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Fast TCP

Fast TCP. Matt Weaver CS622 Fall 2007. FAST TCP: Motivation, Architecture, Algorithms, Performance. David X. Wei, Student Member, IEEE, Cheng Jin, Steven H. Low, Senior Member, IEEE, and Sanjay Hegde. Abstract.

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Fast TCP

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  1. Fast TCP • Matt Weaver • CS622 Fall 2007

  2. FAST TCP: Motivation, Architecture, Algorithms, Performance FAST TCP: Motivation, Architecture, Algorithms, Performance David X. Wei, Student Member, IEEE, Cheng Jin, Steven H. Low, Senior Member, IEEE, and Sanjay Hegde

  3. FAST TCP: Motivation, Architecture, Algorithms, Performance Abstract • FAST TCP is a congestion control algorithm that attempts to solve the problems of congestion control. • This paper covers: • The algorithm itself. • Performance metrics 3

  4. FAST TCP: Motivation, Architecture, Algorithms, Performance Background • “Congestion control is a distributed algorithm to share network resources among competing users.” • A difficult problem to solve... • Resource needs vary, depending on time of day. • Available resources is usually static. 4

  5. FAST TCP FAST TCP: Motivation, Architecture, Algorithms, Performance • FAST is a recursive acronym: • FAST AQM Scalable TCP • AQM: Active Queue Management • TCP: Transmission Control Protocol (duh) 5

  6. Current Issues FAST TCP: Motivation, Architecture, Algorithms, Performance • As congestion is monitored, current algorithms slow down monitoring as packets are dropped, the average sending rate depends on low loss probability. • High data transmission rates are required for low loss. • Usually lower than WiFi can support. 6

  7. Solution FAST TCP: Motivation, Architecture, Algorithms, Performance • FAST TCP uses queues to store a constant number of packets. • If too few packets are queued, the sending rate increases. • If too few, the rate decreases. 7

  8. FAST TCP: Motivation, Architecture, Algorithms, Performance Congestion Control Current TCP congestion control algorithm (aka Reno). • At the packet level, linear increase by one packet per roundtrip time (RTT) is too slow, and multiplicative decrease per loss event is too drastic. • At the flow level, maintaining large average congestion windows requires an extremely small equilibrium loss probability. • At the packet level, oscillation in congestion window is unavoidable because TCP uses a binary congestion signal (packet loss). • At the flow level, the dynamics is unstable, leading to severe oscillations that can only be reduced by the accurate estimation of packet loss probability and a stable design of the flow dynamics. 8

  9. FAST TCP: Motivation, Architecture, Algorithms, Performance Motivations • Two levels of design: • The flow level (macroscopic) covers: • QoS • Stability • etc • Packet level (microscopic) covers: • The same goals, but focused on end to end. • Reno suffered because higher level control was considered after the micro level. 9

  10. Calculations • Congestion and utility: • U calculates utility for each stakeholder (user) at a given flow. FAST TCP: Motivation, Architecture, Algorithms, Performance 10

  11. Calculations • Equilibrium (FAST): • Equilibrium (Reno): FAST TCP: Motivation, Architecture, Algorithms, Performance 11

  12. Calculations • “A key departure of our model from those in the literature is that we assume that a source’s send rate, defined as xi(t) :=wi(t)=Ti(t), cannot exceed the throughput it receives. “ FAST TCP: Motivation, Architecture, Algorithms, Performance 12

  13. FAST TCP: Motivation, Architecture, Algorithms, Performance Dynamic Structure • The weakness of current schemes versus FAST is shown for large window sizes. 13

  14. FAST TCP: Motivation, Architecture, Algorithms, Performance Equilibrium • Equilibrium measures congestion consistency. 14

  15. FAST TCP: Motivation, Architecture, Algorithms, Performance Differences • Though all of the aforementioned algorithms look different at the packet level, they actually have similar structures at the flow and equilibrium levels. 15

  16. FAST TCP: Motivation, Architecture, Algorithms, Performance Performance Test 1 • To test performance, packet data is pushed through a semi-articial network. • Identical sender and receiver boxes, running dummynet on FreeBSD. • Emulated router. • Dummynet running: • Paths with RTTs of 50, 100, 150, and 200ms. • Second path with a bottleneck capacity of 8M/s and a buffer size of 2,000 packets shared by all the delay pipes. 16

