Fast and scalable wireless handoffs in support of mobile Internet audio

Future internetworks will include large numbers of portable devices moving among small wireless cells. We propose a hierarchical mobility management scheme for such networks. Our scheme exploits locality in user mobility to restrict handoff processing to the vicinity of a mobile node. It thus reduces handoff latency and the load on the internetwork. Our design is based on the Internet Protocol (IP) and is compatible with the Mobile IP standard. We also present experimental results for the lowest level of the hierarchy. We implemented our local handoff mechanism on Unix-based portable computers and base stations, and evaluated its performance on a WaveLAN network. These experiments show that our handoffs are fast enough to avoid noticeable disruptions in interactive audio traffic. For example, our handoff protocol completes less than 10 milliseconds after a mobile node initiates it. Our mechanism also recovers from packet losses suffered during the transition from one cell to another. This work helps extend Internet telephony and teleconferencing to mobile devices that communicate over wireless networks.