1 / 22

Service Differentiation at Transport Layer via TCP Westwood Low-Priority (TCPW-LP)

Service Differentiation at Transport Layer via TCP Westwood Low-Priority (TCPW-LP). H. Shimonishi, M.Y. Sanadidi and M. Geria System Platforms Research Laboratories, NEC Corporation UCLA Computer Science Department. IEEE Symp on Computers & Communications (ISCC), 2004. Outline. Introduction

nibaw
Download Presentation

Service Differentiation at Transport Layer via TCP Westwood Low-Priority (TCPW-LP)

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. Service Differentiation at Transport Layer via TCP Westwood Low-Priority (TCPW-LP) H. Shimonishi, M.Y. Sanadidi and M. Geria System Platforms Research Laboratories, NEC Corporation UCLA Computer Science Department IEEE Symp on Computers & Communications (ISCC), 2004

  2. Outline • Introduction • TCP Westwood (TCPW) • TCP Westwood Low Priority (TCPW-LP) • Performance Evaluation • Coexistence with foreground traffic • Comparison of TCPW-LP and TCP-LP • Conclusion

  3. Introduction • TCP Westwood Low-Priority (TCPW-LP) • An end-to-end “foreground/background” priority scheme • Objectives • Non-intrusive to coexisting foreground traffic • Capable of fully utilizing the unused bandwidth • Capable of fairly sharing with other low-priority flows

  4. Introduction • Application • Web objects pre-fetching (cache) • Large bulk transfers, e.g. FTP

  5. Introduction • Related Works • DiffServ (proposed by IETF) • Support from the network router is required • End-to-end schemes (TCP-LP and TCP-Nice) • Unused bandwidth cannot be fully utilized • Pre-set queuing threshold is required

  6. Background - TCPW • TCPW – a sender-side only modification • Reaction to packet losses • Duplicate ACKs • Reno • CWIN = CWIN/2 • Westwood • CWIN = (BWE * RTTmin) • Timeout expiration • Reno and Westwood • CWIN = 1

  7. Background - TCPW • BWE – Bandwidth Estimation • Estimated from the rate of ACK • b = segment size / (ACKtime - lastACKtime) • segment size = average of last n received segment • BWE = αBWE + (1- α)*b • smoothing operator α=0.8

  8. TCPW-LP • Early Window Reduction (EWR) • Congestion window reduction scheme • Dynamic Threshold Adjustment • Foreground Traffic Ratio, r

  9. Early Window Reduction (EWR) • Limit the backlog over the path • Virtual queue length = CWIN – BWE*RTTmin • CWIN = amount of outstanding packets in the path • BWE*RTTmin = amount of packets in the virtual pipe

  10. Early Window Reduction (EWR) • The virtual queue length exceeds a threshold • CWIN = BWE*RTTmin – BWE*Da • Da – the average queuing delay • BWE*Da – the packets backlogged at the bottleneck

  11. Dynamic Threshold Adjustment • Foreground Traffic Ratio (FTR), r • Ratio of Temporal Minimum Queuing Delay to Average Queuing Delay • When all queued packets belong to foreground traffic • r approaches 1 • only background flows • minimum queuing delay is small due to EWR • average queuing delay grows according to the backlog threshold

  12. Dynamic Threshold Adjustment • Dynamic Threshold, Qth = M(1-r) • M = 3 (upper bound on backlogged packets) • FTR, r = Dm /(Da+δ) • Dm = αDm + (1-α) Dmin • Da = αDa + (1-α) Davg • α= 3/4 • δ= 3x10-6/(RTT-RTTmin), ensuring non-zero delay in the calculation of r

  13. Performance Evaluation • Simulation Topology • End-to-end round trip propagation delay = 74ms • FIFO queuing with drop tail discipline

  14. Coexistence with foreground traffic • Throughput

  15. Coexistence with foreground traffic • Congestion Window Behavior

  16. Coexistence with foreground traffic • Completion time evaluation using FTP traffic

  17. Coexistence with foreground traffic • Effect of packet losses

  18. Comparison of TCPW-LP and TCP-LP • Throughput • 20 identical flows • TCP-LP flows utilize only 68% of the link

  19. Comparison of TCPW-LP and TCP-LP • Effect of packet losses

  20. Comparison of TCPW-LP and TCP-LP • Coexistence with UDP traffic • On-off UDP traffic • Available Bandwidth = 3.3Mbps(On), 10Mbps(Off) • Average available bandwidth = 6.7Mbps

  21. Comments • Some Questions • TCP-LP, one-way delay? • Analytical study of Foreground Traffic Ratio? • Packet loss improvement? TCP Westwood? • Insight • No bandwidth guarantee in both TCPW-LP and TCP-LP • Protocol between ordinary TCP and TCPW-LP/TCP-LP • Receiver-side only modification scheme

  22. Conclusion • TCPW-LP – an end-to-end scheme to realize two-class service prioritization • Dynamically adjusting the queuing threshold • Evaluation of its performance by simulation • Comparison of TCPW-LP and TCP-LP

More Related