| 摘要 |
PURPOSE:To switch a current transmission line to a standby transmission line without a momentary break by substituting overlapping cells with idle cells in case of the occurrence of cell overlap and delaying and using reception information in case of the occurrence of drop-out at the time of switching to the stand-by transmission line. CONSTITUTION:A pair of an idle cell discriminating circuit 39 and a variable delay memory 42 are provided for current transmission lines 16a-16b and a stand-by transmission line 17. For example, at the time of switching from the current transmission line 16d to the stand-by transmission line 17, a control circuit 35 discriminates lead/ delay between the information string on the current transmission line 16d and that on the stand-by transmission line 17. When it is discriminated that the information string of the current transmission line 16d leads, an idle cell clock generating circuit 43 is connected to send idle cells corresponding to cell overlap, and the current transmission line is disconnected by a transmission line changeover switch 13 thereafter. When the information string of the current transmission line is delayed, information is delayed for the time corresponding to this delay by the variable delay memory 42 to prevent drop-out of the signal, and the current transmission line is disconnected by the switch 13 thereafter.
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