TCP Friendliness CMPT771 Spring 2008 Michael Jia

Outline  Background  Classification  Achievements  Challenges

TCP Fairness R R equal bandwidth share Connection 1 throughput Connection 2 throughput 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

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

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

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

Outline  Background  Classification  Achievements  Challenges

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

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

Classification End-to-end vs. Router-supported –End-to-end congestion control Easy to deploy Sender-based vs. Receiver-based Rely on collaboration of end systems –Router-supported Require additional functionalities of router Benefit multicast protocols

Outline  Background  Classification  Achievements  Challenges

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

TCP Throughput Equation 2 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 R -- Bandwidth of TCP connection T -- Round-trip delay T (RTT) L --Packet size L q -- Loss event rate q T RTO -- Retransmission timeout (~ 4T)

TCP Throughput Equation 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 Verify through simulation & live Internet measurements Assumption –Steady State (Ignore slow start phase & No timeouts) –Constant packet size

Achievements

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

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

Achievements – FLID-DL Fair Layered Increase/Decrease with Dynamic Layering (2000) Multicast, multi-rate, rate-based Digital-Fountain –Sender encodes data –Receiver can decode when got sufficient distinct packets Dynamic Layering –Reduce join and leave latencies –More flexible bandwidth distribution on layers –A great improvement

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

Outline  Background  Classification  Achievements  Challenges

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 …

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

Questions?

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