摘要
Ad hoc网络是一种工作在无固定结构环境下的自组织的无线移动网络。它适用于军事或是一些战略应用场合。例如,战场上部队快速展开和推进、发生地震或水灾后的营救等。在没有网络基础设施的情况下,Ad hoc网络可以快速组网,其节点可以移动,网络中的每个节点既充当主机又充当路由器。由于Ad hoc网络具有组网快捷、灵活,且不受有线网络约束等优点而具有广泛的应用前景。
由于Ad hoc网络的拓扑动态性,使得常规路由协议在该环境下无法正常运行。因此,对该环境下路由协议的研究成为了Ad hoc网络中研究的主要课题。本文首先简要介绍了移动Ad Hoc网的现状及发展前景,包括移动Ad Hoc网的定义,网络特点,应用领域和面临的一系列问题,并简单比较AODV与DSDV、DSR等路由算法的网络性能。然后基于Ad Hoc网的网络环境,对AODV路由协议进行了详细分析。AODV是DSR和DSDV的综合,依赖中间节点建立和维护动态路由表,使用序列号来避免路由环路,支持组播功能和QOS,可以使用IP地址,依靠网络连接但不支持单向信道。本文通过NS-2设置不同的网络场景选取端到端平均延迟、包传输率、路由开销等作为参数进行测试,全面分析了AODV路由协议的性能,发现AODV协议存在路由开销较大的问题。随着网络负载的增大,AODV的路由开销有明显的增加。
因此本文从改善AODV协议路由开销方面对该协议进行了优化。最后对优化结果进行测试,结果表明优化后的AODV协议在路由开销方面确实有很大改善。本文对AODV路由协议的比较和优化都是在NS-2网络模拟器下完成的,模拟平台为Windows 2000和Cygwin,为实际系统的设计和规划提供了参考方法,参考模型和参考数据。
A mobile Ad hoc network is an autonomous system of mobile hosts connected by wireless links. Such networks are useful in military and other tactical applications, e.g, army's quick spread and advance in the battlefield, emergency rescue or exploration missions after earthquake and flood, where cellular infrastructure is unavailable or unusable. In such a network, each mobile node operates not only as a host but also as a router. This network has a series of the strengths, for example,MANET can be built rapidly and easily, and it is not restrained by wired network, and so on.
Because of constantly changing topology, Ad hoc networks can't adopt traditional routing protocols. Research of routing protocols becomes the most important part of the research of Ad hoc. The actuality and prospect of Ad hoc networks are summarized in chapter one of this paper, including the definition, characteristic, application fields and critical technologies of Ad hoc networks. Then based on Ad hoc networks, this paper gives a particular analysis of AODV routing protocol,and compares some relevant network protocols with AODV such as DSDV, DSR. AODV ,as the synthesis of DSDV and DSR, depends on middle nodes to establish and maintain route table, uses sequence number to avoid the appearance of route circle, supports the function of group broadcast and QOS, uses IP address, depends on the network link and dosen't support single orientation channel. Furthermore, this paper analyses the capability of AODV routing protocol by testing end-to-end average delay, data package transmission ratio and route cost in different network environment with NS-2, and draws a conclusion that AODV routing protocol has a bigger route cost. There is an obvious increase in route cost with the expansion of the network overload.
Thus this paper makes some improvements in the aspect of route cost. These improvements are proved, by a series of tests in the final part of the paper, to be more effective in route cost.The comparison between protocols and improvements of AODV protocol are based on NS-2 network simulation environment, the platform of this paper is Windows 2000 and Cygwin, and this paper provides reference methods, reference model and reference data for the design and programming of practical system.
引文
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