In the previous chapter, the technologies of legacy voice network systems were discussed. Some might find that subject fascinating enough to have spent more than a chapter on it. In fact, there are volumes on the subject, and the ITU web site (http://www.itu.int) is filled with papers that describe it all in painfully unsparing verbosity .
But it's telephony , the application functionality within the voice network, that is the fun part. Telephony accommodates and assists human interaction in a very real, personal way, which is why it's such an engaging subject. Unlike written forms of communication, such as email or instant messaging, telephony's distinguishing traits are its use of sound and its immediate, real-time nature. It's a much more fundamental mode of interaction than the written formbecause when we use telephony, we talk , the same thing we do when we're together.
Telephony can use live, immediate speech or speech that's recorded, stored, and played back later, depending upon the needs of the applicationand it can be largely automated using well-defined standards. In fact, computer-integrated telephony applications have even been programmed to recognize and respond to human voice commands.
Telephony is an extensible, evolving enabler of human communication. Telephony applications such as character terminals have been created for the deaf, and applications such as speaking caller identification devices and Braille terminals have been created for the blind. Developers have expanded call-switching systems to include video features, too.
What all this means is: when you consider the breadth, variety, and social significance of telephony applications in day-to-day life, the details of endpoints and call signaling seem downright mundane. If you want to build a good voice network that enhances the lives of its users, don't lose sight of applications and deliverables because of a technical fascination with clients , servers, data links, and protocols. The users of the system don't care about that stuff anyway. They're a meansnot an end.