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How to configure DTMF types



Overview
DTMF (Dual-tone multi-frequency signaling) is a telecommunication signaling system using the voice-frequency band over telephone lines between telephone equipment and other communications devices and switching centers.


Frequency of each DTMF signal:
 
Frequency of each DTMF signal
Refer to Wikipedia - https://en.wikipedia.org/wiki/Dual-tone_multi-frequency_signaling

Three ways to transmit the current DTMF event
RFC2833: By filtering rtpevent and checking if there is RTP EVENT packet.
SIP INFO: By filtering sip, and checking if there is sip info message.
Inband: Not able to see it in the packets. It is in the voice band, and we can try to play RTP to check.


For example:
Devices: IT8X (IP address: 192.168.35.93, SIP account: 5173 ) and IT8X (IP address: 192.168.35.81, SIP account: 5174 )
Test environment: IT8X and PC are connected to internet via a hub.
Operations:
1. IT8X press 192.168.35.81 to make a direct IP call to IT8X, and IT8X press the number 8, 1, 0 and 3 in the call. RFC2833 will be the default protocol, so you can check in the captured packet:


DTMF
2. IT8X and Akuvox IP phone are registered to SIP Server. IT8X press 5174 to make a sip call to IT8X.
2.1 In the path: Account-Advanced, when you select the DTMF to be RFC2833, like:


DTMF
IT8X press the number 0, 2, 1 and 5 in the call, you can check in the captured packet:

DTMF
2.2 In the path: Account-Advanced, when you select the DTMF to be Info, like:

DTMF
IT8X press the number 1, 8 and 5 in the call, you can check in the captured packet:

DTMF
2.3 In the path: Account-Advanced, when you select the DTMF to be Inband, like:

DTMF
IT8X press the number in the call, you can check as following:
2.3.1 Enter the command-ip.addr==192.168.35.81&&rtp to filter rtp packets and select one packet.
   
DTMF   
2.3.2 Select电话-RTP-流分析,Select save-保存正向音频流(the fifth option),Select audio format ‘raw,’and save.

DTMF   
2.3.3 Import the raw format audio file to cooledit software. Play the audio to check where there are ‘dudu’sound.
   
DTMF   
DTMF      
2.3.4 Select the part of audio file where there are with ‘dudu’sound, and click Analyze-frequency to analyze. There will be occur two frequencies, and find which number it is via checking the DTMF picture (Obtain the frequencies via placing the mouse in the top, like 945Hz and 1359Hz in the picture, which the corresponding number is 0).

DTMF