網際網路使用客戶端回饋機制控制MPEG-4影像傳送的速率

Abstract

隨著網際網路的普及和在影像壓縮上具有彈性的MPEG-4編碼法，在不久的將來，利用網際網路來傳送MPEG-4影像將成為多媒體應用中重要的一環。與其他應用程式不同的是，多媒體應用在資料延遲和遺失的限制上有較嚴格的要求，而現今的網際網路無法保證在這方面能達到嚴格的要求。如何設計一個能夠將資料延遲和遺失減到最少，以及將影像視覺效果增到最大的壅塞控制機制，是網際網路多媒體傳輸一個重要的議題。 我們提出一個以伺服－客戶端模式為基礎的壅塞控制機制。伺服端依據客戶端之前察覺到的網路狀態來調整資料輸出的速率，以避免資料的延遲和遺失。客戶端則持續追蹤收到的資料，用來回傳給伺服端以決定之後的輸出速率。這就是以客戶端回饋為基礎的壅塞控制機制。在實驗中，我們證實這個機制能夠很快的調整輸出速率接近至最大可用頻寬，以及有效的使用網路資源。

With the popularity of the Internet and the flexibility of MPEG-4 encoding, transporting MPEG-4 video in the Internet will be an important component of multimedia applications in the near future. Unlike other applications, video applications typically have the limitations of packet delay and packet loss, which cannot be guaranteed by the current Internet. It is an important issue to design a congestion control mechanism of MPEG-4 delivery system that can minimize delay and packet loss to maximize the perceptual quality of service. We present a congestion control mechanism based on the client-server model. The video server adjusts the data output rate depending on the perceived network feedback from the video client to avoid delay and loss. The client keeps track of the video data received to estimate the future output rate as the feedback for the server. This mechanism is thus referred to as rate control mechanism based on client feedback. It can rapidly adjust the output data rate close to the bandwidth available and utilize network resources efficiently, which is verified by the simulation performed and the experimental results.