A Telephone Switching Network and Its Electronic Controls

362 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1955 tempt to control the same portion of the switching network at the same time. Now consider a switching network and controls much faster than those presently used. Such a system could handle a 10,000-line central office on a "one-at-a-time basis" without requiring duplication of the controls. Thus, the connector problem is almost eliminated and there is no necessity for lockout among competing controls. The switching network and controls which we describe in this paper constitute a model of this type of high-speed system. In addition to reducing the system to one set of control circuits we have devised circuits which perform terminal selection and channel control functions in a greatly simplified fashion. In any project such as this, certain general objectives are established at the outset. These objectives guide the designer in his choice of tools or devices and act as a framework within which the designer works. In our particular case, these general objectives were: (a) Speed of network and controls should permit operation with one set of control circuits. (b) The design should be based on a large central office carrying heavy traffic, specifically, an office with 10,000 subscribers and 2,000 trunks, and handling a total of 50,000 originating and terminating calls per busy hour. (c) The control circuits should be active during 70 per cent or less of a busy hour. (This limit was set to avoid excessive delay in gaining access to the control circuits.) (d) A minimum of maintenance should be required.