A Bis

Nokia Siemens Networks GSM/EDGE BSS, rel. RG10(BSS), operating documentation, issue 04

Plan and dimension

BSS Transmission Configuration

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The information in this document is subject to change without notice and describes only the product defined in the introduction of this documentation. This documentation is intended for the use of Nokia Siemens Networks customers only for the purposes of the agreement under which the document is submitted, and no part of it may be used, reproduced, modified or transmitted in any form or means without the prior written permission of Nokia Siemens Networks. The documentation has been prepared to be used by professional and properly trained personnel, and the customer assumes full responsibility when using it. Nokia Siemens Networks welcomes customer comments as part of the process of continuous development and improvement of the documentation.

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Copyright © Nokia Siemens Networks 2009. All rights reserved

f Important Notice on Product Safety Elevated voltages are inevitably present at specific points in this electrical equipment. Some of the parts may also have elevated operating temperatures.

Non-observance of these conditions and the safety instructions can result in personal injury or in property damage.

Therefore, only trained and qualified personnel may install and maintain the system.

The system complies with the standard EN 60950 / IEC 60950. All equipment connected has to comply with the applicable safety standards.

The same text in German:

Wichtiger Hinweis zur Produktsicherheit

In elektrischen Anlagen stehen zwangsläufig bestimmte Teile der Geräte unter Span-nung. Einige Teile können auch eine hohe Betriebstemperatur aufweisen.

Eine Nichtbeachtung dieser Situation und der Warnungshinweise kann zu Körperverlet-zungen und Sachschäden führen.

Deshalb wird vorausgesetzt, dass nur geschultes und qualifiziertes Personal die Anlagen installiert und wartet.

Das System entspricht den Anforderungen der EN 60950 / IEC 60950. Angeschlossene Geräte müssen die zutreffenden Sicherheitsbestimmungen erfüllen.

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Table of ContentsThis document has 64 pages.

Summary of changes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

1 BSS transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2 BSC configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142.1 BSC location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142.2 BSC capacity limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142.3 A and Ater BSC interface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162.4 Interface to the OMC direction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162.5 LAN interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3 TC configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183.1 Installations with TCSM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183.2 TCSM3i versus TCSM2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203.3 TCSM3i versus TCSM3i for combined BSC3i/TCSM3i installation . . . . 203.4 TCSM versus transcoder in MGW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

4 BTS configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224.1 TRU transmission unit descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234.1.1 O & M arrangement of transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . 244.1.2 Options for transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244.2 FC and FXC units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254.3 FIEA, FIPA, FIQA, FIYA and FIFA units . . . . . . . . . . . . . . . . . . . . . . . . 264.4 Microwave radio relays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

5 GPRS and the Gb interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285.1 Gb over Frame Relay. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285.2 Gb over IP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305.3 GPRS capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

6 BSS redundancy configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

7 Operation and maintenance of transmission equipment . . . . . . . . . . . . 337.1 Supervisory channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337.2 Local O & M . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347.3 Remote O & M . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

8 Requirements on transmission network. . . . . . . . . . . . . . . . . . . . . . . . . 368.1 2 Mbit/s transmission paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368.2 Synchronisation of BSS network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 378.3 Transmission delay of BSS network . . . . . . . . . . . . . . . . . . . . . . . . . . . 388.4 Error rate performance of BSS network. . . . . . . . . . . . . . . . . . . . . . . . . 398.5 Slips in transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398.6 Echo control in BSS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 408.7 Jitter and wander prevention in BSS . . . . . . . . . . . . . . . . . . . . . . . . . . . 408.8 Ethernet based transport / CESoPSN . . . . . . . . . . . . . . . . . . . . . . . . . . 40

9 Digital cross-connect nodes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 439.1 Digital node equipment DN2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

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9.2 MetroHub transmission node . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

10 BSC-BTS transmission examples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4610.1 Overview of transmission network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4610.2 Point-to-point transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4610.3 Multidrop chain transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4710.4 Loop transmission. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4710.5 Radio transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4810.6 UltraSite network example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

11 Time slot allocations in BSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5011.1 Time slot allocation in combined BSC3i/TCSM3i installation (ANSI) . . . 5411.2 Compressed Abis time slot allocation . . . . . . . . . . . . . . . . . . . . . . . . . . . 5611.3 Allocation of Abis time slots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6011.4 Abis allocation, FR, 16 kbit/s signalling. . . . . . . . . . . . . . . . . . . . . . . . . . 6111.5 Abis allocation, FR/HR, 64 kbit/s signalling . . . . . . . . . . . . . . . . . . . . . . 6211.6 Abis allocation, FR/HR, 32 kbit/s signalling . . . . . . . . . . . . . . . . . . . . . . 62

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List of FiguresFigure 1 General BSS/RAN topology: access through multiservice network. . . . 10Figure 2 Through-connected channels configured in the transcoders and in the

MSC switching matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Figure 3 GPRS traffic multiplexed on the same physical connection as used for the

GSM traffic on the Ater interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Figure 4 GPRS traffic concentrated and carried over the Gb interface in a packet

data network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Figure 5 GPRS traffic carried over dedicated 2 Mbit/s PCM links . . . . . . . . . . . . 30Figure 6 GPRS traffic carried over the Gb interface with IP. . . . . . . . . . . . . . . . . 30Figure 7 Radio link hop protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Figure 8 Interconnection of different networks. . . . . . . . . . . . . . . . . . . . . . . . . . . 43Figure 9 Multiplexing of the BSS and external channels with the DN2 . . . . . . . . 44Figure 10 Network principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45Figure 11 BSS network using leased lines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46Figure 12 Point-to-point connection between BSC and BTS . . . . . . . . . . . . . . . . . 47Figure 13 Multidrop chain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47Figure 14 Duplicated point-to-point and multidrop loop . . . . . . . . . . . . . . . . . . . . . 48Figure 15 Loop, radio relay transmission network . . . . . . . . . . . . . . . . . . . . . . . . . 48Figure 16 Example of a UltraSite network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49Figure 17 Time slot allocation for 16 kbit/s bit rate channels (typically full rate, en-

hanced full rate or AMR) on the Ater 2 Mbit/s interface with the TCSM2/TCSM3i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Figure 18 Time slot allocation for half rate traffic with 8 kbit/s TRAU frames on the Ater 2 Mbit/s interface with the TCSM2 . . . . . . . . . . . . . . . . . . . . . . . . . 52

Figure 19 Ater time slot allocation example for the HSCSD application: a combination of 2 x 16 kbit/s channels (HS2) and 4 x 16 kbit/s channels (HS4) . . . . . 53

Figure 20 Time slot allocation of 2 x 16 kbit/s channels of Figure A-PCM1 on A inter-face . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Figure 21 Time slot allocation of 4 x 16 kbit/s channels of Figure A-PCM2 on A inter-face . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Figure 22 Submultiplexing on Ater PCM in ANSI environment (16 kbit/s) . . . . . . . 55Figure 23 Submultiplexing on Ater PCM in ANSI environment (32 kbit/s) . . . . . . . 55Figure 24 Submultiplexing on Ater PCM in ANSI environment (64 kbit/s) . . . . . . . 56Figure 25 Submultiplexing on Ater PCM in ANSI environment (mixed 32 and 64

kbit/s) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56Figure 26 Compressed allocation enabling up to 15 TRXs per 2 Mbit/s circuit . . . 59Figure 27 Allocation example for a three-TRX BTS. . . . . . . . . . . . . . . . . . . . . . . . 60Figure 28 Multidrop chain allocation in the case of 16 kbit/s LAPD . . . . . . . . . . . . 62Figure 29 An example of four-BTS chain (highway) allocation when 32 kbit/s TRX sig-

nalling is used . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

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List of TablesTable 1 BSC configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Table 2 Number of BCSUs in combined BSC3i/TCSM3i installation . . . . . . . . . 15Table 3 Circuit types of TCSM2 and TCSM3i . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Table 4 Matching of circuit type and circuit pools . . . . . . . . . . . . . . . . . . . . . . . . 19Table 5 The transmission units in the Talk-family BTSs . . . . . . . . . . . . . . . . . . . 23Table 6 SAPI values and priorities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Table 7 Connectivity of logical PCUs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Table 8 Compressed Abis time slot allocation . . . . . . . . . . . . . . . . . . . . . . . . . . 57Table 9 Compressed Abis time slot allocation in the case of multi-TRX base

stations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57Table 10 Compressed Abis time slot allocation that supports five 3 x 1 TRX sites .

58Table 11 Compressed Abis time slot allocation with the TRX signalling speed 32

kbit/s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58Table 12 16 kbit/s OMUSIG signalling rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60Table 13 16 kbit/s OMUSIG signalling rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

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Summary of changesChanges between document issues are cumulative. Therefore, the latest document issue contains all changes made to previous issues.

Changes made between issues 14-1 and 14-0Information on InSite BTS has been removed.

Changes made between issues 14-0 and 13-1Updated information in chapter Time slot allocations in BSS. Information on FIEA, FIPA, FIFA, FIYA has been updated in chapter BTS configuration.

Removed Tellabs from figure Interconnection of different networks.

Updated information on Abis allocation in chapter Requirements on transmission network.

A new section on Ethernet based transport / CESoPSN has been added under chapter Requirements on transmission network.

Updated the information in table BSC configurations.

Added an example and calculation of Bandwidth under section Ethernet based transport / CESoPSN in chapter Requirements on transmission network.

Updated information in chapter Time slot allocations in BSS 73.

Information on FIEA, FIPA, FIFA, FIYA has been updated in chapter BTS configuration.

Removed Tellabs from figure Interconnection of different networks.

Updated information on Abis allocation in chapter Requirements on transmission network.

A new section Ethernet based transport / CESoPSN has been added to chapter Requirements on transmission network.

Updated information on TRXSIG in chapter Time slot allocations in BSS.

Changed the title of Chapter from:

• TRU TSL allocation, FR, 16 kbit/s signalling to Abis allocation, FR, 16 kbit/s signal-ling

• TRU TSL allocation, FR/HR, 32 kbit/s signalling to Abis allocation, FR/HR, 64 kbit/s signalling

• TRU TSL allocation, FR/HR, 64 kbit/s signalling to Abis allocation, FR/HR, 32 kbit/s signalling

Added a new paragraph about Abis allocation in chapter Allocation of Abis time slots.

The information about "TRU" is replaced by "multidrop" in chapter Abis allocation, FR, 16 kbit/s signalling.

The information about "FIYA and FIQA plug-in units" is added in chapter BTS configu-ration.

Changes made between issues 13-1 and 13-0The information that the parameter SIGN is used for defining the compressed Abis time slot when creating a TRX has been added in section Compressed Abis time slot alloca-tion in chapter Time slot allocations in BSS.

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Summary of changes

The information that all pseudowire IP solutions and dedicated optimisation solutions add round-trip time delay has been added to section Transmission delay of BSS network in chapter Requirements on transmission network.

Changes made between issues 13-0 and 12-0

Chapter BTS configurationRemoved the bullet Nokia 2nd generation DE21 BTS does not support AMR from the beginning of the section. Removed all references to PrimeSite. Removed FC E1/T1 from the section FC units.

Information on microwave radio relays moved to a section of its own to give it more vis-ibility.

Section FIEA, FIPA and FIFA units: changed the title to FIEA, FIPA, FIQA, FIYA and FIFA units, added the units to the list, and added CESoPSN to the list of growth paths.

Chapter BSC-BTS transmission examplesRemoved the section DN2 in the MSC-BSC path.

Chapter Time slot allocations in BSSMade minor improvements to the introduction to the section Compressed Abis time slot allocation.

Changes made between issues 12-0 and 11-1

Chapter BSS transmissionInformation on SDH/SONET optical interface and TCSM3i for combined BSC3i/TCSM3i installation added.

Chapter BSC configurationSections BSC capacity limits and A and Abis BSC interface have been updated with information on new BSC3i variants and TCSM3i.

Chapter TC configurationInformation on TCSM3i added.

Chapter BTS configurationInformation on Flexi EDGE base station added.

Information on ISDN Abis and TRUC/D transmission units has been removed.

Chapter BSS redundancy configurationsInformation on Abis chain protection has been removed.

Chapter Operation and maintenance of transmission equipmentThe number of Q1 supervisory channels supported by the BSC has been changed from 28 to 56.

Information on V.11 has been removed.

Chapter Requirements on transmission networkSection Error rate performance of BSS network has been updated.

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Chapter Digital cross-connect nodesHardware details in section Digital node equipment DN2 have been updated.

Information on SXC T has been removed.

Chapter BSC-BTS transmission examplesSections Radio transmission and DN2 in the MSC-BSC path have been updated.

Information on SXC T has been removed.

Chapter Time slot allocations in BSSSection Time slot allocation in combined BSC3i/TCSM3i installation (ANSI) has been added.

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BSS transmission

1 BSS transmissionUsually the BSC-BTS Abis transmission configuration is a mixture of point-to-point, mul-tidrop chain, or multidrop ring subnetworks.

Figure 1 General BSS/RAN topology: access through multiservice network

The BSC sees BTSs through 2 Mbit/s PDH ET ports which carry data to and from the BTSs. The transport network in between can be whatever technology when it provides transparent PDH termination points.

• Transport network topologyThe transport network topology can be a star, chain or loop. The star network benefit is that it is very simple to manage but the disadvantages are that the connections are typically only partially filled with payload (extra transmission cost) and any failure in the network causes traffic cut. Use of grooming at star network hub sites will optimise the use of northbound transport capacity. The chain network improves the efficiency of the use of transmission capacity but is still sensitive to failures in the network. From reliability point of view the most secure topology is the loop. Loop disadvantage is the use of doubled transmission paths, which causes extra costs - but this is typical for all protection methods. Loop setup and maintenance may require dedicated skills but training and comprehensive instructions in the users manuals will help. Note that all these topologies are transparent for the Abis traffic.

