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ExOR: Opportunistic Multi-hop routing for Wireless Networks

ExOR: Opportunistic Multi-hop routing for Wireless Networks. by; Sanjit Biswas and Robert Morris, MIT. Traditional Routing. Links are abstracted as wires. B. C. E. A. D. Link transmission is a Broadcast. Probability of reception decreases with distance

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ExOR: Opportunistic Multi-hop routing for Wireless Networks

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  1. ExOR: Opportunistic Multi-hop routing for Wireless Networks by; Sanjit Biswas and Robert Morris, MIT

  2. Traditional Routing • Links are abstracted as wires. B C E A D

  3. Link transmission is a Broadcast • Probability of reception decreases with distance • However, there is always a chance that data travels longer 10% B C 60% 90% E A D

  4. ExOR Exploits Broadcast • Best traditional route over 50% hops: 3(1/0.5) = 6 tx • Throughput 1/# transmissions • ExOR exploits lucky long receptions: 4 transmissions src N1 N2 N3 N4 N5 dst 75% 50% 25%

  5. ExOR Exploits Broadcast N1 • Traditional routing: 1/0.25 + 1 = 5 tx • ExOR: 1/(1 – (1 – 0.25)4) + 1 = 2.5 transmissions 25% 100% N2 25% 100% src dst 100% 25% N3 100% 25% N4

  6. ExOR Realization: Batching • A list of forwarders are prioritized by their ETX values • Priority order : E C D B A • In other words, if E C D B A receive packets, they should forward in that order • Other nodes listen • They forward packets only if a higher priority node has failed to do so dst src src dst

  7. An example • A has transmitted a batch of 10 packets 1-10 • E receives packets 1, 2 • C receives 1 3 4 10 • D receives 1 2 5 9 10 • B receives 1 2 3 4 5 6 7 8 9 10 • E received 1,2 1 2 3 4 5 6 7 8 9 10 • Now C forwards 3, 4,10 1 234 5 6 7 8 9 10 • D forwards 5,9 1 2345 6 7 8 910 • B forwards 6, 7, 8 1 23456 7 8 910 Priority order : E C D B A

  8. 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)

  9. Summary • ExOR opportunistically exploits wireless broadcast • long distance transmission • Avoids retransmission by allowing a low priority node to forward

  10. Issues • Periodic link state flooding • Queuing for batching causes delay for interactive applications • Broadcast property will result in errors in case of optimal bit rate encoding

  11. Thank You • Questions ?

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