Supporting Secure and Transparent Mobility in Wireless Local-Area Networks

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Date
2005-12-01Author
Mishra, Arunesh
Advisor
Arbaugh, William A
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Show full item recordAbstract
Wireless Local Area Networks (WLANs) are experiencing unprecedented growth as
the last mile connectivity solution. Mobility is an important feature of
any wireless communication system. Handoffs are a crucial link level
functionality that enable a mobile user to stay connected to a wireless network
by switching the data connection from one base station or access point to
another. 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 discovery
phase.
The handoff procedure recommended by the IEEE 802.11 standard and closely
implemented by various wireless vendors is an intrusive and a brute-force
approach. My testbed based study of these algorithms showed that they incur
high latencies varying between 400ms to 1.3 seconds depending on the security
settings in effect. Such inefficient handoff mechanisms can have a detrimental
impact on applications especially synchronous multimedia connections such as
Voice over IP.
In my dissertation, I have proposed and evaluated the notion of locality among
APs induced by user mobility patterns. A relation is created among APs which
captures this locality in a graph theoretic manner called neighbor graphs
-- a distributed structure that autonomously captures such locality. Based on
this, I have designed and evaluated efficient mechanisms to address the two
different phases of this handoff process. Through a rigorous testbed based
implementation, I have demonstrated the viability of the concept of mobility
induced locality through good performance improvements. Through extensive
simulations I have studied the performance of proposed handoff mechanisms over
various different topologies. This work has shown that a topological structure
which captures the locality relationship among APs is fundamental to designing
mechanisms that make user mobility transparent from the higher layers of the
networking stack.