Tone Ringing and Pushbutton Calling

i. i Introduction The rapid advances of recent years in the development of electronic techniques and components have brought about both a need and an unusual opportunity for new station apparatus. The need has appeared unmistakably in connection with the development of electronic switching systems, 1 themselves outgrowths of the new technology. To such systems, the relatively large currents and voltages that are associated with signaling functions in existing telephones would represent formidable design difficulties. For example, the conventional ringer draws nearly a watt from a 90-volt, 20-cycle generator, whereas the design of electronic switching networks is properly focused upon handling speech signals that are far smaller, of the order of a volt or a milliwatt. Roughly parallel remarks might be made with regard to dialing, to signals for controlling coin telephones, and even to the direct, currents sent over the lines to power speech transmitters. Electronic switching clearly calls for a fresh attack upon station problems. In a preliminary broad study of this need and opportunity, it was 339 340 T H E B E L L SYSTEM TECHNICAL J O U R N A L , MARCH J 1 ) 5 8 recognized that exploratory development should strive toward certain long-term goals. For instance, it would be desirable to use the same frequency band as speech for signaling functions, thereby avoiding the need to transmit more than the one band; to provide party lines with full-selective ringing and with automatic party identification to facilitate automatic message accounting; 2 to eliminate the use of a "station ground" for purposes other than lightning protection, thus doing away with a troublesome source of transmission noise; and to replace the rotary dial with pushbuttons for the sake of speed, convenience and other benefits.