Protection switching apparatus and method

Claim 1

A protection switching system, comprising: a first stage module having an input and output; a pair of second stage modules, each second stage module having an input and output for connection to the first stage module for transmission and reception of signals therebetween, one of said second stage modules being a working module, the other of said second stage modules being a standby module; a pair of third stage modules, each third stage module having an input and output for connection to an input and output of each of said second stage modules for transmission and reception of signals therebetween, one of said third stage modules being a working module, the other of said third stage modules being a standby module; a controller/monitor circuit to monitor fault conditions of the working modules and to issue a control signal upon detection of a fault condition in a working module to cause at least one of the standby modules of the second and third stage standby modules to function in place of the working module in which a fault condition is detected; and the at least one standby module of the second and third stage standby modules includes means for switching the inputs of the first stage module, standby modules, and working modules, to a standby position corresponding to an activation of the at least one standby module.