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

23 February 2016 Outline  Introduction  Motivation  Techniques for root cause analysis of TCP throughput  Measurement setup  Analysis results  Conclusions

23 February 2016 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 o ISPs want satisfied clients o Need to know what’s going on before things can be improved  How?  Root Cause Analysis of TCP Throughput o Analysis and inference of the reasons that prevent a given TCP connection from achieving a higher throughput. o Passive traffic analysis  Why TCP? o TCP typically over 90% of all traffic

23 February 2016 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

23 February 2016 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 o Receiver advertized window limits the rate o max amount of outstanding bytes = min(cwnd,rwnd) o Flow control o Configuration issue default receiver advertized window is set too low window scaling is not enabled  TCP protocol o Ramp-up period in slow start and congestion avoidance  Network layer  Congestion at a bottleneck link

23 February 2016 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 Two pcap probes here Internet collect network access network

23 February 2016  Connections  Size distribution highly skewed  Use only 1% of the flows for RCA o Represent > 85% of all traffic  Clients  Heavy-hitters: 15% of clients generate 85-90% of traffic (up & down)  Low access link utilization Warming up…

23 February 2016 Results of Limitation Analysis  Few active clients overall  Application limitation dominates  Network limitation by distant bottleneck also experienced contains most bytes contains some bytes

23 February 2016 Application analysis: Application limited traffic  Quite stable and symmetric volumes  Vast majority of all traffic  eDonkey and “other” dominate P2P other eDonkey

23 February 2016 Application analysis: Saturated access link  No recognized P2P  Asymmetric port 80/8080 downstream  Real Web traffic?

23 February 2016 Impact of Limitation Causes  How far from optimal (access link saturation) are we?  Main observations  Very low downlink utilization for application limited traffic o Utilization < 20% during 65% of application limited periods of traffic  Uplink utilization < 50% during most of application and network limited uploads

23 February 2016 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 Interne t Low downlink utilization Low uplink capacity +rate limiter downloading client uploading clients

23 February 2016 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 o Too much?  Asymmetric link capacities  Impact and implications  ISP traffic is mostly application limited traffic  Things can change dramatically with o More intelligent P2P clients o Caches

23 February 2016 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)

Thank you for your attention

Backup slides

23 February 2016 Our approach (suppress)  Analyze passive traffic measurements  Capture and store all TCP/IP headers, analyze later off-line  Observe traffic only at a single measurement point  Applicable in diverse situations  E.g. at the edge of an ISP’s network o Know all about clients’ downloads and uploads  Bidirectional packet traces  Connection level analysis

23 February 2016 Scope (suppress)  Study long lived TCP connections  Short connections are another topic o Dominated by slow start?  Assume FIFO scheduling  Necessary for link capacity estimations with packet dispersion techniques  Reasonable assumption for most traffic  May not hold for cable modem and access networks

23 February 2016  Applications  Port based identification  Connections  Size distribution highly skewed  Use only 1% of them for RCA o Represent > 85% of all traffic  Clients  Heavy-hitters: 15% of clients generate 85-90% of traffic (up & down)  Low access link utilization o Why? Warming up… >5% of traffic each

23 February 2016 Client-level root cause analysis Limitation causes for clients 1.Application 2.Saturated access link 3.Network limitation due to distant bottleneck link 4.TCP configuration Connection-level RCA 1.ALPs 2.network limited BTPs during which utilization > 90% 3.network limited BTPs during which utilization < 90% 4.download (=local problem) BTPs limited by TCP layer associate bytes Extend the InTraBase framework

23 February 2016 Results of Limitation Analysis  Few active clients overall  Application limitation dominates  Network limitation by distant bottleneck also experienced similar contains most bytes contains some bytes

23 February 2016 Application analysis: Distant bottleneck link  Diverse mixture  Cause is not necessarily due to client’s behavior

23 February 2016 Impact of Limitation Causes  How far from optimal (access link saturation) are we?  Main observations  Uplink utilization < 50% during most of application and network limited uploads  Very low downlink utilization for application limited traffic o Utilization < 20% during 65% of ALPs

23 February 2016 Impact of Limitation Causes  Very low downlink utilization for application limited traffic upstream downstream How far from optimal (access link saturation) are we?