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Sourav Pal, Sumantra R. Kundu, Kalyan Basu and Sajal K. Das, the University of Texas at Arlington

IEEE 802.11 Rate Control Algorithms: Experimentation and Performance Evaluation in Infrastructure Mode. Sourav Pal, Sumantra R. Kundu, Kalyan Basu and Sajal K. Das, the University of Texas at Arlington. Intro. IEEE 802.11

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Sourav Pal, Sumantra R. Kundu, Kalyan Basu and Sajal K. Das, the University of Texas at Arlington

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  1. IEEE 802.11 Rate Control Algorithms: Experimentation and Performance Evaluation in Infrastructure Mode Sourav Pal, Sumantra R. Kundu, Kalyan Basu and Sajal K. Das, the University of Texas at Arlington

  2. Intro. • IEEE 802.11 • multi-rate transmission capabilities by dynamically choosing the most appropriate modulation technique for the RSS. • Rate Control Algorithm (RCA) • Open to the device manufacturer to improvise • Software/ Hardware approach • Investigating the performance of software RCAs that interact with the PHY layer of the WNIC

  3. Components • WNIC • AR5212 from Atheros • Driver • Madwifi • 3 RCA algorithms • Onoe • Adaptive Multi Rate Retry (AMRR) • SampleRate

  4. Goals • Link layer • Qualitative and Quantitative Performance analysis of practical RCAs At the wireless link layer due to RSSI variation • Application layer • Expose the impact of RCAs on application level throughput, packet inter-arrival time and jitter for heterogeneous traffic classes.

  5. Rate Control AlgorithmsOnoe • Credit Based RCA where credit is a function of number of successful and erroneous transmission/retransmission over a sampling period (1000ms). • Implementation details: • 10% or more needed retry , decrease credit else increase the credit • 10 (0) credits, increase (decrease) data rate. • Once a data rate is failed, it will not attempt to select that until 10 seconds have elapsed • Less sensitive to individual packet failure.

  6. Rate Control AlgorithmsAdaptive Multi Rate Retry (AMRR) • After 10 consecutive transmission successes • Transmits probe packets at higher rates to test the rate • Success  switch to higher rate • AMRR employs Binary Exponential Backoff to adapt the probing threshold. • When the transmission of the probing packet fails, we switch back to the previous lower rate but we also multiply by two the probing threshold • Reset success threshold to initial value if two consecutive transmission are failed

  7. Rate Control AlgorithmsSampleRate • Starts with the highest possible rate and then decreases till it can support that rate • Four successive failures • Maintain the expected transmission time for each rate • Use the data rate with smallest expected transmission time • Periodically transmits packets at rates higher than current transmission rates. • Computes the transmission time for every 10th packet which it sends in a different rate. • Stale samples are removed based on a EWMA windowing mechanism.

  8. Experiment Setup • Disable RTS/CTS • Upload a 8M file to content delivery server

  9. Link layer Performance

  10. Link layer Performance

  11. Link layer Performance

  12. Evaluation of application Layer Performance • Radio range varied from 12 feet to 80 feet to ensure noticeable RSSI variation. • Assume that mobility model is the same for each experiment. • Ethereal is used to capture packet level statistics at both the AP and the laptop. • tcptrace , an analysis tool written to extract statistics from ethereal dumps. • Throughput presented is not end-to-end.

  13. Application Layer Performance • Skype, Kaffeine, firefox, sftp • Average throughput (kbps)

  14. Observations • Significant difference between upstream and downstream bandwidth • AMRR outperforms other two RCAs for non-real-time traffic • Average Throughput for AMRR and Sample comparable • SampleRate most suitable for Streaming; able to buffer and at distances of more than 70 feet where the rest of the RCAs fail.

  15. Inter-packet Arrival Time Onoe AMRR SampleRate

  16. Observations • AMRR and SampleRate follow the RSSI and tries to move to a higher data rate as soon as wireless channel improves • Causing the transmission rate to fluctuate a lot • Onoe is conservative • Switch to a bit-rate conservatively

  17. Conclusion • Performance Analysis of RCAs at link layer and application layer • RCAs do not perform optimally on Low link condition • Probe, consecutive success/failure, long-term statistics • The effect of RCA on application layer traffic • Problems • Experiment should be carried with more clients • Impact of RTS/CTS has not yet been analyzed

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