PURPOSE: To improve reliability without issuing an unnecessary alarm by providing a circuit transmitting prescribed data as a data signal for a period when a frame signal is made a feedback loop state between a device side loop back setting part and an F-CONV, and preventing the state from becoming a pseudo synchronizing state.
CONSTITUTION: Each transmission line I/F terminal part of a terminal station device duplexed by an operational system and a non-operational system is composed of a transmission line, a device-side loop back setting parts 1 and 2, a terminal part 4 and an F-CONV part 5. In the non-operational system, the setting part 1, the terminal part 4, the setting part 2 and the F-CONV part 5 are defined as circuits where frame signals are made feedback loop states in this order. A data/status and mask setting part 6 is added between this setting part 2 and the CONV part 5, and prescribed data as data signals is transmitted for a period when the setting part 6 makes the frame signals the feedback loop states. Thus, the monitoring is surely performed by preventing the state from by being a pseudo synchronizing state in the execution of the self- monitoring in non-operation to improve the reliability issuing without giving an unnecessary alarm at the time of setting the operational state, etc.
KODACHI HIRONORI
OTSUKA MASANORI
