P2P-based Delivery Method for Multi-Object Video and Its Evaluation

最近，随着Joost和Zatoo等几项服务的推出，互联网上的P2P视频传输变得流行起来。P2P视频分发的优势在于它可以减轻服务器和网络负载，同时为用户提供优质的服务质量。这些已经开始的服务只提供一种固定质量的视频的传送，但是有许多类型的计算终端。因此，我们需要针对具有不同计算能力、不同显示尺寸和不同带宽的多个终端的高效视频传输方法。已经有几项研究努力将视频同时提供给具有不同质量要求的多个用户。在我们的研究项目中，我们提出了一种名为MTcast的视频分发方法，该方法依靠用户节点对视频进行转码和转发，实现了对多个异质用户的高效视频广播。MTcast有几个优点。(I)它可以为每个用户提供非常接近每个用户要求的视频；(Ii)它可以承受节点故障和突然离开；(Iii)传输延迟与节点数量的对数成正比；以及(Iv)新加入的节点不需要等待很长时间就可以第一次收到视频流。MTcast构建了一棵树，其根是原始视频内容的发送者，作为完美n元树的变体，其中具有更高质量要求的节点位于树的根附近。节点之间的父子关系根据带宽和物理路径的拓扑结构来确定。使用Java语言构建了一个可在PlanetLab上运行的MTcast系统原型系统，并在真实的互联网环境中验证了MTcast的实用性和有效性。通过原型系统，我们证实了MTcast具有较短的启动延迟、较短的通道切换时间和较短的节点离开/故障恢复时间

Recently, P2P video delivery on the Internet is becoming popular as several services like Joost and Zatoo has been started. The advantage of P2P video delivery is that it can reduce server and network loads while providing excellent service quality to the users. These already started services only provide delivery of one fixed quality of video, but there are many types of computing terminals. Thus, we need efficient video delivery methods for many terminals with different computation powers, display sizes and bandwidths. There are already several research efforts on simultaneously delivering videos to multiple users with different quality requirements. In our research project, we have proposed a video delivery method named MTcast which achieves efficient video broadcast to multiple heterogeneous users by relying on user peers to transcode and forward video. There are several advantages of MTcast. (i) it can provide a video whose quality is very close to the request of each user to each user ; (ii) it can withstand with node failure and abrupt departure ; (iii) the delivery delay is proportional to the logarithm of the number of nodes ; and (iv) newly joined nodes need not to wait long until it first receives the video stream. MTcast constructs a tree whose root is the sender of the original video content as a variation of a perfect n-ary tree, where peers with higher quality requirements are located near the root of the tree. The parent-child relationship between peers is decided according to bandwidth and topology of physical path. We also constructed a prototype system of MTcast system using Java language, which can be used on PlanetLab, and validated practicability and effectiveness of MTcast in the real Internet environment. With the prototype system, we confirmed that MTcast achieves short start-up latency, small channel switching time, and small recovery time from peer leaving/failure