NQ&O Report

GSM

GSM

What is GSM ?Global System for Mobile Communications (GSM) is a second generation (2G) cellular standard developed to cater voice services and data delivery using digital modulation.

It is the worlds most widely used cell phone technology.

GSM

GSM: HistoryGSM

Standard set developed by the European Telecommunications Standards Institute (ETSI) founded 1982 as Group Spciale Mobile; to describe protocols for second generation (2G) digital cellular networks used by mobile phones.

Aim : to replace the incompatible first generation (1G) analog cellular networks

GSM: Presently.GSM

Presently - GSM standardization resides with special mobile group under ETSI ( European telecommunication Standards Institute )

GSM is the de facto global standard for mobile communications with over 80% market share.

GSM ServicesGSM

Tele ServicesGSM

Telecommunication services that enable voice communication via mobile phones

Offered servicesMobile telephony Emergency calling

Hello1SpeakingSpeaking1Hello

Bearer ServicesGSM

Include various data services for information transfer between GSM and other networks like PSTN, ISDN, etc.Short Message Service (SMS) up to 160 character alphanumeric data transmission to/from the mobile terminalUnified Messaging Services(UMS)Group 3 faxVoice mailboxElectronic mailmessage Bmessage Bmessage Bmessage Amessage Amessage AInformationProvider BInformationProvider A

Supplementary ServicesGSM

These are the added call related services :Call Waiting - Notification of an incoming call while on the handsetCall Hold - Put a caller on hold to take another callCall Barring - All calls, outgoing calls, or incoming callsCall Forwarding- Calls can be sent to various numbers defined by the user

Others are Multi Party Call Conferencing(Link multiple calls together), CLIP(Caller line identification presentation), CLIR (Caller line identification restriction) and CUG ( Closed user group).VoicemessageserverPlease leave a messageafter the toneGSM network1BusyVoice mailboxForwardto voicemail boxWarming up...You have3 voice messages...Retrieving the voicemessages

GSM Architecture High Level 1GSM

SIMME:Mobile equipmentServices / ApplicationsCore Network(CN)UE: User equipmentAccess Network(AN)

GSM Architecture High Level 2GSM

GSM Architecture High Level 3GSM

cellcellcellBTSBSCPacket domainCircuit domainBTSBSCAbisAGb

GSM Architecture VoiceGSM

BTSMSBSCMSCBSCBSCBTSBTSGMSCAccess Networkdatabases

2G Data GPRS/EDGEGSM

BTSMSBSCBTSBTSAccess NetworkPCUGGSNUDP/TCP tunnelSGSNInternet

GSM Architecture - DetailedGSM

GSM Architecture - DetailedGSM

GSM System ArchitectureGSM

Mobile Station (MS)Mobile Equipment (ME)Subscriber Identity Module (SIM)

Base Station Subsystem (BSS)Base Transceiver Station (BTS)Base Station Controller (BSC)

Network Switching Subsystem(NSS)Mobile Switching Center (MSC)Home Location Register (HLR)Visitor Location Register (VLR)Authentication Center (AUC)Equipment Identity Register (EIR)

The MS Mobile StationGSM

The Mobile Station is made up of two entities:Mobile Equipment (ME)Subscriber Identity Module (SIM)SIMME

The MS Mobile StationGSM

Mobile EquipmentPortable - vehicle mounted or hand held device Uniquely identified by an IMEI (International Mobile Equipment Identity)Voice and data transmission Monitoring power and signal quality of surrounding cells for optimum handoverPower level : 0.8W 20 W160 character long SMS. Subscriber Identity Module (SIM)Smart card contains the International Mobile Subscriber Identity (IMSI)Allows user to send and receive calls and receive other subscribed servicesEncoded network identification details - Key Ki,Kc and A3,A5 and A8 algorithmsProtected by a password or PINCan be moved from phone to phone contains key information to activate the phone

The BSS Base Station subsystemGSM

Base Station Subsystem is composed of two parts that communicate across the standardized Abis interface allowing operation between components made by different suppliers. The BSS consists of:Base Transceiver Station (BTS)Base Station Controller (BSCBTS

The BSS Base Station subsystemGSM

Base Transceiver Station (BTS):Encodes, encrypts, multiplexes, modulates and feeds the RF signals to the antenna.Frequency hoppingCommunicates with Mobile station and BSCConsists of Transceivers (TRX) unitsBase Station Controller (BSC)Manages Radio resources for BTSAssigns Frequency and time slots for all MSs in its areaHandles call set upTranscoding and rate adaptation functionalityHandover for each MSRadio Power control It communicates with MSC and BTS

The Core Network Network Switching Subsystem(NSS)GSM

Mobile switching Centre(MSC) Vistor Location Register(VLR)Home Location Register (HLR)

Equipment Identity Register (EIR)Authentification centre (AuC).Media Gateway (MGW).This is the nerve-centre of the network. It consists of the following main elements:

Network Switching Subsystem(NSS)GSM

Mobile Switching Center (MSC)Heart of the networkManages communication between GSM and other networksCall setup function and basic switchingCall routing Billing information and collectionMobility managementRegistrationLocation UpdatingInter BSS and inter MSC call handoffMSC does gateway function while its customer roams to other network by using HLR/VLR.A media gateway (MGW)Converts digital media streams between disparate telecommunications networks such as PSTN, SS7, Next Generation Networks (2G, 2.5G and 3G radio access networks) or PBX.Authentication Center (AUC) Protects against intruders in air interfaceMaintains authentication keys and algorithms and provides security triplets ( RAND, SRES, Kc)Generally associated with HLR

NSS The RegistersGSM

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 Gray ListOnly one EIR per PLMN

Visitor Location Register (VLR)Temporary database which updates whenever new MS enters its area, by HLR databaseControls those mobiles roaming in its area Reduces number of queries to HLR Database contains IMSI, TMSI, MSISDN, MSRN, Location Area, authentication keyHome Location Register (HLR)permanent database about mobile subscribers in a large service area(generally one per GSM network operator) database contains IMSI, MSISDN, prepaid/postpaid, roaming restrictions, supplementary services.

Call RoutingGSM

Call Routing - Outgoing callGSM

MS sends dialled number to BSS BSS sends dialled number to MSC3,4 MSC 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 user7, 8,9,10 Answer back(ring back) tone is routed from called user to MS via GMSC,MSC,BSS

Call Routing - Incoming CallGSM

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

HandoversGSM

Handovers enhances mobility. The main types are:

Between 1 and 2 (Inter BTS / Intra BSC)

Between 1 and 3 (Inter BSC/ Intra MSC)

Between 1 and 4 (Inter MSC)

Security in GSMGSM

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 algorithm for authenticationA5 algorithm for encryptionA8 algorithm for key generation

Authentication in GSMGSM

Key generation and EncryptionGSM

GSM