EXOR OPPORTUNISTIC MULTIHOP ROUTING FOR WIRELESS NETWORKS by
EXOR: OPPORTUNISTIC MULTI-HOP ROUTING FOR WIRELESS NETWORKS by; Sanjit Biswas and Robert Morris, MIT 1
TRADITIONAL ROUTING Links are abstracted as wires. B C E A Destination Path E ADE C ADC D 2
LINK TRANSMISSION IS A BROADCAST Probability of reception decreases with distance However, there is always a chance that data travels longer 10% B 90% C 60% E A D 3
EXOR EXPLOITS BROADCAST src N 1 N 2 N 3 N 4 N 5 dst 75% 50% 25% Best traditional route over 50% hops: 3(1/0. 5) = 6 tx Throughput 1/# transmissions Ex. OR exploits lucky long receptions: 4 transmissions 4
EXOR EXPLOITS BROADCAST N 1 % 5 2 src 25% 25 N 2 N 3 10 0% 100% dst % 0 0 1 % N 4 Traditional routing: 1/0. 25 + 1 = 5 tx Ex. OR: 1/(1 – 0. 25)4) + 1 = 2. 5 transmissions 5
EXOR REALIZATION: BATCHING A list of forwarders are prioritized by their ETX values src dst 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 6
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 2 3 4 5 6 7 8 9 10 D forwards 5, 9 1 2 3 4 5 6 7 8 9 10 B forwards 6, 7, 8 1 2 3 4 5 6 7 8 9 10 Priority order : E C D B A 7
Cumulative Fraction of Node Pairs EXOR: 2 X OVERALL IMPROVEMENT 1. 0 0. 8 0. 6 0. 4 0. 2 Ex. OR Traditional 0 0 200 Median throughputs: 400 600 Throughput (Kbits/sec) 800 240 Kbits/sec for Ex. OR, 121 Kbits/sec for Traditional 8
SUMMARY Ex. OR opportunistically exploits wireless broadcast long distance transmission Avoids retransmission by allowing a low priority node to forward 9
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 10
THANK YOU Questions ? 11
- Slides: 11