• Grooming principleGrooming in the network means the cross-connection functions which allow combi-nation of partially filled transmission containers, for example 2 Mbit/s G.704 frame

BS

BS BS

BS

BS

BS BS

BS

BS

BSBS

BS

BS

BS

BS

BS

BS

BS BS

BS

BS BS

BSC / RNC

Multi ServiceSDH or ATM or IP

Network

Access network compatiblestandard high capacity IF

Access network compatiblestandard low capacity IF

BTS access medium capacity IF

BTS access low capacity IF

Access network element

Base station siteBS

BS

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into a single container. BTS integrated transmission units support this function. The benefit is naturally better efficiency in the transport layer.

• SynchronisationIn the BSS area the BSC is the synchronisation master to the BTSs. Normally the transport layer is also synchronised to the BSC by taking the first transmission equipment synchronisation reference from the master BSC ET port and then deliv-ering this synchronisation in the transmission network downwards. When using other technologies to carry the ET signals, such as SDH, and when the non-PDH network is synchronised to a synchronisation reference on its own, then the ET port synchronisation must be transparently transmitted into the first PDH element through the SDH layer.

• Network management principlesBTS integrated transmission elements are managed by using the Q1 protocol. The essential parts of that protocol are the location of the polling device (Q1 master), the Q1 data communication channel and the Q1 addressing. The most typical set-up is that the local BTS operates as Q1 master and forwards the Q1 messages to/from the NMS using a BTS management channel in the NMS direction and Q1 channel in the transmission direction. The Q1 data communication channel is a bus where all elements hear all the messages along the bus. The devices are accessed by using a unique address for each element on the bus. Often there are also non-inte-grated Q1 elements in the BSS network. Those devices are polled either by the BTS or BSC depending on the Q1 plan. Normally the Q1 plan is such that the polling device is closer to the BSC than the polled device to have management access as deep into the network as possible in case of any failures.

BSS transmission configuration approachThe focus here is mainly on BSC-BTS transmission.

The start of the whole BSS design procedure relies on BSS traffic handling require-ments.

The specific information needed in planning and dimensioning the network includes the following items:

• BTS locations and sizes • BSC location • MSC location • Transcoder equipment location • Available transmission methods

The support for AMR HR approximately doubles the voice capacity of the GSM network without affecting the transmission capacity. EDGE air interface enables four-fold data rates per channel and multiple channels may be in use for single subscriber. Typically EDGE increases transmission capacity requirements. The EDAP pool in Nokia Dynamic Abis optimizes the use of transmission resources for EGPRS.

The design starts from the BTS information, followed by the BSC, the TCSM, and the MSC.

For the transmission part of the network, the following input data is needed for dimen-sioning:

1. The number of traffic channels on the A interface per BSS, full rate (FR/EFR), half rate (HR), AMR, High Speed Circuit Switched Data (HSCSD), General Packet Radio Service (GPRS) and the number of EDGE TRXs

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BSS transmission

• The number of transcoder units (either TCSM2 or TCSM3i), their capacities and BSC A interface connections can be deduced from this number.

• HSCSD will set special requirements for Ater capacity depending on how many HSCSD circuits are used and how many parallel time slots are supported by the transcoder. A given transcoder pool may support both FR/EFR/HR and multislot HSCSD.

• Each HSCSD channel occupies an entity of 64 kbit/s (one time slot) at the A interface. However, the data stream itself may be carried by less than 8 bits of the time slot.

• GPRS service is implemented by a plug-in unit (PCU) in the BSC. For more information, see GPRS and the GB interface..

• Optical STM-1/OC-3 (SDH/SONET) interface can be used to increase the external connectivity of the BSC3i and reduce the transmission costs. One STM-1 interface consists of 63 ETs (ETSI) and one OC-3 interface of 84 ETs (ANSI).

• As a standard up to 6 BSCs (optionally up to 12 BSCs) can be connected to one TCSM3i in stand-alone installation. In combined BSC3i/TCSM3i installation, the transcoding capacity of a TCSM3i can be shared by up to 96 BSCs (ETSI) or 24 BSCs (ANSI).

2. The total number of TRXs controlled by the BSC • If Dual Band is in use, the TRXs operate in different frequency bands. • The capability of the BSC processing can be deduced from this number.

3. The total number of 2 Mbit/s links on the BSC Abis interfaceThe number of BSC Abis 2 Mbit/s connections can be deduced from this number. EDGE TRX can be connected using a shared Dynamic Abis pool which allows dynamic allocation of capacity wherever it is needed. The dimensioning of Dynamic Abis is explained in Abis EDGE Dimensioning in GSM/EDGE BSS System Docu-mentation Set.

Once the required transmission capacity has been calculated, the transmission network planning may start.

The BSS transmission network planning is based on:

• Required BSC BTS Abis capacity • Required Ater capacity • Required Gb capacity • Required IP connectivity • Existing and/or available transmission network and its tariffing • Decision on traffic protection • Network management solution

The details of transmission network planning include:

• Allocating required capacities into usable conduits (such as leased lines and radio links)

• 2M time slot allocation plan for each BSC BTS Abis link, taking into account the Dynamic Abis for EDGE

• Transmission capacity optimisation by grooming cross-connections • Loop network protection planning • Network management channel planning • Synchronisation hierarchy planning

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When the transmission network high level planning is done, the related transmission settings can be entered to the equipment to make the network operate.

Related topics

• BSC configuration • TC configuration • BTS configuration • GPRS and the Gb interface • BSS redundancy configurations • Operation and maintenance of transmission equipment • Requirements on transmission network • Digital cross-connect nodes • BSC - BTS transmission examples • Time slot allocations in BSS

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BSC configuration

2 BSC configurationThe BSC configuration process includes two steps:

1. To determine the BSC location in the BSS network2. To determine the configuration of each BSC

The switching field GSWB of the BSC meets both full rate and half rate speech require-ments.

The dimensioning principles for enhanced full rate (EFR) channels are the same as for FR channels.

2.1 BSC locationLocating BSCs in the BSS network is flexible. BSCs can be co-located or non-co-located with the MSC and the transcoder.

The best location depends mainly on tariff structure on transmission lines. For example, if the tariff correlates strongly with the distance of the transmission line, the best location for a BSC is normally non-co-located with the MSC and the TC. Transmission lines can be saved on the A interface by submultiplexing and concentrating the traffic on fewer lines. Concentration can save a lot of expenses because the number of lines can be dimensioned according to the expected volume of traffic.

2.2 BSC capacity limitsThere are certain limits to the capacity, especially to the number of TRXs and the number of PCM lines. These limits are presented in the table below.

BSC configurations BSC2i BSC3i 660 / BSC3i 1000 / BSC3i 2000

Maximum radio network configuration

248 BCF

248 / 512 BTS

512 TRX

504/1000/2000/3000 BCF

660/1000/2000/3000 BTS

660/1000/2000/3000 TRX

Maximum number of external PCMs

80 / 112 / 144 256/384/800/800

SS7 signalling links 16 16

Minimum number of WO-EX BCSUs

1-8 1-6/1-5/1-10/1-6

Number of BCFSIG LAPD links per BCSU

32 84/200/200/500

Number of TRXSIG LAPD links per BCSU

64 110/200/200/500

Maximum number of LAPD links per BCSU

(BCFSIG + TRXSIG + ET-LAPD)

124 206/412/412/960

Maximum number of TCHs per BCSU

512 880/1600/1600/4000

Table 1 BSC configurations

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To ensure full LAPD signalling capacity for combined BSC3i/TCSM3i installation, there must be a certain number of working BCSUs in the master BSC. The exact number depends on the radio network configuration as follows:

For more information, see the following BSC/TCSM product descriptions:

• Product Description of Base Station Controller BSC3i • Product Description of Base Station Controller BSC2i, BSCi

Abis maximum capacity

• Abis maximum capacity depends on many factors, for example: • Use of AMR HR or traditional HR • EDAP pool size used for EDGE • GPRS territory setup (size and limits) • Use of compressed Abis setup

• The use of AMR HR allows to maximize the number of voice channels and still maintaining the voice quality on a controlled level. 32kbit/s LAPD TRX signalling channels are recommended when utilizing AMR. As traditional HR typically requires smaller 16kbit/s LAPD TRX signalling channels, small amount of additional capacity can be used for voice when using traditional HR. The voice quality of traditional HR is not as good as with AMR HR.

• When needed the Compressed Abis setup can free capacity for additional EDAP pool channels or for additional TRXs. Compressed Abis reduces the capacity of an individual TRX by subtracting the LAPD capacity from TCH capacity.

• The use of flexible GPRS territory allows to adapt the Abis for different voice/data ratios dynamically.

For additional details, calculations and examples concerning Abis capacity, see Com-pressed Abis time slot allocation and Allocation of Abis time slots under section Time slot allocations in BSS.

For the best transmission economy, the PCM lines should be packed as full as possible. The methods of doing this are explained later.

AMR Half RateIntroduction of Adaptive Multi-Rate codec (AMR) Half Rate (HR) causes increased load in measurement reporting; therefore it can happen that a capacity of 16 kbit/s LAPD sig-nalling link is not sufficient in all cases. When the TRX contains merely HR or dual rate (DR) traffic channel (TCH) resources, the situation becomes even worse if the stand-alone dedicated control channels (SDCCH) have also been configured on the TRX. Therefore a 32 kbit/s LAPD link has been introduced to support the telecom signalling.

AMR codecs support in Nokia BSC and TCSM2/TCSM3i:

• All Nokia BSCs have full AMR support, except 7.95 kbit/s on HR channel. • Nokia TCSM2 and TCSM3i have full AMR support.

RNW configuration Number of BCSUs

1 TRX under BTS 5

6 TRXs (2+2+2) under BTS 1

Table 2 Number of BCSUs in combined BSC3i/TCSM3i installation

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• A TC PCM pool type is needed for transcoder configuration on the A interface. The AMR pool type, which supports AMR FR and AMR HR (pool 23 in TCSM2 and pools 23, 28 and 32 in TCSM3i), is implemented.

• Submultiplexing on highway PCM is 8/16 kbit/s, for example if AMR FR (16 kbit/s) is used on the Abis interface, the Ater interface rate is also 16 kbit/s.

• Correspondingly if AMR HR (8 kbit/s) is used on the Abis interface, the Ater interface rate is 2 x 8 kbit/s (the BSC transmits ones (= bit value 1) on the unused 8 kbit/s sub-timeslot).

With the AMR HR implementation, the BSC's maximum channel capacity of 4096 must be taken into account in dimensioning the number of TRXs in the BSC. For example the traffic processing capacity of the BSC2i supports 512 full rate TRXs or 256 half rate TRXs. Connectivity for 512 half rate TRXs is available with Soft Channel Capacity.

BSC TRX capacity can be maintained by using FR to HR load threshold parameters.

The maximum channel capacity of the BSC3i is 5280. BSC3i supports up to 2000 full rate TRXs or up to 1000 half rate TRXs. Connectivity for 2000 half rate TRXs is available with Soft Channel Capacity.

2.3 A and Ater BSC interfaceIn TCSM2, the A and Ater interfaces are supplied by ET2E/ET2A plug-in units with two PCM connections per board). Connector line impedance on 2 Mbit/s trunk lines is either 75 ohm (coaxial, asymmetric) or 120 ohm (pair, symmetric).

In TCSM3i, the A and Ater interfaces are supplied by ET16 plug-in units. In TCSM3i for combined BSC3i/TCSM3i, it is also possible to use STM-1/OC-3 (SDH/SONET) optical interface, in which case the A interface is supplied by ETS2 plug-in units.

The transmission performance of the interfaces is supervised by the BSC according to ITU-T recommendations.

2.4 Interface to the OMC directionThe OMC connection of the BSC can be one of the following:

• one 2 Mbit/s A interface time slot • one ethernet interface according to IEEE 802.3, either 10Base5 (AIU), 10Base2

(COAX) or 10BaseT (TPI); the data rate is 10 Mbit/s • an X.25 data terminal equipment (DTE) interface with the alternatives V.24, V.35,

V.36 and X.21.

Redundant OMC connections can be achieved by using, for example, X.25 on two separate trunk lines.

2.5 LAN interfacesVarious types of IP traffic are transported between network elements with IP connec-tions. The three main types that are relevant to transmission planning are:

• NetAct™ link (O&M traffic)There is O&M traffic in every network element.

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• Signalling traffic with other network elementsThe Lb interface towards a stand-alone Serving Mobile Location Center (SMLC) and BSC-BSC interface with Dynamic Frequency and Channel Allocation (DFCA) or other LAN connections can be used in the future.

• Packet trafficIP connectivity can be used for Gb interface with packet traffic. Some other function-alities will also use IP connectivity for packet traffic in the future.

Before starting to build the IP network, see BSC site architecture and IP network topology in BSC Site IP Connectivity Guidelines. See also Nokia Packet Backbone for Mobile Networks, available in 3G Core Network System Information Set.

For an overview, see BSS transmission.

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3 TC configuration

3.1 Installations with TCSMTCSM refers to the second and third generation BSS transcoder-submultiplexer equip-ment, which provides transcoding for traffic channels in the GSM/EDGE networks.

The TCSM is located between the MSC and the BSC. Normally, to save transmission capacity, the equipment is located at the MSC site. It can, however, also be situated at the BSC site.

With reference to the 3GPP TS 08.08, the circuit types listed in table Circuit types of TCSM2 and TCSM3i are available for use in connection with the TCSMs.

