Gsm Architecture

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  • Topic: GSM, Mobile phone, Network switching subsystem
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GSM 1

Mobile Communications GSM
Manuel P. Ricardo
Faculdade de Engenharia da Universidade do Porto

GSM 2

Acknowledgements


These slides are based on the slides developed by
» Prof. Jochen Schiller
– Slides from the book “Mobile Communication: Wireless Telecommunication Systems” – http://www.jochenschiller.de

» Prof. Mário Jorge Leitão
– http://www.fe.up.pt/~mleitao/

GSM 3

♦ ♦ ♦ ♦ ♦ ♦ ♦

What are the main network elements of GSM? What are the GSM addresses? How is the data transmitted over the air interface? What are the main logical channels? What is the GSM protocol stack for signalling? How is a Mobile Terminated Call processed? How is a Mobile Initiated Call processed?

GSM 4

GSM - Overview
♦ ♦ ♦

Formerly: Groupe Spéciale Mobile (founded 1982) Now: Global System for Mobile Communication Pan-European standard » ETSI, European Telecommunications Standardisation Institute

♦ ♦

Seamless roaming within Europe possible Many providers all over the world

GSM 5

Services


Basic services
» voice services, data services, short message service



Additional services
» emergency number, group 3 fax



Supplementary services
» identification: forwarding of caller number » suppression of number forwarding » automatic call-back

GSM 6

Basic Services


Voice services (speech coding with protection)
» full rate: 13 / 12.2 kbit/s (original coder / enhanced full rate coder) » half rate: 5.6 kbit/s (enhanced half rate coder)



Data services (coding with different levels of protection)
» full rate: 9.6 / 4.8 / 2.4 kbit/s » half rate: 4.8 / 2.4 kbit/s



Enhanced data services

GPRS (General Packet Radio Service)

» various rates (typically up to 53.6 kbit/s)

Public Land Mobile Network (PLMN)
radio cell MS MS BSS radio cell RSS BTS MS

GSM 7

BTS

BSC

BSC

NSS MSC MSC signaling GMSC IWF ISDN, PSTN PDN

VLR HLR OSS

VLR

EIR

AuC

OMC

GSM Architecture – Radio Subsystem (RSS)
» MS - Mobile Station
– Mobile terminal equipment

GSM 8

» BTS- Base Transceiver Station
– Transmitter, receiver and antennas

» BSC - Base Station Controller
– Management of several BTS and MS

BSS Base Station Subsystem

BSC BSC MS

BTS

GSM Architecture – Network Subsystem (NSS)
» » » » » » Switching, mobility management, Interconnection to other networks, system control MSC - Mobile Switching Centre: Management of connections HLR - Home Location Register: Associated to each PLMN VLR - Visitor Location Register: Associated to each MSC GMSC - Gateway MSC: MSC providing interconnection to other networks HLR

GSM 9

GMSC

fixed network

VLR

MSC

MSC
BSC

VLR

BSC

GSM Architecture – Operation Subsystem (OSS)
– Control of the radio and network subsystems

GSM 10

» Centralized operation, management and maintenance of GSM subsystems » OMC - Operation and Management » AuC - Authentication Centre – Security functions

» EIR - Equipment Identity Register
– Mobile station registration

OMC

AuC

EIR

Network Element

HLR

MSC

GSM 11

GSM Architecture - Interfaces
radio subsystem MS MS ISDN PSTN Um BTS BTS Abis BSC A SS7 MSC network and switching subsystem fixed partner networks

Um : radio interface
HLR

Abis : 16/64 kbit/s user channels A: 64 kbit/s user channels VLR

BTS BTS BSS BSC GMSC IWF ISDN PSTN PDN

Voice Transcoding and Rate Adaptation


GSM 12

Need for transcoding and rate adaptation
» BTS - 13 kbit/s air-interface (original coder) » MSC - 64 kbit/s ISDN type switching (PCM, A-law)



3 options for Transcoding and Rate Adapter Unit (TRAU)
Abis A

BTS

BTS

TRAU 64 kbit/s

BSC
64 kbit/s

MSC

BSC

BTS
16 kbit/s

BSC TRAU
64 kbit/s

MSC

MSC

BTS
16 kbit/s

BSC

TRAU 64 kbit/s (4 x 16 sub-mux)

MSC

GSM 13

Mobile Addresses


Several mobile numbers are needed
» IMSI - International Mobile Subscriber Identity
–...
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