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The Global System forMobile Communications

(GSM)

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Contents Overview

GSM Services GSM Architecture

Radio Transmission

Conclusion

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GSM Overview History

Group Special Mobile(GSM) formed tostudy pan-European cellular system in1982

First commercial service in Europe in

1991Accepted as the digital standard in

more than 70 countries

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GSM Overview GSM Features

Hybrid air interface : FDMA/TDMA

Standard based on ISDN and SS7

Standard in both air interface as wellas network interface

Purely digital system DCS1800 Up-banded version of GSM900

PCS1900 North American version of GSM900

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GSM Services Bearer Services

Give the subscriber the capacity

required to transmit appropriatesignals between certain access points

TeleservicesProvide the subscriber with necessary

capabilities to communicate with othersubscribers

Supplementary Services

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GSM Architecture Mobile Station

Mobile Equipment

Identified by International MobileEquipment Identity(IMEI)

Subscriber Identity Module(SIM)

Contains unique subscriber identity(IMSI)

Removable smart card that free fromhandsets

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GSM Architecture Base Station Subsystem

Base Transceiver Station(BTS)

Contains the radio transceivers for a givencell

Base Station Controller(BSC)

Manages radio resources, such as signalprocessing, channel setup/teardown,handover

Responsible for one or more BTSs

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GSM Architecture Network Subsystem

Mobile Switching Center(MSC)

Manages call routing and establishment,authentication, connection to fixed networks

Home Location Register(HLR) Stores subscription information and current

location of all subscribers in a given network

Visitor Location Register(VLR) Contains subscription information needed for callcontrol, for all mobiles in area controlled byassociated MSC

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GSM ArchitectureEquipment Identity Register(EIR)

Contains the IMEI of all registered mobile

equipment, marked as black, gray, orwhite listed, depending on whether it istype approved or has been reportedstolen

Authentication Center(AUC) Stores secret key held in SIM card

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GSM Architecture

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GSM Architecture Mobile Application Part(MAP)

Signaling between components of the NSS

uses the MAP which is built on top of SS7

MAP-B : MSC-VLR

MAP-C : MSC-HLR

MAP-D : HLR-VLR

MAP-E : MSC-MSC MAP-F : MSC-EIR

MAP-G : VLR-VLR

MAP-H : AC-HLR

MAP-I : User application protocol and HLR

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GSM Architecture Identification Codes

IMSI(International Mobile Subscriber

Identity:15digits) Directory number assigned by operators to a

subscriber

TMSI(Temporary Mobile Subscriber

Identity:32bits) Assigned by VLR to a subscriber

Privacy and network security, avoidingtransmission of IMSI

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GSM ArchitectureMSISDN(Mobile Station ISDN no.)

Used to reach a called party in a GSM

network

PSTNGMSC

BTS

BSCMSC

VLR

HLR1.MSISDN

2.MSISDN

3. IMSI 4.MSRN

5.MSRN

6. Route call

7. Route call8. Route call

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GSM Architecture IMEI(International Mobile Equipment

Identity:15digits)

Unique serial number assigned bymanufacturer to a terminal

LAI(Location Area Identity:15digits)

Assigned by operating company to a BTS

Mobile Country Code(MCC), MobileNetwork Code(MNC), Location AreaCode(LAC)

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GSM Architecture Functional Planes

Operations, Administration,& Maintenance (OAM)

CommunicationManagement (CM)

Mobility Management(MM)

Radio ResourceManagement (RR)

Physical

SendingEntity

ReceivingEntity

Channel

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GSM Architecture Radio Resources management(RR)

Responsible for establishing and releasing a reliableconnection between the MS and the MSC(handlingchannel allocation and handover)

Internal Handover

Channels(time slots) in the same cell

Cells controlled by the same BSC

External Handover Cells under the control of different BSCs, but

belonging to the same MSC

Cells under the control of different MSCs

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GSM Architecture Mobility Management(MM)

Responsible for location management andsecurity(authentication and encryption)

Authentication and encryption Ki(Authentication Key)

Secret key assigned by operating companyto a subscriber

Used to compute the cipher key

Kc(Cipher Key) Computed by network and by MS

Protect user information and network controlinformation

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GSM Architecture Algorithm

A3 : Authentication algorithm

A5 : Ciphering algorithm

A8 : Ciphering key generating algorithm

Another level of security :IMEI query to theEIR

White-listed : allow to connect to the

network Grey-listed : under observation from the

network

Black-listed : not allow to connect to thenetwork

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GSM Architecture Location management

