Network Components Of GSM

The Several Network Components Of GSM are Mobile Station (MS), Base Station Subsystem (BSS) & Network Switching Subsystem (NSS).

The MS is composed by:

• ME - Mobile Equipment, which is identified by the International Mobile Equipment Identity (IMEI).
• SIM - Subscriber Identity Module, which contains the subscriber-specified data to access GSM Network, except in emergency calls.
  

The Base Station Subsytem is composed by :

• BTS/BS - Base Transceiver Station/Base Station, which is responsible for the communication to and from MSs via air interface. The MS communicates with mobile station using a radio channel to a BTS.
• BSC - Base Station Controller, which is used to monitor and control several base stations, frequency administration, control of BTSs, exchange functions. It is also responsible for all the radio interface management, channel allocation & release, handover management.

The Network Switching System (NSS) is the main component of the public mobile network GSM and is used for switching, mobility management, interconnection to other networks and system control.

The several components of the NSS are :

• MSC - Mobile Switching Centre: controls all connections via a separated network to/from a mobile terminal within the domain of the MSC - several BSC can belong to a MSC.
• HLR - Home Location Register: central master database containing user data (Subscriber ID - IMSI & MSISDN), permanent and semi-permanent data of all subscribers assigned to the HLR.
• VLR - Visitor Location Register: local database for a subset of user data, including data about all users currently in the domain (each VLR is associated exactly to one MSC) of the VLR.
• EIR – Equipment Identity Register: registers GSM mobile stations and user rights, stolen or malfunctioning mobile stations can be locked and sometimes even localized.
• OMC - Operation and Maintenance Center: different control capabilities for the radio subsystem and the network subsystem.