Stability Analysis And Application For Network Congestion Control Strategy

The development of Internet has been encumbered with the congestion problem. The combination of TCP congestion control algorithm based on the source side and Active Queue Management (AQM) algorithm based on the link has become a main approach to solve the congestion control problem.Based on the corrent situation in review, which focuses in designing protocol parameter of FAST TCP in TCP congestion control algorithm, parameter selection of Random Early Detection (RED) algorithm in AQM algorithm, and the designing of AQM algorithm based on sliding mode control theory, the main research works and conclusions in this paper are as follows:(1) A more accurate FAST TCP congestion control model is proposed, and a more broadly parameter design guidance is obtained based on the stability analsis of the new model.First of all, aiming at the existing FAST TCP model unconsidering the window update interval parameters exponential smoothing filter which the source uses to estimate congestion signal, this paper improves the network congestion control model. Second, the model is linerarized in the vicinity of the equilibrium point, and FAST TCP open-loop system transfer function is obtained after Laplace transforming. The system stability conditions is obtained with the help of Routh stability criterion, then a preferences guidance scheme was proposed to ensure the network stability according to the controller gain parameter and windows update interval and network related parameter. The theory computing and the NS2 simulation results demonstrate that this improved guidance scheme possesses much extensive application area in contrast to other related scheme.(2) A new congestion control model including TCP self-synchronization is proposed, and a more broadly parameter design guidance is obtained based on the stability analsis of the new model. TCP self-synchronization is that TCP window doesn't send a new packet to the link until receiving a confirmation frame,so packet sending rate in the source sind cannot simply expressed by the ratio of the window size and RTT, but by receiving the confirmation of the instantaneous speed frame. Aiming at the existing TCP/RED congestion control models ignoring TCP self-synchronization, this paper proposes a new congestion control model including TCP self-synchronization. Then the model is linerarized in the vicinity of the equilibrium point, and the open-loop system transfer function of TCP/RED is obtained after Laplace transforming. The system stability condition is obtained with the help of Nyquist stability criterion, then we receive a more relaxed RED parameters settings scope. At last, NS2 simulation is used to validate the effectiveness of the obtained RED parameters settings scope. (3) AQM algorithm based on sliding mode control theory is proposed when the system parameter perturbation is unmatched. Firstly the model in common use is modified and linearized at the equilibrium. Then the no time-delay linearization model was obtained by the reduction algorithm. The feasible condition with reachable and asymptotic stability of sliding surface was given through the integral sliding mode control algorithm based on the Lyapunov function and LMI method under the condition of the mismatched but bounded perturbation of system state matrix, in which the robust AQM controller was designed. Finally, the effectiveness of the designed controller is validated by simulation.