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ExOR: Opportunistic Multi-Hop Routing for Wireless Networks

ExOR: Opportunistic Multi-Hop Routing for Wireless Networks. Yin Lin. b y Sanjit Biswas and Robert Morris. Agenda. Motivation Design Evaluation Summary. Traditional Wireless Routing = Wired Routing. ExOR: multi-hop unicast wireless routing protocol

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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 Yin Lin by SanjitBiswas and Robert Morris

  2. Agenda • Motivation • Design • Evaluation • Summary

  3. Traditional Wireless Routing = Wired Routing • ExOR: multi-hop unicast wireless routing protocol • Traditional: fixed routing sequence • Choose best sequence • Always forward through that sequence D B E F A C Routing Table Dst: Destination NH: Next hop

  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. Problem:Unnecessary Retransmission B Buffer it ! C A D G E F

  6. Problem: Unnecessary Hops • Only reach N1: result in retransmission • Luckily reach N3: distance wasted Choose “best” forwarder! src N1 N2 N3 N4 N5 dst

  7. Basic Idea : Route After Reception • Buffer received packets • Node closest to dst forward packet B 2.28 F 1.38 A E C 1.17 1.43 D

  8. Forwarder List: Should I Forward? • Distance metric: ETX to dst • Updated dynamically • Sort nodes w.r.t. distance ETX=2.28 ETX=2.28 ETX=2.28 ETX=2.28 ETX=2.28 B B B B B C C C C C ETX=1.17 ETX=1.17 ETX=1.17 ETX=1.17 ETX=1.17 ETX=2.85 ETX=2.85 ETX=2.85 ETX=2.85 ETX=2.85 A A A A A E E E E E ETX=0 ETX=0 ETX=0 ETX=0 ETX=0 D D D D D D Forwarder List ETX=1.43 ETX=1.43 ETX=1.43 ETX=1.43 ETX=1.43 E > C > D > B > A E > C > D > B > A E > C > D > B > A E > C > D > B > A E > C >D> B > A

  9. Batch Map: Who Has Received What? • ExOR operates on batch • Highest-priority node that received packet B C 1.17 2.28 2.85 A E E > C > D > B > A 0 D 1.43

  10. 3-Packet Batch Example B C 1.17 2.28 2.85 A E 0 D E > C >D > B > A 1.43

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

  12. 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

  13. 25 Lowest Throughput Pairs 1000 ExOR 4 Traditional Hops 3.3x TraditionalRouting 800 600 Throughput (Kbits/sec) 400 200 0 Node Pair Longer Routes

  14. ExOR 7 forwarders 18 links ExOR Uses Links In Parallel Traditional Routing 3 forwarders 4 links

  15. 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)

  16. Cost of ExOR • Memory cost at each node • Overhead # nodes • Choose a subnet

  17. Summary • Exploits radio properties • Send: broadcast • Receive: probabilistic • Solves problems w/ traditional routing • Unnecessary retransmission • Extra hops • Dynamic forwarder choice • Forwarder list – order distances to dst • Batch map – packet sent exactly once • Performance • 2x throughput • Longer & fewer hops Sol: Buffer packets Sol: Choose “best” forwarder

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