Line Device (Windows CE 5.0)
The Windows CE implementation of TAPI 2.0 provides support for line devices. A line device is a physical channel that comprises a telephone line and the hardware that controls it, such as a fax board, a modem, or an ISDN card. The simplest kind of line device corresponds exactly to one telephone line. In general, telephony allows a line to contain a pool of multiple homogeneous channels that can be used to establish calls. A service provider that implements a line as a pool of channels allocates those channels out of a set of physical lines that it controls, or multiplexes multiple channels onto a single physical line. Although the term line often connotes something with two endpoints, within TAPI the term refers just to one endpoint of a communication channel or point of entry into a telephone-switching network.
TAPI 2.0 requires that every TAPI-capable line device support all of Basic Telephony Services. If an application needs to use capabilities beyond those of Basic Telephony (namely Supplementary or Extended Telephony Services), it first must determine the telephony capabilities of the line device, which can vary according to network configuration (client versus client/server), hardware, service-provider software, and the telephone network.
The lineGetDevCaps function queries a specified line device to determine its telephony capabilities. The returned information is valid for all of the addresses on the line device. The dwExtVersion parameter of lineGetDevCaps indicates the version number of the extension information that is requested. If the version number is zero, no extension information is requested; if it is nonzero, it holds a value that was negotiated already for this device with the lineNegotiateExtVersion function. The service provider should fill in device-specific and vendor-specific extended information, according to the extension version that is specified.
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