ZIGZAG

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ZIGZAG

• A Peer-to-Peer Architecture for Media Streaming

By Duc A. Tran, Kien A. Hua and Tai T. Do Appear
on Journal On Selected Areas in Communications,
Special Issue on Advances in Service Overlay
Networks
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Agenda

1. Introduction
2. ZigZag
3. Administrative Organization
4. Multicast Tree
5. Client join/departure
6. Performance analysis
7. Conclusion

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Introduction

• Scenario
• A single live source serving many clients
• Solution
• Broadcasting by IP multicast
• Problem
• IP multicast not widely deployed

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Application-multicast

• What?
• Not all clients receive contents from the source
• Some clients (peers) help streaming data to other
  peers (P2P)

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Design Objectives

• An efficient P2P media streaming scheme should
• The end-to-end delay from source to client should
  be low
• The node degree should be small
• Adapt to free join/leave receivers
• Minimize the amount of control overhead

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ZigZag

• Administrative Organization
• Represents the logical relationships among peers
• Multicast tree
• Specify which peer data is received from
• Built based on C-rules which helps limits the
  degree of a peer (outbound links)
• Control protocol
• Specify the exchange of state information
• Policies adjusting the tree
• Maintaining the robustness of the tree

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Administrative Organization

• What?
• A multi-layer hierarchy of clusters
• Partition peers into clusters of size k, 3k
• Assign the role head and associate head to
  certain peers

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Administrative Organization
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Administrative Organization

• Properties
• H number of layers
• Bounded by log3kN, logkN1
• Max. number of members in a cluster3k
• To prevent cluster undersize in the case of a
  client leave after splitting

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Multicast tree

• What?
• Built based on the administrative organization
• C-rules specify the actual data flow from source
  to any peer
• Some nodes will stream data to more than 1 peers
• Assumption
• The uplink capacity of peer is enough for
  streaming contents to multiple peers

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Multicast Tree
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Multicast Tree

• Properties
• The workload is shared among clients
• Worst-case node degree is 6k-3
• The end-to-end delay is small
• Maximum height of the tree is 2logkN1
• Use of associate head for delivering media
• Number of outbound links is lower
• Bottleneck will less likely to appear in higher
  level

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Control protocol

• Goal
• Minimize the number of peers needed to be
  contacted
• Only exchange information with parent, children
  and clustermates
• Exchange as few states as possible
• Non-head peers
• Peer degree for non-head peers
• Cluster head
• Current end-to-end delay from server to the peer
• List of peers receiving contents from the peer
• List of associate head receiving contents from
  the peer
• Parent
• Reachable and Addable property

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Client join/departure

• Basic principle
• Maintain C-rule so that nice properties of degree
  and end-to-end delay is preserved
• Direct solution
• Reconstruct the administrative organization and
  multicast tree
• Costly in terms of exchange of state information
• Proposed join/departure algorithm
• Limits the number of nodes to connect during a
  join by O(k logkN)
• Limits the number of peers that need to reconnect
  by 6k-2

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Client join

• Procedure
• If X is a layer-0 associate-head
• Add P to the only cluster of X
• Make P a new child of X
• Else
• If Addable(X)
• Select a child Y s.t. Addable(Y) and D(Y)d(Y,P)
  is min
• Forward the join request to Y
• Else
• Select a child Y s.t. Reachable(Y) and
  D(Y)d(Y,P) is min
• Forward the join request to Y

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Client departure

• Tasks to do for client (X) departure
• The parent removes link to X
• The children of X needs a new parent
• Each layer-i cluster X belongs to needs a new
  head
• Layer-j cluster may require a new associate head

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Client departure

• If Xs highest level is at layer 0
• If X is not the associate head
• No extra work needed
• If X is the associate head
• The head of the cluster choose another member to
  take up the responsibilities

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Client departure

• If Xs highest level is j (non zero)
• It implies it is a head in layer 0,j-1
• A non-head peer (X) at layer 0 is randomly
  chosen to replace the head responsibility
• Head of children of X (Y) will choose a new
  parent for X that has a minimum degree

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Performance Analysis

• Comparison with another multicast tree based P2P
  media streaming scheme NICE
• Performance metrics
• Maximum degree The max. no of outbound links
• Join overhead The number of peers to visit
  until admission
• Failure overhead The number of reconnections
  required when a peer fail
• Control overhead The number of peers to
  exchange control information with
• Stretch Ratio between length of data path from
  server to a peer in the system to the shortest
  path
• Stress Number of times the same packet goes
  through a link

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Simulation study

• Simulation environment
• The network has 10,000 nodes
• k is set to 5
• Thus, 5 peers at min. and 15 peers at max. for
  each cluster
• Compare to NICE
• Initially, 3000 clients join sequentially into
  the system
• Then a loop of 2000 runs, a client will fail at a
  probability p while joining the system at 1-p

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Simulation Results I
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Simulation Results II
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Conclusion

• A P2P media streaming scheme
• The maximum degree and end-to-end delay is small
• A client join/leave algorithm is proposed aim at
  reducing the control overhead
• Simulation result suggests that 5000 peers can be
  supported at a max. degree of 15

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Q A

• Thank You