GSM

Presented by-Navin

A

Seminar on

GSM (Global System for Mobile Communications, originally

Groupe Special Mobile), is a standard developed by the European

Telecommunications Standards Institute (ETSI) to describe the

protocols for second-generation (2G) digital cellular networks

used by mobile, first deployed in Finland in July 1991.

What is GSM ?

"GSM" is a trademark owned by the GSM Association.

The GSM study group aimed to provide the followings through the GSM:

Improved spectrum efficiency. International roaming. Low-cost mobile sets and base stations (BSs). High-quality speech. Compatibility with Integrated Services Digital Network

(ISDN) and other telephone company services. Support for new services

Why GSM ?

Tele-services Bearer or Data Services Supplementary services

GSM SERVICES

• Telecommunication services that enable voice communication via mobile phones

• Offered services

- Mobile telephony

- Emergency calling

Tele Services

Voice mailbox Electronic mail Include various data services for information transfer

between GSM and other networks like PSTN, ISDN etc. at rates from 300 to 9600 kbps

Short Message Service (SMS),alphanumeric data transmission to/from the mobile terminal.

Bearer Services

Call related services :•Call Waiting- Notification of an incoming call while on the handset•Call Hold- Put a caller on hold to take another call•Call Barring- All calls, outgoing calls, or incoming calls•Call Forwarding- Calls can be sent to various numbers defined by the user•Multi Party Call Conferencing - Link multiple calls together•CLIP – Caller line identification presentation•CLIR – Caller line identification restriction

Supplementary Services

GSM Specification

Two main standard of GSM :-1. GSM 900 – Designed for extensive radio coverage in rural areas2. GSM 1800 – Designed for radio coverage in areas with very high

subscriber density.

RF SpectrumGSM 900 Mobile to BTS (uplink): 890-915 MHz BTS to Mobile(downlink):935-960 MHz Bandwidth : 2* 25 MHz

GSM 1800 Mobile to BTS (uplink): 1710-1785 MHz BTS to Mobile(downlink) 1805-1880 MHz Bandwidth : 2* 75 MHz

Cellis the radio coverage area of one base transceiver station

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

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GSM Concepts - Cellular Structure

Why a hexagon and not other geometrical shape

represent cells?• When showing a cellular system we want to depict an area totally

covered by radio, without any gaps.

• The circles leave gaps

• Also for a given area, among square, triangle and hexagon, radius

of a hexagon will be the maximum which is needed for weaker

mobiles.

GSM SYSTEM ARCHITECTURE

4 Basic interconnected Subsystem :

Mobile Station (MS)Base station Subsystem (BSS)Network and Switching Subsystem (NSS)Operation Support Subsystem (0SS)

Mobile Station (MS)

The Mobile Station is made up of two entities:

1. Mobile Equipment (ME)

2. Subscriber Identity Module (SIM)

Mobile Equipment

Voice and data transmission Portable, vehicle mounted, hand held device Uniquely identified by an IMEI (International Mobile

Equipment Identity).

Subscriber Identity Module (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)

is the unique 15 digit( 3 for country code, 3 for mobile

network code and 9 for mobile ID )identity number

resides in SIM.

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

Base Station Subsystem is composed of

two parts that communicate across the

standardized Abis interface allowing

operation between components made by

different suppliers

1. Base Transceiver Station (BTS)

2. Base Station Controller (BSC)

Base Station Subsystem (BSS)

Base Transceiver Station (BTS)

Base Station Controller (BSC)

Base Transceiver Station (BTS):

• Encodes, encrypts, multiplexes, modulates and feeds the RF signals to the antenna.

• Communicates with Mobile station and BSC• Consists of Transceivers (TRX) units

Base Station Controller (BSC):

• Manages Radio resources for BTS• Assigns Frequency and time slots for all MS’s in its area• Handles call set up• Transcoding and rate adaptation functionality• Handover for each MS• Radio Power control • It communicates with MSC and BTS

Mobile Switching Centre (MSC)• Heart of the network

• Manages communication between GSM and other networks

• Call setup function and basic switching

• Call routing

• Billing information and collection

• Mobility management

- Registration

- Location Updating

- Inter BSS and inter MSC call handoff

Network Switching Subsystem(NSS)

MSC

Home Location Registers (HLR)

• Permanent database about mobile subscribers in a large service

area(generally one per GSM network operator)

• database contains IMSI ,MSISDN , prepaid/post-paid , roaming

restrictions , supplementary services.

Visitor Location Registers (VLR)

• Temporary database which updates whenever new MS enters its area,

by HLR database

• Controls those mobiles roaming in its area

• Reduces number of queries to HLR

• Database contains IMSI , TMSI,MSISDN,MSRN,Location Area,

authentication key

The OSS (Operation Subsystem) enables centralized operation, management, and maintenance of all GSM subsystems

Components Operation and Maintenance Center (OMC)

Mainly does three operation1.To maintain all telecommunication hardware and network operation with a particular market.2. Manage all charging and billing procedure3.Manage all mobile equipment in the system.

