An optical network comprising: an optical network element , at a second network location (B), comprising a first optical transmitter arranged to generate and transmit a first optical signal, a first controller arranged to control said first optical transmitter to generate and transmit said first optical signal at a wavelength selected from a predetermined plurality of wavelengths, and an optical receiver arranged to detect a second optical signal; at a first network location (A): a second optical transmitter arranged to generate and transmit said second optical signal, a second controller arranged to control said second optical transmitter to generate and transmit said second optical signal, and optical receiver apparatus arranged to detect an optical signal having a wavelength within a receiving wavelength band, said first controller being arranged to control said first optical transmitter to generate and transmit said first optical signal in response no said second optical signal being detected, said first controller being arranged to control said first optical transmitter to iteratively generate and transmit said first optical signal at different wavelengths of said plurality of wavelengths until said second optical signal is detected by said optical receiver , while the optical receiver remains operable in each iteration to detect the second optical signal at the same wavelength, and being further arranged to subsequently maintain generation and transmission of said first optical signal at the last attempted wavelength, and said second controller being arranged to control said second optical transmitter to generate and transmit said second optical signal following detection of said first optical signal by said optical receiver apparatus . an optical network element , at a second network location (B), comprising a first optical transmitter arranged to generate and transmit a first optical signal, a first controller arranged to control said first optical transmitter to generate and transmit said first optical signal at a wavelength selected from a predetermined plurality of wavelengths, and an optical receiver arranged to detect a second optical signal; at a first network location (A): a second optical transmitter arranged to generate and transmit said second optical signal, a second controller arranged to control said second optical transmitter to generate and transmit said second optical signal, and optical receiver apparatus arranged to detect an optical signal having a wavelength within a receiving wavelength band, said first controller being arranged to control said first optical transmitter to generate and transmit said first optical signal in response no said second optical signal being detected, said first controller being arranged to control said first optical transmitter to iteratively generate and transmit said first optical signal at different wavelengths of said plurality of wavelengths until said second optical signal is detected by said optical receiver , while the optical receiver remains operable in each iteration to detect the second optical signal at the same wavelength, and being further arranged to subsequently maintain generation and transmission of said first optical signal at the last attempted wavelength, and said second controller being arranged to control said second optical transmitter to generate and transmit said second optical signal following detection of said first optical signal by said optical receiver apparatus . <EOS>