連續媒體代理伺服器而設計之調變式後置視窗快取演算法

Abstract

代理伺服器通常用來協助用戶端透過網路接收遠端的資訊。本篇論文探討如何設計代理伺服器的快取策略，以利使用者來擷取遠端的連續媒體，如影音串流。我們將快取的資料分為兩種不同的影片區段：(1)prefix：開頭影片和(2)suffix-window：則是開頭影片之後，最近正在從遠端Video Server下載的後續影片。由於Video Server 可能提供數部影片，而影片的點播頻率可能不同且隨時間而變動。基本上我們希望能讓受歡迎程度越高的影片越能佔用代理伺服器的暫存空間，反之受歡迎程度越低的影片越難有機會使用。為了達到上述目的，我們提出『可調變式後置視窗機制』，針對影片的受歡迎程度自動的調整分配代理伺服器的暫存空間來儲存suffix-window，以獲取系統的最佳利益。經由模擬實驗結果得知，我們的快取機制可迅速的適應影片點播頻率的變動，並改善系統的效能，尤其是當使用者的緩衝區越小，這樣的效果就越明顯。

A proxy server is usually deployed for serving a set of clients to access remote information from Internet. This thesis focuses on designing such a proxy server for accessing continuous media, like video streams. In principle, two kinds of segments are stored in the proxy: (1) prefix: the beginning segment of a video and (2) suffix-window: the video segment just transmitted. Different videos usually show different popularity and the popularity may be changed with time. Ideally, the system should allow more popular videos to gain more proxy storage than the less popular ones. For this purpose, we propose an adaptive suffix-window scheme, which is able to self-tune the storage allocation for suffix window in response to the video popularity change to gain the optimal performance. The simulation results reveal that our scheme can quickly adapt to video popularity and improve the system performance with great significance particularly when the client buffer is very limited.