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Assessing the Performance Differences Between 802.11 Wireless and Wired Networks

This study evaluates the performance of 802.11 wireless networks compared to wired connections through a comprehensive analysis of TCP connection characteristics. Conducted on a 729-acre campus with diverse environments, the research involved passive measurements, revealing key insights into packet loss, delay variability, and unnecessary retransmissions. Findings indicate that while wireless connections exhibit higher delay variability and more retransmissions, wired connections generally perform with lower latency and loss rates. Future work will focus on modeling traffic load and characterizing wireless flows under various conditions.

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Assessing the Performance Differences Between 802.11 Wireless and Wired Networks

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  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 theInstitute of Computer Science, Foundation for Research and Technology-Hellas, Greece

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

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

  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. Research Objectives • Characterize packet-level performance • volume • packet loss • unnecessary retransmissions • delay • Contrast • wireless vs. wired • WAN vs. LAN • Perform large-scalepassive measurements

  6. Infrastructure

  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 connectionsfrom wireless clients • ~ 33% of the connections: pathological cases with no useful payload (~0.1% of bytes) • Wireless/wired TCP connections carried ~500GB (each)

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

  9. TCP Connection Payload (Bytes) Download Upload

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

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

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

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

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

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

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

  17. Packet Losses Computed based on retransmissions and triple duplicate ACKs (3DUP) • 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

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

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

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