Circuit type Supported channels and speech coding in TCSM2

Supported channels and speech coding in TCSM3i

A FR speech, EFR speech, FR data (14.5, 12, 6 or 3.6 kbit/s)

B HR speech, HR data (6 or 3.6 kbit/s)

C FR speech, EFR speech, HR speech, FR data (14.5, 12, 6 or 3.6 kbit/s), HR data (6 or 3.6 kbit/s)

D FR speech, EFR speech, HR speech, FR data (14.5, 12, 6 or 3.6 kbit/s), HR data (6 or 3.6 kbit/s), HSCSD max 2 x FR data (14.5, 12 or 6 kbit/s)

E FR speech, EFR speech, HR speech, FR data (14.5, 12, 6 or 3.6 kbit/s), HR data (6 or 3.6 kbit/s), HSCSD max 4 x FR data (14.5, 12 or 6 kbit/s)

F AMR speech

G 1 (FR) / 16 kbit/s

3 (DR) / 16 kbit/s

5 (EFR&FR) / 16 kbit/s

7 (EFR&DR) / 16 kbit/s

20 (EFR&DR&D144) / 16 kbit/s

23 (AMR) / 16 kbit/s

28 (EFR&DR&AMR&D144) / 16 kbit/s

H 10 (HS2) 2 x 16 kbit/s

21 (HS2&D144) / 2 x 16 kbit/s

I 13 (HS4) 4 x 16 kbit/s

22 (HS4&D144) / 4 x 16 kbit/s

32 (EFR&DR&AMR&HS4&D144) 4 x 16 kbit/s

Table 3 Circuit types of TCSM2 and TCSM3i

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Table Matching of circuit type and circuit pools shows the matching of pools from the point of view of the TCSM2/TCSM3i and BSC. For the numbering of the pools, see 3GPP TS 48.008.

AMR implementation with TCSM2A TC PCM type is needed in transcoder configuration of the A interface. The basic AMR type, which supports AMR FR and AMR half rate (HR, pool 23), is implemented for TCSM2.

Submultiplexing on highway PCM is 8/16 kbit/s. For example if AMR FR (16 kbit/s) is used in the Abis interface, then the Ater interface rate is also 16 kbit/s.

Correspondingly if AMR HR (8 kbit/s) is used in the Abis interface, the Ater interface rate is 2 x 8 kbit/s (BSC transmits ones (= bit value 1) on the unused 8 kbit/s sub-timeslot).

The circuit pools 4, 6, 8, 9, 11, 12, 15, 16, 17, 18, and 19 are not supported, but they are all included in at least one of the supported pools (18 in 21, for example). The circuit pools 14 and 24-32 are not supported at all.

AMR implementation with TCSM3iThe AMR type supporting AMR FR, AMR HR, and EFR is implemented for TCSM3i. Pools 28 and 32 are supported in TCSM3i. The 8 kbit submultiplexing (pool 2, HR only) is not supported in TCSM3i.

Pool configuration with Multimedia Gateway (MGW)The BSC can be directly connected to the transcoder in the MGW using the Ater in MGW feature. As a rule, MGW supports the same pool configuration as the BSC except 8 kbit/s submultiplexing on the Ater interface.

Check the detailed pool list in Multimedia Gateway (MGW) Functional Description in MGW documentation.

TCSM type BSC circuit pool numberTranscoder circuit type TCSM2/TCSM3i

TCSM2, TCSM3i 1 A/G

2 B/-

3 C/G

5 A/G

7 C/G

10 D/H

13 E/I

20 C/G

21 D/H

22 E/I

23 F/G

TCSM3i 28 -/G

32 -/I

Table 4 Matching of circuit type and circuit pools

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O & M arrangement with TCSMA LAPD-type 16 kbit/s data channel is dedicated for TCSM fault monitoring and control between the BSC and the TCSM. This channel uses capacity from the TSL1 (bits 1 and 2). Each TCSM has its own LAPD channel towards the BSC. All maintenance operations are carried out over the LAPD channel (supervision and configuration commands). A local user has access to the transcoder site via an interface on the TCSM.

O & M arrangement with MGWThere is no O & M LAPD link between the BSC and MGW so the BSC does not control the MGW at all. The operator is responsible for creating identical transcoder configura-tions in both BSC and MGW.

TCSM2 capacityOne rack houses 8 pre-installed Transcoder cartridges (TC1C) and 4 Exchange Terminal cartridges (ET1TC). The maximum capacity of a rack is 8 x 120= 960 TCHs in the case of 16 kbit/s submultiplexing, and 8 x 210 = 1680 TCHs in the case of 8 kbit/s submultiplexing.

If signalling time slots (TSL16) are not used for speech channels, the maximum capacity is 116 TCHs (16 kbit/s submultiplexing).

TCSM3i capacityOne rack in the TCSM3i cabinet consists of six Transcoder cartridges (TC2C). 16 TR3E/A plug-in units are housed in each cartridge.

The maximum capacity of a cabinet is 6 x 1920 = 11520 TCHs (ETSI) or 6 x 1520 = 9120 TCHs (ANSI).

3.2 TCSM3i versus TCSM2The major differences between the TCSM3i and TCSM2 are:

• TCSM3i has 12 times more capacity compared to current TCSM2 implementation. • Redesigned hardware makes TCSM3i more compact. • Instead of several plug-in units, one transcoder based on TCSM3i hardware tech-

nology consists of one plug-in unit. • TCSM3i allows more flexible pool usage in A-interface. • TCSM3i does not support 8 kbits/s submultiplexing on the Ater interface.

When the traffic capacity of a TCSM2 is dimensioned to a low value, transmission capacity may be saved. This requires that unused time slots of existing BSC-TCSM highways are multiplexed by an external cross-connect device. One option is to use DN2 equipment, as illustrated in section Digital node equipment DN2.


3.3 TCSM3i versus TCSM3i for combined BSC3i/TCSM3i installationThe major differences between the TCSM3i and TCSM3i for combined BSC3i/TCSM3i installation are:

• it is possible to use optical STM-1/OC-3 interface in combined BSC3i/TCSM3i instal-lation

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• in combined installation the transcoding capacity of a TCSM3i can be shared by up to 96 BSCs (ETSI) or 24 BSCs (ANSI)

3.4 TCSM versus transcoder in MGWThe major differences between using the TCSM and the transcoder in the MGW are:

• MGW and TCSM3i do not support 8 kbit/s submultiplexing on the Ater interface, but TCSM2 does.

• MGW does not support the same pool set as the BSC. • Since there is no O & M link between the BSC and MGW, the transcoding alarms

have to be monitored and software changes performed in the MGW. Furthermore, BSC-originated routine testing and diagnostics cannot be used with MGW.

• Exactly the same pool configuration is created to the BSC and MGW separately. • No transcoding related hardware has to be created in the BSC.

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4 BTS configurationThe BTS transmission subsystem is used in the BTS as an interface to the Abis links towards the BSC. FC and FXC units are used in the UltraSite and MetroSite BTSs, and FIEA, FIPA, FIFA, FIYA and FIQA plug-in units in Flexi EDGE BTS.

MetroSite, Flexi EDGE and UltraSite support both full rate (FR) and half rate (HR) speech coding. As the TRX supports both FR and HR framing at the same time, call by call (dual mode operation), a given bit pair in the Abis trunk can either form two HR speech channels or a single FR speech channel.

AMR codecs are supported by different Base Station generations as follows:

• MetroSite, Flexi EDGE and UltraSite base stations have full AMR support. • Talk-family BTS has AMR support for FR modes 4.75, 5.9, 7.4 and 12.2 as well as

for HR modes 4.75, 5.9 and 7.4; with this approach, the link adaptation between full scale of FR modes and almost full scale of HR can be achieved.

For a description of the MetroSite, UltraSite, and Flexi EDGE base station, see the fol-lowing BSC/TCSM product descriptions:

• MetroSite EDGE BTS in MetroSite EDGE BTS Product Documentation. • UltraSite EDGE BTS Product Description in UltraSite EDGE BTS Product Docu-

mentation. • Flexi EDGE BTS Product Description in Flexi EDGE BTS Product Documentation

Logical BTS configurationsThere is no limitation for sector configurations in the MetroSite base station, because each transceiver has an antenna of its own. For diversity, however, more than one TRX is needed per sector.

Dual band BTS configurationThis configuration allows you to use GSM/EDGE 900/1800, 800/1800, and 800/1900 TRX combinations in the same cabinet. The BCF function is common to both bands. The site architecture allows separate or combined TRX configurations. The limitations con-cerning different logical BTSs under the same BCF are also valid for dual band opera-tion.

Combined BCF and TRX functionsThe TRX can be configured as a master or as a slave. The master TRX handles both O & M functions and Abis interface functions.

Chained BTSsThe MetroSite can be concatenated by an extension kit, which contains D-bus and syn-chronising the frame clock between BTSs. Each extension cabinet saves you the cost of one FC or FXC unit. The O & M functionality is centralised to the master cabinet.

You need only one extension cable between cabinets. The maximum number of combined MetroSite BTSs is 3, and the total length of bus cable is limited to five metres. The TRX addresses are sequentially numbered and configured automatically via an extension cable.

The cells can be shared between cabinets to allow flexible upgrading from, for example, 2 + 2 TRXs to 4 + 4 TRXs.

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Only the FXC transmission card can be used with chained MetroSite EDGE BTS con-figuration.

Dynamic AbisDynamic Abis allocation is a solution for higher data rates of EGPRS to ensure cost-effi-cient and flexible Abis transmission capacity addition. The Dynamic Abis functionality allocates Abis transmission capacity to cells when needed instead of reserving a full fixed transmission link per TRX.

As data rates can vary between 8.8 and 59.2 kbps per radio time slot, traditional static Abis allocation does not use transmission resources efficiently. Dynamic Abis uses the existing Abis more efficiently by splitting PCMs into permanent time slots for signalling and a dynamic pool for data. The pool can be shared by a number of transceivers. The Dynamic Abis transmission solution saves a lot in the Abis transmission expansion cost as it allows Abis dimensioning to be performed near the average data rates instead of peak rates. This also applies to the number of 2M BSC interfaces needed.

Dynamic Abis interworking

• (E)GPRS(E)GPRS territory method and EGPRS use the Dynamic Abis.

• Compatibility with base stationsDynamic Abis is compatible with MetroSite, UltraSite EDGE, and Flexi EDGE base station EDGE TRXs.

4.1 TRU transmission unit descriptionsThe Transmission Unit (TRU) is a group of different units making it possible to build various kinds of network topologies with different types of electrical interfaces and trans-mission media. These boards are located in the Common Unit subrack of the Talk-family BTSs.

Either one or two slots for TRU units are reserved in the Common Unit subrack of the Talk-family BTS.

TRUA/BThe TRUA/B is intended for all kinds of BTS E1 PCM networks (2 Mbit/s).

The TRUA/B has three 2 Mbit/s interfaces which can be installed for both types of line impedance (75 ohm or 120 ohm) by jumper settings individually. The drop/insert function where selected time slots are branched to the BTS can be executed at the 8 kbit/s level. Other time slots are connected automatically straight through between inter-faces one and two.

Repeater function in the BTSThe Talk-family BTS can be a part of a line repeater chain without any external line repeater. Two of the BTS Abis interfaces can tolerate 20 dB attenuation. The maximum

ETSI

PCM (E1)

ANSI

PCM (T1)

Talk-family TRUA TRUE

Table 5 The transmission units in the Talk-family BTSs

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distance between these Abis interfaces and the next line repeater depends on the cable type used. A usual distance with symmetrical cables is about one kilometre. Distances greater than that can be achieved by placing a line repeater in line within one kilometre from the BTS site.

If only one unit is installed, the third Abis connection in the BTS can tolerate 6 dB atten-uation and it has a maximum range of 300 metres. If two transmission units are installed, the BTS has four external 20 dB Abis interfaces.

Signal bypass repeater functions in the BTSWhen a sustained power failure takes place in a Talk-family BTS, it is necessary to maintain transmission to other pieces of BTS equipment in the multidrop configuration. This is possible if a terminal repeater, for example, DL2E, is fitted in front of the first BTS in the network. The terminal repeater generates the current needed in the BTS for the signal regeneration. The need for additional line repeaters depends on the distance between the BTS and the terminal repeater.

The bypass function is possible for two 2 Mbit/s interfaces (IF1 and IF2) with twisted pair connections of 120 ohm in the transmission unit. During the bypass function, time slots are connected straight through the BTS from the first interface to the second without any cross-connections.

4.1.1 O & M arrangement of transmissionThe standard control functions of the Nokia equipment are supported. Transmission equipment can be controlled remotely from the network via the Abis interface. The BTS provides a transparent two-way path for remote commands of transmission control and responses.

When the transmission equipment is operated locally with a service terminal, the polling of the transmission equipment will automatically be disabled. This operation prevents the generation of unnecessary alarms that would otherwise be sent to the BSC from the Base Control Function Unit (OMU).

Transmission equipment can be configured to be polled, that is, managed by BSC or BTS. In BTS polling, the BTS polls its local network elements and nearby sites, for example the microwave radio (repeater). The BTS sends a status inquiry to the polled equipment. The BTS then transmits the collected Q1 information to the BSC through a LAPD link using the OMUSIG channel, usually at a bit rate of 16 kbit/s. The BSC forwards the data to NetAct. In BSC polling, the BSC is the master which collects data from all the Q1 transmission equipment connected to it and then transmits the data to NetAct.

The local BTS transmission equipment is configured and controlled via the service terminal or the man-machine interface (MMI).

All cabinets have a Nokia-specific external control port (Q1) for the operation and main-tenance of the external transmission equipment. Flexi EDGE BTS offers a Local Man-agement Port (LMP) for the local connection of Element Manager via Ethernet.

4.1.2 Options for transmission

Duplicated transmission board (option)It is possible to use a second, optional transmission board (TRUx) to expand the number of possible transmission links. This option is not available for the Mini BTSs.

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Integrated radio relay equipment (option)The BTS is compatible with the Nokia Digital Radio Relay Equipment (DMR18-38I). The Talk-family large-capacity BTSs can be equipped with up to two integrated radio relay equipment models that replace a part of the equipment inside the BTS cabinet and need only the compact microwave heads to be installed externally.

The incorporation of the two links makes it possible to build a drop-and-insert microwave relay network for the BTS units when they communicate with the BSC.

A single piece of radio relay equipment carries up to four 2 Mbit/s Abis links. It is effec-tively transparent because it offers the same capacity and configuration possibilities as the cabled Abis connections. Any of the 2 Mbit/s signals, or a part of the 2 Mbit/s signals at 8 kbit/s level, can be dropped to the BTS, and the rest of the capacity is available for other BTSs. The frequency range of the radio relay is 18/23/38 GHz.

The integrated radio relay equipment is connected to the BTS and the microwave head with two cables.

The option is not available for the Mini BTSs.

