Transmission apparatus and network control method

A network control method performed in one of a plurality of transmission apparatuses included in a ring network, the one of the plurality of transmission apparatuses has at least one memory storing wavelength termination information, at least one demultiplexer, at least one multiplexer, a switch, which includes at least one optical-electrical (O/E) converter that performs O/E conversion and at least one electrical-optical (E/O) converter that performs E/O conversion, and a processor which is coupled to the at least one memory, the network control method comprising:

• transmitting, by the at least one E/O converter to the at least one multiplexer, each of a first plurality of optical signals received, by the at least one demultiplexer to the at least one O/E converter, from a first transmission apparatus to a second transmission apparatus, each of the first plurality of optical signals having each of a plurality of wavelengths, the first transmission apparatus and the second transmission apparatus being included in the plurality of transmission apparatuses, the first transmission apparatus being one adjacent transmission apparatuses of the transmission apparatus in the ring network, the second transmission apparatus being another adjacent transmission apparatuses of the transmission apparatus in the ring network;
• and
• by the processor:
• receiving, by the at least one demultiplexer to the at least one O/E converter, a message from the first transmission apparatus, the message being for setting loopback for at least one wavelength in the ring network, the message being transmitted when a failure of at least one optical signal having the at least one wavelength is detected in a link of the ring network, the at least one wavelength being included in the plurality of wavelengths;
• setting a loopback to the switch based on the message and the wavelength termination information, the loopback being set for a wavelength of the at least one wavelength
• when an optical signal having the wavelength is terminated by the switch and converted to an electrical signal by the at least one 0/E converter and
• when the optical signal having the wavelength is not terminated and not converted to an electrical signal by any of transmission apparatuses among the plurality of transmission apparatuses from the second transmission apparatus to a transmission apparatus before the link in which the failure is detected;
• and
• after the loopback is set for the wavelength, when receiving, by the at least one demultiplexer to the at least one O/E converter, an optical signal having the wavelength from the first transmission apparatus,
• switching, by the at least one E/O converter, the wavelength of the received optical signal from the wavelength to a different wavelength and
• transmitting, by the at least one E/O converter to the at least one multiplexer, an optical signal, corresponding to the received optical signal, having the different wavelength to the first transmission apparatus.