A method for measuring a packet delay deviation representing a deviation between the start time of an optical packet and an average start time in an optical node of a synchronous network, the optical node having an input for receiving a plurality of input optical signals carried by a plurality of wavelength channels, each input optical signal including a plurality of time-sequential optical packets carried on a wavelength channel, wherein each optical packet starts with a packet label encoded in the input optical signal, the method comprising for each of the plurality of wavelength channels: - splitting the input optical signal to generate a first optical signal and a second optical signal identical to the input optical signal, - Shifting in time the second optical signal by one timeslot compared to the first optical signal, the method further comprising, for each of the first optical signal and second optical signal: - Detecting the packet label encoded in the optical signal, - generating an electric detection pulse (28, 30) in response to detecting the packet label, And the method further comprising: - sending the first and second electric detection pulses for each wavelength channel to an AND-gate to generate a synchronization pulse representing a time-overlap between the first electronic pulse and the second electronic pulse, - Measuring a wavelength-averaged delay time between the synchronization pulses obtained for each of the wavelength channels and a reference trigger signal having a periodicity of one time slot, - Generating a synchronized trigger signal by phase shifting the reference trigger signal as a function of the wavelength-averaged delay time, and For each wavelength channel: - Comparing the synchronized trigger signal with the electronic detection pulse obtained from the first optical signal to determine a packet delay deviation between the synchronized trigger signal representing an average start time and the electronic detection pulse representing the start time of an optical packet on the first optical signal. - splitting the input optical signal to generate a first optical signal and a second optical signal identical to the input optical signal, - Shifting in time the second optical signal by one timeslot compared to the first optical signal, - Detecting the packet label encoded in the optical signal, - generating an electric detection pulse (28, 30) in response to detecting the packet label, - sending the first and second electric detection pulses for each wavelength channel to an AND-gate to generate a synchronization pulse representing a time-overlap between the first electronic pulse and the second electronic pulse, - Measuring a wavelength-averaged delay time between the synchronization pulses obtained for each of the wavelength channels and a reference trigger signal having a periodicity of one time slot, - Generating a synchronized trigger signal by phase shifting the reference trigger signal as a function of the wavelength-averaged delay time, and - Comparing the synchronized trigger signal with the electronic detection pulse obtained from the first optical signal to determine a packet delay deviation between the synchronized trigger signal representing an average start time and the electronic detection pulse representing the start time of an optical packet on the first optical signal.