Abstract :
When the wires from a home telephone reach the local switching exchange, they enter a system that is unfamiliar to most telephone users ¿ even to those who are engineers. Modern direct dial telephone systems are enormous. In fact, they are the most complex interconnected, automatic systems man has devised. As users we are generally aware of the telephone system only when it frustrates or fails us. But whether we think of them as interesting engineering designs or as increasingly important tools for daily living, telephone systems bear closer examination.
