无线自组织网络中的组合服务技术研究

【作者】 任刚；

【导师】 谢志鹏；

【作者基本信息】 复旦大学 ， 计算机软件与理论， 2010， 硕士

【摘要】 无线自组织网是近年来随着无线通信技术的飞速发展而出现的一种新型网络,网络中所有节点可以任意移动,网络拓扑结构动态变化,节点间以多跳协作的方式进行通讯。作为无需基础设施的网络,无线自组织网络在军事和民用方面都具有广阔的应用前景,是目前网络研究的热点领域。服务组合又称为服务合成,是指将几个简单的服务组合成一个更复杂、更有意义的服务的技术,也就是通过几个简单服务的相互协作来完成一个复杂任务的过程。现有服务组合的工作主要集中于有线网络环境下,采用集中式的服务组合代理来负责服务的发现、组合和执行。随着移动设备和无线通讯技术的发展,人们开始越来越多的关注无线自组织网络中的服务组合问题。对于无线自组织网络中的服务组合技术,本文进行了如下工作：首先,本文提出了跳数限制的组合服务发现方法。在无线自组织网络中,组合服务的执行首先要进行服务发现,找到能够实现服务组合的执行路径,即确定网络中能够实现组合服务的合成方案及提供各原子服务的节点。已有的服务组合服务发现方法并没有考虑所发现执行路径需要的开销和服务的执行情况。本文在保证组合服务发现成功率的前提下,提出了跳数限制的组合服务发现方法,通过限制组合服务执行路径请求包广播的跳数来减少网络中请求包转发的数量,避免无用的传输消耗。其次,本文对服务选择和服务故障恢复的策略进行了探讨。一方面,在通过组合服务发现找到了当前网络下的服务组合方案后,服务选择是实施该方案的过程中所必须面对的主要问题,服务选择的好坏将直接影响服务执行的效果。本文首先根据QoS偏好的不同,分别讨论了消耗能量最小、网络响应时间最短、网络传输失效率最低这三个不同的方面；然后综合这三方面因素提出了一种多维度服务选择策略。另一方面,组合服务在执行的过程中可能会失效,如何进行服务恢复也是服务执行过程中必须面对的问题,本文针对无线自组织网络节点频繁移动、服务执行过程极不稳定的特点,提出了相应的服务故障恢复策略以确保服务的有效执行。最后,本文对上面提出的跳数限制的组合服务发现方法进行了仿真实现,实验结果表明,该方法有效地减少了网络中执行路径请求包的转发量,降低了网络的负载。更多还原

【Abstract】 The advances in mobile devices and wireless communication technology have enabled a new type of network:ad hoc network (MANETs). In ad hoc network, all nodes can move randomly, the network topology changes dynamically, and nodes communicate with each other through miti-hop cooperation. As a special wireless network without fixed network infrastructure, it has extensive application prospect in military and civilian field.Service composition satisfies user’s complex request by combining several atomic services into a more complex one. Traditionally the research of service composition mostly focus on the wired network, which adopts agents to administrate service discovery, service composition and service execution. With the development of wireless communication technology, the service composition in ad hoc network is starting to be paid attention to.Focusing on service composition in ad hoc network, we did the following work:Firstly, we proposed two execution path discovering approaches. In ad hoc networks, the first step for the execution of composite service is to find an effective execution path, in other words, to select atomic service providers as well as an achievable scheme for composing service. However, existing solutions fail to consider the overhead incurred by exploring the execution path and the condition of service execution. In this paper, we present two execution path discovering approaches in ad hoc networks, which constrain the range of execution path discovery under the precondition of ensuring an acceptable success rate of discovering execution path. Our methods reduce the network traffic and avoid discovering useless execution path to a great extent.Secondly, we studied the strategies for service selection and fault recovery. On the one hand, after finding the service composite scheme in the current network by composite service discovery, the next course of service execution is to do the service selection which will directly affect the efficiency of service execution.. Based on the QoS’preference, we discussed three different factors including the lowest energy consumption, the shortest network response time, and the lowest failure rate of network transmission. Then we proposed a multi-dimensional service selection strategy for integrating these three factors together. On the other hand, the services may fail in the execution process, so some kind of mechanism to restore those services in failure should be brought in. Considering the high failure rate of service execution in ad hoc networks, we suggested the fault recovery strategy to assure an effective implementation of services. Finally, we implemented execution path discovering approaches proposed above, and the simulation results proved that our approaches effectively decrease the amount of execution path discovering packet delivered, and reduce the traffic load.更多还原