ZIGZAG

A Peer-to-Peer Architecture for Media Streaming

By Duc A. Tran, Kien A. Hua and Tai T. Do

Appear on “Journal On Selected Areas in Communications, Special Issue on Advances in Service Overlay Networks”

Agenda

1. Introduction

2. ZigZag1. Administrative Organization

2. Multicast Tree

3. Client join/departure

4. Performance analysis

3. Conclusion

Introduction Scenario

A single live source serving many clients Solution

Broadcasting by IP multicast Problem

IP multicast not widely deployed

Application-multicast What?

Not all clients receive contents from the source Some clients (peers) help streaming data to

other peers (P2P)

Design Objectives An efficient P2P media streaming scheme

should1. The end-to-end delay from source to client

should be low

2. The node degree should be small

3. Adapt to free join/leave receivers

4. Minimize the amount of control overhead

ZigZag Administrative Organization

Represents the logical relationships among peers Multicast tree

Specify which peer data is received from Built based on C-rules which helps limits the degree of

a peer (outbound links) Control protocol

Specify the exchange of state information Policies adjusting the tree

Maintaining the robustness of the tree

Administrative Organization What?

A multi-layer hierarchy of clusters Partition peers into clusters of size [k, 3k] Assign the role “head” and “associate head” to

certain peers

Administrative Organization

Administrative Organization Properties

H – number of layers Bounded by [log3kN, logkN+1]

Max. number of members in a cluster=3k To prevent cluster undersize in the case of a client

leave after splitting

Multicast tree What?

Built based on the administrative organization C-rules specify the actual data flow from source

to any peer Some nodes will stream data to more than 1

peers Assumption:

The uplink capacity of peer is enough for streaming contents to multiple peers

Multicast Tree

Multicast Tree Properties

The workload is shared among clients Worst-case node degree is 6k-3

The end-to-end delay is small Maximum height of the tree is 2logkN+1

Use of “associate head” for delivering media Number of outbound links is lower Bottleneck will less likely to appear in higher level

Control protocol Goal

Minimize the number of peers needed to be contacted Only exchange information with parent, children and cluster

mates Exchange as few states as possible

1. Non-head peers1. Peer degree for non-head peers

2. Cluster head1. Current end-to-end delay from server to the peer2. List of peers receiving contents from the peer3. List of “associate head” receiving contents from the peer

3. Parent1. “Reachable” and “Addable” property

Client join/departure Basic principle

Maintain C-rule so that nice properties of degree and end-to-end delay is preserved

Direct solution Reconstruct the administrative organization and multicast tr

ee Costly in terms of exchange of state information

Proposed join/departure algorithm Limits the number of nodes to connect during a join by O(k

logkN) Limits the number of peers that need to reconnect by 6k-2

Client join Procedure

1. If X is a layer-0 associate-head1. Add P to the only cluster of X

2. Make P a new child of X

2. Else1. If Addable(X)

1. Select a child Y s.t. Addable(Y) and D(Y)+d(Y,P) is min

2. Forward the join request to Y

2. Else1. Select a child Y s.t. Reachable(Y) and D(Y)+d(Y,P) is min

2. Forward the join request to Y

Client departure Tasks to do for client (X) departure

1. The parent removes link to X

2. The children of X needs a new parent

3. Each layer-i cluster X belongs to needs a new head

4. Layer-j cluster may require a new associate head

Client departure If X’s highest level is at layer 0

If X is not the “associate head” No extra work needed

If X is the “associate head” The head of the cluster choose another member to

take up the responsibilities

Client departure If X’s highest level is j (non zero)

It implies it is a “head” in layer [0,j-1] A non-head peer (X’) at layer 0 is randomly chosen

to replace the “head” responsibility Head of children of X (Y) will choose a new parent

for X that has a minimum degree

Performance Analysis Comparison with another multicast tree based P2P

media streaming scheme – NICE Performance metrics

Maximum degree – The max. no of outbound links Join overhead – The number of peers to visit until admission Failure overhead – The number of reconnections required

when a peer “fail” Control overhead – The number of peers to exchange control

information with Stretch – Ratio between length of data path from server to a

peer in the system to the shortest path Stress – Number of times the same packet goes through a link

Simulation study Simulation environment

The network has 10,000 nodes k is set to 5

Thus, 5 peers at min. and 15 peers at max. for each cluster Compare to NICE

Initially, 3000 clients join sequentially into the system Then a loop of 2000 runs, a client will fail at a probability p

while joining the system at 1-p

Simulation Results I

Simulation Results II

Conclusion A P2P media streaming scheme

The maximum degree and end-to-end delay is small

A client join/leave algorithm is proposed aim at reducing the control overhead

Simulation result suggests that 5000 peers can be supported at a max. degree of 15

Q & A Thank You