCH, CCCH and SDCCH in concentric cells are put on the outerzone frequencies. Traffic channel assignment during call connection can beallocated to either the outer or inner zones. It depends on the location of themobile station at that time.

The inner and outer zones are part of the same cell, and a frequency carrier isassigned either to the inner or outer zone. This is signalled by the zone_type

flag of 1 or 0, (1=inner, 0=outer).

The outer zone maximum power limit is the same as normal zones. Theinner zone is controlled by two maximum power limit values: one maximumpower limit value for the mobile station and one maximum power limit value forthe BTS.

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7.3 Sectored SiteA sectored site consists of one or more BTS. Each BTS hosts up to sixantennae illuminating up to six sectors, each sector covering a separate singlemacrocell. The figure below shows a three-sector arrangement.

The BTS in a sectored site contains up to three transceivers which are eachallocated to different given sectors. Each sector and its associated cell aremanaged independently and are seen functionally, by the OMC and BSC, asseparate BTSs connected in chain mode.

Within the physical BTS site, there is a master BTS and up to two slave BTSs(for G2 BTS and G3 BTS, each BTS can have three slaves using the SharedCell feature, see Cell Shared by Two BTS (Section 7.6) for more information).Each BTS generates its own clock locally, but the slave BTSs are synchronizedto the master BTS.

Cell 1

Cell 2

Cell 3

BTS

Antenna

Sector 1

Sector 3

Sector 2

Figure 70: Sectored site configuration

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7 Cell Environments

7.4 Extended CellAn extended cell is made up of two cells, an inner and an outer, as shown in thefigure below. The inner cell handles calls up to a distance of 35 km (the same asa normal cell), while the outer cell handles traffic from 33 km up to a maximumrange of 70 km. Extended cells are supported only by EVOLIUM™ BTSs.

Inner Cell

Outer Cell

Highway

Urban Area

35 km max

70 km max

Figure 71: Example of Extended Cell Topology

The inner and outer cells are covered by two synchronized, co-located G2BTSs. The reception (uplink) of the outer cell is delayed to correspond to a 33km shift in range. Radio continuity between the two cells is ensured by theoverlap zone.

The inner cell uses two carrier units:

Carrier Unit BCCH Inner: at the inner cell BCCH frequency

Carrier Unit RACH Catcher: at the outer cell BCCH frequency, but with

transmission switched off.

Because the outer cell can have areas of strong signal within the inner cell’scoverage area, it is necessary to prevent a mobile station in such a regionfrom camping on the outer cell frequency. This could lead to sudden signaldegradation as conditions change, and eventual loss of the call.

The RACH Catcher receives channel_request messages from mobile stationswhich are synchronized on the outer cell BCCH frequency, but are within 33km of the BTS. The BTS knows, from the timing advance sent by the mobilestation, that it is actually in the inner cell, and assigns the mobile stationto an inner cell SDCCH frequency.

The outer cell uses one Carrier Unit with reception delayed by 60 bits. Thiseffectively shifts the logical position of a mobile station 33 km nearer thanits actual position and allows it to be handled in the standard GSM 0-63 bittiming advance range.

The handover procedure is controlled normally, with the settings ensuring thatthe necessary distance has been reached before handing a call over to theouter or inner cell.

Different types of coverage are possible depending on the type of antennaused for the inner and outer cells. The example in the figure above shows anextended cell with an omnidirectional inner cell and directional outer cell.

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Enlarged Extended Cell The enlarged extended cell is an extended cell designed to provide enlargedcapacity for areas where sustained traffic is high. It is especially well-suited forrural areas and dense highways where more than one TRX is necessary tohandle traffic.

The enlarged extended cell relies on the general principles of the extendedcell: it is made up of two sub-cells to handle calls up to a distance of 70 km.However, with enlarged extended cell the two sub-cells are covered by oneBTS, assuring a higher synchronization rate.

The following telecom features are supported:

The TDMA frame time slots can be used independently, providing anyTRX with full capacity

Inner cell mobile station access requests use the outer cell BCCH frequency

Handover between the two sub-cells

BCCH TRX recovery.

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7.5 Umbrella CellIn much denser traffic areas, depending on the required traffic capacity, ahierarchical network is used, where continuous coverage is provided by anumbrella cell (macrocell), and traffic hot-spots are covered with dedicated lowerlayer cells of limited range. Fast moving mobiles are kept in the upper layer cellto avoid a high rate of handovers.

For medium density areas small macrocells (called mini cells) are overlaid withone umbrella macrocell. See Mini Cell (Section 7.5.1) for more information.

For higher traffic densities microcells are installed in all the streets where verydense traffic occurs. Umbrella macrocells provide continuous coverage for leveland quality handovers, and saturated overlaid cells.

Refer to Microcell (Section 7.5.2) for more information about the relationshipbetween umbrella cells and microcells.

7.5.1 Mini Cell

Mini cells are used for dense urban areas where traffic hot-spots are coveredby very small macrocells (500 m to 1 km radius) and continuous coverage isprovided by an overlaid macrocell (5 to 10 km radius). The lower layer minicells handle pedestrian traffic while the umbrella cell handles the faster movingmobiles. As only macrocells are used there is no street corner effect.

The following figure shows the application of the two-layer hierarchical network,with macrocells for both layers, in a small town.

Umbrella Cell

Mini Cells

Urban area

Pedestrian area

Figure 72: Umbrella Cell with Mini Cells

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7.5.2 Microcell

Microcells have a small coverage area (less than 300 m radius). These cellsare usually situated indoors or along streets in built-up areas. Microcellshave an umbrella cell (1 to 2 km radius) to minimize the risk of losing callsby providing maximum coverage.

The microcell’s small radius is created by limiting the maximum power outputstrategically to cover a pre-defined microcell area.

Handover occurs more frequently in a microcell environment due to the smallradius sizes. Microcell handovers occur:

To handle stationary mobile stations (especially mobile stations used

indoors)

When a mobile station moves in a street covered by microcells

To avoid losing calls. Whenever there is a risk of losing a call, a handover

is triggered to the umbrella cell.

Fast moving mobiles are handled by the umbrella cell. A mobile handled by amicrocell is sent to the umbrella cell if the delay between handovers becomestoo small. Conversely a mobile is sent to a microcell if it receives a highlevel of signal for a sufficient time.

Call quality/control is achieved by providing four thresholds for microcellhandover and one handover threshold for macrocell handover.

7.5.2.1 Micro to Micro HandoverMicrocell to microcell handover occurs due to the proximity of the two cells.When the power budget is better in another cell, the mobile station is handedover to the cell which will serve the call more efficiently. This normally occurs inmicrocells serving in the same street.

7.5.2.2 Micro to Macro Handover

High ThresholdHandover

This type of handover occurs when the signal strength has dropped below thetheoretical signal level at the radius of the cell. This would normally mean thatthe mobile station has turned a street corner.

Low ThresholdHandover

This type of handover occurs when the mobile station level is under the highthreshold and the signal level has dropped below the low threshold. Thehandover is to the umbrella/macrocell, which supports the call until the mobilestation moves into another cell. When the macro to micro threshold is exceededin the umbrella/macrocell, the mobile station is passed to a new microcell.

Rescue Handover The mobile station is forced to handover to the umbrella cell when nomeasurement reports are transmitted. This occurs after a number ofconsecutive SACCH reporting periods.

