The effects of mobility on reliable transport protocols

We explore the effects of host motion on the performance of active transport-level connections. Motion causes increased delays and packet losses while the network learns how to route data to a host's new location. Transport protocols interpret these delays and losses as signs of network congestion. They consequently throttle their transmissions, further degrading performance. We quantify this degradation through measurements of protocol behavior in a wireless networking testbed. We show how current retransmission policies introduce unacceptably long pauses in communication (800 milliseconds and longer), and propose a fast retransmission scheme that can reduce these pauses to levels more suitable for human interaction (200 milliseconds). Our work demonstrates that reliable transport protocols most be made aware of mobility, and suggests how to adapt these protocols to mobile computing environments.>