Traffic manager for network switch port

Abstract

A traffic manager for a network switch input or output port stores incoming cells in a cell memory and later sends each cell out of its cell memory toward one of a set of forwarding resources such as, for example, another switch port or an output bus. Data in each cell references the particular forwarding resource to receive the cell. Each cell is assigned to one of several flow queues such that all cells assigned to the same flow queue are to be sent to the same forwarding resource. The traffic manager maintains a separate virtual output queue (VOQ) associated with each forwarding resource and periodically loads a flow queue (FQ) number identifying each flow queue into the VOQ associated with the forwarding resource that is to receive the cells assigned to that FQ. The traffic manager also periodically shifts an FQ ID out of each non-empty VOQ and forwards the longest-stored cell assigned to that FQ from the cell memory toward its intended forwarding resource. The traffic manager separately determines the rates at which it loads FQ IDs into VOQs and the rates at which it shifts FQ IDs out of each non-empty VOQ. Thus the traffic manager is able to separately control the rate at which cells of each flow queue are forwarded and the rate at which each forwarding resource receives cells.