Location area identity

Each location area of a public land mobile network (PLMN) has its own unique identifier which is known as its location area identity (LAI). This internationally unique identifier is used for location updating of mobile subscribers. It is composed of a three decimal digit mobile country code (MCC), a two to three digit mobile network code (MNC) that identifies the GSM PLMN in that country, and a location area code (LAC) which is a 16 bit number thereby allowing 65536 location areas within one GSM PLMN.

The LAI is broadcast regularly through a broadcast control channel (BCCH). A mobile station (e.g. cell phone) recognizes the LAI and stores it in the subscriber identity module (SIM). If the mobile station is moving and notices a change of LAI, it will issue a location update request, thereby informing the mobile provider of its new LAI. This allows the provider to locate the mobile station in case of an incoming call.

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