Patent ID: 7123611

Claim:
A method of operating a packet switch which comprises a plurality of ingress means, a plurality of egress means, a cross-bar and a controller, the cross-bar being connected between the ingress means and the egress means to transfer multicast and unicast data traffic from the ingress means to the egress means, the method comprising the steps of: a) determining if the data traffic to be transferred is unicast or multicast; b) if the data traffic is unicast, invoking a unicast schedule; c) if the traffic is multicast, invoking a multicast schedule; and d) transferring the data traffic in accordance with the invoked schedule; wherein, step c) comprises forming a multicast cell fanout table containing current fanout requirements for a cell at the head of a multicast queue in each ingress means, setting eligible bits for multicast cells which are currently allowed to be scheduled, and determining a priority for each ingress means for sending the cells; the step of determining the priority for each ingress means is based on a combination of send opportunities of the ingress means; the method further comprises a step of e) filling a blank multicast schedule in accordance with the priority assigned to each ingress means; step e) comprises (i) filling the blank schedule with the full fanout of the first priority ingress means, and (ii) filling in as much of the fanout of the next priority ingress means and subsequent ingress means as possible to complete the schedule; and step (ii) comprises selecting fanouts of ingress means in accordance with multicast egress credit allocated to each egress means.