【作者】 刘伟；

【导师】 王辉；

【作者基本信息】 河南科技大学 ， 计算机应用技术， 2011， 硕士

【摘要】 随着无线网络技术的发展,无线网络正在与有线网络逐渐结合起来,形成有线链路与无线信道混合的互联互通的异构网络。一直以来,TCP(Transmission Control Protocol)协议都是为有线网络而设计的,而无线网络的低带宽、长时延和高误码率特性使得无线网络与有线网络有着许多差异。因此,当把TCP应用于异构网络中时,这些特性会影响TCP的发挥,导致性能下降。针对TCP在异构网络中的性能下降问题,本文介绍了三种不同工作机制的智能网关,并分析比较了三种智能网关的优缺点,在OS(Original Split)智能网关基础之上,去除其窗口通告功能,添加两种不同原理的带宽估计算法,经OS智能网关改进后的WM(Watermark)智能网关根据链路状态调用相应的带宽估计算法对链路带宽进行估算,从而调整每条TCP连接的流量,使所有连接公平的享有带宽,尽可能地利用链路资源。仿真结果表明,当无线信道负载较轻时,使用WM智能网关能够使无线信道带宽利用率提高20%以上;当无线信道负载较重时,使用WM智能网关能够使各TCP连接吞吐量迅速收敛到稳定状态,但是,由于每个TCP连接分得的带宽十分有限,使用WM智能网关对于无线信道带宽利用率提高并不十分明显。WM智能网关对异构中TCP传输性能的改善具有一定的理论价值,同时也为WM智能网关从理论研究到现实环境中的应用起到了相应的推动作用。更多还原

【Abstract】 With the development of wireless network technology in recent years, Wireless network is merging into wired network, a interconnected heterogeneous network mixed wired network with wireless network is coming. All the time, TCP is designed for wired network, the characters of wireless network such as low bandwidth, long delay, high error rate make wireless network has many differences according to wired network. Therefore, when TCP is applied to heterogeneous network, those characters will affect TCP and result in performance degradation.With the problem of TCP performance degradation in heterogeneous network, this paper describes three different working mechanism intelligent gateway and compared the advantages and disadvantages of three intelligent gateways, we removed window noticing function of OS intelligent gateway and introduced two different working principle bandwidth estimation algorithms in it. WM intelligent gateway which modified by OS intelligent gateway calls the appropriate bandwidth estimation algorithm to estimate the link bandwidth according to link state, thus The flow of each TCP connection could be adjusted and all connections would have equal bandwidth to utilize the link resources as much as possible.The simulation results show that when the wireless channel load is light, WM intelligent gateway enables wireless channel bandwidth utilization increased by 20% or more. when the wireless channel load is heavy, WM intelligent gateway enables each TCP connection converge to steady state quickly, however, the effect of WM intelligent gateway is not especially noticeable because each TCP connection has a very limited bandwidth. The WM intelligent gateway has a certain theoretical value to TCP performance improvement in heterogeneous network and takes a part of promoting function in applying the WM intelligent gateway from the theoretic research to the practical network environment.更多还原