Tolerating Visitor Location Register failures in mobile environments

For mobile users who move frequently but receive relatively rare calls, a forwarding scheme has been shown to outperform the normal IS-41 location management scheme. But the forwarding scheme is more vulnerable to failure of intermediate Visitor Location Registers (VLRs) than the IS-41 scheme. We propose two simple variations to the forwarding scheme to address the fault tolerance weakness. One is based on the idea of maintaining two paths from the home location server to the last VLR. The second scheme is based on the knowledge of the neighbors of the faulty VLR. We evaluate and compare the performance of these location management schemes.