VLR FUNCTIONS

The role of a VLR in a GSM network is to act as a temporary storage location for subscription information for MSs which are within a particular MSC service area. Thus, there is one VLR for each MSC service area. This means that the MSC does not have to contact the HLR (which may be located in another country) every time the subscriber uses a service or changes its status.Following occurs when MS’s move into a new service area:

1. The VLR checks its database to determine whether or not it has a record for the MS (based on the subscriber’s IMSI)

2. When the VLR finds no record for the MS, it sends a request to the subscriber’s HLR for a copy of the MS’s subscription

3. The HLR passes the information to the VLR and updates its location information for the subscriber. The HLR instructs the old VLR to delete the information it has on the MS

4. The VLR stores its subscription information for the MS, including the latest location and status (idle)

 

VLR-HLR interaction

 

For the duration when the MS is within one MSC service area, then the VLR contains a complete copy of the necessary subscription details, including the following information:

• Identity numbers for the subscriber.

• Supplementary service information (e.g. whether the subscriber has call forwarding on busy activated or not).

• Activity of MS (e.g. idle).

• Current LA of MS.