Method of adding stages to a scalable switching network

Extra stages can be added to a switching network to provide pathwise redundancy for fault tolerance and to alleviate traffic blocking. Also, the addition of extra stages can alleviate the loss of pathwise redundancy when the width of switching networks is increased. An in-service method of upgrading a switching network by adding stages allows the addition of redundancy to an existing network without the need to take the network out of service. From an operational point of view, it is often desirable for the upgrade process to be performed by a plurality of sequential steps. However, it is also desirable to minimize the number of steps performed. Because the insertion of extra stages into an existing network calls. for the rewiring of interconnection networks above and below the insertion point, the number of steps can be minimized while also minimizing the impact to network traffic by concurrently rewiring those interconnection networks through a plurality of disconnection and connection steps.