Handling ATM multicast cells

A method for operating an Asynchronous Transfer Mode (ATM) switching device through which ATM cells are routed to one or more of a plurality of physical output links, the method comprising:

• (1) establishing, in a memory:
• (i) passive leaves queues for each of a plurality of physical output links to which a multicast connection is destined;
• and
• (ii) a leaf table for each leaf of the multicast connection as each leaf is added, the leaf table including a pointer for determining a next cell to be read out of a cell buffer for the respective leaf;
• (2) for a passive leaf of the multicast connection, linking the leaf table for the passive leaf to an appropriate one of the passive leaves queues;
• (3) upon reception of a cell from a switch core, linking the appropriate one of the passive leaves queues to an activation queue and thereafter setting a pointer in an active leaves queue to a leaf table pointed to by the appropriate one of the passive leaves queues.

An ATM switch having an egress port which receives cells from an ATM switch core, the egress port having a plurality of physical outputs and comprising:

• a root data structure having an entry for each multicast connection;
• a leaf data structure having a leaf entry for each leaf of the multicast connection;
• a cell buffer in which are stored cells received from the ATM switch core;
• a passive leaves queue to which leaf entries for passive leaves are linked;
• an active leaves queue to which leaf entries for active leaves are linked, there being one active leaves queue for each physical output;
• wherein, when a new cell enters the cell buffer, all leaf entries linked to a passive leaves queue are relinked to a corresponding active leaves queue.

A method of operating a cell switching device comprising:

• receiving cells from a switch core into a cell buffer;
• providing a leaf table for each leaf of a multicast connection, each leaf table having a pointer to a corresponding cell in the cell buffer whereby the pointers of differing leaf table may point to differing cells in the cell buffer;
• using a pointer of a passive leaf table of a passive leaf to point to a last cell in the cell buffer;
• using a pointer of an active leaf table of an active leaf to point to other than a last cell in the cell buffer.