Visitor Location Register

What is it? 

A visitor location register (VLR) is a database that includes information on subscribers’ roaming within the limits of a mobile switching center’s (MSC) location area. The purpose of VLRs is to decrease the number of queries MSCs need to make to a home location register (HLR). The HLR itself stores permanent data concerning the cellular network’s subscribers. 

How does it work? 

Data held by VLRs (fields) is similar to that stored by HLRs. Additionally, VLRs hold international mobile subscriber identity (IMSI) and the mobile subscriber integrated services digital network (MSISDN) – both allowed for a certain IMSI/MSISDN pair. They also comprise authentication data pertaining to a specific subscription. 

While data in VLRs frequently changes, that in HLRs is more permanent. Furthermore, when each MSC’s location area in the network is served by a single VLR, the VLR will have a smaller number of records compared to the HLR.  

Once a subscriber moves to an MSC’s location area, there is a record update in the VLR. It automatically informs the subscriber’s HLR of the change. 

Other VLR functionalities include monitoring the subscriber’s location, determining whether a subscriber can assess a certain service, assigning roaming numbers during incoming calls, deleting inactive subscribers’ records, and accepting information from the HLR.