Gsm n w Trau n Plan

8/8/2019 Gsm n w Trau n Plan

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GSM N/W ARCHITECTUREGSM N/W ARCHITECTURE


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GSM NETWORK ARCHITECTUREGSM NETWORK ARCHITECTURE

The GSM Network is divided into twoThe GSM Network is divided into twosystems.systems.

Each of these systems are comprised of aEach of these systems are comprised of a

number of functional units.number of functional units.

Which are individual components of theWhich are individual components of themobile network.mobile network.

The two systems are :The two systems are :

SWITCHING SYSTEM (SS)SWITCHING SYSTEM (SS) BASE STATION SYSTEM (BSS)BASE STATION SYSTEM (BSS)

Like all telecommunications networks, GSMLike all telecommunications networks, GSM

networks are Operated, Maintained andnetworks are Operated, Maintained and

Managed from computerized centers.Managed from computerized centers.


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SYSTEM MODELSYSTEM MODEL

AUC

HLR EIR VLR

MSC

B

TS

GMSC

BSC

OTHER

NETWORKS


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GSM NETWORK ARCHITECTUREGSM NETWORK ARCHITECTURE


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ABBREVIATIONSABBREVIATIONS MSMS Mobile StationMobile Station

BTSBTS Base Transceiver StationBase Transceiver Station

BSCBSC Base Station Controller Base Station Controller

MSCMSC Mobile Services SwitchingMobile Services Switching

CenterCenter EIREIR Equipment Identity Register Equipment Identity Register

HLRHLR Home Location Register Home Location Register

VLRVLR Visitor Location Register Visitor Location Register

AUCAUC Authentication Center Authentication Center

OMCOMC Operation and MaintenanceOperation and Maintenance

CenterCenter

NMCNMC Network Management Center Network Management Center


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SWITCHING SYSTEM (SS)SWITCHING SYSTEM (SS)

The SS is responsible for performing callThe SS is responsible for performing callprocessing and subscriber related functions.processing and subscriber related functions.

It includes the following functionalIt includes the following functional

units:units:

Mobile Services Switching Center (MSC)Mobile Services Switching Center (MSC)

Home Location Register (HLR)Home Location Register (HLR)

Visitor Location Register (VLR)Visitor Location Register (VLR)

Authentication Center (AUC)Authentication Center (AUC)

Equipment Identity Register (EIR)Equipment Identity Register (EIR)


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BASE STATION SYSTEM (BSS)BASE STATION SYSTEM (BSS)

The BSS performs all the radioThe BSS performs all the radio--relatedrelatedfunctions.functions.

The BSS is comprised of the followingThe BSS is comprised of the followingfunctional units:functional units:

Base Station Controller (BSC)Base Station Controller (BSC)

Base Transceiver Station (BTS)Base Transceiver Station (BTS)

The OMC performs all the operation andThe OMC performs all the operation andmaintenance tasks for the network :maintenance tasks for the network :

Monitoring Network TrafficMonitoring Network TrafficNetwork AlarmsNetwork Alarms

The OMC has access to both the SS and theThe OMC has access to both the SS and theBSS.BSS.

MSs do not belong to any of theseMSs do not belong to any of these


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SWITCHING SYSTEM COMPONENTSSWITCHING SYSTEM COMPONENTS

FUNCTIONS:FUNCTIONS:

MOBILE SERVICE SWITCHING CENTER(MSC) :MOBILE SERVICE SWITCHING CENTER(MSC) :

The primary node in a GSM network is the MSC.The primary node in a GSM network is the MSC.

It is the node, which controls calls both to MS,sIt is the node, which controls calls both to MS,sand from MS,s.and from MS,s.

The primary functions of an MSC include theThe primary functions of an MSC include thefollowing:following:

Manages the location of mobiles.Manages the location of mobiles.Switches calls.Switches calls.

Manages Security features.Manages Security features.

Controls handover between BSCs.Controls handover between BSCs.


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SWITCHING SYSTEM COMPONENTSSWITCHING SYSTEM COMPONENTS

Resource ManagementResource ManagementInterworks with and manage network databasesInterworks with and manage network databases

Collects call billing data and sends to billingCollects call billing data and sends to billing

systemsystem

Collects traffic statistics for performanceCollects traffic statistics for performancemonitoringmonitoring

SWITCHING AND CALL ROUTING:SWITCHING AND CALL ROUTING:

A MSC controls call setA MSC controls call set--up, supervision andup, supervision andrelease.release.

It may interact with other nodes to successfullyIt may interact with other nodes to successfully

establish a call.establish a call.

This includes routing of calls from MS,s toThis includes routing of calls from MS,s to


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CHARGING:CHARGING:

An MSC contains functions for chargingAn MSC contains functions for charging

mobile calls.mobile calls.

Information about the particular charge ratesInformation about the particular charge rates

to apply to a call at any given time or for ato apply to a call at any given time or for a

given destination.given destination.

During a call it records this information andDuring a call it records this information andstores it after the callstores it after the call-- for output to a billingfor output to a billing

center.center.

SERVICE PROVISIONING:SERVICE PROVISIONING:

Supplementary services are provided andSupplementary services are provided and

managed by a MSC.managed by a MSC.

In addition, the SMS service is handled byIn addition, the SMS service is handled by


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COMMUNICATION WITH HLR:COMMUNICATION WITH HLR:

The primary occasion on which an MSC andThe primary occasion on which an MSC andHLR communicate is during the setHLR communicate is during the set--up of aup of acall to an MS, when the HLR requests somecall to an MS, when the HLR requests somerouting information from the MSC.routing information from the MSC.

COMMUNICATION WITH THE VLR:COMMUNICATION WITH THE VLR:

VLR is associated with each MSC.VLR is associated with each MSC. It communicates for subscription information,It communicates for subscription information,

especially during call setespecially during call set--up and release.up and release.

COMMUNICATION WITH OTHER MSC,s:COMMUNICATION WITH OTHER MSC,s:

It may be necessary for two MSC,s toIt may be necessary for two MSC,s tocommunication with each other during callcommunication with each other during callsetset--up or handovers between cells belongingup or handovers between cells belongingto different MSC,s.to different MSC,s.


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CONTROL OF CONNECTED BSC,s:CONTROL OF CONNECTED BSC,s:

BSS acts as the interface between the MS,sBSS acts as the interface between the MS,sand the SS.sand the SS.s

The MSC has the function of controlling theThe MSC has the function of controlling the

primary BSS node.primary BSS node.

Each MSC may control many BSC,sEach MSC may control many BSC,s

depending on the volume of traffic in adepending on the volume of traffic in a

particular MSC service area.particular MSC service area.

An MSC may communicate with its BSC,sAn MSC may communicate with its BSC,sduring call setduring call set--up and handovers between twoup and handovers between two

BSC,s.BSC,s.


