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2.4 Establishing a Call
- The specific process of call establishment depends on whether the application is acting as a calling fax terminal or as a called fax terminal. Call establishment is accomplished with one or more function calls from the ADI service call control functions. Refer to the CT Access Developer's Manual and the ADI Service Function Reference Manual for complete details on call establishment.
- You must initialize and load the AG board(s) before you can run a CT Access or NaturalFax application. Use the agmon utility to accomplish hardware initialization. For information about agmon, see the AG Access Installation Manual.
2.4.1 Placing a Call
- Call progress analysis in the ADI service includes the capability to detect CED tone. The application uses functions from the ADI service to place a call and detect CED tone. A CED tone is a three second 2100 Hz tone which indicates that a fax terminal has answered.
- An application that uses NaturalFax should keep CED tone detection enabled in the call to adiStartCallProgress. An ADI service call progress event will appear if a CED tone is detected. If no CED tone is detected, a robust application should have a way to handle a call answered by a person or by a modem rather than by a fax machine.
2.4.2 Receiving a Call
- The application uses function calls from the ADI service to answer an inbound call and detect CNG tones. The calling fax terminal sends a CNG tone, a 0.5 second, 1100 Hz tone that indicates a fax terminal is calling.
- If an application needs to handle both fax and human callers, it should start a special tone detector to detect CNG tones in conversation state. The application starts a fax session only if a CNG tone is detected. In a fax-only application, a fax session may be started as soon as the call is answered.
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