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Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,

Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to [email protected]

Global System for MobileCommunication (GSM)

Dr K.Sandrasegaran

Special Acknowledgements to Jochen Schiller



Recommended

Mobile Communications (2nd

Edition) by Jochen SchillerChapter 4: Telecommunications Systems

Reference

GSM Switching, Services, and Protocols by Jrg Eberspcher,Hans-Jrg Vgel, Christian Bettstetter. New York : Wiley, c2001.

Readings

Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to [email protected]

GSM Markets & Evolution

Distinguish between 1G, 2G, 2.5G, 3G and 4G mobile technologies.

Tabulate the differences between GSM 900, 1800 and 1900.

What was the primary goal during the setting up of GSM standards?


What are the trends with mobile phone subscribers worldwide? (Schiller)

0

200

400

600

800

1000

1200

1996 1997 1998 1999 2000 2001 2002year

Subscribers[million]

GSM total

TDMA total

CDMA total

PDC total

Analogue total

Total wireless

Prediction (1998)

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Development of mobile telecommunication systems

1G 2G 3G2.5G

IS-95cdmaOne

IS-136TDMAD-AMPS

GSM

PDC

GPRS

IMT-DSUTRA FDD / W-CDMA

EDGE

IMT-TCUTRA TDD / TD-CDMA

cdma2000 1X

1X EV-DV(3X)

AMPSNMT

IMT-SCIS-136HSUWC-136

IMT-TC

TD-SCDMA

CT0/1

CT2 IMT-FTDECT

CDMA

TDMA

FD

MA

IMT-MCcdma2000 1X EV-DO



GSM: Overview

GSM

formerly: Groupe Spciale Mobile (founded 1982) now: Global System for Mobile Communication

Pan-European standard (ETSI, European TelecommunicationsStandardisation Institute)

simultaneous introduction of essential services in three phases (1991,1994, 1996) by the European telecommunication administrations

(Germany: D1 and D2) seamless roaming within Europe possible

today many providers all over the world use GSM (more than 184countries in Asia, Africa, Europe, Australia, America)

more than 747 million subscribers

more than 70% of all digital mobile phones use GSM over 10 billion SMS per month in Germany, > 360 billion/year worldwide


GSM Introduction


What are performance characteristics of GSM (wrt. analog sys.)?

Communication

mobile, wireless communication; support for voice and data services

Total mobility

international access, chip-card enables use of access points of differentproviders

Worldwide connectivity

one number, the network handles localization

High capacity if needed

better frequency efficiency, smaller cells, more customers per cell

High transmission quality

high audio quality and reliability for wireless, uninterrupted phone calls at

higher speeds (e.g., from cars, trains)

Security functions

access control, authentication via chip-card and PIN

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GSM Architecture

Distinguish between the following GSM subsystems: RSS, BSS, NSS and OSS.

Using an A3 page, draw and name the main elements of the GSM system architecture(BTS, BSC, MSC, VLR, HLR, AuC, EIR, GMSC, SMSC (SMS), IWF, etc.

What are the functions of network elements?

Draw the external entities to which GSM connect to including MS, PSTN, PSPDN. Etc.

On the same diagram, sketch all the interfaces A, Abis, B, C, D, E, F, G, Um, R and S.Draw the protocol stack that is used on each interface above.

What are the advantages of specifying all internal interfaces of the GSM system?

How and where is user-related data represented/stored in the GSM system?

Distinguish between the HLR and VLR.



Architecture of the GSM system

GSM is a PLMN (Public Land Mobile Network)

several providers setup mobile networks following the GSM standard withineach country

