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Comprehensive Bandwidth Testing with BWdetail: A Detailed Overview and Demonstration

This project presentation by Mark McGinley provides an in-depth look at BWdetail, a bandwidth testing tool designed to estimate available bandwidth and monitor flow without requiring kernel modifications. Sponsored by NSF and DOE, the presentation discusses the growing need for effective bandwidth diagnostics in scientific research, particularly for handling large datasets with distributed collaborators. Key features of BWdetail, including its software architecture, reporting capabilities, and multi-threaded operation, are highlighted, alongside a demonstration of its effectiveness in real-world applications.

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Comprehensive Bandwidth Testing with BWdetail: A Detailed Overview and Demonstration

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  1. BWdetail: A bandwidth tester with detailed reporting Masters of Engineering Project Presentation Mark McGinley April 19, 2007 Advisor: Malathi Veeraraghavan Acknowledgement: This work was carried out under the sponsorship of NSF ITR-0312376, NSF ANI-0335190, and DOE DE-FG02-04ER25640 grants.

  2. Outline • Problem Statement • Related Work • Overview of BWdetail • Features and Uses • Demonstration • Conclusion

  3. Problem Statement • Growing eScience traffic Terabytes / month ESnet Monthly Accepted Traffic, January, 2000 – June, 2006 Ref. 1

  4. Problem Statement • Scientific research efforts such as Atlas characterized by: • Large datasets • Geographically distributed collaborators • 1800 physicists, 150 universitiesand laboratories • Supporting high speed transfers of datasets often requires system tuning, diagnostics [2]

  5. Outline • Problem Statement • Related Work • Overview of BWdetail • Features and Uses • Demonstration • Conclusion

  6. Related Work • Iperf from NLANR • Successor to ttcp, similar to nttcp, nuttcp • Web100 • Host system software (autotuning) • Lack of instrumentation/tools for diagnosing performance issues • Iperf100 • Web100-based Iperf

  7. Related Work • Nettest • Incorporates Iperf • Net100 • Leverages Web100 to eliminate “wizard gap” with autotuning • tcpdump

  8. Related Work • Iperf

  9. Related Work • tcpdump

  10. Related Work • BWdetail

  11. Related Work

  12. Outline • Problem Statement • Related Work • Overview of BWdetail • Features and Uses • Demonstration • Conclusion

  13. Overview of BWdetail • Bandwidth estimation ability of Iperf • Instrumentation capabilities similar to Web100, without kernel modification

  14. Overview of BWdetail • Software architecture • C program • TCP_INFO struct associated with each socket • Kernel parameters read/written using getsockopt(), setsockopt(), sysctl(), system()

  15. Outline • Problem Statement • Related Work • Overview of BWdetail • Features and Uses • Demonstration • Conclusion

  16. Features and Uses • Data transfer for goodput estimation • Memory-to-memory is most common usage • Disk/memory-to-disk/memory • Memory transfer can either be a specific size or duration • Disk transfer using a file of specific size, to eliminate caching effects

  17. Features and Uses • Effect of caching • 1 GB disk-to-disk successive transfer

  18. Features and Uses • Multi-threaded client • Client uses separate threads to send data and monitor flow

  19. Features and Uses • Tunable parameters from command line • Socket buffer size • TCP congestion control algorithm • CTCP-enabled Web100 capable • SACK, Nagle, no metrics save

  20. Features and Uses • Adjustable reporting granularity • Client and server report goodput over some small, configurable interval (100ms) • Client reports cwnd, RTT, etc, every smaller, configurable interval (5ms)

  21. Features and Uses • Applications • Research regarding transport protocols • CTCP/Reno/BIC • Cwnd and RTT measurements • Improving performance on a path • Records relevant kernel parameters • Ongoing recording of cwnd, RTT, goodput • Change parameters, repeat

  22. Outline • Problem Statement • Related Work • Overview of BWdetail • Features and Uses • Demonstration • Conclusion

  23. Demonstration Results

  24. Outline • Problem Statement • Related Work • Overview of BWdetail • Features and Uses • Demonstration • Conclusion

  25. Conclusion • Available bandwidth estimation • Instrumentation such as cwnd without requiring kernel modification or privileged access

  26. Thank you Questions?

  27. References • [1] W.E. Johnston, ESnet4: Networking for the Future of DOE Science, http://www.es.net/ESnet4/ESnet4-Internet2Members-Dec-06-2006-1.ppt, Dec. 5, 2006 • [2] The Atlas Experiment, www.atlas.ch

  28. Limitations • Does not replace tcpdump • tcpdump handles content • Needed to detect retransmissions, Ethernet PAUSE frames, verification • Incorporation of libpcap capabilities would degrade the non-interference status of BWdetail • BWdetail is interested in statistics, not content

  29. Limitations • BWdetail does not replace an expert • Still requires knowledge to tune, does not provide autotuning • Use of TCP_INFO struct presents portability issues

  30. Impact of monitoring • Minimal, even at ~1 Gbps

  31. RTT

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