Robustness Research On Active Queue Management In Congestion Control Of Network

As the Internet explodes in size and in the number of users, the robustness of the Internet is highly depended on the congestion control mechanism. To network, congestion control is not only the core issue, but also a very difficult problem. As the development of technology and application demand, researchers began to realize that it is very difficult to meet the demand of complex application, such as QoS, only depending on the policy and algorithm on end system. So some research began to turn to the internal node device, such as routers in the network. By improving their function, they want to reach some technic target which can't be realized on the end system. Therefore, congestion control mechanism must involve the IP layers. The QoS of network can be improved by adopting some policy of droping or marking packages, which is active queue management technology. In term of congestion control, the internal node could grasp the accurate congestion state in time, and implement the effective resourse management policy, which can avoid congestion or resume from congestion immediately. The purpose of the thesis is to design congestion control and queue management algorithm which is helpful to improve the QoS of Internet and robustness of network.At first, we analysed and researched the performance of TCP, which is the most popular congestion control algorithm. Based on the development sequence of active queue management, we analysed the representative AQM of each stage, including their shortage and improved algorithm. Then, in order to solve the problem of parameter configured, from the point of feedback control theory, we analysed tht RED algorithm, and presented a method of configuring RED parameter, which can obtain a good tradeoff between the stability and dynamic characteristics of system. To the various parameter combinations of RED algorithm, we presented a method to estimate the stability margins accurately. Considering time variety of the state parameter of network, based on the variable structure control, we developed a VS active queue management algorithm. Then, to the probleme of steady-state error, we presented the method to revise the Steady-state error. According to the mathematical model of TCP congestion control, we developed a self-tuning fuzzy queue management algorithm with the consideration of fuzzy controller being well suited for model uncertainty. Through properly simplification of the fuzzy algorithm, we developed a more practical queue management algorithm, i.e. the Self-tuning algorithm. By properly modification, ST can not only be used in networks with in and out packets, but also suitable for network service with different priority class. Specifically, the main work and contributions in this thesis are as follows.Based on the mechanism of Additive Increase Multiplicative Decrease of congestion window, we analysed the fairness of TCP congestion control using the method of utility function.In order to solve the problem of parameter configured, from the point of feedback control theory, we analysed tht RED algorithm, and presented a method of configuring RED parameter, which can obtain a good tradeoff between the stability and dynamic characteristics of system. To the various parameter combinations of RED algorithm, we presented a method to estimate the stability margins accurately.According to the mathematical model of TCP congestion control, we developed a VS active queue management algorithm based on the variable structure control. Then, to the probleme of steady-state error, we presented the method to revise the Steady-state error.We combined the Fuzzy control and queue management technology, and developed a self-tuning fuzzy queue management algorithm with the consideration of fuzzy controller being well suited for model uncertainty. The main advantage of this algorithm is that, the queue length can keep stable in a variety of network environments without the difficulty of parameter configuration.Through properly simplification of the fuzzy algorithm, we developed a more practical queue management algorithm, i.e. the Self-tuning algorithm. With the analysis of RIO, we explore the use of ST in Assured Service architecture. By properly modification, ST can not only be used in networks with in and out packets, but also suitable for network service with different priority class.