Reliability Gain of Network Coding - INFOCOM 08

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Reliability Gain of Network Coding- INFOCOM 08

• University of Massachusetts

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Motivation

• NC improves Network Reliability by reducing the
  of retransmission in lossy network
• Capacity gain of NC extensively studied
• Exact reliability gain of NC is not well known
• Goal Quantify the reliability gain of NC

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Contribution

• Define the expected number of transmissions per
  packet

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Network Topology

• Topology Tree based reliable multicast network

• s source
• p probability of pkt loss
• k each node has k children

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Four error control techniques

• End-to-End ARQ
• Source Root of the tree retransmits each pkt
  until it is correctly received by all the
  receivers.
• Others only forward pkts
• End-to-End FEC rateless coding
• Same as End-to-End ARQ
• Src Block coding mechanism is used to create
  coded pkts

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Four error control techniques

• Link-by-Link ARQ
• Each node is responsible for each pkt to its
  children
• Parents retransmit pkts until they are delivered
  to its children
• Link-by-Link FEC NC
• Each node performs encoding and forwards pkts.

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Analysis

• Quantifies..
• Probability distribution of the number of
  transmissions
• Expected number of transmissions

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End-to-End Error Control

• Probability distribution of the number of
  transmissions
• Nr the total of transmissions of a pkt from
  the root of a subtree of height r

- P of j pkts transmitted out of i -
Fr(i) P Nr lt i probability of Nr lt i, r
height
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End-to-End Error Control

• Fo(i) r0, leaf node
• 1) End-to-End ARQ
• 2) End-to-End FEC need at least B pkt for
  decoding..

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End-to-End Error Control

• Expected of transmissions
• At root, height h
• 1) End-to-End ARQ
• Sending a pkt again because the pkt is not
  delivered, so (1 F(h))
• 2) End-to-End FEC
• Need 1 retransmission for B pkts

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End-to-End Error Control

• Xr of transmissions in a subtree per each pkt
  at the root
• The expected of transmissions per pkt in the
  entire tree
• the expected of transmissions at root
• the total of transmission for the pkt

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Link-by-Link Error Control

• Link-by-Link relationship only between a parent
  and its children

• Fr(i) P Nr lt i probability of Nr lt I
• Link-by-Link ARQ
• NC

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Link-by-Link Error Control

• Expected of transmissions at root
• 1) Link-by-Link ARQ
• 2) NC

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Link-by-Link Error Control

• Total of transmissions in the entire tree
• of nodes at height r
• Each node has K children

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Numerical Results

• Expected of transmissions at root w/ different
  p
• B 16, h2

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Numerical Results

• Expected of transmissions in tree w/ different
  p
• B 16, h2

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Numerical Results

• Effect of Block size

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Conclusion

• Quantified the reliability benefit of NC for tree
  based multicasting
• Analyzed the expected number of transmissions at
  source and within tree