1. 1 Assessing The Real Impact of 802.11 WLANs: A Large-Scale Comparison of Wired and Wireless Traffic Maria Papadopouli * Assistant Professor Department of Computer Science University of North Carolina at Chapel Hill (UNC) * This work was partially supported by the IBM Corporation under an IBM Faculty Award 2004 It was done while visiting the Institute of Computer Science, Foundation for Research and Technology-Hellas, Greece

2. 2 Collaborators & Coauthors Felix-Hernandez Campos Department of Computer Science University of North Carolina at Chapel Hill (UNC)

3. 3 Roadmap Motivation & Research Objectives Testbed & Data Acquisition Data Analysis Contributions Future Work

4. 4 Motivation Increasingly deployment of 802.11 wireless networks Plethora of novel research issues such as mobility, power management, capacity planning, QoS support Need for benchmarks More accurate and realistic characterizations of production wireless networks & their performance More representative assumptions in theoretical & simulations studies

5. 5 Research Objectives  Characterize packet-level performance volume packet loss unnecessary retransmissions delay  Contrast wireless vs. wired WAN vs. LAN  Perform large-scale passive measurements

6. 6 Infrastructure

7. 7 Testbed & Data Set 729-acre campus: 26,000 students, 3,000 faculty, 9,000 staff Diverse environment 14,712 unique MAC addresses 488 APs (Cisco 1200, 350, 340 Series) 175 GB packet headers in a 7-day trace 9,766,507 TCP connections from wired clients 21,396,174 TCP connections from wireless clients ~ 33% of the connections: pathological cases with no useful payload (~0.1% of bytes) Wireless/wired TCP connections carried ~500GB (each)

8. 8 TCP Connection Payload (Bytes) Wired Clients vs. Wireless Clients Wireless Clients Wired Clients

9. 9 TCP Connection Payload (Bytes) Download Upload

10. 10 Connection Size (# Packets) Connections with 100 packets represent < 5% of all connections but carry > 85% of the total bytes ≥

11. 11 One-Side Transit Time Measurement WAN OSTT LAN OSTT

12. 12 Minimum One-Side Transit Time WAN Wired LAN Wireless LAN [6ms,250ms] [0.7ms, 1ms] [1ms,7ms] [7ms, 250ms]

13. 13 One-Side Transit Time Statistics Wireless LAN Wired LAN Heavy max & avg

14. 14 Maximum One-Side Transit Time Wired Clients Wireless Clients TCP delay ACK mechanism introduces extra delays of ~ [100ms, 200ms]

15. 15 Large Delay Variability on Wireless LAN Wired LAN mad Wireless LAN mad

16. 16 Fraction of Round-Trip Time from LAN Using Medians & Means Wireless Clients Wired Clients Using medians

17. 17 Packet Losses 2% losses were observed for 17% of the connections for wired clients 23% of the connections for wireless clients 802.11 link layer retransmission is very effective The high delay variability suggests that several losses were recovered  They may be higher under special conditions Client mobility High traffic load at AP Computed based on retransmissions and triple duplicate ACKs (3DUP)

18. 18 Unnecessary Retransmissions (% Tot. Pck) Enough samples for a more conservative timeout that reduces the # of unnecessary retransmissions Wireless Clients Wired Clients 100+ connections

19. 19 Contributions Large-scale passive measurement study on TCP connection characteristics on volume delays losses unnecessary retransmissions lack of termination Wireless vs. Wired LANs Wireless LANs have  substantially higher delay variability  significant more unnecessary retransmissions  only marginally greater packet losses

20. 20 Future Work Characterization of wireless flows under certain conditions (mobility, application, AP, time) Flow modeling Forecasting traffic load using flow-related information Contrast connection models from different wireless environments (campus, institute, metropolitan area, conference) UNC/FORTH Data repository with traces & models

21. 21 More Info http://www.cs.unc.edu/~maria http://www.ics.forth.gr/mobile/ maria@cs.unc.edu Thank You!