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 the location management. In GSM networks, several radio cells are combined to form a Location Area (LA) for this purpose. When the subscriber switches on his mobile phone or changes the radio cell area, the position of the subscriber is updated in the Visitor Location Register (VLR) of the corresponding mobile radio network via a Location Update (LUP).