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Direct access to Internet Services:Direct access to Internet Services:

Traditionally, an MSC accessed the InternetTraditionally, an MSC accessed the Internet

nodes of an Internet Service Provider (ISP)nodes of an Internet Service Provider (ISP)

via existing networks such as the PSTN.via existing networks such as the PSTN.

This function enables an MSC toThis function enables an MSC to

communicate directly with Internet nodes,communicate directly with Internet nodes,thus reducing call setthus reducing call set--up time.up time.

Direct access can be provides by using anDirect access can be provides by using an

access server called Tigris. (from Advancedaccess server called Tigris. (from Advanced

Computer Communications)Computer Communications) This may be integrated in an MSC or StandThis may be integrated in an MSC or Stand--

alone connected to an MSC.alone connected to an MSC.


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DIRECT ACCESS TO INTERNETDIRECT ACCESS TO INTERNET

B

T

S


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VISITOR LOCATION REGISTER(VLR)VISITOR LOCATION REGISTER(VLR)

The role of a VLR in a GSM network is to actThe role of a VLR in a GSM network is to act

as a temporary storage location foras a temporary storage location for

subscription information for MSs, which aresubscription information for MSs, which are

within a particular MSC service area.within a particular MSC service area. There is one VLR for each MSC service area.There is one VLR for each MSC service area.

This means that the MSC does not have toThis means that the MSC does not have to

contact the HLR (Which may be located incontact the HLR (Which may be located in

another country.)another country.)

Every time the subscriber uses a service orEvery time the subscriber uses a service or

changes its status.changes its status.


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Following occurs when MS,s move into

Following occurs when MS,s move intoa new service area:a new service area:

1.1. The VLR checks its database to determineThe VLR checks its database to determine

whether or not it has a record for the MSwhether or not it has a record for the MS

(based on the subscriber's IMSI).(based on the subscriber's IMSI).

2.2. When the VLR finds no record for the MS, itWhen the VLR finds no record for the MS, it

sends a request to the subscriber's HLR forsends a request to the subscriber's HLR for

a copy of the MS,s subscription.a copy of the MS,s subscription.

3.3. The HLR passes the information to the VLRThe HLR passes the information to the VLR

and updates its location information for theand updates its location information for the

subscriber.subscriber.


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The HLR instructs the old VLR to delete theThe HLR instructs the old VLR to delete theinformation, it has on the MS.information, it has on the MS.

4. The VLR stores its subscription information4. The VLR stores its subscription information

for the MS, including the latest location andfor the MS, including the latest location and

status (idle).status (idle).

For the duration when the MS is within oneFor the duration when the MS is within one

MSC service areaMSC service area -- The VLR contains a complete copy of theThe VLR contains a complete copy of the

necessary subscription details, includingnecessary subscription details, including

the following information:the following information:


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Identity number for the subscriber.Identity number for the subscriber.

Supplementary service information (e.g.Supplementary service information (e.g.

whether the subscriber has call forwardingwhether the subscriber has call forwarding

on busy activated or not)on busy activated or not)

Activity of MS (e.g. idle)Activity of MS (e.g. idle)

Current LA of MS.Current LA of MS.

MSC/VLR

HLR

MSC/VLR


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DATA IN VLR :DATA IN VLR :

IMSI & TMSIIMSI & TMSI

MSISDNMSISDN

MSRN.MSRN.

Location AreaLocation Area

Supplementary service parametersSupplementary service parameters

MS categoryMS category

Authentication KeyAuthentication Key


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GMSC IMPLEMENTATIONGMSC IMPLEMENTATION

Any MSC in the mobile network can functionAny MSC in the mobile network can functionas a gateway by integration of the appropriateas a gateway by integration of the appropriatesoftware and definition of HLR interrogationsoftware and definition of HLR interrogationinformation.information.

In effect it then becomes a GMSC/VLR.In effect it then becomes a GMSC/VLR.

In Ericsson's GSM systems, gatewayIn Ericsson's GSM systems, gatewayfunctions are provided within the subsystemfunctions are provided within the subsystemMSS.MSS.

The only additional hardware required isThe only additional hardware required ishardware to interface to the signaling link tohardware to interface to the signaling link to

the HLR.the HLR.

Gateway Function :Gateway Function :

Find and interrogate HLR for roaming number.Find and interrogate HLR for roaming number.

Route the call according to the interrogation.Route the call according to the interrogation.


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HOME LOCATION REGISTER (HLR)HOME LOCATION REGISTER (HLR)

The HLR is a centralized network database.The HLR is a centralized network database.

It stores and manages all mobileIt stores and manages all mobile

subscriptions belonging to a specificsubscriptions belonging to a specific

operator.operator.

It acts as a permanent store for a person'sIt acts as a permanent store for a person'ssubscription information until thatsubscription information until that

subscription is cancelled.subscription is cancelled.

The information stored includes:The information stored includes:

Subscriber Identity (i.e. IMSI, MSISDN)Subscriber Identity (i.e. IMSI, MSISDN)

Subscriber Supplementary ServicesSubscriber Supplementary Services

Subscriber Location Information (i.e. MSCSubscriber Location Information (i.e. MSC

service area )service area )


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THE PRIMARY FUNCTIONS OF THE HLRTHE PRIMARY FUNCTIONS OF THE HLRINCLUDE:INCLUDE:

Subscription database management:Subscription database management:

As a database, the HLR must be able toAs a database, the HLR must be able toprocess data quickly in response to dataprocess data quickly in response to dataretrieval and update requests from otherretrieval and update requests from othernetwork nodes.network nodes.

F

or this reason, it acts as a databaseF

or this reason, it acts as a databasemanagement system.management system.

Each subscriber record contains aEach subscriber record contains asubstantial amount of parameters.substantial amount of parameters.


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GATEWAY MSC (GMSC)GATEWAY MSC (GMSC)

Gateway functionality enables an MSC toGateway functionality enables an MSC tointerrogate a HLR in order to route a mobileinterrogate a HLR in order to route a mobileterminating call.terminating call.

It is not used in calls from MS,s to any terminalIt is not used in calls from MS,s to any terminalother than another MS.other than another MS.

For example:For example: If a person connected to the PSTN, wants toIf a person connected to the PSTN, wants to

make a call to a GSM mobile subscribermake a call to a GSM mobile subscriber

The PSTN exchange will access the GSMThe PSTN exchange will access the GSMnetwork by first connecting the call to a GMSC.network by first connecting the call to a GMSC.

The GMSC requests call routing information fromThe GMSC requests call routing information fromthe HLR.the HLR.

HLR provides information about which MSC/VLRHLR provides information about which MSC/VLRto route the call to.to route the call to.

