[This is preliminary documentation and subject to change.]
Call and media controls are a simple and generic set of methods for making calls between two or more machines. In the context of TAPI 3.0, the word call refers not just to voice transmission over the public switched telephone network (PSTN) but to any medium capable of transferring content.
TAPI 3.0 provides access to the media being transmitted through the use of DirectShow™. DirectShow is a modular system of pluggable components called filters, arranged in a configuration called a filter graph. The filter graph manager oversees the connection of these filters and controls the stream's data flow.
TAPI 3.0 abstracts both call and media functionality to allow different, and seemingly incompatible, communication protocols to expose a common interface to applications. Because TAPI 3.0 is based on the Component Object Model (COM), applications may be written in any language. Some interface methods may not be available to scripting languages such as VBScript.
TAPI 3.0 call and media controls involve four primary sets of code: the TAPI 3.0 COM objects, the TAPI Server, Telephony Service Providers (TSPs), and Media Service Providers (MSPs).
TAPI 3.0 COM Object
TAPI 3.0 COM objects are described in Using Call And Media Controls and detailed in Call and Media Control Reference.
TAPI Server
TAPI 3.0 is implemented as an in-process server and uses TAPISRV.EXE to perform telephony operations, thus making TAPI 3.0 applications compatible with all TAPI 2.1 service providers. The TAPI Server process (TAPISRV.EXE) abstracts TSPI (Telephony Service Provider Interface) from TAPI 3.0 and TAPI 2.1 and maintains the internal state of TAPI.
Additional information concerning the TAPI Server and TSPI can be found in the Platform SDK under "Telephony" or by conducting a search.
Call-control functions are provided by a TSP. The TAPI 2.1 client/server relationship with remote services providers is supported. Telephony Service Providers are responsible for translating the protocol-independent call model of TAPI into protocol-specific call setup and teardown, on a service-by-service basis. TAPI 3.0 has backward compatibility with TAPI 2.1 TSPs. Two new IP Telephony Service Providers (and their associated Media Service Providers) ship by default with TAPI 3.0: the H.323 TSP and the IP Multicast Conferencing TSP.
Additional information concerning Telephony Service Providers can be found in the Platform SDK under "Telephony" or by conducting a search,
Media control functions are provided by an MSP that implements the DirectShow interfaces for a particular provider. Media Service Providers are required for any telephony service that makes use of DirectShow media streaming. Generic streams are handled by the application.
TAPI service providers are strongly encouraged to support DirectShow. A service provider does not have to support DirectShow for all media. For example, a PBX implementation may only offer call control through TAPI 3.0, but not media -stream access.