How TAPI supports programs and hardware

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2, Windows Server 2008, Windows Server 2008 R2, Windows Server 8 Beta

How TAPI supports programs and hardware

Telephony Application Programming Interface (TAPI) supports programs that share the same communication ports and devices. Communication programs use TAPI to communicate with and control the appropriate hardware. TAPI manages the way programs and their call traffic use ports and devices. Telephony service providers provide support for particular devices or classes of devices.

Telephony service providers

Telephony service providers are dynamic link libraries (DLLs) that translate the commands for a specific telephony device, carrying out the low-level tasks required to communicate over telephone and IP networks.

How TAPI makes services available

TAPI arbitrates requests from different communication programs, so they can run simultaneously while sharing communication ports and devices. Each service provider controls its hardware. For example, one Windows Server 2003 family program can use TAPI functions to make outgoing calls while other programs are waiting for incoming calls.

Although only one program controls any single call, the devices are available to other programs, and users do not have to close other programs that share a communication port.

Supplied telephony service providers

The following table lists the telephony service providers that are supplied with Windows Server 2003 operating systems:

Telephony service providers	Used for
HID Phone	Human Interface Device (HID) telephone communications
H.323	IP telephony multimedia communications
Multicast Conference	IP telephony multiparty conferencing
Unimodem 5	Modems
NDIS Proxy	Connection-oriented network devices using NDIS 5
TAPI Kernel-Mode	Connects network devices using NDIS 4
Windows Remote	Client-server telephony

For more information about telephony service providers, see Telephony service providers.

Additional hardware support

Other service providers can be installed, in addition to telephony hardware or software.

Hardware manufacturers normally supply device drivers for their hardware. To provide telephony services for the hardware, the manufacturers or independent software vendors provide telephony service providers to control the hardware. Each service provider supports at least one device specific to that category of communication, such as a fax board, an ISDN card, a telephone or a modem. Some service providers support several devices, or even an entire class of devices.

For more detailed information about how telephony works, see Telephony Resources.