Selective Party-Line Systems

The problem which confronts one in the production of a system of selective ringing on party lines is that of causing the bell of any chosen one of the several parties on a circuit to respond to a signal sent out from the central office without sounding any of the other bells. This, of course, must be accomplished without interfering with the regular functions of the telephone line and apparatus. By this is meant that the subscribers must be able to call the central office and to signal for disconnection when desired, and also that the a ociation of the selective-signaling devices with the line shall not interfere with the transmi ion of speech over the line. A great many ways of accomplishing selective ringing on party lines have been proposed, and a large number of them have been used. All of these ways may be cla ified under four different cla es according to the underlying principle involved.