The components of the tree GSM network subsystems

• Radio Subsystem (RSS) consisting of the BSSs and all BSS connected MS devices .
• Network and Switching Subsystem (NSS)
• Operation Subsystem (OSS)

specified in GSM 01.02 (‘General description of a GSM Public Land Mobile Network(PLMN)’) and the GSM components
·  ME = Mobile Equipment
·  BTS = Base Receiving Station
·  BSC = Base Station Controller
·  MSC = Mobile Switching Center
·  VLR = Visitor Location Register
·  OMC = Operation and Maintenance Center
·  AuC = Authentication Center
·  HLR = Home Location Register
·  EIR = Equipment Identity Register
·  SMSC = Short Message Service Centre

A MSC is also through a Gateway MSC (GMSC) connected to other MSCs and to the Public Switched Telephone Network (PSTN) with the Integrated Services Digital Network (ISDN) option. The Inter-Working Function (IWF) of GMSC connects the circuit switched data paths of a GSM network with the PSTN/ISDN. A GMSC is usually integrated in an MSCNEXT