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Delay-based Congestion Control

Delay-based Congestion Control. CCW 2003 David Wei http://netlab.caltech.edu. Topics. Summary of congestion control algorithms FAST Algorithm Experimental Results Open problems. Decision Function. Decision Function. Congestion Signal. Loss Delay ECN. Queueing delay. Vegas q=q*.

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Delay-based Congestion Control

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  1. Delay-based Congestion Control CCW 2003 David Wei http://netlab.caltech.edu

  2. Topics • Summary of congestion control algorithms • FAST Algorithm • Experimental Results • Open problems

  3. Decision Function

  4. Decision Function

  5. Congestion Signal • Loss • Delay • ECN Queueing delay Vegas q=q* DUAL q>q_max/2? TFRC p=p* ECN CARD q>0? Loss Goodput

  6. Decision Function using Binary Signal

  7. Congestion Signal • Loss • Delay • ECN

  8. Congestion Signal • Loss • Delay • ECN ?

  9. Reno in High Speed… Throughput as function of the time Chicago -> CERN Linux kernel 2.4.19 Traffic generated by iperf (I measure the throughput over the last 5 sec) TCP single stream RTT = 119ms MTU = 1500 Duration of the test : 2 hours Bottleneck=1Gbps By Sylvain Ravot (Caltech)

  10. Difficulties in Large Window • Equilibrium problems • Packet level: AI too slow, MI too drastic • Flow level:requiredloss probability too small • Dynamic problems • Packet level: mustoscillate on binary signal • Flow level: unstable at large window • Measurement • Very small loss probability • Packet out-of order Improvements: HSTCP ScalableTCP 5

  11. FAST (sc2002) Algorithm Do the following every other RTT: per acknowledgment: • Calculation: • Action: • If w(t)>w*: w(t)=w(t)-1 • If w(t)<w*: w(t)=w(t)+1

  12. FAST (sc2002) Algorithm Do the following every other RTT: per acknowledgment: • Calculation: • Action: • If w(t)>w*: w(t)=w(t)-1 • If w(t)<w*: w(t)=w(t)+1

  13. FAST (sc2002) Algorithm Do the following every other RTT: per acknowledgment: • Calculation: • Action: • If w(t)>w*: w(t)=w(t)-1 • If w(t)<w*: w(t)=w(t)+1

  14. FAST (sc2002) Algorithm Do the following every other RTT: per acknowledgment: • Calculation: • Action: • If w(t)>w*: w(t)=w(t)-1 • If w(t)<w*: w(t)=w(t)+1

  15. FAST (sc2002) Algorithm Do the following every other RTT: per acknowledgment: • Calculation: • Action: • If w(t)>w*: w(t)=w(t)-1 • If w(t)<w*: w(t)=w(t)+1

  16. FAST (sc2002) Algorithm Do the following every other RTT: per acknowledgment: • Calculation: • Action: • If w(t)>w*: w(t)=w(t)-1 • If w(t)<w*: w(t)=w(t)+1

  17. Results on Convergence With static link model: • Single link identical sources: converge • Single link heterogeneous sources: bounded by converging sequences • General case (proofs without delay): Contraction mapping

  18. Simulation with Matlab pkt/ms • baseRTT: 550ms,600ms,650ms,700ms,750ms • Alpha=500 pkt • C=5000/12 pkt/ms pkt/ms pkt pkt

  19. Simulation with Matlab ms pkt • baseRTT: 550ms,600ms,650ms,700ms,750ms • Alpha=500 • C=5000/12 pkt/ms

  20. Dummynet Testbed@ Netlab, Caltech

  21. Static throughput Dynamic sharing on Dummynet • capacity = 800Mbps • Delay = 50 - 200ms • # flows: 1 - 10 • iperf throughput • Linux 2.4 (HSTCP: UCL)

  22. Static throughput

  23. queue HSTCP FAST Linux RTT=50ms ~ 200ms 10 Flows loss throughput Linux Scalable HSTCP STCP Bottleneck=800Mbps HSTCP

  24. Questions? Thanks

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