  In recent years, different mathematical models have been proposed for widely
used internet control mechanisms. Simple low order controllers (such as PID,
and Smith predictor based linear controllers that are easy to implement) are
desired for network traffic management. In order to design such simple
controllers for Active Queue Management (AQM), delay based linear models have
been considered. In this paper we discuss tuning of the PID controllers by
using a parameter space method, which computes stability regions of a class of
quasi-polynomials in terms of free controller parameters.
