Patent ID: 7592894

Claim:
A method of operating a data-communications switch in two modes of operation, comprising: operating a first Clos switch in a first mode of operation with a first set of hardware, wherein the first Clos switch comprises overlapping logical links used only in the first mode of operation; combining a second Clos switch with the first Clos switch in an overlapping structure to form a switch fabric which is a superset of the first and second Clos switches for providing a second mode of operation, wherein the second Clos switch comprises logical links configured to receive traffic from the overlapping logical links on the first Clos switch in the second mode of operation, and wherein combining comprises adding a second set of hardware to the first set of hardware without impacting traffic on the first set of hardware; and upgrading from the first mode of operation to the second mode of operation with minimal effect of traffic on the first Clos switch, wherein minimal effect comprises an in-service switch between the first Clos switch and the second Clos switch, wherein upgrading comprises rolling traffic from the overlapping logical links on the first Clos switch to the second Clos switch, and wherein the overlapping logical links on the first Clos switch are not used in the second mode of operation following upgrading; wherein the first mode of operation operates with reduced aggregate bandwidth from the second mode of operation.