A modification to RED AQM for CIOQ switches

In very large networks with heavy traffic, congestion control plays an important role in network resource management. One approach to this is the active queue management (AQM) algorithms. Many AQM algorithms have been proposed and analyzed but they mainly focus on single queued links. Recognizing the fact that input queued switches are limited in throughput and output queued switches require a large speedup factor, we direct our attention to combined input and output queued (CIOQ) switches. We propose a simple modification to the RED AQM algorithm in order to account for the presence of both input and output queues in the switch. Specifically we use the weighted sum of input and output queue lengths as the congestion measure instead of just the output queue length. Simulations show that with such a simple modification, the average backlog in the switch is significantly reduced in the low speedup region as compared to RED without this modification. Unlike the traditional dynamic of having the loss rate grow with the length of the queue, simulations show that for a loss rate in the modified RED slightly larger than that in RED, the output queue length in modified RED is tremendously reduced. The weighting factor used in the computation of the congestion measure provides a means to balance the reduction in the average backlog on the one hand, and the increase in the loss rate on the other hand. Finally, simulations show that the improvement gained in terms of the queue length does not compromise in any way the utilization of the switch as compared to RED and Droptail.