The invention relates to a system and method of communication between optical transceivers in an optical WDM network, wherein a broad-band modulation of optical signals in a primary frequency band is utilized for transmitting primary high-speed data, while a plurality of relatively low-frequency in-band subcarriers is used to modulate the optical signals to transmit secondary data between network nodes, wherein the plurality of low-frequency subcarriers lie at least in part within the primary frequency band.