Nonlinear Dynamic Behavior Analysis And Control Of TCP/AQM Network Congestion Model

At present,the Internet is not only filled with a variety of data from the computer terminal,but also a large number of data sources from the mobile devices and intelligent terminals are pour into the network.A variety of business types,breaking data flow test transmission capacity,system stability and resource control mechanisms of the Internet all the time.The occurrence of Internet congestion makes the normal network system into disorder.With further deterioration of congestion,the network system will get into the serious consequences,and even complete collapse of the network.Concerned about the primary causes of network congestion and the solution of congestion problems have great significance to the development of the Internet.The method analysis of nonlinear dynamic is the basic tool for modeling the network congestion system and describing the detailed theoretical derivation process.Therefore,it is important for enriching the theoretical basis and exploring greater performance of the congestion control algorithm.This thesis mainly analyzes the congestion control algorithm and its nonlinear dynamics behaviors from the perspective of nonlinear dynamics.In particular,Hopf bifurcation phenomenon which under three different control strategies is analyzed in detail.The main innovations of this dissertation are summarized as follows:(1)The FAST TCP/RED Internet congestion system is described.Analyzing the nonlinear Hopf bifurcation behavior with the change of the gain parameter value in the model.In order to realize the purpose of expanding the stability of the system,thesis summarizes the control theories which are widely used in the network congestion model,and adopts state feedback control,time delay feedback control and hybrid control strategy to delay the occurrence of the bifurcation behavior.Furthermore,some simulations for justifying the theoretical results are also provided.Finally,we compare the control effects and the advantages or disadvantages of the three control mechanisms,so that the appropriate control method can be provided under the actual network state and the specific parameters.(2)The Hopf bifurcation and its control in congestion model which include the TCP-Reno algorithm based on the source and the ERED algorithm based on router are analyzed.Generally,the stability of the network model depends on the topology of the network and is affected by the various parameters in the system.In this dissertation,we selects the communication delay in the system model as the bifurcation parameter,and focus the stability of the system and the bifurcation threshold by using the stability mathematical theory.By means of the central popular theorem and the normal theorem,the thesis presents the bifurcation properties.Finally,the correctness of the conclusion is verified and the rationality of the control strategy is obtained.