TheTelephony Application Programming Interface (TAPI) is aMicrosoft WindowsAPI, which providescomputer telephony integration and enablesPCs runningMicrosoft Windows to usetelephone 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 inPBX,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 aPBX 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 asDialogic cards.
TAPI was introduced in 1993 as the result of joint development byMicrosoft andIntel. 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 someMSDN development library CDs still contain the files and patches.
With MicrosoftWindows 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 andLAN connections serving any number of computers.
TAPI 2.0 was introduced withWindows NT 4.0. Version 2.0 was the first version on the Windows NT platform. It made a significant step forward by supportingACD andPBX-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 withWindows 2000. This version enables IP telephony (VoIP) by providing simple and generic methods for making connections between two (usingH.323) or more (usingIP multicast) computers and now also offers the ability to access anymedia stream (MSP driver) involved in the connection.
Windows XP included both TAPI 3.1 and TAPI 2.2. TAPI 3.1 supports theMicrosoft 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. AUSB 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.
TheTelephony Server Application Programming Interface (TSAPI) is a similar standard developed byNovell forNetWare servers.
TAPI uses Microsoft canonical address format for telephone numbers[1][2] to make phone calls. It is a derivative ofE.123 international notation.
The canonical address is a text string with the following format:+Country␣(AreaCode)␣ SubscriberNumber | Subaddress ^ Name CRLF. Area code, subaddress and name are optional; the latter can carry extension number fordirect inward dialing andcalling party name, as used byISDN/E1/T1 telecommunication protocols.
Dialing rules are used to transform the canonical phone number into a dialable calling sequence for themodem, depending on the user's location. The dialing rules include variable-length dialing for area code, trunk access and international access prefixes, as well as central office access andcalling card/credit card numbers.[1][2]
The calling sequence can contain dialable numbers such as digits0-9 andDTMF tonesABCD*#, formatting characters ␣ . -, and control characters! P T , W @ $ ? ; which correspond to the Dial command of the HayesAT command set. The following control characters are defined:[1]
It is a common misconception thatTAPI 3.0 (orTAPI 3.1) replacesTAPI 2.x.
TAPI 2.x and earlier versions were written inC; the API uses pointers to structures. Consequently, TAPI 2.x is easy to access from C orC++ applications, but it can be awkward to use from many otherprogramming languages.[3]
TAPI 3.x was designed with aComponent Object Model (COM) interface. This was done with the intent of making it accessible to higher level applications such as developed inVB 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 Article841712, 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[4] and a 2.x wrapper for .NET.[5] Other developers provide libraries to work indirectly with TAPI enabled PBXs.[6]
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.
OnWindows, TAPI support was almost universal intelephony hardware such asvoice modems (both internal and external) and computer expansion boards such asDialogic telephony cards. The only notable exception who never natively supported TAPI was the Avaya Communication Manager, which relied solely on theTSAPI interface for connectivity.[7]
ManyPBX systems provide TAPI-compliant modem interfaces. TAPI compatible PBX solutions includeAastra (400/800),Aastra (MX-ONE),Alcatel (OXO/OXE),Avaya (BCM, IP Office),Cisco (Call Manager),Ericsson-LG (eMG80, iPECS, ipLDK), NEC-Philips (iS3000, IPC100/500),NEC (SL1000, SV8100/9100), Nitsuko (DXE600/328),Panasonic (KX-TDA/TDE/NCP, KX-NS1000),Samsung (OfficeServ),Unify (3000/4000, Openscape Office),ShoreTel, andZyXEL (X6004/X2002).
Third party drivers are often available for the telephone systems that don't have drivers made by the manufacturers.