Optical transmission system and noise suppression method

1. A noise suppression method for use in an optical transmission system which includes a plurality of nodes transmitting a WDM optical signal, and in which first node equipment drops an optical signal transmitted via a first wavelength channel from the WDM optical signal and guides the dropped optical signal to a communication device, the noise suppression method comprising:

transmitting a failure signal that represents whether or not a failure occurs for each of the plurality of wavelength channels in the WDM optical signal;

transmitting a shutoff signal that represents whether or not a shutoff operation for shutting off an optical output is instructed for the respective wavelength channels; and

shutting off the first wavelength channel when the failure signal represents that a failure occurs in the first wavelength channel and the shutoff signal represents that the shutoff operation is instructed for the first wavelength channel, wherein

when second node equipment arranged on a first route for transmitting an optical signal with the first wavelength channel to the first node equipment detects a failure in the first wavelength channel, the second node equipment transmits the failure signal that represents a failure occurs in the first wavelength channel to the first node equipment via the first route,

when the first node equipment receives the failure signal that represents a failure occurs in the first wavelength channel from the second node equipment, the first node equipment transmits the shutoff signal that represents the shutoff operation is instructed for the first wavelength channel toward the second node equipment via the first route,

third node equipment shuts off an optical output of the first wavelength channel, after the third node equipment relays the failure signal that represents a failure occurs in the first wavelength channel, and when the third node equipment receives the shutoff signal that represents the shutoff operation is instructed for the first wavelength channel, and wherein

the first node equipment periodically or constantly transmits the shutoff signal toward the second node equipment via the first route regardless of the failure signal.

2. The noise suppression method according to claim 1 , wherein

the first node equipment transmits the shutoff signal toward the second node equipment via the first route in response to reception of the failure signal.

3. The noise suppression method according to claim 1 , wherein node equipment that firstly receives the shutoff signal from the first node equipment shuts off the optical output of the first wavelength channel.

4. The noise suppression method according to claim 1 , wherein

an amplifying node equipment for collectively amplifying a WDM optical signal is provided between the first node equipment and the second node equipment,

the amplifying node equipment transfers the shutoff signal toward the second node equipment upon receipt of the shutoff signal, and

the third node equipment shuts off the optical output of the first wavelength channel upon receipt of the shutoff signal that has transferred by the amplifying node equipment.

5. A noise suppression method for use in an optical transmission system which includes a plurality of nodes transmitting a WDM optical signal, and in which first node equipment drops an optical signal transmitted via a first wavelength channel from the WDM optical signal and guides the dropped optical signal to a communication device, the noise suppression method comprising:

transmitting a failure signal that represents whether or not a failure occurs for each of the plurality of wavelength channels in the WDM optical signal;

transmitting a shutoff signal that represents whether or not a shutoff operation for shutting off an optical output is instructed for the respective wavelength channels; and

shutting off the first wavelength channel when the failure signal represents that a failure occurs in the first wavelength channel and the shutoff signal represents that the shutoff operation is instructed for the first wavelength channel, wherein

when second node equipment arranged on a first route for transmitting an optical signal with the first wavelength channel to the first node equipment detects a failure in the first wavelength channel, the second node equipment transmits the failure signal that represents a failure occurs in the first wavelength channel to the first node equipment via the first route,

when the first node equipment receives the failure signal that represents a failure occurs in the first wavelength channel from the second node equipment, the first node equipment transmits the shutoff signal that represents the shutoff operation is instructed for the first wavelength channel toward the second node equipment via the first route,

third node equipment shuts off an optical output of the first wavelength channel, after the third node equipment relays the failure signal that represents a failure occurs in the first wavelength channel, and when the third node equipment receives the shutoff signal that represents the shutoff operation is instructed for the first wavelength channel, and wherein

the third node equipment shuts off the optical output of the first wavelength channel by using a wavelength selecting device for passing or blocking an optical signal having a specified wavelength within the WDM optical signal,

the third node equipment manages states of the failure signal and the shutoff signal, and issues to the wavelength selecting device an instruction to change an operating state only when the operating state of the wavelength selective device is altered due to a change in the state of the failure signal or the shutoff signal.

6. An optical transmission system which includes a plurality of nodes transmitting a WDM optical signal, and in which first node equipment drops an optical signal transmitted via a first wavelength channel from the WDM optical signal and guides the dropped first optical signal to a communication device, wherein

a failure signal that represents whether or not a failure occurs for each of the plurality of wavelength channels in the WDM optical signal is transmitted,

a shutoff signal that represents whether or not a shutoff operation for shutting off an optical output is instructed for the respective wavelength channels is transmitted,

the first wavelength channel is shut off when the failure signal represents that a failure occurs in the first wavelength channel and the shutoff signal represents that the shutoff operation is instructed for the first wavelength channel, wherein

when second node equipment arranged on a first route for transmitting an optical signal with the first wavelength channel to the first node equipment detects a failure in the first wavelength channel, the second node equipment transmits the failure signal that represents a failure occurs in the first wavelength channel to the first node equipment via the first route,

when the first node equipment receives the failure signal that represents a failure occurs in the first wavelength channel from the second node equipment, the first node equipment transmits the shutoff signal that represents the shutoff operation is instructed for the first wavelength channel toward the second node equipment via the first route,

third node equipment shuts off an optical output of the first wavelength channel, after the third node equipment relays the failure signal that represents a failure occurs in the first wavelength channel, and when the third node equipment receives the shutoff signal that represents the shutoff operation is instructed for the first wavelength channel, and wherein

the first node equipment periodically or constantly transmits the shutoff signal toward the second node equipment via the first route regardless of the failure signal.