11. Telephone API (TAPI) and Remote Access Services (RAS)

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Chapter 11. Telephone API (TAPI) and Remote Access Services (RAS)

The Telephone API (TAPI) and Remote Access Service (RAS) are both used to make, maintain, and terminate calls made through modems and other telephonic devices. RAS is used when making calls to a Windows NT or 2000 server where a login to a server with authentication takes place, or to an Internet Services Provider (ISP) with automatic login. In both situations, a protocol like PPP (Point to Point Protocol) is then used to allow TCP/IP connections to be made through a serial connection.

TAPI is used to make telephone calls, but once the call is made, the program can then decide how the connection is to be used. For example, it may hand over the call to the user for an ordinary voice call, or obtain a serial communications handle to perform data transfer, or send a fax. TAPI frees the programmer from having to know how each telephonic device works and the commands needed to control calls. Further, TAPI can be used to modify a simple local telephone number to a form suitable for handling long distance or international calls, depending on where the user is located.

RAS uses TAPI to make the telephone calls, and then manages the connection. You should use RAS to do the following:

• Get a network connection to a Windows 2000 or NT server that is configured to accept RAS calls

• Obtain an Internet connection through an ISP using Point to Point Protocol (PPP)

TAPI can be used to control telephone calls, for example, by doing the following:

• Automatically dialing a telephone number and then handing the call over to the user. This might be an auto-dial feature in a telephone book application.

• Sending a fax message, where TAPI is used to make the call and you handle the necessary fax data transmission.

• Connecting to a computing device that does not support RAS or PPP, where you will be sending data using serial communications techniques (described in Chapter 9).

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