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Communication Part IV Multicast Communication*

Communication Part IV Multicast Communication*. *Referred to slides by Manhyung Han at Kyung Hee University and Hitesh Ballani at Cornell University. Unicast, Broadcast versus Multicast. Key: Unicast transfer Broadcast transfer Multicast transfer. Unicast One-to-one

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Communication Part IV Multicast Communication*

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  1. Communication Part IV Multicast Communication* *Referred to slides by Manhyung Han at Kyung Hee University and Hitesh Ballani at Cornell University

  2. Unicast, Broadcast versus Multicast Key: Unicast transfer Broadcast transfer Multicast transfer • Unicast • One-to-one • Destination – unique receiver host address • Broadcast • One-to-all • Destination – address of network • Multicast • One-to-many • Multicast group must be identified • Destination – address of group

  3. Multicast application examples • Financial services • Delivery of news, stock quotes, financial indices, etc • Remote conferencing/e-learning • Streaming audio and video to many participants (clients, students) • Interactive communication between participants • Data distribution • e.g., distribute experimental data from Large Hadron Collider (LHC) at CERN lab to interested physicists around the world

  4. Routers with multicast support IP multicast Gatech Stanford CMU Berkeley • Highly efficient bandwidth usage • Key Architectural Decision: Add support for multicast in IP layer

  5. So what is the big issue … more than 20 years since proposal, but no wide area IP multicast deployment • Scalability (with number of groups) -- Routers maintain per-group state • IP Multicast: best-effort multi-point delivery service -- Providing higher level features such as reliability, congestion control, flow control, and security has shown to be more difficult than in the unicast case Can we achieve efficient multi-point delivery without IP-layer support?

  6. Application layer multicast Stan1 Gatech Stanford Stan2 CMU Berk1 Berkeley Berk2 Overlay Tree Stan1 Gatech Stan2 CMU Berk1 Berk2

  7. Pros and Cons • Scalability • Routers do not maintain per-group state • End systems do, but they participate in very few groups • Potentially simplify support for higher level functionality • Leverage computation and storage of end systems • Leverage solutions for unicast congestion, error and flow control • Efficiency concerns • redundant traffic on physical links • increase in latency due to end-systems

  8. System structure The overlay comprises of : • A central source (may be replicated for fault tolerance) • A number of overcast nodes (standard PCs with lot’s of storage) - organized into a distribution tree rooted at the source - bandwidth efficient trees • Final Consumers – members of the multicast group - allows unmodified HTTP clients to join

  9. R 1 R R R 1 2 2 1 2 Bandwidth Efficient Overlay Trees 1 100 Mb/s 10 Mb/s 100 Mb/s 2

  10. R R 1 2 3 The node addition algorithm 5 10 10 3 8 1 7 5 2 Physical network substrate Overcast distribution tree

  11. The client side – how to join a multicast group • Clients join a multicast group through a typical HTTP GET request • Root determines where to connect the client to the multicast tree using • Status of overcast nodes • Location of client • Root selects “best” server and redirects the client to that server

  12. R1 R2 R3 1 3 2 4 5 6 Client Joins Key: Content query (multicast join) Query redirect Content delivery

  13. Application level multicasting A survey on ALM

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