7.5.2.3 Macro to Micro Handover

M_to_m ThresholdHandover

This occurs when the mobile station signal level in a microcell is above theM_to_m threshold for a certain period. This threshold value must alwaysbe higher than the low threshold value of the cell. Otherwise, a handoverping-pong effect can occur between the umbrella and the microcell.

Note: If the low threshold is not used, the M_to_m Threshold value must be above thehigh threshold value.

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7 Cell Environments

7.5.2.4 Threshold Handover ExampleThe example in the figure below shows two typical cases of handover inmicrocells:

Micro-micro handover along a street (Case 1 in the figure below)

Signal levels rising and dropping, causing macro/micro handover (Case2 in the figure below). This example shows the use of the two levels

of Macro-micro handover (strong to weak signal, and weak to weakersignal). This is represented by the high and low threshold handovers. This

example also shows the macrocell handing back to a microcell once astronger signal level is received.

Low Signal Level

High Signal Level

dBm

Low Threshold

M_to_m Threshold

High Threshold

4

5

1

2

3 6

Micro−MicroHandover

Figure 73: Example: Handovers due to Threshold Triggering

Micro-Micro Handover(Case 1)

A mobile station is moving along a street.

As it moves along a street, the mobile station is handed over from microcell tomicrocell (1).

Macro-Micro Handover(Case 2)

A mobile station turns a corner then moves indoors.

1. Call starts at (2). The signal level is normal.

2. The mobile station signal level drops below the high threshold level (3), e.g.when turning a corner. To protect the call, it is handed over to the macrocelluntil a better microcell is found. The call remains with the macrocell until astrong signal from another microcell is received (normal case).

3. If a strong signal from a microcell cannot be found, a weaker signal from amicrocell with enough strength to be above M_to_m threshold level, butremain below the high threshold is found (4).

In this case, as long as the signal strength remains above the low thresholdand there is not a better microcell, the call remains with that microcell(e.g. the mobile station is indoors).

4. The signal level drops below the low threshold (5). The mobile station isagain passed to the macrocell (e.g. the mobile station moves further insidea building). The macrocell is used to ensure call quality.

5. The mobile station moves into a position whereby the mobile station reportsa microcell signal level above M_to_m threshold (6). The call is handedover to that microcell, e.g. the mobile station is still indoors, but has astronger signal from a microcell.

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7.5.2.5 Indoor CellThe aim of indoor layer support is twofold:

Firstly, to enable a better radio coverage inside large buildings (hotels,

shopping malls, corporate centers) by the public network.

Secondly, to unloaded the cells provided for outdoor coverage but which areaccessible from these buildings.

Indoor cells can be deployed in all types of network, even in already very densenetworks which already have two layers (upper and lower). The feature easesthe optimization of multilayer networks which include cells dedicated to indoorcoverage. Indoor coverage is performed mostly from outdoor BTS. Althoughalready satisfactory in many cases, the indoor quality of service can beimproved by using dedicated in-building equipment. Together with this improvedquality, an increase in the indoor capacity can be achieved, particularly in highdensity public areas such as airports, train stations, shopping malls, businessparks, etc. A three layer per band management is introduced and a new typeof cell is defined (the indoor cell) that maximizes traffic in these indoor cellswhile preserving quality. In idle mode, classical criteria (C2) allows mobiles tobe forced to camp on indoor cells.

For example, when entering a building covered by an indoor cell, calls areautomatically transferred from outdoor cells, whatever their type. When movinginside the building, calls are transferred from one indoor cell to another one,even if the received power from outdoor cells is higher. It is only when themobile leaves the indoor coverage that it is transferred to an outdoor cell.

It is important for the Operator to minimize interference from indoor tooutdoor. Therefore, indoor cells will often be used with very low radiatedpower (picocells). In this context, the feature provides also enhanced PowerControl algorithms.

The cells added to the network for indoor coverage are referred as indoor cellsand form a new layer referred as the indoor layer. The following figure gives anexample of network structure with three layers and two bands.

Umbrella cell 900

Umbrella cell 1800 Upper layer

Lower layer

Indoor layerIndoor cell 1800

Micro−cell 900

Micro−cell 1800

Micro−cell 900Micro−cell 1800

Micro−cell 900

Micro−cell 1800

Indoor cell 900

Figure 74: Indoor cell example network hierarchy with three layers and two bands

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7 Cell Environments

The already deployed network hierarchy has to be adapted as follows:

If there were already two layers, cells belonging to the upper layer will

remain unchanged. Outdoor cells belonging to the lower layer will alsoremain in the lower layer. New cells introduced for the indoor layer will

belong to the indoor layer.

If there was only one layer, cells having the cell_layer_type single willbecome upper. New cells introduced for the indoor layer will belong to the

indoor layer. There is no lower layer.

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7.6 Cell Shared by Two BTSThe system is able to handle cells whose TRXs are located in two differentBTS. This feature brings important flexibility by allowing:

An existing site to be extended by only adding TRXs in a new BTS, not

changing the arrangement of the existing BTS.

Existing cells to be combined into one, e.g. combine one 900 cell and one

1800 cell in order to get a multi-band cell.

The support of 3x8 TRXs configurations in 2 racks (instead of 3).

The support of 16 TRX per cell.

Note: This feature is applies only to BTS A9100.

Each set of TRX in a certain BTS must have its own coupling. It is possible tocombine the coupling output towards the same antenna through an additionalduplexer, although this is a special installation. The fact that part of the sector isin another BTS does not increase the number of necessary antennae. For BTSA9100, each BTS can have one slave, but each slave can in turn have anotherslave, up to a maximum of 3 linked slaves for one master BTS. If linked BTSssupport part of the same cell, the linked BTSs must be clock synchronized witheach other (master/slave).

With this feature, the operator can associate two physical sectors from differentBTSs into one shared sector. This shared sector can be mono or dual-bandand it can support one cell as a normal sector. It takes the identity of one ofthe physical sectors, called the main sector. The other physical sector isthe secondary sector.

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8 Operations & Maintenance


This chapter provides an overview and describes O&M functions in the contextof an operational network. It describes:

Overview

O&M Architecture and Functions

O&M Control - The OMC-R


Fault Management - Alarms

Performance Management

Audits

Remote nventory.

This chapter does not describe the principles of O&M. For more informationabout O&M, refer to the Operations & Maintenance Principles document.

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8.1 OverviewTo ensure that the BSS operates correctly, O&M actions are implemented atall levels within the BSS. The O&M functions in the BSS are grouped intothree categories:


Fault Management

Performance Management.

These categories are described later.

8.2 O&M Architecture and FunctionsThe BSS subsystems perform O&M functions, as follows:

Configuration ManagementThe main benefit of configuration management is the reduced time neededto perform operations and reduce telecom outages. This is achieved byhaving fewer operator commands and providing smooth migration andequipment configuration. The main functions of configuration managementinclude radio configuration management and equipment management.

Fault Management

The BTS monitors the condition of the hardware modules it manages,

and reports any change in status to the BSC.

The BSC supervises its own hardware modules and reports changes

in status to the OMC-R.

The BSC and Transcoder provide together a set of transmission O&Mfunctions to ensure a high level of fault tolerance and reliability. The

function also provides efficient use of the terrestrial links between theequipment of the BSS.

