Eliminating overflow for large-scale mobility databases in cellular telephone networks

In a cellular phone system, mobility databases called visitor location registers (VLRs) are used to temporarily hold the subscription information of the roaming users who visit the service area of the VLR. When the users leave the VLR area, the corresponding records in the VLR are deleted. Due to user mobility, the capacity of the VLR may not be large enough to hold information for all visitors in the VLR area at some time periods. This issue is called VLR overflow. This paper describes a record replacement policy to allow mobile users to receive services in the VLR overflow situation. We utilize analytic modeling to investigate the performance of the replacement policy. The study indicates that our approach effectively eliminates the VLR overflow problem with insignificant extra overhead.