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Measuring Queue Capacities of IEEE 802.11 Wireless Access Points

Measuring Queue Capacities of IEEE 802.11 Wireless Access Points. Feng Li, Mingzhe Li, Rui Lu, Huahui Wu, Mark Claypool, and Robert Kinicki {lif, lmz, kkboy, flashine, claypool, rek}@cs.wpi.edu Computer Science Department at Worcester Polytechnic Institute Worcester, MA, 01609, USA.

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Measuring Queue Capacities of IEEE 802.11 Wireless Access Points

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  1. Measuring Queue Capacities of IEEE 802.11 Wireless Access Points Feng Li, Mingzhe Li, Rui Lu, Huahui Wu, Mark Claypool, and Robert Kinicki {lif, lmz, kkboy, flashine, claypool, rek}@cs.wpi.edu Computer Science Department at Worcester Polytechnic Institute Worcester, MA, 01609, USA the 4th IEEE International Conference on Broadband Communications, Networks and Systems (BROADNETS) Raleigh, NC, USA September 10-13, 2007

  2. Introduction • Performance bottleneck for many Internet applications exists at last hop from wireless access point (AP) to wireless end host. • Corporate/Campus networks. • Wireless clients have weak wireless connection. • Queue capacity of APs impacts performance of wireless applications. • Too small  may decrease throughput ! • Too large  increase latency ! • Little known on queue capacity choice for APs. • Blackbox devices. BROADNETS September 13, 2007

  3. Outline • Introduction • Access Point Queue (APQ) Method • Validation • APQ Measurements • Discussion and Conclusion BROADNETS September 13, 2007

  4. Access Point Queue Method (APQ) Dh: delay measured with a full queue T: Throughput Sender Client Dl: delay measured with an empty queue AP • Compute queue capacity (qp) with equation: , where L is Packet Length. BROADNETS September 13, 2007

  5. sec APQ Session BROADNETS September 13, 2007

  6. sec APQ Session BROADNETS September 13, 2007

  7. Outline • Introduction • Access Point Queue (APQ) Method • Validation • APQ Measurements • Discussion and Conclusion BROADNETS September 13, 2007

  8. APQ Validation Demonstrated the ability to control Host AP queue capacity BROADNETS September 13, 2007

  9. APQ Validation Results APQ accurately estimates actual Host AP queue capacities with tight confidence intervals. BROADNETS September 13, 2007

  10. Outline • Introduction • Access Point Queue (APQ) Method • Validation • APQ Measurements • Discussion and Conclusion BROADNETS September 13, 2007

  11. Experimental Setup • Test bed similar to validation by replacing Host AP with target AP. • For all APQ measurement runs: • Data rate fixed at 11 Mbps. • RTS/CTS disabled. • Antenna positioned carefully to reach better performance. • MGEN generates UDP traffic for all experiments. • Two packet sizes (1500 bytes/packet and 750 bytes/packet) used to determine packet based queue or byte based queue. BROADNETS September 13, 2007

  12. Target APs • Selected 7 different wireless APs, three from commercial class and four from residential class. BROADNETS September 13, 2007

  13. AP Staturation Negligible loss rate until offered load near saturation. Maximum throughput varies across APs. BROADNETS September 13, 2007

  14. Throughput and Delay Changes During APQ Session Both throughputs are fairly consistent. Approximate half second difference suggests significant difference in queue capacities. BROADNETS September 13, 2007

  15. Dh-Dl • Data from Netgear Commercial AP • Compute queue capacity based on equation: CDF of Delay during APQ Session BROADNETS September 13, 2007

  16. AP Queue Capacities • Packet based queue inside 7 target APs • Queue Capacity varies from venders and classes. BROADNETS September 13, 2007

  17. Discussion • Difficult to decide on “best” queue capacity. • Queue capacity guideline (bandwidth-delay product) not followed. • More research needed to decide “best” queue. • Research on adaptive queue. BROADNETS September 13, 2007

  18. Conclusions • APQ - two step black box method which accurately measures AP queue capacity. • Measured seven off-shelf APs. • AP queue capacities vary across vendors and classes. • AP queue capacity measurements provide: • Realistic queue capacity parameters for WLAN simulations. • Starting point for future AP design strategies. BROADNETS September 13, 2007

  19. Questions ? Measuring Queue Capacities of IEEE 802.11 Wireless Access Points Feng Li, Mingzhe Li, Rui Lu, Huahui Wu, Mark Claypool, and Robert Kinicki {lif, lmz, kkboy, flashine, claypool, rek}@cs.wpi.edu Computer Science Department @Worcester Polytechnic Institute Worcester, MA, 01609, USA BROADNETS September 13, 2007

  20. Thank You! BROADNETS September 13, 2007

  21. Saturates a Wireless Link • Starting from a sending rate(S1) 50 packets/sec. • Increasing sending rate by 50 packets/sec until packet loss rates (pi ) of 20% or more are observed for three successive sending rates (Si−2, Si-1, Si ). • Taking Si-1 as the saturation sending rate. BROADNETS September 13, 2007

  22. Understanding Linux Kernel Queue BROADNETS September 13, 2007

  23. Access Point Queue Method (APQ) • Fill up “downstream” queue inside AP. • Measure delay changes (Dh-Dl)and throughput (T ) at saturation. • Dh: the delay measured with full queue. • Dl: the delay measured with empty queue. • L : Packet Length. BROADNETS September 13, 2007

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