National University of Modern LanguagesTelecomm EngineeringSemester VI-2009Lecturer: Sheraz Alam Khansheraz.alam@gmail.comGlobal System for Mobile (GSM)Network and Protocol Architecture

OutlineGSM Network OverviewRadio Station SystemNetwork Switching SystemOperation and Maintenance SystemNetwork in Reality---exampleNetwork InterfacesGSM Protocol Architecture

Radio Station System (RSS)Mobile Station (MS)Base Station Sub-system (BSS)Network Switching System (NSS)The Operations and Maintenance System (OMS)

GSM Network Overview

1-Radio Station-SystemMobile StationMobile Equipment (ME)Subscriber Identity Module (SIM)Base Station Sub-System (BSS)Base Transceiver Station (BTS)Base Station Controller (BSC)Transcoding and Rate Adaption Unit (TRAU) *TRAU is also called XCDR

Mobile Station (MS)

Vehicle Mounted These devices are mounted in a vehicle and the antenna is physically mounted on the outside of the vehicle. Portable Mobile UnitThis equipment can be handheld when in operation, but the antenna is not connected to the handset of the unit.Hand-portable UnitThis equipment comprises of a small telephone handset not much bigger than a calculator. The antenna is be connected to the handset.

Mobile Equipment (ME)

Mobile Equipment (ME)

Subscriber Identity Module(SIM)International Mobile Subscriber Identity (IMSI)This number identifies the MS subscriber. It is only transmitted over the air during initialization.Temporary Mobile Subscriber Identity (TMSI)This number identifies the subscriber; it is periodically changed by the system management to protect the subscriber from being identified by someone attempting to monitor the radio interface.

Location Area Identity (LAI)Identifies the current location of the subscriberSubscriber Authentication Key (Ki)This is used to authenticate the SIM card.Mobile Station International Services Digital Network (MSISDN)This is the telephone number of the mobile subscriber. It is comprised of a country code, a network code and a subscriber number.

Subscriber Identity Module(SIM)

b. Base Station subsystem (BSS)The Base Transceiver Station BTS

The Base Station Controller BSC

The Transcoder XCDR or TRAU

Base Transceiver Station(BTS)The BTS contains the RF components that provide the air interface for a particular cell. This is the part of the GSM network which communicates with the MS. The antenna is included as part of the BTSConnected to MSs using Air/radio interface and to BSC either by microwave link or wired

BTS Functionality

Base Station controller (BSC)The BSC as its name implies is heart, core and controlling element for the BSS. Responsible for Radio Resource Management Evaluation of signaling information from MSC via TRAU and MSs via BTSs The BSC may control single or multiple BTSsFrequency management of connected BTSsManagement of entire BSS database

BSC Functionality

BSS Functionality

Transcoder (XCDR)TRAU or XCDR is used for Transcoding------compresses/decompresses the incoming speech data from 64kbps to 13 kbps or 12.2 or 5.6 kbpsRate Adaption----filters out the useful data coming from MSC

2- Network switching subsystem(NSS)Mobile Services Switching Centre MSCHome Location Register HLRVisitor Location Register VLREquipment Identity Register EIRAuthentication Centre AUCInterWorking Function IWFEcho Canceller EC

Mobile Switching Centre(MSC)Brain of GSMResponsible for Mobility Resource ManagementInterface between BSS and other network Operators like PSTN,ISDN PDN etc.

MSC FunctionalityOperations and Maintenance SupportIncludes database management, traffic metering and measurement, and a manmachine interfaceInternetwork InterworkingManages the interface between the GSM network and the PSTNBillingCollects call billing data

Home Location Register (HLR)Reference database for subscriber parametersVarious identification numbers and addresses are stored, as well as authentication parametersSubscriber profiles are created, deleted and barred by operator in this database

Visiting Location Register (VLR)Database containing the most precise location of an MSUsually co-located with MSCProvides MSC with all the information Contains additional info likeMobile status (busy/free/no answer etc.)Location Area Identity (LAI)Temporary Mobile Subscriber Identity (TMSI)Mobile Station Roaming Number (MSRN)

Equipment Identity Register (EIR)

The EIR contains a centralized database for validating the International Mobile Equipment Identity (IMEI). This database is concerned solely with MS equipment and not with the subscriber who is using it to make or receive a call.

EIR DatabaseWhite ListContains those IMEIs which are known to have been assigned to valid MS equipmentBlack ListContains IMEIs of MS which have been reported stolen or which are to be denied service for some other reasonGrey ListContains IMEIs of MS which have problems (for example, faulty software) These are not, however, sufficiently significant to warrant a black listing.

Authentication Centre (AUC)

The AUC is a processing system that performs the authentication function. It will normally be co-located with the Home Location Register (HLR) as it will be required to continuously access and update, as necessary, the system subscriber recordsContains different Keys and algos, using which it generates Triples(Kc , SRES and RAND) used for authentication

Interworking Function (IWF)

The IWF provides the function to enable the GSM system to interface with the various forms of public and private data networks currently available. The basic features of the IWF are listed below.Data rate adaption.Protocol conversion.

Echo Canceller (EC)

An EC is used on the PSTN side of the MSC for all voice circuits. Echo control is required at the switch because the inherent GSM system delay can cause an unacceptable echo condition, even on short distance PSTN circuit connections

3-Operations and Maintenance System (OMS)

The operations and maintenance system provides the capability to manage the GSM network remotely. This area of the GSM network is not currently tightly specified by the GSM specifications, it is left to the network provider to decide what capabilities they wish it to have.Divided in toThe Network Management Centre (NMC)The Operations and Maintenance Centre (OMC)

Network Management Centre (NMC)

Operations and Maintenance Centre (OMC)

There are two types of OMCOMC (R) OMC controls specifically the Base Station System.OMC (S) OMC controls specifically the Network Switching System.Following are the main responsibilities of OMCEvent/Alarm Management.Fault Management.Performance Management.Configuration Management.Security Management.

The Network in RealityCity Coverage

The Network in RealityUK Network Coverage

Signaling System 7(SS7)

Acronyms

BSSAP Base Station System Application PartBSSMAP Base Station System Management Application PartDTAP Direct Transfer Application PartISUP ISDN User PartMAPMobile Application PartSCCP Signaling Connection Control PartTUP Telephone User PartTCAP Transaction Capabilities Application Part

SS7 Layer FunctionalitiesInterfacing the PSTN, the MSC performs call signaling functions using the Telephone User Part (TUP), or interfacing the ISDN, the ISDN User Part (ISUP).Between the MSC and the BSC, the Base Station System Management Application Part (BSSMAP) is used. The Direct Transfer Application Part (DTAP) is used to send messages between the MSC and the mobile (MS). MAP is used between the MSC and the VLR, EIR, and HLR.

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Classmark contains following informationRevision Level Identifies the phase of the GSM specifications that the mobile complies with.RF Power Capability The maximum power the MS is able to transmit, used for power control and handover preparation. This information is held in the mobile power class number.Ciphering Algorithm Indicates which ciphering algorithm is implemented in the MS. There is only one algorithm (A5) in GSM phase 1, but GSM phase 2 specifies different algorithms (A5/0A5/7).Frequency Capability Indicates the frequency bands the MS can receive and transmit on. Currently all GSM MSs use one frequency band, in the future this band will be extended but not all MSs will be capable of using it.Short Message Capability Indicates whether the MS is able to receive short messages.*