Maulana Azad National Institute of Technology,BhopalDepartment of Computer Science & Engineering

GSM Guided By:

Mrs. NAMITA TIWARI

Presented By: Priyanka ChhabraPriyanka Chhabra 082112120082112120

GSM – GLOBAL SYSTEM FOR MOBILE COMMUNICATION

HISTORY

• GSM criteria – – Good subjective speech quality– Low terminal and service cost– Support for international roaming– Ability to support handheld terminals– Support for range of new services and facilities– Enhanced Features– ISDN compatibility– Enhance privacy– Security against fraud

HISTORYcontd.

• Phase I of GSM specifications was published in 1990• International demand was so great that the system name

was changed from Groupe Special Mobile to Global Systems for Mobile Communications (still GSM)

• Commercial service started in mid-1991• 1992 first paying customers were signed up for service• By 1993 there were 36 GSM networks in 22 countries• Early 1994 there were 1.3 million subscribers worldwide• By 1996 there were more than 25 million subscribers

worldwide• By October 1997 it had grown to more than 55 million

subscribers worldwide

Building Blocks

• AMPS – Advanced Mobile Phone System

• TACS – Total Access Communication System

• NMT – Nordic Mobile Telephone System

Building Blockscontd.

AMPS – Advanced Mobile Phone System

• analog technology

• used in North and South America and approximately 35 other countries

• operates in the 800 MHz band using FDMA technology

Building Blockscontd.

TACS – Total Access Communication System

• variant of AMPS

• deployed in a number of countries

• primarily in the UK

Building Blockscontd.

NMT – Nordic Mobile Telephone System

• analog technology

• deployed in the Benelux countries and Russia

• operates in the 450 and 900 MHz band

• first technology to offer international roaming – only within the Nordic countries

The GSM Bands

Teleservices (TS) Bearer services (BS) Supplementary Services (SS)

The GSM Services

Tele Services

• Telecommunication services that enable voice communication

via mobile phones

• Offered services

- Telephony

- Emergency calling

– Voice messaging

Bearer Services

• Include various data services for information transfer between GSM and other networks like PSTN, ISDN etc at rates from 300 to 9600 bps

• Short Message Service (SMS) –up to 160 character alphanumeric data transmission to/from the mobile terminal

• Group 3 fax• Voice mailbox• Electronic mail

•Call forwarding.

•Barring of Outgoing Calls.

•Barring of Incoming Calls.

•Advice of Charge (AoC).

•Call Hold..

•Call Waiting.

•Multiparty service.

•Calling Line Identification presentation/restriction..

•Closed User Groups (CUGs).

•Explicit Call Transfer (ECT).

Supplementary Services

GSM Architecture

The Four blocks• Mobile Station Subsystem (MSS)– Mobile Termination (MT) and SIM card (SIM)• Base Station Subsystem (BSS)– BSC and BTS• Network and Switching Subsystem (NSS)– MSC, HLR, VLR, EIR and AuC• Operation and Support Subsystem (OSS)– OMC and NMC

System ArchitectureMobile Station (MS)

The Mobile Station is made up of two entities:

1. Mobile Equipment (ME)

2. Subscriber Identity Module (SIM)

System ArchitectureMobile Station (MS) contd.

Mobile Equipment

• Produced by many different manufacturers

• Must obtain approval from the standardization body

• Uniquely identified by an IMEI (International Mobile Equipment Identity)

System ArchitectureMobile Station (MS) contd.

Subscriber Identity Module (SIM)

• Smart card containing the International Mobile Subscriber Identity (IMSI)

• Allows user to send and receive calls and receive other subscribed services

• Encoded network identification details• Protected by a password or PIN• Can be moved from phone to phone – contains key

information to activate the phone

20

SIM Anatomy

Base Station Subsystem Consists of• Base Transceiver Station (BTS)

– radio equipments responsible for radio coverage• Base Station Controller

• Controls a few BTS• Manages Resources for BTS• Handles call set up• Location update• Handover for each MS• Manage radio resource management, signaling transmission,power control, handover control, frequency hopping control etc.

• Transcoder/Rate Adapter Unit (optional)– A device placed between GSM elements (BTS, BSC and MSC)to conserve bandwidth resources.– Combines four 13 kbps speech channels to one 64 kbps datastream. Thirty 64 kbps channels can then be multiplexed to a E1channel. Located at BTS, BSC (more often) or MSC.

• Perform functions such as call setup, paging,resource allocation, location registration,encryption, interfacing with other networks,handoff control, billing, synchronization, echocanceling and interface with external networks.• Consist of 4 elements– MSC, HLR, VLR, AuC and EIR– MSC is the processor, the others are database units.

