Method for effective data transmission in an optical telecommunications network by wavelength-division multiplexing, WDM, of a plurality of different optical wavelengths, the optical telecommunications network having a plurality of network nodes (21, 22, 23, 24), each pair of network nodes in the plurality of network nodes (21, 22, 23, 24) - comprising a first network node and a second network node - being interconnected by at least one optical transmission path for data transmission, the at least one optical transmission path having a first sub-region and a second sub-region in such a way that the first and second network nodes (21, 22) are interconnected by the first sub-region of the at least one optical transmission path and independently thereof the first and second network nodes (21, 22) are interconnected by the second sub-region of the at least one optical transmission path, the optical transmission path having at least one first optical data transmission line for data transmission in a first direction and at least one second optical data transmission line for data transmission in a second direction counter to the first direction, the data transmission both on the first optical data transmission line and on the second optical data transmission line being unfiltered for the plurality of optical wavelengths, the first sub-region of the at least one optical transmission path connecting the first and second network nodes (21, 22) for data transmission both in the direction from the first network node to the second network node - by means of the first optical data transmission line - and in the direction from the second network node to the first network node - by means of the second optical data transmission line -, the second sub-region of the at least one optical transmission path connecting the first and second network nodes (21, 22) for data transmission both in the direction from the second network node to the first network node - by means of the first optical data transmission line - and in the direction from the first network node to the second network node - by means of the second optical data transmission line -, the first data transmission line and the second data transmission line each complementing the other to form the optical transmission path both in the first and in the second sub-region (151, 152), wherein the method comprises the following steps: - for data transmission from the first network node to the second network node, an optical signal of a first wavelength is coupled - at the location of the first network node - into the first data transmission line and into the second data transmission line, and the optical signal of the first wavelength is coupled - at the location of the second network node - out of at least one of the first and second data transmission lines (155, 156), and - for data transmission from the second network node to the first network node, an optical signal of a second wavelength different from the first wavelength is coupled - at the location of the second network node - into the first data transmission line and into the second data transmission line, and the optical signal of the second wavelength is coupled - at the location of the first network node - out of at least one of the first and second data transmission lines (155, 156). - for data transmission from the first network node to the second network node, an optical signal of a first wavelength is coupled - at the location of the first network node - into the first data transmission line and into the second data transmission line, and the optical signal of the first wavelength is coupled - at the location of the second network node - out of at least one of the first and second data transmission lines (155, 156), and - for data transmission from the second network node to the first network node, an optical signal of a second wavelength different from the first wavelength is coupled - at the location of the second network node - into the first data transmission line and into the second data transmission line, and the optical signal of the second wavelength is coupled - at the location of the first network node - out of at least one of the first and second data transmission lines (155, 156).