EXOR: OPPORTUNISTIC MULTI-HOP ROUTING FOR WIRELESS NETWORKS

Yin Lin

BY SANJIT BISWAS AND ROBERT MORRIS

AGENDA

Motivation

Design

Evaluation

Summary

TRADITIONAL WIRELESS ROUTING = WIRED ROUTING ExOR: multi-hop unicast wireless routing protocol Traditional: fixed routing sequence

Choose best sequence Always forward through that sequence

A

B D

C

E F

Dst NHB BC CD BE CF C

Dst NHA AB A… …F E

Dst NHA CB D… …F F

Routing TableDst: DestinationNH: Next hop

Every packet is broadcast Reception is probabilistic

RADIOS AREN’T WIRES

123456123 63 51 42345612 456 src

A B

dst

C

PROBLEM:UNNECESSARY RETRANSMISSION

A G

B

C

D

E

F

Buffer it !

PROBLEM: UNNECESSARY HOPS Only reach N1: result in retransmission Luckily reach N3: distance wasted

src dstN1 N2 N3 N4 N5

Choose

“best”

forwarder!

BASIC IDEA : ROUTE AFTER RECEPTION Buffer received packets Node closest to dst forward packet

A E

B

F

C

D

2.28

1.17

1.43

1.38

FORWARDER LIST: SHOULD I FORWARD? Distance metric: ETX to dst Updated dynamically Sort nodes w.r.t. distance

E > C > D > B > A

D

A E

B CETX=2.28

ETX=1.17

ETX=1.43

ETX=0

ETX=2.85

D

A E

B CETX=2.28

ETX=1.17

ETX=1.43

ETX=0

ETX=2.85

D

A E

B CETX=2.28

ETX=1.17

ETX=1.43

ETX=0

ETX=2.85

D

A E

B CETX=2.28

ETX=1.17

ETX=1.43

ETX=0

ETX=2.85

E > C > D > B > AE > C > D > B > AE > C > D > B > AE > C > D > B > A

D

A E

B CETX=2.28

ETX=1.17

ETX=1.43

ETX=0

ETX=2.85

DForwarder List

Ethernet Header… FL BM …

Data

ExOR operates on batch Highest-priority node that received packet

Ethernet Header… FL BM …

Data

E > C > D > B > A

BATCH MAP: WHO HAS RECEIVED WHAT?

A E

B C

D

2.28 1.17

1.43

0

2.85

C C D E C A A C C AE E A C B B C D C A

1 2 3

3-PACKET BATCH EXAMPLE

A E

B C

D

2.28 1.17

1.43

0

2.85

A A AA A EC A EE A EE D EE E E

A D AA D DA D EC D EE D EE E E

C A AC A CC A EE A EE D EE E EB A AB B AB B BB B EC B EE B EE D EE E E

A A EE A EE E E

11 21 2 3 11 3

2 3

31 31 2 3

21 2 3

1 2 3

E > C > D > B > A

EXOR: 2X OVERALL IMPROVEMENT 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

00 200 400 600 800Cu

mul

ativ

e Fr

actio

n of

Nod

e Pa

irs

ExORTraditional

25 HIGHEST THROUGHPUT PAIRS

Node Pair

Thro

ughp

ut (K

bits

/sec

)

0200

400

600

8001000 ExOR

Traditional Routing

1 Traditional Hop

1.14x

2 Traditional Hops1.7x

3 Traditional Hops2.3x

25 LOWEST THROUGHPUT PAIRS

Node Pair

4 Traditional Hops3.3x

Longer Routes

Thro

ughp

ut (K

bits

/sec

)

0200

400

600

8001000 ExOR

Traditional Routing

EXOR USES LINKS IN PARALLEL

Traditional Routing3 forwarders

4 links

ExOR7 forwarders

18 links

EXOR MOVES PACKETS FARTHER

ExOR average: 422 meters/transmission Traditional Routing average: 205 meters/tx

Frac

tion

of Tr

ansm

issio

ns

0

0.1

0.2

0.6 ExORTraditional Routing

0 100 200 300 400 500 600 700 800 900 1000Distance (meters)

25% of ExOR transmissions

58% of Traditional Routing transmissions

COST OF EXOR

Memory cost at each node

Overhead # nodes Choose a subnet

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 packetsSol: Choose “best” forwarder