【作者】 席斌；

【导师】 曾华燊；

【作者基本信息】 西南交通大学 ， 计算机应用技术， 2007， 硕士

【摘要】 本论文研究工作的背景是四川省网络通信技术重点实验室的与核工业部九院的合作预研项目：无人机战术网络(UAS-TN-Unmanned Aerial System Tactic Network)。UAS-TN是一种特殊的移动自组织网络(MANET-Mobile Ad hoc Network)，其中的节点移动速度远远大于传统MANET中节点的移动速度，再者UAS-TN工作于战时敌对的环境下，在网络安全性方面也有其特殊要求。对UAS-TN的研究，可以以战时需要为背景，借助国内外对MANET的研究成果来研究。当前网络使用最广泛的传输协议是TCP(Transmission Control Protocol)，本论文研究的重点是TCP在MANET中的传输性能。传统的TCP协议假设丢包是由网络拥塞引起的，当发现丢包事件后就触发拥塞控制机制。但是在无线网络中，信道误码或链路断开等非拥塞因素同样会导致数据包丢失，若TCP因此频繁启动拥塞控制机制，将大大降低其传输性能。这意味着需要TCP发送端清楚网络的真实状态，并采取适当的措施解决不同情况下的丢包问题。同时，研究表明在MANET中，由于IEEE 802.11 DCF机制和暴露终端的存在，使得多个TCP流之间存在竞争信道的不公平性，这也是目前研究MANET中TCP传输性能的一个热点。在本项研究中，笔者的主要工作与贡献有：A．对TCP协议在MANET中的性能进行了综合研究；B．提出一种改进MAC层的算法，解缓解多个TCP流在MANET中的不公平性问题；C．提出一种以多层协作为基础的TCP拥塞控制方法，并通过仿真证明了该方法使TCP在MANET中的传输性能有较大的改善。最后以改善TCP性能的跨层方法为基础，简要地讨论了将来面向服务的网络体系结构(Service Oriented Architecture SOA)和不分层的网络体系结构的优点。更多还原

【Abstract】 The research background of the work presented in this dissertation is the research on UAS-TN (Unmanned Aerial System Tactic Network), undertaking at Sichuan Network Communication Key Laboratory(SC-Netcom Lab). UAS-TN is a special type of Mobile Ad hoc network (MANET), except that the moving speed of nodes is faster than that in traditional MANETs and it demands higher degree of security working in a hostile space. However, the work presented in this dissertation is generally applicable for MANET.The topic of this dissertation is pertainent to performance of TCP in MANET as it is the dominant transport protocol. The congestion control mechanism in TCP is triggered by heavy data losses. However, this may not be true since bad channel or link failur bit enor may also cause data loss in wireless networks. This implies that a better triggering criterion for congestion control is needed. Moreover, observation has also shown that with IEEE802.11 DCF, some TCP streams may overtake channel resources for existence of exposed terminals.In this dissertation, the author has made the following contributions:A. Provided a comprehensive study to TCP performance in MANET;B. Introduced an improved algorithmat MAC layer to solve unfairness problem between TCP streams;C. Provided a cross-layer mechanism to improve TCP congestion control and demonstrated its advantage through simulation.Finally, the author has briefly discussed the advantages of future SOA (Service Oriented Architecture) and layerless architecture based on the necessity and merits of cross-layer operation in improving TCP performance.更多还原