An optical transmission system with bidirectional connection paths and method for establishing at least one bi-directional communication path

An optical transmission system comprising a plurality of switchable optical network node (ONK, ONK ') having a plurality of uni-directional connection units (IN1 to IN4, OUT1 to OUT4), wherein each unidirectional connection unit (IN1 to IN4, OUT1 to OUT4) of a network node (ONK) via a unidirectional connection path portion (FA1) to a uni-directional terminal unit (IN1 to IN4, OUT1 to OUT4) of a further network node (ONK) is connected, characterized in that for setting up a bidirectional communication path (BVP) a matching layer is provided on at least two opposed directions of transmission ( UR1, UR2) having unidirectional connection units (IN1, OUT1) are summarized of an optical network node (ONK) (to a bidirectional terminal unit BA1) and addressed together.