A nonlinear control theoretic analysis to TCP-RED system

Random early detection (RED) is an effective congestion control mechanism acting on the intermediate node. The considerable recent studies have investigated on the stability of TCP/RED system. In this paper, we firstly summarize the contributions and limitations included in the existing works. To reveal a more comprehensive reason why TCP/RED system is apt to oscillate, a new analysis framework is constructed to sufficiently merge the existing valuable results with the aid of the describing function approach, which is rather mature in nonlinear control theory. After a brief introduction of the describing function approach, a proposition about TCP/RED system stability criterion is proposed. Subsequently, we use this criterion to quantitatively analyzed why gentle-RED is more stable than RED, and to investigate the impact of typical system parameters, such as propagation delay, load level, link capacity, and averaging weight factor, on TCP/RED system stability in detail. The simulation results validate our analysis.