The Visitor Location Register (VLR) is a component of the switching subsystem(SSS) of a GSM network. The switching subsystem comprises different databases in which individual subscriber data is stored. One of these databases is the Home Location Register( HLR), and another is the Visitor Location Register (VLR).
The Visitor Location Register is a local database with few control functions. It contains data relevant to call connections. This visitor file contains data about the mobile station and its subscribers who are in its area. The VLR data is dynamically updated by the mobile station and by the location register (HLR) when roaming. When a visitor logs into the network by switching on his mobile station, he does so in a radio cell that belongs to a specific stay area, a location area( LA). A Visitor Area manages a geographical area consisting of several Location Areas.
When logging in, the subscriber announces his identity; the corresponding subscriber data can then be requested in the HLR register, which is located in another GSM network. In this way, the subscriber's authorization ischecked and, if confirmed, the connection to the desired subscriber is established. When receiving calls from foreign networks, with which the location register is addressed, the current visitor register of the subscriber is queried and the connection is forwarded to the corresponding GSM network.