同儕網路電視中透過預取和頻道偵測以改進轉台與播放效能之研究

Abstract

光纖到戶日漸普及使得網路頻寬增大，進而促成即時影音串流之應用，因此現今在網路上可以看到許許多多的電影與電視連續劇，都有不錯之品質。未來數位電視將趨向透過網際網路來傳送影音媒體資料，這可歸功於過去十年來點對點(Peer-to-Peer;P2P)，或同儕網路技術的發展。透過P2P技術提供媒體串流服務，可以節省大筆伺服器軟硬體成本，同時其良好的延展性使得系統擁有處理大量用戶的能力。然而，由於P2P網路中使用者可以隨意加入以及離開的特性，往往造成影音串流供輸不穩定而使媒體播放不順暢或停滯。同時，現行P2P網路中並未將關鍵性的影音片段例如MPEG之I-frame，B-frame，與P-frame分類處理，導致媒體播放器因無法解碼而停格的現象嚴重。加上目前網路影音串流在轉換影音內容或頻道時，重新搜尋、擷取與緩衝所花費的時間過長，至今並沒有一個有效的方式來降低轉台時間。 在本篇論文中，我們提出快速轉台的機制，以及事先預取關鍵性影音資料的機制來改善接收端媒體停滯的現象。我們使用網路模擬器來建構同儕網路串流的環境，數值結果顯示我們提出的方法能有效地降低P2P IPTV轉台時間並降低播放媒體停滯的現象，因此使用者體驗之品質可明顯的提升。

The growing popularity of optical-fiber-based last mile increases the network bandwidth and benefits the application of media streaming. We can watch a variety of movies or video programs on today’s Internet, which is resulted from the development of Peer-to-Peer technique. Service providers can save a lot of cost on both the hardware and software of the server, without worrying about the rapid growth of user population due to the scalability feature of P2P network. However, since the users can join or leave the P2P network arbitrarily, it would cause the unstable streaming traffic and even the pause of video playback on the receiver side. Moreover, the lack of frame classification such as MPEG I-frame, P-frame, of B-frame makes the player difficult to decode and re-buffer. On the other hand, there are no effective approaches to solve the problem of long delay of channel switching in P2P IPTV system. In this thesis, we propose approaches to reduce the channel switching delay and pre-fetching key frame to prevent the unsmooth playback of media player. The combined effect apparently improve the quality of experience of P2P IPTV. We use the OMNeT++ network simulator to create a P2P system which runs the IPTV application. The numerical result shows that our proposed schemes reduce the channel switching delay and enhance the smoothness of playback significantly.