On Congestion Control Based On Active Queue Management Algorithms

With the rapid development in transmission control protocol (TCP/IP) networks, especially in Internet in the last decade, it is very convenient for the production and life of people. But the problem of congestion is more and more severely preventing the fine development of networks. That introduces some control mechanisms to networks is an effective method to solve the problem. Active queue management (AQM) is a kind of congestion control mechanism based on router. Nowadays AQM is extensively studied due to good effect for constraining congestion. But TCP network is a complex time-varying system with respect to the nature of nonlinearity, uncertainty and different structures, which requires designing a kind of more robust AQM algorithm in order to obtain better congestion control effect.This thesis presents some active queue management algorithms based on intelligence control and robust control theories and makes further study on the design of active queue management and stability analysis. The main research works and conclusions are as follows:The responsive speed problem is discussed for AQM algorithm. For sliding mode control possesses the robustness to uncertainty and disturbance, which is suitable for complex time-varying TCP/IP network system, an AQM controller based on sliding mode control theory is proposed, and the stability analysis is given. Both linear sliding mode controller and terminal sliding mode controller are designed, and relatively satisfactory results are obtained. Each algorithm has its own advantage, which can compensate the other's disadvantage. Then based on the two algorithms, a fuzzy sliding mode control method to network is presented. An AQM controller with both good steady-state response and transient response is obtained.A new active queue management scheme based on Fuzzy-Smith is presented to network with dynamic parameter and delay. It combines the advantages of Smith control and fuzzy control.It can compensate the negative impact on the queue stability caused by the large delay, and it also exists strong robust under the condition of dynamic network fluid.The conclusion is drawn for the whole thesis, and the further research aspect is put forward.