【作者】 孙晓；

【导师】 汪浩； 王晖；

【作者基本信息】 国防科学技术大学 ， 管理科学与工程， 2008， 博士

【摘要】 军事环境下大规模的组播数据分发对于未来信息化战争具有重要的作用。现代军事通信环境具有规模大、动态性强、异构、服务质量要求高的特点,尤其是特殊的战场环境造成了军事通信网络强烈的动态性,极大地超越了传统网络技术所能管理的极限。在应用层实现的overlay组播数据分发技术可以更好地完成军事环境下的大规模数据分发任务。通过在物理网络之上构建特定的overlay网络,可以在网络的可靠性、抗毁性、灵活性方面提供更多的支持,实现更复杂地协同通信。同时反观生物网络等自然网络系统,虽然其规模巨大,但是面对诸多突发事故具有灵活的处理能力。通过引入自然网络系统中的适应性特征来改进军事通信网络,可以使网络面对复杂环境具有强自组织、自适应能力。本文采用从流行病传播理论发展而来的流言(Gossip)机制作为overlay拓扑组织和管理的主要手段,对overlay组播拓扑进行优化,增强其面对复杂环境的适应能力。通过分析,非结构化overlay网络和网络编码相结合的方法更适合于完成军事环境下overlay组播数据分发任务,本文对该方法中涉及的拓扑优化问题进行了阐述,选择军事应用背景下亟待解决的几个关键环节进行了优化研究。(1)基于自适应gossip机制的快速overlay拓扑收敛机制的研究。采用gossip机制维护的非结构化overlay拓扑能够随着网络状况的变化及时调整拓扑结构,根据不同的网络状况收敛到不同的状态。Overlay网络拓扑的收敛速度的快慢反映出overlay网络面对动态环境的适应程度,收敛速度越快,适应程度越好。本文通过分析overlay拓扑收敛过程中结点的行为特征,分析了固定周期gossip报文交换的弊端,提出了一种自适应周期的gossip报文交换机制代替固定周期方式。该机制减少了报文交换中的盲目性,节省了网络资源和提高了数据交换的效率,从而允许部分结点在局部加快数据交换的频率,最终提高overlay拓扑的收敛速度。(2)自组织overlay拓扑演化中的连通性保证研究。保证网络的连通性是overlay拓扑管理的一项重要任务。非结构化的overlay拓扑在网络状况发生变化时,通过改变邻居列表,达成与物理网络拓扑匹配的目的,使得overlay网络本身具有良好的灵活性。本文分析了基于gossip机制的overlay拓扑管理方法中overlay拓扑的演化过程,发现真实网络所具有的地域特征和非结构化overlay拓扑的邻居择优策略,可能在overlay拓扑的演化过程中导致拓扑的连通性遭到破坏。通过分析网络连通性被破坏的主要机理,本文提出了一种能够在拓扑演化的同时保证连通性的连接置换算法。而且,通过将各种单一的拓扑管理方法相结合,提出了多邻居列表的非结构化网络成员管理方法,并基于连接置换算法,建立了一个多邻居列表成员管理方法的实例C-MLMM,该方法能够在保证网络拓扑演化速度的同时,保证网络拓扑的连通性。(3)基于gossip机制的分布式网络编码拓扑构建方法研究。网络编码组播方法能够在动态环境中提供较多的结点容错性支持。传统的大多数网络编码构造方法要么需要全局的拓扑知识,要么需要使用较多结点参与编码,对结点的计算能力消耗巨大。军事通信网络环境要求一种资源利用更为有效的分布式网络编码构造方法。本文通过将网络编码方案分解为几个基本的数据“请求—响应”过程,总结出各种类型结点在构成网络编码方案中所进行的典型行为,利用gossip机制的局部信息获取能力,提出了一种以自组织方式构造网络编码方案的分布式方法。该方法相对于随机编码方式,资源利用率更高。通过仿真,在取得相似网络吞吐量的前提下,该方法只使用了约10%的结点参与编码。(4)编码超级结点的动态选择和维护策略的研究。网络编码组播中的编码结点需要付出额外的计算能力,通过动态地在网络中维护一定数量能力较强的超级结点,优先作为候选的编码结点,可以避免编码结点能力不足负载过量造成网络故障。本文通过研究用于编码的超级结点存在的特殊性,使用gossip机制作为基本手段,提出了一种适用于网络编码组播的动态超级结点选择和维护策略。(5)多个网络编码组播组资源共享和竞争的相关问题分析。军事通信网络应用中包括了多种不同的网络服务,服务的共存导致了一部分资源共享和竞争的问题。本文分析了在网络编码组播这种特定的应用模式下,overlay层次多服务共存的特殊性。为了共享不同组播组之间的资源,提出了基于服务无关性的统一overlay成员管理方法;对不同共享模式下的资源竞争,进行了博弈分析,分析发现:为了更好地促进资源的共享,有必要引入一定的网络信任机制。总的说来,本文以复杂军事环境下的大规模数据分发为应用背景,采用gossip机制作为网络拓扑组织和管理的基本手段,对军事环境下overlay组播拓扑优化中亟待解决的几个关键问题进行了研究,为增强军事通信网络的数据获取和分发能力奠定了良好的基础。更多还原

