【作者】 吴家皋；

【导师】 顾冠群；

【作者基本信息】 东南大学 ， 计算机应用技术， 2006， 博士

【摘要】 随着计算机网络的不断发展,互联网已经成为了人类社会主流一个重要组成部分。人们希望互联网能够不断地提供应用所需的各种网络服务。特别是,以视频会议、视频点播、远程教育等为代表的新型多媒体多播应用的大量涌现,对多播通信服务提出了迫切的需求。基于覆盖网络思想的覆盖多播技术是由端系统而不是核心路由器实现多播通信的所有功能,与IP多播相比,其最大的优势在于无需改变下层网络基础设施,易于部署,这体现了下一代网络服务的研究重点正在从网络层向应用层跃迁的趋势。如何提供满足应用需求的覆盖多播路由是其研究的核心内容。本论文主要针对覆盖多播的路由协议及算法等相关问题展开研究,其中,多媒体应用的QoS需求以及网络环境的异构性是本文关注的重点。我们首先提出了通用的覆盖多播网络模型,对覆盖多播中的路由优化问题进行了系统分类,并对当前主要的覆盖多播路由的协议和算法进行了全面的比较和分析,为本论文建立系统理论框架和指明研究方向。在此基础上,我们分别从覆盖多播的集中式路由算法、分布式路由协议和原型系统等几方面开展了研究工作。在集中式算法方面,提出了一种新的基于度约束-延时综合和应用层拓扑优化双重策略的最小延时覆盖多播树生成算法—度-延时紧凑树算法(DDCT),改进了多播树的性能;针对实时多媒体应用对带宽需求的异构性,采用分层的带宽分配策略,提出了一个异构环境下构造最小延时覆盖多播树的启发式算法—分层的紧凑树算法(LCT)。该算法能有效地降低多播树的高度和网络资源使用量。在分布式协议方面,提出了一个新的分布式、树优先的覆盖多播路由协议—BowCast。该协议采用简单、灵活的单向延时探测技术,能很好地适应非对称链路延时环境;面向实时多媒体多播应用,提出了一个支持异构QoS需求的分布式、树优先的覆盖多播路由协议—QoS覆盖多播树协议(QOMTP),并研究了其局部优化算法。该协议能获得较高的节点接纳率,并保持较小的平均接入代价。在原型系统方面,研究并实现了一个新的基于代理服务器的覆盖多播系统—服务可定制的覆盖多播系统(SCOMS)。该系统采用了新的体系结构框架,将结构化P2P路由和树优先的覆盖多播路由构造方法相结合,具有良好的可扩展性、高效的QoS覆盖多播路由和灵活的服务定制能力。本论文的研究成果可为覆盖多播路由协议和算法的研究提供新的理论方法和思路,也可以应用于实际的覆盖多播系统中,具有较高的理论价值和较好的应用前景。更多还原

【Abstract】 With the development of computer network, Internet has been becoming an important part of the mean streaming of human being. People hope Internet could provide all kinds of network services the applications need. Especially, the emergence of many new multimedia group applications, such as video conferencing, video-on-demand and distance learning, require multicast communication service imminently.Based on the concept of overlay network, in overlay multicast, end systems perform all multicast communication functionalities instead of IP routers. Compared with IP multicast, the greatest advantage of overlay multicast is it needn’t change the lower network infrastructure, and can be deployed easily. Overlay multicast embodies the trend that the emphasis of network service research is shifting from network to application layer in the next generation Internet, and its core problem is how to build overlay multicast routing satisfied by applications.In this thesis, overlay multicast routing protocols and algorithms with other related problems are studied, where the QoS requirements of multimedia application and heterogeneity of network are focused. Firstly, a general overlay multicast network model is proposed, and the routing optimal problems in overlay multicast are classified, then some recent important overlay multicast routing protocols and algorithms are fully analyzed and discussed. These construct the theory framework and point out the study direction of this thesis. Based on the above work, our research on overlay multicast is performed in the following aspects, which include centralized routing algorithms, distributed routing protocols and system prototype.In the study of centralized routing algorithms, based on both degree constraints-delay integration and application layer topology optimum strategies, a new minimum delay overlay multicast tree building algorithm called Degree-Delay Compact Tree (DDCT) is proposed to improve the routing performance; To settle the heterogeneity of bandwidth required by real-time multimedia application, adopting the strategy of layered bandwidth allocation, a heuristic routing algorithm called Layered Compact Tree (LCT) is proposed to build a minimum delay overlay multicast tree in heterogeneous condition. The LCT could reduce both hops and network resource usage of the tree effectively.In the study of distributed routing protocols, a new distributed tree-first overlay multicast protocol called BowCast is proposed. Adopting a simple and flexible one-way delay probe method, BowCast can adapt the asymmetric link delay environment well; To support heterogeneous QoS requirements of real-time multimedia multicast applications, a new QoS overlay multicast routing protocol called QoS-aware Overlay Multicast Tree Protocol (QOMTP) is proposed, and its local optimum algorithm is studied, too. QOMTP can reduce the network resource usage of members on the tree as well as achieve a higher admission rate of members.In prototype, a new proxy-based overlay multicast system called Service Customizable Overlay Multicast System (SCOMS) is studied and implemented. Combining DHT-based P2P and tree-first overlay multicast routing protocols, SCOMS can not only keep high scalability, but also provide efficient QoS overlay multicast routing and flexible capability of service customization.The research conclusions of this thesis could not only provide new theoretical method and idea to study overlay multicast routing protocols and algorithms, but also be applied in practical overlay multicast system, therefore, have high theoretical value and wide applied foreground.更多还原