Transcript Week_10_B

VLR & HLR
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.
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.
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