Combined unicast and multicast scheduling

Abstract

The invention provides a method and system for combined unicast and multicast scheduling. Data cells are assigned at each input, to one unicast input queue for each output, or to a single multicast input queue. Each input makes two requests for scheduling to each output for which it has a queued data cell, one unicast request and one multicast request. Each output grants up to one request, choosing highest priority requests first, giving precedence to one such highest priority request using an output precedence pointer, either an individual output precedence pointer which is specific to that output for unicast data cells, or a group output precedence pointer which is generic to all outputs for multicast data cells. Each input accepts up to one grant for unicast data cells, or as many grants as possible for multicast data cells, choosing highest priority grants first, giving precedence to one such highest priority grant using an input precedence pointer. In a preferred embodiment, the individual output precedence pointers each implement a round-robin precedence technique, in which the most recent input to transmit a data cell has the lowest precedence; the pointer is incremented to point to a next input each time a data cell is transmitted from the pointed-to input. The input precedence pointers each preferably implement an identical precedence technique. However, the group output precedence pointer is not incremented until all outputs from the multicast data cell for the pointed-to input have been transmitted.