Common channel interoffice signaling: No. 4 ESS Application

Common channel interoffice signaling (CCIS) is provided as an integral part of No. 4 ESS. The unique hardware required for CCIS consists of a common systems CCIS terminal and associated access circuit, continuity check transceivers, and unitized terminal equipment for CCIS trunks. The control of the CCIS hardware and the logic required for CCIS administrative functions is provided by programs resident in the 1A Processor. This paper discusses the system design requirements, the signaling hardware, and the software design for CCIS in the No. 4 Electronic Switching System.