The same is true of a call from an MS to anotherThe same is true of a call from an MS to another


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Communication with MSC,s:Communication with MSC,s: When setting up calls to an MS,When setting up calls to an MS,

It is necessary for the HLR to contact theIt is necessary for the HLR to contact the

MSC serving the MS for routing information.MSC serving the MS for routing information. By analyzing the MSISDN, MSC knows whichBy analyzing the MSISDN, MSC knows which

HLR to contact worldwide for that MS,sHLR to contact worldwide for that MS,s

subscription.subscription.


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Communication with GMSC,s:Communication with GMSC,s: During call setDuring call set--up to an MSup to an MS

The GMSC requests MS locationsThe GMSC requests MS locations

information from the HLR.information from the HLR.

Which then provides this in the form ofWhich then provides this in the form of

routing information.routing information.

Also, if the subscriber is detached, the HLRAlso, if the subscriber is detached, the HLR

will inform the GMSC that there is no need towill inform the GMSC that there is no need toperform further routing of the call.perform further routing of the call.


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Communication with AUC,s :Communication with AUC,s :

Before any activity involving change or useBefore any activity involving change or use

of subscription information take placeof subscription information take place

The HLR must retrieve new authenticationThe HLR must retrieve new authentication

parameters from an AUC.parameters from an AUC.


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Communication with VLR,s / ILR,s :Communication with VLR,s / ILR,s : When an MS moves into a new MSC serviceWhen an MS moves into a new MSC service

areaarea--

The VLR for that area requests informationThe VLR for that area requests information

about the MS from the HLR of the subscriber.about the MS from the HLR of the subscriber.

The HLR provides a copy of the subscriptionThe HLR provides a copy of the subscription

details.details.

Updates its MS location information andUpdates its MS location information andinstructs the old VLR to delete theinstructs the old VLR to delete the

information, it has about that MS.information, it has about that MS.

As the ILR acts as a VLR for AMPSAs the ILR acts as a VLR for AMPS

subscribers.subscribers.


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HLR IMPLEMENTATIONHLR IMPLEMENTATION

The HLR can be implemented in the sameThe HLR can be implemented in the samenetwork node as the MSC/VLR (i.e.network node as the MSC/VLR (i.e.MSC/VLR/HLR) or as a standMSC/VLR/HLR) or as a stand--alone database.alone database.

A MSC/VLR/HLR node is a suitable solutionA MSC/VLR/HLR node is a suitable solutionfor a small startfor a small start--up GSM network as it savesup GSM network as it saves

hardware and signaling load on the linkshardware and signaling load on the linksbetween MSC/VLR and HLR.between MSC/VLR and HLR.

A standA stand--alone HLR is a suitable solution foralone HLR is a suitable solution forlarge networks.large networks.

It has the following advantages:It has the following advantages:

There are no traffic disturbances creatingThere are no traffic disturbances creatingbetter reliability.better reliability.


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HLR IMPLEMENTATIONHLR IMPLEMENTATION

When the HLR is separate from the MSC/VLR,When the HLR is separate from the MSC/VLR,there is more capacity available for callthere is more capacity available for call

handling in the MSC/VLR.handling in the MSC/VLR.

If the number of subscribers exceeds theIf the number of subscribers exceeds the

capacity of a HLR, additional HLR,s may becapacity of a HLR, additional HLR,s may be

added.added.


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AUTHENTICATION CENTER (AUC)AUTHENTICATION CENTER (AUC)

The main function of the AUC is toThe main function of the AUC is to

authenticate the subscribers attempting toauthenticate the subscribers attempting to

use a network.use a network.

In this way, it is used to protect networkIn this way, it is used to protect networkoperators against fraud.operators against fraud.

The AUC is a database connected to theThe AUC is a database connected to the

HLR.HLR.

Which provides it with the authenticationWhich provides it with the authentication

parameters and ciphering keys used toparameters and ciphering keys used to


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AUTHENTICATION CENTER (AUC)AUTHENTICATION CENTER (AUC)

AUC is a separate entity and physicallyAUC is a separate entity and physicallyincluded in HLRincluded in HLR

Protect against intruders in air interfaceProtect against intruders in air interface

Authentication (Ki) and ciphering (Kc) keyAuthentication (Ki) and ciphering (Kc) keyare stored in this data base.are stored in this data base.

Keys change randomly with each callKeys change randomly with each call

Keys are never transmitted to MS on air OnlyKeys are never transmitted to MS on air Onlycalculated response are sent.calculated response are sent.


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3232

AUTHENTICATION & ENCRIPTIONAUTHENTICATION & ENCRIPTION

AUCAUC

Database

Generation

ofRandom

Number

RANDRAND

IMSI1

IMSI3

IMSI2

ki1ki2

ki3

RANDSRESKc

Algorithm forCiphering

A8

Algorithm for

AuthenticationA3

Kc

64 bits

SRES32 bits

HLR


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EQUIPMENT IDENTITY REGISTER (EIR)EQUIPMENT IDENTITY REGISTER (EIR)

The EIR is a database containing mobileThe EIR is a database containing mobile

equipment identity information.equipment identity information.

Which helps to block calls from stolen,Which helps to block calls from stolen,

unauthorized or defective MS,s.unauthorized or defective MS,s. Due to subscriberDue to subscriber--equipment separation inequipment separation in

GSM, the barring of MS equipment does notGSM, the barring of MS equipment does not

result in automatic barring of a subscriber.result in automatic barring of a subscriber.


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EQUIPMENT IDENTITY REGISTER ( EIR )EQUIPMENT IDENTITY REGISTER ( EIR )

This data base stores IMEI for all registeredThis data base stores IMEI for all registered

mobile equipments and is unique to everymobile equipments and is unique to every

ME.ME.

Only one EIR per PLMN.Only one EIR per PLMN.

White listWhite list: IMEI, assigned to valid ME.: IMEI, assigned to valid ME. Black listBlack list: IMEI reported stolen: IMEI reported stolen

Gray listGray list: IMEI having problems like faulty: IMEI having problems like faulty

software, wrong make of equipment etc.software, wrong make of equipment etc.


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BASE STATION SYSTEM (BSS) COMPONENTSBASE STATION SYSTEM (BSS) COMPONENTS

Base Station Controller (BSC):Base Station Controller (BSC):

The BSC manages all the radioThe BSC manages all the radio--relatedrelated

functions of a GSM network.functions of a GSM network.

It is a high capacity switch.It is a high capacity switch.

Which provides functions such as MSWhich provides functions such as MS

handover, radio channel assignment and thehandover, radio channel assignment and the

collection of cell configuration data.collection of cell configuration data. A number of BSCs may be controlled byA number of BSCs may be controlled by

each MSC.each MSC.


