Scalable Reliable Multicast Architecture Wenjun Zeng Computer Science Department University of Missouri-Columbia

2 Hybrid IP Multicast and ALM IP Multicast (NM)  Pros: bandwidth efficient, low delay, more stable  Cons: deployment issue, reliability/scalability issue ALM:  Pros: super scalability  Cons: less bandwidth efficient, potential longer delay, unstable (high node dynamic) Hybrid NM and ALM  Bridge between NM and ALM, e.g., hybrid tree construction  Adaptation  How about other issues (reliability, congestion control, etc)?

3 Push or Pull? IP Multicast:  Push ALM:  Tree-based approaches: push (e.g., End System Multicast) More efficient but has instability issue (and bandwidth underutilization)  Data-driven randomized approaches: pull (e.g., CoolStreaming) No tree, simple, better suited for addressing reliability but incur latency-overhead trade-off  Hybrid overlay: push and pull E.g. tree-bone based Hybrid NM and ALM?  IP multicast tree bone (push)? Address instability!  Overlay (tree or mesh) for other issues, e.g. scalable reliability?

4 Example: Reliability: IP Multicast Retransmission Potential problems:  Reliability? It is likely that retransmitted packets will go through same (probably congested) routes as the original packets, likely to experience congestion and loss too. (bottleneck problem) Retransmitted packets may deteriorate the congestion.  Scalability? In an IP multicast case, the retransmitted packets will be sent to all participants, wasting bandwidth. Although separate unicast session can be used, it increases the load of the original sender.

5 Path Diversity Overlay Retransmission To exploit path diversity, each client identifies a couple of “good” Retransmission Nodes in overlay. Overlay rtx network (pull) IP Multicast network (push) Sender Receiver Rtx node

6 Observations A pull-based (data-driven) overlay architecture seems to have more flexibility in exploiting path diversity  to reduce the retransmission delay and  to avoid severely congested (bottleneck) path.  to provide load balancing It may be built on top of the traditional IP multicast architecture, ALM architecture or some hybrid