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Accuracy of Link Capacity Estimates using Passive and Active Approaches with CapProbe

Accuracy of Link Capacity Estimates using Passive and Active Approaches with CapProbe. Rohit Kapoor, Ling-Jyh Chen, M. Y. Sanadidi, Mario Gerla Dept. of Computer Science, University of California at Los Angeles. Ideal Case:. Packet pair Techniques. Packet Pair and Train Dispersion.

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Accuracy of Link Capacity Estimates using Passive and Active Approaches with CapProbe

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  1. Accuracy of Link Capacity Estimates using Passive and Active Approaches with CapProbe Rohit Kapoor, Ling-Jyh Chen, M. Y. Sanadidi, Mario Gerla Dept. of Computer Science, University of California at Los Angeles

  2. Ideal Case: Packet pair Techniques ISCC 2004

  3. Packet Pair and Train Dispersion ISCC 2004

  4. Packet Pairs Bandwidth Histogram Packet-pair estimates: multimodality with cross traffic: • Light load conditions(20%) (b) heavy load conditions(80%) • SCDR is caused by dispersion expansion • PNCM is caused by dispersion compression ISCC 2004

  5. Packet Train Bandwidth Histogram • As trains get longer, get “Asymptotic Dispersion Rate” or ADR • ADR is not equal to Residual (available) Capacity • We found and proved a physical interpretation (to be published): ADR is the flow share, when merges are proportional to arrival rates at each link • Dovrolis’ results obtained for non-responsive cross traffic flows ISCC 2004

  6. CapProbe: The Main Idea • Observation: Both expansion and compression of dispersion involve queuing due to cross traffic: • Dispersion expansion => second packet queued more • Dispersion compression => first packet queued more • Packet pair with minimal end-to-end delay sum, is likely to be dispersed corresponding to narrow link capacity • Looking for packet pair with minimal delay sum is inexpensive • CapProbe appears accurate in most of our experiments, simulations and measurements • CapProbe fails under heavy (~>75%) utilization by non-responsive (UDP) traffic ISCC 2004

  7. CapProbe • Ideal Case: no cross traffic • Real Case: dispersion may be compressed or expanded by the cross traffic Under-estimation due to expansion Over-estimation due to compression ISCC 2004

  8. CapProbe • Both expansion and compression are due to queuing • A Packet-Pair sample with Minimal Delay Sum can be used for Capacity Estimation ISCC 2004

  9. Wireless Measurements • Bad channelretransmissionlarger dispersionslower estimated capacity Results for Bluetooth-interfered 802.11b, TCP cross-traffic ISCC 2004

  10. Comparison to Earlier Tools ISCC 2004

  11. Implementation Issues • User vs. Kernel Mode generation of probes and measurements • End systems processing speed • Probe packet size ISCC 2004

  12. Testbed • User mode and kernel mode implementations • Slow system: Pentium II 500MHz CPU; Fast system: Pentium IV 1.8 GHz CPU • Probe packet sizes varied from 500 Bytes to 5K Bytes ISCC 2004

  13. Measurement Experiments on Internet Unit: Mbps ISCC 2004

  14. Discussion • For high speed networks, either a high time resolution machine or a large probing packet size is needed for accuracy • Fine resolution may not be possible in user mode • A large packet size increases the chances expansion of dispersion • Required time resolution T = pksize / C: Required time resolution for accurate estimation ISCC 2004

  15. Passive CapProbe • CapProbe is an active approach and using ICMP packets. • Passive approach is less intrusive, thus more scalable • Passive CapProbing within TCP requires back to back TCP packet transmission • Simulation => 15~20% of TCP data packets are sent back-to-back ISCC 2004

  16. Simulation • The network topology used in our simulations consists of a six-hop path with capacities {10, 7.5, 5.5, 4, 6 and 8} Mbps. • DelACK is disabled in the simulation. • Different cross traffic are used, with packet size 1000 bytes and 200 bytes. ISCC 2004

  17. Active CapProbe Passive CapProbe ISCC 2004

  18. Conclusion • Either a high time resolution machine or a large probing packet size is necessary for accurate capacity estimation • Passive CapProbing within TCP is feasible, minor TCP sender modification helps a lot (future work) • Other Future work: • Experiments at speeds higher than 100 Mbps • Passive CapProbing in TFRC, other applications • Use of capacity estimates in TCPW and overlays construction ISCC 2004

  19. Improving Wireless Link Throughput via Interleaved FEC T h a n k s ISCC 2004

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