【作者】 贺莲；

【导师】 吴产乐；

【作者基本信息】 武汉大学 ， 计算机应用技术， 2010， 博士

【摘要】 随着Internet规模的不断扩大,原有的广播变得越来越昂贵,于是出现了限制广播范围的组播技术,按照组播运行的层次不同有IP组播和应用层组播。IP组播运行在网络层,需要有网络基础结构中路由器的支持,IP组播能避免物理链路上数据包的重复传输,从而节省了网络带宽。但由于规模性、可靠性以及拥塞控制等因素,IP组播并没有在Internet上得到广泛部署。与IP组播相比,应用层组播系统的节点通常都是端系统,因此能够进行更加复杂的操作；同时,这些节点还可以构成随系统要求调整的覆盖网。应用层组播的这些特点使得它能与网络编码技术进行很好的融合。网络编码概念在网络传输方面提出了一个全新的研究方向。传统的网络传送中节点对信息只能进行存储转发,因而不能达到网络的最大吞吐量。而网络编码则提出了对接收的信息进行编码操作,使得同样的容量能容纳更多的信息线索,这样,不仅能提高网络吞吐量使其达到最大流—最小割定理所规定的上限,还能对网络健壮性和安全性等方面起到积极的作用。网络编码的这些特性使得它更适合于组播技术。目前,网络编码的研究主要集中在数学基础理论研究和特定环境下的应用研究两个方面。在数学基础理论研究方面,主要有：用集合论和矩阵理论研究网络编码的构建,用图论和信息论分析网络编码与拓扑的关系,求解与网络编码相关的各项指数的上下限,以及应用各种数学手段从理论上证明网络编码在其它用途中的可行性等等。在特定环境下的应用研究方面,主要包括网络编码技术在无线网络、应用层组播、P2P文件分发和流媒体传输等实际的网络环境中的应用问题。现在,网络编码在应用层组播系统中的应用研究多数还处在理论方面,在实际应用方面的研究尚不多见。尽管基于网络编码的应用层组播在理论上显示出很大的优势,但是这种优势尚未反映在实际应用中。因此,网络编码技术在实际系统中是否能达到理论研究的效果,以及怎样在实际系统中运用网络编码技术均有进一步的研究价值。本文以国家自然科学基金项目“基于网络编码的高质量应用层组播研究”(60672051)研究工作为基础,围绕如何将网络编码技术运用于实际网络环境这一主题,在特定应用层组播系统中设计并实现线性网络编码,主要对媒体数据分片大小策略、编解码机制、缓冲机制等问题进行研究,并探讨如何将网络编码方案扩展到流行组播系统中。通过理论与实验相结合的方式,分析网络编码对实际组播系统性能的影响。在自相似结构化组播模型S3M中设计了相应的确定性和随机线性网络编码方案,通过仿真实验分析了网络编码对S3M性能的影响。在此基础上,针对混合网状应用层组播模型HM-ALM的特点提出了确定性网络编码算法,并进行了编解码算法实验和系统实验,分析了算法特性及其对HM-ALM组播模型性能的影响。此外,本文还选择目前应用广泛的BitTorrent作为网络编码功能扩展的实验载体,利用对BitTorrent系统的仿真,简化其部分机制和操作,并在其上实现随机网络编码算法。研究成果表明,网络编码的编解码算法开销并不大,能够适应应用层组播系统中的端系统异质性的特点,因此,网络编码在应用层组播系统中具有可用性。同时,网络编码对应用层组播系统性能也有影响,通过一定量的包冗余,降低了系统传输延迟,提高系统健壮性,能在系统出现波动时,保持系统性能的平稳。本文创新点有：(1)提出了一个基于应用层组播系统拓扑结构的网络编码机制,并分析了其对组播性能的影响；(2)在确定性线性编码机制中引入随机性因素,有利于编码方案的扩展；(3)对流行组播系统进行了网络编码功能的扩展,研究了网络编码对其系统性能的促进作用。本文后续研究工作包括：研究特定环境下,确定性网络编码与随机网络编码结合方案；在流媒体应用方面,网络编码与信源编码联合解决方案；以及多源多宿情况下,网络编码实际的应用研究等。更多还原