Network and Switching Subsystem (NSS)

Mobile Switching Center (MSC)

Switch speech and data connections between:Base Station ControllersMobile Switching CentersGSM-networksOther external networks

Heart of the network

Three main jobs: 1) connects calls from sender to receiver2) collects details of the calls made and received3) supervises operation of the rest of the network

components

Home Location Register (HLR)• HLR contains a list of subscribers belonging toone or more MSC areas.• Permanent subscriber data including IMSI, MSISDN,roaming restriction, permittedsupplementary services and authentication key.• Temporary subscriber data consist of MSRN,data related to encryption, VLR address, MSCaddress and roaming restriction.• HLR is usually centralized within a network.

Visitor Location Register (VLR)• Similar to HLR but for visitors• When a roamer appears, his HLR data istransferred to the local VLR.• VLR is usually co-located with MSC.

Authentication Center (AuC)• Performs authentication function for eachsubscriber within the system.• A key Ki kept in SIM and AuC. This key is nevertransmitted over air.• Authenticate by using a random challenge.• Vulnerability is present when encryptedauthentication keys must be transmitted fromHLR to VLR.

Equipment Identity Register (EIR)• Records the IMEI of all subscribers in three lists.• White list ---- clean equipment• Black list ---- stolen equipment• Gray list ---- equipment with minor problems

• OSS consists of two entities not fully specifiedin GSM. They are– Operation and Maintenance Center (OMC)– Network Management Center (NMC)• Performs alarm handling, fault management,performance management, configurationmanagement, traffic data acquisition, activateand deactivate functions, and long termplanning. Normally centralized in a network.• Implementation of these functions are operatorspecific.

Operation and Support Subsystem (OSS)

• A-Interface ---- between BSC and MSC, E1 link.• Abis-Interface ---- between BTS and BSC using LADP(Link Access Data Protocol) protocol.• B-Interface ---- between MSC and VLR• C-Interface ---- between MSC and HLR• D-Interface ---- between HLR and VLR• E-Interface ---- between MSCs• F-Interface ---- between MSC and EIR• Um-Interface ---- between MSS and BSS.

Open Interfaces

Call Routing

• Call Originating from MS

• Call termination to MS

Outgoing Call

1. MS sends dialled number to BSS

2. BSS sends dialled number to MSC

3,4 MSC checks VLR if MS is allowed the requested service.If so,MSC asks BSS to allocate resources for call.

5 MSC routes the call to GMSC6 GMSC routes the call to local

exchange of called user7, 8,9,10 Answer back(ring back) tone

is routed from called user to MS via GMSC,MSC,BSS

Incoming Call1. Calling a GSM

subscribers2. Forwarding call to

GSMC3. Signal Setup to HLR4. 5. Request MSRN

from VLR6. Forward responsible

MSC to GMSC7. Forward Call to

current MSC8. 9. Get current status

of MS10.11. Paging of MS12.13. MS answers14.15. Security checks16.17. Set up

connection

Handovers

• Between 1 and 2 – Inter BTS / Intra BSC

• Between 1 and 3 –

Inter BSC/ Intra MSC• Between 1 and 4 –

Inter MSC

Security in GSM

• On air interface, GSM uses encryption and TMSI instead of IMSI.

• SIM is provided 4-8 digit PIN to validate the ownership of SIM

• 3 algorithms are specified :

- A3(Authentication) algorithm for authentication

- A5(Ciphering) algorithm for encryption

- A8(Ciphering Key Generation) algorithm for key generation

Call Management (CM) and Mobility Management (MM)

• CM consists of setup, emergency setup, call proceeding, progress, call confirm, alerting, connect, user information, disconnect, release, status, congestion control, etc all together 18 messages.

• MM consists of authentication request, authentication response, identify request, location update request, etc

GSM Mobile Services

A prepaid mobile phone (also commonly referred to as pay-as-you-go or prepaid wireless) is a mobile phone for which service is purchased in advance of use.

• Advantages– Lower cost for low usage– Easier to control spending– Available to those who do not have an address

• Limitations– Every time pay before– No balance means cant make any call

Advantages of GSM over Analog system

• Capacity increases• Reduced RF transmission power and longer battery

life.• International roaming capability.• Better security against fraud (through terminal

validation and user authentication).• Encryption capability for information security and

privacy.• Compatibility with ISDN,leading to wider range of

services

Future Of GSM

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 Generation

WCDMA(Wide band CDMA) Data rate : 0.348 – 2.0 Mbps

Future -- UMTS (Universal Mobile Telephone System

• Reasons for innovations- new service requirements- availability of new radio bands