Analysis of Active Queue Management

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Analysis of Active Queue Management
Jae Chung and Mark Claypool
Computer Science Department Worcester Polytechnic
Institute Worcester, Massachusetts, USA
http//perform.wpi.edu/
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Active Queue Management

• Advantages
• Reduce packet losses
• (due to queue overflow)
• Reduce queuing delay

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Related Work Analysis of AQM

• Control Theory Approach (Hollot, Infocom 01)
• Model TCP and AQM Behaviors (Laplace domain).
• Apply Classical Control Theory (through
  analysis).
• Params not obvious for understanding control
  info.
• Queue Law (Firoiu, Infocom 00)
• Model Average TCP Throughput and the behavior of
  Average Queue Length at congested router.
• Shows the impact of traffic parameters on AQM.
• Not suitable for system stability analysis.
• Good for analyzing and configuring AQMs using
  average queue.

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Contribution

• Extend Firoius to a General Queue Law
• Simplify the queue law to better illustrate the
  effect of traffic parameters on AQM.
• Extend the queue law to support Explicit
  Congestion Notification (ECN) and study the
  impact of ECN on AQM congestion control.
• Analysis of RED-Family AQM
• Evaluate RED-Family AQMs (RED, Gentle RED and
  Adaptive RED)
• Demonstrate ECN gains on packet loss rates.

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Outline

• Introduction
• Queue Law
• Impact of ECN
• RED Family AQM
• Analysis of REDs
• Summary

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Average TCP Window(Bulk Transfers)

• Function of congestion notification probability
  (CNP) only.
• Not affected by the number of flows (N), RTT or
  Service Rate (SR).
• Same for ECN and non-ECN flows.

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The GeneralQueue Law
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General Queue Law Validation

• Used average TCP throughput model from (Padhye,
  Sigcomm 1998).
• Works well for ECN.
• Inaccurate for non-ECN The TCP throughput model
  does not effectively model Retransmission Timeout.

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Effect of Limiting TCP Window

• Window-limited (and short-lived) flows consume
  less bandwidth.
• Yet, they are less responsive to congestion
  notification

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Outline

• Introduction
• Queue Law
• Impact of ECN
• RED Family AQM
• Analysis of REDs
• Summary

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Impact of ECN on AQM

• ECN has no signaling packet loss.
• Requires higher CNP to keep the average queue at
  the same level.
• Helps the control system stability as less
  sensitive to CNP changes.

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Outline

• Introduction
• Queue Law
• Impact of ECN
• RED Family AQM
• Analysis of REDs
• Summary

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RED-Family AQM
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Simulation Configuration

• Dumbbell topology (SR 20Mbps, Q 500 pkts)
• Increase of TCP flows (N 50300) each 50 sec.
• Implicit (drop) and ECN (configurations shown)

Q 500 pkts
SR 20 Mbps
RTLD 80 ms
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CongestedRouter Queue(ECN Results)
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Packet Loss Rate
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Contribution

• The General Queue Law
• Illustrated the effect of traffic parameters on
  AQM.
• Discussed the impact of ECN traffic on AQM.
• Provides mean to configure RED for ECN traffic.
• RED-Family AQM Evaluation
• Showed the ECN gain on packet loss rate and the
  limitation of AQMs without ECN over Drop-Tail.
• Provided an analysis on RED-Family AQM
• Gentle RED may result in an unstable queue
  oscillation.
• Adaptive RED can support a wide range of traffic
  loads.

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Future Work

• Extend our study to a mixture of ECN and
  non-ECN TCP flows.
• Building an adaptive AQM technique that makes
  use of our queue law to quickly adapt to a
  well-configured state in the presence of
  changing network loads.

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Analysis of Active Queue Management
Jae Chung and Mark Claypool
Computer Science Department Worcester Polytechnic
Institute Worcester, Massachusetts, USA
http//perform.wpi.edu/