Network programming in C#, Network Programming in VB.NET, Network Programming in .NET
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11. TAPI in C# and VB.NET

TAPI, or the telephony application-programming interface is the mechanism by which computers can respond to phone calls. It is the technology behind call-centres, and all CTI (Computer Telephony Integration) applications. This application can be used to detect, pick up, and play a pre-recorded message to callers.

You will need a voice modem to use this application. Data modems can still be used with this, but you will not be able to send and receive audio after the call is accepted.

To use the application, ensure that your modem is plugged into a phone line, then press the ‘Start Modem’ button. With a second phone, ring the number for the phone line which is connected to your PC’s modem. You will see “Event: Ringing” appearing on-screen. Press ‘Accept Call’ to accept the call. At this point, the line is opened (and is probably costing you on your phone bill). You can then play a sound to the recipient by pressing the browse button, selecting an audio (.wav / wave) file, and pressing the ‘play sound’ button. The caller will then hear the sound, -albeit with some degraded sound quality. You may also receive DTMF (dual tone modulated frequency) keypad presses, as they appear on-screen as TAPI events. To drop the line, press ‘Stop modem’.

(Source code availabile in the book Network Programming in .NET (Buy at Amazon UK) (Buy at Amazon US) , Chapter 14, Example 4)

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