【Abstract】 Large-scale multicast data distribution under military circumstances plays an important role in future information warfare. Modern military communication is featured with large scale, drastic dynamics, heterogeneity and high QoS demand. In particular, the combat environment brings about drastic dynamics in military network, which far overruns the limit of conventional network management. Employing overlay multicast data distribution on application layer can better complete the large-scale data distribuition task in military evironment. By employing the overlay networks built on top of physical network, we can get more support in aspects of robustness and flexibility, thus providing the communication networks with better adaptability in complex and dynamic environment.In contrast, some natural networks like the biological network, though giant in size, have strong adaptation to cope with various emergencies. Introducing the adaptation of natural network into military communication network can equip the latter with better adaptation. The thesis applies gossip mechanism developed from theory of epidemic spread as the major approach to construct and manage overlay topology, and optimizes the multicast overlay topology. The thesis takes the combination of unstructured overlay network and network coding as the main method to realize overlay multicast data distribution in military environment, elaborates on the topology optimization involved in this method, studies several unsolved yet urgent key issues in military application and proposes effective solutions.(1) Study of the quick overlay topology convergent mechanism based on self-adaptive gossipGossip-based unstructured overlay topology can adjust itself with the network environment change, enabling the overlay topology to converge to different structures. The topology convergent speed reflects the adaptability of overlay network in dynamic environment. The faster the convergence is, the better the adaptablility is. This paper analyzed the node behavior characteristics in the convergence process and found the flaw of fixed cycle gossip. Then the paper proposed an adaptive cycle mechanism to control the exchange of gossip packets. This mechanism can improve the data exchange efficiency and save the network resource so that some nodes can accelerate the data exchange locally and therefore the convergence speed of overlay topology is increased.(2) Study of connectedness in self-organizing overlay network evolvingGuaranteeing the connectedness of network is an important task in overlaytopology management. The unstructured overlay topology management changes the nodes neighbor lists to match the change of underlying physical network. This paper analyzed the overlay topology evolving process in overlay topology management methods based on gossip mechanism and found the local-area characteristics of actual network and neighbor selection strategy of nodes in unstructured topology may break network connectedness of overlay topology. After analyzing the key factor of breaking connectedness, the paper proposed a simple yet convenient links replacement algorithm based on local connected domain optimization. Furthermore, by combining different simplex topology management mechanisms, the paper presented Multiple Lists Membership Management (MLMM) and gave an example based on MLMM, C-MLMM, which showed the efficiency of MLMM in assuring topology convergence speed and network connectedness as well.(3) Study of distributed network coding construction based on gossipPrevious centralized approaches on network coding construction need global topology knowledge and are difficult to be practically used in large-scale or dynamic network. And the randomized network coding approach is a practical distributed network coding approach, but it employs all nodes to code and consumes enormous computing power. However, the data distribution in military communication network demands a more effective distributed network coding construction approach. Hence this paper decomposed the network coding solution into several basic "request-respond" processes, summarized the typical behavior of different kinds of nodes in the network coding scheme. Then applying gossip mechanism that can obtain the adjacent node information quickly, the paper proposed a distributed network coding construction approach with much fewer coding nodes. Simulation showed that this approach has excellent performance, which achieves the approximate throughput compared with distributed Randomized Network Coding, but only employing about 10% of nodes to code.(4) Study on dynamic selection and maintenance of coding supernodeIn the network coding multicast solution, coding nodes need consume extra computing power. Nodes with stronger abilities may be chosen as candidates for coding, called Supernodes. The prior usage of supernodes in network coding can avoid overload or breakdown caused by the inability of coding nodes. This paper analyzed the characteristics of the supernodes for network coding and presented a dynamic supernode selection and maintenance policy applying gossip mechanism. The policy is proved to suit for network coding multicast.(5) Study of resource sharing and competition among multiple sessions in network coding multicastThere are different network services in military communication application and the problem of resource sharing and competition is inevasible. This paper analyzed the specific characteristics of resource sharing and competition in network coding multicast. To share resources among multiple sessions efficiently, a general integrated membership management approach was presented. Then games theory was used to study resource competition behavior in different sharing models and the paper found the necessity of introducing certain trust mechanism to improve resource sharing.In a word, the thesis studied large-scale data distribution in the complex and highly dynamic military environment, proposed a data distribution multicast scheme combing gossip-based unstructured overlay topology and network coding suitable for military application, and thus laid sound foundation for the capability improvement on data acquisition and distribution in military communication network.更多还原