oStream: Asynchronous Streaming Multicast in Application-Layer Overlay

Networks

Yi Cui, Baochun Li, and Klara Nahrstedt

IEEE Journal on Selected Areas in Communications, vol. 22 (1), Jan, 2004

Presented by Yuk

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Outline

Introduction Temporal Dependency Model Algorithms Analysis: Scalability and Efficiency Performance Evaluation Conclusion and Comment Q & A

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Introduction

Fundamental challenge of on-demand media distribution is unpredictability: Asynchrony Nonsequentiality Burstiness

Previous IP-Multicast-based solutions: Repeat the same media content on different channels over

time Clients are synchronized at the price of service delay

Proposed solution: Asynchronous Multicast

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Introduction

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Temporal Dependency Model

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Hierarchical Stream Merging (HSM)

D. Eager, M. Vernon, and J. Zahorjan, “Minimizing bandwidth requirements for on-demand data delivery,” IEEE Trans. Knowl. Data Eng., vol. 13, pp. 742–757, Sept.–Oct. 2001.

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Asynchronous Multicast (AM)

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Qualitative Comparisons

Asynchronous group Purely end-host based Sequentialized sources

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Problem Formulation

Given a MDG, the optimal solution for MDT, i.e., to minimize the overall transmission cost of media distribution, is to find the minimal spanning tree (MST) on MDG.

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Algorithms – MDT-Delete

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Algorithms – MDT-Insert

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Some Theorems

Y. Cui, B. Li, and K. Nahrstedt, “oStream: Asynchronous streaming multicast in application-layer overlay networks,” Dept. Comput. Sci., Univ. Illinois at Urbana-Champaign, Urbana, IL, Tech. Rep. UIUCDCS-2002-2289/UILU-ENG-2002-1733, 2003.

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Practical Issues

Content Discovery Service MDT algorithms require knowledge of all its predecessors

and successors Degree Constrained MDT

Constrain the outbound degree Modified MDT problem:

NP-complete!

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Practical Issues (cont’d)– Simplified Session Switching

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Scalability – Server Bandwidth Savings

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Scalability (HSM)

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Scalability (AM)

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Scalability – Plots

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Efficiency – Link Bandwidth Reduction

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Efficiency – Plots

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Performance Evaluation

A single CBR video distribution Video length, T = 1hr Simulation time = 12 hrs Topology:

k-ary tree Router-level (transit-stub) AS-level (power-law)

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Server bandwidth consumption

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Link cost

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Operation Complexity

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Conclusion

Concept of AM Take advantage of the strong buffering capabilities of

end hosts Scalability

Required server bandwidth < the theoretical lower bound of traditional IP-multicast

Efficiency The benefit overshadows the topological inefficiency

w.r.t link cost

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Comment

Simple solution provide good results (simply buffering at end-hosts)

In-depth analysis and Extensive evaluation The main drawback:

Outbound > inbound, not realistic

Q & A

Thank you.