Opportunistic Routing Is Missing Its Opportunities!

7/28/2019 Opportunistic Routing Is Missing Its Opportunities!

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Opportunistic Routing Is Missing

Its Opportunities!

Sachin Katti & Dina Katabi
http://web.mit.edu/graphicidentity/symbols/logo.html


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Opportunistic Routing

R1 R2 R3 R4 R5 DS


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R1 R2 R3 R4 R5 DS

Opportunistic Routing leverages opportunistic receptions


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R1 R2 R3 R4 R5 DS

Opportunistic Routing leverages opportunistic receptions


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R1 R2 R3 R4 R5 DS

But Opportunistic Routing is missing the bulk

of its opportunities


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But Opportunistic Routing is missing the bulk

of its opportunities

R1 R2 R3 R4 R5 DS

Loss Loss Loss

Longer jumps by partially correct packets, but dropped

due to packet abstraction


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R1 R2 R3 R4 R5 DS

Leverage longer opportunistic receptions of partially

correct packets!

Opportunistic Routing capitalizes on Partial

Packet Forwarding


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Opportunistic Routing capitalizes on Partial

Packet Forwarding

R1 R2 R3 R4 R5 DS

Leverage longer opportunistic receptions of partially

correct packets!


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Partial Packet Forwarding capitalizes on


R1

R2

DS


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Partial Packet Forwarding capitalizes on


R1

R2

DS

Spatial DiversityRouters are unlikely to have error in the samebyte positions


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Opportunistic

Routing

Partial Packet

Forwarding

Synergy


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Contributions

Byte Level Network Coding Harvests synergy

Provides adaptive error correction

Provides the right abstraction for the PHY

and network layers to maximize throughput


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d k hi h b


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How do routers knows which bytes

are correct?PHY knows how confident it is for every byte it decodes

11b 12b 13b

High

confidence

Clean Byte Dirty Byte

Forward clean bytes, throw away the dirty byte

Low

confidence


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Who should forward what?

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R2

D

Overlap in received correct bytes

Routers forward duplicates


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How to prevent duplicate transmissions?

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R2

DS

Source transmits packets in batches

P1

P2


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R1

R2

DS

Routers use byte level network coding



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R1

R2

D2111

1111

b

b

11

21b

11b

11

2121

1121

b

b

21

21b

11b

21

Routers create random combinations of clean bytes



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R1

R2

D2111

1111

b

b

11

11

Routers create random combinations of clean bytes

kb2

kb1

k

k

b

b

211

111

21

0k

b2

kb1

kb1212121

1121

b

b



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R1

R2

D

Routers transmit coded packets to the destination

2111

1111

b

b

k

k

b

b

211

111

k

b1212121

1121

b

b


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R1

R2

D

Destination decodes by solving simple linear equatio

2111

1111

b

b

k

k

b

b

211

111

kb1212121

1121

b

b

2111,bb

Solve 2

equations


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R1

R2

D


2111

1111

b

b

k

k

b

b

211

111

kb1212121

1121

b

b

kkbb 21 ,

Solve 2

equations


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R1

R2

D


2111

1111

b

b

k

k

b

b

211

111

kb1212121

1121

b

b

kkbb 21 ,

Solve 2

equations

Byte Level Network Coding prevents spurious

transmissions without any co-ordination or scheduling


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How to represent the code?

How to efficiently tell the destination the code of each bit?

Use run length encoding

Original Packets Coded Packet


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0



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0



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Run length encoding to represent contiguous runs of

coded bits with the same code


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Clean bytes can be incorrect

Can be incorrect with

low probabilityHow does the destination recover from

these errors?

11b 12b 13b

Clean Byte Dirty Byte

High

confidence

Low

confidence


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How to recover from errors?

Symbol Level Network Coding

Adaptive Error-Correcting Code

Ifkbytes are combined to produce n (>k) randomcombinations, destination can correct (n-k)/2 byte errors

Routers can keep transmitting until destination decodescorrectlyRateless error-correcting code


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To conclude

MIXIT: Harvests synergy between opportunistic routing

and partial packet forwarding

Provides the right abstraction for the PHY andnetwork layers to maximize throughput

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Opportunistic Routing Is Missing Its Opportunities!