Steady State Error Analysis of RED Queue

Active queue management （AQM） is used to drop the packets actively on the intermediate nodes, so as to control the queue length, in order to control end-to-end delay and jitter while keeping high throughput. As one of the AQM mechanisms, RED is the most widely implemented on the routers. RED takes the average queue length as the main measure of congestion and its parameters have great effect on the algorithm performance. RED is seen as a unit feedback control system. Taking expected queue length as input and instantaneous queue length as output, steady state error of this system is analyzed. The simulation result shows that the slope of the packet’s discarding function influences the queue fluctuating. When closing to the border of the stable conditions, the steady state error of the system will increase rapidly.