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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