The line device is a physical device such as a fax board, a modem, or an ISDN card that is connected to a network. The device may not be physically connected to the computer on which the TAPI application is running, such as a modem pool on a server. Line devices support communications capabilities by allowing applications to send information to or receive information from a network. A line device contains a set of one or more homogeneous channels that can be used to establish calls.

ThbTapiLine represents the TAPI line device and is used to work with calls on the deveice. In general you will have one ThbTapiLine component for each TAPI line device that your application uses. A session or call represents a connection between two or more addresses. ThbTapiLine is able to handle multiple calls on a single line device at the same time - if the telephony device supports this. See the ThbTapiLine.Calls property to read more about calls.

A TAPI line device can support multiple addresses e.g. to represent different phone numbers of the telephony system. The addresses are accessable wit the property ThbTapiLine.Addresses. Each address (phone number) can have certain capabillities. Examine the ThbTapiAddress.Caps property to see what your device/address is able to do.

Supplementary line features are:

Digit Monitoring

Digit monitoring monitors the call for digits. TAPI allows digits to be signaled according to two methods (digit modes):

• Pulse Digits are signaled as pulse or rotary sequences. For detection, these pulses manifest themselves as nothing more than sequences of audible clicks. Valid pulse digits are '0' through '9'.
• DTMF Digits are signaled as DTMF (Dual Tone Multiple Frequency) tones. Valid DTMF digits are '0' through '9', 'A'. 'B', 'C', 'D', '*', and '#'. Both the beginning and the down edge of DTMF digits can be monitored.

See the ThbTapiCall.MonitorDigits property for further information.

Digit Gathering

Besides enabling digit monitoring and being notified of digits one at a time, an application can also request that multiple digits be collected in a buffer. Only when the buffer is full or when some other termination condition is met is the application notified. Digit gathering is useful for functions such as credit card number collection. It is performed when an application calls lineGatherDigits, specifying a buffer to fill with digits.

See the ThbTapiCall.GatherDigits property for further information.

Generating Inband Digits and Tones

After a call is in the connected state, information can be transmitted over it. Two functions are provided that allow end-to-end inband signaling between the application and remote station equipment such as an answering machine.

The function ThbTapiCall.GenerateDigits, ThbTapiCall.GeneratePulseDigits are used to generates inband digits on a call, signaling them over the voice channel either as rotary/pulse sequences or as DTMF tones. The ThbTapiCall.GenerateTone method used to generate one of a variety of multifrequency tones inband (over the media stream).

Media Monitoring

When a call is in the connected state, information can be transported over the call. A call's media type provides an indication of the type of information (for example, its datatype, or higher-level protocol) of this media stream.

See the ThbTapiCall.MonitorMedia property for further information.