Multicast with Network Coding in Application-Layer Overlay Networks

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Multicast with Network Coding in
Application-Layer Overlay Networks

• Y. Zhu, B. Li, and J. Guo
• University of Toronto
• Present by Cheng Huang
• 10.30.2003

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Network Coding
a or b?
How to send 2 pieces of data a and b to nodes Y
and Z simultaneously?
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Basics of Network Coding

• Conventional network nodes
• Route or duplicate traffic
• Network nodes with coding capability
• Perform operations on incoming traffics
• Basic operations ? encoding/decoding
• Linear operations ? Linear Network Coding
• Network coding can increase multicast capacity
• Network Information Flow, IEEE Trans.
  Information Theory, 46(4), 2000.

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Main Resultsof Network Coding

• If the capacity of any sink Ri C, then
  multicast rate of C is achievable, generally with
  network coding.

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Linear Network Coding

• Network nodes only perform LINEAR operations on
  incoming traffics
• Any node can retrieve information at a rate equal
  to its capacity
• Example
• Source multicasts 12 pieces of data
• Node of capacity 4 retrieves all data in 3
  seconds
• Node of capacity 3 in 4 seconds and of capacity 1
  in 12 seconds
• Sufficient condition network is acyclic.
• Linear Network Coding, IEEE Trans. Information
  Theory, 49(2), 2003.

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Preliminaries

• k-redundant multicast graph (DAG)
• Intermediate nodes have indegree k
• Receiver nodes have indegree k
• Nodes of indegree k have maxflow k

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Algorithm

• Rudimentary graph
• Relatively densely connected
• Rudimentary tree
• Multicast graph

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Build Rudimentary Graph/Tree

• Node maintains a list of neighbors and exchanges
  with other nodes
• Edge e has a weight w(e) (ß,?)
• Path p consists of edges
• Preferable path large bandwidth or low delay
• Add/remove edges dynamically
• ?-constraint
• Rudimentary tree
• Z. Wang and J. Crowcroft (1996)
• Distributed algorithm to find shortest widest
  paths

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Construct Multicast Graph

• Basics
• Leaf intermediate node
• All children are receiver nodes
• Saturation
• Intermediate node degree(v) ?
• Leaf intermediate node degree(v) ?-1

? 4
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Construct Multicast Graph

• Basics
• Leaf intermediate node
• All children are receiver nodes
• Saturation
• Intermediate node degree(v) ?
• Leaf intermediate node degree(v) ?-1

? 4
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Construct Multicast Graph

• First path pf
• Unsaturated neighbors exist
• Selects the best path among these neighbors
• All neighbors saturated
• Find (breath-first) k unsaturated nodes from
  source node s
• Select the best path

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Construct Multicast Graph

• Second path ps

S
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Construct Multicast Graph

• Second path ps

S
14
Construct Multicast Graph

• Second path ps

S
15
Construct Multicast Graph

• Second path ps

S
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Construct Multicast Graph

• Second path ps

S
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Linear Coding Multicast (LCM)

• Node with 1 input
• Simple forwarding
• Node with 2 inputs
• Receive X, Y from left, right inputs,
  respectively
• Compute C X Yv1 v2T
• Send C out along all outputs
• How to assign (v1, v2) to each node so as to
  guarantee reception?

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Linear Coding Multicast (LCM)

• Output of any node
• C X Yv1 v2T a bp qT, because X, Y are
  linear combinations of a and b.
• X a bpx qxT and Y a bpy qyT (same
  logic)

X
Y
v1, v2
a bp qT
C X Yv1 v2T
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Performance Evaluation

• INET topology generator (University of Michigan)
• Comparison
• DVMRP
• IP layer multicast protocol
• Narada
• Application layer multicast protocol

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Performance Evaluation
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Performance Evaluation
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Conclusions

• Propose a practical network coding scheme to
  exploit existing theoretical bounds
• Demonstrate throughput advantage of network
  coding, compared to existing application layer
  multicast