Abstract: An optical network (10) comprises a first optical transmitter (12), a first controller (14), optical receiver apparatus (16) and an optical network element (20) comprising an optical receiver (22), a second optical transmitter (24), and a second controller (26). The first controller controls the first optical transmitter to generate and transmit a first optical signal having a first signal format until the optical receiver apparatus detects the second optical signal and subsequently controls it to apply a second signal format to said first optical signal. The second controller (26) controls the second optical transmitter to iteratively generate and transmit the second optical signal at different wavelength until a first optical having a second signal format is detected. The second controller subsequently maintains generation and transmission of the second optical signal at the wavelength at which the first optical signal was identified as having the second signal format.