Abstract: A closed-loop communication system includes a closed-loop communication link with a shared communication channel. A set of communication devices are connected to the closed-loop communication link. Each communication device has un-arbitrated access to the shared communication channel. A responding modem connected to the closed-loop communication link includes a modem signal detection circuit to identify a modem signal on the closed-loop communication link and respond to it by facilitating a squelch disable signal. A transmission squelch circuit squelchs all transmission signals from the responding modem except when the transmission squelch circuit is disabled in response to the squelch disable signal.

Abstract: A fiber optic network includes a fiber optic transmission channel with a first path and a second path. A set of fault-tolerant remote stations are connected to the fiber optic transmission channel, each of the fault-tolerant remote stations is configured to send and receive fiber optic overhead channel data on both the first path and the second path. A fault-tolerant master station connected to the fiber optic transmission channel includes a switch network and a logic network. The logic network generates first switch command signals to force the switch network into a standard configuration which results in the transmitting and receiving of fiber optic overhead channel data on the fiber optic transmission channel during normal operating conditions.