Mobile Station (MS) – The mobile telephone.
The Switching System (SS)
Home Location Register (HLR) – A database which stores data about GSM subscribers, including the Individual Subscriber Authentication Key (Ki) for each Subscriber Identity Module (SIM).
Mobile Services Switching Center (MSC) – The network element which performs the telephony switching functions of the GSM network. The MSC is responsible for toll ticketing, network interfacing, common channel signaling.
Visitor Location Register (VLR) – A database which stores temporary information about roaming GSM subscribers.
Authentication Center (AUC) – A database which contains the International Mobile Subscriber Identity (IMSI) the Subscriber Authentication key (Ki), and the defined algorithms for encryption.
Equipment Identity Register (EIR) – A database which contains information about the identity of mobile equipment in order to prevent calls from stolen, unauthorized, or defective mobile stations.
The Base Station System (BSS)
Base Station Controller (BSC) – The network element which provides all the control functions and physical links between the MSC and BTS. The BSC provides functions such as handover, cell configuration data, and control of radio frequency (RF) power levels in Base Transceiver Stations.
Base Transceiver Station (BTS) – The network element which handles the radio interface to the mobile station. The BTS is the radio equipment (transceivers and antennas) needed to service each cell in the network.
The Operation and Support System (OSS)
Message Center (MXE) – A network element which provides Short Message Service (SMS), voice mail, fax mail, email, and paging.
Mobile Service Node (MSN) – A network element which provides mobile intelligent network (IN) services.
Gateway Mobile Services Switching Center (GMSC) – A network element used to interconnect two GSM networks.
GSM Interworking Unit (GIWU) – The network element which interfaces to various data networks.