Abstract: In a wavelength division multiplexing transmission system, a controller of a relay node of a post-stage notifies level decrease information to a transmission node, upon detecting a decrease in a level of a wavelength in a wavelength multiplex signal received from the transmission node of a pre-stage by the optical channel monitor of the transmission node. The controller of the transmission node of the pre-stage determines that a failure occurs in the wavelength of the transponder of the transmission node, upon detecting a decrease in the level of the wavelength in the wavelength multiplex signal transmitted to the relay node by the optical channel monitor of the transmission node and upon receiving the level decrease information for the wavelength from the relay node. Therefore, a wavelength channel failure in the transponder can be determined in a preferable manner.

Abstract: According to an aspect of an embodiment, an apparatus comprises: a correction level calculating unit that calculates a correction level, which is the input light level necessary to meet an optical signal-to-noise ratio at the maximum level of an optical noise signal; a loss-of-light detection threshold-value setting unit that compares the correction level with an initial threshold value to set a loss-of-light detection threshold value used in detection of any loss of light on the basis of the comparison result; and a loss-of-light detecting unit that compares the level of an input optical signal with the loss-of-light detection threshold value to determine that any loss of light is caused if the level of the input optical signal is lower than the loss-of-light detection threshold value.

Abstract: According to an aspect of an embodiment, an apparatus comprises: a correction level calculating unit that calculates a correction level, which is the input light level necessary to meet an optical signal-to-noise ratio at the maximum level of an optical noise signal; a loss-of-light detection threshold-value setting unit that compares the correction level with an initial threshold value to set a loss-of-light detection threshold value used in detection of any loss of light on the basis of the comparison result; and a loss-of-light detecting unit that compares the level of an input optical signal with the loss-of-light detection threshold value to determine that any loss of light is caused if the level of the input optical signal is lower than the loss-of-light detection threshold value.