External radio relay equipment (option)All BTSs are compatible with most of the standard 2 Mbit/s radio relay equipment supplied by different manufacturers. When the external radio relay equipment is used, all the equipment must be fitted externally to the BTS cabinet and cabled to the Abis ports. The BTS cabinets are equipped with terminals to supply external power for the radio transmission equipment. The control is provided through a 9-pin D-connector.

4.2 FC and FXC unitsThe FC and FXC are transmission units for MetroSite and UltraSite BTSs.

In the MetroSite BTS, you can house either a single FXC unit or single FC unit. UltraSite BTS has slots for up to four FXC units, or one FC unit. In UltraSite BTS, you should always use an FXC unit for flexible capacity growth.

FXC units with cross-connectionThe FXC units include a very powerful cross-connection system with a granularity of 8 kbit/s.

• FXC E1/T1 (4 x 2M/1.5M), symmetric wire line transmission, 120/100 Ohm • FXC E1 (4 x 2M), asymmetric wire line transmission, 75 Ohm • FXC RRI (16 x 2M), radio link transmission (Flexbus connection for 2 outdoor units) • FXC STM-1: Unit with 2 STM-1 interfaces for fibre optic cable (L-1.1 laser interface),

SDH standard compliant, add/drop and cross-connection at VC-12 layer, synchroni-sation functions.

• FXC Bridge: Bridge for the signals between the SDH part of the BTS and the PDH cross-connect of the FXC equipment. Includes Q1 management and cross-connec-tion on 8 kbit/s, 16 kbit/s, 32 kbit/s and 64 kbit/s granularity.This unit is always used with the FXC STM-1 card.

FC unitsThe FC units were designed to be used with MetroSite BTS. With UltraSite BTS, the use of an FXC unit is recommended because of EDGE evolution.

One FC unit is available:

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• FC STM-1: a unit with 2 STM-1 interfaces for fibre optic cable (L-1.1 laser interface), SDH standard compliant, add/drop and cross-connection at VC- 12 layer, synchro-nisation functions (only to be used with MetroSite BTS; CXM 4.1 SW or later is required).

Combined O & M and Telecom signallingWith combined O & M and Telecom signalling, you can use the transmission capacity more efficiently. MetroSite BTS can be configured either as a master or a slave of a BTS. The master TRX handles both the Telecom and O & M functions, which facilitates the combination.

The logical links are identified by the Service Access Point Identifier (SAPI). The SAPI values and priorities have been defined in the GSM specification 08.56. In addition, an access channel is defined for the establishment of the O & M link.

4.3 FIEA, FIPA, FIQA, FIYA and FIFA unitsFlexi EDGE BTS is the future macrocellular EDGE BTS of BTS portfolio. Flexi EDGE BTS is built from two different modules: the System Module, housing all baseband and transport processing functions as well as BTS O&M, and the Radio Frequency Modules, housing the transceivers and power amplifiers. A transport plug in unit is part of the System Module. The following variants are or will be available:

• FIEA: 8 x E1 coaxial 75 Ohms • FIPA: 8 x E1, T1 balanced 120/100 Ohms • FIQA: 4xE1/ T1, balanced with 120/ 100 Ohms plus 2x FE 100 BaseT, 1x GE (SFP) • FIYA: 4x E1, coaxial 75 Ohms plus 2x FE 100 BaseT, 1x GE (SFP) • FIFA: 2 x Nokia Flexbus Interfaces (16x 2 Mbit/s)

To keep the initial roll-out costs low and on the other hand to offer possibilities for future growth, transmission interface units start with basic functionality with two E1/ T1 inter-face or one Flexbus interface. Further functionality can be easily added later on by addi-tional software licence. The following growth paths with advanced features are available by software licence:

• additional blocks of two E1/T1s • second Flexbus • loop protection (slave) • cross-connection and grooming • CESoPSN using Fast Ethernet or Giga Ethernet interfaces on FIQA, FIYA

Flexi EDGE BTS and the transmission interfaces are managed by the same Element Manager. However, Nokia Flexbus for Nokia Flexihopper and Metrohopper requires an own Element Manager.


SAPI 0 Radio signalling procedures Priority 1

SAPI 62 Operation and maintenance Priority 2

SAPI 63 L2 management (Access channel)

Table 6 SAPI values and priorities

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4.4 Microwave radio relaysUltraSite, MetroSite and Flexi EDGE base stations can include a radio relay- specific indoor interface unit that can connect one or two radio relay outdoor units to the BTS. In UltraSite and MetroSite the indoor unit is FXC RRI and in Flexi EDGE it is FIFA. All signal connections (n x 2M, Q1) between the BTS and the indoor unit go through the BTS motherboard.

Up to two radio outdoor units can be connected to MetroSite BTS, and up to eight to UltraSite BTS. The power supply of MetroSite BTS can support two Nokia MetroHopper or Nokia FlexiHopper (Plus) radio relay units.

Nokia FlexiHopper (Plus) radio relay unit supports the capacities 2 x 2, 4 x 2, 8 x 2 and 16 x 2 Mbit/s. The hop lengths can vary between approximately three and 70 kilometres, with the radio frequencies 38 to 7 GHz, respectively.

The Nokia MetroHopper radio relay unit's capacity is 4 x 2 Mbit/s and its hop length is up to 1 km.

Nokia FlexiHopper XC radio relay unit's capacity is 40 x 2 Mbit/s and it is currently avail-able for the 38 GHz frequency band with 16-state modulation (16-QAM) and can be used with UltraSite and MetroSite base stations. The indoor unit of FlexiHopper XC is Nokia FlexiHub.

Stand-alone radio relays are interfaced via standard n x 2M and Q1. Power is supplied directly to the radio, not from the BTS.

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GPRS and the Gb interface

5 GPRS and the Gb interfaceThe BSC provides a Gb interface towards the General Packet Radio Service (GPRS) core network (Serving GPRS Support Node, SGSN). Nokia Siemens Networks offers GPRS support in the BSS with powerful radio resource management algorithms, opti-mised BSS network topology and transmission solutions to ensure optimal investment for operators and high capacity and quality of service for users. The GPRS core network is accessed from the host GSM network via the BSC. This is accomplished by using Packet Control Units (PCU) in the BSC. The Nokia PCU has full support for extensive GPRS radio resource control transactions. This embedded PCU solution provides the most cost-effective solution for the operator. The Gb interface is implemented using Frame Relay (FR) or IP connectivity.

5.1 Gb over Frame RelayFrame Relay can be either point-to-point (BSC-SGSN) or there can be a frame relay network located between the BSC and SGSN. The protocol stack comprises BSSGB, NS and L1. Frame Relay as stated in standards will be part of the Network Service (NS) layer. On top of the physical layer in the Gb-interface the direct point-to-point Frame Relay connections or intermediate Frame Relay network can be used. The physical layer is implemented as one or several E1 PCM lines with G.703 interface in ETSI envi-ronment or with T1 PCM lines in ANSI environment. The FR network will be comprised of third-party off-the-shelf products. The following figures show examples of Gb interface transmission solutions.

Figure 2 Through-connected channels configured in the transcoders and in the MSC switching matrix

Spare capacity of the Ater and A interfaces is used for the Gb. The Gb timeslots are transparently through-connected in the TCSM and in the MSC. If free capacity exists, it is best to multiplex all Gb traffic to the same physical link to achieve possible transmis-sion savings. In many cases the SGSN will be located in the MSC site and thus this mul-tiplexing has to take place there as well. Normal cross-connect equipment like for example Nokia DN2 can be used for that purpose. The following figure shows how the same can be achieved in a different way, by using additional equipment between the transcoder and the BSC.

Gb Interface

Ethernet Switch

GGSN #1GGSN #2

MSC

SGSN

Transcoders

MSC/SGSN site

PCMFrameRelay

BSC

BSC

BSCAbis

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Figure 3 GPRS traffic multiplexed on the same physical connection as used for the GSM traffic on the Ater interface

Another solution is to concentrate GPRS traffic via one network over the Gb interface, with the transmission network providing a point-to-point connection between the BSC and the SGSN.

Figure 4 GPRS traffic concentrated and carried over the Gb interface in a packet data network

Similarly, a Frame Relay network can be used. The Gb interface allows the exchange of signalling information and user data. It also allows many users to be multiplexed over the same physical resources.

Gb Interface

Ethernet Switch

GGSN #1GGSN #2

MSC

SGSN

Transcoders

MSC/SGSN site

BSC

BSC

BSCAbis

FrameRelay

2 Mbit/s PCMAter + Frame Relay

MUX

Gb Interface

Ethernet Switch

GGSN #1GGSN #2

MSC

SGSN

Transcoders

BSC

BSC

BSC

MSC/SGSN siteAbis

FR Switch

FR Switch

Packet DataNetwork

(FR, ATM, etc.)

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GPRS and the Gb interface

Figure 5 GPRS traffic carried over dedicated 2 Mbit/s PCM links

5.2 Gb over IPThe increased demand for packet switched traffic transmission cost efficiency can be met by the deployment of IP in the transmission network. IP can replace Frame Relay networks as the transport medium in the sub-network service layer. Network Service Control Protocol Data Units (PDU) are incapsulated within the UDP datagrams when the IP transport medium is in use. When IP is taken into use, packet-based traffic does not go through the circuit-based Pulse Code Modulation (PCM) network, but IP network instead. The introduction of IP enables to build an efficient transport network for the future IP-based multimedia services, and helps to reduce the transmission costs.

The IP transport can be used in parallel with FR under the same BSC and Base Station Controller Signalling Unit (BCSU). One Network Service Entity (NSE) and each PCU always uses either one, IP or FR. Inside one BCSU, separate PCUs can use different transmission media. In the BSC, there is always one local IP endpoint per PCU. Gb over IP supports both dynamic and static configuration. In dynamic configuration, only one IP address and UDP port pair of remote end SGSN is needed to establish NS-VC config-uration on Gb. Static configuration can be used, if it is seen feasible to have fixed con-figuration between BSCs and SGSNs. This might be feasible when the operator has a direct cable connection between the BSC and the SGSN.

Figure 6 GPRS traffic carried over the Gb interface with IP

Gb Interface

Ethernet Switch

GGSN #1GGSN #2

MSC

SGSN

Transcoders

BSC

BSC

BSC

MSC/SGSN siteAbis

PCM links

Frame Relay

Gb Interface

Ethernet Switch

GGSN #1GGSN #2

MSC

SGSN

Transcoders

BSC

BSC

BSC

MSC/SGSN siteAbis

Router

RouterGb over IP

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5.3 GPRS capacityThere are two generations of Nokia PCUs:

• The first generation PCUs are PCU-B in BSC3i and PCU, PCU-S and PCU-T in older BSCs.

• The second generation PCUs are PCU2-D in BSC3i, and PCU2-U in older BSCs.

The second generation PCU2s are the preferred option and mandatory GPRS CS3 & CS4 product.

Nokia Packet Control Units are state-of-the-art plug-in units with high capacity and reli-ability. They control the GPRS radio resources, receive and transmit TRAU frames to the BTSs and Frame Relay packets to the SGSN. High capacity is provided through a state-of-the-art PCU design and with the possibility of future extension. N + 1 redundant PCUs achieve high reliability.

The Nokia solution provides full TRX capacity with very high reliability and performance. One PCU is installed into every BCSU for redundancy reasons (N + 1). Additionally there is a possibility to add a second PCU per each BCSU to increase the packet switched capacity in the BSC. In BSC3i, one physical plug-in unit consists of two logical PCUs.

The PCU removes the unnecessary TRAU overheads coming from the Abis interface and assembles the data into frame relay for the Gb interface.

Considering the transmission protection it also needs to be decided whether two Frame Relay bearers are needed for each logical PCU using different ETs or if the transmission is protected with cross-connection equipment.

It is possible to multiplex more than one Gb interface directly to the SGSN, or multiplex them on the A interface towards the MSC and from there cross-connect them to the SGSN. The PCM carrying the Gb timeslots can be one of the BSC's existing ETs or an ET can be dedicated to the Gb interface.


PCU2-E PCU2-D PCU-B

BTS Ids 384 128 64

Cells/Segments 1024 64 64

TRXs 1024 256 128

TCHs (16 knit/s Abis TSL

1024 256 256

Table 7 Connectivity of logical PCUs

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BSS redundancy configurations

6 BSS redundancy configurationsDepending on availability targets, BSS networks can be designed with redundant trans-mission paths or equipment.

Redundancy switchover is triggered by pilot bits or directly by equipment alarm condi-tions.

As a consequence of availability objectives, it is recommended that at least two TCSM units are equipped per BSS even if the required traffic capacity could be handled by one unit. Yet, in some cases also external redundancy arrangements can be considered as described below.

Abis loop with MetroSite, UltraSite and Flexi EDGE base stationsThe Abis loop protection is a very effective way to avoid a single faulty transmission link or weather (rain) affecting the cellular network performance. The use of pilot signals for protection switching and MCB & LCB for synchronisation control are applied similarly. For more information, see Radio transmission.

The UltraSite integrated transmission node of the FXC units can operate as a loop master station or a slave station. The single FXC unit in a MetroSite can operate as a loop slave. The Flexi EDGE BTS can operate as a loop slave.

Radio link hop protectionThe hot standby mechanism is a commonly applied system to protect against HW failures of radio outdoor units whenever a chain of BTSs is connected together using radio transmission.

Figure 7 Radio link hop protection


BSC

BTS

FIU19E

1+1 HSB

FXC RRI

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7 Operation and maintenance of transmission equipmentThe ability to monitor and control the whole network is one of the most important features for the GSM operator. To facilitate this, all elements of the GSM network, the BSS, the MSC, the HLR and the VLR, are connected to the NetAct for network monitor-ing and control.

The connection to the NetAct is made via Q3 interface. For transmission equipment in general, typically fault management and performance management are supported. For TRU, DN2 and DMR, basic G.821 signal quality counters are supported. For Nokia FXC and FC transmission equipment as well as Flexi EDGE transmission units, the full or partial set of G.826 signal quality counters are supported. Configuration management for FXC and FC transmission equipment is supported by launching an element manager integrated from the NetAct.

