現今人們已經提出許多種以樹狀架構為基礎的點對點群播疊蓋式網路來提供影音串流服務。然而，當影音串流服務是應用於範圍廣大且多變的環境(如：網際網路)時，要如何減輕串流伺服器的負擔依舊是個嚴峻的挑戰。因此，本篇博士論文提出一個新的點對點影音串流系統，稱作點對點式個人視訊錄影機(P2PVR)，來有效率地提供包含VCR功能的視訊服務。在我們提出的系統架構裡，使用者收看視訊的設備會共同建構出一個播放進度感知的群播樹，來促使播放進度相近的使用者可以互相交換影音資料。此外，我們也設計了一個半分散式的諮詢服務。當使用者想要找尋出擁有他(她)所想要之資料的使用者時，該諮詢服務會協助該使用者去找尋目標使用者位於群播樹中的可能位置，避開目標使用者不可能出現的位置。我們在行星實驗室(PlanetLab)平台上以實驗方式實際測試本系統的效能。其結果顯示，本系統即使在多變的網路環境中，依然可以大幅減輕影音串流伺服器的負擔且提供不錯的收看品質，同時本系統所造成的初始延遲和控制訊息花費也很低。我們也使用模擬的方式來評估本系統的效能。模擬數據顯示本系統可以建構一個短且寬的群播樹來散佈即時影音視訊。

Tree-based peer-to-peer multicast overlays have been widely proposed for the provision of video streaming services. However, alleviating the server load in large-scale, dynamic environments such as the Internet remains a major challenge. Accordingly, this dissertation proposes a new peer-to-peer video streaming system, designated as peer-to-peer personal video recorder (P2PVR), which facilitates essential VCR functions in an efficient manner. In the proposed architecture, the peers are organized into a playback offset aware tree-based overlay, in which they share streaming data with other peers having a similar playback offset. In addition, a semi-decentralized directory service is developed to assist peers in searching only those parts of the tree known to contain eligible parent nodes, i.e. nodes which possess the expected streaming data. The performance of P2PVR is evaluated by performing a series of experiments on PlanetLab platform. The results show that P2PVR yields a significant reduction in the server stream stress and achieves a reasonably low playback discontinuity under dynamic network conditions whilst simultaneously granting a low control overhead and startup latency. We also evaluate the proposed approach through simulation. The simulation results have indicated that P2PVR can construct a short and wide multicast tree for live streaming.

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