The Research And Improvement Of AQM Algorithm Based On Petri NET

Internet has experienced an explosively growth in the past of 10 years, which leads to severe congestion problem. The aim of congestion control is to maximize the link utilization, minimize the packets delay, distribute the network resources among users reasonably and drop packets as few as possible. As the supplementary means of the TCP end-to-end congestion control, AQM (Active Queue Management) makes the intermediate node join network congestion control, and becomes a hot research area in congestion control these years.The main work of this paper includes:It focuses on analyzing the research background of congestion control and significance, and introducing AQM algorithm domestic and international research actuality and problems.Based on systematical introduction of AQM congestion control, some typical AQM algorithms have been summarized and compared. After studying of RED (the typical representative of AQM algorithm), this paper sums up the inadequacies and improvements of RED Algorithm.The improved algorithm (NRED) is presented and the Petri net model of NRED algorithm is built. The description & analysis of the model are given and the equivalent net (net N1) is abstracted. A reachable marking graph of N1 is constructed and the reachability & liveness of N1 is demonstrated based on the reachable marking graph. Then, the feasibility of algorithm (NRED) is proved by the model analysis of the Petri net.Finally, simulations of NRED& RED are carried with NS2 simulation tool. A number of performance indicators, such as throughput, delay, jitter and packet loss rate are analyzed, respectively on the different types of data flow (TCP and UDP), multiple TCP data streams and delay under different flow UDP. Simulation results show the effectiveness of the algorithm.