GSM NetworksGSM NetworksGSM NetworksGSM Networks

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GSM Network OverviewGSM Network Overview

BSCBTS

BTS

Mobile

Station

Access Network:Base Station Subsystem

HLR VLR EIR AuC

MSCPSTN

Um Abis A

Core Network:GSM CS network

SS7

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GSM Network ProtocolsGSM Network Protocols

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GSM Signaling ProtocolsGSM Signaling Protocols

Layer 1 (physical layer)

Uses many channel structures

Layer 2 (data link layer)

Across Um interface uses LAPDm (a slight modification of LAPD protocol used in ISDN)

Across Abis uses LAPD

Across A interface, uses MTP and SCCP of SS7 

SAPI=0 Identifies radio signaling procedures

Layer 3 is sub-divided into 3 sub-layers

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Layer 3 Signaling ProtocolsLayer 3 Signaling Protocols

RR: Radio Resources ManagementEstablishment, maintenance, and termination of radio channels that allow point-to-point dialogue between network and mobile stations; including cell selection and handover procedures

MM: Mobility ManagementManages location updating, registration, security and authentication procedures

CM: Connection ManagementHandles general call control, similar to CCITT Recommendation Q.931, and provides supplementary services & Short Message Services (SMS)

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HandoverHandover

Four types of handovers:

Channels (time slots) in same cell

Between cells within same BSC

Between BSCs, within same MSC

Between MSCs

PSTN

BTS

BTS

BTS

BTS

BTS

BTS

BTS

BSC BSC

MSC

BTS

BTS

BTS

BTS

BTS

BTS

BTS

BSC BSC

MSC

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MAP (Mobile Application Part)MAP (Mobile Application Part)

SS7 top layer protocol

Responsible for signaling between different entities in network, such as between HLR and VLR 

MAP specification is complex

Several variants for the big manufacturers (Ericsson, Motorola …)

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SummarySummary

GSM is the dominant cellular technology today

GSM offers high quality voice with advanced services

GSM is the stepping-stone to 3G networks