The NetAct management functions include fault management (FM), performance man-agement (PM) and configuration management (CM) of network elements.

The BSC can support up to 56 Q1 supervisory channels. Also, a maximum of 1024 separate transmission equipment with Q1 interface can be supervised, including the transmission equipment supervised by the BSC and the BTS. The DN2, TRU, Nokia FXC equipment and Flexi EDGE transmission units are able to transfer Q1 data between TSL0 and some other time slot within E1 (in many cases TSL31 is used), or to the Q1 overhead channel of a Flexbus signal.

7.1 Supervisory channelsBSCThe BSC is connected to the NetAct with a dedicated X.25 connection, using a trunk time slot for the BSC-MSC- NetAct path, or a LAN connection using Ethernet. The NetAct connection can also be duplicated for protection. Direct access to packet network is also available.

The supervisory channel for BSC-supervised transmission equipment is carried in a PCM time slot. Remote maintenance or control of a piece of transmission equipment can be done with BSC MML commands, or by launching the equipment element managers integrated from the NetAct.

BTSA BTS is connected via the BSC to the NetAct. The BTS-BSC path is realised through a LAPD channel and the path BSC-MSC-NetAct by using an X.25 channel or LAN.The transmission equipment can be connected to BTS supervision in different ways. The connection is an internal Q1 bus connection if the equipment is integrated in the BTS.

Remote maintenance or control of a piece of transmission equipment can be done with BSC MML commands or by launching the equipment element managers integrated from the NetAct.

TCSMFor the transcoder's remote supervision and control, one LAPD-type data channel per TCSM is used between the BSC and the TCSM. This channel uses the 16 kbit/s capacity

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Operation and maintenance of transmission equipment

from trunk time slot 1. BSC MML commands are used for supervision and control. The TCSM can be brought into test state and diagnostic tests can be run via the BSC.

MGWSupervisory channels are not supported.

Nokia Q1 managed transmission equipmentNokia Q1 managed transmission equipment, not integrated to a BTS, is managed remotely via a Q1 management channel. DN2 and MetroHub can pick up the Q1 man-agement channel from the PCM time slot. In some Nokia Q1 managed equipment such as FIU 19 and FIFA, the Q1 management channel must be connected to the equipment via a Flexbus overhead.

7.2 Local O & MBSCThe BSC has two V.24 local user interfaces.

BTSThe UltraSite BTS and MetroSite BTS has a V.24 local user interface. The interface is used for the BTS's own O & M and for the transmission equipment that is under BTS supervision. The FlexiEdge BTS has a Fast Ethernet interface used for BTS own O&M, including supervision of BTS integrated transmission.

TCSM2/TCSM3iA V.24 local user interface is available for each TCSM unit in a TCSM2/TCSM3i.

Transmission equipmentMost Nokia transmission equipment has a Q1 interface connector. The interface is com-patible with Nokia's Transmission Management System (TMS) protocol. The Nokia FXC/FC transmission equipment used with MetroSite, UltraSite or MetroHub, and the FIU 19 support the Nokia Q1 protocol that is an enhancement to the transmission man-agement system (TMS) protocol. The TMS comprises equipment ranging from a hand-held service terminal to a TMS-OS work station.

In Flexi EDGE, the Q1 interface is provided by the System Module. It also offers the LMP for the local management of the BTS and integrated transmission.

The Nokia Service Terminal is a tool for local configuration and maintenance of the TRU (and any other piece of Nokia transmission equipment). It is normally needed in the installation phase. The Service Terminal emulator is also available as PC software.

The DN2 manager is a special package of software for the DN2's local configuration management. It requires a standard PC with Windows. The DN2 manager allows easy and user-friendly configuration of transmission equipment (such as the DN2). It also includes software for service terminal emulation. Also TRU Manager, analogous to the DN2 Manager, is available.

For configuration management of the FXC/FC transmission equipment, a suite of element managers is provided. With UltraSite BTS, the element manager is UltraSite BTS Hub Manager. With MetroSite BTS, the transmission card managers are integrated in the BTS manager. With MetroHub, the element manager is MetroHub Manager.

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For Flexi EDGE, there is a common Element Manager for the BTS and transmission. However, the FIFA plug-in unit for Flexbus interfaces requires Nokia Hopper Manager.

7.3 Remote O & MThe NetAct remotely monitors and controls all GSM network elements including the TCSM and transmission equipment. To enable remote configuration and interrogation of the transmission elements involved, NetAct provides the remote use of node manag-ers, remote access via Service Terminal Emulator session, and remote access via MML session. The Transmission Node Management feature in NetAct offers the users access to node managers through a Node Manager Server.

As for the GSM OMC, the Nokia NMS is designed for full GSM network monitoring and control including transmission equipment.

Remote O & M requires a Q1 management channel between Node Manager Server (at NetAct) and the remote BTS. This Q1 channel reserves some capacity from the trans-mission path.


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Requirements on transmission network

8 Requirements on transmission networkThere are different scenarios for the realisation of the network:

1. The network is owned by a GSM operator and built along with the GSM BSS.It is possible to tailor the transmission of the network and O & M features exactly for GSM BSS.

2. The GSM BSS network is built by using the existing transmission network owned by the GSM operator.Old transmission equipment may set restrictions on the network use.

3. Transmission network capacity is only leased to the GSM operator.The GSM operator may not be allowed to supervise the transmission network directly. The actual network realisation may be unknown.

8.1 2 Mbit/s transmission pathsThe basic functional requirements on the 2 Mbit/s transmission paths are the following:

1. Time slot sequence must be maintained between the TCSM and the BSC and also between the BSC and the BTS.

2. It is recommended that the entire 2 Mbit/s stream is transparent between the TCSM and the BSC. If n x 64 kbit/s cross-connect devices are used (that is, fractional 2 Mbit/s), individual time slots may go out of service because of faults in certain trans-mission sections without the BSC, TCSM, or MSC directly detecting it. This fault condition will eventually be detected by failing calls in certain circuits.

3. DN2 loop protection prefers TSL0 to be transparent through the whole loop. Loop synchronisation control bits (master clock bit, MCB, and loop control bit, LCB) are normally transmitted using TSL0 bits. The TRUA, FXC/FC and FIxAunits have no restrictions; MCB and LCB can be transmitted in any time slot.

4. The EGPRS dynamic Abis pool (EDAP) size at the BSC and BTS, the time slot order in the BSC and BTS EDAPs and the EDAP starting time slot at BTS Abis allocation configuration and the incoming PCM to the BTS must be the same. Because of maintenance reasons, using the same timeslot allocation at the BSC and BTS is rec-ommended.If required, the EDAP starting timeslot at the BSC and the incoming PCM to the BTS can be different. Cross-connections are allowed, but the PCM frame or the n x 64 cross-connection must comply with the G.796 standard to maintain the octet sequence integrity of signals being cross-connected. EDAP and the TRXs tied to it (including traffic/EGPRS master and signalling channels) have to share the same monolithic Abis connection and PCM frames should have octet sequence integrity which can be achieved in two ways: a) Using 1-3 PCM lines that function according to the G.796 standard.

If the BTS capacity requires several PCM lines, a normal network delay variance between the PCM lines does not impact EDGE performance. The EDAP pool and the TRXs tied to it have to be located on a single PCM.

b) Using fractional E1, n x 64 k connection that complies with the G.796 standard. This means that this n x 64 k cross-connection block is handled with a single cross-connection command at every transmission node. This means that the EDAP pool and the TRXs tied to it must have a connection made with a single monolithic PCM or a single monolithic n x 64 k connection which comply to the octet sequence integrity of the G.796 standard. This structure needs to be main-

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tained throughout the network. In case the PCM line does not fulfil the octet sequence integrity requirement as specified in ITU-T G.796, a maximum of +/- three PCM frame delay between time slots is tolerated when the BSC SW S10.5 ED CD1.2 or newer release is being used. For more information on Dynamic Abis dimensioning, see Abis EDGE Dimen-sioning.

5. All E1 type interfaces conform to the ITU-T Recommendations G.703 and G.704 and the T1 interfaces conform to T1.403. All PCM interfaces are of repeater type, with no power feeding from the interface.

8.2 Synchronisation of BSS networkThe accuracy requirement for the primary reference clock (PRC), which is the master clock source of the whole network, is given in the ITU-T recommendation G.811. PRC equals the so-called Stratum 1 level clock and the requirement for the maximum long-term frequency departure of PRC is 1 x 10-11. In live networks, the network timing is affected by jitter/wander, but when the synchronisation of the network is correct, the same basic accuracy exists all over the network when metered over a long period.

The synchronisation of the entire network should be constructed so that the synchroni-sation delivery to all over the network is hierarchical (leveling). This reduces the possi-bility for the synchronisation to be corrupted. Even though most of the jitter is filtered when passing through transmission nodes (because of jitter transfer function), wander accumulates in synchronisation distribution chains; the limits for network jitter/wander are set in G.823.

The BSC clock system (CL3TG) is a Stratum level 3 synchronisation source, which works slaved to the traffic trunks or from external synchronisation source. Its control range is +/- 15 x 10 exp -6 and pull-in range +/- 2 x 10 exp -6. Accuracy of automatic control is 5 x 10 exp -10. If traffic trunks/external sources are deemed invalid, the clock enters plesiochronous operation. CL1TG has the same characteristics, but external syn-chronisation sources are not possible.

The BTS clock system can be divided into two independent parts, transmission node part and BTS internal. The clock of the transmission part is in Phase Locked Loop (PLL) to the incoming 2M signal (selectable to be synchronised to one of the 2 Mbit/s Abis sig-nal(s) or 2MHz synchronisation input, according to the priority list). This transmission part clock is used for timing the outgoing data of all the 2Mbit/s interfaces, including the one towards the other units of BTS.

The principle is that in the mobile network the synchronisation goes from MSC to BSC to BTS. However, in reality that synchronisation chain might be broken somewhere and, for example when using leased lines, the BTS may take the reference synchronisation from the transmission network of another operator. This does not harm the system if also that transmission synchronisation is originated from PRC and it is accurate enough; if occasional data slips occur, the mobile network system can tolerate it.

The same 1 x 10-11 long-term accuracy should exist all over the network if the network synchronisation is correct, only jitter/wander instability should exist. The long-term Abis interface accuracy requirement for BTSs is ± 0.015 ppm or better (1.5 x 10-8), which is 1500 times more loose than the PRC requirement. The GSM specification for the BTS Air interface accuracy is ± 0.05 ppm, which can be attained easily even with the worst case situation inside the BTS (RF part inaccuracy), if the Abis accuracy is ± 0.015 ppm.

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Because the Abis reference signal contains jitter/wander, it cannot be used directly for timing the BTS air interface. The jitter/wander instability must be filtered away before that. Therefore the BTS master clock (OCXO) is not in a phase-locked loop (PLL) to the incoming Abis signal coming from the transmission part, but it is using the Abis signal as a reference for 'calibrating' the BTS master clock periodically. There is a several-layer averaging algorithm which takes care of controlling the OCXO frequency and also of fil-tering away the effects of transmission jitter/wander.

Therefore, in practise the BTS runs fully under its own OCXO. The OCXO frequency is only adjusted automatically towards the 2M reference. This does not mean it is moved sharply to the point the adjustment calculations show, but there is a limit in the algorithm for the maximum frequency step in order to improve stability, that is, to reduce wander effects.

In case of synchronisation fault there are two cases for BTS operation:

• If BTS O & M signalling is cut, BTS OCXO starts an independent operation (free run) and takes no reference from the Abis interface. Then the mistuning towards the faulty reference is avoided and the air interface frequency is in most cases correct immediately after the O & M recovery.

• O & M signalling exists but the synchronisation reference is not correct. In this case the OCXO frequency will slowly start to drift towards the faulty synchronisation. Because the maximum adjustment step is limited, it may take several hours for the BTS to exceed the GSM specifications in the air interface

An alarm ('Difference in frequencies between the PCM and BTS master clock') is raised when the BTS clock unit notices a difference between the incoming 2M reference and the internal OCXO frequency - the difference limit for the alarm activation is 0.1 ppm. This means the synchronisation disruption is noticed at the BSC.

Then, if the BSC does not get a proper synchronisation reference, it leads in the long run to the situation that the BSC cannot feed BTSs with a reference which is accurate enough (0.015 ppm). The effect on BTSs is explained above.

8.3 Transmission delay of BSS networkRound trip delay refers to the amount of the time it takes for an electrical signal to travel from one end of a transmission medium to the other end and back.

The 3GPP TR 03.05 defines a maximum of 188.5 ms for a round trip delay from the A interface to the mobile station and back. The transcoder (TC) encoder/decoder loop alone requires about 30 ms. Taking all delay contributions into account leaves approxi-mately 6 ms for pure BSS transmission delay. Based on measurements the BSS works with acceptable KPIs up to 15ms one way delay at BSS.

The TC and the BTS framing unit together form a control loop for adjusting the transcod-ing and rate adaptation unit (TRAU) frame phase for a minimum delay. The stable oper-ation of this controller requires that the transmission delay between the TC and the BTS is less than 40 ms. This forms the upper limit to the delay.

A satellite circuit will nominally cause a delay of 260 ms. Therefore satellite circuits cannot be directly tolerated in a BSS network between the TC and the BTS. On the other hand, satellite circuits between the TC (for example a TC located at the BSC site) and the MSC are acceptable despite the added delay.

Satellite Abis or Ater circuits can be used as options. This requires certain system level changes and the whole BSS has to be reserved for satellite use.

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According to the ITU-T Recommendation G.114, the delay should be kept under 400 ms and echo cancellers should be used. When using satellite circuits, this value is exceeded.

Other GSM network-related traffic, such as signalling, accounting and O & M, can be transmitted through satellite circuits with due case by case consideration of delay. Channel throughput may suffer because of the protocol used.

In the case that acoustic echo cancellation (to cancel echo in the loop BSS - MS - BSS) is activated in the TCSM, its performance will degrade if the one-way delay between TCSM and BTS is more than 5 ms.

