分散式視訊系統之影片擺放

Abstract

大部分的隨選視訊系統把焦點放在設計一個能力強的視訊伺服器。但 因網路的頻寬，資料儲存空間及目前伺服器的技術有限，必須結合多個伺 服器來提供同時多人的要求，並符合經濟效益。 在這篇論文，在任意 的網路中，我們將視訊資料的擺放及複製之問題轉換為最佳檔案放置的問 題來減少儲存空間及網路頻寬的成本。因影片受歡迎程度常改變，影片必 須定期地重新擺放。但此問題的最佳解之計算複雜度跟影片的數目及用戶 區域個數有關，必須花很多時間且不實際。 為了減少網路頻寬的需求 ，影片愈熱門的複製愈多份且放置離用戶近的地方。另一方面，為了減少 儲存空間的需求，較不熱門的影片不必複製。於是我們可將網路簡化為樹 的架構，將受歡迎的影片複製放在下層，不受歡迎的影片放在上層。在多 個伺服器提供的資源有限下，為了讓使用者發出觀看影片之可成功建立連 線的機率最大，或被拒絕的機率最小，我們提出一個影片擺放的策略，並 且分析其要求被拒絕的機率，儲存空間及網路頻寬的需求。 In the design of video on demand (VOD) systems most focus is on designing a single powerful server to deliver video streams to users. Due to the limitationof network bandwidth, storage capacity of a single server and current servertechnologies, a cost-effective distributed VOD system is formed to provide theservice for a large amount of customers concurrently. In this paper, we will formulate the problem of placement and replication ofvideo programs as optimal file allocation problem to minimize the cost of storage space and the requirement of network bandwidth in general network topology. Dueto rapid changing of video popularity, the placement of videos should beeorganized periodically. The optimal solution of this problem is related to thenumber of video programs and the number of user communities. It takes atremendous time to reorganize and is not feasible in real world. In order to reduce the requirement of bandwidth, the most popular videos shouldbe replicated and placed closer to the users. On the other hand, for reducingstorage requirement, the unpopular videos do not have to be replicated. Hence,we can simplify the network model as a tree model. The most popular videos areplaced and replicated in leaf nodes closer to users and the unpopular videos areplaced in higher levels of the tree. In order to maximize the chance ofsuccessful call setup or to minimize the blocking probability of a request for avideo program under limited resources provided by multiple servers, we propose aplacement policy. And then we analyze the blocking probability, the cost ofstorage space and the requirement of netwo