請用此 Handle URI 來引用此文件:
http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/35142
標題: | 串流視訊代理伺服器暫存機制之研究 A Study of Proxy Cache Mechanism in Video Streaming Applications |
作者: | Shin-Hung Chang 張信宏 |
指導教授: | 歐陽彥正 |
關鍵字: | 異質性網路,視訊暫存,階段式視訊儲存,視訊串流,變動位元速率視訊, Heterogeneous Network,Video Cache,Video Staging,Video Streaming,VBR Video, |
出版年 : | 2005 |
學位: | 博士 |
摘要: | 高畫質的視訊內容,通常採用壓縮後的格式進行儲存,或透過網路傳輸提供串流服務。壓縮後的視訊內容,先天具備有變動位元速率 (VBR, variable bit rate) 特性,因此進行串流服務時,網路上流量需求變化是非常劇烈的。假如在客戶端沒有一套緩衝機制 (Buffering Mechanism) 來調整視訊資料的傳送,我們需要使用視訊內容資料的最高頻寬需求,進行網路頻寬配置,以保證視訊在串流播放時的品質。為了降低網路頻寬的使用需求,之前的研究者提出了一套階段式視訊儲存機制 (Video Staging)。此暫存機制將部分需要從遠端伺服器傳送的視訊資料,置於靠近客戶端的視訊代理伺服器中。在本論文中,我們提出了使用一回合 (One Pass)即可完成的 OC (Optimal Cache) 演算法,來處理階段式視訊儲存機制。透過數學理論分析,我們證明了使用OC 演算法,對於任一視訊內容在進行串流服務時,可以使用最少的視訊代理伺服器的儲存空間,卻可同時降低與傳統演算法等值的網路頻寬需求。更進一步,我們也考慮到資料封包在透過網路傳輸時,是容易出錯或遺失的。然而,這些載有視訊資料的封包若遺失,很可能影響視訊播放品質,更進一步可能會造成視訊無法完成播放。因此,我們精鍊了 OC 演算法,並提出一套 PSC (Priority Selected Cache) 演算法,選擇暫存最重要的視訊資料在視訊代理伺服器中。此 PSC 演算法具備與 OC 演算法同樣的特性,能使用最少的代理伺服器暫存空間,降低網路頻寬需求。但同時,當網路出現封包遺失狀況時,PSC 演算法能有效避免重要視訊資料遺失,而維持客戶端串流視訊的播放品質。我們透過實驗,針對一些標準視訊資料測試我們的演算法。我們發現,我們提出的演算法確實達到我們的目的,且效果較傳統的演算法,效果有著非常顯著的改進。 High quality video content for on-demand services is usually stored and streamed in a compressed format with a VBR (Variable Bit Rate) property; however, the streaming traffic is extremely bursty. If there is no client buffer to regulate the video’s delivery, the backbone WAN (Wide Area Network) bandwidth needs to allocate the video's peak bit rate to guarantee playback quality. To reduce the bandwidth requirement in the backbone WAN, previous researchers have proposed a Video Staging Mechanism to cache portions of the video in a video proxy close to clients. In this dissertation, a one-pass OC (Optimal Cache) algorithm is proposed to handle the Video Staging Mechanism and prove theoretically that the proxy cache computed by our OC algorithm for each video is minimal when all other resources remain constant. Additionally, data packets are often lost while streaming video data over the unreliable Internet. These lost packets are often important enough to affect video playback quality and even halt the video playback. Therefore, we refine the OC algorithm and propose a novel PSC (Priority Selected Cache) algorithm to select maximum high-priority video data for caching in a video proxy. The PSC algorithm inherits to use minimum storage in video proxy and reduces the maximum bandwidth requirement of video server (as does the OC algorithm). Additionally, the PSC algorithm also prevents the decoding errors caused by packet loss, improve error recovery, and provide QoS-guaranteed video playback. On the basis of experiment results, we cache the least amount of video data in the video proxy by using the OC algorithm, and reduce the WAN bandwidth requirement by an amount equal to that of conventional algorithms. In contrast, given the equal size of the storage in a video proxy, the OC algorithm reduces the bandwidth requirement in the backbone WAN much more than conventional algorithms. Furthermore, we show that the PSC algorithm caches more high priority video data in a video proxy server than the original OC algorithm. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/35142 |
全文授權: | 有償授權 |
顯示於系所單位: | 資訊工程學系 |
文件中的檔案:
檔案 | 大小 | 格式 | |
---|---|---|---|
ntu-94-1.pdf 目前未授權公開取用 | 1.28 MB | Adobe PDF |
系統中的文件,除了特別指名其著作權條款之外,均受到著作權保護,並且保留所有的權利。