Controlling logical queue depth in an input buffer of an ATM switch

摘要

An input butter 22 of an ATM switch has a number of logical queues each for storing cells of a different priority (1,2....P). The logical queue depth (fill level) of each queue varies according to traffic conditions and incoming cells of a particular priority may be lost if there is no free space in the logical queue for that priority. To reduce the amount of cell loss the allocation of buffer space to each logical queue (logical queue size) is dynamically controlled according to a back pressure signal from the switch element 23 and the current depth being occupied in that logical queue. If the occurrence rate of a backpressure signal reaches a threshold and the logical queue depth reaches a threshold for a particular queue then an algorithm checks to see it there is unused buffer space in one of the other logical queues. If so this space is reallocated to the overfull logical queue.