Design a robust controller for active queue management in large delay networks

AQM (active queue management) can maintain the smaller queuing delay and higher throughput by the purposefully dropping the packets at the intermediate nodes. Almost all the existed schemes for AQM neglect the impact of large delay on performance. In this study, we firstly verify a fact through simulation experiments, which is the queues controlled by the several popular AQM schemes, including RED, PI controller and REM, appear the dramatic oscillations in large delay networks, which decreases the utilization of the bottleneck link and introduces the avoidable delay jitter. After some appropriate model approximation, we design a robust AQM controller to compensate the delay using the principle of internal mode compensation in control theory. The novel algorithm restrains the negative effect on queue stability caused by large delay. The simulation results show that the integrated performance of the proposed algorithm is obviously superior to that of several well-known schemes when the connections have large delay, at the same time, the buffers keep at small queue length.