GSM by himu

8/2/2019 GSM by himu

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GSM : System Architecture

Prepared byMehrin Meher


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Contents

GSM

Introduction

Services

Tele Services

Bearer Services

Supplementary services

System Architecture


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Contents (continues)

System Architecture Mobile Station (MS)

Mobile Equipment (ME)

Subscriber Identity Module (SIM)

Base Station Subsystem (BBS)Base Transceiver Station (BTS)

Base Station Controller (BSC)

Network Subsystem

Mobile Switching Center (MSC)

Home Location Register (HLR)

Visitor Location Register (VLR)

Authentication Center (AUC)

Equipment Identity Register (EIR)


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GSM : Introduction

What is GSM?

GSM (Global System for Mobilecommunication) is a digital mobiletelephony system

Operates at either the 900 MHz or 1800MHz frequency band.

Most widely used cellular system


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GSM: Introduction- History

CEPT, a European group began todevelop the System for Mobile TDMAsystem in June 1982.

Based on GSM technology were firstlaunched in Finland in 1991.

More than 690 mobile networks across

213 countries and 82.4% of all globalmobile connections.

2 billion GSM mobile phone users

worldwide


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GSM : Introduction

- objectives

Pan-European roaming, which offerscompatibility throughout the Europeancontinent.

Integrated Service Digital Network(ISDN),which offers the capability to extend the

single-subscriber-line system to amultiservice system. But currently whichare offered through diverse telecommun-ications networks.


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GSM: Services

Tele-services

Bearer or Data Services

Supplementary services


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GSM: Services - TeleServices

Provide the service visible to theuser

Require support by higher layers


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GSM: Services - Bearer Services

Provide lower layer access (GSM layers1-3)

Classified by demands bearer service makes

on network In order to provide end-to-end bearer GSM

must connect to other networks

PSTN, ISDN, PSPDN, CSPDN

Group 3 fax

Voice mailbox

Electronic mail


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GSM: Services

- Supplementary services

(SS) Supplementary services SS supplementbearer and teleservices

Supplementary Services are devided into

Call-related SS Call-independent or non-call related SS

Unstructured SS

Offerings of SS depend on which ones thenetwork can technically handle and/or theoperator wants to provide to subscribers


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GSM: System Architecture

Mobile Station (MS)Mobile Equipment (ME)

Subscriber Identity Module (SIM)

Base Station Subsystem (BBS)Base Transceiver Station (BTS)

Base Station Controller (BSC)

Network SubsystemMobile Switching Center (MSC)

Home Location Register (HLR)

Visitor Location Register (VLR)

Authentication Center (AUC)

Equipment Identity Register (EIR)

Public Switched Telephone Network (PSTN)

Integrated Services Digital Network (ISDN)


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GSM: Network Architecture


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GSM : System Architecture- Mobile Station (MS)

The Mobile Station is made up of two entities:

1. Mobile Equipment (ME)

2. Subscriber Identity Module (SIM)


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GSM : System Architecture- Mobile Station (MS)

- Mobile Equipment (MS)

Portable Device. (Handset / Vehicle)

Two types

Vehicle-mounted

Handheld

Uniquely identified by an IMEI (International Mobile Equipment Identity)

Voice and data transmission

3 Bands

Standard GSM Band: 890-915 MHz Uplink and 935-960 MHz downlink

Extended GSM Band: 880-915 MHz Uplink and 925-960 MHz downlink

GSM 1800 Band: 1710-1785 MHz Uplink and 1805-1880 MHz downlink

Power level : 0.8W

20 W


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- Mobile Station (MS)

- Subscriber Identity Module (SIM)

Integrated circuit that securely stores the IMSI and the

related key used to identify and authenticate subscribers on

mobile telephony. Allows user to send and receive calls and

receive other subscribed services

Encoded network identification details - Key Ki,Kc and A3,A5 and

A8 algorithms

Two types of passwords:

Personal Identification Number (PIN)

Personal Unblocking Code (PUK) for PIN unlocking.

Can be moved from phone to phone contains key information to

activate the phone


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GSM : System Architecture- Base Station Subsystem (BSS)

The Base Station Subsystem is responsible for managing the

radio network, and it is controlled by an MSC. Typically, one

MSC contains several BSSs. A BSS itself may cover a

considerably large geographical area consisting of manycells(a

cell refers toan area covered by one or more frequency

resources).

Three elements:

1. Base Transceiver Station (BTS)

2. Base Station Controller (BSC)

3. Transcoder and Rate Adaptation Unit (TRAU)


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GSM : System Architecture- Base Station Subsystem (BBS)

-Base Transceiver Station(BTS)

Functionality:

Encoding, encrypting, multiplexing, modulating, and feeding the RF signals to

the antenna.

