【作者】 黄明杰；

【导师】 徐丽萍；

【作者基本信息】 华中科技大学 ， 计算机软件与理论， 2007， 硕士

【摘要】 随着网络技术的进步,Internet己经发展成为信息社会中最重要的内容发布系统,但Internet中传统的以应用服务器为中心的内容分发网络(Content Distribution Network,CDN)存在着性能瓶颈,不利于网络扩大和维护费用高等问题。与此同时,一种新的分布式资源利用模式——对等网络(Peer-to-Peer,P2P)计算产生了。与传统的C/S计算不同的是,P2P计算一般不需要中心服务器。网络中每个节点既是客户端,又是服务器。P2P允许计算节点之间的直接交流和协作。P2P计算可以充分利用Internet边缘日益丰富的闲置资源,包括计算、存储、带宽等资源。内容发布和共享是P2P计算的一个主要应用领域,基于P2P的内容发布系统的特点是能够充分利用大量的客户端资源,减轻或者抛却应用服务器的负载。P2P内容分发机制的核心是负载均衡算法以及文件分块选择算法。其中负载均衡算法的目的是选择更接近的、性能更好的节点作为分发服务器。为适应P2P网络的各个节点随时变化的状态以及性能,内容分发机制采用动态的基于优先级的负载均衡算法——根据节点CPU和内存的状况、两节点之间的逻辑距离以及网络状况进行优先级计算并排序,然后顺序选择节点发出资源请求。文件分块选择算法依据文件两层分块的原理划分为两部分:部分选择算法以及块选择算法。前者采用基于优先级的原则:通过该部分在各节点的分布情况、完成度等因素计算出优先级,选择优先级最大的部分进行分发。后者采用顺序选择以及节点反馈相结合的方法:正常情况下,按照块的顺序进行选择;否则,跳跃到下载点所反馈回来的下一块进行顺序选择。负载均衡算法使得下载者趋向于向更接近的、性能更好的上传者发出资源请求,以获得更好的分发速度;文件分块选择算法有助于增大网络中文件分块在各个下载者之间的差异性,以便加快下载者之间的分发速度。以此为核心的内容分发机制可以更快的速度从更接近、性能更好的节点处获得资源。更多还原

【Abstract】 With the development of network technology, Internet has become the most important content distribution system in the information society, but the traditional server-centric content distribution mode is also confronted with performance bottle neck. At the same time, P2P computing as a new mode of utilizing distributed computing resources comes into being. It is different from Client/Server computing, commonly there is no special server in P2P network and nodes can communicate and collaborate directly with each other. P2P computing can utilize increasingly unused resources in the edge of the Internet. Content distribution and sharing is one of the main applications of P2P computing, P2P-based content distribution system can fully utilize resources of vast clients and lighten the load of application server.The core of the P2P-based content distribution mechanism is the load balance arithmetic and the file’s part choosing arithmetic. The purpose of the load balance arithmetic is to choose the node which is nearer or has a better performance as the distribution server. To adapt to the momentarily changing of the state and the performance of the nodes, the priority-based load balance arithmetic is used, whose principle is: calculating and sorting the priority by the states of the CPU and memory, the logic distance of the nodes and the states of network, then send a resource request to the node that has the highest priority. Like the principle of the file’s partition, the file’s part choosing arithmetic is divided into two: the Part-choosing arithmetic and the Block-choosing arithmetic. The Part-choosing arithmetic is priority-based: calculating and sorting every Part’s priority by the situation of the Part in the nodes and the finish percentage, then sending the Part that has biggest priority. The Block-choosing arithmetic’s principle is choosing in the order and the node’s feedback: In the normal condition choosing the Block in the order; otherwise, choosing the Block beginning with the feedback.The load-balance arithmetic could make the download-node to send the resource request to the upload-node which is nearer and has better performance; the file’s part choosing arithmetic is good for making the difference of the file’s Part in the download-nodes bigger, and making the speed of the distribution faster. The content distribution mechanism whose core is the two arithmetics can make the node to get the resource faster from the nearer and better performance nodes.更多还原