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References

References. [Single flow] F.Baccelli, D.Hong TCP is Max-Plus Linear, Sigcomm 00 [Competition of N flows] F.Baccelli, D.Hong AIMD, Fairness and Fractal Scaling of TCP traffic, Infocom 02 [TCP on Network] F.Baccelli, D.Hong Interaction of TCP Flows as Billiards, INRIA Report 02

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  1. References • [Single flow] F.Baccelli, D.HongTCP is Max-Plus Linear,Sigcomm 00 • [Competition of N flows] F.Baccelli, D.Hong AIMD, Fairness and Fractal Scaling of TCP traffic, Infocom 02 • [TCP on Network] F.Baccelli, D.Hong Interaction of TCP Flows as Billiards, INRIA Report 02 • [TCP pacing] D.Hong FTCP, Internet Draft, March 02: • www.ietf.org/internet-drafts/draft-hong-ftcp-00.txt • http://www.di.ens.fr/~trec/aimd

  2. Impact of Synchronization on Performance Caltech, CA 02/07/2002 D. Hong INRIA-ENS

  3. Outline • AIMD model • Link/Router level • Packet bursty

  4. I. AIMD model

  5. Model: fluid dynamic

  6. Model: to get an idea sources 10 Mbps destinations

  7. sources Congestion! Congestion! 10 Mbps destinations

  8. The model includes… • N parallel sources • data transfer: ftp, http… • Network extension • Downstream, Upstream, RTT coupling • Non linear model • queueing impact: RTT(t) • QM: DropTail, RED, … • Policy: FIFO, WFQ, Min Rate… • Priority flows: real time constraint • voice over IP, video broadcast, video on demand, game on line

  9. II. Synchronization at Router

  10. AIMD interaction equation : 1 link Evolution equation: Affine map representation: (Xn+ n / R2) = C vector of size N matrix NxN

  11. Steady state solution • Xn = Bn + AnBn-1 + AnAn-1Bn-2 + AnAn-1An-2Bn-3 + … • Variance, covariance, autocorrelation: • var(X) = • cov(X) = • Corr(X0,Xn) =

  12. Performance formula Square root formula: Throughput = With synchronization: Throughput = Synchronization (main) effect:

  13. Impact on Performance • Whatever - C, B, N, RTT, QM, Service Policy if « input rate >= C » at congestion epoch: Synchronization impact is Impact on performance: up to 25%

  14. III. Packet bursty

  15. AIMD by fluid model: If W=10, 1 RTT

  16. Packet bursty: intuition 1/10 RTT time 1 RTT

  17. 10 sources 10 destinations Packet bursty: example RTT = 1 s 100 Pkts/s

  18. 10 flows RTT Packet bursty: example

  19. Packet bursty: example In mean, each flow should get: C/10 = 10 pkts/s 1 flow : congestion with input rate = C/10 2 flows collision : congestion with input rate = C/20 3 flows collision : congestion with input rate = C/30 In fluid model, input rate = C !!!

  20. C Discrete Fluid Packet bursty: input rate at Congestion t real input rate

  21. Packet bursty: impact HugeImpact !! about 90% loss on perf Multiplexing effect ?? proba. of no collision = 0,00036 Collision increases collision probability ! increase also synchronization

  22. Conclusion What to do ? use FTCP ? (tcp pacing) gain up to 900% optimal AQM control ? gain up to 30%

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