Abstract

N/n first-stage switches of an existing N×N three stage network are decomposed into 2N/n virtual switches having n inlets and 2n outlets, and N/n third-stage switches are likewise decomposed into 2N/n virtual switches having 2n inlets and n outlets. The outlets of each first-stage virtual switch are connected respectively to the inlets of different second stage existing switches, the inlets of each third-stage virtual switch being connected respectively to the outlets of different second stage existing switches. When expansion stages are installed, existing connections from the outlets of the N/n first-stage virtual switches are removed and new connections are established therefrom to the inlets of different expansion second-stage switches, and existing connections to the inlets of the N/n third-stage virtual switches are removed and new connections are established therefrom to the outlets of different expansion second-stage switches. New connections from the outlets of the expansion first-stage switches to the inlets of different second stage existing switches and to the inlets of differnet expansion second-stage switches are established, and new connections from the inlets of the expansion third-stage switches to the outlets of different second stage existing switches and to the outlets of different expansion second-stage switches are established. The first and third stages virtual switches are then composed into the original physical switches.