Tracking Highly Mobile Endpoints

Abstract

We consider the problem of routing to endpoints with very high "effective" mobility, i.e., when the period between changes in an endpoint's location is comparable to the time it takes for the location tracking mechanism to converge. This could happen due to increased endpoint speed, decreased cell size, or increased control message latency. When this happens, conventional location tracking approaches fail -- by the time such mechanisms converge, the endpoint has already moved to a new location.We characterize the performance degradation of a location tracking mechanism with increasing effective mobility. Specifically, we show that a typical mobile network has three operating states -- reactable, late-reactable, and unreactable, and identify theoretically and experimentally, the endpoint speeds at which the system transitions from one state to another. We then describe "spray routing" -- a new routing mechanism that uses controlled multicasting to the vicinity of the endpoint's last-known location. We show experimentally that the throughput is dramatically increased to acceptable levels even for highly mobile endpoints while maintaining reasonable end-to-end delay.