Encourages competition which lowers prices and speeds up development of

new services

Open interfaces (eg Um, A, Abis) encourages vendor competition

What are the subsystems of GSM? RSS (radio subsystem): covers all radio aspects

NSS (network and switching subsystem): call forwarding, handover, switching

OSS (operation subsystem): management of the network

RSSRadio SubsystemRadio and mobility

NSSNetwork and Switching

SubsystemLocation and call

handling

OSSOperation SubsystemNetwork Management

Um A


Um

Abis

ABSS

radiosubsystem

MS MS

BTS

BSCBTS

BTS

BSCBTS

network andswitching subsystem

MSC

MSC

fixedpartner networks

IWF

ISDNPSTN

PSPDNCSPDN

SS7

EIR

HLR

VLR

ISDNPSTN

GSM: system architecture

TC

TC


Network Elements

BSSBase Station

Subsystem

OSSOperation SubsystemNetwork Management

Um A

BTS

BSCBTS

BTS

BSCBTS

TC

NSSNetwork and

Switching Subsystem

MSC

MSCIWF

EIR

HLR

VLR

AUC

Abis Ater

FixedPartnerNetworks

ISDNPSTN

PSPDNCSPDN

MobileTerminals

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Handover decision

receive levelBTSold

receive levelBTSold

MS MS

HO_MARGIN

BTSold BTSnew



Handover procedure

HO access

BTSold BSCnew

measurementresult

BSCold

Link establishment

MSCMS

measurementreport

HO decision

HO required

BTSnew

HO request

resource allocation

ch. activation

ch. activation ackHO request ackHO commandHO commandHO command

HO completeHO completeclear command

clear commandclear complete clear complete



GSM Security

4.1.7 Security in GSM

What are the security services offered by GSM?

State the names, location and purpose of all the keys (PIN, PUK, Ki, Kc) andalgorithms (A3, A5, A8) used for GSM security?

Describe the steps involved in the authentication of a GSM user? (Figure 4.13)

Describe the steps involved in the encryption of user data? (Figure 4.14)

How is system security maintained?



Security in GSM

Security services

access control/authentication

user SIM (Subscriber Identity Module): secret PIN (personalidentification number)

SIM network: challenge response method

confidentiality

voice and signaling encrypted on the wireless link (after successfulauthentication)

anonymity

temporary identity TMSI(Temporary Mobile Subscriber Identity)

newly assigned at each new location update (LUP)

encrypted transmission

3 algorithms specified in GSM

A3 for authentication (secret, open interface)

A5 for encryption (standardized)

A8 for key generation (secret, open interface)

secret: A3 and A8available via theInternet network providerscan use strongermechanisms

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GSM - authentication

A3

RANDKi

128 bit 128 bit

SRES* 32 bit

A3

RAND Ki

128 bit 128 bit

SRES 32 bit

SRES* =? SRES SRES

RAND

SRES

32 bit

mobile network SIM

AC

MSC

SIM

Ki: individual subscriber authentication key SRES: signed response



GSM - key generation and encryption

A8

RANDKi

128 bit 128 bit

Kc64 bit

A8

RAND Ki

128 bit 128 bit

SRES

RAND

encrypteddata

mobile network (BTS) MS with SIM

AC

BSS

SIM

A5

Kc

64 bit

A5

MSdata data

cipherkey



HSCSD

4.1.8 New Data Services (HSCSD only)

What are the limitations of data services offered by GSM networks?

How can the data rates associated with GSM be increased?

Explain the important characteristics of HSCSD?

What is the maximum data rate that can be achieved with HSCSD?

Which resources need to be allocated during handover for data transmissionusing HSCSD?

What are the limitations of HSCSD?



Data services in GSM I

Data transmission standardized with only 9.6 kbit/s

advanced coding allows 14,4 kbit/s

not enough for Internet and multimedia applications

HSCSD (High-Speed Circuit Switched Data)

mainly software update

bundling of several time-slots to get higherAIUR (Air Interface User Rate)

(e.g., 57.6 kbit/s using 4 slots, 14.4 each) advantage: ready to use, constant quality, simple

disadvantage: channels blocked for voice transmission

AIUR [kbit/s] TCH/F4.8 TCH/F9.6 TCH/F14.44.8 19.6 2 114.4 3 119.2 4 228.8 3 238.4 443.2 357.6 4

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MBS(Mobile Broadband System)

Future mobile telecommunication networks

terminalmobility

fast

mobile

slow

portable

fixed

10 kbit/s 2 Mbit/s 20 Mbit/s 30 Mbit/s 150 Mbit/s

SAMBA

DECT

WAND MEDIAN

UMTS

GSM

ISDN B-ISDN

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