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BASE STATION SYSTEM (BSS) COMPONENTSBASE STATION SYSTEM (BSS) COMPONENTS

Base Transceiver Station (BTS):Base Transceiver Station (BTS):

The BTS controls the radio interface to theThe BTS controls the radio interface to the

MS.MS. The BTS comprises the radio equipmentThe BTS comprises the radio equipment

such as transceiver and antennas, which aresuch as transceiver and antennas, which are

needed to serve each cell in the network.needed to serve each cell in the network.

A group of BTSs are controlled by a BSC.A group of BTSs are controlled by a BSC.


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NETWORK MONITORING CENTERSNETWORK MONITORING CENTERS

Operation and Maintenance CenterOperation and Maintenance Center(OMC) :(OMC) :

An OMC is a computerized monitoringAn OMC is a computerized monitoring

center.center.

Which is connected to other networkWhich is connected to other network

components such as MSCs and BSCs viacomponents such as MSCs and BSCs via

X.25 data network links.X.25 data network links. In the OMC, staff are presented withIn the OMC, staff are presented with

information about the status of the networkinformation about the status of the network

and can monitor and control a variety ofand can monitor and control a variety of

system parameters.system parameters.


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NETWORK MANAGEMENT CENTER (NMC)NETWORK MANAGEMENT CENTER (NMC)

Centralized control of a network is done at aCentralized control of a network is done at a

Network Management Center (NMC).Network Management Center (NMC).

Only one NMC is required for a network andOnly one NMC is required for a network and

this controls the subordinate OMCs.this controls the subordinate OMCs.

The advantage of this hierarchical approachThe advantage of this hierarchical approachis that staff at the NMC can concentrate onis that staff at the NMC can concentrate on

long term systemlong term system--wide issues.wide issues.

Whereas local personnel at each OMC canWhereas local personnel at each OMC can

concentrate on short term, regional issues.concentrate on short term, regional issues. OMC and NMC functionality can be combinedOMC and NMC functionality can be combined

in the same physical network node orin the same physical network node or

implemented at different locations.implemented at different locations.


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MOBILE STATION (MS)MOBILE STATION (MS)

An MS is used by a mobile subscriber toAn MS is used by a mobile subscriber tocommunicate with the mobile network.communicate with the mobile network.

Several types of MSs exist, each allowing theSeveral types of MSs exist, each allowing the

subscriber to make and receive calls.subscriber to make and receive calls.

Manufacturers of MSs offer a variety ofManufacturers of MSs offer a variety ofdesigns and features to meet the needs ofdesigns and features to meet the needs of

different markets.different markets.

The range or coverage area of an MSThe range or coverage area of an MS

depends on the output power of the MS.depends on the output power of the MS.

Different types of MSs have different outputDifferent types of MSs have different output

power capabilities and consequentlypower capabilities and consequently

different ranges.different ranges.


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For Example :For Example :

HandHand--held MSs have a lower output powerheld MSs have a lower output power

and shorter range than carand shorter range than car--installed MSsinstalled MSs

with a roof mounted antenna.with a roof mounted antenna.VoiceChannels

Lines toBSC

MS


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Mobile Station consist of two units : Mobile Hand set

Subscriber Identity Module

Mobile Hand set is one of the most complicated

GSM device. It provides user the access to the

Network. Each handset has unique identity no.

called IMEI.


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MOBILE STATION (MS)MOBILE STATION (MS) SIM is a removable module goes into the Mobile

Handset. Each SIM has unique number calledInternational Mobile Subscriber Identity (IMSI). It

contains the entire customer related information

(Identification, Secret Key for authentification

etc.) It has built in Micro-computer & memoryinto it. It contains the ROM of 6 to 16KB, RAM of

128 to 256 bytes.


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GSM MOBILE STATIONSGSM MOBILE STATIONS

For Example :For Example :

Subscriber A mobile terminal may have beenSubscriber A mobile terminal may have been

stolen.stolen.

Subscriber A own SIM can be used in anotherSubscriber A own SIM can be used in another

person,s mobile terminal.person,s mobile terminal.

The call will be charged to subscriber A.The call will be charged to subscriber A.


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GSM GEOGRAPHICAL NETWORK STRUCTUREGSM GEOGRAPHICAL NETWORK STRUCTURE

Every telephone network needs a specificEvery telephone network needs a specific

structure to route incoming calls to the correctstructure to route incoming calls to the correct

exchange and then on to the subscriber.exchange and then on to the subscriber.

In a mobile network, this structure is veryIn a mobile network, this structure is veryimportant because the subscribers are mobile.important because the subscribers are mobile.

As subscribers move through the network, theseAs subscribers move through the network, these

structures are used to monitor their location.structures are used to monitor their location.


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CELLCELL

CELLCELL

A cell is the basic unit of a cellular system.A cell is the basic unit of a cellular system.

It is defined as the area of radio coverage givenIt is defined as the area of radio coverage given

by one BS antenna system.by one BS antenna system.

Each cell is assigned a unique number calledEach cell is assigned a unique number called

Cell Global Identity.Cell Global Identity.

In a complete network covering an entireIn a complete network covering an entirecountry, the number of cells can be quite high.country, the number of cells can be quite high.


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GSM MOBILE STATIONSGSM MOBILE STATIONS

It consist of :It consist of :

A Mobile TerminalA Mobile Terminal

A Subscriber Identity Module (SIM)A Subscriber Identity Module (SIM)

In GSM, the subscriber is separated from theIn GSM, the subscriber is separated from the

mobile terminal.mobile terminal. Each subscriber's information is stored as aEach subscriber's information is stored as a

Smart Card SIM.Smart Card SIM.

The SIM can be plugged into any GSM mobileThe SIM can be plugged into any GSM mobileterminal.terminal.

This bring the advantages of security andThis bring the advantages of security and

portability for subscribers.portability for subscribers.


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LOCATION AREA (LA)LOCATION AREA (LA)

When an MS crosses a boundary from a cellWhen an MS crosses a boundary from a cellbelonging to one LA into a cell belonging tobelonging to one LA into a cell belonging toanother LA.another LA.

It must report its new location to the network.It must report its new location to the network.

When an MS crosses a cell boundary within anWhen an MS crosses a cell boundary within anLA, it does not report its new cell location to theLA, it does not report its new cell location to thenetwork.network.

When there is call for an MS, a paging messageWhen there is call for an MS, a paging message

is broadcast within all cells belonging to an LA.is broadcast within all cells belonging to an LA.


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MSC SERVICE AREAMSC SERVICE AREA

An MSC service area is made up of a number ofAn MSC service area is made up of a number of

LA,s and represents the geographical part of theLA,s and represents the geographical part of the

network controlled by one MSC.network controlled by one MSC.

In order to be able to route a call to an MS, theIn order to be able to route a call to an MS, thesubscriber,s MSC service area is stored insubscriber,s MSC service area is stored in

recorded and monitored.recorded and monitored.

The subscriber's MSC service area is stored inThe subscriber's MSC service area is stored in

the HLR.the HLR.


