| 摘要 |
An optical transmission device for transmitting and receiving SONET signals has a path switch controlled in operation depending on the states of signals received bidirectionally over optical transmission lines. The optical transmission device generates one of a plurality of path switch alarms indicative of respective faults of the signals, based on the states of the signals transmitted to the path switch, and actuates the path switch depending on the generated path switch alarm to output one of the signals from two line terminal equipment units to a lower-level receiver. When SONET signals are transmitted and received in an A/B ring mode, the path switch is actuated in at least one of five control modes to output one of the signals from the two line terminal equipment unit to the lower-level receiver. When SONET signals are transmitted and received in a linear mode, a tributary path function added to the path switch is activated to meet a requirement for the reception of an optical signal transmitted over a unidirectional one of the optical transmission lines.
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