| 摘要 |
PURPOSE:To quickly discover the fault of the 1st and 2nd transmission loop systems, especially, the fault of a terminal station device, by respectively providing a system controlling section and 1st and 2nd status controlling sections to a central station device and plural terminal station devices. CONSTITUTION:A specific control channel 19 of '0' system reaches the '0' system status controlling section 14 of a terminal station device 10 and, if no fault information exists from the controlling section 14, the channel 19 passes through the controlling section 14. The control channel 19 then reaches the '0' system status controlling section of the next terminal station device 20 and, if fault information from the controlling section exists, a bit having a content of '0' is rewritten to '1' and transmitted to the next terminal station device 5. After the control channel 19 reaches the central control system 2 of '0' system in the same manner, the channel 19 returns to a system controlling section 4. In the case of a specific control channel 19 of '1' system, the same operations are carried out. Accordingly, when the specific control channels 19 are sent out at an interval of 2.5 ms and bits having a content of '0' are sent to transmission loops 17 and 18 of '0' and '1' systems through the central control sections 2 and 3 of '0' and '1' systems, the system controlling section 4 can monitor an entire communication network at cycles of 2.5 ms.
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