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<title>Chapter 22 -- What Is TAPI?</title>
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<h1><font COLOR="#FF0000">Chapter 22</font></h1>
<h1><b><font SIZE="5" COLOR="#FF0000">What Is TAPI?</font></b> </h1>
<hr WIDTH="100%">
<h3 ALIGN="CENTER"><font SIZE="+2" COLOR="#000000">CONTENTS<a NAME="CONTENTS"></a> </font></h3>
<ul>
<li><a HREF="#TheTelephonyAPIModel">The Telephony API Model</a> <ul>
<li><a HREF="#Lines">Lines</a> </li>
<li><a HREF="#Phones">Phones</a> </li>
</ul>
</li>
<li><a HREF="#TAPIandtheWOSAModel">TAPI and the WOSA Model</a> </li>
<li><a HREF="#TypicalConfigurations">Typical Configurations</a> <ul>
<li><a HREF="#PhoneBasedConfigurations">Phone-Based Configurations</a> </li>
<li><a HREF="#pcBasedConfigurations">pc-Based Configurations</a> </li>
<li><a HREF="#SharedorUnifiedLineConfigurations">Shared or Unified Line Configurations</a> </li>
<li><a HREF="#MultilineConfigurations">Multiline Configurations</a> </li>
</ul>
</li>
<li><a HREF="#TelephoneLineServices">Telephone Line Services</a> <ul>
<li><a HREF="#TheTelephoneSwitchingNetwork">The Telephone Switching Network</a> </li>
<li><a HREF="#PlainOldTelephoneServicePOTS">Plain Old Telephone Service (POTS)</a> </li>
<li><a HREF="#DigitalT1Lines">Digital T1 Lines</a> </li>
<li><a HREF="#IntegratedServicesDigitalNetworkISD">Integrated Services Digital Network
(ISDN)</a> </li>
<li><a HREF="#PrivateBranchExchangePBX">Private Branch Exchange (PBX)</a> </li>
</ul>
</li>
<li><a HREF="#Summary">Summary</a> </li>
</ul>
<hr>
<p><font COLOR="#000000">The </font><i>Telephony Application Programming Interface</i>
(TAPI) is one of the most significant API sets to be released by Microsoft. The telephony
API is a single set of function calls that allows programmers to manage and manipulate any
type of communications link between the pc and the telephone line(s). While telephony
models for the pc have been around for several years, the telephony API establishes a
uniform set of calls that can be applied to any type of hardware that supplies a
TAPI-compliant service provider interface (SPI). </p>
<p>This chapter provides a general overview of the Telephony API and how it fits into the
WOSA (Windows Open Services Architecture) model. You'll learn about the two main devices
defined within the TAPI model:
<ul>
<li><font COLOR="#000000">Line devices</font> </li>
<li><font COLOR="#000000">Phone devices</font> </li>
</ul>
<p>You'll also learn about the typical physical configurations used in a TAPI model, which
can be:
<ul>
<li><font COLOR="#000000">Phone-based </font></li>
<li><font COLOR="#000000">pc-based </font></li>
<li><font COLOR="#000000">Shared or unified line </font></li>
<li><font COLOR="#000000">Multiline </font></li>
</ul>
<p>You'll also learn about the different types of telephone service lines used to provide
media transport services for TAPI applications, including:
<ul>
<li><font COLOR="#000000">POTS</font> </li>
<li><font COLOR="#000000">Digital T1</font> </li>
<li><font COLOR="#000000">ISDN service</font> </li>
<li><font COLOR="#000000">PBX service</font> </li>
</ul>
<p>When you complete this chapter you should have a good understanding of the TAPI model,
including the meaning and use of line and phone devices. You'll also know the most common
TAPI hardware configurations, their advantages, and their drawbacks. Finally, you'll
understand the various physical telephone services available for use in TAPI applications.
</p>
<h2><a NAME="TheTelephonyAPIModel"><font SIZE="5" COLOR="#FF0000">The Telephony API Model</font></a></h2>
<p>The telephony API model is designed to provide an abstracted layer for access to
telephone services on all Windows platforms. In other words, the telephony API is a single
set of functions that can be used to access all aspects of telephony services within the
Windows operating system. </p>
<p>This is a huge undertaking. The aim of TAPI is to allow programmers to write
applications that work regardless of the physical telephone medium available to the pc.
Applications written using TAPI to gain direct access to telephone-line services work the
same on analog or digital phone lines. Applications that use TAPI can generate a full set
of dialing tones and flash-hook functions (like that of the simple analog handset found in
most homes), and can also communicate with sophisticated multiline digital desktop
terminals used in high-tech offices. </p>
<p>The TAPI design model is divided into two areas, each with its own set of API calls.
Each API set focuses on what TAPI refers to as a <i>device</i>. The two TAPI devices are:
<ul>
<li><i>Line devices</i> to model the physical telephony lines used to send and receive voice
and data between locations. </li>
<li><i>Phone devices</i> to model the desktop handset used to place and receive calls. </li>
</ul>
<h3><a NAME="Lines">Lines</a></h3>
<p>The line device is used to model the physical telephone line. It is important to
understand that, in TAPI, the line device is not really a physical line; it's just a model
or object representing a physical line. In TAPI applications, a program could keep track
of several line devices, each of which is connected to a physical line. That same TAPI
application could also keep track of multiple line devices that number more than the total
physical lines available to the pc. </p>
<p>For example, a single TAPI application could be designed to provide voice, fax, and
data links for a user. The TAPI application would identify three line devices. One for
voice calls, one for fax transmission, and one for sending and receiving data via an
attached modem. If the pc has only one physical phone line attached, the TAPI application
would share the one line between the three defined line devices. This is called <i>dynamic
line mapping </i>(see Figure 22.1). </p>
<p><a HREF="f22-1.gif"><b>Figure 22.1 :</b> <i>TAPI dynam </p>
</i></a>
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