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MSC SERVICE AREA :MSC SERVICE AREA :

PLMN SERVICE AREAPLMN SERVICE AREA A Public Land Mobile Network (PLMN) serviceA Public Land Mobile Network (PLMN) service

area is the entire set of cells served by onearea is the entire set of cells served by onenetwork operator.network operator.

It is an area in which an operator offers radioIt is an area in which an operator offers radiocoverage and access to its network.coverage and access to its network.

In any one country there may be several PLMNIn any one country there may be several PLMNservice areas, one for each mobile operator'sservice areas, one for each mobile operator's

network.network.

MSC/VLR

LA 1 LA 2

LA6

LA 3

LA4

LA 5


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GSM SERVICE AREAGSM SERVICE AREA

The GSM service area is the entire geographicalThe GSM service area is the entire geographical

area in which a subscriber can gain access to aarea in which a subscriber can gain access to aGSM network.GSM network.

The GSM service area increases as moreThe GSM service area increases as more

operators sign contracts agreeing to workoperators sign contracts agreeing to work

together.together.

Currently, the GSM service area spans dozensCurrently, the GSM service area spans dozens

of countries across the world from Ireland toof countries across the world from Ireland to

Australia and South Africa.Australia and South Africa. International roaming is the term applied whenInternational roaming is the term applied when

an MS moves from one PLMN to another whenan MS moves from one PLMN to another when

abroad.abroad.


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RELATION BETWEEN AREAS IN GSMRELATION BETWEEN AREAS IN GSM

Location AreaCell

Area served by a BTS

Location Area

MSCService AreaPLMN Service Area

GSMService Area


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GSM FREQUENCY BANDSGSM FREQUENCY BANDS

As GSM has grown worldwide, it has expandedAs GSM has grown worldwide, it has expandedto operate at three frequency bands : 900, 1800to operate at three frequency bands : 900, 1800

and 1900.and 1900.


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GSM 900GSM 900

The original frequency band specified for GSMThe original frequency band specified for GSM

was 900 MHz.was 900 MHz.

Most GSM networks worldwide use this band.Most GSM networks worldwide use this band.

In some countries an extended version of GSMIn some countries an extended version of GSM900 can be used.900 can be used.

Which provides extra network capacity.Which provides extra network capacity.

This extended version of GSM is called EThis extended version of GSM is called E--GSM,GSM,while the primary version is called Pwhile the primary version is called P--GSM.GSM.


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GSM 1800GSM 1800

In 1990, in order to increase competition betweenIn 1990, in order to increase competition between

operators, the United Kingdom requested the start of aoperators, the United Kingdom requested the start of anew version of GSM adapted to the 1800 MHz frequencynew version of GSM adapted to the 1800 MHz frequencyband.band.

Licenses have been issued in several countries andLicenses have been issued in several countries andnetworks are in full operation.networks are in full operation.

By granting licenses for GSM 1800 in addition to GSMBy granting licenses for GSM 1800 in addition to GSM900, a country can increase the number of operators.900, a country can increase the number of operators.

In this way, due to increased competition, the service toIn this way, due to increased competition, the service tosubscribers is improved.subscribers is improved.

GSM 1800 Mhz Mobile to Cell (UP-LINK) - 1710 to 1785 MHz Cell to Mobile (DOWN -LINK) - 1805 to 1880 MHz


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GSM 1900GSM 1900

In 1995, the Personal Communications ServiceIn 1995, the Personal Communications Service

(PCS) concept was specified in the United(PCS) concept was specified in the United

States.States.

The basic idea is to enable PersonThe basic idea is to enable Person--toto--PersonPersoncommunication rather than Stationcommunication rather than Station--toto--Station.Station.


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GSM 1900GSM 1900

PCS does not require that such services bePCS does not require that such services beimplemented using cellular technology.implemented using cellular technology.

But this has proven to be the most effectiveBut this has proven to be the most effective

method.method.

The Frequencies available for PCS are aroundThe Frequencies available for PCS are around1900 MHz.1900 MHz.

As GSM 900 could not be used in North AmericaAs GSM 900 could not be used in North America

due to prior allocation of the 900 MHzdue to prior allocation of the 900 MHz

frequencies.frequencies.

GSM 1900 MHz is seen as an opportunity toGSM 1900 MHz is seen as an opportunity to

bridge this gap.bridge this gap.

The main differences between the AmericanThe main differences between the American


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GSM 400GSM 400

Ericsson and Nokia support the work of ETSI onEricsson and Nokia support the work of ETSI ona global standard for GSM on the 450 MHza global standard for GSM on the 450 MHz

frequency band.frequency band.

Ericsson and Nokia are aiming to make GSMEricsson and Nokia are aiming to make GSM

450 products available for the market during450 products available for the market during2001.2001.

The believe is that the introduction of GSM in theThe believe is that the introduction of GSM in the

450 MHz frequency band will further leverage450 MHz frequency band will further leverage

the success of global GSM.the success of global GSM. GSM 400 also provides NMT system operators aGSM 400 also provides NMT system operators a

logical way to introduce quality digital serviceslogical way to introduce quality digital services

and seamless international roaming possibilities.and seamless international roaming possibilities.


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GSM KEY TERMSGSM KEY TERMS

During the development of mobile systems,During the development of mobile systems,many terms arose which are used to describemany terms arose which are used to describe

the call cases and situations involving MSs.the call cases and situations involving MSs.

The primary terms used are described below.The primary terms used are described below.

An MS can have one of the following states:An MS can have one of the following states:

IDLE:IDLE: The MS is ON but a call is not in progress.The MS is ON but a call is not in progress.

ACTIVE:ACTIVE: The MS is ON and a call is in progress.The MS is ON and a call is in progress. DETACHED:DETACHED: The MS is OFF.The MS is OFF.


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THE FOLLOWING KEY TERMS USED TO DESCRIBETHE FOLLOWING KEY TERMS USED TO DESCRIBE

GSM MOBILE TRAFFIC CASES:GSM MOBILE TRAFFIC CASES:

No traffic cases in Detached Mode.No traffic cases in Detached Mode. IDLE:IDLE:

REGISTRATIONREGISTRATION--

This is the process in which an MS informs aThis is the process in which an MS informs anetwork that is attached.network that is attached.

ROAMINGROAMING

When an MS moves around a network in IdleWhen an MS moves around a network in Idle

Mode, it is referred to as roaming.Mode, it is referred to as roaming.INTERNATIONAL ROAMINGINTERNATIONAL ROAMING-- When an MSWhen an MSmoves into a network which is not its homemoves into a network which is not its homenetwork, it is referred to as internationalnetwork, it is referred to as international

roaming.roaming.


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MSs can only roam into networks with whichMSs can only roam into networks with which

the home network has a roaming agreement.the home network has a roaming agreement.

