Research On The Issue Of Congestion Control In Computer Networks Based On Robustness

With the evolvement of Internet based on TCP/IP, the scale, users and traffics of it have experienced an explosive growth since 1990's. The network congestion has become more serious and complex due to the ever-increasing network application types and dynamic network parameters such as active sessions and round trip time.Congestion often results in decline of quality of service (QoS) in terms of transmission delay and throughput, while the network resource utilization like bandwidth and buffers are also affected seriously. The congestion control is always a hot spot in the field of network research.Internet primarily depends on TCP end-to-end congestion control to avoid network congestion. However TCP's trategies could not meet many various demands of every application on the complex network. In fact, it will be more effective for detecting and preventing congestion if the routers perform queue management schemes. Congestion control strategies for the routers have been discussed widely. There is also a new method of congestion control which act on application layer. From the high application level, using game theory combined with utility function for flow control can avoid or lighten the congestion in computer network. It is a new field of the research on congestion control.The physical significations and the correlativities of the often-used H_∞ performance targets are summarized, the selection strategies of the weighting functions are researched, and loop-shaping method as well as standard problems of robust H_∞ control are introduced. The frequency domain methods of robust H_∞ control are also introduced to solve the rate-based congestion control problem of the high-speed communication networks, and the H_∞ based controller are designed to deal with the time-delay problem of the single bottleneck node and multiple resources networks.Considering the nonlinear, time-varying and uncertain characteristics of networks, a new active queue management (AQM) algorithm, i.e. PID-AQM is proposed based on control theory, which requires less model accuracy. In order to realize fast control, a differentiator is constructed using PI-AQM to...