No. 1 ESS Maintenance Plan

The No. 1 electronic switching system has a much higher concentration of control than previous telephone systems. This makes the task of providing continuous telephone service more challenging than ever. It is important that troubles be detected almost instantaneously, before many calls are affected. The main subjects of this article are (1) a scheme for duplicating control equipment and (2) a description of circuit and program facilities for taking advantage of this duplication to detect, to automatically recover from, and to analyze troubles.