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Dynamics of Random Early Detection by D. Lin and R. Morris Appeared in SIGCOMM 97

2 of 23. Outline. Review of REDDeficiencies of RED wrt fairnessProposed solutions through FREDImprovement 1Improvement 2Improvement 3Conclusion. 3 of 23. Traffic Categories. . . 1) Non-adaptive. Adaptive. 2) Robust. 3) Fragile. . . 4 of 23. 1. Non-Adaptive Traffic. Non-responsive to implicit c

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Dynamics of Random Early Detection by D. Lin and R. Morris Appeared in SIGCOMM 97

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    1. Dynamics of Random Early Detection by D. Lin and R. Morris Appeared in SIGCOMM ‘97 February 19, 2002 Presented by Suleyman Uludag

    2. 2 of 23 Outline Review of RED Deficiencies of RED wrt fairness Proposed solutions through FRED Improvement 1 Improvement 2 Improvement 3 Conclusion

    3. 3 of 23 Traffic Categories

    4. 4 of 23 1. Non-Adaptive Traffic Non-responsive to implicit congestion indication from the network (i.e. packet loss) Assumption: Share resources with best-effort data traffic They compete unfairly with adaptive sources UDP-based multimedia applications

    5. 5 of 23 2. Robust Traffic Always has data to send Can adjust rates in response to congestion TCP-based applications Usually have larger windows and shorter RTT values

    6. 6 of 23 3. Fragile Traffic Congestion-aware More sensitive to loss Smaller windows and/or longer RTT than robust traffic

    7. 7 of 23 Unfair Link Sharing under RED Traffic interaction scenarios: Bias against fragile connections Non-proportional dropping among identical flows Starvation of adaptive by non-adaptive flows.

    8. 8 of 23 1.Bias against fragile connections

    9. 9 of 23 Observations 1 RED distributes the loss rate uniformly regardless of the resource usage of the connections Proportional (uniform) dropping by RED does NOT guarantee fair bandwidth sharing.

    10. 10 of 23 2.Non-proportional dropping among identical flows

    11. 11 of 23 2.Non-proportional dropping among identical flows --II

    12. 12 of 23 Observations 2 RED can pick the same connection arbitrarily to drop packets for a short period of time, leading to temporary non-uniform dropping between identical flows. Accepting a packet from one connection may cause higher drop probability for future packets from other connections, even if the latter consumes less bandwidth.

    13. 13 of 23 3.Starvation of adaptive by non-adaptive flows.

    14. 14 of 23 Solution : FRED Goal : Reduce unfairness of RED Additional parameters: minq ? Min # of pkts each flow is allowed to buffer maxq ? Max # of pkts each flow is allowed to buffer avgcq ? estimate for avg per-flow buffer count qleni ? # of buffered pkts for flow i strikei ? # of times flow i failed to respond to congestion indication

    15. 15 of 23 FRED vs. RED Accept if qleni < minq and avg < maxth If N(# of flows) is small then minq = avg / N If strike is high restrict flow to less than avgcq Update the avg both at arrival and departure of packets

    16. 16 of 23 FRED Algorithm

    17. 17 of 23 FRED Algorithm II

    18. 18 of 23 FRED: 1.Bias against fragile connections

    19. 19 of 23 RED vs. FRED

    20. 20 of 23 FRED: 3.Starvation of adaptive by non-adaptive flows.

    21. 21 of 23 Many Flows

    22. 22 of 23 FRED Extension When N is large limit qlen to 2 for all flows

    23. 23 of 23 Conclusion FRED provides Fair buffer allocation Selective Dropping based on per-active-flow buffer counts Guards against different window sizes and RTTs Complexity comparable to RED, which is comparable to FIFO.

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