Information can be transmitted over a call that is in the connected state. Two functions are provided that allow end-to-end inband signaling between tapi32.dll and remote station equipment such as an answering machine. One function is TSPI_lineGenerateDigits, which signals digits over the voice channel on a call. Digits can be signaled as either rotary/pulse sequences or as DTMF tones. The other function is TSPI_lineGenerateTone, which enables tapi32.dll to generate one of a variety of multifrequency tones over the media stream on a call. This generates telephony tones, such as ringback, beep, busy, as well as arbitrary multifrequency multicadenced tones.
Only one digit or tone generation can be in progress on a call at one time. When digit or tone generation completes, a LINE_GENERATE message is sent to tapi32.dll. In the case of generation of multiple digits, only a single message is sent back after all digits are generated. Calling TSPI_lineGenerateDigits or TSPI_lineGenerateTone while digit or tone generation is in progress aborts the generation currently in progress and sends the LINE_GENERATE message to tapi32.dll with a cancel indication.