DTMF
From Snom Asterisk Portal
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Feature description
In SIP there exist different ways to transmit DTMF (Dual Tone Multiple Frequency). When a key, which corresponds to a DTMF Code is pressed, the phone needs to inform the Asterisk of this event. The transmission of DTMF codes may happen in one of these three ways:
- via inband audio, which does not work with all codecs. Basically it only works with ulaw and alaw, which are the ISDN codecs
- via outband by the RTP protocol, specified in RFC2833
- via SIP info packets
In fact, rfc2833 (outband) and SIP info packets both work perfectly, but both endpoints have to agree to one of them. Otherwise no DTMF information will be transmitted.
Configure Asterisk
Asterisk does support all three methods. You can set DTMF mode in sip.conf per peer using the dtmfmode option. You can choose between rfc2833, inband or info. To get it working in combination with a factory defaulted snom phone, set it to rfc2833. You may choose info, too, but you have to configure your snom phone accordingly. It is possible, but not recommandable to choose inband for SIP.
Example sip.conf:
[my-sweet-snom-370-phone] type=peer secret=password dtmfmode=rfc2833 #dtmfmode=info # you can use this too #dtmfmode=inband # generally a bad idea for sip
Configure snom phones
snom 3xx
Snom phones can send either SIP info messages or use RFC2833 or both (depending on the firmware version). This can be set per identity in your phone using the user_dtmf_info setting.
Firmware version 6.5.18
- for RFC2833 mode: In the web user interface go to "Identity" > Tab "SIP" > "DTMF via SIP INFO:": Set this option to "off".
- for SIP info packets: In the web user interface go to "Identity" > Tab "SIP" > "DTMF via SIP INFO:": Set this option to "on".
Firmware version 7.1.33
- for both RFC2833 mode and SIP info packets: In the web user interface go to "Identity" > Tab "SIP" > "DTMF via SIP INFO:": Set this option to "on".
- for only SIP info packets: In the web user interface go to "Identity" > Tab "SIP" > "DTMF via SIP INFO:": Set this option to "SIP INFO only".
- for only RFC2833 mode: In the web user interface go to "Identity" > Tab "SIP" > "DTMF via SIP INFO:": Set this option to "off".
snom m3
- for RFC2833 mode: In the web user interface go to "Identity" > "DTMF Signalling:" Set this option to "RCF2833".
- for SIP info packets: In the web user interface go to "Identity" > "DTMF Signalling:" Set this option to "SIP INFO".
- for inband audio: In the web user interface go to "Identity" > "DTMF Signalling:" Set this option to "Inband".
