1. VLR & HLR

2. Visitor Location Register (VLR): AVLR is acurrent subset of HLR for a particular cell. Whenever a subscriber enters a new cell, its current location is stored in VLR representing that cell. The entry is removed when the subscriber leaves that cell. The information about a subscriber is replicated in HLR and VLR to achieve faster location search which begins from VLR and ends in HLR if the entry is not found in the VLR. The VLR data are not used for any administrative purpose; it merely serves as a location identifier.

3. VLR & HLR HLR and VLR are huge databases maintained by high-power servers, often a Unix workstation. Tandem, which is part of Compaq (a part of HP), made the server and called it HLR when used for cellular system. A large number of mobile units use the same HLR, and there are usually more than one HLR for nationwide cellular system.

4. VLR & HLR For example, Motorola uses more than 60 HLRs nationwide. The processing of HLR is not complex, so it does not need sophisticated database functionality. The recent trends is to distribute HLRs and use distributed processing approaches for its management