VLR

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VLR HLR
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VLR HLR

• 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.

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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.

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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