GSM architecture

The basic architecture of GSM is not dissimilar to other cellular radio systems and comprises base transceiver stations (BTS), Base Station Controllers (BSC), Mobile Switching Centres (MSC), a variety of registers and a network management system, as shown in Figure 47.9. The mobile station comprises a mobile equipment and a subscriber identity module (SIM). In addition to these functional entities, GSM also defines several interfaces, the Radio Interface (Um), the interface between the MSC and BSC (A interface) and the signalling interface which allows roaming between networks. This is based on the CCITT No.7 signalling standard and is defined as a Mobile Application Part (MAP).

The BTS and BSC together form the Base Station Subsystem (BSS) and carry out all the functions related to the radio channel management. This includes the management of the radio channel configurations, allocating radio channels for speech, data and signalling purposes, and controlling frequency hopping and power control. The BSS also includes, as does the MS, the speech encoding and decoding, and channel coding and decoding.

The MSC, VLR and HLR are concerned with mobility manage­ment functions. These include authentication and registration of the mobile customer, location updating, and call set up and release. The HLR is the master subscriber database and carries information about individual subscribers numbers, subscription levels, call restriction-s, supplementary services and the current location (or most recent location) of subscribers. The VLR acts as a temporary subscriber database forall subscribers within its coverage area, and contains similar information to that in the HLR. The provision of a VLR means that the MSC does not need to access the HLR forevery transaction.

The authentication centre (AUC) works closely with the HLR and provides information to authenticate all calls in order to guard against fraud. The equipment identity register (EIR) is used for equipment security and validation of different types of mobile equipment. This information can be used to screen mobile types from accessing the system, for example if a mobile equipment is stolen, not type approved, or has a fault which could disturb the network.

Network management is used to monitor and control the major elements of the GSM network. In particular, it monitors and reports faults and performance data. It can also be used to re-configure the network.

MS Mobile Station

MSC Mobile Switching Centre

BTS Base Transceiver Station

BSC Base Station Controller

VLR Visited Location Register

HLR Home Location Register

EIR Equipment Identity Regsiter

AUC Authentication centre

Figure 47.9 GSM architecture

Дата добавления: 2015-11-16