【作者】 彭利民；

【导师】 肖文俊；

【作者基本信息】 华南理工大学 ， 计算机应用技术， 2011， 博士

【摘要】 随着无线通信技术的快速发展以及移动终端处理能力的日益增强,移动终端用户可以随时随地访问无线网络服务,为P2P应用扩展到无线网络环境中创造了有利的条件。但是,无线网络高度的动态性、有限的无线链路带宽以及无线节点有限的处理能力等因素使Internet上现有的P2P技术很难直接应用到无线网络环境中。因此,如何在现有的无线网络环境中,充分地利用无线网络的自身优势,使P2P技术在无线网络环境中得到广泛地应用,成为当前亟待解决的研究课题。Cayley图是一种利用群构造图的方法,人们可以使用成熟的代数图论方法分析Cayley图的结构特征和设计Cayley图上的相关算法。特别是由于基于Cayley图的网络模型具有对称性、点传递性、低度、低直径、良好的嵌入性、较高的容错性和路由算法简单等优点,因此,利用代数图论方法研究P2P网络中的相关问题具有较好的理论意义和实用价值。本文围绕Cayley图进行以下三个方面的研究:1.根据无线Mesh网络的实际特点,本文利用代数群论中的半直积方法,构造了一个基于Cayley图的无线P2P覆盖网络模型。通过采用直接在物理网络拓扑上构造P2P覆盖网络的方法,使覆盖网络与物理网络具有较好的拓扑一致性;通过在无线P2P网络的路由算法中嵌入无线网络中的跨层方法,无线节点的广播特性在资源查找中得到了充分地利用,有效地减少了查找资源的路由跳数。实验结果表明,在动态的无线网络环境下,文中提出的无线P2P网络具有较好的资源查找性能。2.在结构化P2P网络中,节点上存放资源对象个数的差异性、节点处理能力的异构性以及无线网络的动态性等因素导致P2P网络容易出现负载不均衡问题。本文利用Cayley图优良的可嵌入特性,在基于超立方体结构的P2P覆盖网络上,构建一个二叉树结构的负载均衡模型,用于收集节点的负载和容量信息、生成负载均衡策略和执行负载转移操作;通过在该模型中应用均衡域的操作模式,P2P网络的负载均衡任务可按照并行与分布式进行处理。实验结果表明,在动态的无线网络环境下,文中提出的无线P2P网络具有较好的负载均衡性能,并有效地减少负载转移开销。3.针对无线P2P网络可用性较差等问题,本文在基于Cayley图的无线P2P网络中,利用Mesh路由器较强的存储和处理能力,提出一个自适应的资源副本管理模型。该模型根据P2P网络中资源流行度的分布特征,动态地调整网络中的资源副本个数;通过利用Cayley图的构造特征和多邻接编码理论,该模型将给定数量的资源副本完美地放置在P2P网络中合适位置的节点上,有效地减少节点接入资源的路径长度。实验结果表明,在动态的无线网络环境下,资源副本管理模型具有较好的自适应调节能力,文中提出的无线P2P网络具有较好的可用性、容错性和可扩展性。更多还原

【Abstract】 Recently, with the development of wireless communication technology quickly and the processing capability of mobile devices increasingly, users of the mobile devices can access wireless networks services anywhere and anytime, which brings an advantageous opportunity for P2P applications extending into wireless networks. However, the practical characteristics of wireless networks, such as dynamic topology, restricted link transmission bandwidth, limited processing capability of wireless nodes, and so on, which resulted in that the existed P2P technologies designed on the Internet may not be applicable to wireless networks easily. Therefore, how to extend the P2P technology into wireless networks widely by considering the particular nature of wireless networks, and taking full advantage of wireless networks, is becoming an urgent research task.Cayley graph is a method of constructing graphs using algebra groups, thus people can analyze constructional characteristics and design correlative algorithms of Cayley graphs by using mature algebra graphs theories. In particular, due to symmetry, vertex transitivity, low degree, low diameter, perfect embeddability, high fault tolerance, simple routing algorithms, and other excellent properties of network models based on Cayley graphs, therefore, researches on the key technologies in the P2P networks by using the method of algebra graphs theories has high theoretical significance and applied value. The following three issues based on Cayley graph are studied in this paper:1. According to particular characteristics of wireless mesh networks, and by using semi-direct product of two groups in the algebra groups theories, a wireless P2P overlay model which is based on Cayley graph, is presented in this paper. A simple approach that P2P overlay network depends upon nodes’neighborhood in the physical network topology, is used during designing P2P overlay networks, then, topology consistency between the overlay network and the physical network is kept well. In addition, the method of cross-layer in wireless networks is also used in the proposed routing algorithm, then, the 1-hop broadcast communication occurring in wireless networks is utilized adequately during searching resources in an distributed way, which speed up the lookup operations by exploiting the information that is available at the MAC layer evidently. Simulation results show our proposed P2P network can achieve optimal performance of searching resources under dynamic wireless network condition.2. The non-uniform distribution of resource objects stored at a peer node, the heterogeneity nature of nodes’capabilities and the dynamic character of wireless networks, which are resulted in load imbalance issue in dynamic structured P2P networks. By using perfect embeddability of Cayley graphs, a binary-tree based load balancing model which is constructed on top of the hypercube P2P overlay network is presented in this paper. Then, collecting load and capacity information of nodes, making the decision of load balancing and transferring the overloaded loads can be finished in each balancing domain independently. By using of the balancing domain in the proposed model, therefore, the operation of load balancing can be implemented in each balancing domain in a distributed and parallel way. Simulation results show that the proposed scheme achieves load balancing under dynamic wireless network condition, and the load movement cost is reduced greatly during the process of load balancing.3. Aim at the bad availability and other existed problems of wireless P2P networks, and by using powerful storage and processing capability of wireless mesh routers, an adaptive management model of resource replicas which is based on Cayley graph in wireless P2P networks, is proposed in this paper. According to the dynamic feature of resource popularity and nodes’load state, the proposed model can adjust the number of resource replicas adaptively in the P2P networks. Besides, by using multiple-adjacency code theories and construction character of Cayley graphs, the proposed model can place the known number of resource replicas onto the appropriate nodes perfectly in the P2P networks, then, access hops between the resource requester node and the offering resource nodes are greatly reduced. Simulation results show that the proposed model has perfect adjustable capability, and yields improvement on the availability, fault tolerance and scalability under dynamic wireless network environment in the P2P network.更多还原