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WiFox: Scaling WiFi Performance for Large Audience Environments Arpit Gupta, Jeongki Min and Injong Rhee NC State University Slide 2 Interesting ?? Faster WiFi !! Manageable solution !! WiFox: AP-only S/W solution WiFox: AP-only S/W solution Slide 3 Large Audience Environments (LAEs) Slide 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) Slide 5 What about User Experience ? As number of active clients increases, user experience diminishes significantly Slide 6 Problem Anatomy Slide 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 Slide 8 Downlink Traffic dominates for 90% of data traces Slide 9 Traffic Asymmetry Majority of data traffic is Web based Downlink Traffic dominates compared to uplink Majority of data packets are for HTTP based web activities Slide 10 Traffic Asymmetry In scope of our problem it is: Downlink/Uplink Asymmetry Channel Access Asymmetry Implications: Packets spend more time at APs TxQ Frequent packet drops Slide 11 Wireless Channel Uplink Traffic Downlink Traffic Channel access for uplink traffic is more Slide 12 Performance Bottleneck TxQ saturates as associated clients increase Associates Users Slide 13 Goodput Performance Traffic Asymmetry causes TxQ saturation resulting in poor goodput performance Slide 14 Possible Solutions Slide 15 Wireless Channel Uplink Traffic Downlink Traffic Equal Channel Access for Uplink/Downlink Slide 16 Wireless Channel Uplink Traffic Downlink Traffic Statically Assign Higher Priority to Downlink Traffic Slide 17 Wireless Channel Uplink Traffic Downlink Traffic Dynamically Assign Higher Priority to Downlink Traffic Slide 18 Our Solution Slide 19 Priority Control Packet A ACK DIFS DIFS H Channel Access N Slots Busy medium Wins Contention STA C STA B STA A Smaller IFS ClassCWminCWmaxAIFSTXOP Limit AP15164 STAs510N/A Slide 20 Linear Scaling Priority Model Priority Level Linear relationship between Goodput and Priority Level Slide 21 Adaptive Prioritization 100 ms DHDHDDDHDD Time High Priority Default Priority Decision Points Priority Level 3 Slide 22 Evaluation Slide 23 Test Bed 2600 Sqft Area with multiple APs, 45 STAs Netgear 802.11 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 Slide 24 Performance Downlink: N/W Goodput WiFox W/O WiFox Significant improvement in Networks Downlink Goodput Slide 25 Performance Experiment involves sending 25 requests and observe response for 4 minutes duration Request Serving rate is 4 times better than NPC Experiment involves sending 25 requests and observe response for 4 minutes duration Request Serving rate is 4 times better than NPC Slide 26 Robustness Performance in presence of Multiple Aps ?? WiFox w/o WiFox Slide 27 Robustness w/o WiFox WiFox Unfair Distribution Fairness Realization ?? Slide 28 Performance: TxQ Dynamics WiFox w/o WiFox Slide 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 Slide 30 30 Merci !! Slide 31 Multi AP Scenario DDDDDD DDDDDDD AP 1 ( Priority Level 4) AP 2 ( Priority Level 3) DDDDDDD DDDDD AP 1 ( Priority Level 3) AP 2 ( Priority Level 5) time 100 ms Slide 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 Slide 33 Robustness: Uplink Traffic Scenarios where few users indulge in heavy uplink activities like video uploading, cloud synchronization etc. Slide 34 Observations Source: Rodrig et al.