1. Peer-to-Peer Streaming: An Hierarchical Approach
Duc A. Tran
(with Kien A. Hua and Tai T. Do)
Data Systems Group (UCF)

2. Roadmap What is P2P? Why P2P Streaming? Problem Statement
Solution: ZIGZAG
Performance Study
Future Work

3. What is P2P?
The sharing of computer resources and services by direct exchange between systems:
exchange of information, processing cycles, cache storage, and disk storage for files.
P2P uses existing desktop computing power and networking connectivity,
allowing economical clients to leverage their collective power to benefit the entire enterprise

4. P2P Streaming Sharing of network bandwidth
Streaming: The user plays the data as as it arrives.
Consider a new user A:
If A is the first user, A gets the stream from the central site
Else, A can get the stream from the central site or a set of users who have already been receiving the stream

5. Why P2P Streaming? source Oh, I am exhausted! Client/server approach
P2P approach

6. Problem Statement Live media streaming High Liveness Scalability
Low Overhead
Robustness

7. Goal 1: High Liveness source Is it too far?
Don’t make me a bottleneck!
new
I want to join fast

8. Goal 2: Robustness The server is already busy source
Too many reconnections!

9. Goal 3: Low Control Overhead
A peer may have to periodically exchange information with others to maintain its position and connections.
The overhead of this task should be small and independent of the system size

10. Our goal: Minimizing the above effects
Goal 4: Scalability
When more peers join the system:
Control overhead may be increased
A peer may have to serve more others
The P2P tree may be deeper
A failure may result in many reconnections
Our goal: Minimizing the above effects

11. Proposed Solution: ZIGZAG
The 4 goals are achieved, especially:
Peer degree: bounded by a constant
Tree height: logarithmic with the system size
Control overhead: bounded by a constant (on average)
Failure recovery: done regionally,
affecting at most a constant number of peers
mostly no effect on the server
Administrative Organization (AO): A clustering of peers
Multicast tree: Built atop the AO based on C-rules

12. Administrative OrganizationL 4 2 L S 5 4 1 3 7 1 2 6 L 8 11 3 14 4 17 S 7 29 1 2 20 23 5 26 6 9 10 12 13 15 16 18 19 21 22 24 25 27 28 30 31
others
head
S: server
vice-head
Cluster size: [k, 3k], Highest-layer cluster: [2, 3k]
(k  4)

13. Terms Foreign head Foreign inferior Super peer Foreign cluster1 2
Foreign inferior
Foreign head 1 3 4 2
inferior

14. Connectivity Rules (C-rules)
(In this example, k = 4)

15. C-rules
Rule 1: A peer, when not at its highest layer, neither has a link out nor a link in
Rule 2: Non-head members of a cluster must receive the stream from their vice-head
Rule 3: The vice-head of a cluster, except for the server, must receive the stream from a foreign head

16. P2P Tree The tree height is at most 2logkN+1
The node degree is at most 6k-3

17. Control Overhead A peer exchanges soft-state information with
Its parent
Its children
Its clustermates
The worst-case control overhead is O(klogkN)
The average control overhead is O(k)

18. Max number of contacts: O(klogkN)
Join
The new user sends a request to the server
The request is forwarded down the tree until reaching a vice-head of a layer-0 cluster of size [k, 3k-1]
Goal: to be as close to the server as possible
Among children to forward the request, choose Y: Addable(Y) and D(Y)+d(Y,new) is min
Max number of contacts: O(klogkN)

19. Failure Recovery A node X at layer j is down:
The parent of X removes its link to X
X is vice-head: the layer-j cluster of X needs to a new vice-head
The children of X need a new parent to get the stream
i < j: Each layer-i cluster of X needs a new head since X no longer exists

20. Peer 3 fails L L L others head S: server vice-head 2 1 S 4 S 5 4 7 3 16 L 8 11 1 2 3 14 4 17 S 7 29 20 23 5 26 6 9 10 12 13 15 16 18 19 21 22 24 25 27 28 30 31
others
head
S: server
vice-head

21. Failure Recovery (peer 3 fails)
others
head
S: server
vice-head
Max number of reconnections: 6k-2

22. Goal: The conditions of C-rules must be met
Cluster Maintenance
As new peers are added to the administrative organization (AO):
A cluster may become oversize => split this cluster into two smaller clusters
As peers are removed from the AO:
A cluster may become undersize => merge this cluster with another to make a larger cluster
Goal: The conditions of C-rules must be met

23. Cluster Split Split algorithm: run by the head Xhead
Max number of reconnections: old cluster size + 6k - 1

24. Cluster Merge Merge algorithm: run by the head Xhead
Max number of reconnections: old cluster size + 6k - 1

25. Performance Study Underlying network: P2P network: k = 5 10,000 nodes
Generated by GT-ITM Generator
P2P network:
5000 peers
Up to 2500 failures
k = 5

26. Peer Degree

27. Control Overhead

28. Failure Overhead

29. Split Overhead

30. Merge Overhead

31. Join Overhead

32. ZIGZAG versus NICE NICE: (Banerjee et. al., Sigcomm 2002) ZIGZAG:
Administrative organization: there is no “vice-head”
P2P tree: head is always the parent of its clustermates
ZIGZAG:
Administrative organization: “head” and “vice-head”
P2P tree: “vice-head” is the parent of its non-head clustermates

33. Peer Degree

34. Control Overhead

35. Failure Overhead

36. Link Stress

37. Conclusions A clustering method for the administrative organization
JOIN
FAILURE
DEGREE
MERGE/SPLIT
CONTROL
NICE
O(klogkN)
ZIGZAG
O(k)
A clustering method for the administrative organization
C-rules: A multicast tree construction method
Future Work: Multi-send multi-receiver, client heterogeneity, Zigzag in MANETs?