Dynamic queue length thresholds in a shared memory atm switch

Abstract

A dynamic threshold system and method is disclosed for allocating memory among different output queues in a shared-memory ATM switch. The maximum permissible length for any individual queue at any instant of time is a function of the unused buffering in the switch. The dynamic threshold system and method deliberately reserves a small amount of buffer space, not allocating it to any currently active output queue, but attempts to equally share the remaining buffer space among the currently active output queues. The dynamic threshold system and method improve fairness and switch efficiency by guaranteeing access to the buffer space for all output queues, and by preventing any single output queue from monopolizing the memory at the expense of the others. The dynamic threshold system and method adapt to uncertain or changing load conditions. The packet losses that occur with dynamic thresholds tend to be clustered at a few offending queues, which is desirable in ATM systems, since it results in fewer messages being disturbed at higher protocol layers and, hence, fewer message retransmissions. The dynamic threshold system and method are also extendable to handle traffic with multiple space priorities.