No. 4 ESS: System integration and early office experience

This article describes the special equipment and test procedures developed for system-testing the No. 4 ess toll system. It discusses novel methods developed for the coordination of hardware and software changes and testing in various system laboratory configurations. Planning, engineering, installation, and testing of early offices are described. Early field experience with the first operational No. 4 ess is presented. This office, a selective routing tandem located in Chicago, went into service on January 17, 1976.