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Enhancing Throughput in Wireless Networks Using Opportunistic Routing

Explore ExOR, a novel approach to routing in multi-hop wireless networks for high-throughput and capacity. The protocol exploits probabilistic broadcast to optimize packet forwarding and minimize duplicate transmissions. Learn how ExOR increases throughput, implements batch processing, reliable summaries, and priority ordering for efficient data transmission. Evaluation shows a significant 2x improvement in throughput compared to traditional routing. Discover the impact of ExOR on different network configurations and potential applications in future work.

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Enhancing Throughput in Wireless Networks Using Opportunistic Routing

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  1. Opportunistic Routing in Multi-hop Wireless Networks Sanjit Biswas and Robert Morris MIT CSAIL http://pdos.csail.mit.edu/roofnet/

  2. ExOR: a new approach to routing in multi-hop wireless networks • Dense 802.11-based mesh • Goal is high-throughput and capacity 1 kilometer

  3. Initial approach: Traditional routing packet packet • Identify a route, forward over links • Abstract radio to look like a wired link A B src dst packet C

  4. Radios aren’t wires • Every packet is broadcast • Reception is probabilistic A B src dst 1 2 2 2 3 3 3 4 4 4 5 5 5 6 6 6 1 1 2 3 4 5 6 1 C

  5. ExOR: exploiting probabilistic broadcast packet packet packet packet • Decide who forwards after reception • Goal: only closest receiver should forward • Challenge: agree efficiently and avoid duplicate transmissions A B src dst packet packet packet packet packet C

  6. Outline • Introduction • Why ExOR might increase throughput • ExOR protocol • Measurements • Related Work

  7. Why ExOR might increase throughput (1) • Best traditional route over 50% hops: 3(1/0.5) = 6 tx • Throughput 1/# transmissions • ExOR exploits lucky long receptions: 4 transmissions • Assumes probability falls off gradually with distance src N1 N2 N3 N4 N5 dst 75% 50% 25%

  8. Why ExOR might increase throughput (2) N1 • Traditional routing: 1/0.25 + 1 = 5 tx • ExOR: 1/(1 – (1 – 0.25)4) + 1 = 2.5 transmissions • Assumes independent losses 25% 100% N2 25% 100% src dst 100% 25% N3 100% 25% N4

  9. Outline • Introduction • Why ExOR might increase throughput • ExOR protocol • Measurements • Related Work

  10. rx: 40 rx: 0 rx: 57 rx: 85 rx: 22 rx: 0 rx: 99 rx: 88 rx: 53 rx: 23 ExOR batching • Challenge: finding the closest node to have rx’d • Send batches of packets for efficiency • Node closest to the dst sends first • Other nodes listen, send remaining packets in turn • Repeat schedule until dst has whole batch tx:0 N2 N4 tx:100 tx:57 -23  24 tx:9 src dst N1 N3 tx: 8 tx:23

  11. Reliable summaries tx: {2, 4, 10 ... 97, 98} summary:{1,2,6, ... 97, 98, 99} • Repeat summaries in every data packet • Cumulative: what all previous nodes rx’d • This is a gossip mechanism for summaries N2 N4 src dst N1 N3 tx: {1, 6, 7 ... 91, 96, 99} summary:{1, 6, 7 ... 91, 96, 99}

  12. Priority ordering • Goal: nodes “closest” to the destination send first • Sort by ETX metric to dst • Nodes periodically flood ETX “link state” measurements • Path ETX is weighted shortest path (Dijkstra’s algorithm) • Source sorts, includes list in ExOR header • Details in the paper N2 N4 src dst N1 N3

  13. TCP TCP ExOR Batches (not TCP) Using ExOR with TCP • Batching requires more packets than typical TCP window Web Server Client PC Node Gateway Proxy Web Proxy ExOR

  14. Outline • Introduction • Why ExOR might increase throughput • ExOR protocol • Measurements • Related Work

  15. ExOR Evaluation • Does ExOR increase throughput? • When/why does it work well?

  16. 65 Roofnet node pairs 1 kilometer

  17. Evaluation Details • 65 Node pairs • 1.0MByte file transfer • 1 Mbit/s 802.11 bit rate • 1 KByte packets

  18. ExOR: 2x overall improvement 1.0 • Median throughputs: 240 Kbits/sec for ExOR, 121 Kbits/sec for Traditional 0.8 0.6 Cumulative Fraction of Node Pairs 0.4 0.2 ExOR Traditional 0 0 200 400 600 800 Throughput (Kbits/sec)

  19. 25 Highest throughput pairs 3 Traditional Hops 2.3x 2 Traditional Hops 1.7x 1 Traditional Hop 1.14x 1000 ExOR TraditionalRouting 800 600 Throughput (Kbits/sec) 400 200 0 Node Pair

  20. 25 Lowest throughput pairs 1000 ExOR 4 Traditional Hops 3.3x TraditionalRouting 800 600 Throughput (Kbits/sec) 400 200 0 Node Pair Longer Routes

  21. Traditional Routing 3 forwarders 4 links ExOR 7 forwarders 18 links ExOR uses links in parallel

  22. 58% of Traditional Routing transmissions 25% of ExOR transmissions ExOR moves packets farther • ExOR average: 422 meters/transmission • Traditional Routing average: 205 meters/tx 0.6 ExOR Traditional Routing Fraction of Transmissions 0.2 0.1 0 0 100 200 300 400 500 600 700 800 900 1000 Distance (meters)

  23. Future Work • Choosing the best 802.11 bit-rate • Cooperation between simultaneous flows • Coding/combining

  24. Related work • Relay channels [Van der Meulen][Laneman+Wornell] • Flooding in meshes / sensor nets [Peng][Levis] • Multi-path routing [Ganesan][Haas] • Selection Diversity [Miu][Roy Chowdhury][Knightly][Zorzi]

  25. Summary • ExOR achieves 2x throughput improvement • ExOR implemented on Roofnet • Exploits radio properties, instead of hiding them

  26. Thanks! For more information and source code: http://pdos.csail.mit.edu/roofnet/

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