Practical Localized Network Coding

1
Practical Localized Network Coding in Wireless
Mesh Networks
S. Omiwade, R. Zheng and C. Hua (SECON 2008)
Presented by Xiaoyuan GUO
2
Background and Motivation

• Wireless mesh network (WMN)
• Multi-hop network
• Mesh nodes self-organized, self-configured
• High throughput requirement
• Network coding
• What is it?
• Intermediate nodes code packets
• Increase throughput
• Increase information content of each transmission

3
Network Coding

• Famous butterfly example
• COPE
• One practical network coding in wireless network
• S. Katti, H. Rahul, W. Hu, D. Katabi, M. Medard,
  and J. Crowcroft. Xor in the air Practical
  wireless network coding. In Proc. of ACM SIGCOMM,
  2006
• XOR packets together

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Classical Routing in X-topology
A

• X-topology
• Flow1?4, 2?3
• transmission
  number 4

B
Classical routing
5
COPE Coding in X-topology
A
A
B
B


B
A
COPE coding
Coding Gain
6
Drawbacks of COPE Coding

• Drawbacks
• Coded packets are decoded in one hop
• Require associated remedy packets available one
  hop away ? coding opportunities limited

7
Classical Routing in Butterfly
A
B
Butterfly topology Flows 1?4, 2?3
Classical routing
transmission number 6
8
COPE Coding in Butterfly
A
B
COPE coding
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COPE Coding in Butterfly


COPE coding
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COPE Coding in Butterfly
A
B
COPE coding
Coding Gain
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If Forwarding Coded Packets
A
B
A
B
If forwarding coded packets
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If Forwarding Coded Packets


A
B
A
B
If forwarding coded packets
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Contribution

• BFLY
• Localized network coding protocol
• Allow forwarding of coded packets

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BFLY Scheme

• Where to code?
• Butterfly structure discovery
• Periodically determine butterflies
• Use HELLO messages
• Such message contains neighbor information
• When to code?
• Probabilistic model
• Characterize throughput with VS. without NC
• Adaptive coding decision

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BFLY Scheme(2)

• How to encode and decode?
• Encoding
• UM makes coding decision
• Use source routing information in packet header
• Coding
• XOR entire portion excluding MAC header
• Insert BFLY header after MAC header

Native Coded-no-forward Coded-forward
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BFLY Scheme(3)

• Decoding
• Packet pool stores packets overheard
• Check if is recipient
• XOR coded packets with the portion of the coded
  message not destined to it
• How to increase coding opportunities?
• Localized route optimizations
• Why ?
• Coding opportunities affected by route selection
  a lot
• Routing may not go through butterfly structures

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Non BFLY Routes
A
B
Non BFLY routes
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Non BFLY Routes(2)
A
B
Non BFLY routes
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Route Optimizations
UM
UL
UR
LM
LR
LL
Route optimizations
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Route Optimizations result
B
A
Route optimizations
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Hybrid Network Coding

• Hybrid network coding
• BFLY COPE(Flow 1?4, 2?3)

B
A
A
B


A
B
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Performance Evaluation

• Settings
• ns-2 simulator
• Metric
• Coding gain
• Throughput ratio throughput before coding /
  after coding

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Performance Evaluation(2)
Butterfly topology
6X6 grid-backbone random topology
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Conclusion

• BFLY
• Allow forwarding coded packets
• Complemented with COPE
• Topology dependent
• Future work
• Exploit other structures benefit of NC
• Develop distributed coding aware routing
  algorithm