Voice through full- or half-rate services

Transcoding and rate adaptation

Time and frequency synchronizing

Random access detection

Timing advances

Uplink channel measurements

Decoding, decrypting, and equalizing received signals


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- Base Station Subsystem (BBS)

-Base Station Controller (BSC) Functionality:

Control of frequency hopping

Performing traffic concentration to reduce the number of linesfrom the MSC

Providing an interface to the Operations and MaintenanceCenter for the BSS

Reallocation of frequencies among BTSs

Time and frequency synchronization Power management

Time-delay measurements of received signals from the MS


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GSM : System Architecture- Base Station Subsystem (BBS)

- Transcoder and Rate Adaptation Unit (TRAU)

Performs transcoding function for speech channels andRA (Rate Adaptation) for data channels in the GSMnetwork.

Features

Easy and quick installation

Easy and quick commissioning

Smooth system expansion

Easy maintenance & operation

Full rate traffic with Enhanced Full Rate (EFR)

Half rate traffic with EFR

MCT-Transcodin

Rate Adaptation Unit Solution


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- Network Subsystem

- Mobile Switching Center (MSC) Heart of the network

Connects calls by switching the digital voice data packets from one network path to

another( called routing )

Billing information and collection

Mobility management

- Registration

- Location Updating

- Inter BSS and inter MSC call handoff

MSC does gateway function while its customer roams to other network by using

HLR/VLR.


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- Network Subsystem

-Home Location Registers (HLR)

The Home Location Register or HLR is a central databasethat contains details of each mobile phone subscriber that

is authorized to use the GSM core network. Data stored in an HLR

International mobile subscriber identity.

Mobile subscriber international ISDN number (MSISDN).

Mobile subscriber category (prepaid or postpaid). Roaming restriction (allowed or not).

Supplementary services (allowed or not)

Authentication key


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- Network Subsystem

-Visitor Location Registers (VLR)

Temporary database which updates whenever new MS enters its area, by

HLR database

Database contains IMSI, TMSI, MSISDN, MSRN, Location Area,

authentication key

Functions

Works with the home location register and authentication center regarding the

mobile subscribers authentication. Relays cipher key from the home location register to the BSS for encryption and

decryption.

Controls allocation of new TMSI numbers.

Support paging.

Tracks state of all mobile subscribers in its area.


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- Network Subsystem

-Authentication Center (AUC)

Usually located in the HLR of a GSM system

Provides security function to network Maintains authentication keys and algorithms and

provides security triplets (RAND,SRES,Kc)


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GSM : System Architecture- Network Subsystem

-Equipment Identity Register (EIR)

A Database, that contains information on theidentity of mobile equipment to prevent callsfrom stolen, unauthorized or defective mobilestations.

operators maintain three lists of IMEI in EIR:

grey - GSM mobile phones to be tracked

black - barred GSM mobile phones

white - valid GSM mobile phones


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- Network Subsystem

-Public Switched Telephone Network (PSTN)

The network of the world's public circuit-

switched telephone networks. (Basically the normal phone network, orland line.)

Consists of Telephone lines

Fiber optic cables

Microwave transmission links Cellular networks

Communications satellites

Undersea telephone cables

Routed through the switchboard

Unreliable


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- Network Subsystem

-Integrated Services Digital Network (ISDN)

A set of communications standards forsimultaneous digital transmission of voice, video, data, and othernetwork services over the traditional circuits of the PSTN.

A circuit-switched telephone network system

Provides

Access to packet switched networks

Allow digital transmission of voice and data over ordinary telephonecopper wires, resulting in potentially better voice quality than an analog

phone can provide. A maximum of 128 kbit/s in both upstream and downstream directions

ISDN b-channels of 3 or 4 bris (6 to 8 64 kbit/s channels) arebonded.

Used heavily by the broadcast industry


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GSM : System Architecture- Network Subsystem

-Gateway Mobile Switching Center (GMSC)

A gateway that interconnects two networks: the cellularnetwork and the PSTN

routing calls from the fixed network towards a GSM use. is often implemented in the same machines as the MSC.


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- Short message service center (SMSC)

Is a network element in the mobile telephone networkwhich delivers SMS messages routing calls from the

fixed network towards a GSM use. Features

Store and forward

Responsible for handling the SMS operations

When an SMS message is sent from a mobile phone, it will reach anSMS center first

Stored SMS temporarily.

Delete sms after expiry period.

Send sender a status report

GSM by himu

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