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GSM Operation SubSystem

The GSM system is broken up in to three parts, the first two parts have already been discussed, the third part of the GSM system is the operational subsystem (OSS). The OSS contains all the functions necessary for network operation and maintenance. The OSS possesses network entities of its own and accesses other entities via SS7 signaling. The following section describes the entities:

Operation and Maintenance Centre (OMC): The OMC monitors and controls all other GSM network entities via the O interface (SS7 with X.25), typically the OMC functions are Traffic Monitoring, Status reports of the network entities, subscribers and security management, or accounting and billing.

Authentication Centre (AuC): The Radio Air interface and the MS’s are particularly vulnerable, therefore a separate AuC has been defined to protect user identity and data transmission. The AuC contains the algorithms for authentication, the keys for encryption and generates the values needed for user authentication for the HLR.

Equipment Identity Register (EIR): EIR is a database for all IMEIs that stores all the device identifications registered for the GSM network. As MSs are mobile they can be stolen easily. If a user has a valid SIM of their own, then they can use any stolen MS. Hence the EIR has a ‘black list’ of stolen or locked devices so the MS on this list is useless as soon as the owner of the MS has reported it as stolen. Furthermore the EIR holds a list of valid IMEIs, and a list of malfunctioning devices.

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