Design of rate-based controllers for active queue management in TCP/IP networks

In our previous work [J. Aweya, M. Ouellette, D. Montuno, K. Felske, Rate-based proportional-integral control scheme for active queue management, International Journal of Network Management, John Wiley & Sons, Ltd., vol. 16, issue 3, May-June 2006, pp. 203-231] we argued that rate-based active queue management (AQM) schemes are most appropriate for high speed links which, typically, have small buffers in relation to the bandwidth-delay product of the link. We continue our discussion in this paper to study the performance of other rate-based AQM controllers. We consider integral (I) and proportional (P) rate-based controllers for the AQM problem, we then characterize all stabilizing feedback gains for the closed-loop TCP/AQM system. Using a network topology with short- and long-lived TCP flows, we present simulation results for the rate-based AQM controllers. We observe that the I-controller is able to control properly the system compared to the P-controller. The P-controller in most cases produces offsets from the target values. To further support our observations, we use a closed-loop control model and control theory to explain why the P-controller has major limitations in the control of a first-order plant like our TCP/AQM first-order plant.