25513638 GSM Protocols Only

7/28/2019 25513638 GSM Protocols Only

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CONTENTS

GSM PROTOCOLS

RADIO INTERFACE PROTOCOL

ABIS INTERFACE PROTOCOL

ATER INTERFACE PROTOCOL A-INTERFACE PROTOCOL


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PROTOCOL

Protocol is defined as:

Set of Rules which make communication

possible between two devices.


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GSM PROTOCOLS

GSM Protocols Include: LAPDm on Air Interface between MS and Base Station

LAPD on Abis Interface between Base Station and BSC

LAPD on Ater Interface between BSC and TCU.

SS7 on A-interface between TCU and MSC

The Radio Resource [RR] procedure handles Setup, Re-establishment,Handover, TCH mode modify and release of calls.

The Mobility Management [MM] procedures provide Registration,Location and Authentication of MS.

The Connection Management [CM] procedures provide SupplementaryServices [SS], Call Control [CC], Short Message Service [SMS].

To establish a connection with MS, CM must require MM, which in turnrequires RR to open the radio connection.

RR includes LAPDm and LAPD protocols on Air, Abis & Ater interface.

MM and CM messages are transparent to BSS and include SS7 protocol onA-Interface.


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PROTOCOL MODEL

NSS

BSCBTS

MS

MM

BSSAP

SCCP

MTP3

MTP2

TCA

P

M

AP

PCM

CM

MM

MTP3

MTP2

SCCP

PCM E1/T1PCM

SCCP

MTP3

MTP2

D

TA

P

R

R

O & M

R SM

LA

PD

RSM

O & M

RADIORADIO

RR

I

SUP

/

TU

P

CM

Um

Interface

Abis

Interface A-Interface

BSSAP

MTP1

RR

BS

SM

AP

LA

PD

LA

PD

m

LA

PD

m

RR D

T

A

P

BS

SMA

P


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RADIO INTERFACE

Radio Interface is between MS and Base Station. Radio Interface has

features:

Totally Normalized Full Inter-operability between Mobile Stations and infrastructure from different

manufacturers

Radio Interface is organized in three levels:

Level-1 Physical Support TDMA and FDMA

Logical Channels Multiplexing

Level-2 LAPDm Protocol

No Flag

No error retransmission mechanism due to real time constraints

Level-3 Radio Interface Layer [RIL] Protocol involves three sub-layers

Radio Resource Management [RR]: Paging, Power Control, Ciphering, Handovers

Mobility Management [MM]: Security, IMSI Attach / Detach, Location

Connection Management [CM]: Call Control, SMS, DTMF


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RADIO INTERFACE

Connection ManagementConnection Management

Mobility ManagementMobility Management

Radio Resource ManagementRadio Resource Management

Multiplexing

RACH BCCHPCH

AGCH SDCCH FACCH SACCH

TC0 TC11 SACCH TC13 TC24 IDLE

Level 3

Level 2 = LAPDmLogical Channels

Level 1

Physical Channels

Protocols Involved


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ABIS INTERFACE

Abis Interface is between BTS and BSC.

PCM digital links at 2.048Mbps [E1] or 1.544Mbps [T1], carrying 32 or

24 timeslots at 64kbps are used for physical interconnection betweenBTS and BSC.

Abis Interface has following features: Partly Normalized

No Inter-Operability

Radio Interface is organized in three levels: Level-1 PCM Transmission [E1 or T1]

Speech coded at 16kbps and sub multiplexed in 64kbps timeslots

Data which rate is adapted and synchronized

Level-2 LAPD Protocol RSL = Radio Signaling Link

OML = Operation and Maintenance Link

Level-3 Application Protocols

RSM = Radio Subsystem Management

O&M = Operation and Maintenance Procedures


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ABIS INTERFACE

RSMO&M

RSL OML

RSM O&M O&M

Level 1 layer

RSL OML

TRXBCF

Level 3

layer

LAPD

Level 2

layer

BTS side BSC side


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ABIS INTERFACE

Speech 1 TS = 4 channels

LAPD Radio O&M

P

CM

PC

MData300, 1200, 1200/75, 2400,

4800, 9600, 14400 bit/s


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ATER INTERFACE

Ater Interface is between BSC and TCU.

Ater Interface carried 120 communications using E1 and 92

communications using T1. PCM digital links at 2.048Mbps [E1] or 1.544Mbps [T1], carrying 32 or

24 timeslots at 64kbps are used for physical interconnection between

BSC and TCU carrying:

Reserved Signaling Channels for CCS7

Speech and Data Channels [16kbps]

BSC-TCU signaling Link LAPD

O&M data to OMCR [X.25] via MSC

Signaling messages are carried on specific timeslots [TS]: LAPD signaling TS between the BSC and TCU

SS7 TS between the BSC and the MSC

X.25 TS2 reserved for specific configurations


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ATER INTERFACE

Ater interface A interface

LAPD TS 1

SS7 TS

X.25 TS 2 *

SS7 TS

X.25 TS 2 *

BSC

PCM link PCM link

O&M

Speech TS Speech TSTranscoding

Data TS Data TSRate

Adaptation

TCU

MSC

OMC


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ATER INTERFACE

LAPD

SS7

Speech 1 TS = 4 channels

Data 300, 1200, 1200/75, 2400,4800, 9600, 14400 bit/s

O&M

X.25


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A-INTERFACE

A- Interface is between MSC and BSS and has following features:

Totally normalized to allow multi vendor equipment

Full Inter operability in most cases and after testing SS7 is the signaling used on A-Interface, SS7 signaling has two parts:

Message Transfer Part [MTP]

SignalingConnection Control Part [SCCP]


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A-INTERFACE

Speech/Data 1 TS = 1 channel

SS7

BSS NSS

X.25


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THANK YOU!

25513638 GSM Protocols Only

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