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