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GSMGlobal System for

Mobiles Communication

TOPICS

TELECOM BASIS GSM HISTORY GSM CONCEPT AND STRUCTURE IDENTITIES USED IN GSM MOBILITY MANAGEMENT CALL MANAGEMENT

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TELECOM BASICS

Communication Voice and Data Analog and Digital Circuit Switched and Packet Switched Media - Copper Wire, Co-axial cable, Air, Optical

Fibre Networks -PSTN, ISDN, PDN and Mobile

Networks

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BACKGROUND TO GSM

1G : Advanced Mobile Phone Service (AMPS) Analog, Circuit Switched, FDMA

2G : Digital Advanced Mobile Phone Service (D-AMPS) Digital, Circuit Switched, FDMA

2G : Global System for Mobile (GSM) Digital, Circuit Switched, FDMA and TDMA

2G : Code Division Multiple Access (CDMA) Digital, Circuit Switched, CDMA

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DEVELOPMENT OF THE GSM STANDARD

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1982: Groupe Spécial Mobile (GSM) created

1984: Description of GSM features

1985: List of recommendations settled

1987: Initial MoU (Memorandum of Understanding) aside the drafting of technical specifications was signed by network operators of 13 countries:

1988: Validation and trials, of the radio interface.

1991: First system trials are demonstrated at the Telecom 91 exhibition.

1992: Official commercial launch of GSM service in Europe. First Launch in Finland1993: The GSM-MoU has 62 signatories in 39

countries worldwide.

1995: Specifications of GSM phase 2 are frozen.

1999: GSM MoU joins 3GPP (UMTS) GPRS Trials begins

2000: 480M GSM Network operators WorldwideFirst GPRS Networks roll out

End 2002: 792M GSM Net work Operators

Worldwide

INCREASING GSM DATA RATES

Transmission TimeGPRS = General Packet Radio ServiceHSCSD = High Speed Circuit Switched DataEDGE = Enhanced Data rate for GSM EvolutionUMTS = Universal Mobile Telecommunication System

10 sec 1 min 10 min 1 hour0

UMTS

E/GPRS

ISDN

PSTN

GSM

webe-mail photo

web photoe-mail

web photo

video clipreportphoto

web photoe-mail

video clipreport

video clipreport

video clipreport

video clipreport

WIRELESS DATA TECHNOLOGY OPTIONS

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thro

ug

hp

ut

kbp

s

10 k

100 k64 k

1 M

2 M

1 k1998 1999 2000 2001 2002

Time frame

UMTS

GPRS

HSCSD

9.614.4

packet

GPRS = General Packet Radio ServiceHSCSD = High Speed Circuit Switched DataEDGE = Enhanced Data rate for GSM EvolutionUMTS = Universal Mobile Telecommunication System

EDGEcircuit

CIRCUIT-SWITCHED OR PACKET-SWITCHED

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Circuit mode

Packet mode

A→FD→H

C→G

C→G

C→G

C→G

C→G

D→H

D→H

A→FD→H

D→H

A→F

A→F

A→F

A

B

C

D

E

F

G

H

GSM CONCEPTS - CELLULAR STRUCTURE

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CellularNetworking technology that breaks geographic area into cells shaped like honey comb

Cellis the radio coverage area of one base transceiver station

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23

45

6

76

72

1

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MULTIPLE ACCESS TECHNIQUE

Multiple Access – Achieved by dividing the available radio frequency spectrum, so that multiple users can be given access at the same time.

FDMA - Frequency Division Multiple Access ( eg: GSM each Frequency channel is 200KHz)

TDMA - Time Division Multiple Access ( eg: GSM each frequency channel is divided into 8

timeslots) CDMA - Code Division Multiple Access

(eg: IS95- Each User data is coded with a unique code)

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DUPLEX TECHNIQUE

Duplex - How the up link and Down link of a user is separated

FDD - Frequency Division Duplex (eg:In GSM the up link and down link of a user is separated by

45MHz ) TDD - Time Division Duplex

(the up link and down link of a user will be at the same frequency but at different Time )

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GSM IN COMPARISON WITH OTHER STANDARDS

GSM gives mobility without any loss in Audio quality Encryption techniques used gives high security in the air

Interface and also use of SIM. Bit Interleaving for high efficiency in Transmission. Variable Power (Power budgeting- extend battery life) Minimum Interference. Features-CCS7 Signaling

SMS (Short Message Services) Emergency Calls CELL Broadcast

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Time Division Multiple AccessEach carrier frequency subdivided in time domain into 8 time slots Each mobile transmits data in a frequency, in its particular time slot - Burst period = 0.577 milli secs.8 time slots called a TDMA frame. Period is .577 * 8 = 4.616 milli secs

0 1 2 3 4 5 6 7

4.616 ms

0.577 ms

ACCESS TECHNIQUES ...

