This paper studies how to design a congestion controller in TCP/AQM networks. In Hollotetal. (IEEE Trans. on Automatic Control, Vol.47, No.6,2002), the congestion controller is conservatively designed due to using the linearized model of the TCP/AQM networks in which a structured time-delay related term is treated as an unstructured uncertainty. Without treating anytime-delay related term as uncertainty, we provide a necessary and sufficient a condition of existence of PI stabilizing controller for the system, and we propose a new design of the congestion controller via solving a stabilization problem of the system with a time delay in the variables of both statand input. The simulation results are provided to validate the proposed design method.