The MFS, like the BSC, supervises its own hardware modules andreports changes in status to the OMC-R.Hardware and software management of the MFS is provided usingthe IMT.

The OMC-R is the primary control station for the BSS/MFS and isthe heart of the O&M function.

Performance ManagementPerformance Management consists of three main system activities:

The collection of raw measurement data from network elements by

the BSC and the MFS

The transfer of the raw measurements to the OMC-R

The processing of the raw measurements and presentation of the

results on the OMC-R.

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8.2.1 O&M ArchitectureControl of O&M

FunctionsLocal Maintenance Terminals are used when performing maintenance tasks atthe BSC, BTS, and Transcoder. LMTs are connected directly to the equipment.The operations available at the LMTs act only on the local hardware, noton logical resources.

The IMT performs maintenance tasks at the MFS, using a Netscape browser.All these tasks (except for three tasks associated with alarms, enable/disablesound, view history file, and enable/disable external alarm management) canalso be accessed from the OMC-R terminal. The IMT alarm tasks are notprovided when the IMT is accessed from the OMC-R because the OMC-Ralready has its own alarm management tasks.

The IMT software can be accessed from either the IMT or the OMC-R. It hasthree different user profiles: administrator, operational, basic.

If the IMT software is accessed from the IMT, only one session at a time can berun. Two instances of the IMT can be in use at the same time. For example,if there is one IMT connected to the MFS, then only one IMT window canbe opened at the OMC-R.

For more information about LMTs, refer to one of the following:

BSC Terminal User Guide

Transmission Terminal User Guide

BTS Terminal User Guide

EVOLIUM A925 Compact TC Terminal User Guide

EVOLIUM A935 MFS IMT User Guide

OML Auto-detection An OML auto-detection feature has been introduced in order to take fulladvantage of the transmission configuration via OML feature (it is morereliable and more robust than configuration via the Qmux channel). The OMLauto-detection feature provides the following benefits:

Transmission configuration via OML on all EVOLIUM™ BTS

No LMT configuration necessary during Move BTS

Secure recovery after OML breakdown

A simplification of the BTS installations (in the idea of Plug&Play BTS).

See OML Auto-detection (Section 8.4.5) for more information.

Managed Objects Managed Objects are used to represent elements of the TelecommunicationTMN environment on the Q3 interface in terms of system resources. Thisconcept is also used to represent the activities of management function blocksperformed on these resources.

In Alcatel’s network management model, Managed Objects can be physicalentities, such as a BSS, BTS, BSC, or a hardware module within one of theseentities. They can also be a logical entity, such as programs or programroutines which implement communication protocols.

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Security Blocks Alcatel has an internal object model structure, based on objects calledSecurity Blocks. Security Blocks are only used for the BSC, the BTS, andthe Transcoder. Security Blocks are only visible to an operator performinglocal maintenance using certain LMTs, i.e. BSC terminal, BTS terminal, ortransmission terminal. The SBL model is not used by the OMC-R or the IMT.The OMC-R can display SBLs in certain circumstances, e.g. in BSSUSM.

8.2.2 O&M Functions

Each BSS subsystem has its own O&M function.

ConfigurationManagement

Configuration Management is the process of viewing and controlling networkresources. Configuration Management allows the operator to:

Configure the BSS/MFS hardware and software when it is first installed

Change the network by adding, deleting, or moving network entities

Upgrade to new hardware or software

Change equipment and telecom parameters to improve system performance.

Fault Management Fault Management allows the operator to supervise and to repair the networkwhen anomalies occur. It does this through a sequence of steps fromdetection to reporting and recovery. These are carried out by all the BSS/MFSsubsystems, and are reported to the operator at the OMC-R.

PerformanceManagement

Performance Management allows the operator to monitor the efficiency of thesystem and the telecom services. It is controlled entirely from the OMC-Rand provides measurements and statistics about various traffic events andresource usage in the BSS.

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8.3 O&M Control - The OMC-RThe OMC-R is the primary control station for the BSS/MFS and is the heartof the O&M function. Its principal operations are:

Network configuration. Provides the operator with an interface to the

system to:

Perform software configuration management (files, version downloading)

Perform hardware configuration management (e.g. update the

configuration according to extension-reduction operations, configurecertain BSS parameters such as Abis link characteristics and some

BTS characteristics)

Provide configuration functions for logical parameters.

Network supervision. Provides the operator with an interface to the systemto:

Display alarm status and history

Display equipment and resource states

Monitor and display Performance Measurements

Provide Usage State on Demand observations

Definition and supervision of counter thresholds (Quality of Servicealarms).

Network maintainance. Provides the operator with an interface to the

system to:

Access to equipment management functions (test)

Access to resource equipment state management.

Locking and unlocking equipment and resources

Keeping track of hardware and software configurations in the system andmanaging software versions

Providing mediation between the Alcatel BSS and one or more NMCs.

This uses the Q3 interface.

Provide an interface to the electronic documentation collection.

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8.3.1 Multiple Human-Machine Interface

This feature permits one OMC-R operator to perform actions normally done byseveral OMC-Rs, typically during off-duty hours. The connection between themultiple access workstation and the other OMC-R hosts is made via an X.25network. The following figure illustrates the principle of operation.

Central Site

Additional Workstation

Printer

HMI Server

Multiple Access Workstation

OMC−R Host 1

OMC−R Host 2

OMC−R Host n

X.25 Network

HMI : Human Machine Interface

Figure 75: Multiple HMI Access to OMC-Rs

The implementation of this feature takes advantage of the distributedconfiguration of the OMC-R which usually consists of a host machine anddistinct local or remote HMI servers.

Central SiteConfiguration

The site used for multiple access contains the following:

Printing facilities

Additional workstations which connect to the multiple access workstation,

but only connect to the same OMC-R

Configuration of each OMC-R is specific to the multiple access workstation

and its peripherals.

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8.3.2 ACO

Alarm Call Out (ACO) is a process within the HMI server to perform alarmmanagement tasks for a complete network. Alarms from the BSSs controlledby other OMC-Rs are directed to one OMC-R. These links are used to transferalarm notifications from the controlled OMC-Rs to the ACO OMC-R as shown inthe figure below. The ACO OMC-R collects alarms from these OMCs, appliesfilters defined by the on duty operator, sends the filtered results to a dedicatedprinter and sends e-mail to support technicians.

ACO can be started and stopped from any OMC-R.

OMC−R 1

OMC−R 3

OMC−R 2

Area 1

Area 3

Area 2

ACO OMC−R

Workstation

ACO : Alarm Call Out

Figure 76: ACO Links

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8.3.3 Secured X.25 Connection From BSC to OMC-R

The Secured X.25 Connection feature provides redundant links in the event of alink failure on either the OMC-R or BSC side. When a link failure occurs, theinitiator system involved must process the change over.

The configuration for the X.25 links consists of two physical links, one forCMISE, and one for FTAM. The following figure illustrates the configurationwithout redundancy.

OMC−RX.25 Network

CMISE BSC A

FTAM BSC A

CMISE

FTAM

BSC A

OSI CPRA 1

OSI CPRA 2

HSI BOARD

012

3

CMISE : Common Management Information Service Element

CPRA : Common Processor Type A

FTAM : File Transfer Access and Management

HSI : High Speed Interface

OSI : Open System Interconnection

Figure 77: X.25 Without Redundancy

Definition of the primary and the secondary links based on their hardwareconfiguration can achieve various types of redundancy, such as:

OMC-R side redundancy

BSC side redundancy

Complete redundancy.

