1. 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

2. 2 Outline  Introduction  Temporal Dependency Model  Algorithms  Analysis: Scalability and Efficiency  Performance Evaluation  Conclusion and Comment  Q & A

3. 3 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

4. 4 Introduction

5. 5 Temporal Dependency Model

6. 6 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.

7. 7 Asynchronous Multicast (AM)

8. 8 Qualitative Comparisons  Asynchronous group  Purely end-host based  Sequentialized sources

9. 9 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.

10. 10 Algorithms – MDT-Delete

11. 11 Algorithms – MDT-Insert

12. 12 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.

13. 13 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!

14. 14 Practical Issues (cont’d)– Simplified Session Switching

15. 15 Scalability – Server Bandwidth Savings

16. 16 Scalability (HSM)

17. 17 Scalability (AM)

18. 18 Scalability – Plots

19. 19 Efficiency – Link Bandwidth Reduction

20. 20 Efficiency – Plots

21. 21 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)

22. 22 Server bandwidth consumption

23. 23 Link cost

24. 24

25. 25

26. 26 Operation Complexity

27. 27 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

28. 28 Comment  Simple solution provide good results (simply buffering at end-hosts)  In-depth analysis and Extensive evaluation  The main drawback: Outbound > inbound, not realistic

29. Q & A Thank you.