Transcript ppt
Analysis of a Campus-wide Wireless Network David Kotz Kobby Essien Dartmouth College September 2002 Wi-Fi is becoming pervasive But how do people use it? How to design Wi-Fi networks? How to deploy Wi-Fi networks? Dartmouth College 5,500 students 3,330 live on campus 40% own laptops Class of 2006 just arrived 88% own Wi-Fi laptops; 100% of MBA students do The Dartmouth network 476 access points (now over 500) Cisco model 340 or 350 Dartmouth campus • Complete Wi-Fi coverage • 200 acre campus • 161 buildings – – – – – 82 Residential 32 Academic 22 Administrative 6 Library 19 Social The largest Wi-Fi study • • • • • • • • Fall 2001 Wi-Fi at Dartmouth 11 weeks Over 1700 users Diverse population 161 buildings 476 access points Campus-wide coverage [Tang and and [Hutchins [Balachandran Baker Zegura] 2002] 2000] • Wi-Fi at Stanford GA Tech SIGCOMM • 12 20 weeks 2.5 or days 7 weeks • 74 444users 195 users • Computer Diverse population scientists • 1 18building One buildings room • 12 109 4 access access access points points points • Small Partialsample coverage Data Collection 1: Syslog data collection • AP reports interesting events – – – – Authenticate Associate Deauthenticate Disassociate • Record date, time, MAC, AP name • Sent by access point to syslog recorder 2: SNMP data collection • Every 5 minutes, poll each AP • Record: – MAC of associated clients – Counter: inbound bytes – Counter: outbound bytes Outbound Inbound 3: tcpdump data collection Hub AP Tiny Linux box promiscuously sniffed all packet headers Results Traffic Daily traffic (GB) Median: 53 GB/day GB/day Average daily traffic, by weekday Average hourly traffic, by hour GB/hour To 11.4 GB (60% inbound) Average daily traffic per AP Median: 39 MB GB/day GB/day Average daily traffic (GB) (by category) GB/day/card Average GB/day per card (by category) Average daily traffic (GB) (10 busiest buildings) Results Sessions Session duration Deauthenticated Reassociated Associated Sessions time 30 mins Session length Median session length is 16.6 minutes Hours Flickering sessions Associated Reassociated time 10 seconds Roams per session Plot of the 18% of sessions that involve at least one roam Max: 19,902 Median: 2 Results Users Activity per card (distribution) Maximum: 77 days, 64 buildings, 161 APs Median: 28 days, 5 buildings, 9 APs Active cards per day Active cards per hour (category) Results Protocols Brown (dormitory) Berry Library Collis Student Center Sudikoff Lab for Computer Science Common IP protocols 99.7% of all wireless frames contained IP packets Protocol GB Percent PIM ~0 0.0% NARP ~0 0.0% RSVP ~0 0.0% IGMP ~0 0.0% ICMP ~0 0.0% UDP 5.7 2.5% TCP 221.9 97.5% 227.595 100.0% Total TCP and UDP traffic (GB) (by building) These top ten account for 85% of traffic TCP and UDP traffic (by direction) TCP connections (by building) TCP connections (by direction) Correction: Figures 27-28 Dartmouth College Computer Science Technical Report TR2002-432 http://www.cs.dartmouth.edu/~campus/ Summary • Largest trace-based study of a WLAN • Large, diverse population – Residential university campus – Mixture of academic and residential patterns – Results may be different for other populations Conclusions • High variance in traffic and activity – From day to day, hour to hour – From place to place, user to user • No clear dominance of inbound or outbound – Varies by protocol and user • Dormitories dominated traffic – Especially the Tuck School of Business • We need: – – – – Cards that avoid roaming across subnet boundary Support for roaming across subnets (Mobile IP, etc) Symmetric bandwidth Full-campus coverage: critical to acceptance Thank you David Kotz Kobby Essien http://www.cs.dartmouth.edu/~campus/