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标题: TAP into the Future
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TAP into the Future
Nancy Winnick Cluts
Microsoft Developer Network Technology Team

November 1995

Abstract
The Microsoft? Windows? Telephony Application Programming Interface (TAPI)
provides a way for applications to support telephone communication. This is
very important for all of you who want to jump on that band wagon (which is
groaning under all of the weight) and move your applications online. In this
article, I give you a brief overview of what TAPI is, how applications interact
with TAPI, some telephony basics, and where you can find information and tools
to help you create your telephony application. So, as Sir Dennis Eton Hogg said
to the assembled throng, "And so say all of us: It's time to TAP into America!"

What Is TAPI?
TAPI is an application programming interface that is used to communicate by
means of telephones. Some of the abilities that TAPI facilitates are:

Connecting directly to a telephone network

Automatic phone dialing

Transmission of data (files, faxes, electronic mail)

Access to data (news, information services)

Conference calling

Voice mail

Caller identification

Control of a remote computer

Collaborative computing over telephone lines
Microsoft? Windows? 95 comes with a telephony application, DIALER.EXE, that can
dial voice calls, act as a proxy for applications making simple telephony
requests, and maintain a call log. Figure 1 shows the main screen for the phone
dialer application.

Figure 1. The Phone Dialer dialog box in the DIALER application

If you play with the DIALER application, you will see some of the things an
application can do to give a user the ability to dial calls, set dialing
properties, do speed dialing, and set up a connection. The DIALER application
allows the user to set the dialing properties by using the dialog box shown in
Figure 2.

Figure 2. The Dialing Properties dialog box

The TAPI Architecture
TAPI operates independently of the underlying telephone network and equipment.
An application that uses TAPI doesn't have to worry about what it is hooked up
to梚t just needs to interact with the API itself. Figure 3 shows the
relationship among the application, TAPI, and the telephony service provider.

Figure 3. TAPI and applications

As Figure 3 shows, the application interacts with the telephony dynamic-link
library (DLL) by means of TAPI. The telephony DLL is part of the Windows
operating system and implements TAPI support. The telephony DLL interacts with
service providers through the Telephony Service Provider Interface (TSPI).
Service providers can be thought of much as one thinks of printer drivers梩hey
are written by telephony hardware vendors to support operating within Windows.

Some Technical Issues
To avoid some pitfalls when you develop an application that includes TAPI
functionality, you must understand a couple of things about how TAPI works.
These are lower-level than what I have covered above. So, if you are interested
only in the overview, go ahead and skip this section. If, on the other hand,
you like learning about some of the nitty-gritty details, you'll probably want
to read this.

TAPI and the Hidden Window
When your application supports TAPI, your application must first initialize
TAPI by using the lineInitialize function. When your application makes this
call, the Telephony DLL creates a hidden window on behalf of your application.
This hidden window is used as a method to send notifications and messages.
These messages are posted to the hidden window for the different asynchronous
events, completion notifications, and state messages (whether the line is
connected, proceeding, dialing, and so on). If your application is
multithreaded, you need to ensure that the thread that made the call to
lineInitialize has a message loop and that the thread services this message
loop. If the thread does not service the message loop or if it doesn't have a
message loop, your application will not get the notifications meant for it. In
short, your application won't work.

Service Providers Dictate Structures
When you make calls into TAPI that require a structure to be filled in, you
will need to check the amount of space needed for the structure and re-allocate
memory until you have a memory block that is large enough to hold the
structure. The reason for this is that each service provider, much like a
printer driver, supports different capabilities and holds different amounts of
information. As a result, if you pass a pointer to a structure that is not
large enough and you don't check to be sure that you have allocated enough
space (by checking the dwNeededSize versus dwTotalSize members of the structure
that is returned), the structure will be filled in with zeros and your
application won't work.

Documentation and Development Tools
The Win32? Software Development Kit (SDK) contains documentation, tools, and
sample code to help you to learn about TAPI. Two documents, the Microsoft
Telephony Programmer's Reference and the Microsoft Telephony Service Provider
Interface (TSPI) for Telephony, are provided to give you some reference
material and development guidance. The programmer's reference is intended to
document the functionality that an application using TAPI will need. The
service provider documentation is for developers who are going to write their
own TAPI services (that is, vendors of telephony equipment).

Also, some tools come with the Win32 SDK that help the developer understand
TAPI and incorporate TAPI functionality into an application. TB14.EXE is a
32-bit telephony browser that allows you to play around with the different TAPI
calls and your COM ports. You will be able to test whether your COM port and
modem are set up correctly to begin with (if they aren't, you'll be wasting a
lot of your own time and pulling your hair trying to figure out why your
application doesn't work). TB14.EXE also allows you to see how the different
TAPI structures get filled in. This will help you to see whether your
application is calling the different TAPI functions correctly. Figure 4 shows
the main screen displayed by TB14.EXE.

Figure 4. The TAPI browser: TB14.EXE

Another tool that you can use is the service provider tool, ESPEXE.EXE. This
tool is a TAPI service provider that supports multiple virtual line and phone
devices. You can configure it for your application. It doesn't require any
special hardware, and it supports the entire Telephony Service Provider
Interface (including the Windows 95 TAPI extensions). You can use this tool in
both Windows 3.1 using TAPI 1.0 and in Windows 95 using TAPI 1.1.

The TAPICOMM Sample
Tucked away in the Sample Code tree of the MSDN Library, you will find the
TAPICOMM sample. This sample demonstrates how to do data transmission over a
telephone. Figure 5 shows the main screen of the TAPICOMM sample.

Figure 5. The TAPICOMM sample from the Win32 SDK

If you take a look at the source code for this sample, you will learn how to
implement basic telephony functions such as initializing TAPI, opening a phone
line, gathering line device capabilities, transmitting data by means of the
COMM (Communications) API, closing a line, and shutting down TAPI.

If you would like more detailed information, take a look at some of the
references listed in the bibliography or read another one of my articles,
"Creating a TAPI Connection Using CTapiConnection." The article describes the
details of implementing basic TAPI functionality using CTapiConnection, a
Microsoft Foundation Class Library (MFC)-based class that I created.

Bibliography
"Developing Applications Using the Windows Telephony API" by Toby Nixon. (MSDN
Library Archive, Conferences and Seminar Papers, Tech稥d March 1994, Microsoft
At Work)

Microsoft Telephony Programmer's Reference

Microsoft Telephony Service Provider Interface (TSPI) for Telephony

? 1999 Microsoft Corporation. All rights reserved. Terms of use.

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