使用Peer-to-peer(P2P)技術來提供點播服務，可以大幅減輕影音服務提供商的頻寬成本，因此成為趨勢。然而， 網路服務提供商卻傾向使用防火牆來限制P2P系統可用的網路資源， 導致被防火牆屏蔽的用戶不易與位於防火牆外的公開用戶交換影音資料。為此，我們提出一新穎的協同式傳輸方法，來改善上述問題。當用戶被防火牆屏蔽時，僅會使用被防火牆許可的傳輸方法傳輸資料。當不被防火牆屏蔽時， 則同時採用被防火牆許可的傳輸方法以及現有的P2P傳輸方式， 如此便可以把被防火牆屏蔽的用戶之頻寬資源加以利用。為提高協同式傳輸方法之效益，用戶依據實際下載情況智慧調節兩傳輸方法的下載工作。與無法利用屏蔽用戶上傳頻寬的傳統傳輸方法相比， 模擬結果證實本論文提出的方法可以大幅縮減伺服器的頻寬花費與用戶下載資料之時間。

Video-on-Demand(VoD) systems based on peer-to-peer (P2P) technology can reduce a tremendous amount of bandwidth cost than those based on traditional client/server architecture. However, internet service providers tend to use firewalls to limit the network resource of P2P systems. Thus, it becomes difficult for the peers behind the above-mentioned firewalls to share the media data with the peers in public network. To this end, we propose a novel cooperative transmission scheme. In our scheme,peers behind the firewalls adopt only the transmission method allowed by the firewalls. When the peers locate in public networks, they adopt not only the firewall allowed transmission method but also the p2p one. To improve the transmission efficiency, the downloading targets of the above two transmission methods will be adjusted based on the actual throughput. Compared with the traditional scheme which underutilizes the upload bandwidth of the peers behind firewalls, the simulation results prove that our scheme can remarkably reduce the bandwidth requirement of the media server and the downloading time of the peers.