在點對點隨選視訊系統中兩大主要的功能區塊為：供應者搜尋、及內容傳輸。其中，供應者搜尋的任務是：當一個使用者需要某些影片內容時，找出系統內有其他哪些使用者的緩衝區中存有這些內容。若我們找到的供應者較多，就有機會找到網路連線狀態較佳的供應者、蒐集到足夠的下載頻寬，從而能夠更順暢地播放影片。供應者搜尋方法的關鍵，在於能夠在系統中辨認出哪些使用者之間存在供需關係，並加以追蹤。在點對點隨選視訊系統中，供需關係是否成立，取決於使用者緩衝區中所存的影片內容，然而在使用者播放影片的同時，這些內容會頻繁地變動；尤其當使用者執行暫停、快轉、跳轉等操作時，其變動的方式還會更形複雜。要能有效地追蹤這些這些快速變動的資料內容與供需關係並不容易。
在本篇論文中，我們首先提出一個供應者搜尋方法：重疊關係網路(ORN)。它以使用者緩衝區之間的內容重疊性來定義使用者間的關係，並持續追蹤和維護這些關係。當此種重疊關係得以妥善維護時，使用者就可與其供應者建立連結，而這些連結結構又可被用來作為路由資訊，幫助新加入的使用者找到它們的供應者。實驗數據顯示，在多種不同的情況下，ORN都能搜尋出系統中超過96%的供應者，這樣的表現優於過去其他研究中所提出的方法，並可有效地提高資料傳輸的效能。
雖然ORN的搜尋效能優異，但它的維護成本卻也很高。因此，本篇論文也提出另一個延伸自ORN的供應者搜尋方法：節流閥(Throttle)。在Throttle中，一個使用者必須維護和追蹤的網路鄰居，是一個ORN使用者所需維護的鄰居的子集合。亦即，一個Throttle使用者要維護的邏輯連線數較ORN少，維護成本較低，同時，與它直接互連的供應者數量也比較少。但是，若一個使用者需要更多供應者，它可以詢問與自己直接連接的供應者的網路鄰居，即可取得更多供應者； Throttle確保了此種彈性搜尋機制能在有限的步數內找到與ORN所能追蹤的一樣多的使用者。簡言之，Throttle具備與ORN一樣高的搜尋能力，同時，它還允許使用者可以自行選擇是否要降低當下的搜尋率以減少過程中所耗費的訊息量。在系統中的供應者擁有較豐沛資源的情況下，Throttle可以為使用者節省不必要的通訊成本。數學分析與模擬實驗都顯示，與ORN相比，Throttle大大地提升了其在大型系統中的適用性。

There are two major building blocks in operating a peer-to-peer (P2P) video-on-demand (VOD) network: supplier discovery and content delivery. Supplier discovery concerns the discovery of peer nodes in the network that can provide the streaming data blocks needed for playing by a local node. The more suppliers one can discover, the higher the chance of locating quality suppliers for delivering contents smoothly to ensure uninterrupted playback. The key to supplier discovery is to establish and track the supply-demand relationship among the peers. For P2P VOD, the supply-demand relationship is determined by the buffer contents of the peers. Unfortunately, the buffer contents change rapidly as peers play the video, especially under VCR operations. The challenge is to track all the dynamic relationships in an efficient way.
To achieve better supplier discovery, first we propose an Overlapping Relation Network (ORN). The idea is to track the dynamic supply-demand relationship by tracking the overlapping of peers' buffer contents. Once such overlapping relations are maintained, peers can be linked with their suppliers as overlay neighbors. When a new peer joins the system or a peer changes its demand and requires different contents, it can traverse via these overlay links to locate new suppliers quickly. Extensive analyses and simulation experiments show that in most cases ORN can discover more than 96% of the suppliers in the network, resulting in a streaming continuity superior to other approaches.
Though the high discovery performance, ORN is not economic in term of maintenance cost. ORN requires each peer to discover and track all the eligible suppliers, even if the amount of suppliers is beyond the demander’s need. In this thesis, we also propose an adaptive method extended from ORN: the Throttle. In Throttle, the overlay neighbors that a peer should maintain are only a subset of that in ORN. Therefore, a Throttle peer incurs fewer maintenance costs and only needs to link to relatively fewer suppliers. Whenever needed, it can crawl upon the overlay to collect more suppliers. With a careful design of the neighbor selection rule, it is guaranteed that such crawling process can return as many suppliers as in ORN in a deterministic manner. In summary, Throttle is able to achieve full discovery as ORN, but can also discover peers incrementally by trading of communication costs. In ORN, the maintenance overhead grows as the system size increases. On the contrary, Throttle incurs constant overhead, which is independent of the system size. Analyses and simulation experiments have confirmed this property and the good scalability of Throttle in large systems.

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