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The following figure illustrates these redundancy types.

OMC−RX.25

NetworkBSC

OSI CPRA 1

OSI CPRA 2

HSI Board

0

1

2

3

Primary Link

1

2

3

Secondary Link Configurations

1. OMC−R side redundancy2. BSC side redundancy3. Complete redundancy

Secondary Link

CPRA : Common Processor Type A

HSI : High Speed Interface

OSI : Open System Interconnection

Figure 78: X.25 With Redundancy

X.25 Link TransferScenario

When the OMC-R or the BSC sets up a CMISE or FTAM association, thesubsystem chooses the active link. The active link is the primary link if it is intraffic, otherwise it is the secondary link. The following events occur:

The transfer is performed on the primary link if the association is successful.

The association is attempted three times.

The primary link is set out of service if the association is unsuccessfulafter the third try.

If the secondary link is in traffic, it becomes the active link and the

association is tried on this link.

If the secondary link is out of service, the application is impossible.

Links are periodically tested for availability. When the primary link is recoveredit becomes active and in traffic. Loss of one link (i.e. primary or secondary)triggers an alarm and the recovery triggers the end of alarm.

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8.3.4 Electronic Documentation

Installation and use of the electronic documentation collection depends of theconfiguration.

Small Configurations The documentation collection is installed on each OMC-R as a collectionwithout a Verity search engine. To search the documentation collection, installthe documentation collection CD-ROM on a single PC, and use the searchfunction provided on the CD-ROM.

Standard, Large, andXLarge Configurations

The license for the documentation collection and Verity search engine isinstalled on one OMC-R. All other OMC-R on the same site are connectedto this OMC-R. The maximum number of users that can be managed foreach search engine license is 75. This corresponds to a site with five Largeconfiguration OMC-R.

Refer to A1353-RA Capacity per BSS Category for more information on thevarious OMC-R configurations.

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8.4 Configuration ManagementConfiguration Management, simply, is the process of putting in place theessential hardware and software components of the network, and determiningtheir operating capabilities. The table below shows the configurationmanagement functions of each network element.

Network Element Configuration Management Functions

BSC Software and database replacement

Reading and modifying logical parameters.

BTS Supervision of the BTS equipment. This includesinitializing and configuring the BTS.

Transfer of software and data files to the FUs(G1/G2 BTS) or TREs (BTS A9100/A910)

Software and database replacement

Auto Identification (BTS A9100/A910 only).

See Auto Identification (Section 8.4.4) for moreinformation.

Application of the logical configuration of the BTS.

Transcoder Communication through the Q1 interface with theTranscoder, SM and BIE modules

Permission for configuration and reconfiguration

of the Transcoder, SM and BIE modules.

TSC Communication through the LAPD link with the

BSC

MFS Reading and modifying parameters

Control station and GPU configuration

Framer configuration for Gb Interface messages

GPU switch configuration for circuit-switchedconnections.

Table 21: Configuration Management Functions

For detailed information about configuration management refer to theConfiguration Management chapter in the Operations & Maintenance Principlesdocument or the descriptive documentation.

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8.4.1 Hardware Configuration

Hardware Configuration enables the operator to control the placement inservice of both BSS and MFS hardware, the manner in which deployedhardware elements will act and interact within the BSS and MFS, and to modifythe parameters that control these elements. It also permits the operator to viewthe current hardware configuration status of the network.

8.4.2 Logical Configuration

There are three types of Logical Configuration:

Radio Logical Configuration allows the operator to change the parameters

that control the Air Interface. This includes channel definitions, manipulatingand reconfiguring the Carrier Units or TREs and defining the Frequency

Hopping System.

Cell Logical Configuration displays and modifies BSS logical parameters

and threshold values which influence a cell’s operational behavior. These

are divided into several classes which simplify searches.

GPRS Logical Configuration allows the management of the following:

The telecommunications application, including bearer channels, GbInterface, Ater Mux Interface towards the BSC, and cell management

domains.

Synchronization of the logical GPU resource states after a serverchangeover.

Configuration of a logical GPU when requested by the GPU (after astart, reset or changeover).

Network service configuration and the supervision of the Gb Interface

domain.

8.4.3 Software Configuration

Software Configuration enables new versions of the BSS software to beinstalled in the BSS. This feature also allows the operator to display currentsoftware versions of the BSS. BSC and BTS software is managed from theOMC-R, MFS software is managed from the IMT.

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8.4.4 Auto Identification

Auto Identification gives the BTS A9100 and the BTS A910 the capacity torecognize their own hardware configuration, and to provide this informationto the OMU and the BTS Terminal.

The auto identification procedure is triggered by the OMU in the followingsituations:

BTS/SUM power up

BTS reset

OMU reset/auto reset

Module initialization (on maintenance operator command, or during a Local

Recovery Action or Hardware Extension, the auto identification takes placeonly for the module(s) concerned by the operation).

The BTS A9100 and the BTS A910 capabilities received by the OMU at autoidentification are stored and can be used internally by the OMU software orsent to the BSC at Hardware audit.

Auto identification has two components:

Remote Inventory

RF Cable Identification.

Remote Inventory Remote inventory identifies the following:

RIT type of each managed module

Hardware capabilities of each RIT.

RF Cable Identification RF Cable Identification provides the following information:

Location of each RIT (subrack and slot)

Sector to antenna network x mapping

TRE to antenna network x mapping.

For more information, refer to the BTS Functional Description and the BTSTerminal User Guide.

Consistency Checks When a new Configuration Data Message is received from the BSC, the BTSA9100 and the BTS A910 performs a consistency check of its capabilitiesagainst the Configuration Data Message. It also does this at moduleinitialization due to maintenance operator command or to a Hardware Extensionoperation. The BTS A9100 and the BTS A910 also checks that the receivedOMU Configuration Parameter Data File is valid for this generation of BTS.Consistency checks are also performed by G1 and G2 BTS.

For more information, refer to the following:

EVOLIUM BTS A9100/A910 Functional Description

EVOLIUM BTS A9100 Hardware Description


BTS Terminal User Guide

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8.4.5 OML Auto-detection

An OML auto-detection feature has been introduced in order to take fulladvantage of the transmission configuration via OML feature (it is morereliable and more robust than configuration via the Qmux channel). The OMLauto-detection feature provides the following benefits:

The feature allows one extra time slot to be used for signalling (if no G1/G2BTS are present on the Abis interface). This provides an increase of telecom

traffic on one Abis (because there are no time slots dedicated to the Qmux).

There is no need of on-site BTS reconfiguration during a move BTS scenario(using the LMT to reconfigure the BTS). Also, the Qmux address for the

EVOLIUM™ BTS can be modified remotely from the OMC-R.

No need of on-site BTS reconfiguration during an OML multiplexing change(from 16k to 64k)

Secure recovery after OML breakdown

Simplification of the commissioning procedure: No synchronization anymore between OMC-R and commissioning people. The BTS can be

installed before or after the BTS is created at the OMC-R.

The OMC-R operator no longer needs to know on which time slot is theOML, and no longer needs to configure it manually.

Transmission configuration via OML for all EVOLIUM™ BTS.