All pseudowire IP solutions and dedicated optimisation solutions (such as Abis optimis-ation solutions) add round-trip time (RTT) delay. The additional delay may have an impact on the LAPD and signalling performance, particularly in the case of congested Abis LAPD links. For more information on minimising the impact of the delay, contact your local Nokia Siemens Networks representative.

8.4 Error rate performance of BSS networkIn the BSS network the speech signal is transmitted at a speed of 16 kbit/s using FR transcoding, and at 8 kbit/s using half rate (HR). The transcoded signal has less bit redundancy than a normal PCM but still its robustness against transmission bit errors is good.

Speech quality is good if the ITU-T Recommendation G.821 performance objectives are met. If this is the case, fewer than 10% of one-minute intervals have a BER value higher than 10E-6, fewer than 0.2% of one-second intervals have a BER value higher than 10E-3, and fewer than 8% of one-second intervals have any errors.

For digital transmission links with a data rate of 1.5 Mbit/s and higher performance sta-tistics and objectives according to ITU-T Recommendation G.826 are applicable. The G.826 performance objectives are more stringent than G.821, which means meeting those will result in good speech quality, too. The performance measurement is block error based with G.826, in difference to the bit error based measurement with G.821. The ESR and SESR values gained by performance measurement from both standards can be approximated to each other, but are as result not the same.

At BER=10E-3 most transmission equipment starts sending 2M AIS (alarm indication signals). EDGE applications are more sensitive to degraded BER than GSM voice.

GSM signalling channels are robust to errors because of the protocol used.

8.5 Slips in transmissionSlips in the transmission equipment are caused by synchronisation problems. A 2M trunk signal frame (controlled) slip will affect two consecutive FR TRAU frame bits in roughly the same way as bit errors. Even modest slip rate requirements, 30 slips/hour, will result in rare background clicks only. Trunk circuits conforming to the ITU-T Recom-mendation G.822 perform well.

Usually there are practically no slips as BSS network synchronisation is hierarchic. If faults occur, PCM signal frequencies in stand-by trunks may differ by up to 50 ppm, resulting in a slip in two seconds.

GSM signalling channels are robust to slips because of the protocol used.

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8.6 Echo control in BSS As internal delays are noticeable in the GSM system, echo cancelling devices are included at the MSC-PSTN interface to cancel any echoes resulting from PSTN network 4/2 wire hybrids. Problems may arise if additional echo controllers (satellite circuit echo controllers, acoustic echo controllers and so on) are tandem connected with GSM echo cancellers.

Besides slips, also clock frequency differences cause convergence problems to echo cancellers.

The TCSM includes an acoustic echo cancellation function that removes the acoustic echo generated in the MS.

8.7 Jitter and wander prevention in BSSExcessive jitter and wander will stress equipment clock recovery and buffer circuitry, causing errors and slips. It is also possible that jitter and wander accumulate in long transmission chains.

The GSM equipment is designed to meet the requirements of the ITU-T Recommenda-tion G.823 as regards the maximum input jitter from the PCM line. In network nodes (such as the BSC), the jitter transfer function is designed to prevent jitter accumulation.

If a 2 Mbit/s signal from the BSC used for BTS synchronisation is carried transparent via a SDH network where the SDH network is not synchronised to the BSC, the 2 Mbit/s line may have abrupt frequency deviations (pointer jitter) even if data is transmitted without problems on the line. The BSC and BTS are designed to tolerate these deviations. If a line used for synchronisation extraction for the BSC experiences these deviations, the BSC frequency may start to fluctuate. However, this fluctuation will not typically mistune the frequency of the BTSs considerably, since the BTS has a long averaging time. Oth-erwise if the fluctuation frequency is low, the amplitude of fluctuation is also low.


8.8 Ethernet based transport / CESoPSN Interface:

The Flexi Edge BTS integrated CESoPSN solution, does provide Fast Ethernet Inter-face and via SFP (SFF 8074) module Gigabit Ethernet Interface.

With the SFP port modules from type 1000-Base Lx and 1000-Base Sx are supported. The Ethernet frame format provided to the Flexi Edge BTS integrated CESoPSN solution has to provide Ethertype after the source MAC address (so called Ethernet II or DIX frame).

The transport network has to ensure that at the last link these interface requirements from Flexi Edge BTS are met.

With using Pseudowire technologies like CESoPSN (RFC 5086) for transferring A-bis via Ethernet based transport networks, following recommendations exist for ensuring that BSS performance is comparable to a BSS which relies completely on circuit switched TDM transport technologies.

• One way delay of frames should be equal to or less than 13.5 ms (including delay introduced by Jitter Buffer, Packetization delay).

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• The frame loss rate should be equal to or less than 10^-5 (including lost frames, due to excessive packet delay variation).

• The frame delay variation should be equal to or less than +-20ms.

Jitter Buffer should get tailored by configuration to be able to equalize expected frame delay variation at network, with introducing minimum delay and minimizing impact to frame loss. Finding optimal configuration is a trade-off decision, because with optimizing jitter buffer for minimum delay, frame loss can get increased. Recommendation is to pri-oritize low frame loss, as BSS is more sensitive to frame loss.

The BSS is tolerant if the above listed recommended network performance get exceeded. KPI performance will decrease, but BSS will continue to work. Following the minimum performance a network has to provide, otherwise BSS KPIs will get degraded to an unacceptable level.

• One way delay of frames should be equal to or less than 40 ms (including delay introduced by Jitter Buffer, Packetization delay). With 40ms one way delay the frame loss rate shall be at least equal to or less than 10^-5.

• One way delay of frames should be equal to or less than 25ms (including delay intro-duced by Jitter Buffer, Packetization delay). With 25ms one way delay the frame loss rate shall be at least equal to or less than 10^-4.

By increasing the number of TDM frames transmitted per Ethernet frame, the robust-ness of the BSS system against frame loss can get increased slightly, with trade-off of additional introduced packetization delay.

BSS can recover from short disruptions at Ethernet network of up to ~600ms with minimal impact to ongoing calls and connections. With disruptions of >600ms <5seconds, recovery time is ~1 sec. A disruption of >5 seconds can cause worst case recovery time of up to 2 minutes.

Synchronization:

With the Flexi Edge BTS synchronization of the BTS based on received stream of frames is supported. This function is called adaptive clock recovery.

No measurable definition exists for network performance at which it can get guaranteed that adaptive clock recovery will work. Thus, it is recommended to evaluate use of adaptive clock recovery per individual network.

Following general applicable recommendations for optimized use of adaptive clock recovery.

• The BTS access media should not be xDSL, WiFi or WiMAX (such technologies cause relative high PDV due to the media access arbitration).

• Routers/switches used at the transport backhaul network should provide Hardware accelerated switching/routing (minimizing PDV by high performances non-SW based routing/switching).

• Ratio of large non CESoPSN frames vs. CESoPSN frames should be low (minimiz-ing PDV caused by waiting until large frames are send).

• Assign high priority to CESoPSN traffic (minimizing PDV at QoS aware switches/routes by prioritization of CESoPSN traffic).

• Load of traffic at a link where CESoPSN traffic gets transported should not exceed 80% (for avoiding that high load increases PDV).

• The number of switches/routers, between the device generating CESoPSN traffic and connected to the master clock and the FlexiEdge BTS, should be minimized. Guideline is that it should not exceed ~10 switches/routers.

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• Only full duplex mode at any link which is part of PW tunnel (minimizes PDV).

Due to use of high stable OCXO BTS is robust against short periods of time, when adaptive clock recovery does not work.

Bandwidth

An example of PWE dimensioning showing the calculation of bandwidth in the backhaul for 1 E1 line using PWE.

• 1 E1 line with 30 TSL for emulation • Packetization latency of 1 ms (configurable) • Protocol stack with CESoPSN/UDP/IP/VLAN/Eth requires header of 54 bytes

(Ethernet header is 18 bytes, excluding 20bytes for pre-amble, start of frame delim-iter and interframe gap. 20bytes need to be added when bandwidth needed at a physical Ethernet link gets calculated ).

Calculations:

1. Based of packetization time the number if TDM frames per packet is computed as: #frames = packetization_latency / 0.125 => 1 / 0.125 = 8.

2. Payload length. payload (byte) = #frames * #TSL_for_emulation = 8 *30 = 240 bytes; payload size cannot be larger than 512 bytes (in this example it is fine; if it would be greater then TSL_for_emulation would need to be split into 2 different packets what would lead to bigger transport overhead)".

3. Header length header (bytes) = 54 bytes 4. Total packet size total_packet_size = payload + header = 240 + 54 = 294 bytes.5. Bandwidth required per packet (kbps) bw/packet (kbps) = 8 * total_packet_size /

packetization_latency = 8 * 294 bytes / 1 msec = 2352 kbps.6. Transport overhead oh = header / total_packet_size = 54 bytes / 294 bytes =

~18,4 %.

Note: The longer packetization time the smaller bw needed but longer delay (as pack-etization contributes to other transport related latencies), e.g. for packetization time of 2 ms we only need bw of 2136 kbps but experience additional delay of 1 ms (overhead reduced to ~10 %).

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BSS Transmission Configuration Digital cross-connect nodes

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9 Digital cross-connect nodes

Figure 8 Interconnection of different networks

9.1 Digital node equipment DN2The Digital Node equipment DN2 is a general-purpose transmission cross-connect and multiplexing device. For details of the DN2, see the appropriate handbooks, such as DN2 Operating Handbook.

Applications in GSM BSSThe DN2 equipment is normally used to save transmission costs by packing the 2 Mbit/s channels more effectively. Application examples are shown in Figure Multiplexing of the BSS and external channels with the DN2. It is possible to multiplex other services on a transmission link (to use the otherwise unused capacity).

Another important application area is redundancy. Some examples are given in the sections discussing redundancy.

The DN2 is normally supervised by the BSC.

Mechanically the DN2 comprises one (or two, if expanded) 19-inch subrack. A fully equipped NDM 19 in Subrack has 16 board slots (+ one for the power unit):

MSCBSC

DN2/MetroHub

MetroHub

3rd partyDXX

BTS integratedcross-connection function

BTS integrated transmissionterminal function

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Digital cross-connect nodes

• A bus power unit BPU (or EBPU if expanded DN2) requires one slot. • A control unit CU requires one slot. • Dual 2M interface units IU2 require one slot. The number of IU2s is 1 - 13 (or the

number of 2M interfaces 2 - 26). • A power supply unit NDU (NDM DC Unit), NAU (NDM AC/DC Unit) or NDA (NDM

DC Adapter); the right-hand board slot is wide and reserved for power supply units

When the DN2 is supervised by the BSC, the maximum number of usable 2 Mbit/s inter-faces in a DN2 subrack is 24. With two subracks, the maximum is 38 interfaces.

The Q1 supervision bus from the BSC to the DN2 uses a loop-back cross-connection set-up in the DN2 (to change Q1 from TSL31 over to TSL0, requiring one IU2 board). It is also possible to form the TSL31/0 loop between the CU and one of the IU2 interfaces. This will save one IU2 interface.

Figure 9 Multiplexing of the BSS and external channels with the DN2

By-pass traffic may also flow through the BSC to the MSC.


9.2 MetroHub transmission nodeMetroHub transmission node is an outdoor capable stand-alone cross-connect, which is developed especially to support radio link based BSS transport networks. Its main traffic protection feature is the loop protection. MetroHub provides a flexible, expandable and cost-effective solution for the purposes required by a GSM/EDGE operator. The maximum cross-connection capacity of the MetroHub is 56 x 2 Mbit/s with a switching granularity of 8 kbit/s. With MetroHub, the same FXC units can be used as with inte-grated UltraSite BTS transmission. Therefore E1, T1, Flexbus and STM-1 interfaces can be integrated to MetroHub.

BSC2 Mbit/s

G.703DN2 DN2

by-pass traffic

by-pass traffic

BTS1

BTS2

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BSS Transmission Configuration Digital cross-connect nodes

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Figure 10 Network principle

MetroHub grooms the traffic from several base stations. Partially filled connections are thus combined and trunk efficiency increased. To ensure transmission availability, the Nokia PDH loop protection concept and SDH ring protection are supported. For more information on PDH loop protection, see Nokia PDH loop protection in GSM networks (the document can be obtained upon request from your Nokia Siemens Networks rep-resentative).

BSC

n x E1

BTS

Protected loop

Nokia MetroHub

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BSC-BTS transmission examples

10 BSC-BTS transmission examplesThe following examples are intended to give you a more practical view of network design.

10.1 Overview of transmission networkFigure BSS network using leased lines presents a BSS network that is mainly based on using leased lines. Even in a case such as this, some lines (BTS2-BTS3) are directly owned and controlled by the GSM operator. The GSM operator has only a limited super-vision and control access to the main transmission network.

Figure 11 BSS network using leased lines

10.2 Point-to-point transmissionThe most common and straightforward transmission configuration is the point-to-point connection between the BSC and all the BTSs. Figure Point-to-point connection between BSC and BTS presents an example of this type of connection. Only one TRU unit is required.

PSTN

by-pass traffic

Transmission network fromwhere capacity can be leased(e.g. PSTN)

MSC TC

NetAct

BTS4

BTS2

BTS chainBTS1

BTS3

BSC DN2

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BSS Transmission Configuration BSC-BTS transmission examples

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Figure 12 Point-to-point connection between BSC and BTS

10.3 Multidrop chain transmissionThe multidrop chain (see Figure Multidrop chain) is an important network configuration, especially when new services are covered. The advantage of the chain is that many low-capacity stations can be tied to a single 2M PCM line. GSM service area often suggests this kind of approach.

As with point-to-point connections, the transmission media selection is unrestricted.

Figure 13 Multidrop chain

10.4 Loop transmissionA point-to-point connection can be duplicated to look like a loop and a multidrop chain can be looped back to increase circuit availability, as shown in Figure Duplicated point-to-point and multidrop loop.

