Abstract: A data communications device (101, 119) may be controlled from a centrally-located network management system controller (109) located some distance from the device. The data communications device is coupled to the network management system controller by a local channel (155, 157). The device includes a link adapter (133, 143) that communicates with the controller by a protocol that allows the device to exchange messages with the controller. As many as 512 devices may be coupled to the same local channel.

Abstract: A flow control method (200) is suitable for use with a synchronous modem (101). The modem clocks data signals (107) from the terminal under control of a clock signal (109) supplied by the modem. The clock signal operates at a clock rate. The modem stores the data signals in a buffer (111), and thereupon transmits the data signals to a channel, the channel operating at a channel rate. When the quantity of data signals stored in the buffer exceeds a maximum threshold, the modem removes the clock signal from the terminal, thereby interrupting the flow of data signals from the terminal. When the quantity of data signals stored in the buffer is less than a minimum threshold, the modem again applies the clock signal to the terminal, thereby restoring the flow of data signals from the terminal.

Abstract: A two-wire, carrier-type communication system is provided which enables simultaneous two-way transmission over two-wire circuits in the same spectrum. Carrier signals in quadrature are used to allow separation of signals within the same frequency spectrum. The carrier recovered at each subscriber station is used to demodulate the received signal and, after being phase shifted 90.degree., is applied as carrier to the transmitter modulator. The transmitters at the subscriber stations are thus the same as that at the central office but are locked to the receiver and 90.degree. out of phase. A bidirectional control phase adjustment network at the central station adjusts the phase of the signal received thereby until the received carrier is 90.degree. out of phase with the transmit carrier.