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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.
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