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 Destination Path E A D E C A D C

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

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

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

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

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

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

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

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

Thank You Questions ?