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Telephony Application Programming Interface

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Telephony Application Programming Interface

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.


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 earlier versions were written in C; the API uses pointers to structures. Consequently, TAPI 2.x is easy to access from C or C++ applications, but it can be awkward to use from many other programming languages.

TAPI 3.x was designed with a Component Object Model (COM) 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 cards.

The following telephone systems provide Tapi drivers. Often these are only available for 32 bit operating systems. Many of these drivers are licensed and thus incur a charge to use. In other cases, alternative drivers are available for separate purchase from iQ NetSolutions, C4B Com For Business, Estos and Mondago:

Manufacturer Model Manufacturer Support (32 bit) Manufacturer Support (64 bit) Alternative suppliers Notes
3Com NBX Yes - - Platform has been discontinued.
Aastra 400 Yes Yes C4B, Mondago
Aastra 800 - - C4B, Mondago, ESTOS Based on a PBX from Detewe
Aastra MX-ONE Yes - C4B, Mondago, ESTOS New version of Ericsson MD110
Alcatel OXO Yes - C4B, ESTOS, Mondago
Alcatel OXE Yes - C4B, ESTOS, Mondago
Allworx 6x, 6x12, 10x, 24x, and 48x Yes Yes Mondago Native driver only supports 1st party TAPI
AltiGen AltiGen Yes - -
Avaya BCM Yes - Mondago Formerly Nortel BCM
Avaya Communication Manager - - C4B, ESTOS, Mondago
Avaya CS1000 - - C4B, ESTOS, Mondago Formerly Nortel CS
Avaya Index Yes - - Platform has been discontinued. Formerly SDX Index
Avaya IP Office Yes Yes C4B, Mondago
Broadsoft Broadworks - - ESTOS, Mondago
Broadsoft M6 Yes - Mondago
Cisco 320 - - TAPI drivers may be possible for the handsets rather than the PBX
Cisco 500 / Call Manager Express - - C4B, ESTOS, Mondago
Cisco Call Manager Yes Yes C4B, Mondago
E-MetroTel UCx50, UCx450, UCx1000 Yes Yes
InterTel Axxess - - Mondago
Innovaphone Innovaphone Yes - C4B
LG eMG80 Yes Yes Mondago Driver uses UDP for communication. Can be sensitive to poor network conditions.
LG LDK Yes - Mondago Driver uses UDP for communication. Can be sensitive to poor network conditions.
LG-Ericsson iPECS Yes Yes C4B, Mondago Driver uses UDP for communication. Can be sensitive to poor network conditions.
LG-Ericsson ipLDK Yes - C4B, Mondago Driver uses UDP for communication. Can be sensitive to poor network conditions.
Mitel 3000 - - Mondago Sold as BT Versatility in the UK
Mitel 3250 - - Mondago Sold as BT Quantum in the UK
Mitel 3300 ICP - - Mondago, iQ NetSolutions, ESTOS Mitel did have a TAPI driver until it was discontinued in 2007
Mitel 5000 - - Mondago
NEC-Philips iS3000 Yes -
NEC-Philips Aspire (aka IPC500) Yes - Platform has been discontinued.
NEC-Philips XN120 (aka IPC100) Yes - Mondago Platform has been discontinued.
NEC SL1000 Yes Yes
NEC SV8100 Yes Yes Mondago
NEC SV9100 Yes Yes
Nitsuko DXE600 Yes - Platform has been discontinued.
Nortel Meridian Yes - Platform has been discontinued. See Avaya CS1000
Nortel Norstar Yes - Hardware (DTA) required
Panasonic KX-TD Yes -
Panasonic KX-TDA Yes Yes Mondago
Panasonic KX-TDE Yes - C4B, Mondago
Panasonic KX-NCP Yes - Mondago
Panasonic KX-NS1000 Yes - Mondago
Samsung OfficeServ Yes - Mondago
Selta SAMIP Yes -
Siemens 3000 Yes - C4B, ESTOS, Mondago
Siemens 4000 - - C4B, ESTOS, Mondago
Siemens 8000 - - C4B, ESTOS, Mondago
Siemens OpenOffice Yes - C4B, ESTOS, Mondago
Sipleo Sipleo Yes Yes
ShoreTel ShoreTel Yes Yes
SpliceCom Maximizer Yes - Mondago
Tadiran IS2000 Yes -
Talkswitch IS2000 Yes -
Tekelec M6 Yes - See Broadsoft M6
Teldat Hybird Yes - Mondago
Teltronics Cerato IP Yes -
Toshiba CIX - - Mondago
Toshiba CTX - - Mondago
Toshiba ipEdge - - Mondago
Way2Call Hi-Phone Desktop Lite Yes Yes
Way2Call Hi-Phone Desktop Pro Yes Yes
Way2Call Way2Call Maestro Yes Yes
Wildix All Wildix WMS UC Series > rel. 2.0 Yes Yes
Zultys MX Yes -
ZyXEL X6004/X2002 Yes -

See also

External links

  • MSDN Library about TAPI
  • Andreas Marschall's TAPI and TSPI FAQ
  • Former TAPI MVP Michael Dunn's TAPI FAQ
  • Wiki Site about TAPI
  • Way2Call - Hi-Phone telephony modem, TAPI compliant telephony device
  • ExceleTel TeleTools - Telephony development tools for VCL, ActiveX, and .NET TAPI programming
  • JulMar (Mark Smith) ATAPI.NET and ITAPI3 (.NET Managed Libraries for TAPI 2.x and 3.x), TSP++ for TSPI development, and samples
  • iQ NetSolutions
  • PhonePc CTI - telephony MiddleWare for TAPI
  • Voice CTI - telephony software for TAPI
  • Mondago
  • C4B Com For Business, XPhone TAPI Server
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