No. 4 ESS: System Integration and Early Office Experience

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. The new system was cut into service on January 17, 1976. During a three-month period, 150 local Chicago switching offices were connected through the new Chicago toll office to 57 toll offices in California, Illinois, Florida, and Ohio. This cutover was the culmination of seven years of designing, manufacturing, and testing the new No. 4 ESS toll switching system. A second No. 4 ESS office in Kansas City, Missouri, was cut into service on July 3, 1976. Two more offices, Jacksonville, Florida, and Dallas, Texas, went into service in December 1976, and nine more offices are scheduled for service in 1977. The development and testing of a toll system of this complexity was a sizable undertaking. The framework for integrating such a system was laid down in the initial planning stages of the project, and was supported throughout by the existence of design standards, documentation re1279