IEEE 802'11 Rate Control Algorithms: Experimentation and Performance Evaluation in Infrastructure Mo

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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

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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

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Components

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

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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.

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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.

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Rate Control Algorithms Adaptive 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

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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.

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Experiment Setup

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

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Link layer Performance
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Link layer Performance
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Link layer Performance
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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.

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Application Layer Performance

• Skype, Kaffeine, firefox, sftp
• Average throughput (kbps)

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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.

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Inter-packet Arrival Time
Onoe
AMRR
SampleRate
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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

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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