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Empirical Evaluation of Techniques for Measuring Available Bandwidth

Empirical Evaluation of Techniques for Measuring Available Bandwidth. 2009. 3.17 Alok Shriram and Jasleen Kaur Presented by Moonyoung Chung. Outline. Introduction Available Bandwidth ABETs Related Work Motivation and Goal Experimental Framework Experimental Results Accuracy Cost

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Empirical Evaluation of Techniques for Measuring Available Bandwidth

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  1. Empirical Evaluation of Techniques for Measuring Available Bandwidth 2009. 3.17 AlokShriram and JasleenKaur Presented by Moonyoung Chung

  2. Outline • Introduction • Available Bandwidth • ABETs • Related Work • Motivation and Goal • Experimental Framework • Experimental Results • Accuracy • Cost • Conclusion Infocom '07

  3. Available Bandwidth (AB) • End-to-End AB: • minimum unused capacity of path. • varies with time • Tight link: minimum avail-bw link Tight Link or Available Bandwidth (AB) Narrow Link • Applications • Network monitoring • Congestion control • Design of transport protocol • Streaming applications 100 Mbps 10 Mbps 1000 Mbps 950 Mbps 2500 Mbps 1200 Mbps • ui : utilization of link i in time interval t ( 0 ≤ui≤ 1 ) • Available bandwidth in link i: • Available bandwidth in path (Avail-bw): Infocom '07

  4. Methodology for AB estimation Send probe packet(s) into the network and measure a response 1. Design of Probes 2. Inference Logic End-to-End Path Feedback for successive Iterations closed-loop tools closed-loop tools Infocom '07

  5. Algorithmic Techniques • Packet Pair [Jacobson ’88, Keshav ’91] • Spruce • Packet Train • Pathload, PathChirp, IGI, Cprobe dispersion Narrow Link T1 T0 Tn+1 Tn Gap one way delay dispersion receiving rate Gap Gap t t cross traffic Infocom '07

  6. Implementation techniques • High time-stamping accuracy • variations in end-to-end delays, in the sub-millisecond rage • OS support • for detecting and discarding probe streams that appear to not have been time-stamped accurately • Collect observations from several probe streams before converging on a robust estimate of AB Infocom '07

  7. Questions • Which algorithmic technique performs the best? • To what extend does current implementation technology limit tool performance? • How well would tools perform if technology advances in the future? Infocom '07

  8. Related Works • a small subset of ABETs • Robeiro et. al. [6] compares PathChirp to Pathload and TOPP • Hu et. al. [4] compares IGI/PTR to Pathload and Iperf • Strauss et. al. [7] compares Spruce to Pathload and IGI • only simple network and traffic scenarios • biased by current implementation technology • ignores two key quantities: MT and SI Infocom '07

  9. Motivation and Goal • Motivation • Existing evaluations are either non-comprehensive and biased, or are affected by implementation issues • Goal • Conducting an extensive experimental study of existing techniques for measuring AB • Approach • Evaluation independent of current implementation technology • simulation environments • Evaluation against diverse probing and network conditions • Gigabyte network path/ diverse conditions Infocom '07

  10. Evaluating Conditions • dynamic traffic load • measurement timescales (MT) • the time-scale at which AB is observed. • sampling intensities (SI) • the duration for which the AB is sampled per unit time. • number of bottleneck links • location of bottleneck • Both MT and SI impact the accuracy and variability of the AB sampled by an ABET. [Shriram et al. 2006] Infocom '07

  11. AB Time Measurement Timescale (MT) • Definition • Timescale at which we observe the AB process • the duration of a single probe stream = length of the probe stream Packet Pair Packet Train MT MT MT Infocom '07

  12. MT effect on AB Smaller MT expect more variability, expect lower accuracy Infocom '07

  13. Sampling Intensity (SI) • Definition • the duration for which the AB is sampled per unit time. • the number of probes • the product of the MT and the number of probe streams sent per unit time Higher SI expect better accuracy Infocom '07

  14. ABET Implementation • Tools: • Pathload, PathChirp, Spruce, IGI, Fast-IGI, and Cprobe • Implement in the NS-2 network simulation environment • Incorporating MT • Incorporating Si • Open-loop tools : Cprobe, Spruce, PathChirp • SI = MT/(MT+G) • G: the gap between successive probe-streams • Closed-loop tools: Pathload, IGI, Fast-IGI • The construction of a probe-stream is determined by the delays experienced by the previous probe-stream. • RTT instead of SI Infocom '07

  15. Performance Metrics • Accuracy-related • AB estimation error: the estimated AB – the actual AB (* actual AB = the number of bits that traverse the link during the tool run/the tool run-time) • Cost-related • run time: the time taken by a tool to return an estimate • probing overhead: the total amount of network probe traffic sent by the tool in order to arrive at a single estimate of AB • intrusiveness: the average bit-rate of a tool (overhead/runtime) • Impact on responsive cross-traffic • probe traffic on the response time of ongoing TCP connections Infocom '07

