架構於有線電視網路的隨選即播視訊系統之研製

Abstract

隨選即播視訊服務系統 ( VOD ) 是將影片資料儲存在視訊伺服器中 ，其用戶端則利用網路來與伺服器連接，經由網路的連接，伺服器便能提 供用戶端類似一般放影機的諸如播放、暫停、快轉或回轉等播放功能，如 此便可以使用戶能隨意選擇自己想看的節目來欣賞，並且能在自己想看的 時間播放影片。 而這樣的 VOD 系統有著資料量龐大、非對稱性的傳 輸量與連續性播放之特性，因此從伺服器中以大型檔案為主的儲存配置、 須時時維持高輸出頻寬的條件與網路上非對稱性的傳輸量等要求來看，傳 統的檔案系統不足以滿足我們的需求，故我們針對上述的需求設計一個系 統架構，稱為 VOD on CableNet ( VODC )，採用生產線式檔案系統架構 ( Pipelining File System;PFS ) 來作為 VODC 之系統架構，並利用現 有普遍存在的有線電視網路來作為用戶端和伺服端之間傳送影片與系統控 制命令之用。PFS 其設計的原理是採用類似生產線般的分層架構，各層之 間分工合作維持整個系統順暢的資料輸出，每一層的處理器都能夠獨立運 作，故可達到並行處理與提高系統輸出頻寬的目的。而利用現有之有線電 視的兩個頻道以傳送系統控制命令，其餘的頻道作為播放影片服務客戶之 用，可以以較低成本提供高品質的VOD 服務並且不會因網路壅塞而降低影 片的播放品質。 利用這樣的架構，我們實際製作了一個 VODC 的雛形 系統，並驗證了系統處理來自網路上的系統命令之能力，足以承受系統實 際運作時的忙碌工作分派。 總之，本論文針對 VOD 系統提出了一個 VODC 系統架構，並加以實作而得到一個雛形系統，進而證實了此種系統 架構於有線電視網路的可行性。 VOD system keeps video data in the video server and clients can make use of network to connect with the server. By communication over network, the server can provide clients VCR- like functions such as play, pause, fast forward andfast backward, etc. As a result, VOD system users can choose desired programs and the time to watch the programs. Such a VOD system possesses the properties of a mass of data, asymmetric network traffic and continuous playback. Therefore, to consider the condition of VOD system designs (1. The video server mainly keeps large files. 2. The video server must support very high system throughput bandwidth. 3. There is asymmetric network traffic.), we found that traditional file system can not satisfy our demands. We design a system architecture to satisfy such a requirement. It is called VOD on CableNet (VODC). It uses "Pipelining File System" (PFS) architecture as its system architecture and uses the currently popular CATV network as the communication medium between clients and the server. The design theorem of PFS is layered architecture similar to pipeline. Every layer (or level) performs its own work and cooperates to make the system operates more smoothly. Every layer consists of one or more processors. Because of independent operations of all processors, concurrent processing can be achieved and system throughput bandwidth can also be increased. By using two of current CATV channels to transmit system control commands and using other CATV channels to play programs to serve users, we can afford high quality VOD service with lower cost and the program playback quality will not be decreased due to heavy network traffic. By making use of above architecture, we build a prototype of the VODC system . We also verify the system ability to handle commands from the CATV network. The result of analysis shows the system has enough capability to handle all assigned commands. In a word, this thesis proposes VODC system architecture and builds a prototype system by the architecture. Further, we certify the practicability of VOD system based on cable television network.