Ratul Mahajan, Maya Rodrig, David Wetherall, and John Zahorjan
We present Wit, a non-intrusive tool that builds on passive monitoring to analyze the detailed MAC-level behavior of operational
wireless networks. Wit uses three processing steps to construct an
enhanced trace of system activity. First, a robust merging procedure combines the necessarily incomplete views from multiple, independent monitors into a single, more complete trace of wireless
activity. Next, a novel inference engine based on formal language
methods reconstructs packets that were not captured by any monitor and determines whether each packet was received by its destination. Finally, Wit derives network performance measures from this
enhanced trace; we show how to estimate the number of stations
competing for the medium. We assess Wit with a mix of real traces
and simulation tests. We ﬁnd that merging and inference both signiﬁcantly enhance the originally captured trace. We apply Wit to
multi-monitor traces from a live network to show how it facilitates
802.11 MAC analyses that would otherwise be difﬁcult or rely on
less accurate heuristics.
Publisher Association for Computing Machinery, Inc.
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