A passive optical transmission network having a protection mechanism which comprises an optical line terminal that is connected to at least one remote node to which a plurality of network termination nodes are linked, (a) wherein bidirectional optical signal-transmission can be established between each network termination node and the optical line terminal, (b) wherein the connection between the optical line terminal and the at least one remote node is made by way of a first bidirectional optical transmission section by way of which in each case an optical wavelength-multiplexed signal is transmitted in the downstream direction from the optical line terminal to the at least one remote node and in the upstream direction from the at least one remote node (RN1 to RNn) to the optical line terminal, (c) wherein a second bidirectional optical transmission section is provided between the optical line terminal and the at least one remote node, and (d) wherein in the at least one remote node the wavelength-multiplexed signal is fed in the upstream direction by means of a passive optical splitter unit (17, 170) both to the first optical transmission section and to the second optical transmission section, characterised in that (e) provided in the optical line terminal there is a control unit which, in the event of detection of an error state that points to impairment of the first or second optical transmission section, activates a controllable optical switch unit in such a way that in order to send the wavelength-multiplexed signal in the downstream direction and/or to receive the wavelength-multiplexed signal in the upstream direction there is a switch-over to the respective other optical transmission section, (f) the first and second optical transmission section each comprise two unidirectional optical paths (191, 192; 211, 212) with in each case opposite transmission directions for the transmission of the wavelength-multiplexed signals in the downstream direction and the upstream direction, (g) in the at least one remote node in each case the two splitting ports of a respective splitter unit (170; 172) are connected to the two optical paths (191, 211; 192, 212) for the same transmission direction, the common port of the splitter unit, to which the wavelength-multiplexed signal is fed in the downstream direction, is connected to a demultiplexer unit, and the common port of the splitter unit, to which the wavelength-multiplexed signal is fed in the upstream direction, is connected to a multiplexer unit. (a) wherein bidirectional optical signal-transmission can be established between each network termination node and the optical line terminal, (b) wherein the connection between the optical line terminal and the at least one remote node is made by way of a first bidirectional optical transmission section by way of which in each case an optical wavelength-multiplexed signal is transmitted in the downstream direction from the optical line terminal to the at least one remote node and in the upstream direction from the at least one remote node (RN1 to RNn) to the optical line terminal, (c) wherein a second bidirectional optical transmission section is provided between the optical line terminal and the at least one remote node, and (d) wherein in the at least one remote node the wavelength-multiplexed signal is fed in the upstream direction by means of a passive optical splitter unit (17, 170) both to the first optical transmission section and to the second optical transmission section, characterised in that (e) provided in the optical line terminal there is a control unit which, in the event of detection of an error state that points to impairment of the first or second optical transmission section, activates a controllable optical switch unit in such a way that in order to send the wavelength-multiplexed signal in the downstream direction and/or to receive the wavelength-multiplexed signal in the upstream direction there is a switch-over to the respective other optical transmission section, (f) the first and second optical transmission section each comprise two unidirectional optical paths (191, 192; 211, 212) with in each case opposite transmission directions for the transmission of the wavelength-multiplexed signals in the downstream direction and the upstream direction, (g) in the at least one remote node in each case the two splitting ports of a respective splitter unit (170; 172) are connected to the two optical paths (191, 211; 192, 212) for the same transmission direction, the common port of the splitter unit, to which the wavelength-multiplexed signal is fed in the downstream direction, is connected to a demultiplexer unit, and the common port of the splitter unit, to which the wavelength-multiplexed signal is fed in the upstream direction, is connected to a multiplexer unit.