支援實況與移時串流影音服務之P2P系統

Abstract

現今的P2P影音串流主要分為實況影音串流和隨選視訊串流，透過P2P的方式來提供影音串流的服務。然而收看實況影音串流的使用者只能收看最新的影音內容，無法收看過去時間的影音內容；收看隨選視訊串流的使用者雖然可以隨自己喜好隨選隨看，但無法收看即時的實況影音。 我們提出一個可以同時支援實況和移時串流的系統，使用者可以依自己喜好來選擇收看實況的影音串流或是移時串流。在收看實況影音串流時，使用者之間會交換最新可用檔案和訂閱子串流的資訊，並依據此資訊來向其它使用者要求傳輸所需的影音區塊，並且根據我們設計的儲存和取代策略以及和索引伺服器的註冊動作有效的存取這些檔案。在收看移時串流時，使用者首先透過索引伺服器來找出擁有要收看特定時間的影音區塊和緊鄰連續影音區塊的使用者，並且形成一個可互相交換資訊之群組，藉由可用檔案資訊的交換來獲得播放所需的影音區塊。此群組的管理機制，如使用者加入/離開和群組名單的管理。有別於實況串流，我們對於移時群組的影音檔案儲存會做不一樣的處理，以達成有效延長影音涵蓋範圍的目的。

P2P multimedia streaming today can be categorized into live streaming and video-on-demand (VoD) streaming, both adopt P2P techniques to provide multimedia streaming services. However, live streaming users can only watch the latest media contents but cannot watch previous ones. Although VoD streaming users can watch what they want at any given time, they cannot watch live media content. We propose a streaming system providing both live streaming and time-shift streaming. Users can watch each one of them at any given time. When watching live streaming, peers exchange the information of block availability and sub-streaming subscription to request the latest media contents. Each user efficiently stores these media contents according to our storage policy and replacement strategy we design, including the interaction between the index server and the peer itself. When watching time-shift streaming, each user first locates the media contents it wants to watch through the index server - users having that specific media content will be found. According to our storage policy, these users may have the up-coming media contents with high probability. They form a group that each user can exchange information with each other to request the media content it needs. We also design the group management mechanism like peer join, peer leave and list maintenance. The storage policy in time-shift streaming is different from that in live streaming. It could help extend the coverage length of media contents.