The Network Switching System has at it's core the Mobile Switching Centre
(MSC). This takes the communication from the BSS and dependent on the destination,
will switch to another part of it's home network for an intra network call;
to another mobile network for a inter mobile call or to the PSTN.
To support the role of the NSS in 2G networks there are
4 key sub-systems there as part of the Operational Support
- The Home Location Register (HLR) that holds the data about the subscriber to
- The Visitor Location Register (VLR) records a subset of the HLR data those
subscribers connected to the MSC including records of phones whilst roaming.
- The Authentication Centre (AuC) used to authenticate each device and SIM
attempting to connect to the network.
- Equipment Identity Register (EIR) holds the IMEI for all banned equipment
thus preventing stolen or other banned devices from accessing the network.
- Operations and Management Centre that maintains and manages the network.