  16. Single Bottleneck • Topology with a Single Bottleneck Link • Tool Traffic: traffic by ABETs • Cross Traffic: traffic with a constant bit-rate (CBR) link capacity = 1Gbps link delay = 1ms sufficient buffer Infocom '07

  17. Validation of ABET Implementation • Cross wit a constant bit-rate (CBR) • Pathload, Spruce  quite accurate • pathChirp slightly higher • Cprobe based on Receiving Rate  poor • IGI -> R-IGI  good • Cprobe based on Receiving Rate  poor Infocom '07

  18. Dynamic Traffic Load • Trace used for evaluation • Collect five 1-hour packet traces from four different Internet links for 1 Gbps links Infocom '07

  19. Variability • The estimation errors vary widely around the average. • least for Pathload • quite high for Spruce and PathChirp Single Bottleneck • Tool errors with default parameters MT=1ms MT=1ms MT=10ms MT=0.5ms MT=10ms 95-percentiles average 5-percentiles • Accuracy • The average estimation errors are higher with dynamic cross-traffic than with CBR. • Pathload, PathChirp, Fast-IGIhave similar average error. • R-IGI has lower error. • Sprucehas higher error. Infocom '07

  20. Impact of MT • IPLS-CLEV: Impact of MT (SI=0.1, RTT=60ms) • Increasing the MT improves the accuracy of all ABETs • The gain are negligible beyond an MT of 50ms. • MT impact on PathChirp is lower. • Spruce now is the most accurate (it was the least with default settings) Infocom '07

  21. Impact of SI • IPLS-CLEV: Impact of SI (MT=10ms) open-looped tools • SI and RTT has a negligible impact on the accuracy Infocom '07

  22. Bottleneck Location • Different tight and narrow links tight link narrow link cross traffic: IPLS-CLEV(410Mbps), IPLS-KSCY(530Mbps) Infocom '07

  23. Bottleneck Location : Result • MT=50ms, SI=0.1 Single Bottleneck Different tight and narrow links PathChirp Spruce IPLS-CLEV • The error of PathChirp and Spruce increases by a factor of 2-3. • Other ABETs are not impacted much. Infocom '07

  24. Multiple bottlenecks • Single narrow link: two tight link tight link IPLS-CLEV IPLS-KSCY narrow link Infocom '07

  25. Multiple bottlenecks : Result • MT=50ms, SI=0.1 Single Bottleneck Single narrow link: two tight link PathChirp Spruce IPLS-CLEV, IPLS-KSCY IPLS-CLEV • PathChirp and Spruce further degrades and the most inaccurate. • The accuracy of the others are not significantly impacted. Infocom '07

  26. Overhead PathChirp Pathload Spruce R-IGI Fast-IGI • PathChirp, R-IGI, Fast-IGI have the least overhead. • Overhead increase with MT. • SI and RTT has no impact on the overhead. Infocom '07

  27. Run-time Pathload Spruce • Spruce is the fastest tool. • Pathload is the slowest tool. • Increase the MT  a proportional increase in the runtime. Infocom '07

  28. Intrusiveness • Non-intrusiveness: cross traffic should not be affected • All closed-loop tools are quite intrusive. • Spruce has the highest value of intrusiveness. • PathChirp is the most non-intrusive tool Infocom '07

  29. Responsive Cross-Traffic • Responsive cross-traffic • TCP uses congestion-control mechanism to reduce the data sending rate on detecting network congestion. • queuing delays • losses on the subsequent packet transmissions • How adversely do these tools impact the performance of applications that rely on such responsive transport protocols? • Tmix: traffic-generation tool that incorporate the responsive behavior of TCP link capacity = 1Gbps average traffic = 300Mbps buffer size = 100 MSS-sized packets Infocom '07

  30. Impact on Responsive Cross-Traffic • CDF of response times with default parameters CDF of connections no tool & PathChirp Pathload Fast-IGI • PathChirp has no noticeable impact on the response time. • Pathload and Fast-IGI can significantly impact on the response times. Infocom '07

  31. Conclusion • Conduct a comprehensive empirical evaluation of existing algorithmic techniques used for measuring end-to-end AB. • Key Observations • Accuracy • The accuracy can be improved by using an MT of 50ms. • SI and path RTT have negligible impact on the accuracy. • While Spruce is the most accurate for paths with a single bottleneck link, its accuracy worsens for paths for multiple bottleneck links. • Cost • PathChirp has the lowest overhead, and it has no impact on the response times of TCP. • Spruce is the fastest, but has the highest value of intrusiveness. • The cost of Pathload, R-IGI, and Fast-IGI seems to be highest. • Responsive Cross-traffic • If an application needs to run an ABET repeatedly on a given internet path, it should use PathChirp. Infocom '07

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