No. 4 ESS: Prologue

July-August 1981 Copyright © 1981 American Telephone and Telegraph Company. Printed in U.S.A. Number 6 No. 4 ESS: Prologue By K. E. MARTERSTECK (Manuscript received July 30, 1980) Since the cutover of the first No. 4 Electronic Switching System (ESS) office in January 1976, a program of system evolution has been carried out. As a result significant cost reduction was achieved, major new features have been added to the No. 4 ESS, and the system's performance has been enhanced. This paper gives an overview of the continuing development of the No. 4 ESS carried out during the period 1976 to 1980 as a prologue to a series of papers in this volume which describe some of the specifics of this activity.