The invention refers a method and an arrangement for channel set up in an optical network. An optical signal path is configured for a certain optical channel signal (OC1) of a WDM-signal. This channel signal (OC1) is on-off-modulated by a modulation test signal (MT1) having a predetermined lower frequency and is generating a channel test signal (OT1). This channel test signal (OT1) is combined with other optical channels (OC2-OCn) to the WDM-signal (WS) and transmitted via said path. At a start node (1) or a downstream node (3, 5) a measurement signal (EMI, EM3) is derived from the complete WDM-signal (WS) without wavelength de-multiplexing. The measurement signal (EMI, EM3) is compared with a correlation signal (MC1) and an obtained power level (PC1) is used to adjust the channel power (PC1, PC2, PC3) to achieve predetermined target power values (PC1-PC4) at different power monitoring points (19, 40, 41, 58). The adjustment step is repeated for all downstream nodes (3, 5) and all further channel signals (OC2-OCn).