Abstract: A communication system for linking a central computer to a plurality of remotely spaced terminals employs a single run of coaxial cable formed in a loop extending in the vicinity of each of the terminals with its two ends terminating adjacent the head-end computer. The output of the computer is provided to a normally operative primary channel transmitter connected to one end of the cable as well as to a normally inoperative, secondary channel transmitter connected to the other end of the cable. Each of the terminals includes receivers for both the primary and secondary channel. Primary channel signal detectors located at the head-end and at each of the terminals energize the secondary channel transmitter and/or the secondary channel receivers at their respective detectors when they fail to receive the primary channel carrier.

Abstract: A computer system consists of a central station and a plurality of remote terminals, some having a relatively low data acceptance and/or transmission rate and others having a higher data rate. The communication link between the central station of the terminals consists of a low speed channel and a high speed channel. The terminals are permanently connected to receive signals over the low speed channel and a control signal, sent by the central station, to a particular addressed terminal over the low speed channel connects an associated terminal to the high speed channel.