Patent ID: 8165467

Claim:
An optical transmission system comprising a plurality of optical nodes capable of dropping or adding optical signals and a monitoring and controlling device that monitors and controls the plurality of optical nodes, wherein: each of the optical nodes is provided with an optical transceiver and an optical add-drop unit that sends out to a transmission line or receives from the transmission line transmit or receive signals from the optical transceiver; the optical add-drop unit: regarding add signals, selects the optical signals of the optical transceiver of an own node thereof or optical signals from a second transmission line for optical signals to be sent out to a first transmission line, and regarding drop signals, drops signals from the first transmission line to the own node thereof, and sends out to the same to the second transmission line or blocks the same from being sent out to the second transmission line; and an alarm inhibiting device is further provided that, regarding transmit signals from a first optical transceiver of a first optical node, inhibits any unexpected alarm from being issued by the first optical transceiver when selection is made by the optical add-drop unit of a second optical node to drop the signals to the own node thereof and to send the signals out to a transmission line in a downlink direction.