In this paper we rethink the tradeoff between proportional controller and PI controller in AQM (active queue management) algorithm design. With the introduction of integral factor, the steady state error in a proportional controller such as RED is eliminated. However the integral factor also slows down the response speed. We present a simple algorithm P/sup 2/I to solve this problem. P/sup 2/I combines the advantage of the proportional controller and the PI controller. The performance of P/sup 2/I is verified and compared with the PI controller using ns-2 simulations. P/sup 2/I is shown to respond much faster than the PI controller while retaining the merits of the PI controller. We also analyze the impact of the traffic pattern on the design and success of AQM.