exor: opportunistic multi- hop routing for wireless networks by; sanjit biswas and robert morris,...
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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
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OVERVIEW
Traditional Routing ExOR: key intuitions and ideas ExOR: Realization Evaluation
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TRADITIONAL ROUTING
Links are abstracted as wires.
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A
B C
D
E
Destination Path
E A D E
C A D C
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LINK TRANSMISSION IS A BROADCAST Probability of reception decreases with distance However, there is always a chance that data travels longer
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C
E
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90%60%
10%
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A
D
B
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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%
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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%
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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
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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
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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
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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
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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
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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
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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
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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
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SUMMARY ExOR opportunistically exploits wireless broadcast
long distance transmission Avoids retransmission by allowing a low priority node to forward
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ISSUES Periodic link state flooding Queuing for batching causes delay for interactive
applications Uses constant data rate for evaluation
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THANK YOU Questions ?
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