Opportunistic Routing in Multihop Wireless Networks Sanjit Biswas

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Opportunistic Routing in Multi-hop Wireless Networks Sanjit Biswas and Robert Morris MIT CSAIL http:

Opportunistic Routing in Multi-hop Wireless Networks Sanjit Biswas and Robert Morris MIT CSAIL http: //pdos. csail. mit. edu/roofnet/

Ex. OR: a new approach to routing in multi-hop wireless networks 1 kilometer •

Ex. OR: a new approach to routing in multi-hop wireless networks 1 kilometer • Dense 802. 11 -based mesh • Goal is high-throughput and capacity

Initial approach: Traditional routing packet A packet B src dst C • Identify a

Initial approach: Traditional routing packet A packet B src dst C • Identify a route, forward over links • Abstract radio to look like a wired link

Radios aren’t wires A 1 2 33 4455 56 66 B src dst C

Radios aren’t wires A 1 2 33 4455 56 66 B src dst C • Every packet is broadcast • Reception is probabilistic

Ex. OR: exploiting probabilistic broadcast packet A packet B src dst C • Decide

Ex. OR: exploiting probabilistic broadcast packet A packet B src dst C • Decide who forwards after reception • Goal: only closest receiver should forward • Challenge: agree efficiently and avoid duplicate transmissions

Outline • • • Introduction Why Ex. OR might increase throughput Ex. OR protocol

Outline • • • Introduction Why Ex. OR might increase throughput Ex. OR protocol Measurements Related Work

Why Ex. OR might increase throughput (1) src N 1 N 2 N 3

Why Ex. OR might increase throughput (1) 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 Assumes probability falls off gradually with distance

Why Ex. OR might increase throughput (2) N 1 % 5 2 src 25%

Why Ex. OR might increase throughput (2) 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 • Assumes independent losses

Outline • • • Introduction Why Ex. OR might increase throughput Ex. OR protocol

Outline • • • Introduction Why Ex. OR might increase throughput Ex. OR protocol Measurements Related Work

Ex. OR batching tx: 100 9 src rx: 99 88 N 1 tx: 8

Ex. OR batching tx: 100 9 src rx: 99 88 N 1 tx: 8 rx: 85 57 N 2 tx: 57 -23 24 N 3 N 4 rx: 40 0 tx: 0 rx: 22 0 dst rx: 53 23 tx: 23 • Challenge: finding the closest node to have rx’d • Send batches of packets for efficiency • Node closest to the dst sends first – Other nodes listen, send remaining packets in turn • Repeat schedule until dst has whole batch

Reliable summaries tx: {2, 4, 10. . . 97, 98} summary: {1, 2, 6,

Reliable summaries tx: {2, 4, 10. . . 97, 98} summary: {1, 2, 6, . . . 97, 98, 99} N 2 N 4 src dst N 1 N 3 tx: {1, 6, 7. . . 91, 96, 99} summary: {1, 6, 7. . . 91, 96, 99} • Repeat summaries in every data packet • Cumulative: what all previous nodes rx’d • This is a gossip mechanism for summaries

Priority ordering N 2 N 4 src dst N 1 N 3 • Goal:

Priority ordering N 2 N 4 src dst N 1 N 3 • Goal: nodes “closest” to the destination send first • Sort by ETX metric to dst – Nodes periodically flood ETX “link state” measurements – Path ETX is weighted shortest path (Dijkstra’s algorithm) • Source sorts, includes list in Ex. OR header • Details in the paper

Using Ex. OR with TCP Client PC Node Proxy Web Server TCP Gateway Ex.

Using Ex. OR with TCP Client PC Node Proxy Web Server TCP Gateway Ex. OR Batches (not TCP) Web Proxy Ex. OR • Batching requires more packets than typical TCP window

Outline • • • Introduction Why Ex. OR might increase throughput Ex. OR protocol

Outline • • • Introduction Why Ex. OR might increase throughput Ex. OR protocol Measurements Related Work

Ex. OR Evaluation • Does Ex. OR increase throughput? • When/why does it work

Ex. OR Evaluation • Does Ex. OR increase throughput? • When/why does it work well?

65 Roofnet node pairs 1 kilometer

65 Roofnet node pairs 1 kilometer

Evaluation Details • • 65 Node pairs 1. 0 MByte file transfer 1 Mbit/s

Evaluation Details • • 65 Node pairs 1. 0 MByte file transfer 1 Mbit/s 802. 11 bit rate 1 KByte packets Traditional Routing 802. 11 unicast with linklevel retransmissions Hop-by-hop batching UDP, sending as MAC allows Ex. OR 802. 11 broadcasts 100 packet batch size

Cumulative Fraction of Node Pairs Ex. OR: 2 x overall improvement 1. 0 0.

Cumulative Fraction of Node Pairs Ex. OR: 2 x overall improvement 1. 0 0. 8 0. 6 0. 4 0. 2 Ex. OR Traditional 0 0 200 400 600 Throughput (Kbits/sec) • Median throughputs: 800 240 Kbits/sec for Ex. OR, 121 Kbits/sec for Traditional

25 Highest throughput pairs Throughput (Kbits/sec) 3 Traditional Hops 2. 3 x 1000 800

25 Highest throughput pairs Throughput (Kbits/sec) 3 Traditional Hops 2. 3 x 1000 800 2 Traditional Hops 1 Traditional Hop 1. 7 x 1. 14 x Ex. OR Traditional Routing 600 400 200 0 Node Pair

Throughput (Kbits/sec) 25 Lowest throughput pairs 1000 800 Ex. OR Traditional Routing 4 Traditional

Throughput (Kbits/sec) 25 Lowest throughput pairs 1000 800 Ex. OR Traditional Routing 4 Traditional Hops 3. 3 x 600 400 200 0 Node Pair Longer Routes

Ex. OR uses links in parallel Traditional Routing 3 forwarders 4 links Ex. OR

Ex. OR uses links in parallel Traditional Routing 3 forwarders 4 links Ex. OR 7 forwarders 18 links

Ex. OR moves packets farther Fraction of Transmissions 58% of Traditional Routing transmissions 0.

Ex. OR moves packets farther Fraction of Transmissions 58% of Traditional Routing transmissions 0. 6 Ex. OR Traditional Routing 0. 2 25% of Ex. OR transmissions 0. 1 0 0 100 200 300 400 500 600 700 800 900 Distance (meters) • Ex. OR average: 422 meters/transmission • Traditional Routing average: 205 meters/tx 1000

Future Work • Choosing the best 802. 11 bit-rate • Cooperation between simultaneous flows

Future Work • Choosing the best 802. 11 bit-rate • Cooperation between simultaneous flows • Coding/combining

Related work • Relay channels [Van der Meulen][Laneman+Wornell] • Flooding in meshes / sensor

Related work • Relay channels [Van der Meulen][Laneman+Wornell] • Flooding in meshes / sensor nets [Peng][Levis] • Multi-path routing [Ganesan][Haas] • Selection Diversity [Miu][Roy Chowdhury][Knightly][Zorzi]

Summary • Ex. OR achieves 2 x throughput improvement • Ex. OR implemented on

Summary • Ex. OR achieves 2 x throughput improvement • Ex. OR implemented on Roofnet • Exploits radio properties, instead of hiding them

Thanks! For more information and source code: http: //pdos. csail. mit. edu/roofnet/

Thanks! For more information and source code: http: //pdos. csail. mit. edu/roofnet/