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ABSTRACT
The wide-scale deployment of IEEE 802.11 wireless networks has
generated significant challenges for Information Technology (IT) departments
in corporations. Users frequently complain about connectivity
and performance problems, and network administrators are expected
to diagnose these problems while managing corporate security
and coverage. Their task is particularly difficult due to the unreliable
nature of the wireless medium and a lack of intelligent diagnostic
tools for determining the cause of these problems.
This paper presents an architecture for detecting and diagnosing
faults in IEEE 802.11 infrastructure wireless networks. To the best
of our knowledge, ours is the first paper to address fault diagnostic
issues for these networks. As part of our architecture, we propose and
evaluate a novel technique called Client Conduit, which enables bootstrapping
and fault diagnosis of disconnected clients. We describe
techniques for analyzing performance problems faced in a wireless
LAN deployment. We also present an approach for detecting unauthorized
access points. We have built a prototype of our fault diagnostic
architecture on the Windows operating system using off-the-shelf
IEEE 802.11 cards. The initial results show that our mechanisms are
effective; furthermore, they impose low overheads when clients are
not experiencing problems.
Categories and Subject Descriptors
C.2.3 [Computer-Communication Networks]: Network Operations
General Terms
Management, Reliability
Keywords
Infrastructure wireless networks, fault detection, fault diagnosis, disconnected
clients, IEEE 802.11, Rogue APs
1. INTRODUCTION
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MobiCom’04, Sept. 26-Oct. 1, 2004, Philadelphia, Pennsylvania, USA.
Copyright 2004 ACM 1-58113-868-7/04/0009 ...$5.00.
The convenience of wireless networking has led to a wide-scale
adoption of IEEE 802.11 networks [22]. Corporations, universities,
homes, and public places are deploying these networks at a remarkable
rate. However, a significant number of “pain points” remain for
end-users and network administrators. Users experience a number of
problems such as intermittent connectivity, poor performance, lack of
coverage, and authentication failures. These problems occur due to
a variety of reasons such as poor access point layout, device misconfiguration,
hardware and software errors, the nature of the wireless
medium (e.g., interference, propagation), and traffic congestion.
Figure 1 shows the number of such wireless-related complaints
logged by the Information Technology (IT) department of Microsoft
corporation over a period of six months. The company has a large
deployment of IEEE 802.11 networks with several thousand Access
Points (APs) spread over more than forty buildings. Each complaint
is an indication of end-user frustration and loss of productivity for
the corporation. Furthermore, resolution of each complaint results in
additional support personnel costs to the IT department; our research
revealed that this cost is several tens of dollars and this does not include
the cost due to the loss of end-user productivity.
To resolve complaints quickly and efficiently, network administrators
need tools for detecting, isolating, diagnosing, and correcting
faults. To the best of our knowledge, there is no previous research
that addresses fault diagnostic problems in IEEE 802.11 infrastructure
networks. In contrast, the importance of diagnosing these problems
in the “real-world” is apparent from the number of companies
that offer solutions in this space [2, 4, 20, 16, 37]. These products do
a reasonable job of presenting statistical data from the network; however,
they lack a number of desirable features. Specifically, they do
not do a comprehensive job of gathering and analyzing the data to establish
the possible causes of a problem. Furthermore, most products
only gather data from the APs and neglect the client-side view of the
network. Some products that monitor the network from the client’s
perspective require hardware sensors, which can be expensive