Multicast scheduling for a network device

Contained herein is material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction of the patent disclosure by any person as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all rights to the copyright whatsoever. A method and apparatus are provided for scheduling multicast data in an input-queued network device. According to one aspect of the present invention, deterministic and bounded delay for high priority multicast cells is guaranteed by the multicast scheduler. The scheduler receives a transmit request associated with each of a plurality of input ports. The transmit request identifies output ports to which pending multicast cells are ready to be transmitted, if any. Then, for each of multiple classes of service, the scheduler performs a single scheduling iteration. The single scheduling iteration includes a grant phase, an accept phase, and an update phase. During the grant phase, the scheduler grants one or more of the input ports access to the fabric by issuing grants based upon the transmit requests and a priority indicator that identifies an input port that is given scheduling priority for the scheduling iteration. During the accept phase, on behalf of each of the input ports, the scheduler accepts all grants corresponding to the input port. Finally, during the update phase, the scheduler updates the priority indicator for use in a subsequent scheduling cycle.