The SLC@ 96 carrier system has been developed to bring digital capability to the local loop network, and ultimately it may be a component of a completely integrated digital network. It uses two unique channel banks: one located in the central office to interface to the local switching machine, and the other located remotely in the vicinity of a group of subscribers. The SLC 96 carrier can provide, through the use of different channel units, message telephone service, coin service, special services, and data services. For digital transmission, it interfaces to standard Tllines or optical fibers. The design is patterned after the D4 channel bank, and many of D4 carrier's channel units can be used in the SLC 96 carrier system. The resultant system has the versatility to serve both rapidly growing metropolitan, as well as rural, areas. Features that provide highly reliable service and easy maintenance have been included in the design of the system.

Over the past 100 years the telephone loop connecting central office switching equipment and the telephone customer's premises has evolved from aerial open wire to buried plastic‐insulated twisted pairs. In the last 20 years the use of electronic circuits for range extension has become popular. These circuits allow use of higher resistance loops (finer gauge wires) than central offices are normally designed to accept. This paper reviews some of this history, describes rural and suburban systems of voice frequency range extension, presents requirements and circuit design considerations, and compares several electronic range extender circuits currently used to implement these systems.

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