opportunistic routing in multi-hop wireless networksbiswas/exor-sigcomm.pdf · opportunistic...
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![Page 1: Opportunistic Routing in Multi-hop Wireless Networksbiswas/exor-sigcomm.pdf · Opportunistic Routing in Multi-hop Wireless Networks Sanjit Biswas and Robert Morris MIT CSAIL ... (Dijkstra™s](https://reader033.vdocuments.net/reader033/viewer/2022042908/5f37c43e4da5c84b564be69c/html5/thumbnails/1.jpg)
Opportunistic Routing in Multi-hop Wireless Networks
Sanjit Biswas and Robert MorrisMIT CSAIL
http://pdos.csail.mit.edu/roofnet/
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ExOR: a new approach to routing in multi-hop wireless networks
• Dense 802.11-based mesh
• Goal is high-throughput and capacity
1 kilometer
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packet
packet
packet
Initial approach: Traditional routing
• Identify a route, forward over links
• Abstract radio to look like a wired link
srcsrcsrcsrc
AAAA BBBB
dstdstdstdst
CCCC
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Radios aren’t wires
• Every packet is broadcast
• Reception is probabilistic
1 2 3 4 5 61 2 3 63 51 42 3 4 561 2 4 5 6 srcsrcsrcsrc
AAAA BBBB
dstdstdstdst
CCCC
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packet
packetpacketpacketpacketpacket
ExOR: exploiting probabilistic broadcast
srcsrcsrcsrc
AAAA BBBB
dstdstdstdst
CCCC
packetpacketpacket
• Decide who forwards after reception• Goal: only closest receiver should forward• Challenge: agree efficiently and avoid duplicate transmissions
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Outline
• Introduction
• Why ExOR might increase throughput
• ExOR protocol
• Measurements
• Related Work
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Why ExOR might increase throughput (1)
• 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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Why ExOR might increase throughput (2)
• 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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Outline
• Introduction
• Why ExOR might increase throughput
• ExOR protocol
• Measurements
• Related Work
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ExOR batching
• 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
src
N3
dst
N4
tx: 23
tx: 57 -23≅ 24
tx: ≅ 8
tx: 100
rx: 23
rx: 57
rx: 88
rx: 0
rx: 0tx: 0
tx: ≅ 9
rx: 53
rx: 85
rx: 99
rx: 40
rx: 22
N1
N2
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Reliable summaries
• Repeat summaries in every data packet
• Cumulative: what all previous nodes rx’d
• This is a gossip mechanism for summaries
src
N1
N2
N3
dst
N4
tx: {1, 6, 7 ... 91, 96, 99}
tx: {2, 4, 10 ... 97, 98}summary: {1,2,6, ... 97, 98, 99}
summary: {1, 6, 7 ... 91, 96, 99}
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Priority ordering
• 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 ExOR header• Details in the paper
src
N1
N2
N3
dst
N4
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Using ExOR with TCP
Node
Proxy
ExORExORExORExOR
Gateway
Web Proxy
Client PC Web ServerTCPTCPTCPTCP TCPTCPTCPTCP
ExORExORExORExOR Batches (not TCP)Batches (not TCP)Batches (not TCP)Batches (not TCP)
• Batching requires more packets than typical TCP window
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Outline
• Introduction
• Why ExOR might increase throughput
• ExOR protocol
• Measurements
• Related Work
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ExOR Evaluation
• Does ExOR increase throughput?
• When/why does it work well?
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65 Roofnet node pairs
1 kilometer
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Evaluation Details
• 65 Node pairs
• 1.0MByte file transfer
• 1 Mbit/s 802.11 bit rate
• 1 KByte packets
802.11 broadcasts
100 packet batch size
802.11 unicast with link-level retransmissions
Hop-by-hop batching
UDP, sending as MAC allows
ExORTraditional Routing
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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
00 200 400 600 800
Cu
mu
lati
ve F
ract
ion
of N
od
e Pa
irs
ExORTraditional
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25 Highest throughput pairs
Node Pair
Thro
ug
hp
ut
(Kb
its/
sec)
0
200
400
600
800
1000 ExOR
Traditional Routing
1 Traditional Hop1 Traditional Hop1 Traditional Hop1 Traditional Hop1.14x1.14x1.14x1.14x
2 Traditional Hops2 Traditional Hops2 Traditional Hops2 Traditional Hops1.7x1.7x1.7x1.7x
3 Traditional Hops3 Traditional Hops3 Traditional Hops3 Traditional Hops2.3x2.3x2.3x2.3x
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25 Lowest throughput pairs
Node Pair
4 Traditional Hops4 Traditional Hops4 Traditional Hops4 Traditional Hops3.3x3.3x3.3x3.3x
Longer RoutesLonger RoutesLonger RoutesLonger Routes
Thro
ug
hp
ut
(Kb
its/
sec)
0
200
400
600
800
1000 ExOR
Traditional Routing
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ExOR uses links in parallel
Traditional Routing3 forwarders
4 links
ExOR7 forwarders
18 links
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ExOR moves packets farther
• ExOR average: 422 meters/transmission• Traditional Routing average: 205 meters/tx
Frac
tio
n o
f Tra
nsm
issi
on
s
0
0.1
0.2
0.6 ExOR
Traditional Routing
0 100 200 300 400 500 600 700 800 900 1000
Distance (meters)
25% of 25% of 25% of 25% of ExORExORExORExOR transmissionstransmissionstransmissionstransmissions
58% of Traditional Routing transmissions58% of Traditional Routing transmissions58% of Traditional Routing transmissions58% of Traditional Routing transmissions
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Future Work
• Choosing the best 802.11 bit-rate
• Cooperation between simultaneous flows
• Coding/combining
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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]
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Summary
• ExOR achieves 2x throughput improvement
• ExOR implemented on Roofnet
• Exploits radio properties, instead of hiding them
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Thanks!
For more information and source code:http://pdos.csail.mit.edu/roofnet/