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Telephony Application Programming Interface

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The Telephony Application Programming Interface (TAPI) is a Microsoft Windows API, which provides computer telephony integration and enables PCs running Microsoft Windows to use telephone services. Different versions of TAPI are available on different versions of Windows. TAPI allows applications to control telephony functions between a computer and telephone network for data, fax, and voice calls. It includes basic functions, such as dialing, answering, and hanging up a call. It also supports supplementary functions, such as hold, transfer, conference, and call park found in PBX, ISDN, and other telephone systems.

TAPI is used primarily to control either modems or, more recently, to control business telephone system (PBX) handsets. When controlling a PBX handset, the driver is provided by the manufacturer of the telephone system. Some manufacturers provide drivers that allow the control of multiple handsets. This is traditionally called "third-party control". Other manufacturers provide drivers that allow the control of a single handset. This is called "first-party control". Third-party drivers are designed to allow applications to see and/or control multiple extensions at the same time. Some telephone systems only permit one third-party connection at a time. First-party drivers are designed to allow applications to monitor and/or control one extension at a time. Telephone systems naturally permit many of these connections simultaneously. Modem connections are by nature first-party.

Tapi can also be used to control voice-enabled telephony devices, including voice modems and dedicated hardware such as Dialogic cards.

History

TAPI was introduced in 1993 as the result of joint development by Microsoft and Intel. The first publicly available version of TAPI was version 1.3, which was released as a patch on top of Microsoft Windows 3.1. Version 1.3 drivers were 16-bit only. Version 1.3 is no longer supported, although some MSDN development library CDs still contain the files and patches.

With Microsoft Windows 95, TAPI was integrated into the operating system. The first version on Windows 95 was TAPI 1.4. TAPI 1.4 had support for 32-bit applications.

The TAPI standard supports both connections from individual computers and LAN connections serving any number of computers.

TAPI 2.0 was introduced with Windows NT 4.0. Version 2.0 was the first version on the Windows NT platform. It made a significant step forward by supporting ACD and PBX-specific functionality.

In 1997, Microsoft released TAPI version 2.1. This version of TAPI was available as a downloadable update and was the first version to be supported on both the Microsoft Windows 95 and Windows NT/2000 platforms.

TAPI 3.0 was released in 1999 together with Windows 2000. This version enables IP telephony (VoIP) by providing simple and generic methods for making connections between two (using H.323) or more (using IP Multicast) computers and now also offers the ability to access any media streams involved in the connection.

Windows XP included both TAPI 3.1 and TAPI 2.2. TAPI 3.1 supports the Microsoft Component Object Model and provides a set of COM objects to application programmers. This version uses File Terminals which allow applications to record streaming data to a file and play this recorded data back to a stream. A USB Phone TSP (Telephony Service Provider) was also included which allows an application to control a USB phone and use it as a streaming endpoint. TAPI 3.0 or TAPI 3.1 are not available on operating systems earlier than Windows 2000 and Windows XP respectively.

The Telephony Server Application Programming Interface (TSAPI) is a similar standard developed by Novell for NetWare servers.

TAPI 2.x vs TAPI 3.x

It is a common misconception that TAPI 3.0 (or TAPI 3.1) replaces TAPI 2.x.

TAPI 2.x (and all earlier versions) is written in C/C++ and requires applications to make heavy use of C style pointer arithmetic. This makes TAPI 2.x fast and easy to access from C/C++ applications, but it also makes it difficult to use from many other programming languages.

TAPI 3.x was designed with a COM (Component Object Model) interface. This was done with the intent of making it accessible to higher level applications such as developed in VB or other environments that provide easy access to COM but don't deal with C-style pointers.

TAPI 3.x has a slightly different set of functionality than TAPI 2.x. The addition of integrated media control was the most significant addition. But TAPI 3.x doesn't include all functionality that TAPI 2.x does, like support for the Phone class.

One very notable issue with TAPI 3.x is the lack of support for managed code (.NET environment). As documented in Microsoft KB Article 841712, Microsoft currently has no plans to support TAPI 3.x directly from .Net programming languages. However, Mark Smith has provided a Managed C++ library called ITAPI3 and other developers such as Mondago provide .Net libraries to work indirectly with TAPI enabled PBXs.

One often overlooked reason an application developer might choose between TAPI 2.x and TAPI 3.x should be the hardware vendors recommendation. Even though TAPI provides an abstract model of phone lines, telephony applications are still heavily impacted by the specific behavior of the underlying hardware. Troubleshooting behavior issues usually requires both software and hardware vendors to collaborate. Because there is almost a 1:1 relationship between the TAPI Service Provider (TSP) interface and the TAPI 2.x interface, collaboration is often easier if the application is designed using TAPI 2.x. Experience with TAPI 3.x varies significantly between hardware vendors.

TAPI compliant hardware

Telephony hardware that supports TAPI includes most voice modems and some telephony cards such as Dialogic boards.

The following telephone systems provide Tapi drivers. Many of these drivers are licensed and thus incur a charge to use. In other cases, drivers are available for separate purchase from iQ NetSolutions, Estos and Mondago:

  • 3Com NBX (First and third party)
  • Aastra 800 (Third party by Mondago)
  • Aastra Intelligate (First and third party)
  • Aastra MD Evolution
  • Alcatel OXO (Third party)
  • Alcatel OXE (Third party)
  • Allworx 6x, 10x, & 24x (using Call Assistant license)
  • AltiGen
  • Aastra Communication Manager/Definity (Third party by Mondago)
  • Avaya Index (Third party)
  • Avaya IP Office (First and third party)
  • BroadSoft BroadWorks (Third party by ESTOS/Mondago)
  • Cisco Call Manager (First and third party)
  • Cisco Call Manager Express (First-party by Cisco and Third Party by ESTOS/Mondago)
  • Elmeg
  • InterTel Axxess (First-party and third party by Mondago)
  • Innovaphone
  • LG LDK (Third party)
  • LG-Ericsson IPLDK-20 (First and third party)
  • LG-Ericsson IPLDK-50/100/300/600 (First and third party)
  • LG-Ericsson iPECS release 5.5 (First and third party)
  • Mitel 3000 (Third party by Mondago)
  • Mitel 3300ICP (TAPI Gateway by iQ NetSolutions, ESTOS and Mondago)
  • Mitel 5000 (Third party by Mondago)
  • NEC-Philips iS3000
  • NEC Aspire / Philips IPC500 (Third party and first party)
  • NEC XN120/Topaz / Philips IPC100 (Third party and first party)
  • NEC SV8100 (Third party and first party)
  • Nitsuko DXE600 (Third party)
  • Nortel BCM (First and third party)
  • Nortel CS
  • Nortel Meridian
  • Nortel Norstar (First party)
  • Panasonic KX-TD (Third party)
  • Panasonic KX-TDA (Third party)
  • Panasonic KX-TDE (Third party)
  • Panasonic NCP (Third party)
  • Samsung OfficeServ (First and third party)
  • Selta SAMIP (First and third party)
  • Siemens 3000 (First & Third-party by Siemens and Third Party by ESTOS/Mondago)
  • Siemens HiPath 4000
  • Siemens HiPath 8000
  • Siemens Open Office/HOOME (First & Third-party by Siemens and Third Party by Mondago)
  • Siemens TC35i
  • Shoretel
  • Splicecom Maximiser (Third party)
  • Tadiran
  • Tekelec (First-party)
  • Teltronics Cerato IP
  • Toshiba CT (First-party and Third party by Mondago)
  • Way 2 Call
  • ZyXEL X6004/X2002 PBX

See also

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