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GSM ArchitectureCommunication Management(CM)

Responsible for call establishment and

routing Call routing

Supplementary services management

Short message services management

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Radio Transmission Frequency Allocation

GSM900 radio frequencies

890-915MHz and 935-960MHz 125 carriers of 200KHz bandwidth

GSM1800 radio frequencies

1710-1785MHz and 1805-1880MHz

375 carriers of 200KHz bandwidth

PCS1900 radio frequencies

1850-1910MHz and 1930-1990MHz

300 carriers of 200KHz bandwidth

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Radio Transmission Frame and Time Slot

9

8

51

26

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Radio Transmission

FLAG : 1bit

Indicates whether user information orcontrol information

TAIL bits : 3bit

All set to 0

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Radio Transmission GUARD(Guard time) : 8.25bits(30.5Qsec)

Reduce interference to signals in nearly cells usingthe same carrier

TRAIN(Training sequence) : 26bits Used to train the adaptive equalizer, which

compensates for effects of multipath propagation

Used to estimate the characteristics of the time-varying radio channel

8 different sequences with low mutual cross-correlation

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Radio Transmission Logical Channels

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Radio TransmissionBroadcast channels

FCCH(Frequency correction channel)

Used to allow MS to accurately tune to BS SCH(Synchronization channel)

Used to provide TDMA frame-orientedsynchronization data to MS

BCCH(Broadcast control channel)

Transmit the information that MS need tosetup a call

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Radio TransmissionCommon control channels

PCH(Paging channel)

Used to notify MS of arriving calls AGCH(Access grant channel)

Used to assign MS to a stand-alone dedicatedcontrol channel

RACH(Random access channel)

Used to send messages to originate calls,transmit short messages, respond to pagingmessages

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Radio TransmissionDedicated control channels

SDCCH(Stand-alone dedicated control

channel) Used for system signaling during idle periods and

call setup before allocating TCH

FACCH(Fast associated control channel)

Call establish progress, authentication, handover

SACCH(Slow associated control channel)

Used for non-urgent procedures

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BTSMS

Physical Channels

FCCHTraining&slot information

SCHSystem parameters

BCCHChannel request

RACHChannel assignment

AGCHLocation update request

SDCCHAuthentication request

SDCCHAuthentication response

SDCCH

Ciphered mode command

SDCCH

ACK ciphered mode command

SDCCH

Location update confirm

SDCCHACK of the update

SDCCH

1. Lock onto highest power level& best freq. (of a FCCH)

2. Synchronization data

3. LAC,MNC, other frequencies,etc

4. Request & grant of a stand-alone dedicated control

channel5. Move to SDCCH & make a

location update request6. Prove who you claim to be

7. This is who I am

8. We will cipher traffic

9. I agree

10. Update VLR(s) & HLR asnecessary

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BTSMS

Page request

PCHChannel request

RACH

Immediate assignment

AGCH

Paging response

SDCCH

Authentication requestSDCCH

Authentication response

SDCCH

Ciphering mode command

SDCCH

Ciphering mode complete

SDCCH

TMSI reallocation command

SDCCH

TMSI reallocation complete

SDCCH

Continue

1. Page the mobile station

2. Request & grant of a stand-alone dedicated controlchannel

3. Move to SDCCH & answer the

page

4. Prove who you claim to be

5. This is who I am

6. We will cipher traffic

7. I agree

8. Set up temporary ID

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Assignment command

SDCCH

Assignment complete

FACCH

ALERTING messageFACCH

CONNECT message

FACCH

CONNECT ACK message

FACCH

ConversationTCH

Conversation

TCH

SETUP message

SDCCHSETUP ACK message

SDCCH

Continued

9. You have a call

10. I will accept it

11. Assign a traffic channel

12. (ringing)

13. Mobile off-hook, sendCONNECT & ACK

14. Conversation ensues

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Conclusion Very complex standard

First serious attempt to fulfill the

requirements for a universalpersonal communication system

Foundation for DCS1800 and

PCS1900 Defines both the air interface andthe network interface