【作者】 王波；

【导师】 范平志；

【作者基本信息】 西南交通大学 ， 计算机应用技术， 2004， 硕士

【摘要】 无线Ad hoc网络，又名无线自组织网络，是一种特殊的对等式网络。它没有固定的控制中心，各节点通过无线链路连接并在网络中作为路由器。传统的TCP协议在有线网络中能够良好地工作，但用于Ad hoc网络时则性能有很大下降。其原因在于，传统的TCP协议无法分辨网络丢包原因，如网络拥塞、链路断开、信道错误或者链路改变等。由于TCP协议应用的广泛性，如何提高TCP在Ad Hoc网络中的性能成为目前研究的热点问题。本论文围绕Ad hoc网络中TCP的性能展开了分析讨论，深入研究了TCP性能下降的原因并提出改进方案。 论文首先对Ad hoc网络的特性以及TCP协议作了简要介绍。然后，深入研究了TCP在Ad Hoc网络中的性能问题，并提出了一种新的TCP改进方案，即TCP Freeze-Probing，以有效地提高TCP在Ad hoc网络中的吞吐量。 从已有的TCP Reno协议吞吐量模型出发，本文还提出了一种基于TCP Freeze-Probing的吞吐量模型，并通过仿真方法验证了其有效性。 论文使用Network Simulator (NS2)作为仿真工具，并以吞吐量作为主要性能参数，验证了TCP Freeze-Probing协议的正确性和有效性。通过对不同的移动拓扑环境下的仿真结果进行分析，确认了TCP Freeze-Probing在移动Ad hoc网络环境下与传统TCP协议相比有很大的性能提高。而与其它改进方案相比较，由于TCP Freeze-Probing在端节点使用简单而有效的算法，不需要中间节点的配合，使得其更易于实现。 TCP在Ad hoc网络中的稳定性也是一个值得关注的问题。论文深入分析了TCP在静态Ad hoc网络中性能不稳定的原因，并根据已有的MAC层和路由层改进算法提出了改进方案。仿真结果表明，改进方案是正确而有效的。 最后，论文给出了研究工作总结，并提出了进一步工作的研究思路。更多还原

【Abstract】 Wireless ad hoc network is a special peer-to-peer network without fixed infrastructure such as base stations. Mobile nodes are connected by wireless links and each node acts as a router in the network. Traditional Transmission Control Protocol (TCP) works well in wired network but suffers from performance degradation in wireless ad hoc networks due to the fact that it cannot distinguish packet losses due to congestion from packet losses due to link breakage, channel error and route changes. Due to the prevalence of TCP application, the research on TCP performance improvement in wireless ad hoc networks becomes a hot issue. This thesis analyzes the possible reasons of TCP’s poor performance in ad hoc networks and proposes enhancements.At first the thesis introduces briefly the characteristics of wireless ad hoc networks and the TCP protocol. Afterwards, the thesis investigates the TCP performance problem in mobile ad hoc networks and proposes an enhancement of TCP named TCP Freeze-Probing to effectively improve the TCP throughput.Based on TCP Reno throughput model, the thesis introduces a new throughput model for TCP Freeze-Probing. The model is validated then through simulation.Analysis and computer simulation in Network Simulator 2 have proved the correctness and the effectiveness of the TCP Freeze-Probing protocol by using throughput as a main performance metric. By analyzing the simulation results in various mobile topology environments, TCP Freeze-Probing has been proved to outperform traditional TCP protocol. Compared with other improved schemes, TCP Freeze-Probing is much easier to implement in real systems because it uses simple yet effective algorithms in end nodes and does not require the cooperation of intermediate nodes.TCP instability in wireless ad hoc network is also a well-known problem. The thesis investigates the Teasons of TCP instability in static wireless ad hoc networks and proposes schemes combing MAC layer and route layer enhancements to solve this problem. Simulation results show that the proposed schemes are correct and efficient.Finally, the thesis concludes by summarizing the main contributions of the research and presenting directions for future work.更多还原