CONTENTS

GSM PROTOCOLS RADIO INTERFACE PROTOCOL ABIS INTERFACE PROTOCOL ATER INTERFACE PROTOCOL A-INTERFACE PROTOCOL

PROTOCOL
Protocol is defined as:

Set of Rules which make communication possible between two devices.

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 Supplementary Services [SS], Call Control [CC], Short Message Service [SMS]. To establish a connection with MS, CM must require MM, which in turn requires 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 on A-Interface.

PROTOCOL MODEL
MS
CM MM RR CM MM

NSS
M A P I S U P / T C A P T U P

BTS
O&M RR RSM O&M R

BSC
BSSAP R R S M B D S T S M A A P P SCCP MTP3 MTP2

BSSAP
B RR D S T S M A A P P SCCP MTP3 MTP2 PCM E1/T1

L A P D m RADIO

L A P D m

L A P D

L A P D

SCCP MTP3 MTP2 MTP1

RADIO

PCM

PCM

Um Interface

Abis Interface

A-Interface

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

RADIO INTERFACE
Protocols Involved
Level 3 Connection ConnectionManagement Management Mobility MobilityManagement Management Radio RadioResource ResourceManagement Management Level 2 = LAPDm
Logical Channels

Multiplexing

RACH

BCCH TC0

PCH AGCH TC11 SACCH TC13

SDCCH TC24

FACCH IDLE

SACCH

Level 1 Physical Channels

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 between BTS 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

ABIS INTERFACE
BTS side
TRX BCF

BSC side

RSM O&M

O&M

Level 3 layer

RSM O&M

RSL

OML

LAPD Level 2 layer

RSL

OML

Level 1 layer

ABIS INTERFACE
Speech 1 TS = 4 channels

PCM

PCM

Data

300, 1200, 1200/75, 2400, 4800, 9600, 14400 bit/s LAPD • Radio • O&M

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

ATER INTERFACE
Ater interface TCU
LAPD TS 1 SS7 TS

A interface

O&M
SS7 TS MSC

BSC

Speech TS

Transcoding

Speech TS

Data TS

Rate Adaptation

Data TS

X.25 TS 2 * PCM link

X.25 TS 2 * PCM link

OMC

ATER INTERFACE
Speech 1 TS = 4 channels Data 300, 1200, 1200/75, 2400, 4800, 9600, 14400 bit/s LAPD • O&M SS7 X.25

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] Signaling Connection Control Part [SCCP]

A-INTERFACE
BSS NSS
Speech/Data 1 TS = 1 channel SS7

X.25

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