A method for establishing a communication channel, preferably an embedded control channel, between a central network node and at least one network unit to be integrated in a communication network comprising the central network node and an arbitrary but limited number of network units, the central network node being adapted to create and output a WDM downstream signal (SD WDM) comprising downstream channel signals to be transmitted to the network units and to receive a WDM upstream signal (SU WDM) comprising upstream channel signals (SU i) created by the network units, the method comprising the steps of: a) in a setup mode, creating a setup channel signal at the at least one network unit, the frequency spectrum of which comprises, as a modulation component, a setup label which is selected from a predetermined set of at least two setup labels, a predetermined setup address label being associated with each setup label, and transmitting from the at least one network unit the setup channel signal in the direction of the central network node; b) wherein the setup labels comprised by the set of at least two setup labels differ from operating labels comprised by a list of operating labels, which is used for establishing a communication between the at least one network unit and the central network node in an operating mode, c) detecting at the central node the presence of a new upstream channel signal created by the at least one network unit within the WDM upstream signal (SU WDM) by detecting a respective new setup label and determining the setup address label associated with the setup label detected, and creating at the central node a downstream channel signal (SD i) receivable by the at least one network unit by modulating the WDM downstream signal (SD WDM) according to a downstream modulation signal (S mod) comprising, as information to be transmitted to the at least one network unit, a setup information and an address information comprising the setup address label associated with the setup label detected; and d) at the at least one network unit, receiving the respective downstream channel signal (SD i) and extracting and further processing the setup information in case the setup address label included within the respective downstream channel signal (SD i) equals the setup address label associated with the setup label of the setup channel signal that has been sent by the at least one network unit. a) in a setup mode, creating a setup channel signal at the at least one network unit, the frequency spectrum of which comprises, as a modulation component, a setup label which is selected from a predetermined set of at least two setup labels, a predetermined setup address label being associated with each setup label, and transmitting from the at least one network unit the setup channel signal in the direction of the central network node; b) wherein the setup labels comprised by the set of at least two setup labels differ from operating labels comprised by a list of operating labels, which is used for establishing a communication between the at least one network unit and the central network node in an operating mode, c) detecting at the central node the presence of a new upstream channel signal created by the at least one network unit within the WDM upstream signal (SU WDM) by detecting a respective new setup label and determining the setup address label associated with the setup label detected, and creating at the central node a downstream channel signal (SD i) receivable by the at least one network unit by modulating the WDM downstream signal (SD WDM) according to a downstream modulation signal (S mod) comprising, as information to be transmitted to the at least one network unit, a setup information and an address information comprising the setup address label associated with the setup label detected; and d) at the at least one network unit, receiving the respective downstream channel signal (SD i) and extracting and further processing the setup information in case the setup address label included within the respective downstream channel signal (SD i) equals the setup address label associated with the setup label of the setup channel signal that has been sent by the at least one network unit.