隨選即播視訊系統架構與其服務管理機制之研究

Abstract

隨選即播視訊服務系統(VOD)是多媒體諸多應用中的一項，其是將影 片資料儲存在影像伺服器中，而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暫停、快轉或 回轉等播放功能。 而這樣的VOD系統有著資料量龐大與連續性播放的 特性，因此在系統頻寬的要求上亦是很高的，故我們針對這樣的需求設計 了一個系統架構，稱為生產線式檔案系統架構(Pipelining File System; PFS)，其設計的原理是採用類似生產線般的分層架構，每一層有其自己的 工作，各層間分工合作來使得整個系統的輸出工作更暢通！每一層都是由 一或數個處理器來組成，而由於每個處理器都能夠獨立運作，所以能達到 並行處理的目的，也加大了系統的輸出頻寬！ 利用這樣的架構，我們 也實際製作了一個VOD的雛形系統，而由實際的效能測量中，也驗證了PFS 架構確實有相當的能力來解決I/O上的問題。 由此雛形系統中，我們 發現配置不同的緩衝區大小會影響系統的整體效能，因此對於這樣的問題 ，我們也做了一些理論上的分析與探討。我們是將此雛形系統加以簡化而 得到一個簡化後的系統模型，並利用此模型做緩衝區大小與系統平均整體 效能的關係之理論分析，由分析的結果所得到的理論曲線在與實驗曲線做 一比較後，發現兩者的曲線走向確實是吻合的，也驗證了理論曲線的參考 價值，而這樣的理論分析結果對於VOD系統而言也是非常有用的資訊！ 總而言之，本論文針對VOD系統提出了一個系統架構，並加以實作而得到 一個雛形系統，進而對其中緩衝區大小與系統效能的關係做理論上的分析 ，也得到了一些有用的分析結果！ Vedio On Demand(VOD) system is one of multimedia applications. The video server stores wideo data and clients make use of network to connect withserver. By communication over network, server can provide clients VCR-likefunctions. Such a VOD system possesses the properties of a mass of data andcontinuous playback. Therefore, the requirement of system bandwidth is veryhigh. We design a system architecture to such a requirement. It is called"Pipelining File System" (PFS) architecture. The design theorem is layeredarchitecture similar to pipeline. Every layer(or level) performs its ownwork. All layers cooperate to make system operates more smoothly. Every layerconsists of one or more processors. Because of independent operations of allprocessors, concurrent processing can be achieved and output throughput ofsystem can also be increased. By making use of PFS architecture, we build a prototype of the VODsystem. By the observations of practical measurement result of systemperformance, we verify that FPS architecture has the capability of solvingI/O problem. In the prototype system, we find that allocations of different buffersizes will affect overall system performance. Therefore, we make sometheoretical analyses on this problem. We simplify the prototype system andobtain a simplified system model. By making use of the model, we analyze therelation of buffer size and overall system performance. The trend oftheoretical curve that is obtained by the analytical result tallies with theone of the practical measurement curve. This verifies referential value oftheoretical curve. Such an analytical result is also a very useful informationto VOD system. In a word, this thesis proposes a VOD system architecture and builds a prototype system by the architecture. Further, we analyze the relation ofbuffer size and system performance and acquire some useful analytical results.