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Community Member

"Outbound" DTMF not working on a SIP Trunk

Hi all,

we route external calls towards a SIP Trunk (with MTP Required, RFC2833 for dtmf, and G711ALAW) using a software MTP through a dspfarm on a Cisco 2951( IOS 15.0(1r)M12 )

. External Calls, transfers, MOH,  fax, ringbacks work as expected, and DTMF inbound works (we got an IVR on customer premise and it is fully functional) but we are unable to use DTMF for outbound calls at all...
I've checked all configurations (regions, locations, dspfarm and media resource on phones and trunk) and everything seems ok. Any help/suggestions would be very appreciated, thanks in advance

Gianstefano Monni

Hall of Fame Super Silver

"Outbound" DTMF not working on a SIP Trunk

What DTMF method is used on the SIP trunk?

Is there a CUBE involved if so can you post the config?

I would also recommand upgrading to 15.1M train.


Community Member

"Outbound" DTMF not working on a SIP Trunk

to update the case, the issue was due to the

Default MTP Telephony Event Payload Type 
in the SIP Profile of the trunk

the default value was 101, but here in Italy with our Carrier
the correct value should be 96

Changing this value to 96 solved the issue.

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