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Performance Limitations of ADSL Users: A Case Study

Performance Limitations of ADSL Users: A Case Study. Matti Siekkinen , University of Oslo Denis Collange, France T é l é com R&D Guillaume Urvoy-Keller, Ernst W. Biersack, Institut Eurecom PAM April 6, 2007. Outline. Introduction Motivation

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Performance Limitations of ADSL Users: A Case Study

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  1. Performance Limitations of ADSL Users:A Case Study Matti Siekkinen, University of Oslo Denis Collange, France Télécom R&D Guillaume Urvoy-Keller, Ernst W. Biersack, Institut Eurecom PAM April 6, 2007

  2. Outline • Introduction • Motivation • Techniques for root cause analysis of TCP throughput • Measurement setup • Analysis results • Conclusions

  3. Introduction • What? • Analyzed 24h packet trace from France Telecom’s ADSL access network • Studied throughput limitations experienced by clients • Why? • Knowing throughput limitations (=performance) is useful • ISPs want satisfied clients • Need to know what’s going on before things can be improved • How? • Root Cause Analysis of TCP Throughput • Analysis and inference of the reasons that prevent a given TCP connection from achieving a higher throughput. • Passive traffic analysis • Why TCP? • TCP typically over 90% of all traffic

  4. Background • “On the characteristics and origins of Internet flow rates” by Zhang et al. (SIGCOMM 2002) • Pioneering research work • Congestion is not always the cause for throughput limitations

  5. Limitation Causes for TCP Throughput • Application • The application does not even attempt to use all network resources • E.g. streaming applications and “bursty” applications (Web browsing) • Transport layer • TCP receiver • Receiver advertized window limits the rate • max amount of outstanding bytes = min(cwnd,rwnd) • Flow control • Configuration issue • default receiver advertized window is set too low • window scaling is not enabled • TCP protocol • Ramp-up period in slow start and congestion avoidance • Network layer • Congestion at a bottleneck link

  6. Measurement Setup • 24 hours of traffic on March 10, 2006 • Passively capture all TCP/IP headers analyze offline • 290 GB of TCP traffic • 64% downstream, 36% upstream • Observed packets from ~3000 clients, analyze only 1335 • Excluded clients did not generate enough traffic for RCA Internet access network collect network Two pcap probes here

  7. Warming up… • Connections • Size distribution highly skewed • Use only 1% of the flows for RCA • Represent > 85% of all traffic • Clients • Heavy-hitters: 15% of clients generate 85-90% of traffic (up & down) • Low access link utilization

  8. Results of Limitation Analysis contains most bytes • Few active clients overall • Application limitation dominates • Network limitation by distant bottleneck also experienced contains some bytes

  9. Application analysis:Application limited traffic other • Quite stable and symmetric volumes • Vast majority of all traffic • eDonkey and “other” dominate eDonkey P2P

  10. Application analysis:Saturated access link • No recognized P2P • Asymmetric port 80/8080 downstream • Real Web traffic?

  11. Impact of Limitation Causes • How far from optimal (access link saturation) are we? • Main observations • Very low downlink utilization for application limited traffic • Utilization < 20% during 65% of application limited periods of traffic • Uplink utilization < 50% during most of application and network limited uploads

  12. Connecting the evidence… • Most clients’ performance limited by applications • Very low link utilizations for application limited traffic • Most of application limited traffic seems to be P2P • Peers often have asymmetric uplink and downlink capacities • P2P applications/users enforce upload rate limits  Poor aggregate download performance uploading clients Internet downloading client Low downlinkutilization Low uplink capacity+rate limiter

  13. Conclusions • Analyzed 24h packet trace from France Telecom’s ADSL access network • Studied throughput limitations experienced by clients • Majority of clients mostly throughput limited by applications • P2P clients throttle upload rate • Too much? • Asymmetric link capacities • Impact and implications • ISP traffic is mostly application limited traffic • Things can change dramatically with • More intelligent P2P clients • Caches

  14. For the future… • Play with time scale • Extended case study on ADSL clients • We saw a day, what about a week? • Could we do things on-line? • Improving RCA techniques • Short connections • Non FIFO traffic (e.g. wireless)

  15. Thank you for your attention

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