Thursday, September 3, 2009

GSM- Global System for Mobile Communications

GSM Network Architecture

GSM Network consists of three main parts:

  • Mobile Station (MS) carried by the subscriber
  • Base Station Subsystem(BSS) controls radio link with mobile station
  • Network and Switching Subsystems (NSS) mobility management and switching of calls between mobile users, and between mobile and fixed network users.
Mobile Station consists of:
  • Mobile Equipments(ME) such as hand portable and vehicle mounted unit.
  • Subscriber Identity Module (SIM) contains the entire customer related information.
Base Station Subsystem (BSS) consists of:
  • Base Transceiver Station (BTS) defines a cell and is responsible for radio link protocols with Mobile Station
  • Base Station Controller (BSC) controls multiple BTSs and manages radio channel setup, and handovers. The BSC is the connection between the Mobile Station and Mobile Switchning Center.
Network and Switching Subsystems consists of:
  • Mobile Switching Center (MSC) is the central component of the NSS. It operates all switching functions for the mobiles within its jurisdiction. Interface between mobile and other network including fixed network. Its functions:
  • Manages the location of mobiles.
  • Swtiches cells
  • Manages Security features.
  • Controls handover between BSCs.
  • Resource Management.
  • Interworks with and manages network databases
  • Collects call billing data and sends to billing system
  • Collects traffic statistics for performance monitoring.

  • Network Databases - Home Location Register and Visitor Location Register together with MSC provides the call routing and roaming capabilities of GSM.
  • Home Location Register(HLR) contains all the subscriber information for the purposes of call control and location determination. There is logically one HLR per GSM network although it may be implemented as adistributed database.
  • Visitors Location Register(VLR) is only a temporary storage while the particular subscriber is located in the geographical area controlled by the MSC/VLR. Contains on the necessary information provision of subscribed services.
  • Authentication Center (AuC) is a protected database that stores the security information for each subscriber ( a copy of the secrte key stored in each SIM).
  • Equipment Identity Register (EIR) is a list of all valid mobile equipment on the network.


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