摘　要
過去在隨選視訊的研究中，有效的利用同儕間的資源一直是被研究的重點。最直覺的做法就是讓一個正在觀看影片的使用者，留下部份剛剛已經看過的片段，藉此服務其它的使用者，如此一來即可有效的降低影片伺服器的負擔。
而在過去的研究當中，主要在於網路拓撲的方式，在拓撲方式建立後，即可利用彼此儲存在記憶體或硬碟的暫存片段，而緩衝片段的大小，一直沒有被深入的討論，大多是假設使用者可以暫存相當大的片段，或者是假設它是一個固定的值。在這篇論文當中，我們針對緩衝大小做深入的研究，我們探討在緩衝過小，適中，以及過大時，對於本地端系統效能，以及整體分散式系統效能的影響。接著，我們提出了動態分配緩衝大小的機制，更合理的去運用使用者的系統資源。最後，我們利用實驗比較我們提出的動態分配緩衝大小機制與舊有的固定緩衝大小機制，實證結果證明，我們提出的方法表現得比過去的方法能夠更有效率的去使用每個本地端系統的資源，藉此提升整體系統的效能，以降低中央伺服器的負擔。

Abstract
Many video-on-demand (VOD) systems have adopted a peer-to-peer (P2P) approach to deliver the video streams. By leveraging the resources in the participating peers, the P2P VOD systems can alleviate the severe resource demands at the video servers. A typical use of the peer resources in P2P VOD systems is to let the peers buffer the video streams after viewing so that other peers can download the streams from those buffers instead of from the servers. Most previous works assume a fixed buffer size for simplicity of implementation. When the buffer is full, old video segments are just discarded. The problem is that the peer may miss the chance of serving another peer if the latter happens to behind the former by a buffer-full of video. If the buffer size can be extended dynamically, a peer may serve more peers and the server load may be further reduced. However, extending the buffer will likely incur virtual memory overhead and degrade the performance of the local computer. Apparently, the idea of dynamic buffering must be applied carefully. In this thesis, we study the various issues of dynamic buffering for P2P VOD systems. We first introduce a realistic model of system performance under different streaming buffer size. We then propose a system DBS-Net to adjust the available buffers according to the condition of peers so that the memory space could be better utilized. Simulation shows that DBS-Net outperforms the systems with a fixed buffer size.

[1] X. Zhang, J. Liu, B. Li, and T.S. P. Yum, “CoolStreaming/DONet: A Data-driven Overlay Network for Live Media Streaming,” Proc. of IEEE International Conference on Computer Communications (INFOCOM), March 2005.
[2] X. Liao, H. Jin, Y. Liu, L. M. Ni, and D. Deng, “AnySee: Peer-to-Peer Live Streaming,” Proc. of IEEE International Conference on Computer Communications (INFOCOM), 2006.
[3] D. Tran, K. Hua, and T. Do, “A Peer-to-Peer Architecture for Media Streaming,” IEEE Journal on Selected Areas in Communications, 22(1):121-133, Jan. 2004.
[4] C. Zheng, G. Shen, S. Li, and S. Shenker , “Distributed Segment Tree: Support of Range Query and Cover Query over DHT,” Proc. of the International Workshop on Peer-to-Peer Systems (IPTPS), 2006.
[5] S. Sheu, K. Hua, and W. Tavanapong, “Chaining: A Generalized Batching Technique for Video-on-Demand Systems,” Proc. of the IEEE International Conference on Multimedia Computing and Systems (ICMCS), 1997.
[6] K. A. Hua, Y. Cai, and S. Sheu, “Patching: A Multicast Technique for True Video-on-Demand Services,” Proc. of the ACM International Conference on Multimedia, 1998.
[7] T. T. Do, K. A. Hua, and M. A. Tantaoui, “P2VoD: Providing Fault Tolerant Video-on-Demand Streaming in Peer-to-Peer Environment,” Proc. of the IEEE International Conference on Communications (ICC), Jun. 2004.
[8] Y. Guo, K. Suh, J. Kurose, and D. Towsley, “P2Cast: Peer-to-peer Patching Scheme for VoD Service,” Proc. of the 12th International Conference on World Wide Web, 2003.
[9] J.-K. Chen and J.L. C. Wu, “Adaptive Chaining Scheme for Distributed VOD Applications[J],” IEEE Transactions on Broadcasting, 45(2) :215∼224, 1999.
[10] C.S. Liao, W.H. Sun, C.T. King, and H.C. Hsiao, “OBN: peering for finding suppliers in P2P on-demand streaming systems,” Proc. of the IEEE International Conference on Parallel and Distributed Systems (ICPADS), 2006.
[11] M.T. Sun, C.T. King, W.H. Sun, and C.P. Chang, “Attribute-based Overlay Network for Non-DHT Structured Peer-to-peer Lookup,” Proc. of International Conference on Parallel Processing (ICPP 2007), Sep. 2007.
[12] S. Jin and A. Bestavros, “Cache-and-relay Streaming Media Delivery for Asynchronous Clients,” Proc. of International Workshop on Networked Group Communication (NGC), 2002.
[13] A. Vlavianos, M. Iliofotou, and M. Faloutsos, “BiToS: Enhancing BitTorrent for Supporting Streaming Applications,” Proc. of 25th IEEE International Conference on Computer Communications (INFOCOM), April 2006.
[14] TVAnts. http://www.tvants.com.
[15] PPLive. http://www.pplive.com.
[16] DSopCast. http://www.sopcast.com/cn/vod/index.jsp.