The Shaman Automatic 802.11 Wireless Diagnosis System

Yu-Chung Cheng, MIkhail Afanasyev, Patrick Verkaik, Peter Benko, Jennifer Chiang, Alex C. Snoeren, Stefan Savage and Geoffrey M. Voelker
May 25, 2010

In this paper, we describe the design and implementation of an automated 802.11 wireless network diagnostic system called Shaman. Since the end-to-end performance of user traffic is some combination of factors across all network layers, Shaman incorporates comprehensive, cross-layer models of 802.11 network behavior and performance. These mod- els include broadband interference at the physical layer, per- packet link layer media access delays and losses, network layer device mobility and association management, and trans- port layer congestion and flow control. No one anomaly, fail- ure or interaction is singularly responsible for all network problems, and that a holistic analysis is necessary to cover the range of problems experienced in real networks. When users experience unsatisfactory performance at a particular time, they can query Shaman for a diagnosis. Shaman will then profile a user’s traffic at that time, deter- mine the network events that shape the performance profile, infer the causal sources of those events, and report the re- sults to the user. We demonstrate the use of Shaman on an enterprise wireless network deployed in a university campus building, and illustrate the underlying analysis Shaman per- forms on real network trouble reports submitted by users of the enterprise network.

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