【Abstract】 Along with the unceasing expansion of Internet, the original broadcast becomes more and more expensive. Therefore the multicast technology is presented which limit the broadcasting range. And according to the different levels of multicast, there are IP multicast and the application layer multicast (ALM).IP multicast is in the network level, and needs router support in the network foundation structure. IP multicast can avoid the data packet redundant transmission on the physical link, thus it can save the network bandwidth. But because of the scale, reliability, congestion control and so on, IP multicast has not obtained the widespread deployment in Internet.Compared with the IP multicast, the nodes in ALM are usually the end system. So those nodes can carry out more complex operations. At the same time, these nodes may also constitute overlay network along with the system request. These characteristics of ALM enable it to carry on the fusion with the network coding technique well.The concept of network coding put forward a brand-new research direction in the network transmission. In traditional network transmission, the node can only store and forward the information and it cannot achieve the maximum throughput of the network. While the network coding is proposed to encode the received information makes more information clues be hold with the similar capacity. So that it not can only improves the network throughput to the upper limit of maximum flow-minimum cut theorem, but can plays the positive role on network toughness and security. These features of network coding make it more suitable for multicast.At present, the study of network coding has two directions. (1) Basic math theoretical research. It mainly includes studying the structure of network coding with set theory and matrix theory, studying the relationship between network coding and topology with graph theory and information theory, solving various parameters of network coding, proving theoretically the other uses feasibility of network coding, and so on. (2) Application of network coding under specific circumstances. It mainly includes the applications of network coding in wireless networks, ALM, P2P file distribution and streaming media delivery network.Now, the most applied research of network coding in ALM is still in theory. And the research of practical application is still rare. Although network coding based ALM shows a great advantage in theory, but this kind of superiority not yet reflects in the practical application. Therefore, in real system if the network coding can achieve the theoretical effects and how to use it are worth further study.This dissertation takes the research work of the National Natural Science Foundation project "Research on High Quality Application Layer Multicast with Network Coding" (60672051) as a foundation. The subject is how utilize the network coding technique in actual network environment. It designs and realizes the linear network code in the specific ALM system, mainly to the media data partition strategy, encoding/decoding mechanism, and buffer mechanism, and discusses how to expand the network coding to the popular multicast system. Through the combination of theoretical and experimental methods, it analyzes the network coding system performance on the actual multicast system.In Self-Similar Structured Multicast (S3M), it designs deterministic linear coding and random linear coding strategy, and through the simulation experiment analyzes the influence of network coding on the S3M performance. On this basis, for the characteristics of hybrid mesh multicast model (HM-ALM), it designs the deterministic network coding algorithm. Through the experiments on encoding /decoding algorithm and the system experiments, it analyzes the algorithm characteristics and the performance on HM-ALM.In addition, this dissertation also chooses BitTorrent as the experiment carrier on which the network coding used. With the simulation of BitTorrent, simplifying its part mechanisms and operations, the random network encoding algorithm is realized.Studies show that network coding overhead of encoding/decoding algorithm is not large, it able to adapt to multicast system characteristics of the end systems’ heterogeneity. Therefore, the network coding has usability in ALM. Network coding is also influential to the ALM system performance. With the ration package redundancy, it reduces the system transmission delay, enhances the system robustness, and maintains the system performance steadiness when the system presents the fluctuation.The innovation of this dissertation are:(1) Proposes a network coding mechanism based on the ALM network topology, and analyzes its impact on the multicast performance; (2) Introduces the random factor in the deterministic linear coding, that is advantageous in the coding scheme expansion; (3) Carries on the network coding function to the popular multicast system, studies the promotion of network coding to its system performance.The following research work include:the combination of deterministic linear coding and random linear coding under particular circumstances; the network coding and source coding joint solution in streaming media applications; and the network coding actual applied research under the situation with multi-source multi-sink, and so on.更多还原