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WebTP: Protocol Design Issues

WebTP: Protocol Design Issues. Jeng Lung & Yogesh Bhumralkar. Introduction. Following key issues related to the design and testing of the protocol: Congestion Window Control Retransmission Timeout Scheme Performance under Network Jitter. Congestion Control. Background

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WebTP: Protocol Design Issues

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  1. WebTP: Protocol Design Issues Jeng Lung & Yogesh Bhumralkar

  2. Introduction • Following key issues related to the design and testing of the protocol: • Congestion Window Control • Retransmission Timeout Scheme • Performance under Network Jitter

  3. Congestion Control • Background • WebTP uses TCP-style congestion control • 2 Phases: • Slow Start • Congestion Avoidance: Additive Increase/Multiplicative Decrease • TCP biased against long connections; therefore, WebTP faces same dilemma.

  4. Improving Fairness • Maximize fairness by modifying Additive Increase • Instead of increasing cwnd by 1/cwnd, increase it by K=c*rtt*rtt. This makes it more fair • Problem: Find optimal K for fairness • K is topology dependent but still want to ensure that the scheme works for WebTP.

  5. Network Topology

  6. Retransmission Scheme • Current timeout set to: • M is the receiver’s tolerance to jitter. • Examine the effects of changing M on the number of dropped and duplicate packets.

  7. Jitter Study • Any network has considerable random delays. • The time between when the packet is transmitted to when it reaches the receiver varies a great deal - this phenomenon is called jitter. • Simulated jitter by introducing random delay to each packet on the sender side.

  8. Conclusion • Congestion Window Scheme: Optimal K depends on network topology. • Retransmission Scheme: Dropped packets increase with M whereas the number of duplicate packets goes down at higher M. • Network Jitter: Higher jitter implies that a higher M is required to handle the delays that are introduced.

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