Telephony Service Providers

Two new IP Telephony Service Providers, and their associated Media Stream Providers (MSPs), are included as part of TAPI 3.0.

H.323 Service Provider

The Microsoft H.323 Telephony Service Provider and its associated Media Service Provider allow TAPI-enabled applications to engage in multimedia audio/video sessions with any H.323-compliant terminal (such as Microsoft NetMeeting) on a local area network (LAN) or the Internet.

Specifically, the H.323 TSP and MSP implement the H.323 signaling stack. The H.323 TSP accepts a number of different address formats, including user name, computer name, and e-mail address.

The H.323 MSP is responsible for constructing the Microsoft® DirectShow® filter graph, including the Real-Time Transport Protocol (RTP), codec, sink, and render filters, for an H.323 connection.

Multicast Conferencing Service Provider

The multicast conferencing service provider uses IP multicast to provide efficient multiparty audio and video conferencing facilities over the IP network, intranets and the Internet. Due to large bandwidth usage by video streams, multiparty video conferencing services have been difficult to achieve. By using IP multicast, the TSP makes it possible to reduce the number of video streams.

NDIS Proxy Service Provider

The NDIS Proxy Service Provider offers a TAPI interface to wide area network (WAN) devices, such as ISDN or ATM. As such, these devices (written to the Microsoft Network Driver Interface Service (NDIS) interface version 5.0) can be used by TAPI applications. The NDIS Proxy is a generic service provider, meaning that it supports all such WAN devices—without those devices needing to be individually TAPI-aware.

An important feature of the NDIS Proxy Service Provider is that underlying NDIS 5 components need not be aware of TAPI in order to be provided with a proxied TAPI interface. In this way, TAPI applications, such as the Routing and Remote Access service, can use NDIS 5 drivers to establish connections across wide area networks.

Remote Service Provider

TAPI includes a Remote Service Provider to support client/server telephony. The Remote SP exposes TAPISRV telephony service extensions for client access to TAPI devices that reside on networked server computers. Remote SP resides on the client, where it appears as just another service provider to TAPI. When a TAPI request is made through Remote SP, it communicates with a remote telephony server in order to service the request. The service provider on the server that ultimately services the request need not be aware that it is operating in this client/server environment. An example of such a service provider would be a CTI link installation, whereby client applications communicate with a server, which in turn is connected through a CTI link to a PBX. In this way, those applications gain third-party control of telephones on the attached PBX.

TAPI Kernel-Mode Service Provider

The TAPI Kernel-Mode Service Provider communicates with NDIS 4 components in order to provide a TAPI interface for backward compatibility to NDIS 4 WAN drivers. An example of the sorts of driver that can take advantage of the NDIS Proxy would be an ISDN driver offering connection-oriented services. Using such a driver, TAPI applications such as Routing and Remote Access service can use the TAPI Kernel-Mode Service Provider in order to establish PPP connections across wide area networks.

Unimodem 5 Service Provider

Unimodem 5 is a Telephony Service Provider that provides an abstraction for modem devices such that applications can operate transparently across a wide variety of types and makes of modems. In addition, modem installation is greatly simplified since Unimodem is aware of the operating characteristics of these modems, and their drivers are already available in the operating system. Unimodem 5 also adds support for voice modems.

Third-Party Service Providers

Independent hardware and software vendors can write their own Telephony Service Providers, compatible with TAPI.