The Research Of Congestion Control Based On Improved Algorithm Of Active Queue Management

Internet congestion occurs when the aggregate demand for a resource exceeds the available capacity of the resource. With the raid development of the Internet, network congestion is occurring more frequently. The network congestion is an important factor to affect the network quality of service (QoS). So congestion control mechanism of Internet and quality of service are the central issues of the current research.With the development of the Internet technology and the network conditions, the congestion control provided by the end to end system is not enough, which has some limitations. There is a certain time interval between the congestion occurring and the source reducing the transmission rate, the network will continue in a state of congestion in this time. The researches indicate that the network congestion occurs mainly on intermediate nodes, so it is very necessary to perform congestion control in the intermediate nodes of network. At present, the network congestion control mechanism in nodes is the active queue management technology (AQM Active Queue Management).The active queue management mechanism is an essential technology based on the router congestion control, which is recommended by IETF, and combines with the TCP end to end congestion that is a main method to solve the congestion control question of the present Internet. RED (Random Early Detection) is a typical algorithm of active queue management technology, but which exists some limitation on stability and parameter sensitivity. So a new improved RED algorithm is put forward after analyzing RED which is named IARED (Improved Adaptive RED).The calculating of discarding probability and the adjustment of maximum drop probability is modified in IARED algorithm.(1) IARED is nonlinear smoothing to RED. According the principle of packet discarding strategy on router, IARED makes a nonlinear smoothing to the RED algorithm by using a high order function, whose range of action is between the minimum threshold and the buffer of router.(2) The range of target queue length is introduced in IARED algorithm, which is calculated by the minimum threshold and the buffer of router. IARED algorithm makes the average queue length closing to as far as possible this range. (3) The parameter is adaptive adjusted in IARED algorithm. The parameter is dynamic adjusted by the range of target queue length and the average queue length so that makes the algorithm can adapt the different environment of network.The IARED algorithm can adapt different network environment by a lot of simulation results in NS2, and which has a small sensitivity of parameters. IARED is better than RED algorithm in network throughput, packet loss rate and other network performance.