| 摘要 |
PURPOSE:To constitute a loop even when input interruption takes place to both active and spare systems by detecting reception signal input interruption with frame synchronism of a transmission data frame, taking frame out of synchronism as a reception signal error and switching an input transmission line. CONSTITUTION:A subsequent synchronizing station 20 detects out of frame synchronism of a reception signal through transmission line interruption (p) of an active system transmission line, a reception signal of the transmission line 1 is disconnected and a reception signal of a spare system transmission line (j) is transmitted via a transmission line (i). Further, the station 20 stops the transmission to a loop control station 19 through the line (j), the station 19 discriminates the line (j) as input interruption and outputs a reception signal from the line (i) to the line (j). A synchronizing station 21 outputs a reception signal from the line (i) to the line (j) by the transmission line interruption (q) of the line (j). In this case, a loop is constituted between the station 20 and 21, since no loop synchronizing control station exists, the reception signal from the line (j) is outputted to the line (i) by the station 22. Thus, the transmission line through the control station 19 and the synchronizing stations 22-24 is constituted in a double fault.
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