bandwidth measurement

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  • 1. NetworkmeasurementJeromy FuPresentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 1

2. Agenda Why what and how Roadmap Bandwidth measurement Current Implementation Future workSource: Placeholder for Notes is 14 pointsPresentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 2 3. Why measurement is needed A big black cloud No explicit feedbackSource: Placeholder for Notes is 14 pointsPresentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 3 4. Application area Congestion control(QoS, transport layer etc) Overlay networks, (relay, overlay route etc) CDNs (select best server) Streaming(adjust encoding rate) And many moreSource: Placeholder for Notes is 14 pointsPresentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 4 5. What to measure?MetricsToolsRTTpingJitter iperfPacket LosspingAvail bandwidthBottleneckLink capacityThroughput iperfRoute info tracerouteMTUpingTopology GNP SkitterSource: Placeholder for Notes is 14 pointsPresentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 5 6. How to measure? Using special probing packets or application packets The aim:accuracy, when cross traffic existnon-intrusiveness, do not saturate pathtimelessSource: Placeholder for Notes is 14 pointsPresentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 6 7. Roadmap Measurement bandwidth using probing packets Link congestion detection using probing packets Congestion group identification based on congestion similarity. Using app packets instead of probing packets Topology(GNP like ordinate system etc)Source: Placeholder for Notes is 14 pointsPresentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 7 8. Bandwidth measurement One packet model and packet pair (train) model link capacity, bottleneck bandwidth, available bandwidth. Lots of experiment tools exist, but none production exist, the most previous tools are using TCP flooding.Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 8 9. TerminologyPresentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 9 10. Terminology Hop : Link at layer 3 Segment : Link at layer2Source: Placeholder for Notes is 14 pointsPresentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 10 11. Terminology Link aggregation http://wenku.baidu.com/view/64d752a6f524ccbff12184ca.htmSource: Placeholder for Notes is 14 pointsPresentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 11 12. Vuze use Network Diagnostic Tool http://www.measurementlab.net/measurement-lab-tools#tool1 http://netspeed.stanford.edu/Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 12 13. uTorrent use M-labs tool pathload2 http://www.utorrent.com/faq#mlabs http://www.measurementlab.net/measurement-lab-tools#tool4Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 13 14. Limitation of Tcp Throughput Other metrics may have significant effect on TCP throughput TCP is inefficient in high BDP networks and packet loss link) Other applications and transport protocols (e.g. for video and audio streaming) have different performance characteristics. Too intrusive, place too much additional load on the network.Source: Placeholder for Notes is 14 pointsPresentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 14 15. Available bandwidth Toolspathload, pathchrip, IGI/PTR MethodSelf-Induced CongestionPresentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 15 16. IGI/PTR insightSource: Placeholder for Notes is 14 pointsPresentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 16 17. IGI/PTR AlgorithmPresentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 17 18. Pathload InsightSource: Placeholder for Notes is 14 pointsPresentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 18 19. Pathload AlgorithmSource: Placeholder for Notes is 14 pointsPresentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 19 20. (Path or hop) capacity Toolspathchar, click, etc One packet ModelMeasures per-hop capacity, using icmp packets, liketraceroutePresentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 20 21. One packet ModelSource: Placeholder for Notes is 14 pointsPresentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 21 22. One packet Model Sender set TTL=1, send out the packet, and wait for the ICMP TTL-exceeded packet back. Upon receiving ICMP, estimate the RTT. Estimate the RTT multiple times for various size packets. The minimum RTT of various packets are believed to be the valid sample. The first link capacity is C=1/b , b is slope of RTT graph. Set the TTL=2,3n, repeat the process of step1 to 3, to Calculate the C=1/ bi bi-1Source: Placeholder for Notes is 14 pointsPresentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 22 23. One packet Model Transmission delay is linear with respect to packet size. Most implementation use RTT instead of one-way delay. Using linear regression to filter the queue results. Links are single-channelSource: Placeholder for Notes is 14 pointsPresentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 23 24. Drawbacks Linear regression is expensive (done for every link, need many packets, can alleviate through convergence of result). ACKs may not be sent in timely manner (ICMP packets are often limited or blocked). Some nodes are invisible (such as bridge etc work in layer 2, thus wont decrease IP TTL and no icmp ack), layer2 effect (underestimate lay3 capacity) Reverse path adds noise. Response packets may come back through a different path.Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 24 25. Bottleneck bandwidth Pathrate, capprobe, udt etc Packet pair ModelSource: Placeholder for Notes is 14 pointsPresentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 25 26. Packet pair Model Cross traffic Time compression: Other packet queue ahead of thefirst probe packet when it is downstream of thebottleneck link. This leads to high estimates. Time extension: Other packets delay the second probepacket and extend the spacing between the two probepackets. This leads to low estimates. Only support FIFO-queuing of router Doesnt support multi-channel linksPresentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 26 27. Packet pair Model Transmission time of L-byte packet at link with capacity C. t = L/C Send two packets back-to-back from source to sink/ Measure dispersion of packet pair at receiver.Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 27 28. Drawbacks Though simple, Packet pair technique can produce widely varied estimate and erroneous results, mainly due to cross traffic in the path and error in measurement(it relies on high precision timestamp)Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 28 29. Packet Train Model Packet train of length N. Source can send N back-to- back packets of size L to sink. Sink measures total dispersion D, computes bandwidth estimate as b = (N-1)L/D. eliminate measurement errors, but more likely to be interfere with cross traffic packets.Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 29 30. Quick Review Active probing including three kinds of method, one packet, packet pair and packet train. All assumes store-and-forward behavior of the intermediate node. All works on single channel. Receive based or Sender based. All have their pros and crons.Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 30 31. Which one is better Most people said their tool is better than the others. No business product using yet. Do test of those tools by ourselves. We need a benchmark tool first. Here comes iperf.Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 31 32. Which one is betterPresentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 32 33. Which one is betterPresentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 33 34. Which one is better After overall test on current implemented tools in various environments including nistnet environment and ADSL environment . Unfortunately, none of them gives reasonable result in both environment. Iperf works well. For more information, pls refer to iperf.doc and bw tech report.docxPresentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 34 35. Previous implementation More or less like iperf. measure throughput, but not TCP. Based on UDT, which uses UDP for reliable data transfer . UDT has its own flow/congestion control algorithm which is more efficient for data transfer than TCP. UDT has very flexible design which enable using used defined flow/congestion control algorithm. Good for later optimization, for example, slow down when detecting OWD increasing trend, so not affecting normal traffic.Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 35 36. Problems remains Flooding way will affect the normal traffic and interfere the user. UDT is too aggressive, even for constant rate UDP stream. Should review the research materials before to find a better solution. Besides, flooding way is not feasible when we need the metrics about the network most of the time, for example in QoS. Need further research into these area, so new version of netdect in being developed.Presentation_ID 2008

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