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8.4.6 NE Provisioning

Network element provisioning allows equipment that is not yet in commercialuse to be distinguished from equipment that is under maintenance. This is motimportant for network monitoring. The feature introduces the status "commercialuse" that can be associated to the BTS. This status is changeable online fromthe OMC-R. It is also available at the radio configuration export/import interfaceof the OMC-R for coordination with the operators‘ information systems. For theBTS marked as "not in commercial use", potential alarms are raised with only a"warning" severity and the performance measurement results are not takeninto account. The BTS marked as "not in commercial use" are not reportedin the topology files sent to the A985-NPA and A956-RNO. They can be alsofiltered from the supervision view.

Previously, as soon as a BTS was declared, it was supervised, but this raisedpermanent alarms when the BTS was not physically connected. If cells werecreated on this BTS, PM cell measurements were running on the BTS, and thislead to very poor PM results as the BTS was not in commercial service.

An attribute (commercialUse = On or Off) is associated to each BTS. Theattribute can be changed from both the SC and the PRC radio network levelto mark the BTS as out of commercial use, or in commercial use. When thisattribute is set (i.e. the BTS is out of commercial use), all alarms related to theBTS have a severity maximum equal to a warning (except for the alarms fromthe MFS). At the OMC-R, the operator still sees all of the alarms and alarmstates, and is able to trigger all O&M commands, as usual. This allows theoperator to be aware of the fault situation of the BTS, but does not give a falsestatus of the network. There is no PM handling and storage for the BTS that aremarked out of commercial use (except for the PM counters that are relative toRSL/OML traffic which are not filtered).

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8.5 Fault Management - AlarmsThe BSS generates alarms to signal a change in the behavior of a particularfunction within the system, such as a potential problem or a confirmed failurein the system.

This section describes the alarm generation process. It describes the alarmsand their effects on the system.

The following table shows the fault management functions of each networkelement.

NetworkElement

Fault Management Functions

BSC Fault detection, fault correlation and fault localization onall devices controlled by the processor

BSC reconfiguration in case of loss of the BCCH,Terminal Control Unit/FU or a Carrier Unit (G1 or G2

BTS)

BSC reconfiguration in case of loss of the BCCH,TCU/TRE (BTS A9100/A910).

Through the TSC, the BSC also performs the followingfunctions:

Status monitoring of the Transcoder, SM and BIEmodules

Local access provision to configuration of theTranscoder, SM and BIE modules via an RS-232

connection to the BSC terminal.

Giving access to the fault localizing features of the TSC(for example, the ability to set up loop-back tests)

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BTS Testing of the equipment. This includes collecting

alarms and reporting to the BSC.

Fault detection, fault correlation and fault localizationfor the BTS

Management of equipment states. This includes

triggering BTS channel configuration in case of a failure.

Access provision for the local diagnostics andconfiguration of the BTS

BTS power supply control

Event report management. See Alarm Generation(Section 8.5.1) for further information concerning

events.

MFS Collects all fault information for telecom and externalalarms, the telecommunications hardware and the

active server

Records the fault information in a table

Allows the IMT and the OMC-R to access the fault

information

Generates the ending alarm for pending alarms

Manages the communications with the IMT.

Table 22: Fault Management Functions

For additional information about fault management refer to the descriptivedocumentation and the Fault Management chapter of the Operations &Maintenance Principles document.

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8.5.1 Alarm Generation

When an Alarm is generated, it is indicated as either:

Fault (begin or end)If a fault arises, the related alarm is stored in the relevant BSS unit, and alsoin the OMC-R. The alarm begin message signals that a particular systemactivity has stopped due to an error. When the error is corrected, an alarmend message is sent to indicate that the condition no longer exists, and thealarm is taken out of the Alarms-in-Force List.

EventAn Event occurs when an unexpected situation arises during systemoperation.

Alarms can be generated as a result of previous alarms or events whichinfluence other parts of the system. For example, when the Carrier Unitproduces an alarm to signal an internal fault, the FU and the Radio SignallingLink produce alarms to signal that no information is being received from theCarrier Unit. Fault correlation and filtering actions are performed by the O&Mmodules in each unit, so that a single fault is sent as an alarm. In the case ofthe faulty Carrier Unit, an alarm is sent signalling a Carrier Unit fault. In thisexample, the loss of the RSL link is signalled from the BSC but is not correlated.

Refer also to the Alarm Handling section of the Operations & MaintenancePrinciples document.

8.5.2 Alarm FunctionsCorrelation Correlation refers to the collection and analysis of all available fault indications

for a particular problem. Fault correlation is performed to define where and whythe fault occurred.

An example of correlation is as follows:

1. When several boards in the BTS report clock problems, these reports arecorrelated by the OMU.

2. The ’clock generator is faulty’ alarm is sent to the OMC-R via the BSC.

Filtering Alarms are filtered to minimize the number of fault alarms reported anddisplayed to the operator. Alarms are displayed in order of severity.


Persistency A fault is signalled only if there is no recovery after the timer expiration. Forexample, in the case of an LAPD failure of an RSL link, an alarm is sent only ifthe LAPD link has not recovered before the persistency timer has expired.

Alarm Surveillance AS is an OMC-R application that supports fault management integration inTMN functions. It collects alarms issued by applications residing in the variousManagement Layers and processes them.

Alarms-in-Force List Each BSS component keeps an Alarms-in-Force List, so that the systemknows that an alarm has begun. This list ensures synchronization of alarmsthroughout the BSS components. This makes the alarm situation visibleat all times. The OMC-R also keeps track of all the Alarms-in-Force Listsfor each BSS component.

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8.5.3 BSC Alarms

The BSC detects alarms on the Abis and A trunk via the TCU and the DTC. Italso detects alarms from each functional unit of the BSC.


Processor Failure The active S-CPRA creates a daisy-chain map of all the processors in theBSC. Every ten seconds, the S-CPRA sends the map to the next processor.This processor sends the information to the next processor in line, until theS-CPRA receives the daisy-chain map.

The daisy-chain map can be modified by an intermediary processor when thatprocessor cannot send the map to the next processor in line. In this case, theintermediary processor skips the processor and removes that processorfrom the daisy-chain map. When the S-CPRA receives the map with thesame processor missing twice in a row, it tries to recover the processor. Ifthe processor cannot be recovered, the S-CPRA places the processor inthe FLT state.

The S-CPRA signals the processor failure to the OMC-R as follows:

If the processor failure is in the TCU, recovery only takes place to ensure

BCCH functionality.

If a DTC processor fails, the BSC tries to inform the MSC, so that the MSC

is aware the SS7 link is out of service. This implies:

The loss and, if possible, the change-over of the SS7

The blocking of circuits.

Telecom Link or TrunkFailure

The TSC supervises its trunks between the Transcoder, BTS, and MSC.

Failure of the Abis interface is signalled to the BSC by all of the RSLs of theassociated BTS. A single RSL failure reflects the status of the correspondingLAPD and FU.

All A interface faults are controlled by the Transcoder and the MSC. Howeverthey are also monitored by the BSC, in order to define the status of each"end-to-end" A-trunk. The following figure shows RSL fault correlation onthe Abis interface.

Note: The BTS_TEL SBL describes the status of the GSM defined BTS telecomfunctions. Its state is defined by operator commands, and correlation of theLAPD RSL states or of the different Carrier Units.

