A Study Of Congestion Control Algorithm Based On Active Queue Management

Active Queue Management is a key technic of congestion control based on Routers recommended by Internet Engineering Task Force. Up to now, there are already a few number of Active Queue Management arithmetics. Random Early Detection arithmetic is the representation of Active Queue Management algorithms, it is widely attented and studied by people. But the newly large number of researches indicates that there is some fairness problem with the Random Early Detection algorithm. It can't deal with the flows which don't answer to congestion informs effectively. In addition, it is comparatively sensitive to the parameters and running status of the network. There will be node-queue surging, throughput-reducing and delay-increasing in the network. In this paper, we make some improvements on the fairness problem in Active Queue Management algorithms.In this paper, we firstly give introduce the researching status quo of the congestion control algorithms, and the problemes of the congestion control algorithms nowadays. We expatiate the definition of congestion, congestion collapse and congestion control, we also analyse the causations of congestion. We make a deep research in Active Queue Management algorithms which belong to congestion control algorithms. We analyse five kinds of algorithms concretely. They are RED, FRED, CHOKe, CSFQ and AFD. The method and the degree of the latter four algorithms to implement the fairness are all different. Because RED is lack of fairness, so we use it for contrasting with other four algorithms. In this paper, we analyse the algorithms above in theory, then we compare the fairness capability of these algorithms combining with the simulate experiments in different network environments.The paper gives a detailed description of CHOKe algorithm of Active Queue Management algorithms, we make a deep research in the problem that CHOKe algorithm can not punish the unresponsive flows enough and it can not distribute bandwidth fairly. Because of this problem, we propose an improved algorithm W-CHOKe based on drop_priority. Then we simulate the W-CHOKe algorithm. Using the NS-2 under Linux Operation System, we simulate the W-CHOKe algorithm with the three kinds of primary CHOKe algorithms under network simulator based on the same network topology, link, bandwidth, and source to compare these four algorithms in the performance. And the simulation results show that the W-CHOKe algorithm punish the unresponsive flows efficiently and improve the CHOKe performance.This article is made up of 6 parts. Section 1 introduces the background and significance of the investigation. Section 2 introduces some base conceptions of congestion control, the sorts of queue management algorithms and the fariness problem of Active Queue Management algorithms. In section 3, we introduce five typical Active Queue Management algorithms, and we compare the fairness capability of these algorithms combining with the simulate experiments in NS-2. Section 4 analyses the shortcoming of the CHOKe algorithm and proposes an improved algorithm W-CHOKe,then gives the simulation of the W-CHOKe algorithm. In the final part, section 5, we give a summarization of this paper and present the next work we will do.