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AuC

MS

MS

BTS

BTS

BTS

BSC

BSC

MSC

MSC

VLR

VLR

GMSC

HLR

PSTN

EIR

Um

A

A

OMC Server

Um

GSM - NETWORK STRUCTURE

B

E

E

C

F

H

AuC -Authentication CenterPSTN - Public Switched Telephone Network.OMC Operation And Maintenance CenterGMSC -Gateway Mobile Switching Centre

GSM ARCHITECTURE

EIR AuC

FROM SPEECH TO RADIO TRANSMISSION

Blah… Blah… Blah...Blah... Blah... Blah...

Digitizing andSource Coding

Channel Coding

Interleaving

Ciphering

Burst Formatting

Modulating Demodulating

Burst De-formatting

Deciphering

De-interleaving

Channel Decoding

Source Decoding

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GSM NETWORK

OMC

AUC

HLR

MSC

EIRVLR

BSC

BTS

MS

ExternalPSTN &PDN N/W

SS

BSS

SwitchingSystem

Base StationSystem

MS Mobile Station

BTS Base transceiver System

BSC Base Station Controller

MSC Mobile Switching Center

HLR Home Location Register

VLR Visitor Location Register

EIR Equipment Identity Register

AUC Authentication Center

OMC Operation And Maintenance Center

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MOBILE STATION (MS)

Hand portable unit

Contains Mobile Equipment(ME) and Subscriber Identity Module (SIM)

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MOBILE EQUIPMENT(ME)

Frequency and Time Synchronization Voice encoding and transmission Voice encryption/decryption functions Power measurements of adjacent cells Display of short messages International Mobile Equipment Identifier (IMEI)

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SIM Portable Smart Card with memory (ROM-6KB to 16KB-A3/A8

algorithm, RAM- 128KB TO 256KB, EEPROM- 3KB to 8KB ) Static Information

International Mobile Subscriber Identity(IMSI) Personal Identification Number (PIN) Authentication Key (Ki)

Dynamic Information Temporary Mobile Subscriber Identity(TMSI) Location Area Identity (LAI) Phone memories, billing information Ability to store Short Messages received

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BASE STATION CONTROLLER (BSC)

Provides all the control functions and physical links between the MSC and BTS

External Interfaces ‘Abis’ interface towards the BTS ‘A’ interface towards the MSC

Monitors and controls several BTSs Management of channels on the radio interface Alarm Handling from the external interfaces Performs inter-cell Handover Switching from ‘Abis’ link to the ‘A’ link Interface to OMC for BSS Management

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MOBILE SWITCHING CENTER (MSC)

Performs call switching Interface of the cellular network to PSTN Routes calls between PLMN and PSTN Queries HLR when calls come from PSTN to mobile user Inter-BSC Handover Paging Billing

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HOME LOCATION REGISTER (HLR)

Stores user data of all Subscribers related to the GMSC International Mobile Subscriber Identity(IMSI) Users telephone number (MS ISDN) Subscription information and services VLR address Reference to Authentication center for key (Ki)

Referred when call comes from public land network

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VISITOR LOCATION REGISTER (VLR)

Database that contains Subscriber parameters and location information for all mobile subscribers currently located in the geographical area controlled by that VLR

Identity of Mobile Subscriber Copy of subscriber data from HLR Generates and allocates a Temporary Mobile

Subscriber Identity(TMSI) Location Area Code Provides necessary data when mobile

originates call

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AUTHENTICATION CENTER (AUC)

Stores Subscriber authentication data called Ki, a copy of which is also stored in in the SIM card

Generates security related parameters to authorize a subscriber (SRES-Signed RESponse)

Generates unique data pattern called Cipher key (Kc) for user data encryption

Provides triplets - RAND, SRES & Kc, to the HLR on request.

