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

最近，随着Joost和Zatoo等服务的推出，互联网上的P2P视频传输正在流行起来。P2P视频传输的优点是在为用户提供优质服务的同时，可以减少服务器和网络的负载。这些已经开始的服务只提供一种固定质量的视频传输，但有许多类型的计算终端。因此，我们需要针对不同计算能力、不同显示尺寸和不同带宽的终端，采用高效的视频传输方法。目前已经有几项研究致力于同时向具有不同质量要求的多个用户提供视频。在我们的研究项目中，我们提出了一种名为MTcast的视频传输方法，它依靠用户对等体对视频进行转码和转发，实现了对多个异构用户的高效视频广播。MTcast有几个优点。(i)能够向每个用户提供质量非常接近每个用户要求的视频；（ii）能够承受节点故障和突然偏离；（iii）交付延迟与节点数的对数成正比；（iv）新加入的节点不需要等待很长时间，直到它第一次接收到视频流。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元树的一种变体，其中对质量要求较高的节点位于树的根附近。对等体之间的父子关系取决于物理路径的带宽和拓扑结构。我们还利用Java语言构建了MTcast系统的原型系统，该系统可以在PlanetLab上使用，并在真实的Internet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MTcast实现了短的启动延迟、小的信道切换时间和小的对等端离开/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