Crossbar dial telephone switching system

IT IS the purpose of this paper to describe briefly the crossbar dial-telephone central-office switching system which has recently been developed by the Bell System for use in large cities. Sixteen years ago, in February 1923, a paper was read before the Institute, by E. B. Craft, L. F. Morehouse, and H. P. Charlesworth of the Bell System, which outlined the history and the problems involved in telephone central-office switching and described the panel dial central-office system which had just been developed and was being introduced in the large cities. The first central office of this type was placed in service in December 1921, and since that time 456 panel dial offices serving nearly 4 1/2 million subscriber stations have been installed in 26 different cities throughout the country. During these years many improvements have been made in the panel system to make it more serviceable to the telephone public and to meet the new problems which have arisen, but in addition, the engineers of the Bell System have continued their search to find new and better means for meeting telephone switching demands. This work has resulted in the adoption of the crossbar-type central-office switching equipment. Two offices of this type were placed in successful operation during 1938 and others are in process of manufacture and installation.