ExOR: Opportunistic Multi-hop routing for Wireless Networks

by;

Sanjit Biswas and Robert Morris, MIT

Presented by;

Mahanth K Gowda

Some pictures/graphs adopted from authors’ slides

1

OVERVIEW

Traditional Routing ExOR: key intuitions and ideas ExOR: Realization Evaluation

2

TRADITIONAL ROUTING

Links are abstracted as wires.

Edraw Trial Version

Edraw Trial Version

Edraw Trial Version

Edraw Trial Version

Edraw Trial Version

Edraw Trial Version

Edraw Trial Version

Edraw Trial Version

Edraw Trial Version

Edraw Trial Version

Edraw Trial Version

Edraw Trial Version

A

B C

D

E

Destination Path

E A D E

C A D C

3

LINK TRANSMISSION IS A BROADCAST Probability of reception decreases with distance However, there is always a chance that data travels longer

Edraw Trial Version

Edraw Trial Version

Edraw Trial Version

Edraw Trial Version

Edraw Trial Version

Edraw Trial Version

C

E

Edraw Trial Version

Edraw Trial Version

Edraw Trial Version

Edraw Trial Version

Edraw Trial Version

Edraw Trial Version

90%60%

10%

4

A

D

B

EXOR EXPLOITS BROADCAST

Best traditional route over 50% hops: 3(1/0.5) = 6 tx Throughput 1/# transmissions

ExOR exploits lucky long receptions: 4 transmissions Assumes probability falls off gradually with distance

src dstN1 N2 N3 N4

75%50%

N5

25%

5

EXOR EXPLOITS BROADCAST

Traditional routing: 1/0.25 + 1 = 5 tx

ExOR: 1/(1 – (1 – 0.25)4) + 1 = 2.5 transmissions Assumes independent losses

N1

src dst

N2

N3

N4

25%

25%

25%

25%

100%

100%

100%

100%

6

EXOR REALIZATION: BATCHING Packets are queued and sent in Batches A list of forwarders prioritized by their ETX values is included In the below topology ---> Source: A, Destination: E

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

7

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

8

BATCHING A batch map indicates highest priority node that

received each packet in the batch The map is updated and sent over along with data Gossip mechanism: updated batch map propagates from

high priority nodes to low priority nodes and ultimately to source

When the source receives the updated batch map, it restarts transmission if all packets haven’t got through

9

EVALUATION Comparison between traditional 802.11 is done with ExOR Throughput between 65 randomly selected node pairs

evaluated 1 mega-byte file exchanged Batch size is 100 Data rate 1 megabit/second

10

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 800C

um

ula

tive F

ract

ion o

f N

ode P

air

s

ExORTraditional

11

25 HIGHEST THROUGHPUT PAIRS

Node Pair

Thro

ughput

(Kbit

s/se

c)

0

200

400

600

800

1000 ExORTraditional Routing

1 Traditional Hop

1.14x

2 Traditional Hops1.7x

3 Traditional Hops2.3x

12

25 LOWEST THROUGHPUT PAIRS

Node Pair

4 Traditional Hops3.3x

Longer Routes

Thro

ughput

(Kbit

s/se

c)

0

200

400

600

800

1000 ExORTraditional Routing

13

EXOR MOVES PACKETS FARTHER

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

Fract

ion o

f Tra

nsm

issi

ons

0

0.1

0.2

0.6 ExORTraditional Routing

0 100 200 300 400 500 600 700 800 900 1000

Distance (meters)

25% of ExOR transmissions

58% of Traditional Routing transmissions

14

SUMMARY ExOR opportunistically exploits wireless broadcast

long distance transmission Avoids retransmission by allowing a low priority node to forward

15

ISSUES Periodic link state flooding Queuing for batching causes delay for interactive

applications Uses constant data rate for evaluation

16

THANK YOU Questions ?

17