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RSL−1

RSL−2

RSL−N (last RSL)

Fault Start CPR Informed RSL State Change

Persistency Correlation

Alarm begin BTS_TEL

Fault Start

Fault Start

INACTIVE

ACTIVE

CPR : Common Processor

RSL : Radio Signalling Link

Figure 79: RSL Correlation on the Abis Interface

Abis Interface FaultMonitoring

The BSC monitors the Abis interface faults as follows:

1. The BSC detects the first LAPD RSL link failure of the BTS. The BSCstarts a persistency timer. It puts the SBL of the RSL into a MaintenanceSeized-Auto state while the following actions occur:

The RITs are now in the SOS state. This is because the RTS belonging

to the RSL still functions, but cannot communicate with the BSC.

Telecoms resources are blocked to prevent new activity at the BSCend of this link.

The RSL SBL is put into the FLT state, reflecting the loss of the RSL.

2. The persistency timer expires and the CPR is informed of the fault. If thelink recovers during the persistency period, nothing is reported. Otherwisea correlation timer starts and waits for further RSL link failures belongingto the same BTS.

3. Once the correlation timer expires, the BSC sends a state-change-report

message to the OMC-R. The message contains a list of all RSL that are inthe FLT state.

4. The OMC-R is then informed about the state of the BTS_TEL. If all the RSLsbelonging to the BTS have failed, then an alarm is sent to the OMC-Rsignalling the loss of the cell. When an SBL is put in to the FLT state, it isshown in the Alarms-In-Force List.

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A Interface FaultMonitoring

When the BSC detects a DTC failure, the BSC puts the DTC SBL in theMSD-Auto state, then into the FLT state. Through the TS0 signalling, the MSCis informed that the trunk is no longer operational and prevents all transactionsrequiring the A channel (includes new mobile station-originated calls) fromusing the failed link of the DTC. The failure is also signalled to the OMC-R. TheTSC also detects a failure of the Ater link and signals the failure to the OMC-R.

Note: The A channel is allocated only by the MSC.

Failures Detected bySoftware

Software throughout the BSC detects error and alarm conditions. It reportsthese conditions to the alarm handling software. The alarm handling softwareperforms persistency, filtering and correlation actions on the received alarmindicators, and determines the required action (e.g. to isolate a faulty SBL).

The figure below shows an example alarm report.

If one or more RSL links remain for the failed BTS, an event change is sent. TheBTS_TEL is put in a FIT state, as some channels for that cell are in operation.The AIFL shows the new alarm. The BSC marks the cell as degraded inservice and reconfigures the BTS.

Figure 80: Example: Alarm Report

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8.5.4 BTS Alarms

Alarms in the BTS are tracked by the OMU. The following tables show theOMU hardware and functions.

Alarm OMU Function

G1/G2 Alarm Buses The OMU has a Q1 interface to the CarrierUnits, MCLU, EACB, and FHU modules inthe system, as well as a Token Bus interfacewith all of the FU modules.

BTS A9100/A910 AlarmBuses

The BSII provides the OMU with an interfaceto the TRE functional unit, and to theantenna network x and TRANS & CLOCKfunctional entities, which have their ownon-board controllers. The BCB provides aninterface to all the functional entities in theBTS.

Table 23: BTS Alarm Hardware Description

Alarm OMU Function

Q1 Interface (G1/G2 BTS) On the Q1 interface, a system of doublepolling takes place. The OMU polls eachsubsystem individually to find out if thereis an error. If there is an error, the OMUdemands an error report from that board.Normally, the information from the errorreport is used as an alarm or an eventnotification.

Token Bus Interface (G1/G2BTS)

The OMU is informed by the FU about thetype of error that has occurred. The OMUsends the alarm information to the BSC.

BSSI (BTS A9100/A910) Each module spontaneously reports errorsto the OMU, which processes the report asan alarm or an event notification.

BCB (BTS A9100/A910) The Base Station Control Bus operates in amaster/slave configuration where the SUMfunctions as Pilot (master) and the functionalentities function as Terminals (slaves) innormal conditions. The OMU collects alarminformation on the BCB and sends it to theBSC.

Table 24: BTS Alarms Functional Description

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Alarm Collection The mechanism for BTS alarm collection on all buses is as follows:

1. The alarm is added to the AIFL.

2. The OMU enters alarm information in a queued buffer. In this way, alarmsare queued even if the link between the BTS and the BSC is temporarilyunusable. If the buffer becomes full (over 100 messages):

All fault/state change messages are deleted

No more messages are sent until a state and alarm audit takes place

to synchronize the BSC and the OMC-R. An audit BTS request istransmitted on a regular basis until an audit occurs.

3. The alarm messages containing the alarm information are transmitted to theBSC. The alarm messsages are described in the BTS Alarm Dictionaryand the BSC/TC Alarm Dictionary.

4. The message is sent to the CPR-A, where it is date and time stamped.

5. The BSC performs one of two activities:

If possible, it converts the alarm into a CMISE message, performs

an action and sends a different alarm/event to the OMC-R, via thealarm queue

Otherwise, it re-transmits the message to the OMC-R, via the alarm

queue.

6. The message is put in the alarm queue for BTS alarms. If the queueoverflows, the BSC performs an Alarms-in-Force audit on all the modulesin the BTS. This signals that information was received and lost when thequeue overflowed, and that resynchronization is required.

7. The OMC-R receives the alarm over the CMISE link. The alarm is put intothe AS component where it is logged.

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8.5.5 Alarms Detected by the TSC

TSC O&M activities are similar to those performed by the BTS. The TSC hasa Q1 interface to the transmission equipment. A system of double pollingoccurs on the Q1 interface:

The first poll checks if there was a change in states.

The second poll occurs only if the state has changed, in order to obtain

more information about the changes.

The Transcoder supervises PCM links. The loss of a link between the BSC andTranscoder is reported by the Transcoder to the TSC.

8.5.6 MFS Alarms

The MFS generates alarms to signal a change in the behavior of a particularfunction within the system, such as a potential problem or a confirmed failurein the system. The Global Alarm Manager manages the MFS alarms. Itprocesses all hardware and telecom alarms and is responsible for:

Collecting all fault information relating to GPUs, the active server, andtelecom and external alarms

Recording alarms in a table

Allowing the IMT and the OMC-R to access the alarms

Generating ending alarms when a fault is cleared (for example, when a

GPU is replaced)

Managing a communication session with the IMT.

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8.5.7 Recovery Example: Carrier Unit Failures with BCCH

This recovery example considers a BTS with two Carrier Units. One CarrierUnit is used for BCCH channel handling, another is used for normal traffic.If the Carrier Unit holding the BCCH fails, it is switched out and the secondCarrier Unit takes the place of the first.

As an example, this section describes the system’s reactions when a CarrierUnit (TRE for a BTS A9100 or a BTS A910) which has the BCCH channel fails.

Note: In the BTS A9100 or the BTS A910, the SBLs FU and Carrier Unit have beenmerged into one indivisible SBL, called the TRE. At the BSC, however, all BTSA9100 and BTS A910 TRE faults are mapped to the Carrier Unit to providecompatibility with G1 and G2 BTSs. Thus, at the BSC all such errors aredisplayed as Carrier Unit faults. That is how they are presented in this example.

FU faults in G1 and G2 BTSs continue to be reported as such.

