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Congestion Window Control Algorithms

Congestion Window Control Algorithms. David Wei For Pizza Talk @ Netlab. Topics. History Component of Congestion Window Control Algorithm FAST (sc2002 version) Synchronization Model Layered Architecture based on Time Scale Open Issues. History of TCP Congestion Control. John Nagle’s

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Congestion Window Control Algorithms

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  1. Congestion Window Control Algorithms David Wei For Pizza Talk @ Netlab

  2. Topics • History • Component of Congestion Window Control Algorithm • FAST (sc2002 version) • Synchronization Model • Layered Architecture based on Time Scale • Open Issues

  3. History of TCP Congestion Control • John Nagle’s • Lixia Zhang’s, Karn’s Algorithm • DEC-bit, Tahoe, CARD • Tri-S, DUAL • Reno • Vegas • New Reno • HSTCP, Scalable TCP, FAST, Westwood …

  4. ??? Raj Jain’s “Three Questions that a congestion control algorithm should answer”: • How frequent to make decision • Decision function • How to Increase/Decrease Window

  5. How Frequent? • Time Scale of a Congestion control algorithm

  6. Layered-Architecture based on Time Scale

  7. Decision Function

  8. Decision Function under Binary Signal

  9. Congestion Signal • Delay • Loss • ECN

  10. Congestion Signal • Transition Point • Non-Transition Point

  11. Increase/Decrease Function • Under Synchronization Model (Chui and Jain):

  12. Congestion Control Algorithms

  13. FAST (sc2002) Algorithm Do the following every other RTT: • per acknowledgement: • Calculate: • If w(t)>w*: w(t)=w(t)-1 • If w(t)<w*: w(t)=w(t)+1 Or Randomize the Increase/Decrease

  14. Synchronization Model Assume: • All the sources make the decision slow enough that the queues converge whenever the sources make its decision. (queue dynamics has a faster time scale than source dynamics)

  15. Results • Single link identical sources: converges • Single link heterogeneous sources: bounded by converging sequences • General case: Contraction Mapping

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

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

  18. Verification of Synchronization Model • sources#: 3 • baseRTT:200ms • BW: 100Mbps • Green: Sync. Model • Magenta: Fluid Model • Red: avg queue size • Blue: avg var queue size

  19. Verification of Synchronization Model # of sources may not be enough

  20. Layered-Architecture • What’s an “architecture”? • Functions that TCP Congestion control should be considered • Rate smoothening • Available bandwidth estimation • Response to Loss/Retransmission

  21. Layered-Architecture based on Time Scale

  22. Open Issues • Synchronization Model vs Fluid Model • Properties of different congestion control algorithms under the synchronization model • New optimization model based on time scale architecture • Alpha adaptation based on large time scale signals (loss, long averaged RTT…) • Conformance Testing Method based on the time scale architecture

  23. Questions? Thanks

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