1. An Evaluation of Scalable Application-level Multicast Using Peer-to-peer Overlays Miguel Castro, Michael B. Jones, Anne-Marie Kermarrec, Antony Rowstron, Marvin Theimer, Helen Wang and Alec Wolman Presented by Ricky Taing Authors:

2. Outline Motivations and Goals of Paper Overview of Overlay Networks Overview of p2p Multicast Implementations Experimental Methodology Results Conclusions

3. Motivations and Goals Lack of IP multicast adoption has increased development in app-layer multicast Different versions available to use, with different implementations Determine the best application layer multicast system from different overlays and implementations

4. P2P Overlay Networks Two main approaches Divide and conquer in a ring Pastry, Chord, Tapestry Cartesian hyper-space CAN

5. Pastry Routes by nodeID Circular 128-bit namespace Get to destination in log 2^b N time b is configurable, usually b=4 (hex) Each node maintains a leaf set pointers to l nodes closest to it

6. CAN Route in multiple dimensions Each node is assigned a particular zone Many optimizations Neighbor with lowest network delay Multiple nodes per zone Uniform partitioning Landmark based placement

7. Set of well known landmarks ordered by distance placed into evenly sized bins Nodes with same landmark ordering end up close to each other

8. P2P Multicast Implementations Flooding Unique overlay-per-group Only nodes in group get group messages CAN broadcast to neighbors, use seq numbers Pastry Forwards copies to all nodes in routing table Notes levels, sends to greater levels

9. Tree-based Scribe Reverse path forwarding to create one tree per group Joins route messages to groupId (root) Registers if a node along the route is in the tree

10. Evaluation Simulation Five different topologies 5050 routers, 80000 end nodes Two sets of experiments Single multicast group, all nodes are members Large number of groups (1500)

11. Criteria Relative Delay Penalty RMD: Ratio of Maximum delay between app and IP multicast RAD: Ratio of Average delay between app and IP Multicast Link Stress number of packets sent over link

12. Criteria (2) Node Stress Number of nodes in a routing table Number of messages received by a join Duplicates Number received by end nodes

13. CAN+Flooding Results Landmark based and NDR (lowest network delay) was best Benefits from increased table state is uneven Link stress for 80,000 joins is huge Increases with state size Link stress is significantly lower for sent messages

14. Link stress CAN+Flooding

15. CAN+Tree Results Landmark based assignment of nodes better Delay is better than flooding by a factor of 2 to 3 Link stress for joins and sends are relatively similar

16. Pastry: Tart and Tangy varied b from 1 to 4 TART Topology aware routing table construction default optimization nodes probe each other to estimate delay TOP Topology aware nodeId assignment currently random / distributed

17. Pastry+Flooding Results delay decreases as b increases delay of b=4 is 50% lower than b=1 TART and TOP both decrease delay TOP reduces average link stress by factor of 3 and max link stress by a factor of 30 Large number of duplicates when b is large (16% b=4) due to holes in routing tables

18. Pastry+Tree Results delay decreases as b increases, and with TART and TOP similar to flooding results TART reduces both max and avg link stress TOP reduces avg but increases max link stress Pastry with TART and without TOP is best for tree-based

19. Multiple multicast Tree based Pastry was best for delay Interesting is CAN + Flooding average CDF curve not tightly bound Flooding is better in the 1500 group experiment than the single group

20. Max Delay Penalties

21. Average Delay Penalties

22. Evaluation For delay, Pastry is 20-50% better than CAN For average link stress, Pastry was 15% lower Max link stress: CAN was 25% lower

23. Conclusion Separate overlays are only better if you want to limit nodes that route traffic More overhead for flooding approach Tree base can reuse the same overlay for multiple groups Less delay, joins and sends are more lightweight Multicast trees with Pastry have better performance than CAN