Patent ID: 6876663

Claim:
A data switching device having a plurality of ingress routers, a plurality of egress routers, a switching matrix and a connection controller, the switching matrix having input ports connected to respective said ingress routers and output ports connected to respective said egress routers, and controlled by the controller to form connections between pairs of input and output ports; each ingress router including one or more virtual output queues for each egress router, each virtual output queue being arranged to store fixed length cells having a header defining the egress router to be used in the switching matrix connection; each ingress router being arranged, upon receipt of a new cell by that ingress router, to store the cell in a virtual output queue of the ingress router corresponding to the egress router for the cell; characterized in that: each input port of the switching matrix includes for each virtual output queue in the ingress router connected to that input port a respective head of queue buffer; the switching matrix is arranged, upon the switching matrix forming a connection between a given input port and output port, to transmit to that output port a cell from a corresponding one of the head of queue buffers; each egress router is arranged, upon error free receipt by that egress router of a cell from one of the virtual output queues of one of the ingress routers, to transmit a receipt signal to that ingress router; each ingress router is arranged, upon storing a cell in a virtual output queue, and, if a credit count, indicative of the number of free cells of the corresponding head of queue buffer, is not zero, to transmit a replication of the cell to that head of queue buffer and a connection request to the controller; and each ingress router is further arranged to retain each received cell in the corresponding virtual output queue until receiving the corresponding receipt signal.