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Reviewer: Jing Lu, Qian Wan

CS770x. A Comparison of Application-Level and Router-Assisted Hierarchical Schemes for Reliable Multicast Pavlin Radoslavov Christos Papadopoulos Ramesh Govindan Deborah Estrin. Reviewer: Jing Lu, Qian Wan. Outline. Introduction ALH: RMTP RAH: LMS Metric Space Analysis Using k-ARY Trees

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Reviewer: Jing Lu, Qian Wan

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  1. CS770x A Comparison of Application-Level and Router-Assisted Hierarchical Schemes for Reliable MulticastPavlin RadoslavovChristos PapadopoulosRamesh GovindanDeborah Estrin Reviewer: Jing Lu, Qian Wan

  2. Outline • Introduction • ALH: RMTP • RAH: LMS • Metric Space • Analysis Using k-ARY Trees • Simulation Results • Conclusion

  3. IP Multicast • Send packet from a source to the members of a multicast group. • Class D IP addresses (250 million) • IGMP & MOSPF • Best-effort packet forwarding • Applications: multimedia, teleconferencing, distributed computing, etc.

  4. Reliable IP Multicast • Scalability issues: • Implosion: redundant messages triggered by packet loss • Exposure: redundant retransmissions to receivers who haven't experienced loss • Long recovery latency • Hierarchical data recovery schemes: • ALH (Application-Level Hierarchical): End systems assist in hierarchy creation and maintainance. • RMTP • RAH (Router-Assisted Hierarchical): Routers assistance • LMS

  5. RMTP Data Recovery • Static hierarchical scheme • Designated Receivers (DRs) are chosen statically • A receiver dynamically chooses a closest DR as its Ack and retransmission processor • A DR collects Nack from its local group members and retransmits packet within the group using unicast/multicast • A DR emits its own Nack to its parent DR in the upper hierarchy • Sender deals with Nacks from DRs at the top level hierarchy

  6. sender R1 Rx7 Rx1 Rx8 R2 Rx2 R3 R4 Rx3 Rx4 Rx5 Rx6 ALH Data Recovery Optimal Hierarchy

  7. sender R1 Rx7 Rx1 Rx8 R2 Rx2 R3 R4 Rx3 Rx4 Rx5 Rx6 ALH Data Recovery Optimal Hierarchy

  8. ALH Data Recovery Sub-optimal Hierarchy sender R1 Rx7 Rx1 Rx8 R2 Rx2 R3 R4 Rx3 Rx4 Rx5 Rx6

  9. ALH Data Recovery Sub-optimal Hierarchy sender R1 Rx7 Rx1 Rx8 R2 Rx2 R3 R4 Rx3 Rx4 Rx5 Rx6

  10. Heuristic Dynamic Hierarchy Creation in ALH • Each receiver obtains distance info to each other • Dynamically create the hierarchy from bottom-up: • Initially all receivers are eligible to become parents • A fraction (fracpc) of receivers with the smallest sum of distances becomes parents. • Receivers that are not elected choose the closest parent as its parent. • Repeat the selection process among receivers chosen from the previous iteration until the number of receivers left <= 1/fracpc, so their parent is the sender itself.

  11. LMS Data Recovery • LMS extends router forwarding • Enhance routers to: • Replier selection • Forward Nacks to replier and discover root of loss subtree • Perform DMCAST

  12. LMS Replier Selection sender • Router state per-source tree: • Upstream link • List of downstream links • Replier link id R1 Rx7 Rx1 Rx8 R2 Rx2 R3 R4 Rx3 Rx4 Rx5 Rx6

  13. LMS Nack Forwarding LMS router handles Nacks [1]

  14. LMS DMCAST • DMCAST: • Replier encapsulates a multicast packet into a unicast packet and sends to the turning-point router • LMS router decapsulates and multicasts it on the specified link interfaces

  15. LMS Enhanced Two-Step DMCAST • Nack from a downstream replier specifies reply should be unicast back to it rather than to its turning point • Replier then performs DMCAST when necessary

  16. Summary of ALH and RAH RAH is finer-grained with many more “internal nodes” RAH is more congruent to the underlying multicast tree RAH doesn’t have explicit group concept, so it is easily adaptive to membership change; membership maintenance cost is minimal

  17. Metric Space • Data Recovery Latency • Receiver Exposure • Data Traffic Overhead • Control Traffic Overhead

  18. sender R1 Rx7 Rx1 Rx8 R2 Rx2 R3 R4 Rx3 Rx4 Rx5 Rx6 Data Recovery Latency

  19. sender R1 Rx7 Rx1 Rx8 R2 Rx2 R3 R4 Rx3 Rx4 Rx5 Rx6 Receiver Exposure

  20. sender R1 Rx7 Rx1 Rx8 R2 Rx2 R3 R4 Rx3 Rx4 Rx5 Rx6 Data Traffic Overhead

  21. sender R1 Rx7 Rx1 Rx8 R2 Rx2 R3 R4 Rx3 Rx4 Rx5 Rx6 Control Traffic Overhead

  22. Analysis using k-ARY Tree • Purpose: • Gain initial understanding of the scalability of the ALH and RAH schemes • Parameters: • k, L • q: fraction of leaf nodes that are receivers is 1/kq-1 • Assumptions: • Each parent (ALH) has k-1 children. • Single link loss and average per link-loss across all links

  23. Analysis using k-ARY Tree ALH RAH

  24. Control Overhead Analysis L = 10

  25. Data Overhead Analysis L = 10 • RAH is slightly better than ALH • In some cases, RAH replier multicast data to all receivers within a subtree • ALH has to perform multiple multicasts within local groups

  26. Data Recovery Latency Analysis

  27. Data Recovery Latency Analysis L = 10

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