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Comparison of Routing Metrics for a Static Multi-Hop Wireless Network

Comparison of Routing Metrics for a Static Multi-Hop Wireless Network. Richard Draves, Jitendra Padhye, Brian Zill Microsoft Research. Presented by: J ón T. Grétarsson. CS577: Advanced Computer Networks. Outline. Introduction Setup Results Conclusions Discussion.

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Comparison of Routing Metrics for a Static Multi-Hop Wireless Network

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  1. Comparison of Routing Metrics for a Static Multi-Hop Wireless Network Richard Draves, Jitendra Padhye, Brian Zill Microsoft Research Presented by: Jón T. Grétarsson CS577: Advanced Computer Networks

  2. Outline • Introduction • Setup • Results • Conclusions • Discussion CS577: Advanced Computer Networks

  3. Introduction CS577: Advanced Computer Networks

  4. The Problem • In recent years, ad hoc wireless networks have emerged as a hot topic • Started with Military Applications • Commercial Applications of multi-hop wireless networks becoming popular (Roofnet, BAWUG, Seattle Wireless) • Quality of links aren’t taken into account in current routing algorithms CS577: Advanced Computer Networks

  5. The Authors • Richard Draves • Jitendra Padhye • Brian Zill CS577: Advanced Computer Networks

  6. The Paper • About Routing Metrics in Mesh Networks • Presented in ACM SIGCOMM, 2004 • A summary for the impatient CS577: Advanced Computer Networks

  7. Setup CS577: Advanced Computer Networks

  8. The Metrics • Hop Count (HOP) • Per-hop Round Trip Time (RTT) • Per-hop Packet Pair Delay (PktPair) • Expected Transmission Count (ETX) CS577: Advanced Computer Networks

  9. Ad Hoc Routing Architecture • Mesh Connectivity Layer • Layer 2.5 Architecture • Link Quality Source Routing CS577: Advanced Computer Networks

  10. LQSR • Modified DSR to include Link Quality Metrics • Link-State routing CS577: Advanced Computer Networks

  11. Testbed CS577: Advanced Computer Networks

  12. Testbed • 23 Nodes • Not Wireless-Friendly • High Node Density • Wide Variety of Multi-Hop Paths • 801.11a Wireless Network • Static Positions CS577: Advanced Computer Networks

  13. Results CS577: Advanced Computer Networks

  14. LQSR Overhead • CPU Bottleneck for shorter paths • Channel Contention for longer paths CS577: Advanced Computer Networks

  15. Link Variability • 183 of 506 Links displayed activity CS577: Advanced Computer Networks

  16. Link Variability • 90 Links with non-zero bandwidth in both directions CS577: Advanced Computer Networks

  17. Long Lived TCP Flows • Transfer duration fixed • One active transfer at a time • Semi-Inter Quartile Range bars • Large variations in throughput • UDP vs TCP • Self-Interference CS577: Advanced Computer Networks

  18. Median Throughput CS577: Advanced Computer Networks

  19. Median Number of Paths CS577: Advanced Computer Networks

  20. Path Length • As path length increases, throughput decays • Testbed diameter is 6 ~ 7 hops • Self-Interference is still a big problem for RTT and PktPair • ETX appears to approach a non-zero asymptote CS577: Advanced Computer Networks

  21. Median Path Length CS577: Advanced Computer Networks

  22. Average Path of ETX vs HOP CS577: Advanced Computer Networks

  23. RTT Throughput vs Path Length CS577: Advanced Computer Networks

  24. PktPair Throughput vs Path Length CS577: Advanced Computer Networks

  25. HOP Throughput vs Path Length CS577: Advanced Computer Networks

  26. EXT Throughput vs Path Length CS577: Advanced Computer Networks

  27. Variability of Throughput • Coefficient of Variation • 6 periphery nodes to 5 receivers • 1 active transfer at any time CS577: Advanced Computer Networks

  28. Median Throughput CS577: Advanced Computer Networks

  29. CoV of ETX vs HOP CS577: Advanced Computer Networks

  30. Competing TCP Transfers • RTT not worth demonstrating • Multiple Median Throughput (MMT) CS577: Advanced Computer Networks

  31. Competing TCP Transfers CS577: Advanced Computer Networks

  32. Web Traffic • Only one client active at any time • 1300 files fetched • Transfer using Surge • File size within the range [77B, 700KB] • Measured latency CS577: Advanced Computer Networks

  33. Median Overall Latency CS577: Advanced Computer Networks

  34. Median Latency <1KB CS577: Advanced Computer Networks

  35. Median Latency >8KB CS577: Advanced Computer Networks

  36. Web Traffic Conclusions • In longer paths, ETX dominates • In shorter paths, HOP sometimes wins CS577: Advanced Computer Networks

  37. Mobile Scenario CS577: Advanced Computer Networks

  38. Mobile Results CS577: Advanced Computer Networks

  39. Mobile Results • ETX has problems adjusting quickly enough • HOP has no such problems CS577: Advanced Computer Networks

  40. Conclusions

  41. Paper Conclusions • RTT and PktPair are load-sensitive and suffer from Self-Interference • ETX significantly outperforms HOP in the stationary ad hoc network • ETX relative performance gain increases as path length increases • HOP responds faster to the changes of a mobile ad hoc network CS577: Advanced Computer Networks

  42. Discussion

  43. Discussion • Experimental Flaws • Logical Fallacies • “Beating Up” competition • What didn’t the authors do? CS577: Advanced Computer Networks

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