Optical network system, optical node device, and optical network control method

An optical network control method, comprising:

• depending on a variation in a data volume of a client signal to be transmitted using a plurality of optical subcarriers:
• changing an active optical subcarrier, of the plurality of optical subcarriers, to be used for transmitting the client signal, synchronously between a transmitting side and a receiving side;
• and
• remapping the client signal onto an active optical subcarrier after having been changed, synchronously between the transmitting side and the receiving side,
• wherein the changing of the active optical subcarrier is performed based on respective results of a process of selecting a change candidate optical subcarrier whose operation to be stopped from among the active optical subcarrier, and a process of setting a wavelength of a changed optical subcarrier that becomes the active optical subcarrier due to a change,
• wherein the process of selecting the change candidate optical subcarrier includes selecting an optical subcarrier with a maximum number of consecutive unused optical subcarriers in an adjacent link in an identical wavelength band as the change candidate optical subcarrier from the plurality of optical subcarriers, and
• wherein an optical subcarrier with a maximum number of unused optical subcarriers is selected as the change candidate optical subcarrier from optical subcarriers in an adjacent wavelength band when a number of consecutive unused optical subcarriers is equal.