LOCATION UPDATINGLOCATION UPDATING--

An MS roaming around the network mustAn MS roaming around the network mustinform the network , when it enters a new LA.inform the network , when it enters a new LA.

This is called Location Updating.This is called Location Updating.

PAGINGPAGING--

This is the process whereby a networkThis is the process whereby a network

attempts to contact a particular MS.attempts to contact a particular MS. This is achieved by broadcasting a pagingThis is achieved by broadcasting a paging

message containing the identity of that MS.message containing the identity of that MS.

ACTIVE MODE:ACTIVE MODE:


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ACTIVE MODE:ACTIVE MODE:

HANDOVERHANDOVER--

This is the process in which control of a callThis is the process in which control of a call

is passed from one cell to another, while theis passed from one cell to another, while the

MS move between cells.MS move between cells.

MS REGISTRATION AND ROAMING:MS REGISTRATION AND ROAMING:

When an MS is powered OFF, it is detachedWhen an MS is powered OFF, it is detached

from the network.from the network.

When the subscriber switches power ON.When the subscriber switches power ON.

The MS scans the GSM frequencies forThe MS scans the GSM frequencies for

special channels called Control Channel.special channels called Control Channel.


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When it finds a control channel, the MSWhen it finds a control channel, the MS

measures the signal strength, it receives onmeasures the signal strength, it receives on

that channel and records it.that channel and records it.

When the MS has just been powered ON, theWhen the MS has just been powered ON, the

MS must register with the network, which willMS must register with the network, which willthen update the MSs status to idle.then update the MSs status to idle.

If the location of the MS is noticed to beIf the location of the MS is noticed to be

different from the currently stored locationdifferent from the currently stored location

then a location update will also take place.then a location update will also take place. As the MS moves through the network, itAs the MS moves through the network, it

continues to scan the control channels tocontinues to scan the control channels to

ensure that it is turned to the strongestensure that it is turned to the strongest

possible channel.possible channel.


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If the MS finds one which is stronger, thenIf the MS finds one which is stronger, then

the MS returns to this new control channel.the MS returns to this new control channel.

If the new control channel belongs to a newIf the new control channel belongs to a new

LA, the MS will also inform the network of itsLA, the MS will also inform the network of itsnew location.new location.


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MSC/VLR

B

T

S

B

T

S

B

T

S

MSC/VLR


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IMSIIMSI

The IMSI (International Mobile SubscriberThe IMSI (International Mobile SubscriberIdentity) is a unique 15Identity) is a unique 15--digit code used todigit code used toidentify an individual user on a GSM network.identify an individual user on a GSM network.

The IMSI consists of three components:The IMSI consists of three components:-- Mobile Country Code (MCC)Mobile Country Code (MCC)

-- Mobile Network Code (MNC)Mobile Network Code (MNC)

-- Mobile Subscriber Identity NumberMobile Subscriber Identity Number

(MSIN)(MSIN) The IMSI is stored in the Subscriber IdentityThe IMSI is stored in the Subscriber Identity

Module (SIM).Module (SIM).

GSMGSM


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6767

GSMGSM

IMSIIMSI

MCC MNC MSIN

3 digits 3 digits Not more than 9 digits

NMSI

IMSI : Not more than 15 digits

TMSITMSI


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TMSITMSI

The TIMSI (Temporary IMSI) is aThe TIMSI (Temporary IMSI) is a

pseudopseudo--random number generatedrandom number generated

from the IMSI (International Mobilefrom the IMSI (International Mobile

Subscriber Identity) number.Subscriber Identity) number.

The TIMSI is utilized in order to removeThe TIMSI is utilized in order to remove

the need to transmit the IMSI overthe need to transmit the IMSI over--thethe--

air. This helps to keep the IMSI moreair. This helps to keep the IMSI moresecure.secure.


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TMSITMSI

To track a GSM user via the IMSI/TIMSI,To track a GSM user via the IMSI/TIMSI,

an eavesdropper must intercept thean eavesdropper must intercept the

GSM network communication whereGSM network communication where

the TIMSI is initially negotiated.the TIMSI is initially negotiated.

In addition, because the TIMSI isIn addition, because the TIMSI is

periodically renegotiated, theperiodically renegotiated, theeavesdropper must intercept eacheavesdropper must intercept each

additional TIMSI readditional TIMSI re--negotiation session.negotiation session.


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What are Ki, Kc, RAND, and SRES ?What are Ki, Kc, RAND, and SRES ?

KiKi is the 128is the 128--bit individual Subscriberbit individual SubscriberAuthentication Key utilized as aAuthentication Key utilized as a secret keysecret key sharedshared

between the Mobile Station and the Home Locationbetween the Mobile Station and the Home Location

Register of the subscriber's home network.Register of the subscriber's home network.

RANDRAND is 128is 128--bit random challenge generated bybit random challenge generated by

the Home Location Register through AUC.the Home Location Register through AUC.


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What are Ki, Kc, RAND, and SRES ?What are Ki, Kc, RAND, and SRES ?

SRESSRES is the 32is the 32--bit Signed Response generatedbit Signed Response generatedby the Mobile Station and the Mobile Servicesby the Mobile Station and the Mobile Services

Switching Center.Switching Center.

Kc is the 64Kc is the 64--bit ciphering key used as a Sessionbit ciphering key used as a Session

Key for encryption of the overKey for encryption of the over--thethe--air channel.air channel.

Kc is generated by the Mobile Station from theKc is generated by the Mobile Station from the

random challenge presented by the GSMrandom challenge presented by the GSMnetwork and the Ki from the SIM utilizing the A8network and the Ki from the SIM utilizing the A8

algorithm.algorithm.

GSMGSM


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7272

GSMGSM

MSCMSC--BSS ConfigurationsBSS Configurations

BTSBTS

BTS

BTS BTS

BTSBTS

A-bis

BSC

BSS

Configuration -6 Multi - cell site =multi--BTS site

Many single

cell sites

BSSBTS

MSC

BTS

A

A

A

Single - cell site

Configuration -1

Multi - cell site (sector Cells

Configuration -5

MSC: Mobile Switching Centre

BSS: Base Station System

BSC: Base Station Controller

BTS: Base Transceiver Station

A-bis


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TRANSCODER CONTROLLERTRANSCODER CONTROLLER

TRC FUNCTIONS:TRC FUNCTIONS:

The primary functions of a TRC are to performThe primary functions of a TRC are to performtranscoding and to perform rate adaptation.transcoding and to perform rate adaptation.

TRANSCODING:TRANSCODING:

The function of converting from the PCM CoderThe function of converting from the PCM Coderinformation (following A/D conversion) to the GSMinformation (following A/D conversion) to the GSMSpeech Coder information is called transcoding.Speech Coder information is called transcoding.

