On Congestion Control Algorithms Of Large-Delay Networks

Nowadays,with the development of science and technology,the network congestion become a bottleneck problem,which restricts the development and application of network.Therefore,the congestion control has become an active issue in the field of network research.The TCP congestion control implemented in source node can not feed the quality of service,Therefore,congestion control which is based on router gradually becomes the main direction in current research.Active queue management(AQM)is the significant constituent.The active queue management(AQM)acting on the intermediate nodes is able to control the queue length effectively on the basis of the high through put of the routers.However,most AQM algorithms in the design and verification process do not fully consider the impact of the large-delay network Moreover,with the maturity of various advanced control theories,many effective new methods have been provided in solving the problem of large-delay network.so the application of advanced control theory to the AQM algorithm of the large-delay network becomes a research direction.Considering large-delay of networks and uncemty of networks model,based on the Analysis of congestion control mechanism of TCP/IP in control theory,the research work is summarized as follows:Considering the time varying and uncertain characters of networks,an active Queue management(AQM)algorithm,Prevent model unfitness and disturbance Smith-IMC algorithm is proposed based on the combining of inner model controller,with Smith estimate controller.The simulation results of the algorithm under different instances show the superiority of the Smith-IMC algorithm.Considering the weakness of depending on precise model of the Smith controller,and the controls of improved Smith controller is imperfact,an active queue management algorithm is proposed based on the combining of the self-tuning gain fuzzy-PID controller with improved Smith(DCSmith)controller.The defect of depending on precision model of Smith controller can be overcameby the self-tuning gain fuzzy-PID controller,which may work well without the precise model ofreal process.The self-tuning gain fuzzy PID-DCSmith control is robust to dynamic network parametersand suitable for networks with large-delay.At last,the research work is summarized and the next research work is prospected.