Patent ID: 7606488

Claim:
A wavelength-division-multiplexing optical transmission system in which optical-node apparatuses that perform relay transmission of wavelength-division-multiplexed light are located at specified nodes, respectively, in a main optical transmission path, comprising at each respective specified node: a multiplexed-wavelength-number monitoring unit that monitors the number of multiplexed wavelengths; a multiplexed-wavelength-number transmission unit that transmits the number of multiplexed wavelengths in the downstream direction; and an optical amplifier that is located at a stage before the respective optical-node apparatus located at said respective specified node and that switches level control to constant-gain control when there is notification from upstream of a change in the number of multiplexed wavelengths, and after a specified amount of time, restarts level control so that the level becomes a target level that corresponds to the actual number of multiplexed wavelengths; and further comprising an optical-transmission-system-control unit that performs control so that the following equation T<Y /( N·v ) is satisfied, wherein T (sec) denotes a period from the time when a change in the number of multiplexed wavelengths occurs until said constant-gain control starts, v (dB/sec) denotes output-level-recovery speed of said optical amplifier, Y (dB) denotes fluctuation allowance of a receiving unit after wavelength-division-multiplexing transmission, and N denotes a maximum number of spans.