IMPLEMENTATION OF SELECTIVE PUSHOUT FOR SPACE PRIORITIES IN A SHARED MEMORY ASYNCHRONOUS TRANSFER MODE SWITCH

摘要

A system for queueing and selective pushout and method are disclosed for a packet communications module such as a shared memory asynchronous transfer mode (ATM) switch. The shared memory stores packets in queues, each packet having a field and at most two pointers. Within each queue, the packets having respective space priorities are stored in sub-queues each having the respective space priorities. The packets are stored in these priority sub-queues using a first pointer pointing to the next packet of the same space priority in the queue. The second pointer associated with a stored packet points to the previous packet of greater than or equal space priority in the FIFO order in the queue. The field of a packet is used to store the priority value corresponding to the next packet in FIFO order in the queue, and this field is used by a processor to decide priority sub-queues to serve next. The packets are stored in the queues in a FIFO order using the two pointers and the fields of the packets. Theprocessor controls the selective pushout to push out a packet and uses the two pointers and the fields of the packets to restore the FIFO order. A method is also disclosed including the steps of storing packets in a queue, with each of the queued packets associated with the two pointers and a field; serving the queue; pushing out packets from the queue; and maintaining queue-lengths and a state information table.