r existing equipment. And both provide a means for extending the specification. Beyond these points, however, each takes a different approach.
TAPI
Microsoft and Intel were the primary developers of the originally client-based TAPI. TAPI 2.0, however, is built into both the Windows NT Server 4.0 and the Windows NT Workstation 4.0, which allows the OS to function as either a telephony client or server. (Windows 95 currently has built-in support for TAPI 1.4 applications, which are compatible with TAPI 2.0.)
In practice, TAPI 2.0 is focused on the desktop -- a PC and a phone. That is, TAPI assumes the desktop to be one end point of each
call. It preserves the ability to do third-party call control (calling from one desktop on behalf of another). The
specification allows
for several telephony applications to run simultaneously -- over either a single or multiple phone lines -- on a client or server PC. It provides a means to distinguish different media streams (data, voice, fax) and route calls to the appropriate application or device. Incoming faxes, for example, go to the fax application or machine.
TAPI is part of the Windows Open Services Architecture (WOSA). Like other WOSA services, such as those for printing or display, TAPI has two interfaces. The first is the API for developers writing the software. The second is the service provider interface, which provides a means of connection to a specific device -- in TAPI's case, the telephone network. With TAPI 2.0, you can build applications for Public Switched Telephone Network (PSTN), ISDN, PBX, and IP networks. Want your applications to reach out over the Intern
et? TAPI can handle that, too. It essentially sees the Internet as just another service provider. Other TAPI features include support for Unicode, ActiveX controls, and Intel's universal serial bus (USB), a 12-Mbps port that can connect up to 127 devices to a single PC.
Microsoft has announced several planned enhancements for TAPI 2.0. They include a remote-service provider, intended to speed development of client/server telephony applications; remote administrative tools to aid with client/server configuration issues and reports; and Windows Telephony Service extensions for client access. (The company expects these features to appear in the next beta version of Memphis. At about the same time, Windows 95 will gain TAPI 2.0 support.) TAPI is closed: Microsoft controls it, which makes developers of telephony products nervous. Microsoft claims that since many other companies (more than 40) have contributed to the TAPI specification, it is effectively industry-defined and, therefore, open. However, where in
dependent organizations define and approve other industry standards, Microsoft remains the final arbiter of what TAPI is.
TSAPI
Server-based TSAPI, developed by Novell and AT&T, is designed to integrate PBX or Centrex phone systems with Netware networks. The only physical link in the system is between the NetWare file server and the phone network. Applications built with TSAPI have a logical link between the PC and the desktop phone. You can control calls through the applications from either end of the connection or hand off that control to a third party. A server telephony model also eliminates the need for additional hardware to connect desktop PC to phone. This can save a lot of money in a large organization, but there is a trade-off. Because there's no physical connection between the PC and the phone, TSAPI applications cannot identify different media streams as TAPI can. Thus, with TSAPI, you cannot automatically route a fax to a fax application, for example.
The TSAPI s
pecification has wide industry support, especially among PBX and Centrex vendors, virtually all of which offer NetWare drivers for their systems. Just as important, TSAPI supports all the major OSes, including Windows (all versions), the Mac OS, OS/2, and Unix. This, obviously, appeals to companies building cross-platform telephony applications. Unlike Microsoft with TAPI, Novell and AT&T have handed over the TSAPI specification to the European Computer Manufacturers Association (ECMA), which developed the Computer-Supported Telecommunication Applications (CSTA) standard on which TSAPI is based. ECMA is currently working on Phase II of the CSTA specification, due to roll out sometime this spring. Slated improvements to TSAPI include access to voice services, so that you can perform all functions of your phone system (e.g., play or record a message) from within a TSAPI application. Phase II will also allow TSAPI applications to transfer data with calls, so that, for example, help-desk personnel can take in
formation from a customer and transfer that data and customer to another person. In addition, Novell is working with Sun Microsystems to support its initiative for JTAPI, the API for building Java-based telephony applications.
Pros and Cons
TAPI is by far the more popular interface for telephony applications. For many companies, its tight integration with Windows is a plus, but more important is the fact that both client and server components come bundled with the OS. Novell charges $26,995 for a 250-seat TSAPI implementation (including a NetWare run-time module). For businesses with NT-based networks, TAPI is a no-brainer for a server-based telephony model. It also makes sense for small companies that tend to use a direct connection between the PC and phone.
Thanks to its multiplatform support, TSAPI is better suited for more diverse environments running on a NetWare backbone. And despite its cost, TSAPI actually is cheaper to implement in non-Windows NT environments. The alterna
tive there is client-based TAPI 1.3, which requires an add-in board on each PC.
TAPI 2.0 TSAPI
Server- or client-based Both Server
Required server Windows NT NetWare
Supported OSes Windows NT, Windows (all),
Windows 95
1
Unix, Mac, OS/2
32-bit support * *
16-bit support *
2
*
Call-center support * *
High-speed bus support USB N/A
3
Third-party call support * *
Media stream routing *
Connection types supported ISDN, PBX, PSTN, PBX, Centrex
IP
Extensible * *
1
Release to coin
cide with next
beta release of Memphis.
2
Applications must be based on Win 16 and
be fully TAPI 1.3-compliant.
3
Because TSAPI uses only the server model,
bus support on the desktop is irrelevant.
* = yes
illustration_link (19 Kbytes)
TAPI provides hooks into applications and communications systems.
Michael Nadeau is a freelance author who writes extensively about communications, the Internet, and storage technologies. You can contact him at
m_nadeau@conknet.com.editors@bix.com
.
Building Bridges with TAPI and TSAPI
