Study On Congestion Control Algorithms Based On Control Theory

With the development of network communications and the expansion of the number of users, network congestion problems are becoming more and more serious. Congestion is a direct result of the performance of the entire network degradation. For example, the packet loss rate increasement, end to end delay increasement, network throughput decreasement and may even crash the whole system. Therefore, the network congestion control is the main way to improve the network performance and reform the quality of sevice.The design of simple and effective congestion control algorithms in network management are the problems to be solved. Network congestion can be seen as a feedback control system. From the perspective of control theory, much more effective results about research network congestion control can be achieved. Using control theory analysis of the existing congestion control system stability and the design of new congestion control algorithms show important theoretical significance and application value. Therefore, it is very necessary to explore the network congestion control method based on control theory. This paper studys on network congestion control algorithms based on control theory, to obtain the main research results and innovation are as follows:1. A new congestion control algorithm called PID control algorithm with improved chaos optimization based on improved model is proposed in the large delay network situations. According to the model, the PID parameters are tuned with chaos optimization in AQM routers. PID controller can not turn parameters online in dynamic network condition. A novel active queue management algorithm for large delay network based on Fuzzy PID control and Gain Adaptive Smith (GAS-FPID) is proposed, which can achieve PID parameters on-line self-adapting by fuzzy control under the dynamic delay network circumstances. And, gain adaptive Smith is successfully introduced into feedback data's advanced prediction to compensate delay.2. The model of TCP/AQM including the state and the input delay is presented in state variables. State feedback control based observer is introduced to estimate online output of congestion control for AQM router for variable network parameters. According to the Linear Matrix Inequality(LMI) technique and the Lyapunov-Krasovskii theorem, control laws and delay-independent stability criteria for the AQM controllers are derived. An AQM algorithm is presented for network congestion, which is based on uncertain parameters and variable link bandwidth. The available link bandwidth is modeled as a nominal constant value, which is known to the link, plus a time-variant disturbance, which is unknown. The model of TCP/AQM including the state and the input delay was presented in state variables. Then, the network congestion problem is solved by using the time-domain H∞control approach.3. The congestion control algorithm based on Concensus is designed for network congestion over wireless sensor network by distributed dynamic system. The congestion problem is modeled by graph theory, it can be proved that the send rate for all nodes converges to the minimal available bandwidth by the proposed CCBC. Via Lyapunov function, the validity of the proposed algorithm is shown under the varying network topology and time-delay.4. Study on the Hopf bifurcation analysis of a fluid-flow model with time-delay for the congestion control algorithm in the wireless networks. By choosing the communication delay as a bifurcation parameter, the model exhibits of Hopf bifurcation are proved. The formulas for determining the direction of the Hopf bifurcation and the stability of bifurcating periodic solutions are obtained by applying the center manifold theorem and the normal form theory. Finally, a numerical simulation is presented to verify the theoretical results.Finally, based on summary of full text, some problems which need to be further researched are discussed.