1. Scribe An application level multicast infrastructure Kasper Egdø and Morten Bjerre

2. Motivating Scribe: Tracking stock prices Users wish to track the price of stocks Prices need to be broadcast Many stocks, many users Dynamic set of users and stocks Faulttolerant and decentralized

3. Overview Pastry: Object location and routing scheme used by Scribe Scribe: An application level multicast infrastructure Anycast: An application layer built using Scribe Conclusion

4. Quick Pastry 128-bit node/object space Prefix routing Good locality ”Short routes” property Non-FIFO deliver, forward, newLeafs

5. What is Scribe? Application level multicast infrastructure Built ontop of Pastry Scales well Best effort delivery

6. Group management Rendezvous Point (RP) Access control done at RP

7. Creating a group (1100) 11001101 1111 1001 0111 0100 Rendezvous Point (Pastry root) Group Creator creates Group 1100 GroupID1100 ACLxxx ParentNull

8. Member management Joining a group Children table Leaving a group A multicast tree is created

9. Joining a group GroupID1100 Parent1100 Child1001 GroupID1100 Parent1001 Child0100 GroupID1100 Parent1101 Child0100 Child0111 11001101 1111 1001 0111 0100 Rendezvous Point (Pastry root) Joining member Join request GroupID1100 Parent1001 Child0111 GroupID1100 ACLxxx ParentNull

10. Leaving a group GroupID1100 Parent1100 Child1101 GroupID1100 Parent1101 11001101 1111 1001 0111 0100 Rendezvous Point (Pastry root) Leaving member Leave request Member Leave request GroupID1100 Parent1001 GroupID1100 ACLxxx ParentNull Child1101

11. Multicasting 11001101 1111 1001 0111 0100 Rendezvous Point (Pastry root) Message Multicast down tree

12. Maintaining the tree Parent heartbeats check if nodes are alive Children rejoin group if parent dies RP state information replicated to leaf nodes

13. Repairing the tree GroupID1100 Parent1100 Child1001 GroupID1100 Parent1001 Child0100 GroupID1100 Parent1111 Child0100 Child0111 11001101 1111 1001 0111 0100 Rendezvous Point (Pastry root) Failed Node Join request GroupID1100 Parent1001 Child0111 GroupID1100 ACLXxx ParentNull Child1111

14. Problems with Scribe Best-effort delivery No built-in protection of information Possible concurrency problems

15. More reliability Number and buffer messages Applications can choose to improve reliability Encryption of messages

16. Comparing Scribe and IP multicast Scribe scales better and supports dynamic groups Scribe nearly as efficient as IP multicast

17. Application of Scribe Anycast offers anycast and manycast

18. Anycast Scribe group Client A Client B Resource offered

19. Conclusion Scribe is very good for large scale multicast Easy to implement applications which use Scribe