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EIR (EQUIPMENT IDENTITY REGISTER)

EIR is a database that contains a list of all valid mobile station equipment within the network,

where each mobile station is identified by its International Mobile Equipment Identity(IMEI).

EIR has three databases., White list - For all known,good IMEI’s Black list - For all bad or stolen handsets Grey list - For handsets/IMEI’s that are

on observation

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GSM PROTOCOLS

CM - Connection Management MM - Mobility Management RR - Radio resource LAPDm - LAPD for mobile LAPD - Link Access Procedure for D channel BTSM - BTS Management Part BSSAP - BSS Application Part (BSC - MSC) DTAP - Direct Transfer Application Part (MS - MSC) MAP - Mobile Application Part MTP - Message Transfer part of SS7 SCCP - Signalling Connection Control Part of SS7 TCAP - Transaction Capabilities Application Part ISUP - ISDN User Part

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Functional Plane of GSM

MS BTS BSC MSC/ HLR GMSC VLR

MS BTS BSC MSC/VLR HLR GMSC

CM

MM

RR

Trans

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SUBSCRIBER IDENTITY -MSISDN

The MSISDN is a GSM directory number which uniquely identifies a mobile subscription in the Public Switched Telephone Network (PSTN).

Calls will be routed from the PSTN and other networks based on the Mobile Subscribers’ MSISDN number.

MSISDN= CC + NDC + SN CC= Country Code (91) NDC= National Destination Code(98370) SN= Subscriber Number (12345)

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INTERNATIONAL MOBILE SUBSCRIBER IDENTITY [IMSI]

Subscriber always identified within the GSM network by the IMSI

This is used for all signaling in the PLMN stored in SIM and HLR/VLR

The IMSI consists of three different parts MCC = Mobile Country Code(3 Digits) MNC = Mobile Network Code(2 Digits) MSIN = Mobile Station Identification Number(Upto 10 digits)

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TEMPORARY MOBILE SUBSCRIBER IDENTITY [TMSI]

The TMSI is used for the subscriber’s confidentiality. It should be combined with the LAI to uniquely identify a MS. Since the TMSI has only local significance (that is, within the

MSC/VLR area), the structure may be chosen by each administration.

The TMSI should not consist of more than four octets.

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INTERNATIONAL MOBILE EQUIPMENT IDENTITY [IMEI]

The IMEI is used for equipment identification. An IMEI uniquely identifies a mobile station as a piece or

assembly of equipment. IMEI = TAC + FAC + SNR + sp

TAC= Type Approval Code (6 digits),determined by GSM body FAC= Final Assembly Code (2 digits), identifies

themanufacturer SNR= Serial Number (6 digits), uniquely identifying all

equipment within each TAC and FAC sp = Spare for future use (1 digit)

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TRAFFIC CHANNELS-TCH

TCH carries the voice data. Two blocks of 57 bits contain voice data in the normal burst. One TCH is allocated for every active call. Full rate traffic channel occupies one physical channel(one

TS on a carrier) and carries voice data at 13kbps Two half rate (6.5kbps) TCHs can share one physical

channel.

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FRAMES TYPES ON UM INTERFACE TDMA Frame

8 Time slots (Burst Period) Length is 4.62 ms(8 * 0.577ms)

26-TDMA Multiframe 26 TDMA Frames (24 TCH, SACCH, Idle) 120 ms (26 * 4.62ms)

51-TDMA Multiframe 26 TDMA Frames (FCCH, SCH, BCCH, SDCCH, CCCH) 235.6 ms (51 * 4.62ms)

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BTS commands MS at differentdistances to use different power levelsso that the power arriving at the BTS’s Rx isapproximately the same for each TS

- Reduce interference- Longer battery life

POWER CONTROL

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HANDOVER

Means to continue a call even a mobile crosses the border of one cell to anotherProcedure which made the mobile station really roamHandover causes

RxLev (Signal strength , uplink or downlink)RxQual (BER on data)O & M interventionTiming AdvanceTraffic or Load balancing

