characterising the use of a campus wireless network 徐 志 賢 paper from: d. schwab and r.b. bunt,...
TRANSCRIPT
Characterising the Use of a Campus Wireless Network
徐 志 賢
Paper From: D. Schwab and R.B. Bunt, "Characterising the Use of a Campus Wireless
Network", Proc. IEEE Infocom 2004, Hong Kong, March 7-12, 2004.
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Outline
• Overview
• Campus Characteristics
• Wireless Network Environment
• Trace Methodology
• Trace Results
• Conclusion
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Overview
• Analysis of wireless usage at the University of Saskatchewan– Where– When– How much
• Trace allows evaluation of network design principles and plans for future development
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Campus Characteristics
• 40 Buildings with over 363 acres of land
• 18,000 students attend the university
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Wireless Network Environment
• Initial deployment in 2001 with 18 APs– Dispersed through various buildings– Not well advertised
• Wireless traffic is routed on a virtual private network with a unique subnet– Assign internal IP address by a DHCP
Server
• Cicsco LEAP authentication is used to provide access to wireless
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LEAP Authentication Process
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Trace Methodology
• Re-programming campus router and Mirrored wireless packets to a computer port monitoring traffic
• Used EtherPeek to log packet data• Used LEAP server to track
authentication data• Trace began Jan 22, 2003 and lasted
one week• Data analyzed with perl script
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Trace Methodology (Cont)
• Anonymisation– authentication log was stripped of user
identifications, leaving only machine addresses as identifiers.
– IP addresses were only temporary addresses assigned by campus DHCP server.
– No message bodies 、 No private information
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Trace ResultsAttribute Value
Total Packets 24,431,794
Total Seconds 603,054
Average Seconds
40.5 packets per second
Total Time6 days, 23 hours, 30 minutes, and 54 seconds
Spurious wired multicast overhead recorded (38% of traffic)
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Authentication Data
• Large number of authentications per user– Wireless cards store
user/pass– Typical of low and
fluctuating signal strength
– Oscillations between two APs
Attribute Value
Total Authentications 24973
Unique Users 134
Mean Authentications per User 186.4
Mode Authentications per User 5
Median Authentications per User 54.5
Access Points 18
Mean Authentications per AP 1387.4
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Data Analysis
• Number of authentications not related to packet rate– Reasons stated previously
• Older access points are used more often– More well-known to campus
• Weekend traffic– Minimal at office locations– Average at social and study locations
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Traffic vs. Authentications
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Daily Traffic Patterns
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Roaming
• Users connected to average 3 AP and max 8• Direct relation between roaming and proximity• Large well clusters of well-known APs incur the most
roaming
No. of unique user who authenticated at each access point
Connected to the location of the access point on the map
No. of unique users who authenticatedat both the access points connected by the line.
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Number of Access Points Visited Per User
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The College of Law
• Generated 86% of authentications and 33% of packets during trace
• Law students roamed more frequently
• Reasons– Center of study and work for law students– Early shift to wireless connectivity– Legal community utilizes digital technology
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Conclusion• Avg wireless user connects a small number of
times and only to a few APs• Well-known APs were used most heavily• Authentications have no relation to usage• Roaming is limited• Design Principles
– Wireless networks should focus on location instead of mobility
– APs should be focused on departments with online material
– Wireless technology is designed for users of modern mobile computers.
