一個在非對稱網路環境下改善同儕式網路電視播放品質之方法

Abstract

隨著網路頻寬的普及，越來越多的網路應用興起，而這些技術有部份採用了同儕式網路(Peer-to-Peer Network)架構。不同於以往的用戶伺服器(Client-Server Model)架構，每位使用者(user)將可同時扮演兩種角色，藉以提高整體網路的效能。隨著早期應用如檔案傳輸(File-Sharing)、網路電話(Voice over Internet Protocol)等成功的普及，近年來網路電視(Internet Protocol Television)開始採取同儕式網路(Peer-to-Peer Network)架構，其中最常見的兩種方法分別為：Tree-Push和Mesh-Pull，尤其以後者更是已經產品化，最近這幾年，結合Tree-Push和Mesh-Pull優點的Push-Pull機制興起。 當一個或多個同伴離開網路時，傳統的隨機方法將會根據事先定義的標準作業程序和關於這些同伴的資訊來任意的挑選一些代理者(Successor)，這樣一來，將會導致恢復的轉換時間(Recovery switching time)相當冗長，即必須等待長久的時間在於當一個或多個同伴離開後，代理者的尋找。 在本篇的論文中，我們提出了一個和傳統隨機方法比較起來，可以大幅的減低恢復的轉換時間的方法。主要的概念是從同區域的本地端選取事先已經定義好的伙伴做為暫時的代理者，直到系統從伺服器端得到一個固定的代理者。根據同伴離開的方式，我們將它分為規律和不規律兩種模式，在方法上有些差異。另外本篇論文考慮了非對稱網路環境(Asymmetric network environment)，並充分使用所有伙伴的上傳頻寬，而非只有利用高上傳頻寬的伙伴。本篇論文採用OMNet++模擬環境來驗證所提出之方法。模擬實驗結果顯示，我們所提出之方法大幅改善了伙伴離開而造成的播放品質下降問題。

As network bandwidth increases quickly and Internet service becomes popular, more and more network applications use peer-to-peer model (i.e. P2P network) model to provide services. Comparing to earlier client-server model, every P2P network user can play two roles, the client and the server. Based on this model, the whole network performance could be improved significantly. As the success of P2P file-sharing and Voice over Internet Protocol (VoIP), more and more IPTV (Internet Protocol Television) employ P2P model to improve their performance, in which, there are two main approaches, tree-push and mesh-pull. The latter has already been deployed widely in the market. In recent years, the combination of these two approaches is emerging. In traditional random approach, tracker servers will arbitrarily choose one or more peers as successor partners via standard operating procedure with the information of the departed peers, this way will significantly cost long recovery switching time (the time duration from peer leaving to the system recovery). In this thesis, we propose a method that significantly reduces recovery switching time comparing to traditional random approach. The main idea is to choose one or more pre-defined partners as temporarily successor partners from local partnership side until it finds one or more stationary successor partners from tracker servers. The approach has a little difference between normal and irnormal mode. This approach can be applied in asymmetric network environment and to fully utilize all of the peers’ upload bandwidth instead of only those peers with high upload bandwidth. Finally, we use OMNet++ simulation tool to evaluate the performance of our approach, and the results show that our proposed method improve the quality of experience significantly.