GSM ARCHITECTURE

GSM ARCHITECTURE

 

MOBILE STATION (MS)

Ø  Mobile Equipment (ME)

Ø  Subscriber Identity Module (SIM)

BASE STATION SUBSYSTEM (BSS)

Ø  Base Transceiver Station (BTS)

Ø  Base Station Controller (BSC)

NETWORK SWITCHING SUBSYSTEM(NSS)

Ø  Mobile Switching Center (MSC)

Ø  Home Location Register (HLR)

Ø  Visitor Location Register (VLR)

Ø  Authentication Center (AUC)

Ø  Equipment Identity Register (EIR) 

MOBILE STATION (MS)

Ø  A GSM mobile phone consists of two components, the mobile radio telephone itself and the SIM (Subscriber Identity Module). This enables a distinction to be made in the GSM network between user and mobile terminal.

Ø  The mobile radio telephone is characterized by its internationally unique serial number or International Mobile Equipment Identity ( IMEI).

Ø   The user is identified by his customer number (International Mobile Subscriber Identity or IMSI), which is stored on the SIM card.

Ø  This is assigned to the subscriber when he registers with the network provider and must be distinguished from the telephone number assigned to him, which is the Mobile Station ISDN Number ( MSISDN). This distinction enables a subscriber to use different mobile radio telephones with the same SIM card.

BTS (Base Transceiver Station)

Ø  A GSM Base Transrceiving Station ( BTS) houses the transmit and receive equipment for one or more cells. It constitutes the interface between the network provider and the mobile phone.

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

Ø  Frequency hopping

Ø  Communicates with Mobile station and BSC

Ø  Consists of Transceivers (TRX) units

BSC (Base Station Controller)

Ø  The Base Station Controller (BSC) administers the transmit and receive resources of the connected base stations. For example, the channels for signaling and for payload traffic are provided here and the data traffic between BTS and MSC is controlled here.

Ø  Manages Radio resources for BTS

Ø  Assigns Frequency and time slots for all MS’s in its area

Ø  Handles call set up

Ø  Transcoding and rate adaptation functionality

Ø  Handover for each MS

Ø  Radio Power control 

Ø  It communicates with MSC and BTS

 

SWITCHING CENTRE MSC  

Ø  The base station is controlled via the Mobile Switching Centre ( MSC). This switching node assumes all the technical functions of a landline network switching node, for example, path search, signal path switching and processing of supplementary services.

Ø  If there is a requirement for a connection to a subscriber in the landline network, this is forwarded by the MSC to the landline network over a switching path.

Ø  Heart of the network

Ø  Manages communication between GSM and other networks

Ø  Call setup function and basic switching

Ø  Call routing

Ø  Billing information and collection

Ø  Mobility management

Ø  Registration

Ø  Location Updating

Ø  Inter BSS and inter MSC call handoff

Ø  MSC does gateway function while its customer roams to other network by using HLR/VLR.

Ø  In order that the network provider is in a position to provide all the services for which demand exists, it must store various items of data. For example, it must know which subscribers are using its network and which services they wish to use.

Ø   This data, such as the name of the subscriber, his customer number and the services he requires, is stored in the Home Location Register ( HLR).

Ø  If a connection is to be established, for example from a landline network connection to a mobile phone, the network provider needs to know where the subscriber is and whether his mobile phone is switched on. This information is held in the Visitor Location Register ( VLR) and the HLR.

Main Switching Center

Ø      To check whether a subscriber is entitled to use the mobile telecommunication network (i.e.   he has taken out a card contract), the network provider maintains an Authentication Centre ( AUC). This holds algorithms and subscriber-related keys which amongst other things are required during authentication.

Ø  The network provider can also maintain the Equipment Identity Register ( EIR), which holds details of all the mobile transceivers permitted on the network, broken down into three groups known as the white, grey and black lists.

Ø  The white list is a register of all the mobile phones which are functioning reliably, the grey list contains all the phones which may possibly be defective, while the black list holds details of all the phones which either have a fault or have been reported stolen. However, not all network providers maintain an equipment register.

CDMA

Ø  Multiple users occupying the same band by having different codes is known as  CDMA - Code Division Multiple Access

Ø  ESN SYSTEM (EQUIPMENT SERIAL NUMBER)