Abstract: An optical transmission system allows quick switching to protection side transmitting and receiving circuits by providing sub optical or subsidiary transmitting and receiving circuits for each current side transmission unit and each protection side transmission unit. A controller or exerciser successively starts the sub optical transmitting circuits of the current side transmission units for a predetermined time when no fault is detected. When a fault is detected, the defective portion of the system is bypassed using the protection side transmission units and the sub optical transmitting and receiving circuits of the affected current side transmission units. In this manner, the time required for the received signal to stabilize is reduced to about 10 msec.

Abstract: A line terminal equipment provided in a drop-insert station of a transmission system for receiving a signal from a preceding station of the drop-insert station through a preceding protection line is electrically connected in a protection switching equipment provided in the drop-insert station, to a line terminal equipment provided in the drop-insert station for transmitting the signal to a succeeding station of the drop-insert station, by a connecting line provided in the protection switching equipment, in any one of cases where no disconnection trouble occurs on preceding and succeeding work lines, where disconnection troubles occur on one of the preceding work lines and a succeeding work line associated with the preceding work line and where a disconnection trouble occurs on one of the preceding work lines. The connecting line is disconnected in a case where a disconnection trouble occurs on one of the succeeding work line.

Abstract: Disclosed is a password security method in a man-machine system for keeping the secrecy of a password during a setting process of the system. To keep not only the secret of the password but also the presence of the password from unauthorized users, the method comprises a prompt displaying step for prompting to enter an equipment name and not prompting to enter the password; a password discriminating step to discriminate whether or not a correct password is entered; a step for entering a normal mode when the correct password is not detected; and step for entering a password mode when the correct password is detected.

Abstract: An initial status setting system in a multi-unit system constructed of a plurality of units wherein at least a set of status data is held in registers in at least two of the plurality of units, both units indicating whether or not the set of status data held in each of the registers is valid. The output of each of the registers is applied to the other of the registers, and each of the registers is controlled so that only a valid set of status data is input thereto.