  17. FAST TCP: Motivation, Architecture, Algorithms, Performance Results • Dynamic state I: • Small flows, large windows • Dynamic state II: • Larger flows 17

  18. FAST TCP: Motivation, Architecture, Algorithms, Performance Dynamic State I 18

  19. FAST TCP: Motivation, Architecture, Algorithms, Performance Throughputkbps Queue(avg)# of pkts FAST vs Reno I Sec 19

  20. Dynamic State II FAST TCP: Motivation, Architecture, Algorithms, Performance 20

  21. Dynamic State II FAST TCP: Motivation, Architecture, Algorithms, Performance 21

  22. FAST TCP: Motivation, Architecture, Algorithms, Performance FAST vs Reno II 22

  23. FAST TCP: Motivation, Architecture, Algorithms, Performance BIC 23

  24. Performance Test 2 FAST TCP: Motivation, Architecture, Algorithms, Performance • Dummynet tests are limited to a single bottleneck and the same protocols. • NS-2 Simulation run in lab: • Same algorithm. • Noise added to eliminate phase artifacts. 24

  25. FAST TCP: Motivation, Architecture, Algorithms, Performance 25

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  27. FAST TCP: Motivation, Architecture, Algorithms, Performance 27

  28. FAST TCP: Motivation, Architecture, Algorithms, Performance 28

  29. FAST TCP: Motivation, Architecture, Algorithms, Performance 29

  30. FAST TCP: Motivation, Architecture, Algorithms, Performance 30

  31. Conclusion FAST TCP: Motivation, Architecture, Algorithms, Performance • Because of the use of queues, FAST TCP can handle lower transmission rates. • The paper also covers some simulated scenarios (too lengthy to cover properly here). 31

  32. FAST TCP: Motivation, Architecture, Algorithms, Performance Caveat Emptor • Possibly biased research: • Jin Cheng, Steve Low, and David Wei (the authors) patented and market the FAST TCP algorithm. • FAST TCP implementation sold as FastSoft Aria (a 1 U rack mountable hardware solution). http://www.fastsoft.com/ • Ao Tang proposed that these measurements were somewhat misleading in another paper. 32

  33. FAST TCP: Motivation, Architecture, Algorithms, Performance Other CC Algorithms • BIC TCP • Compound TCP • CUBIC • H-TCP • High Speed TCP • HSTCP-LP • Hybla • New Reno • Tahoe • TCP-Illinois • TCP-LP • TCP-SACK • TCP-Veno • Westwood • Westwood+ • XCP • YeAH-TCP 33

  34. FAST TCP: Motivation, Architecture, Algorithms, Performance Related Work • Tang, A., Wang, J., Low, S. H., and Chiang, M. 2007. Equilibrium of heterogeneous congestion control: existence and uniqueness. IEEE/ACM Trans. Netw. 15, 4 (Aug. 2007), 824-837. DOI= http://dx.doi.org/10.1109/TNET.2007.893885 • Ma, J., Ruutu, J., and Wu, J. 2000. An enhanced TCP mechanism—fast-TCP in IP networks with wireless links. Wirel. Netw. 6, 5 (Nov. 2000), 375-379. DOI= http://dx.doi.org/10.1023/A:1019118421144 • Gu, Y., Hong, X., and Grossman, R. L. 2004. Experiences in Design and Implementation of a High Performance Transport Protocol. In Proceedings of the 2004 ACM/IEEE Conference on Supercomputing (November 06 - 12, 2004). Conference on High Performance Networking and Computing. IEEE Computer Society, Washington, DC, 22. DOI= http://dx.doi.org/10.1109/SC.2004.24 • Grieco, L. A. and Mascolo, S. 2004. Performance evaluation and comparison of Westwood+, New Reno, and Vegas TCP congestion control. SIGCOMM Comput. Commun. Rev. 34, 2 (Apr. 2004), 25-38. DOI= http://doi.acm.org/10.1145/997150.997155 34

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