In the No. 1 electronic switching system, individual circuits are needed on a per‐line, per‐trunk, and per‐call basis to provide an interface between the outside world and the centralized call processing equipment. These circuits, including digit transmitters and receivers, are characterized by simplicity and compactness, and are program controlled. This article discusses their electrical and mechanical design along with transmission properties and maintenance procedures.

A high‐speed multiposition electronic switch has been developed to act as a time‐division information‐gathering device for the experimental electronic switching system. This switch, called the scanner, provides central control with random access to all lines and trunks terminating in the central office and permits sampling their states for the reception of supervisory and dial pulse signals.