Fault RecoveryMechanism

The recovery mechanism in the BSS allows a failed unit to switch to areplacement unit, such as:

Redundant hardware

A similar unit which had lower priority active use than the failed unit. (Forexample, the BCCH has to exist for the cell to function, so another Carrier

Unit/FU pair (TRE for a BTS A9100 or a BTS A910) is expendable toreplace the failed Carrier Unit).

The recovery mechanism of the BSS recognizes that the Carrier Unit canchange to its twin Carrier Unit.

Below is a step-by-step scenario of Carrier Unit recovery.

Carrier Unit RecoveryScenario

1. The Carrier Unit holding the BCCH fails.

2. The BTS sends the BSC a recovery request, reporting that the Carrier Unitis faulty and is out of service, and that a recovery is required. The BTS alsosuggests a new Carrier Unit to the BSC, to be used to carry the BCCH.When the recovery request is received, the BSC temporarily blocks theresources while it checks if reconfiguration is available. If reconfiguration isavailable, the BTS_TEL SBL becomes FIT and all calls on the Carrier Unitare immediately released. The RSL is blocked. All calls on the Carrier Unitare immediately released.

3. The BSC sends an alarm to the OMC-R, signalling the loss of BCCH.

4. The BSC attempts a recovery. The recovery command isBTS-CONF-DATA(2).

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5. The BTS receives and acknowledges the recovery message. It thenswitches off the faulty Carrier Unit and switches on the second Carrier Unit.The second Carrier Unit adjusts its frequency to the BCCH frequency.

6. If the configuration was successful, the BTS sends a confirmation to theBSC. The BSC then sends the new SYS_INFO (1-6).

7. The BCCH is now broadcasting on the same frequency as before, viathe newly configured Carrier Unit.

8. The BSC sets the BTS_TEL SBL to FIT and informs the OMC-R by sendingan end of alarm. The BTS_TEL remains FIT due to the loss of a channel.

9. If the new Carrier Unit was previously IT, its previously attached resourcesare lost. An alarm is sent to the OMC-R to update the information onlost channels.

The following figure shows the redundancy process for a failed Carrier Unitwith BCCH.

OMC BSC BTS

Resourcesblocked, BCCHreconfiguration possible

BTS_TEL=FIT

BTS_TEL=IT

BTS_TEL=FIT

CU Fault

BTS_TEL=FIT

1

2

3

4

6

8

9

BTS performs the reconfiguration5

Alarm (cell, loss of BCCH begin)

Alarm (cell, loss of BCCH end)

Alarm (cell, loss of TCH begin)

Reco_req (CU, FOS)

BTS_CONF_DATA (2)

BTS_CONF_COMPL

SYS_INFO (1..6)

BCCH : Broadcast Control Channel

CU : Carrier Unit


Figure 81: Example: Loss of Carrier Unit Holding BCCH.

Note: BTS_TEL SBL describes the status of the GSM defined BTS telecom functions.Its state is driven by operator commands, or by correlation of the LAPD RSLstates or of the different Carrier Units.

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8.5.8 Automatic Power-Down

This feature is available only on the BTS A9100. It is used typically in anoutdoor installation where the BTS has a backup battery power supply.

In case of main power-supply failure, the BTS A9100 is automatically switchedto battery power. This situation continues until the main power is restored or thebattery is drained, whichever happens first.

To extend the time during which the BTS A9100 can function under batterypower, the BTS is reduced to a minimum configuration to reduce powerconsumption.

Power-Down AlarmProcessing

Once a power-supply failure alarm arrives, the OMU starts a timer. If, once thetimer expires, the alarm is still active, the OMU switches off all TREs exceptthe BCCH TRE (one per sector for a sectored site), by placing the TREsto be powered down in FOS state.

If, in a given sector of a sectored site, the BCCH TRE is configured without atraffic channel, another TRE (which carries the SDCCH) is kept powered on, sothat calls are still possible in this sector, though limited to one TRE.

When the power-supply failure alarm disappears, the OMU starts a timer. If thealarm re-occurs before the timer expires, the OMU takes no further action. Thisis to guard against a possible unstable restoration of power.

If the BTS power-supply remains stable until the timer expires, the OMUperforms an autonomous auto reset with BTS activation. This re-initializesall available TREs.

For more information on this feature, refer to the following:

EVOLIUM BTS A9100/A910 Functional Description



8.5.9 BSC Alerter

The BSC Alerter is a telecom supervision function which generates an alarmevent when the system suspects abnormal behavior of a resource. This issystem defined and not dependent on site configuration or traffic conditionsin a particular cell.

An Alerter functions by monitoring and computing the levels of specificPerformance Management counters. If the count exceeds the operator-definedparameters, the Alerter generates an alarm for the BSC resource. This alarm issent to the OMC-R operator.

Note: For performance reasons, each alerter type has a maximum limit of 16 alarms.

For further information concerning BSC Alerters, refer to the BSC Alerterssection of the Operations & Maintenance Principles document.

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8.6 Performance ManagementThe following provides a brief overview of performance management facilities inthe BSS.

For detailed information on performance management, refer to the PerformanceManagement chapter of the Operations & Maintenance Principles document.

For a description of individual counters, refer to the PM Counters and Indicatorsdocument.

The following table shows the performance management functions of theBSC and the MFS.

Network Element Performance Management Functions

BSC Result collection and collation

X.25 related counters

Traffic measurements on radio channels

Performance Measurement result reporting

Trace invocation result reporting.

MFS Collects the performance management countersassociated with each logical GPU

Creates a file to counter values.

Table 25: Performance Management Functions

8.6.1 Traces

Trace management coordinates and triggers trace activities within the BSS.Tracing is originated from the MSC. There are two types of tracing:

Call tracing

IMSI tracing.

Call tracing follows a specified transaction (subscriber call, location update,short message, etc.) inside the BSC. When the specified transaction ends, orthe transaction changes to another BSC, the trace activity ends.

IMSI tracing is not restricted to speech. It includes information about the radioresources set up for the mobile. This includes, for example, location updating,supplementary services, short messages, etc.

For more information on trace management, refer to the Trace Managementsection of the Operations & Maintenance Principles document.

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8.6.2 Performance Monitoring

Monitoring system performance provides information that can be used toimprove the system performance, optimize traffic levels, perform network radioplanning and optimization, and plan network reconfiguration. The OMC-Rmanages the gathering of data collected from all the network elements bymeans of PM counters. PM counter values are collected into results files inthe BSC.

In the BSS, there are two types of raw counters: standard and detailed. Thesetwo counter types are gathered in the following counter groups:

Cumulative counters

Status inspection counters

DER counters

RMS counters

For the MFS, the counters are all standard counters. These counters aredivided into two groups

Counters monitoring activity between the BSC and the MFS

Counters monitoring activity between the MSC and the MFS.

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8.6.3 Radio Measurements Statistics

In order to help the operator find "clean" frequencies for better frequencyplanning, the Radio Measurements Statistics (RMS) counters provideinformation based on the Mobile Assisted Frequency Allocation (MAFA) feature.MAFA is a standardized GSM feature that provides a way for the system to askeach mobile station to measure extra frequencies (frequencies of non-neighborcells). MAFA can also be used to check interferences from non-neighborcells. RMS is a BSC/BTS feature that records measurements from the BTSand mobile stations. For MAFA, specific mobiles supporting this standardizedGSM feature are required. Every mobile station supporting MAFA acts as apotential spectrum analyzer and provides excellent information on the radioconditions for each single cell.

