17
Figure 7 DTMF keypad frequencies
A DTMF tone must last at least 45 milliseconds. A minimum interval of 23 milliseconds is required
between two DTMF tones to make sure DTMF tones are recognizable. Such requirements are roughly the
same in all countries. For more information, see the ITU-T Recommendation Q.24.
Configuring DTMF tone sending
Step Command Remarks
1. Enter system view.
system-view N/A
2. Enter voice view.
voice-setup N/A
3. Configure the duration of
DTMF tones and the interval
between DTMF tones.
dtmf time {interval | persist }
milliseconds
The default duration and interval
are both 120 milliseconds.
4. Configure the amplitude of
DTMF tones.
dtmf amplitude value The default is –9.0 dBm.
Configuring DTMF tone detection
Use the following ways to detect DTMF tones:
• Energy detection—Calculates the spectrum shape of input DTMF signals and matches the spectrum
shape with the threshold parameters. A DTMF tone is considered valid if it matches all threshold
parameters.
• Sensitivity detection—A higher DTMF detection sensitivity reduces the possibility of missing a true
DTMF tone but increases the possibility of false detection. A lower DTMF detection sensitivity
reduces the possibility of false detection but increases the possibility of missing a true DTMF tone.
To configure DTMF tone detection:
4
1 2 3 A
B65
7 8 9
*
0 #
C
D
1209Hz 1336Hz 1477Hz 1633Hz
697Hz
770Hz
852Hz
941Hz
Column Frequency Group
