Publications

The No. 4 ESS is a digital time-division toll and tandem switching system first placed in service in Chicago.

Electronic switching systems, in modern terminology, are composed of two parts, the central processing unit and the peripheral system. In No.

A large development undertaking like No.

Prologue By A. E. SPENCER, Jr. (Manuscript received February 23, 1977) No.

July-August 1981 Copyright © 1981 American Telephone and Telegraph Company. Printed in U.S.A. Number 6 No. 4 ESS: Prologue By K. E.

The No. 4 Electronic Switching System (No. 4 ESS), a stored program switching system, has most of its required control, administrative, and maintenance functions provided via program.

A No. 4 Electronic Switching System was installed in Chicago to provide toll service between metropolitan Chicago and selected area codes in the United States.

System Objectives and Organization By A. E. RITCHIE and L. S. TUOMENOKSA (Manuscript received February 8, 1977) This article is an introduction to a series of articles that describe the No.

System Power By H. J. LUER and R. OSTAPIAK (Manuscript received July 26, 1976) The No. 4 ESS system is powered from a 140-volt battery plant.

The selection of a digital format for the No. 4 ESS switch represents a significant step in the continuing evolution of the intertoll network in the United States.