GSM architecture : Network Subsystem (NSS) (6/6)

GSM architecture : Network Subsystem (NSS)

The Equipment Identity Register (EIR) can be implemented as an option by the network
operator. The EIR permits the detection of stolen terminal equipment used in GSM networks
by checking the IMEI (International Mobile Equipment Identity) against the data stored in the
EIR. This check is carried out independently of the SIM card, and only applies to the mobile
station in question.

All the components which control and forward the call, and are responsible for security and
mobility management, that is the MSC, HLR, VLR, AUC and EIR, form the Network
Subsystem (NSS).