2008年4月2日 星期三

CoolStreaming/DONet: A Data-driven Overlay Network for Efficient Live Media Streaming

Xinyan Zhang, Jiangchuan Liu, Bo Li, Tak-Shing Peter Yum
CoolStreaming/DONet: A Data-driven Overlay Network for Efficient Live Media Streaming
In Proceedings of IEEE INFOCOM 2005

[Summary]
This paper presents Coolstreaming/DONet, which is a peer to peer media streaming system. For any peer to peer network system, member management, network structure, and content delivery management are critical issues to deal with. This paper performed a study to these issues. Furthermore, they evaluate this system through Planetlab environment.
DONet, which stands for data-driven overlay network, forms network structure by data availability. In previous peer to peer system, dedicated root node collects all information of nodes in this network and forms the tree, and data flow is also fixed, from roots to leaves. In DONet, however, network structure and data flow depends on if a data is available. Video data are sliced into segments, in this paper one segment mean one second. Each node keeps a buffer map that denotes data segment availability. Membership and partnership management is also a key issue in DONet. Each node keeps a partial member list called mCache. They use SCAM protocol to maintain and update membership list, and buffer map information. When a node enters this network, it contacts the server (or a specified node), gets a randomly selected deputy node, then gets partner candidates from deputy node’s mCache. And when a node wants to leave this network, it will issue a message. For the partnership management, each node periodically establishes new partnerships randomly from its mCache. An interesting scoring mechanism is used here, they calculate the average segment flow throughput, the higher the better. Better ones will be kept while this node is exploring new partners.
The scheduling algorithm is also an interesting issue in this paper. Since dynamic scheduling is a variation of NP-Hard problem. The author suggests a heuristic algorithm. This algorithm starts from knowing potential supplier for each segment. Since a segment with fewer suppliers has better chance that will miss the deadline, this algorithm starts from these segments, and scans these node for bandwidth. The one with the highest bandwidth and available time is selected.
This paper also presents the performance evaluation of this system. They use the PlanetLab platform to form the network, and perform tests on this system. They also termed CI, continuity index, which represents the smoothness of streaming, as a metric. Tests are performed in order to know CI and control overhead under different situation. Different streaming rate, partner number, and node dynamic period are considered. The performance of tree topology and DONet is also shown and compared.
The application of DONet is called Coolstreaming, which is a peer to peer streaming application. This study also reveals interesting facts. First, the current Internet has enough available bandwidth to support TV-quality streaming. The CI stays above 0.95 most of the time; this tells the smoothness of streaming. Second, as the nature of peer to peer system, the larger the network size, the better streaming quality obtained. The relationship of CI and user number is also shown.

[Comments]
Clarity:
This paper does well on clarity. The author stated some problems that every peer to peer system may meet, and come forward some solutions and observations. Started from previous work, the author discussed membership management, content management, transmission scheduling, implementation experience, and evaluation of this system. We can know the big picture of this system easily.
Correctness: The result and analysis of the evaluation seems to be reasonable. The function derived in this paper meets the result obtained.
Originality: The concept of DONet is quite novel. The flow of data sounds like energy balance in nature world. The new metric “CI” also tells the fact of streaming experience.
Significance: Due to that it is quite complete study; I think this paper is significant. The concept of DONet impacts the design of p2p network. The experiences of peer to peer streaming application is also valuable.

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