1. E X OR: O PPORTUNISTIC M ULTI -H OP R OUTING FOR W IRELESS N ETWORKS Yin Lin BY S ANJIT B ISWAS AND R OBERT M ORRIS

2. A GENDA Motivation Design Evaluation Summary

3. T RADITIONAL W IRELESS R OUTING = W IRED R OUTING ExOR: multi-hop unicast wireless routing protocol Traditional: fixed routing sequence Choose best sequence Always forward through that sequence A A B B D D C C E E F F DstNH BB CC DB EC FC DstNH AA BA …… FE DstNH AC BD …… FF Routing Table Dst: Destination NH: Next hop

4. Every packet is broadcast Reception is probabilistic R ADIOS A REN ’ T W IRES 1234561 23635 1 42345612456 src AB dst C

5. P ROBLEM : U NNECESSARY R ETRANSMISSION AG B C D E F Buffer it !

6. P ROBLEM : U NNECESSARY H OPS Only reach N1: result in retransmission Luckily reach N3: distance wasted srcdstN1N2N3N4N5 Choose “best” forwarder!

7. B ASIC I DEA : R OUTE A FTER R ECEPTION Buffer received packets Node closest to dst forward packet A A E E B B F F C C D D 2.28 1.17 1.43 1.38

8. F ORWARDER L IST : S HOULD I F ORWARD ? Distance metric: ETX to dst Updated dynamically Sort nodes w.r.t. distance D D A A E E B B C C ETX=2.28 ETX=1.17 ETX=1.43 ETX=0 ETX=2.85 D D A A E E B B C C ETX=2.28 ETX=1.17 ETX=1.43 ETX=0 ETX=2.85 D D A A E E B B C C ETX=2.28 ETX=1.17 ETX=1.43 ETX=0 ETX=2.85 D D A A E E B B C C ETX=2.28 ETX=1.17 ETX=1.43 ETX=0 ETX=2.85 D D A A E E B B C C ETX=2.28 ETX=1.17 ETX=1.43 ETX=0 ETX=2.85 D D Forwarder List Ethernet Header …FLBM… Data

9. ExOR operates on batch Highest-priority node that received packet Ethernet Header …FLBM… Data E > C > D > B > A B ATCH M AP : W HO H AS R ECEIVED W HAT ? A A E E B B C C D D 2.28 1.17 1.43 0 2.85 CCDECAACCA EEACBBCDCA

10. 123 3-P ACKET B ATCH E XAMPLE A A E E B B C C D D 2.28 1.17 1.43 0 2.85 AAAAA ECAEEAEEDEEEE ADAADD AD E CD EEDEEEE CAACACCAEEAEEDEEEE BAABBABBBBBECBEEBEEDEEEE AA EEAEEEE 112123 113 23 313123 2123 123

11. E X OR: 2 X O VERALL I MPROVEMENT Median throughputs: 240 Kbits/sec for ExOR 121 Kbits/sec for Traditional Throughput (Kbits/sec) 1.0 0.8 0.6 0.4 0.2 0 0200400600800 Cumulative Fraction of Node Pairs ExOR Traditional

12. 25 H IGHEST T HROUGHPUT P AIRS Node Pair Throughput (Kbits/sec) 0 200 400 600 800 1000 ExOR Traditional Routing 1 Traditional Hop 1.14x 2 Traditional Hops 1.7x 3 Traditional Hops 2.3x

13. 25 L OWEST T HROUGHPUT P AIRS Node Pair 4 Traditional Hops 3.3x Longer Routes Throughput (Kbits/sec) 0 200 400 600 800 1000 ExOR Traditional Routing

14. E X OR U SES L INKS I N P ARALLEL Traditional Routing 3 forwarders 4 links ExOR 7 forwarders 18 links

15. E X OR M OVES P ACKETS F ARTHER ExOR average: 422 meters/transmission Traditional Routing average: 205 meters/tx Fraction of Transmissions 0 0.1 0.2 0.6 ExOR Traditional Routing 01002003004005006007008009001000 Distance (meters) 25% of ExOR transmissions 58% of Traditional Routing transmissions

16. C OST OF E X OR

17. S UMMARY 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