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WiFox : Scaling WiFi Performance for Large Audience Environments

WiFox : Scaling WiFi Performance for Large Audience Environments. Arpit Gupta , Jeongki Min and Injong Rhee NC State University. Interesting ??. WiFox : AP-only S/W solution. Faster WiFi !!. Manageable solution !!. Large Audience Environments (LAEs). Large Audience Environments.

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WiFox : Scaling WiFi Performance for Large Audience Environments

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  1. WiFox: Scaling WiFi Performance for Large Audience Environments Arpit Gupta, Jeongki Min and InjongRhee NC State University

  2. Interesting ?? WiFox: AP-only S/W solution Faster WiFi !! Manageable solution !!

  3. Large Audience Environments (LAEs)

  4. Large Audience Environments • Any location with a large WiFi user population • WBA projected a growth rate of 350% per year for such WiFi deployments • Various successful deployment models such as Boingo-Google, Mobily-Aruba etc. already exist Source: WBA(Wireless Broadband Alliance) Source: Wireless Broadband Alliance (WBA)

  5. What about User Experience ? As number of active clients increases, user experience diminishes significantly

  6. Problem Anatomy

  7. Well Known Factors • Contention and collision • Increases with growing competition • Rate Diversity • Slower STA slows down all other STAs • Various fairness realizations like WFQ, TBR etc. • Random Losses and TCP performance • TCP treats packet losses as congestion signals • Usage of TCP ECN and proxy servers isolate wired and wireless networks • Traffic Asymmetry

  8. Traffic Asymmetry Downlink Traffic dominates for 90% of data traces

  9. Traffic Asymmetry Downlink Traffic dominates compared to uplink Majority of data traffic is Web based Majority of data packets are for HTTP based web activities

  10. Traffic Asymmetry • In scope of our problem it is: • Downlink/Uplink Asymmetry • Channel Access Asymmetry • Implications: • Packets spend more time at AP’s TxQ • Frequent packet drops

  11. Channel access for uplink traffic is more Wireless Channel Uplink Traffic Downlink Traffic

  12. Performance Bottleneck TxQ saturates as associated clients increase Associates Users

  13. Goodput Performance Traffic Asymmetry causes TxQ saturation resulting in poor goodput performance

  14. Possible Solutions

  15. Wireless Channel Uplink Traffic Downlink Traffic Equal Channel Access for Uplink/Downlink

  16. Wireless Channel Uplink Traffic Downlink Traffic Statically Assign Higher Priority to Downlink Traffic

  17. Wireless Channel Uplink Traffic Downlink Traffic Dynamically Assign Higher Priority to Downlink Traffic

  18. Our Solution

  19. Priority Control STA A Packet A ACK N Slots STA B DIFS Busy medium Wins Contention Smaller IFS N Slots STA C DIFS H Channel Access Busy medium

  20. Linear Scaling Priority Model Linear relationship between Goodput and Priority Level Priority Level

  21. Adaptive Prioritization Decision Points 100 ms Time Default Priority High Priority D H D H D D D H D D Priority Level 3

  22. Evaluation

  23. Test Bed • 2600 Sqft Area with multiple APs, 45 STAs • Netgear802.11 b/g wireless cards with Atheros chipsets and MADWIFI drivers • Latency emulation using DummyNet • Modified SURGE for web traffic generation • Requests inter-arrival closely follows the ones observed for SIGCOMM traces • Uplink UDP traffic using Iperf to emulate Background Traffic

  24. Performance Downlink: N/W Goodput Significant improvement in Network’s Downlink Goodput W/O WiFox WiFox

  25. Performance • Experiment involves sending 25 requests and observe response for 4 minutes duration • Request Serving rate is 4 times better than NPC

  26. Robustness WiFox Performance in presence of Multiple Aps ?? w/o WiFox

  27. Robustness w/o WiFox WiFox Unfair Distribution Fairness Realization ??

  28. Performance: TxQ Dynamics w/o WiFox WiFox

  29. Conclusion • WiFox Delivers: • Deployment Ready Solution • Enhanced user experience with • 400-700% Downlink Goodput improvements • 40-60% faster response time • Open Problems: • Characterizing asymmetry problem for 802.11n • Support for real time applications like chats etc. • QoS

  30. Merci !!

  31. Multi AP Scenario D D D D D D AP 1 ( Priority Level 4) D D D D D D D 100 ms AP 2 ( Priority Level 3) time D D D D D D D AP 1 ( Priority Level 3) D D D D D AP 2 ( Priority Level 5)

  32. Performance: Insight • Enables AP to switch to HIGH priority state under heavy load • Avoids TxQ saturation • Significant reduction in ReTx rate compared to stock WiFi implementation

  33. Robustness: Uplink Traffic • Scenarios where few users indulge in heavy uplink activities like video uploading, cloud synchronization etc.

  34. Observations Source: Rodrig et al.

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