Switching-unit markers for electronic automatic exchange

THE BASIC FUNCTION of a marker is to provide the controls for connecting a switching-unit inlet to an outlet by way of an available idle path through the switching unit; this paper describes the three types of markers, line group, trunk group, and group selector, used in a common-control space-divided central-office telephone system, the No. 1 Electronic Automatic Exchange (E-A-X^∗) developed by Automatic Electric Laboratories. The E-A-X markers also provide class-of-service facilities, automatic number identification, and alternate routing. Use of reliable semiconductor electronics and high-speed matrix switching has reduced marker holding time and, therefore, the amount of common equipment necessary.