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HANDOVER TYPES

Internal Handover (Intra-BSS) Within same base station - intra cell Between different base stations - inter cell

External Handover (Inter-BSS) Within same MSC -intra MSC Between different MSCs - inter-MSC

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HANDOVER TYPES

BSC

BSC

BSC

BSC

MSC

MSC

GMSC

C-1 C-2

C-3

C-4

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Periodic Measurement Reports (SACCH)

Periodic Measurement Reports

HO requiredActivate TCH(facch)with HoRef#

if 1. Check for HO passed2. Channel avail in new BTS

Acknowledges and alloctes TCH (facch)

HO cmd with HoRef#Receives new BTS data(FACCH)

MS tunes into new frequency and TS and sends HO message to new BTS (facch)

Periodic Measurement Reports (SACCH)

HO performed

Release TCH

Cell 1

Cell 2

BSC

BTS 1

BTS 2

Intra BSC handover

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WIRELESS DATA

98 99 2000 2001

GSMDATAGSMDATA

HSCSDHSCSD

GPRSGPRS

EDGEEDGE

UMTSUMTS

SIMToolkitSIMToolkit

WAPWAP

Data Application

Time

Circuit Switched technology

Packet Switched technology

Technology for Applications

SMS Data: 160 -numeric charactersUser Data Rate : 9.6kbpsOne time slot over the air interface

High Speed Circuit Switched DataUser Data Rate:14.5kbpsUse multiple timeslots (max=8), hence max rate = 115.2kbps.Needs a duplexor in MS for simultaneous Tx and Rx

Add-on to GSM network : PCU; Packet Segmentation/re-assembly and scheduling• Radio channel access control and management• Transmission error detection and retransmission.• Power controlSGSN: GPRS mobility• Encryption• Charging GGSN : Interface to the PDN, Internet

Max user data rate : 21.4 kbpsDynamic rate adaptation to suit the radio conditions at that time ( 9.05 kbps, 13.4 kbps, 15.6 kbps 21.4 kbps)

W@P Gateway W@P ServiceW@P

Fone

InternetMobile Network

Surf the Internet while on the move

W@P Gateway :• Adaptation of the information to the mobile• Compression of the data• Buffering of the information

Enhanced Data rate for GSM Evolution• EDGE is an enhancement of GPRS and CSD technologies.• Based on the current GSM technology - same TDMA frame structure, same bandwidth (200 kHz).• Uses 8-PSK modulation instead of GMSK.• Requires good propagation conditions. • Allows upto 48 kbps (EGPRS) and upto 28.8 kbps (ECSD) on every radio channel• EDGE helps GSM-Only operators to compete with UMTS.

Universal Mobile Telecommunication Standards • Innovative Service Architecture : VHE Concept - providing the us the same look and feel of its personalized services independent of network and terminal.• Global Convergence : Fixed/Mobile, Telecom/Datacom, public/private• Mobile Multimedia driven market.• Wideband bearers - 2GHz band ( 5 MHz per carrier), -max. 2Mbps

Radio tower

Base Station

Radio tower

Mobile Switching Station

Regional Switch Office Regional Switch Office

Trunk

5. Destination switch officereceives call, and forwardsto Mobil Switching Station

4. Regional Switch Officeforwards calls

Radio tower Base Station

Radio tower

Mobile Switching Station

1. Cell phone transmits tolocal towers

2. Towers are serviced bya local base station

3. Basestations areservices by MobilSwitching Station

5. Mobile SwitchingStation forwards to Base

Station

6. Base Station forwardsto local towers.

7. Local towers completethe loop

MOBILE-TO-MOBILE LONG DISTANCE

MOBILE IS IN ROAMING

2.Receiving Mobile on Roaming

3. Both Mobiles are on Roaming

INTERNATIONAL ROAMER TERMINATED CALL

Location AreaCode

Global Cell Identification

CountryCode404

NetworkCode

49

CellIdentity

BSC3BSC2BSC1

MSC B MSC A

404 49 100 53

404 49 100 54

404 49 100 55

404 49 100 51

404 49 100 52

404 49 089 20

404 49 089 21

404 49 089 22

404 49 100 50

Location Area-100Location Area-089

INDIA-AP-AirtelMCC-MNC404 -49(INA49)

HANDOVER

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