Nonlinear queue management in TCP/IP networks

In the nodes of computer networks the Active Queue Management (AQM) is responsible for managing the messages to be transmitted. Because of the time required for this service the messages delay in the nodes. This delay is much larger than a message transmission time is. The delays of these services lead to the congestion problem. These services can be examined as typical control systems. Although studies indicate that in AQM systems a PI controller works better than a TCP/IP RED algorithm, in a simplified model of TCP these differences decrease the effectiveness of the controller which was designed by the classical control theory. In these cases the structure of the Differentiated Services is proposed to apply to achieve adequate levels of the QoS services in a TCP/IP network. In this article an AQM system is designed, which is met on the demands of intensive usage and it includes the round trip delays as well as detection of lost packets if any. To achieve our goals, a predictive sliding mode control system (SMC) is designed to control congestion. This control strategy helps us to take into consideration the effects of round trip time, too. Implementation results demonstrate the effectiveness of the controller in providing queue management.