Operation Support System (OSS)

Authentication Centre (AUC) • Protects against intruders in air interface

• Maintains authentication keys and algorithms and provides

• security triplets ( RAND , SRES ,Kc)

Equipment Identity Register (EIR)• Database that is used to track handsets using the IMEI

(International Mobile Equipment Identity)

• Made up of three sub-classes: The White List, The Black List and

the Grey List

GSM Frame Structure

Speech decoding

Channel decoding

De-interleaving

Burst Formatting

De-ciphering

DemodulationModulation

Ciphering

Burst Formatting

Interleaving

Channel Coding

Speech coding

Radio Interface

Speech Speech

13 Kbps

22.8 Kbps

22.8 Kbps

33.6 Kbps

33.6 Kbps

270.83 Kbps

GSM Operation from transmitter to receiver

Example: GSM location update (1)

MESIM

HLR

MSCVLR 1

Most recently allocated Temporary Mobile Subscriber Identity (TMSI) and last visited LAI (Location Area ID) are stored in SIM even after switch-off.

After switch-on, MS monitors LAI. If stored and monitored LAI values are the same, no location updating is needed.

(most generic scenario)

MSCVLR 2

LAI 1IMSITMSI

LAI 1IMSITMSI

IMSILAI 1

(in broadcast messages)

GSM location update (2)

MESIM

MSCVLR 1

Different LAI values => location update required !

MSCVLR 2

LAI 2HLR

IMSILAI 1

IMSITMSI

LAI 1IMSITMSI

(in broadcast messages)

GSM location update (3)

MESIM

MSCVLR 1

SIM sends old LAI and TMSI to VLR 2.

VLR 2 does not recognize TMSI since there is no TMSI-IMSI context. Who is this user?

MSCVLR 2

LAI 1, TMSIHLR

IMSILAI 1

IMSITMSI

LAI 1IMSITMSI No TMSI - IMSI

context

GSM location update (4)

MESIM

MSCVLR 1

However, VLR 2 can contact VLR 1 (address: LAI 1) and request IMSI. IMSI is sent to VLR 2.

MSCVLR 2

HLRIMSILAI 1

IMSITMSI

LAI 1IMSITMSI IMSI

TMSI

IMSI address: LAI 1

GSM location update (5)

MESIM

MSCVLR 1

Important: HLR must be updated (new LAI). If this is not done, incoming calls can not be routed to new MSC/VLR.

HLR also requests VLR 1 to remove old user data.

MSCVLR 2

HLRIMSILAI 1LAI 2

IMSITMSI

LAI 1IMSITMSI

IMSI TMSI

LAI 2

GSM location update (6)

MESIM

MSCVLR 1

VLR 2 generates new TMSI and sends this to user. User stores new LA2 and TMSI safely in SIM.

Location update successful !

MSCVLR 2

HLRIMSILAI 2

LAI 1IMSITMSILAI 2 TMSI

IMSI TMSI TMSI

LAI 2TMSI

MS sends dialled number to BSS BSS sends dialled number to MSCMSC checks VLR if MS is allowed the requested service.If so, MSC asks BSS to allocate resources for call.MSC routes the call to GMSCGMSC routes the call to local exchange of called user.Answer back(ring back) tone is routed from called user to MS via GMSC,MSC,BSS

Outgoing Call

Call Originating from MS Call termination to MS

Call Routing

Incoming Call

Calling a GSM subscribersForwarding call to GSMCSignal Setup to HLR5. Request MSRN from VLRForward responsible MSC to GMSCForward Call to current MSC9. Get current status of MS11. Paging of MS13. MS answers15. Security checks17. Set up connection

ADVANTAGES OF GSM :- It can be use repeaters.

It is easy to implement.

International roaming is not a big problem.

DISADVANTAGES OF GSM:- Manufactures are not release IS-95 devices due to the lack

of the big market and it come in late in market.

GSM has fixed max call sites range up to 35 km that is

very limited.

Development of the Market Share of Mobile Standards

Mobile phone subscribers by technology (left Y axis) and total number of subscribers globally (right Y axis)

In a fast-growing market, GSM/3GSM (red) grows faster than the market and is gaining market share, the CDMA family (blue) grows at about the same rate as the market, while other technologies (grey) are being phased out.

GSM in India

2nd Generation GSM -9.6 Kbps (data rate)

2.5 Generation ( Future of GSM)HSCSD (High Speed ckt Switched data)

Data rate : 76.8 Kbps (9.6 x 8 kbps)GPRS (General Packet Radio service)

Data rate: 14.4 - 115.2 KbpsEDGE (Enhanced data rate for GSM Evolution)

Data rate: 547.2 Kbps (max)

3 GenerationWCDMA(Wide band CDMA)

Data rate : 0.348 – 2.0 Mbps

3.5 GenerationHigh Speed Downlink Packet Access(HSDPA)

Data rate : 1.4– 5.8 Mbps

4 GenerationLong Term Evolution (LTE)

Data rate : up to 20.0 Mbps

FUTURE OF GSM