1 / 16

Is the Round-trip Time Correlated with the Number of Packets in Flight?

Is the Round-trip Time Correlated with the Number of Packets in Flight?. Saad Biaz, Auburn University Nitin H. Vaidya, University of Illinois at Urbana-Champaign. published in ACM IMC ’ 03. Overview. TCP Reno keeps increasing sending rate till packet loss detected

rozene
Download Presentation

Is the Round-trip Time Correlated with the Number of Packets in Flight?

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Is the Round-trip Time Correlated with the Number of Packets in Flight? Saad Biaz, Auburn University Nitin H. Vaidya, University of Illinois at Urbana-Champaign published in ACM IMC’03

  2. Overview • TCP Reno keeps increasing sending rate till packet loss detected • some Congestion Avoidance Techniques (CATs) are proposed to avoid such aggressive behavior • some CATs use RTT / throughput to detect queue build-up and adjust congestion window size • Can RTT reflect queue build-up?

  3. Outline • Terminology • Correlation coefficients used • Experimental data • Analysis results • Conclusion

  4. Terminology Pi , PWi , PFi , PTi , W(Pi) / Wi , RTT(Pi) / RTTi , Sign(X) , Cl , B(Cl)

  5. Correlation Coefficients

  6. Correlation Coefficients • Similar correlation coefficients for direction change (increase or decrease)

  7. Throughput and RTT against load

  8. TCP-Vegas • compare the quantity with two thresholds, alpha and beta (alpha < beta) • if the quantity < alpha, cwnd increases • if the quantity > beta, cwnd decreases • otherwise, cwnd holds constant

  9. Experiments • Data is collected by Paxson in 1994-95 • span many paths with different RTT • two data sets N1 and N2 are collected, which are tcpdump traces over 37 sites across USA, Europe and Australia • this study uses only N2 of 20000 tcpdump traces for bulk transfers of 100 KB between pairs of sites among the 37 concerned sites • N2 contains both the tcpdump traces at sender and receiver, but only sender is consider in this study

  10. Experiments • 14218 out of 20000 tcpdump traces are analyzed for technical reasons • These 14218 connections were between 31 different sites • Not all sites send to all sites; span only 737 paths • RTT and data in flight (W) are found from those tcpdump traces

  11. Partitioning connection sets • to see if and how bottleneck bandwidth affects correlation coefficients, the TCP connections are divided into two sets: fast and slow

  12. Correlation bwt RTT and W Slow Fast frequency distribution

  13. Correlation in Direction of Change

  14. Can corrcoef characterize a path?

  15. From corrcoef in direction of change in RTT and W for PW, about 88% connections have positive correlation In general, RTT is sensitive to load However, corrcoef is not strong enough to be relied (on RTT) to build congestion avoidance scheme 88% Conclusion

  16. Conclusion • RTT observed by a TCP connection is dependent on other traffic; effect is more significant if that TCP connection only share a small fraction of bandwidth • vagaries of transport protocol like delayed ACK

More Related