On the performance limitation of active queue management (AQM)

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^∞ 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.