1 / 22

A High-Throughput Path Metric for Multi-Hop Wireless Routing

A High-Throughput Path Metric for Multi-Hop Wireless Routing. Douglas S.J. Couto Daniel Aguayo John Bicket Robert Morris Presented by: Eric Rozner. Overview. Hop count metric Describe ETX Implementation Experiments and Comparisons Related Work Conclusions Discussion. Hop Count Metric.

alexia
Download Presentation

A High-Throughput Path Metric for Multi-Hop Wireless Routing

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. A High-Throughput Path Metric for Multi-Hop Wireless Routing Douglas S.J. Couto Daniel Aguayo John Bicket Robert Morris Presented by: Eric Rozner Eric Rozner - ETX.ppt

  2. Overview • Hop count metric • Describe ETX • Implementation • Experiments and Comparisons • Related Work • Conclusions • Discussion Eric Rozner - ETX.ppt

  3. Hop Count Metric • Paths decided upon by shortest route • Maximizes the distance traveled by each hop • Minimizes signal strength -> Maximizes the loss ratio • Uses a higher TxPower -> Interference • Possibly many shortest routes • Avoid lossy links? Eric Rozner - ETX.ppt

  4. Hop Count vs. “Optimal” x axis: throughput y axis: fraction of pairs with less throughput Eric Rozner - ETX.ppt

  5. Hop Count Route Selection Eric Rozner - ETX.ppt

  6. Motivation for a Better Routing Metric Bidirectional loss rates Fine-grained choices Intermediate loss rates Eric Rozner - ETX.ppt

  7. Potential Ideas (and their cons) • Product of per-link delivery ratios • A perfect 2-hop route is viewed as better than a 1-hop route with 10% loss ratio • Throughput of a path’s bottleneck link • Same as above • End-to-End delay • Changes with network load as interference queue lengths vary… can cause oscillations • Everyone convinced? Eric Rozner - ETX.ppt

  8. ETX • The predicted number of data transmissions required to send a packet over a link • The ETX of a path is the sum of the ETX values of the links over that path • Examples: • ETX of a 3-hop route with perfect links is 3 • ETX of a 1-hop route with 50% loss is 2 Eric Rozner - ETX.ppt

  9. ETX continued… • Expected probability that a transmission is successfully received and acknowledged is df x dr • df is forward delivery ratio • dr is reverse delivery ratio • Each attempt to transmit a packet is a Bernoulli trial, so… Eric Rozner - ETX.ppt

  10. Hooray for ETX! • Based on delivery ratios, which affect throughput • Detects and handles asymmetry by incorporating loss ratios in each direction • Uses precise link loss ratios measurements to make fine-grained decisions between routes • Assumes you can measure these ratios precisely • Penalizes routes with more hops, which have lower throughput due to inter-hop interference • Assumes loss rates are generally equal over links • Tends to minimize spectrum use, which should maximize overall system capacity (reduce power too) • Each node spends less time retransmitting data Eric Rozner - ETX.ppt

  11. ETX always the best? Eric Rozner - ETX.ppt

  12. Acquiring ETX values • Measured by broadcasting dedicated link probe packets with an average period τ (jittered by ±0.1τ) • Delivery ratio: • count(t-w,t) is the # of probes received during window w • w/τ is the # of probes that should have been received • Each probe contains this information Eric Rozner - ETX.ppt

  13. Implementation and such… • Authors modified DSDV and DSR • See paper for details • τ = 1 packet per second, w = 10 sec • Multiple queues (different priorities) • Loss-ratio probes, protocol packets, data packets • Are these experiments unfair or unrealistic? • In DSDV w/ ETX, route table is a snapshot taken at end of 90 second warm-up period • In DSR w/ ETX, source waits additional 15 sec before initiating the route request Eric Rozner - ETX.ppt

  14. DSDV Performance One hop Asymmetric ETX inaccurate Eric Rozner - ETX.ppt

  15. DSDV and High Transmit Power Eric Rozner - ETX.ppt

  16. Packet Size Problems • Less throughputadvantage than whendata packetsare smaller(134 bytes) Eric Rozner - ETX.ppt

  17. Packet sizes continued ACK’s smaller than probe packets ETX underestimates ACK delivery ratios -> overestimates total number of transmissions per packet Eric Rozner - ETX.ppt

  18. DSR Performance Link-layer transmission feedback disabled Link-layer transmission feedback enabled Eric Rozner - ETX.ppt

  19. Related Work • Yarvis et al. [33] propose a path metric which approximates the product of the per-link delivery ratios. • Link hand-shaking to avoid “gray areas” [8], [22] • SNR ratio is also a possible path metric [14] • SNR threshold value to filter links discovered by DSR Route Discovery. • See Related Works section of “Comparison of Routing Metrics for Static Multi-Hop Wireless Networks “ Eric Rozner - ETX.ppt

  20. Related Work Continued… • WCETT proposed in MR-LQSR • Weighted Cumulative Expected Transmission Time Eric Rozner - ETX.ppt

  21. Conclusions • Pros • ETX performs better or comparable to Hop Count Metric • Accounts for bi-directional loss rates • Can easily be incorporated into routing protocols • A lot of other work built off this paper • Cons • May not be best metric for all networks • Mobility, Power-limited, Adaptive Rate (multi-rate), Multi-radio • Predications of loss ratios not always accurate • Experiments (30 sec transfer of small packets) may not complement real-world scenarios Eric Rozner - ETX.ppt

  22. Questions? Eric Rozner - ETX.ppt

More Related