TCP Westwood Network Congestion Protocol Analysis And Control Research

Nowadays, with rapid development of Internet, there is more and more users and new application service. Congestion will occur when the demand resource goes beyond the total link capacity. Network congestion may lead to information loss, delay increase, or even congestion collapse. So network congestion control has been a hot research issue. So far, the mainstream research of network congestion control includes building the nonlinear dynamic model of network congestion control system and studying bifurcation control strategies.Internet is a very complicated nonlinear network and data flow is chaotic and self-similar. In order to understand the nature of congestion control system better and improve network performance, research method has been changed from traditional subjective decisions to accurate mathematical dynamical model analysis. Firstly, the thesis built TCP Westwood/AQM continuous congestion control system fluid flow model. Secondly, based on the model, the author used nonlinear dynamic analysis and bifurcation control theory to analyze the dynamic behaviors of the system. Moreover, three different bifurcation control methods were applied to delay or even eliminate the Hopf bifurcation phenomenon. Main content and innovation points are as follows:(1) The thesis made a deep analysis on the reason why traditional TCP congestion control protocol has not been suitable for HBDP and wireless network. Among many modified TCP protocols, TCP Westwood, which will increase bandwidth utilization and improve performance of network, is specially designed for high-speed wireless network and fits the character of high-speed wireless network entirely.(2) We built TCP Westwood/AQM congestion control system continuous fluid flow model with TCP Westwood mechanism and RED strategy. Taking advantage of nonlinear dynamic knowledge and bifurcation theory, the conditions of Hopf bifurcation and correlation character parameters had been achieved. Numerical simulation was made to verify correction of theory analysis.(3) The thesis presented three Hopf bifurcation control method, delay feedback control, state feedback control and hybrid control mechanism. First, Hopf bifurcation conditions were analyzed. Second, the parameters of Hopf bifurcation nature, direction and period were derived. Third, MATLAB simulation tool was used. By comprehensive analysis, we got the conclusion that hybrid control algorithm is the best bifurcation control method for TCP Westwood/AQM system.