Signaling Systems for Control of Telephone Switching

1382 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 19()0 than 15 million main telephones in the Bell Telephone Companies had access to nationwide dialing, and eventually many more millions of telephone users will be able to quickly and accurately communicate with each other in the same way. To a large degree this modern "miracle" has been made possible not only by the development of the common control switching system but also by advances in the art of signaling. Just as the switching function has sometimes been called the "giant brain", the signaling function might indeed be thought of as a gigantic "nerve system" carrying sensing and action impulses to and from the "brain" to every part of the system, near and far. Today's communication system, which lets millions of telephone users throughout the nation get in touch with each other within seconds after dialing a number, has resulted from the effort of imaginative telephone people working over the years to evolve new techniques to meet the ever growing communication needs of our nation. The present highly developed state of the art has been brought about by an orderly evolution -- an evolution wherein communication needs, plans and techniques, the one stimulating the other, have formed a continuously improving technology. Some appreciation of the place of the signaling art in the modern telephone system can be gained by reviewing this evolution.