GSM/2G Architecture

The GSM network can be broadly divided into-

  • Mobile Station(MS)
  • Base Station Sub-System(BSS)
  • Network Switching Sub-System(NSS)
  • Operation Support Sub-System(OSS)
GSM/2G Architecture


  1. Mobile Station : 
  • ME(Mobile Equipment) :Hardware used by subscriber containing IMEI(International Mobile Equipment Identity).
  • SIM(Subscriber Identity Module) :Detachable smart card containing IMSI(International Mobile Subscriber Identity).
     2. Base Station Subsystem :
  • BTS(Base Transceiver Station) :Sends & Receives signals from MS. Also does Encoding, Multiplexing, Encryption, Modulation, ..etc.
  • BSC(Base Station Controller) :Controls group of BTS, Allocation of radio channels, Handover from one BTS to another.
     3. Network Switching Subsystem :
  • MSC(Mobile Switching Centre) :Performs call routing, call setup & call switching. Communicates with other NSS component like HLR ,VLR, AUC &EIR, Management of  mobile services like registration, authentication, ..etc.
  • HLR(Home Location Register) :Stores permanent data about subscribers Profile, Location info, Status, Subscription info, ..etc.
  • VLR(Visitor Location Register) :Stores temporary information. Integrated with MSC. Work in co-ordination with HLR.
  • AuC(Authentication Centre) :Authenticate each SIM card that attempts to connect to GSM core network(typically when the phone is powered on).Store a copy of secret key.
  • EIR(Equipment Identity Register) :Database that contain list of all valid Mobile on network. IMEI used to identify each MS. IMEI is marked as invalid in case of stolen. 
      4. Operation Support Sub-System :
         Oss is connected to components of the NSS and the BSC. It is used to control and monitor the               overall GSM network and it is also used to control the traffic load of the BSS.                              





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