In mobile communications, it is important that subscribers can receive and make calls from anywhere. The mobile network must therefore be able to locate the subscriber. This is done by location management.
InGSM networks, several radio cells are combined to form a location area( LA) for this purpose. When the subscriber switches on his cell phone or changes the radio cell area, the position of the subscriber is updated in the Visitor Location Register( VLR) of the corresponding mobile network via a Location Update( LUP).