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TCP Friendliness

This outline discusses the background, classification, achievements, and challenges of achieving TCP friendliness in congestion control protocols. It explores the fairness and fairness definitions for both unicast and multicast traffic and addresses the improvements needed in TCP traffic models. The challenges include the lack of standard methods for comparison and treating short-lived flows. References are included for further reading.

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TCP Friendliness

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  1. TCP Friendliness CMPT771 Spring 2008 Michael Jia

  2. Outline • Background • Classification • Achievements • Challenges

  3. TCP Fairness Fair:1. Equal share 2. Full utilization if K TCP sessions share same bottleneck link of bandwidth R, each should have average rate of R/K equal bandwidth share R Connection 2 throughput Connection 1 throughput R

  4. Why UDP? UDP Preferred Applications • Video Streaming • VoIP UDP Advantages • Simplicity • Lower overhead (light weight) • No re-transmission required

  5. Problem with UDP: Unresponsive Flows • No congestion control • No response to packet drops • TCP competing with unresponsive UDP • TCP flows reduce sending rates in response to congestion • Uncooperative UDP flows capture the available bandwidth • Unfair to TCP, or even starve TCP

  6. Objective: TCP-friendly “long-term throughput does not exceed the throughput of a conformant TCP connection under the same conditions” non-TCP non-TCP Internet TCP TCP

  7. Outline • Background • Classification • Achievements • Challenges

  8. Classification • Window-Based vs. Rate-Based • window-based: • Window size controls rate • Sender or receiver(s) • Similar to TCP • rate-based: • TCP throughput models • More smoother rate • Good for media streams

  9. Classification • Unicast vs. Multicast • Multicast: more difficult • RTT is required for Rate-based schemes • Window-based approach is more suitable • Single-rate vs. Multi-rate • Unicast = Single-rate • Multicast: multi-rate protocols are preferred • More flexible allocation of bandwidth • Layered multicast • Group management

  10. Outline • Background • Classification • Achievements • Challenges

  11. TCP Throughput Equation 1 R -- Bandwidth of TCP connection (Long term throughput) T -- Round-trip delay T (RTT) L --Packet size L p -- Loss event rate p T. Ott, J.H.B. Kemperman, M. Mathis, 1996 The Stationary Behavior of Ideal TCP Congestion Avoidance

  12. TCP Throughput Equation 2 R -- Bandwidth of TCP connection T -- Round-trip delay T (RTT) L --Packet size L q -- Loss event rate q TRTO -- Retransmission timeout (~ 4T) Padhye, J., Firoiu, V., Towsley, D., and Kurose, J., Modeling TCP Throughput: a Simple Model and its Empirical Validation, UMASS CMPSCI Tech Report TR98-008, Feb. 1998.

  13. TCP Throughput Equation • Verify through simulation & live Internet measurements • Assumption • Steady State (Ignore slow start phase & No timeouts) • Constant packet size M. Mathis, J. Semke, J. Mahdavi, and T. Ott. The macroscopic behavior of the TCP congestion avoidance algorithm. Computer Communication Review, 27(3), July 1997

  14. Achievements

  15. Achievements - TFRC • TCP-Friendly Rate Control Protocol (2000) • Unicast, rate-based • Based on TCP equation 2 • Using more sophisticated methods to gather parameters • Average-Loss-Interval  loss rate estimation • Stable sending rate • Sufficient responsiveness

  16. Achievements - TEAR • TCP Emulation At Receivers (2000) • Multicast, single-rate • Rate-based + Window-based • Receiver maintains a congestion window • Receiver calculates average rate • then send back to the sender • avoid saw-tooth-like behavior • Scalable in multicast case • use the minimum rate

  17. Achievements – Rainbow • Rainbow (2000) • Multicast, multi-rate, window-based • Digital-Fountain • Receivers individually request each data packet • Routers process requests • Receiver controls congestion • Limitation – router supporting

  18. Outline • Background • Classification • Achievements • Challenges

  19. Challenges • Lack of standard methods for comparison • Fairness definitions for multicast • Improvement of the models for TCP traffics • How to treat short-lived flows • Much more…

  20. References • Robert Denda Joerg Widmer and Martin Mauve, 2001, A survey on tcp-friendly congestion control • T. Ott, J.H.B. Kemperman, M. Mathis, 1996, The Stationary Behavior of Ideal TCP Congestion Avoidance • Padhye, J., Firoiu, V., Towsley, D., and Kurose, J., 1998, Modeling TCP Throughput: a Simple Model and its Empirical Validation • M. Mathis, J. Semke, J. Mahdavi, and T. Ott., 1997, The macroscopic behavior of the TCP congestion avoidance algorithm • Jitendra Padhye Sally Floyd, Mark Handley and Joerg Widmer, 2000, Equation-based congestion control for unicast applications • Volkan Ozdemir Injong Rhee and Yung Yi., 2000, Tear: Tcp emulation at receivers – flow control for multimedia streaming

  21. Questions?

  22. Thank You

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