The Research On Of Controlling Queue Of Routers Based On Differential Equation Traffic Model

With the rapid development of the Internet, network congestion which is caused by competing network resource becomes more critical. In order to improve network performance, it is far important that applying effective queue management algorithm on routers. All kinds of multimedia real-time applications have been made widely available during recent years and require shorter delay and lower jitter to satisfy their demands. Because the length and fluctuation of queue affect network delay and jitter directly, the key point of how to control delay and jitter is to make use of effective method to control the queue length and degrade the queue fluctuation level.For some limitations of end-to-end congestion control, IETF suggests using active queue management (AQM) on routers and recommends RED as the candidate algorithm. RED now has been most widely implemented as one of the AQMs. Being lack of systematical theory and analysis, it is too difficult to adjust the parameters of RED. Improper parameters setting will lead to bad network performance which may be no better than Droptail's.Basing on analysis of TCP flow control stochastic differential equation model, this paper presents a new method to analysis queue fluctuation. It regards RED as a unit feedback control system. By taking expected queue length as input and instantaneous queue length as output, we analyses the steady state error of this system. The analysis results show that the slope of the packet's discarding function influenced the queue fluctuation significantly. In addition, because UDP has no flow control mechanism like congestion control, differential equation which takes window-based control as main character could not descript UDP running process. This paper modifies the original TCP flow control stochastic differential equation. By means of adding UDP affections to the changing of router's queue length, we set up a new model to analysis the mixture flows of TCP and UDP. After getting the root of steady state packet's discarding possibility, the original RED queue length control method for TCP flow could be applied to the mixture flows of TCP and UDP.We use NS2 as the simulation platform to verify the research result. The experiments show that, under the steady state, adjusting the slop of the packet's discarding function properly will decrease the queue fluctuation significantly. Improved method of RED queue length control is fit for not only TCP flows but alsothe mixture flows of TCP and UDP. Using this method could make actual router queue length keeping on fluctuating around the vicinity of expected queue length.