3 21

FC/FXC/FIxA

BTS

3 21

FC/FXC/FIxA

BTS

BSC

3 21

FC/FXC/FIxA

BTS

3 21

FC/FXC/FIxA

BTS

3 21

FC/FXC/FIxA

BTS

BSC

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BSC-BTS transmission examples

Figure 14 Duplicated point-to-point and multidrop loop

10.5 Radio transmissionThe radio relays provide a fast method of building networks, as Figure Loop, radio relay transmission network indicates. If needed, radio relays can be replaced by fibre, espe-cially when the station capacity later grows.

Figure 15 Loop, radio relay transmission network

10.6 UltraSite network exampleThe UltraSite network can implement the Abis loop protection or simpler star or chain network topology. Figure Example of a UltraSite network shows a HSB protected link.

With UltraSite BTS and FXC/FC units as well as Flexi EDGE BTS and FIFA, the same transmission topologies as with Talk BTS/TRUA units are supported. With UltraSite BTS, the maximum possible number of transmission interfaces and capacity is enhanced.

3 21

FC/FXC/FIxA

BTS

BSC

3 21

FC/FXC/FIxA

BTS

DN2

3 21

FC/FXC/FIxA

BTS

BSCMetroHub

FX

CR

RI

BTS

FXC RRI

BTS

FXC RRI

BTS

FXC RRI

FXC RRI FXC RRI FXC RRI

BTS BTS BTS

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BSS Transmission Configuration BSC-BTS transmission examples

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Figure 16 Example of a UltraSite network


BSC

ETMetro-Hub

E1

IF1

Dir 2

Dir 1

FB1FIU19

FB2 FB1

FB2FB3

Ultra-Site orFlexiEDGE

Flexi-Hopper

Flexi-Hopper

Flexi-Hopper

Flexi-Hopper

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Time slot allocations in BSS

11 Time slot allocations in BSSThe TCSM has the capability to support different time slot allocations on the Ater inter-face. Figure Time slot allocation for 16 kbit/s bit rate channels (typically full rate, enhanced full rate or AMR) on the Ater 2 Mbit/s interface with the TCSM2/TCSM3i shows the 16 kbit/s allocation and Figure Time slot allocation for half rate traffic with 8 kbit/s TRAU frames on the Ater 2 Mbit/s interface with the TCSM2 shows the 8 kbit/s allocation. In addition to these, it is possible to configure a combination of 16 kbit/s and 8 kbit/s portions of time slots. For the HSCSD service capacity, units of 16 kbit/s, 32 kbit/s and 64 kbit/s are allocated. It is also possible to combine HSCSD channels with FR/EFR and HR channels (as well as AMR with TCSM3i) on a common Ater interface.

Signalling channels between the BSC and the MSC, and sometimes OMC channels, are carried by entire 64 kbit/s time slots. They lower the maximum number of traffic chan-nels, especially in the case of 16 kbit/s allocation.

TSL0 carries normal ITU-T type framing overhead information (synchronisation, alarms and trunk line performance).

Figure Time slot allocation for 16 kbit/s bit rate channels (typically full rate, enhanced full rate or AMR ) on the Ater 2 Mbit/s interface with the TCSM2/TCSM3i illustrates the Ater time slot allocation for 16 kbit/s bit rate channels (typically full rate, enhanced full rate or AMR) on the Ater 2 Mbit/s interface with the TCSM2/TCSM3i. 64 kbit/s channels that must be through-connected between the BSC and MSC are not shown explicitly in this figure; the TCSM2/TCSM3i allows any time slot to be through-connected. Typically, for example, time slot 31 could be used for that purpose, in which case the traffic channels 24 - 27 would be left out.

Figure Ater time slot allocation example for the HSCSD application: a combination of 2 x 16 kbit/s channels (HS2) and 4 x 16 kbit/s channels (HS4) shows an example of Ater allocation for HSCSD. Channels of different capacities can be combined at the Ater interface. Each A-PCM may be allocated a certain (single) type of channels. In TCSM2, the channels are A, B, C, D, E, or F, whereas in TCSM3i they are G, H, or I (see Table Circuit types of TCSM2 and TCSM3i). Thus it is also possible to share a common Ater line between HSCSD channels and 16 kbit/s submultiplexed channels (FR/EFR speech, FR data, non-HSCSD data, and, with TCSM3i, also AMR). Figure Time slot allocation of 2 x 16 kbit/s channels of Figure A-PCM1 on A interface shows how the channels appear at the A interface.

Unused bits are marked with x in the figures.

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BSS Transmission Configuration Time slot allocations in BSS

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Figure 17 Time slot allocation for 16 kbit/s bit rate channels (typically full rate, enhanced full rate or AMR) on the Ater 2 Mbit/s interface with the TCSM2/TCSM3i

1 2 3 4 5 6 7 8

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

LAPD TCH.1 TCH.2 TCH.3 TC_PCM 1

TCH.4 TCH.5 TCH.6 TCH.7







x TCH.1 TCH.2 TCH.3 TC_PCM 2























LINK MANAGEMENT

BIT

TSL

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Figure 18 Time slot allocation for half rate traffic with 8 kbit/s TRAU frames on the Ater 2 Mbit/s interface with the TCSM2

The numbers in the cells refer to the number of traffic channels within a PCM trunk.

#7 signalling / NetAct connection

2 3 4 5 6 7 81

0 LINK MANAGEMENT

1 LAPD 1 2 3 4 5 6 TC_PCM 1

8 9 10 11 12 13 1472

17 18 19 20 21 22 23153

25 26 27 28 29 30 31244

x5 TC_PCM 21 2 3 4 5 6

8 9 10 11 12 13 1476

17 18 19 20 21 22 23157

25 26 27 28 29 30 31248

x9 TC_PCM 31 2 3 4 5 6

8 9 10 11 12 13 14710

17 18 19 20 21 22 231511

25 26 27 28 29 30 312412

x13 TC_PCM 41 2 3 4 5 6

8 9 10 11 12 13 14714

17 18 19 20 21 22 231515

25 26 27 28 29 30 312416

x17 TC_PCM 51 2 3 4 5 6

8 9 10 11 12 13 14718

17 18 19 20 21 22 231519

25 26 27 28 29 30 312420

x21 TC_PCM 61 2 3 4 5 6

8 9 10 11 12 13 14722

17 18 19 20 21 22 231523

25 26 27 28 29 30 312424

x25 TC_PCM 71 2 3 4 5 6

8 9 10 11 12 13 14726

17 18 19 20 21 22 231527

25 26 27 28 29 30 312428

29

30

31



BIT

TSL

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Figure 19 Ater time slot allocation example for the HSCSD application: a combination of 2 x 16 kbit/s channels (HS2) and 4 x 16 kbit/s channels (HS4)

TC_PCM 1(HS2)

TC_PCM 2(HS4)

0 LINK MANAGEMENT

LAPD X HS2.11

2

3

4

5

6

HS2.2 HS2.3

HS2.4 HS2.5

HS2.6 HS2.7

HS2.8 HS2.9

HS2.10 HS2.11

7 HS2.12 HS2.13

8 HS2.14 HS2.15

9 HS2.16 HS2.17

10 HS2.18 HS2.19

11 HS2.20 HS2.21

12 HS2.22 HS2.23

13 HS2.24 HS2.25

14 HS2.26 HS2.27

15 HS2.28 HS2.29

16 HS2.30 HS2.31

17 HS4.1

18 HS4.2

19 HS4.3

20 HS4.4

21 HS4.5

22 HS4.6

23 HS4.7

24 HS4.8

25 HS4.9

26 HS4.10

27 HS4.11

28 HS4.12

29 HS4.13

30 HS4.14

31 HS4.15

1 2 3 4 5 6 7 8BIT

TSL

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Figure 20 Time slot allocation of 2 x 16 kbit/s channels of Figure A-PCM1 on A inter-face

Figure 21 Time slot allocation of 4 x 16 kbit/s channels of Figure A-PCM2 on A inter-face

11.1 Time slot allocation in combined BSC3i/TCSM3i installa-tion (ANSI)In combined BSC3i/TCSM3i installation, the transcoding capacity of a TCSM3i can be shared by the master BSC, installed together with the TCSM3i, and one or more remote BSCs that are connected to the master BSC. The Ater interface between the master BSC and TCSM3i is internal and always based on ETSI PCM with 32 timeslots and it is therefore able to carry five ANSI T1 TC-PCMs.

Since the external PCMs carry only 24 timeslots in ANSI environment, the group switch capacity of the master BSC is therefore not effectively used, unless a fifth TC-PCM is connected to a TR3E plug-in unit and submultiplexed into the free space on the Ater PCM. This extra PCM cable is called BRANCH PCM.

The following figures describe how the MAIN PCM and BRANCH PCM are submulti-plexed into the Ater PCM between the master BSC and TCSM3i with different data rates. Note that timeslot 31 on the Ater PCM cannot be used for through-connection.

xHS2.1

HS2.2

HS2.3

0

1

2

3

1 2 3 4 5 6 7 8

LINK MANAGEMENT

4

5...28

29

30

31

HS2.4

...

HS.29

HS.30

HS.31

x

x

x

x

x

x

BIT

TSL

HS4.1

HS4.2

HS4.3

0

1

2

3

1 2 3 4 5 6 7 8

LINK MANAGEMENT

4

5...13

14

15

16

HS4.4

...

HS4.14

HS4.15

X

17 X

18

...

31

X

BIT

TSL

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Figure 22 Submultiplexing on Ater PCM in ANSI environment (16 kbit/s)


TC_PCM 1

Main PCM Branch PCM Ater PCM

1..6

7..12

13..18

19..24

1..6

7..12

13..18

19..24

1..6

7..12

13..18

19..24

TCH 1-24

TC_PCM 2

TCH 1-24

TC_PCM 3

TCH 1-24

TC_PCM 4

TCH 1-24

TC_PCM 5

TCH 1-24

25..30

LAPD

TC_PCM 1

TCH 1-24

TC_PCM 2

TCH 1-24

TC_PCM 3

TCH 1-24

TC_PCM 4

TCH 1-24

TC_PCM 5

TCH 1-24

LAPD


1..12

13..24

1..6

7..12

13..18

19..24

1..12

13..24

TC_PCM 1

TCH 1-24

TC_PCM 2

TCH 1-24

TC_PCM 3

TCH 1-12

25..30

LAPD

TC_PCM 1

TCH 1-24

TC_PCM 2

TCH 1-24

TC_PCM 3

TCH 1-12

LAPD

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Figure 25 Submultiplexing on Ater PCM in ANSI environment (mixed 32 and 64 kbit/s)

11.2 Compressed Abis time slot allocationCompressed Abis means an allocation where the signalling channel has been put (allo-cated) on top of the payload channel (TCH). The compressed Abis time slot allocation is defined with the parameter subslots for signaling (SIGN) when creating a TRX. This facilitates more TRXs per given transmission capacity, but simultaneously it has an impact (reduction) on the individual TRX's capacity. When using this feature, it is required that both the BTS and BSC must support the same traffic types/allocations. As the implementation of Compressed Abis differs between BTS generations, the


1..24 1..6

7..12

13..18

19..24

1..24TC_PCM 1

TCH 1-24

TC_PCM 2

TCH 1-6

25..30

LAPD

TC_PCM 1

TCH 1-24

TC_PCM 2

TCH 1-6

LAPD

TC_PCM 1


1..12

13..24

1..6

7..12

13..18

19..24

1..12

13..30

TCH 1-24

TC_PCM 2

TCH 1-12

TC_PCM 2 cont.

TCH 13-18

LAPD

TC_PCM 1

TCH 1-24

TC_PCM 2

TCH 1-18

LAPD

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detailed/dedicated BTS documentation gives the most detailed description of the features supported by the BTS.

In traditional transmission solutions some capacity is left unused, especially in the case of BTSs with one TRX, because one radio interface time slot is always used for the BCCH. The compressed Abis time slot allocation makes it possible to use this capacity for TRX signalling. It is also possible to use another 16 kbit/s slot to carry the O & M sig-nalling required for the site. This slot can 'steal' the TCH transmission slot thus leaving capacity for six full rate TCHs or twelve half rate TCHs for that TRX.

In environments where it is not necessary to use the full traffic capacity of a TRX, com-pressed Abis time slot allocation offers an ideal solution for using the transmission medium more efficiently. With this configuration, it is possible to fit 15 TRXs to one 2 Mbit/s PCM. The tableFigure 26. Compressed allocation enabling up to 15 TRXs per 2 Mbit/s circuit illustrates this solution.

The allocations in this section are examples of Compressed Abis. Please look at the cor-responding BTS documentation to see which traffic types (and allocations) are sup-ported by each BTS generation/BTS release.

The solution is particularly advisable in low traffic areas where it is essential to have cov-erage.

The time slot allocation of both BSC and BTS is of semipermanent type and cannot be dynamically altered. In a multi-TRX sector, radio network recovery may swap the posi-tions of BCCH-TRXs and TCH-TRXs and so make it impossible to predict the branching requirements of the transmission.

Another option for making the use of Abis interface more efficient is better suitable for multi-TRX BTSs. The following table illustrates the time slot allocation in this case.

Here the first time slot of every TRX must be disabled at the BSC to leave space for the signalling. Possible reconfigurations may influence the time slot allocation. An additional 16 kbit/s subslot must be allocated for O & M signalling.

By combining the above solutions it is possible to support five 3 x 1 TRX sites with a single 2 Mbit/s PCM link. The time slot allocation of one site in this case is illustrated in the following table.

TRX-SIG/OMUSIG

TCH, TSL1 TCH, TSL2

TCH, TSL3

TCH, TSL4 TCH, TSL5 TCH, TSL6

TCH, TSL7

Table 8 Compressed Abis time slot allocation

TRXSIG TCH, TSL1 TCH, TSL2 TCH, TSL3

TCH, TSL4 TCH, TSL5 TCH, TSL6 TCH, TSL7

Table 9 Compressed Abis time slot allocation in the case of multi-TRX base stations

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If the TRX signalling speed is 32 kbit/s, the following allocation is also possible.

