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The effect of router buffer size on the TCP performance

The effect of router buffer size on the TCP performance. K.E. Avrachenkov*, U.Ayesta** , E.Altman*, P.Nain*,C.Barakat*. *INRIA - Sophia Antipolis, France ** FT R&D - Sophia Antipolis, France. TELECOMMUNICATION NETWORKS AND TELETRAFFIC THEORY Thursday, January 31, 2002

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The effect of router buffer size on the TCP performance

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  1. The effect of router buffer size on the TCP performance K.E. Avrachenkov*, U.Ayesta**, E.Altman*, P.Nain*,C.Barakat* *INRIA - Sophia Antipolis, France ** FT R&D - Sophia Antipolis, France TELECOMMUNICATION NETWORKS AND TELETRAFFIC THEORY Thursday, January 31, 2002 Saint Petersburg, Russia

  2. Fixed Point Approach. sending rate TCP IP packet loss prob delay propagation Outline • Is there an optimal value for the buffer size in IP routers? • Persistent TCP connections: Average sending rate and goodput. • Short TCP connections: Latency

  3. 10Mbps, 1ms 100Mbps, 2ms 10Mbps, 11ms • Short Transfers: New sessions arrive according to a Poisson distribution. Simulated Scenario • Persistent Connections: 100 connections.

  4. Mean queueing delay Prop Delay For the formula for see for example: J.Padhye, V.Firoiu,D. Towsley, and J. Kurose, « Modeling TCP Throughput: a Simple Model and its Empirical Validation   », in Proceedings of ACM SIGCOMM ’1998 conference. Persistent TCP Connections: Fixed Point (I)

  5. Solved iteratively Substituting we get the values for p,RTTi and Ti. Persistent TCP Connections: Fixed Point (II)

  6. Rate (bps) Buffer size (packets) Persistent TCP connections: Result (I)

  7. Rate (bps) Buffer size (packets) Persistent TCP connections: Result (II)

  8. Solved iteratively Short TCP Transfers: Fixed Point (I)

  9. *) B. Sikdar et. al. An integrated model for the latency and steady-state throughput of TCP connections. Perf .Eval. 01 Short TCP Transfers: Fixed Point (II) Substituting we get the values for RTTi and Latency.

  10. Latency (bps) Buffer size (packets) Short TCP Transfers: Result

  11. Conclusions • Persistent TCP connections has poor sending rate and goodput in the cases of small and large buffer sizes. Consequently there is an optimal value of the buffer size. • Short TCP transfers. There seems not to be an optimal value for the IP router buffer size. The larger the buffer size, the better. • Fairness improves with increasing buffer size. Connections with large propagation delays get more bandwith and those with short propagation delays less.

  12. Future work • More sophisticated network topologies with several bottleneck links. • Formula of Sikdar et al. Does not work well in the case of large number of packet losses.

  13. Formula for the Sending rate

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