The Interconnection of Telephone Systems - Graded Multiples

I T H the completion of the third commercial telephone instrument some fifty odd years ago was born the problem of interconnection. And as the system has grown so has the demand for a universal service. The present complexity of our communication network makes it difficult to appreciate that in those early days it was a comparatively simple thing to provide a direct line from each subscriber to every other subscriber, as shown in the schematic interconnection of the six telephone stations in Fig. 1. In such schemes there 531 532 BELL SYSTEM TECHNICAL JOURNAL is no possibility of the line being busy; the only faults a subscriber may properly find with the service (over and above transmission troubles) are that "the called party is busy" on another line, and "he does not answer," conditions beyond the control of the interconnecting system. For a very small number of subscribers all in close proximity such a scheme would and does serve admirably. As soon as the number of subscribers, "w," is increased, however, the number of lines, which equals --12^ g0es up at an enormous rate, almost as the square