隨著科技不斷的進步, 在網路多媒體影片傳送服務的串流技術上, 有許多不同的傳送方法. 最傳統的方法是以點對點的方式傳送, 不僅沒有效率, 而且使用者的等待時間很長. 此外, 還有許多廣播式的傳送方法被提出來. 他們能有效的降低使用者等待時間, 但是相對的, 使用者所需要的影片預存空間很大, 最多須將50%的影片存在使用者的硬碟中, 造成使用者的影體設備上相當大的負擔. 因此, 我們在這篇論文中提出了一個有效率的方法叫做 “Dynamic Periodic Broadcast Method”. 在這方法中, 我們根據使用者多寡來決定影片傳送的頻寬. 因此, 對於熱門的影片, 就分配較多的網路頻寬來傳送以減低多數使用者的等待時間. 相對的, 如果影片較不熱門, 我們就用少量的頻寬來傳送, 以免造成網路頻寬的浪費. 此外, 在減低使用者等待時間的同時, 我們還降低了使用者的影片預存空間. 除此之外, 為了考量每個使用者的網路狀況的不同, 我們希望能將Receiver-Driven Bandwidth Adaptation的概念應用在Dynamic Periodic Broadcast方法上. 所謂Receiver-Driven Bandwidth Adaptation的概念就是根據每個使用者的網路狀況, 以不同的傳送速率傳送影片資料. 因此, 對於擁有較多頻寬的使用者, 他們的等待時間較短; 相反的, 對於頻寬較少的使用者, 他們的等待時間就必須比較久了. 透過這個概念, 我們就能讓所有使用者都能順利的觀看影片, 不會因為網路狀況的不同而造成資料流失而導致影片欣賞斷斷續續的狀況發生. 因此, 在這篇論文中, 我們還提出了一個方法 “Channel Adjustment”, 利用Channel Adjustment 方法將 “Receiver-Driven Bandwidth Adaptation”的概念應用在我們的Dynamic Periodic Broadcast方法上.

Today modern multimedia delivery services usually distribute their contents by means of the streaming technology. In conventional platform, the point-to-point delivery model is adopted but also known as less efficient. To extent scalability, some services apply periodic broadcast to provide an efficient platform that is independent of the number of clients. Fast Broadcasting, Staircase Broadcasting, Harmonic Broadcasting and Skyscraper Broadcasting are some novel schemes in this subject. For a popular video, these periodic broadcast services can significantly improve viewer initial delay by distributing cyclic video segments through multiple channels. However, the requirement of a large amount of client buffers is a major drawback of them. Additionally, video segments are broadcasted periodically by a per-determined schedule. If the prediction of the popularity of a video is incorrect, some bandwidth will be wasted. Moreover, period broadcasting also should not be adequate to carry out on heterogeneous networks. In this thesis, we propose a novel dynamic periodic broadcasting scheme that gets the benefit of less buffer usage and flexibility for bandwidth adaptation. That is, to prevent unnecessary bandwidth wasted, only requisite video segments will be transmitted. We also integrate a receiver-driven bandwidth adaptation strategy on our dynamic periodic broadcasting scheme to fit the channel bandwidth of each client. We then design our channel adjustment scheme. Instead of using a fixed number of channels to serve all clients, we can adjust the transmission rate as well as the required channel number owing to the available bandwidth on the path from the server to the client. Our experimental results show that this dynamic scheme can perform well in heterogeneous networks.

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