一個以NAT擷取為主的環境下提昇同儕式網路電視播放品質的方法

Abstract

網路電視(Internet Protocol Television)是現今網路上一個方興未艾的服務，透過電腦上線，使用者可以利用網路接收到影音串流的資料，進而觀賞世界各地的電視節目。過去，網路電視服務業者採用網際網路上傳統的用戶伺服器(client-server)架構來提供服務，也就是用伺服器以提供所有用戶所需要的串流資料，然而當用戶數量過大時，服務業者將面臨可容納度及高成本問題。近幾年來同儕式(peer-to-peer)檔案分享與網路電話的發展，證明了透過同儕式架構也可以在網際網路上有效的傳遞各式各樣的資料內容。因此，許多同儕式網路電視已經實現在網際網路上。不過也產生了另外一個問題：當網路轉址器(NAT)的使用者過多時，位於網路轉址器後面的使用者(NATed peer)無法直接分享自己的串流資料給其它位在網路轉址器後面的使用者，使得這些同儕端點很容易造成搭便車問題(free rider problem)。 在本篇論文中，我們提出一個分組的方法來提高NAT 擷取為主的的分享率。藉由限制擁有公共IP位址端點彼此之間的傳輸連結性，以及對資料通道(data trunk)的適當分配，來促使位在網路轉址器後面的使用者貢獻更多的資料在整個網路上。另外，所提出的方法是很容易新增在現有的網路電視的軟體上，不需要大幅修改，是相當實用且容易實現的。我們發展出一套模擬軟體以評估我們所提出的方法，數值結果顯示我們所提出的方法能夠提高NAT使用者的分享率並改善影像播放的穩定性。

Internet Protocol Television (IPTV) is a quickly growing Internet service. Through computer online, users can access the network service to receive video streaming data and watch TV programs from around the world. Traditionally, IPTV service provider adopted client-server architecture. However, when the client population grows up to a certain amount, it usually faces the scalability and high cost problems. Fortunately, the P2P file sharing success and VoIP application has proved that the P2P paradigm is an efficient solution to deliver many kinds of content over the Internet. Nowadays, P2P IPTV services have been popularly deployed on the Internet. We may face the problem that there are more and more Network Address Translator (NAT) users, and peers behind NAT (NATed Peer) can not directly deliver its streaming data to other NATed peers. This situation easily leads to the so-called free rider problem. In this thesis, we propose a “grouping” scheme to increase the share rate of NATed peers. By restricting transmission connectivity of those peers with public IP address and properly arrange data chunk delivery, we could allow NATed peer to contribute more data on the overlay network. We developed a simulation program to evaluate our proposed scheme. The numerical result shows that our proposed scheme is able to increase the share rate of NATed peer and improve the video playback quality. In addition, our scheme can be easily added to the existing IPTV software. It’s practical and feasible for implementation.