A channel control system for a scattered loop type information transmission channel has posts that are linked in a single loop and are served both ways by the same loop. Each post consists of an A-system working in one direction and a similar B-system working in the opposite direction. A mode switch circuit switches between a relay mode for relaying the signal and a terminal mode for separating the A and B systems and returning the signal. Each system has a detection circuit for detecting a channel carrier signal OFF and a carrier ON-OFF signal transmission circuit and a monitor circuit for approach and circulation of the channel code. The mode switch circuit of a post which has detected a channel carrier signal OFF switches to the terminal mode and returns a carrier ON-OFF signal, while a post which has detected a carrier ON-OFF signal switches to the terminal mode and continues to issue a second carrier ON-OFF signal. A portion of the loop which contains a source of the channel carrier signal OFF is cut off from the rest of the loop containing no such source and when the monitor circuit of a post in the terminal mode confirms that the channel code has been circulated to both sides of the loop which has been cut off, its mode switch circuit switches the post to the relay mode and merges itself into the loop when the channel carrier signal OFF has vanished.
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.
Method and apparatus that verifies integrity of communications facilities leased from another network. An idle signal is routed to the lessor network at a first point of interface and should be returned from the lessor network at a second point of interface. If the idle signal is not returned, it indicates a failure of integrity in the leased transmission facilities. If the idle signal is not returned, the type of signal that is returned may indicate a type of error that has occurred, such as equipment failure or allocation of the facility for a different purpose.
