Device Control

Device control at the end-user or server application level requires a relatively small set of basic information. The service provider abstraction layer performs detailed device control. The service providers report required device information to an application through TAPI.

Key device categories include:

• Network: The transport layer for communications. From an application's point of view, information about the network is typically embedded in the address type, such as LINEADDRESSTYPE_PHONENUMBER.
• Line: A connection to a network. This concept is heavily used within TAPI 2.2 (TAPI/C).
• Channel: A subdivision of a line. Knowledge of channels is normally not required of an application because the service provider configures how they will appear as addresses.
• Address: A network location on a network. Each line or channel has one or more associated addresses. The address is a key concept in both TAPI 3.0 (TAPI/COM) and TAPI 2.2 (TAPI/C).
• Terminal: A source or renderer for a particular address and media type.

The service providers report device characteristics to TAPI in response to application queries. Service providers also initiate reports on changes in device state. These changes are then reported to an application based on the notifications requested during initialization.

Basic device characteristics are:

• Device Class
• Device Identifier
• Address Type
• Address Identifier
• Device Events
• Media Type
• Terminal Type

In addition, the service providers supply information concerning the capacity of a given address to perform various session operations.

Supplemental characteristics may be associated with certain devices, if the service providers support them. A TAPI 2 application discovers capabilities by using the lineGetDevCaps and lineGetAddressCaps functions. TAPI 3 applications use the ITAddressCapabilities interface for this purpose.

TAPI 2 provides a special set of supplemental operations that the service provider may implement for use with phone devices. See Phone Devices Overview.

Extended capabilities are provider-specific and not directly covered by the Microsoft Telephony API. See TAPI 2 Extended Line Functions, Extended Telephony Phone Functions, or TAPI 3 Provider-Specific Interfaces.

Below is a summary of TAPI operations that query service providers on device characteristics and provide data on current state.