Sync-scan: A fast hand-off procedure for 802.11 link layer roaming

ishwar ramani and stefan savage
May 3, 2004

Wireless networks scale by stitching together services from multiple overlapping base stations. To provide location transparency, individual clients must seamlessly ”hand-off” between base-stations as they move across the network. However, in many such systems, the overhead of locating the candidate base stations limits the continuity of hand-off - making it inappropriate for highly interactive applications such as voice. In this paper, we describe a technique for minimizing this cost by synchronizing short listening periods at the client with periodic transmissions from each base station. We have implemented this SyncScan algorithm for 802.11 infrastructure networks and show that we can practically support low overhead handoff in this environment. Moreover, our approach only requires trivial implementation changes, is incrementally deployable and is completely backward compatible with the existing 802.11 standard.

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