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Analysis of Active Queue Management

Analysis of Active Queue Management. Jae Chung and Mark Claypool. Computer Science Department Worcester Polytechnic Institute Worcester, Massachusetts, USA. http://perform.wpi.edu/. ACK…. Drop!!!. ACK…. ACK…. AQM. AQM. TCP. TCP. TCP. TCP. TCP. TCP. TCP. TCP. TCP. TCP. TCP.

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Analysis of Active Queue Management

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

  2. ACK… Drop!!! ACK… ACK… AQM AQM TCP TCP TCP TCP TCP TCP TCP TCP TCP TCP TCP TCP Congestion Queue Queue Queue Queue Queue Queue Sink Sink Sink Sink Sink Inbound Link Inbound Link Inbound Link Inbound Link Inbound Link Inbound Link Router Router Router Router Router Router Outbound Link Outbound Link Outbound Link Outbound Link Outbound Link Outbound Link Sink Sink Sink Sink Sink Sink Sink Congestion Notification… ACK… ACK… ACK… Active Queue Management • Advantages • Reduce packet losses • (due to queue overflow) • Reduce queuing delay WPI

  3. 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. WPI

  4. Contribution • Extend Firoiu’s 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. WPI

  5. Outline • Introduction • Queue Law • Impact of ECN • RED Family AQM • Analysis of REDs • Summary WPI

  6. 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. WPI

  7. The GeneralQueue Law WPI

  8. 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. WPI

  9. Effect of Limiting TCP Window • Window-limited (and short-lived) flows consume less bandwidth. • Yet, they are less responsive to congestion notification WPI

  10. Outline • Introduction • Queue Law • Impact of ECN • RED Family AQM • Analysis of REDs • Summary WPI

  11. 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. WPI

  12. Outline • Introduction • Queue Law • Impact of ECN • RED Family AQM • Analysis of REDs • Summary WPI

  13. Random Early Detection (RED) Adaptive RED (w/ Gentle) Adaptive RED Gentle RED q q q q Queue law: p = g(q) 2 maxth 2 maxth RED control function: p = h(q) maxth maxth maxth maxth Stable RED operating point minth minth minth minth maxp maxp variable maxp variable maxp 1 1 1 1 p p p p RED-Family AQM WPI

  14. q N=300 N=50 N=100 N=150 N=200 N=250 N=300 s d (300) maxth s d s r r d s d s d (100) minth maxp(0.1) maxp limit (0.5) p Simulation Configuration • Dumbbell topology (SR = 20Mbps, Q = 500 pkts) • Increase # of TCP flows (N = 50~300) each 50 sec. • Implicit (drop) and ECN (configurations shown) Q = 500 pkts SR = 20 Mbps RTLD = 80 ms WPI

  15. CongestedRouter Queue(ECN Results) WPI

  16. Packet Loss Rate WPI

  17. 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. WPI

  18. 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. WPI

  19. 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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