Automatic Switching for Nationwide Telephone Service

824 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1952 connected with another in the same town. It was a natural step to develop the equipment so that operators in nearby towns could complete toll calls through this local dial equipment. This was done first by using the local equipment and then with progressive modifications making it more and more suitable for toll. By these means through the decades of the 20's and 30's regional networks were developed for operator toll dialing, using step-by-step types of equipment, particularly in Southern California, Connecticut and Ohio. Also many short haul toll calls in metropolitan areas were handled in connection with the panel type dial equipment which was developed for automatic switching in these areas. Also during this period the range of customer dialing in large metropolitan areas was extended, where local service is measured by message registers, through arrangements for the multiple registration of calls for which the charge was more than one local unit. An important feature of switching development in this period was the perfecting of "common control" switching systems for large metropolitan areas endowed with a high degree of intelligence and great reliability. As will be shown, still more extensive and complicated functions must be performed by the common control systems of a nationwide automatic switching system. Also throughout this period great advance was made in the quality and stability of long distance circuits. Telephone connections, some with as many as five circuits in tandem, were being regularly established by telephone operators with satisfactory overall transmission.