1. P2PCAST A Peer-to-Peer Multi-Cast Scheme for Streaming Data
Antonio NICOLOSI
Siddhartha ANNAPUREDDY

2. Motivation Want to stream data to lots of users Easy solution
Pay for lots of bandwidth
Only fat cats can afford it
More democratic alternative
Users donate bandwidth to help disseminate the data

3. The Setting A single content provider (the source)
Other participants are peers
Each node has limited bandwidth
Assume users exhibit fail-stop behavior

4. Goals Scale to thousands of nodes Participants join/leave dynamically
Users donate as much bandwidth as they take
Fault-tolerance
Security

5. Design Guidelines Join by contacting a random node in system
No need to give notice while leaving
Forest of multicast trees
Each node is internal in exactly one tree
Trees are repaired locally upon node failures

6. Algorithm Forest of f trees (of arity f)
Insertion — Joining the system
Deletion — Survive node loss

7. Insertion Users are leaf in all trees of the forest but one
Place new user in the next-to-last level of one (random) tree
Each node is either complete or incomplete
Incomplete nodes only at the next-to-last level
Randomness ensures (almost) balanced trees

8. Insertion (cont’d) Contact a random node in the system
The node contacted can be
Complete
Incomplete
Lonely child

9. Insertion (cont’d) Complete node Join tree where the contact is a leaf
Search down the other tree
Two Subcases
Complete/Incomplete

10. Insertion (cont’d) Incomplete node Lonely Child
Adopt the contact node in one tree
Become its child in the other tree
Lonely Child
Redirect to the parent (back to case above)

11. Deletion Ideally, undo the join process Get as close as possible
Not easy  — failed node can be high up in the tree
Get as close as possible
Push “bubble” down the tree
Repair the last level — easy 

12. Deletion (cont’d) Get down to the next-to-last level
Just exchange parent with an arbitrary child
Finally, bubble can end up being
Complete
Incomplete

13. Deletion (cont’d) Complete bubble Incomplete bubble
Drop an arbitrary child
Ask failed node’s other parent to adopt it
Incomplete bubble
Drop child in the other tree

14. … … Architecture P2Pcast Protocol encode decode decode stream stream
source
peer
peer
P2Pcast Protocol …
peer
peer
registry

15. Implementation
Random node selection simulated via centralized registry — can be replaced using any routing overlay
For fault-tolerance, stream of data is forward-error corrected

16. RPC Protocols Control Protocol Registry Protocol
TAKEON, SUBSTITUTE, SEARCH (Insertion)
REPLACE, DIRECT (Deletion)
INSPECT, UPDATE (Misc)
Registry Protocol
JOIN, DELETE

17. Related Work Scribe/SplitStream Assume some users have spare bandwidth
Require users to be willing to relay data for groups they do not belong to
Properties of the forest of multicast trees bound to parameters of Pastry

18. Conclusions and Future Work
Scale to thousands of nodes
Participants join/leave dynamically
Users donate as much bandwidth as they take
Fault-tolerance
Security