Abstract: The invention relates to a method for the protection of a passive optical transmission network comprising an optical line terminal (OLT) that is connected to at least one remote node to which a plurality of network termination nodes (ONU) is linked. Between each ONU and the OLT, a bidirectional optical signal transmission can be established, wherein the connection between the OLT and the one or more RNs is realized via a first bidirectional optical transmission route by means of which an optical wavelength-multiplexed signal is transmitted in the downstream direction from the OLT to the one or more RNs and in the upstream direction from the one or more RNs to the OLT.