Traffic properties relevant to active queue management (AQM) and the resulting pole/zero and Bode limitations are examined. ARX models of TCP are derived from data collected in a fixed "dumbbell" simulation environment. The pole dynamics at short time scales can be traced to the RTT, which serves as a confirmation of the relevance of the models. It is shown that the weighted sensitivity function is a reasonable metric for AQM performance. However, H/sup /spl infin// design shows that the sensitivity can only be slightly reduced. The conclusion of this work is that the goal of smoothing TCP's oscillations (a principle design goal of AQM) is likely not met in general.