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