Using this feature, the operator can:

Detect interfered frequencies

Assess the quality of the cell coverage

Detect and quantify cell unexpected propagation

Assess the traffic distribution in the cell from statistics on reported neighborcells

Evaluate the voice quality in the cell.

During the observation period, the BTS/FU keeps track of all the RMSstatistics derived from the measurements reported by the mobile stationsor measured by the BTS/FU itself on the TCH (SDCCH are not used withRMS). At the end of the observation period when the RMS data has beencollected from the concerned BTS/FUs, the BSC builds a report (called theRMS result file). The transfer towards the OMC-R occurs via FTAM. Inaddition, it is possible during the observation period to apply MAFA (also calledExtended Measurement Reporting). This procedure consists in sending anExtended Measurement Order (EMO) to the mobile stations. On receipt ofthe command, the mobile stations take one SACCH multiframe to performmeasurements on specific frequencies. The measurements are reported viathe EXTENDED_MEASUREMENT_REPORT message. The EMO is sent onlyonce per call. The statistics related to MAFA are collected in the BTS andintegrated in the RMS results. The statistics are based on the measurementsperformed at the BTS and the mobile station, on the TCH only.

The statistics can be classified as follows:

Radio related statistics. These can be classified as follows:

Statistics related to the whole serving cell

Statistics related to the TRXs

Voice quality statistics. Nine counters and indicators that provide anoverview of the communications quality (TCH only) for each TRX.

Radio Measurement Statistics is available on G1 BTS Mk2 and G2 BTSequipped with DRFU, EVOLIUM™ BTS, and Micro BTS M1M and M2M.

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8.6.4 Results Analysis

Using the OMC-R, an operator can view alarms and PM measurements fromthe OMC-R databases, and use this information to analyze data and producereports. The OMC-R also generates QoS alarms to notify the operator ofpossible network problems.

Counter and indicator information can be processed by a tool, in one of twoversions:

MPM, which is integrated in the OMC-R. It provides instant access to

results files.

NPA is usually a stand-alone tool that runs on a separate Sun workstation(but in the case of a small configuration, NPA can be embedded into the

OMC-R). It has nearly the same functionality as MPM, with the followingdifferences:

NPA can aggregate the data on a day, week, or month basis, where MPMcan only aggregate on a daily basis.

NPA cannot manage alerters.

For more information on results analysis and the tools available to processcounter and indicators information, refer to the Results Analysis section of theOperations & Maintenance Principles document.

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8.7 AuditsAudits can be automatic or initiated by an operator. They can be performed atseveral levels:

From the OMC-R to the Transcoder, the BSC, or the MFS

From the BSC to the BTS.

More information on Audits can be found as follows:

Configuration Management Audits in the Configuration ManagementAudits/Resynchronization section of the Operations & MaintenancePrinciples document.

Fault Management Audits in the Fault Management Audits section of the

Operations & Maintenance Principles document..

Using the IMT, it is possible to perform a radio re-initialization, or a radioresynchronization of the MFS.

Audit Types There are several types of audits, as described in the following table.

Type Description

Logical Audit A logical audit is performed on logical parameters. Thelogical parameters include dynamic cell information,its power ratings, information on adjacent cells, theradio configuration of the cell, and hopping and paginggroups. No logical audit is provided for the MFS side.

Software VersionAudit

The software version audit controls the versions ofsoftware that exist on the subsystem.

Hardware Audit Hardware audits control the hardware on thesubsystem. This audit provides a physical list of allcomponents in the subsystem, their SBLs, and theirassociated RITs. The OMC-R updates the databasewith this information.

Alarm Audit The OMC-R requests the AIFL from a unit of the BSS.The OMC-R then compares this with its own list andupdates its database if there are any differences.

State Audit A state audit checks the state of SBLs on a particularsubsystem, to ensure that SBL databases aresynchronized. All the SBLs and their states arecompared with the data in the OMC-R. If the SBL doesnot exist in the database, it is created and its state isregistered.

Table 26: Audit Types

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Two types of action are possible for the MFS:

Re-initialize GPRS configurationAllows the OMC-R to force the logical configuration of the MFS, by deletingthe current one, and then recreating one from scratch, using the currentOMC-R configuration. This is roughly the equivalent of a Force configurationat the BSS side. However, it always induces some outages.

Re-synchronize GPRS configurationAllows the OMC-R to force the logical configuration of the MFS, bycomputing the differences with the current OMC-R configuration. It isthe preferred synchronization action at the MFS side, as it minimizes theMFS outage.

A suite of audits is automatically invoked by the OMC-R or the BSC, toresynchronize the system. This is done:

To perform a RESET/RESTART

When there is a loss of links between subsystems. This ensures that the

system databases are synchronized after autonomous operation while the

link was down (i.e. the BTS_O&M was disabled).

To make changes in the databases, without the possibility of aligning

both subsystems

To start a BSC Alarms-in-Force audit if the BSC alarm queue overflows

To perform software database replacement.

Audit information for the whole system is stored in the OMC-R.

Audit Flow Audit flow is based on an action request from the OMC-R, or on an automaticrequest.

The subsystem receiving the audit request performs an audit of its functionalunits.

The reply can have one or several report messages to pass the information backto the request originator. The request originator can generate more actionsbased on the information received. For example, when the state of the CarrierUnit and its pair FU do not match, the BSC disables the FU/Carrier Unit pairs.

The OMC-R, on reception of the audit report, updates its database. Duringdownload the results of the software audit are used to provide the list ofmodules the OMC-R needs to update the BSS subsystem. This is done bycomparing the OMC-R lists of modules to transfer, and their version numbers,to see if they already exist in the subsystem. Only the newer versions aretransferred to the subsystem.

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8.8 Remote InventoryThe Remote Inventory feature allows an operator to get hardware and firmwareinformation from the OMC-R. This information is used for retrofit, deployment ormaintenance. The main benefit is that the amount of site visits can reducedconsiderably. The Remote Inventory data is reported to the OMC-R by the BTSA9100 and the BTS A910 which are very numerous and spread out on thefield. The operator can get this data in two ways, automatic or on-demand. Theon-demand mode remains available when the automatic mode is selected.Among the reported data is information that is very useful for retrofit ormaintenance actions, e.g. the site name, the exact location of the board, theserial number, the part number and the variant. Sending the data to externaltools is possible due to the ASCII file format. This format is the same as theone obtained when using a BTS Terminal at a BTS site. Existing external toolscan therefore be re-used.

The Remote Inventory feature brings the following benefits:

ReliabilityInventory data is reported directly (periodically if requested) by the BTSto the OMC-R (through the BSC which is transparent), so the operatoralways has the correct information. To keep the OMC-R at a high level ofperformance, Alcatel recommends using the automatic mode with a sevenday acquisition period.

Cost cuttingIt is no longer necessary to go on site to get hardware and firmwareinformation before performing a retrofit or a maintenance action.

Remote Inventory can be performed at the MFS. Information can be displayedfor the selected subrack. For more information, refer to the online help of theIMT.

For more information on Remote Inventory, see the Remote Inventory section inthe Operations & Maintenance Principles document.

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Alcatel BSS System Description

Documents

lowest priority

tx rx

international

cm se

cm ser

visitor location

home location

bscbtsmobile