Page 61 - Asterisk™: The Future of Telephony

tions terminal to serve as a telephone and install a softphone program onto it to provide
the functions we desire.
Having thus muddied the waters, the best we can do at this point is to define what the
term softphone will refer to in relation to this book, with the understanding that the
meaning of the term can be expected to undergo a massive change over the next few
years. For our purposes, we will define a softphone as any device that runs on a personal
computer, presents the look and feel of a telephone, and provides as its primary function
the ability to make and receive full-duplex audio communications (formerly known as
†
“phone calls”) through E.164 addressing. ‡
Telephony Adaptors

A telephony adaptor (usually referred to as an ATA, or Analog Terminal Adaptor) can
loosely be described as an end-user device that converts communications circuits from
one protocol to another. Most commonly, these devices are used to convert from some
digital (IP or proprietary) signal to an analog connection that you can plug a standard
telephone or fax machine into.
These adaptors could be described as gateways, for that is their function. However,
popular usage of the term telephony gateway would probably best describe a multiport
telephony adaptor, generally with more complicated routing functions.
Telephony adaptors will be with us for as long as there is a need to connect incompatible
standards and old devices to new networks. Eventually, our reliance on these devices
will disappear, as did our reliance on the modem—obsolescence through irrelevance.

Communications Terminals
Communications terminal is an old term that disappeared for a decade or two and is
being reintroduced here, very possibly for no other reason than that it needs to be
discussed so that it can eventually disappear again—once it becomes ubiquitous.

First, a little history. When digital PBX systems were first released, manufacturers of
these machines realized that they could not refer to their endpoints as telephones—
their proprietary nature prevented them from connecting to the PSTN. They were
therefore called terminals, or stations. Users, of course, weren’t having any of it. It
looked like a telephone and acted like a telephone, and therefore it was a telephone.
You will still occasionally find PBX sets referred to as terminals, but for the most part
they are called telephones.

† OK, so you think you know what a phone call is? So did we. Let’s just wait a few years, shall we?
‡ E.164 is the ITU standard that defines how phone numbers are assigned. If you’ve used a telephone, you’ve
used E.164 addressing.

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