Analysis of Different Models for Optimal P2P Content Distribution Network

1
Analysis of Different Models for Optimal P2P
Content Distribution Network

• Subhamoy Ghosh
• sghosh_at_cc.hut.fi

2
Agenda

• Introduction
• The Next Step Problem
• Analysis of the Next Step Problem
• Chunk based CDS
• Analysis of Chunk based CDS
• Discussion Other Models Merits/Demerits
• Conclusion
• References

3
Introduction

• P2P systems
• designed to share computer resources by direct
  exchange, w/o any central authority.
• Application overlay network on top of
  conventional protocols.
• Fault-tolerant, reliable, scalable massive
  content distribution system.
• Only possible option to manage flash crowds.
• Content Distribution
• Has been the main focus of P2P research.
• Responsibility is spread amongst all
  downloader(s).
• Clients contribute resources of the system as a
  function of their upload capacities.

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Introduction

• Performance perceived by user
• Time taken to fulfill request for a particular
  file.
• Download time as the dominant factor.
• Generic trend for file dissemination
• Partition the file to N equal parts.
• User can download either from server or from a
  peer who has the requested chunk.

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The Next-Step Problem

• Source node s divides a file into k equal parts
  to disseminate amongst n peers.
• Assumptions
• Communications are synchronous.
• Ignores link latencies
• File reaches the destination in the same round,
  as the departure.
• Graph G (V,E) with V n, WVxV---gtR
• File is divided into k-parts such that
• Next Step problem calculates the actions of
  each node, represented by Action Matrix

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The Next-Step Problem

• Max-Product Belief Propagation Network
• Calculates the MAP estimates of the nodes.
• Provides a vector of node beliefs and selects the
  action with the highest probability.
• Algorithm converges, when a node receives
  duplicate packets for two consecutive rounds from
  all nodes.
• With the Next-Step Solution and a pre-defined
  Cost function, the problem reduces to

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Analysis of Next-Step Problem
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Optimizing Chunk-Based CDS

• Provide a network model independent lower bound
  on the time taken for file dissemination in a
  chunk based CDS.
• Makespan Time taken to disseminate M parts of a
  file to I peers in a centralized scenario.
• Assumptions
• Peers upload only 1 file in each round.
• Upload capacities are considered to be equal.
• Lower bound on minimum number of rounds for any
  CDS is
• Delay Stretch Captures the delay in download of
  a peer, for sharing chunks with other peers.
  Maximum delaystretch is calculated as

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Analysis of Chunk based CDS

• Scatter plots of data with M 10 and M 50 8.
• 100 independent simulations with N 2, 4, 215.
• In each case of M 1 5, 8,10, 15, 20 ,50 fits
  a linear model.

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Discussion Other Models Merits/Demerits

• Maximize peer bandwidth utilization
• P2P is scalable since bandwidth increases with
  increase in participants.
• Models focus on i) peer selection strategy
  self-organization, ii) chunk selection strategy -
  duplication, iii) network degree choose
  in-degree/out-degree of client based on
  upload/download capacity.
• Uniform Workload Distribution
• Fairness in workload minimizes average download
  time.
• Incentive driven P2P Networks
• Minimizes download time subject to budget
  constraint.
• Network Coding based P2P CDS
• Improves delay in transmission time, and makes
  network more robust and adaptive.
• But almost all models suffer from the churning
  problem, and network coding models do not perform
  well, in case multiple nodes fail to reach every
  client.

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Conclusion

• Loopy BP algorithm -
• Approximate solution in case of cycled graphs,
• Currently the experiment is terminated after a
  user-defined threshold of operations.
• The authors in 1 consider to use gradient
  descent algorithm here instead, to overcome this
  fluctuation in local optimum.
• Pre-emptive operations in belief propagation -
• improve on the computational delay and the final
  response on the choice of nodes.
• The generic file dissemination approach -
• equal service capacity for all peers, and the
  model can be extended to consider the case of
  selfish peers.
• However it provides a model independent
  performance benchmark, that can be used to
  compare the dissemination times of different
  overlay networks.

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References

• Bickson Danny, Dolev Danny, Weiss Yales,
  Efficient Peer-to-Peer Content Distribution
  Network, School of Computer Sc. Engg, Hebrew
  University of Jerusalem.
• Zheng Xiaoying, Cho Chunglae, Xia Ye, Optimal
  Peer-to-Peer Techniques for Massive Content
  Distribution, IEEE INFOCOMM (2008).
• Felber Pascal, Biersack W. Ernst, Cooperative
  Content Distribution Scalability Through
  Self-Organization, LNCS 3460, pp 343-357 (2005).
• Li Jin, Chou A. Philip, Zhang Cha, MutualCast An
  Efficient Mechanism for Content Distribution in a
  P2P Network, ACM SIGCOMM Asia 04, Beijing, China
  (2004).
• Hamra Al Anwar, Felber A. Pascal, Design Choices
  for Content Distribution in P2P Networks, ACM
  SIGCOMM, Vol 35, pp 29-40 (2005).
• Tewari Saurabh, Kleinrock Leonard, On Fairness,
  Optimal Download Performance and Proportional
  Replication in P2P Networks, LNCS 3462, pp 709
  717, IFIP (2005).
• Adler Micah, Kumar Rakesh, Ross Keith, Rubenstein
  Dan, Suel Torston, Yao D. David, Optimal Peer
  Selection for P2P Downloading and Streaming, IEEE
  INFOCOMM, Vol. 3, pp 1538 1549 (2005).
• Kangasharju Jakko, Kangasharju Jussi, An Optimal
  basis for Efficient P2P Content Distribution
  Algorithms, 15th . Intl. Conf. on Computer
  Communications and Networks, Washington D.C.
  (2006).

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References

• Mudinger Jochen, Weber Richard, Weiss Gideon,
  Optimal Scheduling of Peer-to-Peer File
  Dissemination, Mathematical Performance Modeling
  and Analysis (MAMA) (2006).
• Loginova Oksana, Lu Haibin, Wang X. Henry,
  Peer-to-Peer Networks A Mechanism Design
  Approach, JEL Classification, Working Papers,
  Dept. of Economics, University of Missouri
  (2007).
• Androutsellis Theotokis Stephanos, Spinellis
  Diomedis, A Survey of Peer-to-Peer Content
  Distribution Technologies, ACM Computing Surveys,
  Vol. 36, pp 335 371, (2004).
• Small Tara, Li Baochun, Liang Ben, On Optimal
  Peer-to-Peer Topology Construction with Maximum
  Peer Bandwidth Contributions, Biennial Symposium
  on Communications, Kingston, Canada (2006).

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Thanks to all !