Method and apparatus for managing multiple atm cell queues

Abstract

Methods for managing multiple queues of ATM cells in shared RAM while efficiently supporting multicasting include providing a common memory for storing ATM cells and for storing at least one pointer to each ATM cell stored, providing a management memory for storing an index to the pointers stored in common memory, a table for each multicast session, and an index to the free space in common memory. According to the presently preferred method, cells entering the switch are examined, placed in shared RAM, and a pointer to the RAM location is written in another location in the shared RAM. Table entries in management RAM are updated each time a cell is added to a queue. When a multicast session is begun, a multicast table is created with all of the addresses in the multicast session. When a multicast cell is received, the multicast session table is consulted and pointers to the cell are copied to queues for each address in the table. When a pointer exits a queue, the cell pointed to by the pointer is read and transmitted to the address of the queue. As the cell is read, the destination count for the cell is decremented. When the destination count is reduced to zero, the RAM location used to store the cell is added to the free list. Each time a pointer is read, the table entry for the affected queue is updated. When the queue becomes empty, an active bit in the table entry is toggled.