Today we will try to peek at another huge and equally important topic, this is a collection of services/API's for communication and is called TAPI or Telephony API's. TAPI does not just contain Telephony services, but also media, medium access, device management and host of other things. All the IVR, soft EPBAX etc. types of applications are written using TAPI. The dial up connections we make are implemented using TAPI and much more.

Usually all the TAPI functions either start with line... or phone.... Now, to try out these functions, or use TAPI, you will need certain hardware devices, at least a modem and a telephone line. Let's see what will be the basic steps to make a phone call programmatically using TAPI and this hardware. Before using any TAPI function, you should initialize the TAPI subsystem.

This is done by calling lineInitializeEx() function. This gives us a usage handle which is then used in most other functions. Now, we would need to open a device handle, which is done by calling lineOpen(). lineOpen() will give us handle to a telephone line. This we can use to make phone calls using either lineMakeCall() or lineDial(). There is a slight difference between these two functions, look in the MSDN to know more about these. You can disconnect an established connection using lineDrop(). You can also accept in incoming call using lineAccept() or redirect the call to another telephone (soft epbax) using lineRedirect(). Once you are finished, you should close the line handle using lineClose() and then shutdown TAPI subsystem instance for your application by calling lineShutdown().

These were some of the basic operations you can do with TAPI. As I said, TAPI is a huge topic and we just picked a drop out of this ocean. There are COM interfaces for TAPI as well to enable VB types of applications to use TAPI features. TAPI also provides support for Call center types of operations, you can write applications for media transfer, telephony conferencing, and others. There is also another very important topic called TAPI service providers ( we will see if we can cover that in some future topic). TSP is an abstraction layer between tapi applications and the actual hardware devices. Then there is another associated topic called MSP or media service provider which provides abstraction for control over media of a call.

1.Study about TAPI in MSDN. Write a simple application which can dial a telephone number. You can use the modem we have to test your applications, you can test your application by dialing our internal telephone extensions.

4. Study about STT (Speech to Text) and TTS (Text to Speech) SDK from MS. Search the net and find out how IVR's can be implemented using these (basic things such as how you can play wav files over telephone lines etc.).

I would again reiterate that TAPI is an extremely important topic for us. None of the commercial telephony applications can be written without using some part of TAPI. So it's very important that we are aware of what is available to us in form of TAPI. Also understand that TAPI is a huge and very challenging topic to grasp. So go gradually at understanding it's services and don't get disheartened if you find it difficult at first.