| 摘要 |
A wait-to-restore section corresponding to a first channel has a selector for switching an output side under the control of a mode setting section, and a timer which is reset at the time of mode change. The selector of the wait-to-restore section corresponding to the first channel supplies its output only to a path switch corresponding to the first channel in STS-1 mode and commonly supplies the output to path switches corresponding to the first to third channels. The mode setting section supplies selector change signals to respective alarm detecting sections corresponding to the first to third channels, and supplies a selector change signal and a timer reset signal to the selector of the wait-to-restore section corresponding to the first channel. At the time of mode change from the STS-1 mode to the STS-3c mode or vice versa, the timer of the wait-to-restore section corresponding to the first channel is reset. In STS-3c mode, timers of the wait-to-restore sections corresponding to the second and third channels exclusive for the STS-1 mode are reset.
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