The Telephony service included with Windows Vista® and Windows Server® 2008 supports programs that share the same communication ports and devices through the use of TAPI. Telephony 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 remote architecture

Architecture of telephony service over a network

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 telephony makes services available

The Telephony service prioritizes TAPI 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 program can use telephony 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 Vista and Windows Server 2008.

Telephony service provider Usage

HID Phone

Human Interface Device (HID) telephone communications

Unimodem 5


NDIS Proxy

Connection-oriented network devices using NDIS 5

TAPI Kernel-Mode

Network devices using NDIS 4

Windows Remote

Client-server telephony


The IP Telephony H.323 and Multicast Conference telephony service providers that were included in previous versions of Windows are no longer available.

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

Additional hardware support

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

Hardware manufacturers typically 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.

Additional references