| 摘要 |
PURPOSE:To set a line even if the command from a monitor station is received erroneously, by inverting the loop back state when synchronization cannot be acquired for a constant time after the loop back to each terminal station, in the system where a current system and a stand-by system can perform the loop back independently of each other. CONSTITUTION:If a current transmission line 3-2 and a stand-by transmission line 4-2 are faulty together and a normal loop back command is not transferred from a monitor station 1 to each terminal station and a correct loop back is not performed, a control circuit 5 detects the impossiblility of acquisition of synchronization on transmission lines to start a timer 6-2. If synchronization is not restored when the timer 6-2 counts a predetermined constant time, the control circuit 5-2 inverts the folding state in a terminal station 2-2 to fold the transmission line from the stand-by transmission line to the current transmission line. Under this state, the loop back command of the stand-by system from the monitor station 1 is accepted by the terminal station 2-2, and thus, a line is set effectively. |
