Patent ID: 7613177

Claim:
An in-service method of adding stages comprising: designating a multistage switching network for adding stages, where the multistage switching network comprises a plurality of stages comprising a plurality of switching elements comprising a plurality of top ports and a plurality of bottom ports and the multistage switching network further comprises a plurality of connections each providing communications between two adjacent stages of switching elements and coupled to a bottom port of a switching element of the upper adjacent stage and a top port of a switching element of the lower adjacent stage; providing an insertable unit comprising at least one stages each comprising a plurality of switching elements comprising a plurality of top ports and a plurality of bottom ports, having an uppermost stage and lowermost stage; providing a desired topology having a first desired interconnection pattern above the uppermost stage of the insertable unit and a second desired interconnection pattern below the lowermost stage of the insertable unit; selecting a first stage of switching elements from the plurality of stages of the multistage switching network and a second stage of the multistage switching network of switching elements from the plurality of stages, where the second stage is adjacent to and below the first stage, and where the multistage switching network has a set of connections interconnecting the first stage and the second stage; making sacrificial connections prior to the insertion to provide better connectivity between switching elements within the same stage in the insertable unit; and inserting the insertable unit by concurrently: breaking the set of connections interconnecting the first stage and the second stage; making a set of connections between the first stage and the uppermost stage of the insertable unit having the first desired interconnection pattern; and making a set of connections between the lowermost stage of the insertable unit and the second stage having the second interconnection pattern.