VOICE SWITCHING IN CELLULAR NETWORKS :Radio subsystem and Network & switching system

1. Radio subsystem :

The radio subsystem(RSS) comprises all radio specific entities, i.e., the mobile stations(MS) and the base station subsystem(BSS).the above fog. Shows the connection between the RSS and the NSS via the A interface and the connection to the OSS via the O interface.

● Base station subsystem(BSS): A GSM network comprises many BSSs, each controlled by a base station controller(BSC).The BSS performs all functions nessary to maintain radio connections to an MS,coding/decoding of voice.The BSS contains several BTSs.

● Base transceiver station(BTS): A BTS comprises all radio equipment, i.e., antennas,signal processing,amplifiers necessary for radio transmission.It is connected to MS via the Um interface(ISDN U interface for mobile use),and to the BSC via the Abis interface.The Um interface contains all the mechanisms necessary for wireless transmission. The Abis interface consists of 16 or 64 kbits/s connections.

● Base station controller(BSC): The BSC basically manages the BTSs.It reserves radio frequencies, handles the handover from one BTS to another within the BSS, and performs paging of the MS.

● Mobile station(MS): The MS comprises all user equipment and softwere needed to communication with a GSM network.An MS consists of user independent hard-and softwere and of the subscriber identity module(SIM), which stores all user-specific data that is relevant to GSM. MS can be identified via the international mobile equipment identity(IMEI). SIm card contains many identifiers and tables, such as card-type, serial number, list of subscribed services, a personal identity number(PIN), a PIN unblocking key(PUK).

2. Network & switching system :

The “heart” of the GSM system is formed by the Network and switching subsystem(NSS).The NSS consists of the following switches and databases:

● Mobile services switching center(MSC): MSCs are high-performance digital ISDN switches.They set up connections to other MSCs and to the BSCs via the A interface, and form the fixed backbone network of a GSM system.An MSC manages several BSCs in a geographical region.It handles all signaling needed for connection setup, connection release and handover of connections to other MSCs.

● Home location register(HLR): The HLR is the most important database in a GSM system .It stores all user-relevent information.

● Visitor location register(VLR): The VLR associated to each MSC is a dynamic database which stores all important information needed for the MS users currently in the LA that is associated to the MSC.