GSM SYSTEM ARCHITECTURE

GSM SYSTEM ARCHITECTURE

·   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)

·         Operational Support Subsystem (OSS)

SYSTEM ARCHITECTURE MOBILE STATION (MS):

The Mobile Station is made up of two entities:

1. Mobile Equipment (ME)

2. Subscriber Identity Module (SIM)

1. MOBILE EQUIPMENT (ME):

·         Portable, vehicle mounted, 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 handover

·         Power level : 0.8W – 20 W 160 character long SMS.

2. SUBSCRIBER IDENTITY MODULE (SIM)

·         Smart card contains the International Mobile Subscriber Identity (IMSI)

·         Allows user to send and receive calls and receive other subscribed services

·         Protected by a password or PIN

·         Can be moved from phone to phone – contains key information to activate the phone

SYSTEM ARCHITECTURE BASE STATION SUBSYSTEM (BSS):

·         Base Station Subsystem is composed of two parts that communicate across the standardized Abis interface allowing operation between components made by different suppliers

1.Base Transceiver Station (BTS)

2.Base Station Controller (BSC)

1. BASE TRANSCEIVER STATION (BTS):

·         Encodes, encrypts, multiplexes, modulates and feeds the RF signals to the antenna.

·         Communicates with Mobile station and BSC

·         Consists of Transceivers (TRX) units

2. BASE STATION CONTROLLER (BSC):

·         Manages Radio resources for BTS

·         Assigns Frequency and time slots for all MS's in its area

·         Handles call set up

·         Handover for each MS

·         It communicates with MSC and BTS

SYSTEM ARCHITECTURE NETWORK SWITCHING SUBSYSTEM(NSS)

Manages the switching functions of the system and allows the MSCs to communicate with other networks such as PSTN and ISDN. It consist of

1.      MOBILE SWITCHING CENTER (MSC)

·         Heart of the network

·         Manages communication between GSM and other networks

·         Billing information and collection

·         Mobility management

-Registration

-Location Updating

-Inter BSS and inter MSC call handoff

2.      HOME LOCATION REGISTERS (HLR)

·         Stores information about each subscriber that belongs to it MSC in permanent and temporary fashion.

·         As soon as mobile subscriber leaves its current local area, the information in the HLR is updated.

·         database contains IMSI, IMSISDN, prepaid/ postpaid, roaming restrictions, supplementary services.

3.      VISITOR LOCATION REGISTERS (VLR)

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

·         Assigns a TMSI to each MS entering the VLR area which keeps on changing.

·         Controls those mobiles roaming in its area o Database contains IMSI, MSISDN, Location Area, authentication key

4.       AUTHENTICATION CENTER (AUC)

·        Contains the algorithms for authentication as well as the keys for encryption.

·        Protects network operators from fraud.

·        Situated in special protected part of the HLR.

5.      EQUIPMENT IDENTITY REGISTER (EIR)

·        Stores all devices identifications registered for this network.

·        Database that is used to track handsets using the IMEI (International Mobile Equipment Identity)

·        Prevents calls from stolen, unauthorised or defective mobile devices

 OPERATIONAL SUPPORT SUBSYSTEM (OSS):

 It supports the operation and maintenance of GSM and allows system engineers to monitor, diagnose and troubleshoot all aspects of GSM system. It supports one or more Operation Maintenance Centres (OMC) which are used to monitor the performance of each MS, Bs, BSC and MSC within a GSM system. It has three main functions:

 • To maintain all telecommunication hardware and network operations with a particular market.

• To manage all charging and billing procedures

• To manage all mobile equipment in the system.

Interfaces used for GSM network: (fig 2)

1)UM Interface -Used to communicate between BTS with MS

2)Abis Interface- Used to communicate BSC TO BTS

3)A Interface-- Used to communicate BSC and MSC

4)Singling protocol (SS 7)- Used to communicate MSC with other network.