Cellular Principle and Archi3

7/29/2019 Cellular Principle and Archi3

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GSM Architecture


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GSM

Various subsystems1. Network Subsystem includes the equipments

and functions related to end-to-end call.

2. Radio Subsystem includes the equipments andfunctions related to the management of theconnections on the radio path.

3. Operations and Maintenance subsystemincludes the operation and maintenance of GSMequipment for the radio and network interface.


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Network Architecture

B

TS

MSC VLR

HLR

PSTNISDN

Data

Networks

(

Air interface

OSS

B

T

S

B

T

S

MSC VLR

BSC

BSC

1 MSC=16 BSC

1 BSC=1024 TRU

A Interface

A-bis interface

BSC:BASE STATION CONTROLLER, BTS: BASE TRANSRECEIVER STATION, OSS: OPERATION AND SUPPORT

SUBSYSTEM.ss


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GSMPLMN Service Area

V

MSC

MSC

MSC

MSC

VLR

VLR

VLR

I II

IVIII

I


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GSM

MSC Service Area

MSC

VLRLA1

LA2

LA3

LA6

LA4

LA5


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GSMCells

MSC

VLR

LA1

LA2

LA3

LA6LA4

LA5

C1C2 C3

C6C5

C4

C=CELL


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GSM

Relation between areas in GSM

Location AreaCell

Area served by a BTS

Location AreaMSC Service AreaPLMN Service Area

GSM Service Area


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GSM

Functions of Mobile Station Voice and data transmission

Frequency and time synchronization

Monitoring of power and signal qualityof the surrounding cells

Provision of location updates even

during inactive state

Equalization of multi path distortions


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GSM

Mobile Station

Portable, vehicle mounted, hand held

MS identified by unique IMEI(International Mobile EquipmentIdentity)

Shall display at least last ten received, dialledand missed calls

Minimum talk time of 1hr 30 min. andstandby time of 80 hrs

160 characters long SMS


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GSM

Mobile Station - Power LevelsPower

Class

Max. Peak

Power

Tolerance (dB)

Normal Extreme

1 20W

(43 dBm)

+/- 2 +/- 2.5

2 8W

(39 dBm)

+/- 2 +/- 2.5

3 5W

(37 dBm)

+/- 2 +/- 2.5

4 2W

(33 dBm)

+/- 2 +/- 2.5

5 0.8W

(29 dBm)

+/- 2 +/- 2.5

Vehiclemounted


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GSM

SIM Card

SIM Module

Unique Subscribers ID IMSI and ISDN PIN( Personal Identification Number)

Key Ki( Identification Key) , Kc and A3 and A8

algorithms SIM has CPU, ROM, RAM and EPROM


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GSM

Mobile Identification Numbers IMEI

MSISDN

IMSI

TMSI

MSRN


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GSMFUNCTION OF BTS -I

Encodes, encrypts, multiplexes, modulatesand feeds the RF signals to the antenna

Transcoding and rate adaption Functionality

Time and frequency synchronisation signalstransmission.

11 power classes from .01 watts to 320watts


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GSMFUNCTION OF BTS -II

Frequency hopping

Random access detection

Uplink radio channel measurements

BTS mainly consists of a set of transceivers(TRX).


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GSMFUNCTIONS OF BSC-I

It is connected to BTS and offloadsMSC

Radio resource management

Inter-cell handover

Reallocation of frequencies

Power control


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GSMFUNCTIONS OF BSC-II

Time delay measurement of the receivedsignals from MS with respect to BTS clock.

Performs traffic concentration to reduce thenumber of lines from BSC to MSC.


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GSMMSC ( MOBILE SWITCHING CENTRE) Manages communication between GSM &

other network

Call setup functions, basic switching are done MSC takes into account the RR allocation in

addition to normal exchange functions

MSC does gateway function while its customers

roams to other network by using HLR /VLR


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GSM

MSC Functions - I Paging, specifically call handling

Location updation

Handover management

Billing for all subscribers based in its area

Reallocation of frequencies to BTSs in its area

to meet heavy demands


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GSM

MSC Functions - II Echo canceller operation control

Signaling interface to databases like HLR, VLR.

Gateway to SMS between SMS centers andsubscribers

Handle interworking function while working asGMSC


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INTERWORKING FUNCTION

-It provide the Interfacing Capability to Data N/Ws.

-IMF. A part of MSC, provides the subscriber with

access to data rate and protocol conversion facilities so

that data can be transmitted between GSM Data

Terminal Equipment ( DTE ) and a land line DTE.


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GSMVISITOR LOCATION REGISTER (VLR)-I

It controls those mobiles roaming in its area.

VLR reduces the number of queries to HLR

One VLR may be incharge of one or more LA.

VLR is updated by HLR on entry of MS its area.

VLR assigns TMSI which keeps on changing.

IMSI detach and attach operation


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GSM

Data in VLR IMSI & TMSI

MSISDN

MSRN. Location Area

Supplementary service parameters

MS category Authentication Key


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GSM

Home Location Register(HLR)-I

Reference store for subscribers parameters,numbers, authentication & Encryption values.

Current subscriber status and associated VLR.

Both VLR and HLR can be implemented in the

same equipment in an MSC.

one PLMN may contain one or several HLR.

GSM


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GSMAUTHENTICATION CENTRE (AUC )-I

AUC is a separate entity and physicallyincluded in HLR

Protect against intruders in air interface

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

Keys change randomly with each call

Keys are never transmitted to MS on air

Only calculated response are sent.


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GSMEQUIPMENT IDENTITY REGISTER ( EIR )

This data base stores IMEI for all registeredmobile equipments and is unique to every ME.

Only one EIR per PLMN.

White list: IMEI, assigned to valid ME.

Black list: IMEI reported stolen Gray list: IMEI having problems like faulty

software, wrong make of equipment etc.


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The centralized operation of the various units inthe system and functions needed to maintain thesubsystems.

Dynamic monitoring and controlling of thenetwork

Operations and Maintenance Centre

OMC

F i Of OMC


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functions-O&M data function

-Configuration management

--Fault report and alarm handling

-Performance supervision/management

-Storage of system software and data

Functions Of OMC

Authentication


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Authentication

Authentication is used to check the validity of a

mobile subscriber.

At MS At N/W

KiRAND( 128 bits )

Ki

A3 A3

SRES SRES

( 32 bits )=?

AUTHENTICATION


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RAND ( 128 bits ):Random Number

SRES ( 32 bits) :Signed Response

Kc ( 64 bits ) : Ciphering Key

- Ki is stored in SIM and HLR.

Ki ( 128 bits) : Identification Key

- Purpose : Ki is used to calculate SRES and Kc.

- Ki is never transmitted over signalingnetwork.

- Purpose : Kc is used to encrypt data over radiointerface.

- Purpose : RAND is used to calculate SRES and Kc.

Ciphering


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Ciphering

Ciphering is used to encrypt data on radio interface.

Frame

No. (22

bits )

A5

Information Bits ( 114 bits )

CIPHERING

Kc generation is done at the

time of Authentication.

RAND Ki

Kc ( 64 bits)

A8

Ciphering Stream

XORCiphered Bits

Cellular Principle and Archi3

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