Wireless Local Area Networks (WLANs) are experiencing unprecedented growth asthe last mile connectivity solution. Mobility is an important feature ofany wireless communication system. Handoffs are a crucial link levelfunctionality that enable a mobile user to stay connected to a wireless networkby switching the data connection from one base station or access point toanother. Conceptually the handoff process can be subdivided into two phases:(i) Discovery - wherein the client searches for APs in vicinity and (ii)Authentication - the client authenticates to an AP selected from the discoveryphase. The handoff procedure recommended by the IEEE 802.11 standard and closelyimplemented by various wireless vendors is an intrusive and a brute-forceapproach. My testbed based study of these algorithms showed that they incurhigh latencies varying between 400ms to 1.3 seconds depending on the securitysettings in effect. Such inefficient handoff mechanisms can have a detrimentalimpact on applications especially synchronous multimedia connections such asVoice over IP. In my dissertation, I have proposed and evaluated the notion of locality amongAPs induced by user mobility patterns. A relation is created among APs whichcaptures this locality in a graph theoretic manner called neighbor graphs-- a distributed structure that autonomously captures such locality. Based onthis, I have designed and evaluated efficient mechanisms to address the twodifferent phases of this handoff process. Through a rigorous testbed basedimplementation, I have demonstrated the viability of the concept of mobilityinduced locality through good performance improvements. Through extensivesimulations I have studied the performance of proposed handoff mechanisms overvarious different topologies. This work has shown that a topological structurewhich captures the locality relationship among APs is fundamental to designingmechanisms that make user mobility transparent from the higher layers of thenetworking stack.
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