OMU/TRXSIG_1 TCH, TSL1 TCH, TSL2 TCH, TSL3


TRXSIG_2 TCH, TSL1 TCH, TSL2 TCH, TSL3


TRXSIG_3 TCH, TSL1 TCH, TSL2 TCH, TSL3

TCH, TSL4 TCH, TSL TCH, TSL6 TCH, TSL7

Table 10 Compressed Abis time slot allocation that supports five 3 x 1 TRX sites

TRXSIG/OMU TCH, TSL2 TCH, TSL3


Table 11 Compressed Abis time slot allocation with the TRX signalling speed 32 kbit/s

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Figure 26 Compressed allocation enabling up to 15 TRXs per 2 Mbit/s circuit

This is achieved at the cost of speech capacity.

As presented in Figure Compressed allocation enabling up to 15 TRXs per 2 Mbit/s circuit above, some speech capacity is lost for signalling. FR or HR speech can be used. HR can in this case be used with 16 kbit/s TRX signalling; 32 kbit/s is also possible but it may waste capacity. TCH capacity is gained by filling TSL31 with up to four OMUSIG channels.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

TRXSIG1

TCH5/9-10

TRXSIG2

TCH5/9-10

TRXSIG3

TCH5/9-10

TRXSIG4

TCH5/9-10

TRXSIG5

TCH5/9-10

TRXSIG6

TCH5/9-10

TRXSIG7

TCH5/9-10

TRXSIG8

TCH5/9-10

TRXSIG9

TCH5/9-10

TRXSIG10

TCH5/9-10

TRXSIG11

TCH5/9-10

TRXSIG12

TCH5/9-10

TRXSIG13

TCH5/9-10

TRXSIG14

TCH5/9-10

TRXSIG15

TCH5/9-10

x/OMUSIG

TCH2/3-4

TCH6/11-12

TCH2/3-4

TCH6/11-12

TCH2/3-4

TCH6/11-12

TCH2/3-4

TCH6/11-12

TCH2/3-4

TCH6/11-12

TCH2/3-4

TCH6/11-12

TCH2/3-4

TCH6/11-12

TCH2/3-4

TCH6/11-12

TCH2/3-4

TCH6/11-12

TCH2/3-4

TCH6/11-12

TCH2/3-4

TCH6/11-12

TCH2/3-4

TCH6/11-12

TCH2/3-4

TCH6/11-12

TCH2/3-4

TCH6/11-12

TCH2/3-4

TCH6/11-12

x/OMUSIG

TCH3/5-6

TCH7/13-14

TCH3/5-6

TCH7/13-14

TCH3/5-6

TCH7/13-14

TCH3/5-6

TCH7/13-14

TCH3/5-6

TCH7/13-14

TCH3/5-6

TCH7/13-14

TCH3/5-6

TCH7/13-14

TCH3/5-6

TCH7/13-14

TCH3/5-6

TCH7/13-14

TCH3/5-6

TCH7/13-14

TCH3/5-6

TCH7/13-14

TCH3/5-6

TCH7/13-14

TCH3/5-6

TCH7/13-14

TCH3/5-6

TCH7/13-14

TCH3/5-6

TCH7/13-14

x/OMUSIG

TCH4/7-8

TCH8/15-16

TCH4/7-8

TCH8/15-16

TCH4/7-8

TCH8/15-16

TCH4/7-8

TCH8/15-16

TCH4/7-8

TCH8/15-16

TCH4/7-8

TCH8/15-16

TCH4/7-8

TCH8/15-16

TCH4/7-8

TCH8/15-16

TCH4/7-8

TCH8/15-16

TCH4/7-8

TCH8/15-16

TCH4/7-8

TCH8/15-16

TCH4/7-8

TCH8/15-16

TCH4/7-8

TCH8/15-16

TCH4/7-8

TCH8/15-16

TCH4/7-8

TCH8/15-16

x/OMUSIG

TRX1

TRX2

TRX3

TRX4

TRX5

TRX6

TRX7

TRX8

TRX9

TRX10

TRX11

TRX12

TRX13

TRX14

TRX15

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Figure 27 Allocation example for a three-TRX BTS

11.3 Allocation of Abis time slotsThe allocation of time slots is based on the following principles:

• One 2 Mbit/s time slot 0 is reserved for ITU-T-type frame alignment and supervision of the link.

• One 16 kbit/s (or 64 kbit/s) channel is required between the BTS and the BSC for BTS O & M (marked as OMUSIG).

• Each TRX at the BTS processes up to 8 TCH/F traffic channels of 16 kbit/s or up to 16 TCH/H traffic channels, and a 16 kbit/s, 32 kbit/s (or 64 kbit/s) signalling link to the BSC (marked as TRXSIG). The FR and HR channels can be used at the same time call by call in the TRX.

The principles of PCM based Abis allocation apply with PWE protocols like CESoPSN as well, since from BTS perspective a PCM is available. With using CESoPSN the exact number of transferred PCM timeslots can be tailored to the Abis allocation of a BTS, optimizing those needed transmission bandwidth.

The following tables present the different maximum numbers of TRXs per 2Mbit/s PCM with 16 kbit/s and 64kbit/s OMUSIG channel rates. For chain and loop configuration the number is applicable with 1 TRX per BTS, requiring 1 OMUSIG per BTS. The number of supported TRX per 2 Mbit/s PCM can increase with loop/chain configurations, in case more TRX are allocated per BTS. Exact number depends on the individual BTS config-uration.

*) The maximum capacity is not possible because the number of TRXs that can be installed per BTS cabinet is 12.

1

2

3

4

5

6

TRX1

TRX2

TRX3

TRXSIG

TCH5/9-10

TRXSIG

TCH5/9-10

TRXSIG

TCH5/9-10

OMUSIG

TCH6/11-12

TCH2/3-4

TCH6/11-12

TCH2/3-4

TCH6/11-12

TCH3/5-6

TCH7/13-14

TCH3/5-6

TCH7/13-14

TCH3/5-6

TCH7/13-14

TCH4/7-8

TCH8/15-16

TCH4/7-8

TCH8/15-16

TCH4/7-8

TCH8/15-16

TRXSIG signalling rate Point-to-point Chain Loop

16 13* 12 11

32 12 11 10

64 10 9 9

Compressed 15 *) 15 14

Table 12 16 kbit/s OMUSIG signalling rate

TRXSIG signalling rate Point-to-point Chain Loop

16 13 *) 9 9

32 12 8 8

Table 13 16 kbit/s OMUSIG signalling rate

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*) The maximum capacity is not possible because the number of TRXs that can be installed per BTS cabinet is 12.

The required time slot allocation is selected from the TRU menu from among certain time slot allocations.

The TRU is able to drop and insert full time slots (for 64 kbit/s signalling) or parts of a time slot (for 16 kbit/s signalling) without restrictions. This means that the allocation on the 2 Mbit/s highway between the BSC and the BTS (or between the BTSn and BTSn + 1) can be freely selected.

11.4 Abis allocation, FR, 16 kbit/s signallingThe time slot allocation principle is the following:

• Eight 16 kbit/s TCH/Fs per each TRX • One 16 kbit/s TRXSIG (LAPD TRX - BSC) per each TRX • One 16 kbit/s OMUSIG (LAPD OMU - BSC) per each BTS

Space is allocated for these so that the 8 TCHs occupy two entire time slots. The TRXSIG uses one quarter of a time slot and the OMUSIG uses another quarter.

A multidrop chain time slot allocation is presented in Figure Multidrop chain allocation in the case of 16 kbit/s LAPD. This allocation can be used on the 2M highway. Note that the TRU drop/insert function must be used to build a correct internal D-bus allocation. This can be done by conforming to the rules given in the figure mentioned. It is possible to use any other allocation on the 2M highway.

Along the BTS chain, time slots will be dropped or inserted and vacant time slots will be formed. These vacant time slots can be used for other purposes with suitable equip-ment.

This allocation is flexible enough to cover typical applications where the number of TRXs per BTS is not greater than 12.

Unused bits, marked with x, are set to one.

64 10 7 7

Table 13 16 kbit/s OMUSIG signalling rate (Cont.)

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Figure 28 Multidrop chain allocation in the case of 16 kbit/s LAPD

The number of BTSs served may be anything up to 12, with the TRXs shared between them; TSL31 is unused or reserved for redundancy purposes, such as loop control bits.

11.5 Abis allocation, FR/HR, 64 kbit/s signallingThis allocation is not normally used because of its high requirement of capacity.

11.6 Abis allocation, FR/HR, 32 kbit/s signallingThe allocation principle is the following:

• Eight 16 kbit/s TCH/Fs or sixteen 8 kbit/s TCH/Hs

1 2 3 4 5 6 7 8

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

LINK MANAGEMENT

TRX12

TRX11

TRX10

TRX9

TRX8

TRX7

TRX6

TRX5

TRX4

TRX3

TRX2

TRX1TCH.1

TCH.5

TCH.1

TCH.5

TCH.1

TCH.5

TCH.1

TCH.5

TCH.1

TCH.5

TCH.1

TCH.5

TCH.1

TCH.5

TCH.1

TCH.5

TCH.1

TCH.5

TCH.1

TCH.5

TCH.1

TCH.5

TCH.1

TCH.5

TRXSIG1

TRXSIG3

TRXSIG5

TRXSIG7

TRXSIG9

TRXSIG11

X

TCH.2

TCH.6

TCH.2

TCH.6

TCH.2

TCH.6

TCH.2

TCH.6

TCH.2

TCH.6

TCH.2

TCH.6

TCH.2

TCH.6

TCH.2

TCH.6

TCH.2

TCH.6

TCH.2

TCH.6

TCH.2

TCH.6

TCH.2

TCH.6

OMUSIG1

OMUSIG3

OMUSIG5

OMUSIG7

OMUSIG9

OMUSIG11

X

TCH.3

TCH.7

TCH.3

TCH.7

TCH.3

TCH.7

TCH.3

TCH.7

TCH.3

TCH.7

TCH.3

TCH.7

TCH.3

TCH.7

TCH.3

TCH.7

TCH.3

TCH.7

TCH.3

TCH.7

TCH.3

TCH.7

TCH.3

TCH.7

TRXSIG2

TRXSIG4

TRXSIG6

TRXSIG8

TRXSIG10

TRXSIG12

x

TCH.4

TCH.8

TCH.4

TCH.8

TCH.4

TCH.8

TCH.4

TCH.8

TCH.4

TCH.8

TCH.4

TCH.8

TCH.4

TCH.8

TCH.4

TCH.8

TCH.4

TCH.8

TCH.4

TCH.8

TCH.4

TCH.8

TCH.4

TCH.8

OMUSIG2

OMUSIG4

OMUSIG6

OMUSIG8

OMUSIG10

OMUSIG12

x

BIT

TSL

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• One 32 kbit/s TRXSIG (LAPD TRX - BSC) per TRX • One 16 kbit/s OMUSIG (LAPD OMU - BSC) per BTS

These are arranged so that one TRX TCH occupies two entire time slots. The TRXSIG uses half of one time slot and the OMUSIG uses one quarter of time slot 31.

It is possible to use 16 kbit/s TRX signalling with HR, but for the best results, 32 kbit/s is recommended. During the network transition phase, 16 kbit/s may be advantageous.

In the allocation example given in Figure An example of four-BTS chain (highway) allo-cation when 32 kbit/s TRX signalling is used presented below, the number of BTSs served can be up to four with the 12 TRXs shared between them. The number of OMUSIGs can be increased by decreasing the number of TRXSIGs — a trade-off between the number of BTSs and the number of TRXs in the BTSs.

In the following figure, for example T1/1-2 denotes either the first full rate channel TCH/F.1 or the first two half rate channels TCH/H.1 and TCH/H.2 of an Abis trunk. The BTS/TRX will dynamically support any combination of full rate and half rate channels call by call.

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Figure 29 An example of four-BTS chain (highway) allocation when 32 kbit/s TRX sig-nalling is used

The number of OMUSIG channels can be increased at the cost of reducing the total number of TRXs.


1 2 3 4 5 6 7 8

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

LINK MANAGEMENT

TRX12

TRX11

TRX10

TRX9

TRX8

TRX7

TRX6

TRX5

TRX4

TRX3

TRX2

TRX1T1/1-2

T5/9-10

T1/1-2

T5/9-10

T1/1-2

T5/9-10

T1/1-2

T5/9-10

T1/1-2

T5/9-10

T1/1-2

T5/9-10

T1/1-2

T5/9-10

T1/1-2

T5/9-10

T1/1-2

T5/9-10

T1/1-2

T5/9-10

T1/1-2

T5/9-10

T1/1-2

T5/9-10

TRXSIG1

TRXSIG3

TRXSIG5

TRXSIG7

TRXSIG9

TRXSIG11

OMUSIG1

T2/3-4

T611-12

T2/3-4

T611-12

T2/3-4

T611-12

T2/3-4

T611-12

T2/3-4

T611-12

T2/3-4

T611-12

T2/3-4

T611-12

T2/3-4

T611-12

T2/3-4

T611-12

T2/3-4

T611-12

T2/3-4

T611-12

T2/3-4

T611-12

OMUSIG2

T3/5-6

T7/13-14

T3/5-6

T7/13-14

T3/5-6

T7/13-14

T3/5-6

T7/13-14

T3/5-6

T7/13-14

T3/5-6

T7/13-14

T3/5-6

T7/13-14

T3/5-6

T7/13-14

T3/5-6

T7/13-14

T3/5-6

T7/13-14

T3/5-6

T7/13-14

T3/5-6

T7/13-14

TRXSIG2

TRXSIG4

TRXSIG6

TRXSIG8

TRXSIG10

TRXSIG12

OMUSIG3

T4/7-8

T8/15-16

T4/7-8

T8/15-16

T4/7-8

T8/15-16

T4/7-8

T8/15-16

T4/7-8

T8/15-16

T4/7-8

T8/15-16

T4/7-8

T8/15-16

T4/7-8

T8/15-16

T4/7-8

T8/15-16

T4/7-8

T8/15-16

T4/7-8

T8/15-16

T4/7-8

T8/15-16

OMUSIG4

BIT

TSL

A Bis

Documents

octet sequence

bsctcsm product

adaptive clock

vacant time

combined bsc3itcsm3i

enhanced full

time slot

error rate