| 摘要 |
PURPOSE:To quickly restore quickly a line by sending a trigger signal and a polling signal from a station to be controlled when the trigger signal from one control station among plural ring-form connection stations is not detected by the station to be controlled so as to substitute the polling control. CONSTITUTION:A trigger station 1 and plural node stations 2-4 are connected in a ring by a transmission line 6. The trigger station 1 sends the trigger signal at a prescribed period. When the node stations 2-4 detect no trigger signal by a reception section 10 for a prescribed time decided by the address given to themselves and the said constant period, a transmission section 14 is driven via a control section 12 to change over the switch 11 from the line 6 to the transmission section 14. Then the trigger signal and the polling signal are sent. Thus, the line is restored quickly normally.
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