This function is present in both the MS and the BSS.This function is present in both the MS and the BSS.

RATE ADAPTATION:RATE ADAPTATION:

Rate Adaptation involves the conversion of informationRate Adaptation involves the conversion of information

arriving from the MSC/VLR at a rate of 64 Kb/s to a ratearriving from the MSC/VLR at a rate of 64 Kb/s to a rateof 16 Kb/s or transmission to a BSC (for a full rate call).of 16 Kb/s or transmission to a BSC (for a full rate call).



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These 16 Kb/s contains 13 Kb/s of traffic and 3 Kb/s ofThese 16 Kb/s contains 13 Kb/s of traffic and 3 Kb/s of

Inband Signaling information.Inband Signaling information. This is an important function.This is an important function.

Without rate adaptation the links to BSC, would require fourWithout rate adaptation the links to BSC, would require fourtimes the data rate capabilities.times the data rate capabilities.

Such transmission capabilities from an expensive part ofSuch transmission capabilities from an expensive part ofthe network.the network.

By reducing the rate to 16 Kb/s, it is possible to use oneBy reducing the rate to 16 Kb/s, it is possible to use onequarter of the transmission links and equipment.quarter of the transmission links and equipment.

In Ericssons GSM Systems, the TRC contains units, whichIn Ericssons GSM Systems, the TRC contains units, which

perform Transcoding & Rate Adaptation.perform Transcoding & Rate Adaptation. These hardware units are called Transcoder & RateThese hardware units are called Transcoder & Rate

Adaptation units (TRAU).Adaptation units (TRAU).



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All TRAUs are pooled, meaning that any BSCAll TRAUs are pooled, meaning that any BSC

connected to the TRC can request the use ofconnected to the TRC can request the use ofone of the TRAUs for a particular call.one of the TRAUs for a particular call.

The TRC also supports discontinuousThe TRC also supports discontinuous

transmission.transmission.

If pauses in speech are detected, comfort noiseIf pauses in speech are detected, comfort noise

is generated by the TRAU in the direction of theis generated by the TRAU in the direction of the

MSC/VLR.MSC/VLR.

T d C fi tiT d C fi ti


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7676

Transcoder ConfigurationsTranscoder Configurations

BTS TRAU BSC MSCTo MS To fixed

networks

BSC TRAUBTS MSCTo MS To fixednetworks

TRAU MSCBTS BSCTo MS To fixed

networksRF AirInterface

A-bis

InterfaceA

Interface

13 kbps encoded voice/ 12

kbps data

16 kbps transmission

64 kbps transmissionTranscoder (XC) configurations

Network and SwitchingNetwork and Switching


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7777

Network and SwitchingNetwork and Switching

Subsystem (NSS)Subsystem (NSS)

MSC

(PSTN)

VLR

HLR AUC

EIR

D

C

SS7Signalling

Traffic Path

F

(BSS)

A

E

Other

MSC


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NUMBERING PLANNUMBERING PLAN


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NUMBERING PLANNUMBERING PLAN

( Network Identities)( Network Identities)

Network Identities are numbers that a GSMNetwork Identities are numbers that a GSMNetwork uses to locate a mobile subscriber, when itNetwork uses to locate a mobile subscriber, when it

is establishing a call to that subscriber.is establishing a call to that subscriber.

As the network relies on these identities to routeAs the network relies on these identities to route

calls to subscribers.calls to subscribers. It is important that each identity is unique andIt is important that each identity is unique and

correct.correct.

Numbering Plans are used to identify differentNumbering Plans are used to identify different

networks as specified by the ITUnetworks as specified by the ITU--T.T.

For a telephone number in the PSTN/ISDNFor a telephone number in the PSTN/ISDN

Network, ITUNetwork, ITU--T,s numbering plan E.164 is used.T,s numbering plan E.164 is used.

SUBSCRIBERSUBSCRIBER RELATED IDENTITIESRELATED IDENTITIES


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SUBSCRIBERSUBSCRIBER--RELATED IDENTITIESRELATED IDENTITIES

MOBILE STATION ISDN NUMBER(ISDN) :MOBILE STATION ISDN NUMBER(ISDN) :

The Mobile Station ISDN Number uniquelyThe Mobile Station ISDN Number uniquely

identifies a mobile telephone subscription inidentifies a mobile telephone subscription in

the PSTN Numbering Plan.the PSTN Numbering Plan.

This is the number dialed when calling a mobileThis is the number dialed when calling a mobilesubscriber.subscriber.

As the MSISDN is the actual telephone numberAs the MSISDN is the actual telephone number

of the mobile subscriber.of the mobile subscriber.

It is the only network identity that subscribersIt is the only network identity that subscribers

are aware of.are aware of.

CME 20 MSISDNCME 20 MSISDN


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In CME 20, the MSISDN consists of the following :In CME 20, the MSISDN consists of the following :

CC Country CodeCC Country Code

NDC National Destination CodeNDC National Destination Code

SN Subscriber NumberSN Subscriber NumberAn NDC is allocated to each PLMN.An NDC is allocated to each PLMN.

For Example: In Ireland the NDC,s 086 and 087For Example: In Ireland the NDC,s 086 and 087

indicate the PLMN,s of two different networkindicate the PLMN,s of two different network

CC NDC SN



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In some countries, more than one NDC may beIn some countries, more than one NDC may be

required for each PLMN.required for each PLMN.

The International MSISDN number may be ofThe International MSISDN number may be of

variable length.variable length.

The maximum length is 15 digits, prefixes notThe maximum length is 15 digits, prefixes notincluded.included.

A German subscriber calling an Irish GSMA German subscriber calling an Irish GSM

subscriber world dial the following Number:subscriber world dial the following Number:

International Prefix In Germany CC NDC SNInternational Prefix In Germany CC NDC SN

00 353 87 123456700 353 87 1234567

IMSIIMSI


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IMSIIMSI

The IMSI (International Mobile SubscriberThe IMSI (International Mobile Subscriber

Identity) is a unique 15Identity) is a unique 15--digit code used todigit code used toidentify an individual user on a GSM network.identify an individual user on a GSM network.

The IMSI consists of three components:The IMSI consists of three components:

-- Mobile Country Code (MCC)Mobile Country Code (MCC)-- Mobile Network Code (MNC)Mobile Network Code (MNC)

-- Mobile Subscriber Identity NumberMobile Subscriber Identity Number(MSIN)(MSIN)

The IMSI is stored in the Subscriber IdentityThe IMSI is stored in the Subscriber IdentityModule (SIM).Module (SIM).

