Abstract: An optical line terminal of the type including sets of optical signal processing components arranged in an identical manner in mutually redundant parallel branches includes an input switch that routes an incoming optical signal for processing into either one of two branches to the exclusion of the other. Following amplification, a part of an optical signal propagating in the one branch is branched-off and routed through the same input switch into the other branch to be processed therein identically to the one branch processing for monitoring the status of the other branch. On detection of faulty processing in the one branch, the input switch is switched into its other state in which it reroutes the incoming optical signal into the other branch for processing therein, while also routing a part of the amplified optical signal from the other branch into the one branch for monitoring the one branch.