A Comparison of Application-Level and Router-Assisted Hierarchical Schemes for Reliable Multicast

1. Part 2 of the paper A Comparison of Application-Level and Router-Assisted Hierarchical Schemes for Reliable Multicast Pavlin Radoslavov, Christos Papadopoulos, Ramesh Govindan, and Deborah Estrin CSE 770x Fall 2004 Qian Wan following Jing Lu’s Part 1 presentation Thursday, October 21, 2004

2. Application-level hierarchy vs. Router Assisted hierarchy • SIMULATION RESULTS A. Simulation Setup B. Simulation Results C. Simulation Results Sensitivity • RELATED WORK • CONCLUSION

3. A. Simulation Setup Diameter: average shortest path between two points in a network. Observation: Average Links/Nodes values are bigger than 2.

4. A. Simulation Setup details • Assume a single-source multicast distribution tree with the source at the root of the tree. • Receiver placement sensitivity: random, extreme affinity, extreme disaffinity, extreme clustering(extreme disaffinity for cluster centers, and affinity for receivers belonging to the same center). • For ALH, the maximum number of children a parent may have at each level is based on hierarchy creation parameter. • Two Application-Level Hierarchy creation approaches: one uses the inter-receiver distance heuristics as in Section II-A, and the other randomly select parents per level and each child chooses randomly its parent. • Results averaged across all simulations with 95% confidence interval included. • Data recovery latency, exposure, data overhead, and control overhead for a single link loss are measured.

5. B. RAH and ALH Simulation Results • RAH latency decreases when the number of receivers increases, because probability increase that there is a topologically closer replier that has received the data. • The ALH-heuristic has similar result as RAH because similar construction of the hierarchy. • The ALH-random perform worse as the number of receivers increase because of the parent is further off the shortest path. • (Observation)The near linear recovery latency of RAH and ALH-heuristic on Figure 11. match the tree hierarchy. Data recovery time doesn’t change, but the RTT increase linearly as the receivers fraction increase exponentially. • RAH exposure is always zero for a single link loss, but not necessary true for multiple link losses. Because for latter case, more than one repliers can exist for the same data. • ALH-random outperforms ALH-heuristic in Fig. 12 most of the time. Since in the simulation, only when at least 50% of the children did not receive the data, the parents will use multicast to send the data and generate exposure. ALH-heuristic has same-parent children closer to each other topologically. • (Observation)The sacrifice of the exposure measure by its definition of ALH-heuristic comparing to ALH-random actually contributed to the Recovery latency measure.

6. B. RAH and ALH Simulation Results • Results similar for RAH and ALH-heuristic. • Data and the control overhead seemed to be almost identical. For RAH, control overhead is about 5% to 10% higher than data overhead because extra control traffic only over the path between a router-turning point and its replier. • ALH-random’s overhead increase a lot faster than the other two hierarchies. • (Observance) RAH overheads decrease as the receivers fraction increase, and the ALH-heuristic’s overhead actually increase slowly as the receivers fraction increases. Because more receivers for RAH, more closer the same-parent children, and the more efficient and effective use of multicast.

7. C. Simulation Results Sensitivity1) ALH Hierarchy Organization Sensitivity • Three different hierarchy creation parameter valued 0.02, 0.1 and 0.4 are used for comparison • For latency, they are almost the same. • For overheads( only data overhead figure is put here because the control overhead is similar), the higher the number of parents a child has to choose from, the smaller overhead. • The exposure increases when the number of parents are bigger.

8. C. Simulation Results Sensitivity2) Network Topology Sensitivity • For the smaller topologies the smallest fraction was 0.0002 or 0.001. • For mesh topology, since the multicast distribution tree is composed of long, skinny branches. So ALH-heuristic parent selection will have a bigger impact in efficiency. • (Observation) For mesh, even the recovery latency of RAH is not appearing as a straight line due to the variance of recovery time.

9. C. Simulation Results Sensitivity 3) Receiver Placement Sensitivity RAH random placement is compared with ALH’s three different receiver placements on average data overhead. Only in the case of extreme clustering placement, there were four times mor more order difference. 4) Link Loss Model Sensitivity Intenet core topology with lossy inter-AS links are simulated among the original three hierarchies. The loss link does not affect the metrics comparing to earlier same loss assumptions.

10. RELATED WORK • Previous comparison Limited scope, topology and analysis • Other ALH or RAH schemes ALH: SRM, RMTP, TMTP, LGMP, TRAM RAH:AIM, AER, OTERS, PGM

11. Conclusion • Surprise • ALH scheme can perform reasonably well compared to RAH schemes presumed to be a lot better in terms of average latency in recovery of loss data. • Explanation • One possible is the Congruence between a well-constructed application level hierarchy and a router-assisted hierarchy. Thanks goes to Jing, Shobana, Phillip and Dr. Crowley for the discussion.