IMSI = MCC + MNC + MSINIMSI = MCC + MNC + MSIN

GSMGSM


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8484

GSMGSM

IMSIIMSI

MCC MNC MSIN

3 digits 3 digits Not more than 9 digits

NMSI

IMSI : Not more than 15 digits

TEMPORARY MOBILE SUBSCRIBERTEMPORARY MOBILE SUBSCRIBER


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TEMPORARY MOBILE SUBSCRIBERTEMPORARY MOBILE SUBSCRIBER

IDENTITY(TMSI)IDENTITY(TMSI)

The Temporary Mobile Subscriber Identity (TMSI)The Temporary Mobile Subscriber Identity (TMSI)is a temporary IMSI number made known to an MSis a temporary IMSI number made known to an MS

at registration.at registration.

It is used to protect the subscriber's identity on theIt is used to protect the subscriber's identity on the

air interface.air interface. The TMSI has local significance only i.e. within theThe TMSI has local significance only i.e. within the

MSC/VLR area.MSC/VLR area.

It is changed at time intervals or when certainIt is changed at time intervals or when certain

events occur such as location updating.events occur such as location updating.

Every operator can choose TMSI structure, butEvery operator can choose TMSI structure, but

should not consist of more than 8 digits.should not consist of more than 8 digits.

EQUIPMENTEQUIPMENT RELATED IDENTITIESRELATED IDENTITIES


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EQUIPMENTEQUIPMENT RELATED IDENTITIESRELATED IDENTITIES

International Mobile Equipment Identity (IMEI) :International Mobile Equipment Identity (IMEI) :

The International Mobile Equipment IdentityThe International Mobile Equipment Identity

(IMEI) is used to uniquely identify MS(IMEI) is used to uniquely identify MS

equipment to the network.equipment to the network.

The IMEI is used for security proceduresThe IMEI is used for security proceduressuch as identifying stolen equipment andsuch as identifying stolen equipment and

preventing unauthorized access to thepreventing unauthorized access to the

network.network.

According to the GSM specifications, IMEIAccording to the GSM specifications, IMEIhas a total length of 15 digits, and consistshas a total length of 15 digits, and consists

of the following:of the following:


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TAC : Type Approval Code, determined by aTAC : Type Approval Code, determined by a

central GSM body.central GSM body. FAC: Final Assembly Code, identifies theFAC: Final Assembly Code, identifies the

manufacturermanufacturer

SNR: Serial Number, an individual serial number ofSNR: Serial Number, an individual serial number ofsix digits uniquely identifies all equipment withinsix digits uniquely identifies all equipment withineach TAC & FACeach TAC & FAC

SPARE: A spare digit for future use. WhenSPARE: A spare digit for future use. Whentransmitted by the MS, this digit should always betransmitted by the MS, this digit should always be

zero.zero.

TAC FAC SNR SPARE

LOCATION RELATED IDENTITIESLOCATION RELATED IDENTITIES


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LOCATION RELATED IDENTITIES:LOCATION RELATED IDENTITIES:

MOBILE STATION ROAMING NUMBER (MSRN):MOBILE STATION ROAMING NUMBER (MSRN):

MSRN is a temporary network identity which isMSRN is a temporary network identity which is

assigned during the establishment of a call to aassigned during the establishment of a call to a

roaming subscriber.roaming subscriber.

The MSRN consists of three parts:The MSRN consists of three parts:

SN is the address to servicing MSC/VLR.SN is the address to servicing MSC/VLR.

SN = Servicing NodeSN = Servicing Node

CC NDC SN

LOCATION AREA IDENTITY (LAI)LOCATION AREA IDENTITY (LAI)


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LOCATION AREA IDENTITY (LAI)LOCATION AREA IDENTITY (LAI)

The LAI is a temporary network identity.The LAI is a temporary network identity. Which is also required for routing.Which is also required for routing.

The two main purposes of the LAI are:The two main purposes of the LAI are:

1.1. PAGING, which is used to inform the MSC ofPAGING, which is used to inform the MSC of

the LA in which the MS is currently situated.the LA in which the MS is currently situated.

2.2. Location updating of mobile subscribers.Location updating of mobile subscribers.

The LAI contains the following:The LAI contains the following:

MCC MNC LAC

LAC L ti A C d th i l thLAC L ti A C d th i l th


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LAC : Location Area Code, the maximum lengthLAC : Location Area Code, the maximum length

of LAC is 16 Bits.of LAC is 16 Bits.

CELL GLOBAL IDENTITY (CGI):CELL GLOBAL IDENTITY (CGI): The CGI is used for identifying individual cellsThe CGI is used for identifying individual cells

within a LA.within a LA.

Cell Identification is achieved by adding a CellCell Identification is achieved by adding a Cell

Identity (CI) to the LAI components.Identity (CI) to the LAI components.

The CI has a maximum length of 16 bits.The CI has a maximum length of 16 bits.

MCC MNC LAC CI


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LOCATION NUMBER (LN)LOCATION NUMBER (LN)


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LOCATION NUMBER (LN)LOCATION NUMBER (LN)

LN is a number related to a certain geographicalLN is a number related to a certain geographical

area, which the network operator specifies byarea, which the network operator specifies byTyping the location numbers to Cells, LocationTyping the location numbers to Cells, Location

Areas, or MSC/VLR service areas.Areas, or MSC/VLR service areas.

The LN is used to implement features likeThe LN is used to implement features like

regional/local subscription and geographicalregional/local subscription and geographical

differentiated charging.differentiated charging.

The LN consists of the following:The LN consists of the following:

CC NDC LSP

SUBSCRIBER IDENTITY CONFIDENTIALITYSUBSCRIBER IDENTITY CONFIDENTIALITY


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SUBSCRIBER IDENTITY CONFIDENTIALITYSUBSCRIBER IDENTITY CONFIDENTIALITY

PROCEDURE:PROCEDURE:

Each time a mobile station requests a systemEach time a mobile station requests a systemprocedure i.e. Location Updating, Call attempt orprocedure i.e. Location Updating, Call attempt or

Service activation, the MSC/VLR can allocate aService activation, the MSC/VLR can allocate a

new TMSI to an IMSI.new TMSI to an IMSI.

The MSC/VLR transmits the TMSI to MS thatThe MSC/VLR transmits the TMSI to MS thatstores it on the SIM Card.stores it on the SIM Card.

Signaling between MSC/VLR and MS utilized onlySignaling between MSC/VLR and MS utilized only

the TMSI from this point on.the TMSI from this point on.

Thus, the real subscriber identity, IMSI, is notThus, the real subscriber identity, IMSI, is not

transmitted over the radio path again.transmitted over the radio path again.

TMSI is half the length of IMSI.TMSI is half the length of IMSI.


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Thus allowing twice as many MS,s to be pagedThus allowing twice as many MS,s to be paged

in the same paging message.in the same paging message.

IMSI is only used in cases when locationIMSI is only used in cases when location

updating fails or when the MS has no allocatedupdating fails or when the MS has no allocated

TMSI.TMSI.

Gsm n w Trau n Plan

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