GSM Network Architecture

This is a simplified description of GSM Network Architecture. We will discuss major components of the network and their functions.

Structurally GSM Network can be divided into two basic systems (networks):

BSS – Base Station System

SS – Switching System

The network management is performed by NMC (Network Management Center) and by OMC (Operation and Maintenance Center).

A system of Base Stations performs management of Um interface between Mobile and Base Stations.

BSS consists of:

BTS – Base Transceiver Station

BSC – Base Station Controller

BSC configures and controls a group of Base Stations. It is responsible for radio channels allocation, connection control, working in the frequency hopping mode, cell

configuration data collection, and handover. Of course it is not the full list of functions that the controller performs. Here we mention only the main ones. The core

component of GSM network, in general, and of BSS, in particular, is a Base Transceiver Station. BTS performs management of Um interface with Mobile Station (MS).

Base Station is a complex of transreceivers (transmitters) and antennas that maintains operation of a particular cell.

A system of Base Stations passes the information into Switching System (SS) through a transcoder TCE. SS consists of:

MSC - Mobile Switching Center

HLR – Home Location Register

VLR – Visit Location Register

EIR – Equipment Identify Register

AUC – Authentication Center

A brief overview of these components in GSM network.

MSC manages a group of cells that are geographically united (ex. situated within one and the same territory - city or region). In other words a regional mobile operator

may have only one MSC. This centre is also called ‘commutator/switching circuit’. Judging by its name, commutator/switching circuit’ is responsible for call routing

between different networks (standard public switched telephone network (PSTN), data transmission network (DTN), etc.). It is also responsible for call control,

‘handover’ (continuous connection while subscriber’s navigation through cells), switching of radio channels within cell, registration of MS location. Actually, HLR is a

distributed data base that contains information about permanent subscribers of this network, namely:

Identification numbers

Subscriber’s authenticity parameters

Scope of services provided to a subscriber

Service information

It is this data base which contains all the information that you’ve provided when signing an agreement with mobile operator. VLR is also a data base. It temporary

stores the information about subscribers who are in the coverage area of a particular MSC. It means that each Switching Center has its own VLR. Equipment Identify

Register (EIR) contains centralised data base that is used for storage of Mobile Stations’ identification numbers. In simple terms, the information about your phone’s

IMEI is stored in this data base. In theory, the mobile operator may forbid to provide services to the phone if it’s been stolen, for example. Unfortunately, such

equipment is not used by mobile operators in Russia.

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And finally, Authentication Center. AUC helps your phone to register with a network successfully. In the process of registration your SIM-card is involved directly as it

contains an individual key of authentication.

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