Controlling the B-Channels • 9-7 •
The H.110 Basic Rate ISDN Board
B-channel 00. The tone will stop playing if another command is issued for
the B-channel such as a connect.
9.4.3 Sending DTMF Tones
A string of DTMF tones can be sent using the “CT” command. Any of the
16 DTMF tones can be sent. Pauses may be embedded that are one or ten
digit times (.2 or 2 sec.) Single tones of 697 and 941 Hz. are also possible.
The tone string length can be up to 27 characters long. The command
consists of CT followed by the B-channel number and the string of tones.
As an example, the command CT039P7654321 would send the digit “9”,
pause two seconds, and then send the digits “7654321”.
On receiving the command, the board will respond with an “SL” state
change message to indicate that the B-channel is listening to a DTMF
generator. When the tone string has finished, the board will send an “SE”
message to indicate the string is ended and place the B-channel in the hold
state.
9.4.4 Detecting DTMF Tones
The on-board DSP can be used to detect DTMF tones on a B-channel.
The Listen for DTMF command takes the form CLxxo, where xx is the B-
channel number and o is an option. If no option is given, dial tone will
automatically be played to the B-channel until the first tone is detected. If
the option is “Q”, then no dial tone will be played. If the option is “M”,
then detection will take place without interrupting existing connections. The
“F” option will disable detection that is in progress. As an example, the
message CL00 will enable DTMF detection on B-channel 00 and play dial
tone.
As each tone is detected, the board will send a Tone detected state change
message of the form STxxd where xx is the B-channel number and d is the
tone. As an example, the message ST005 indicates that the digit 5 has been
detected on B-channel 00. All sixteen DTMF tones can be detected.
Detection will remain active until a command is issued for the B-channel.
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