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Performance Limitations of ADSL Users: A Case Study

This case study by Matti Siekkinen and team analyzes 24-hour packet traces from France Telecom's ADSL access network to understand throughput limitations experienced by clients. The study uses root cause analysis of TCP throughput and examines factors such as application, transport layer, and network layer. Results show that most clients are limited by applications, with P2P clients throttling upload rates. The findings highlight the need for improved RCA techniques and intelligent P2P clients to enhance overall network performance.

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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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