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DTMF on SIP Trunk

Hi Folks,

Need quick suggestion on the dtmf method usage for the below call follow:

PSTN >> PRI >> VG >> MGCP >> CUCM >> SIP Trunk >> CUBE

VG supports - OOB

CUBE supports - RFC2833

DTMF on SIP Trunk configured as:

No Preference: Will the trunk utilize OOB as the dtmf method as being supported by the VG??

RFC 2833: When VG sends dtmf as oob to cucm and SIP trunk has rfc2833 configured. What will happen in this case ? What will the dtmf flow ??

OOB and RFC2833: Which method would be selected and why. If OOB is selected by looking at the VG's dtmf method, then there would be the MTP requirement due to the mismatch. Please correct if I am wrong.

VIP Advisor

I am pretty sure that the SIP

I am pretty sure that the SIP trunk will use SIP NOtify for OOB DTMF,

I would suggest to use RFC2833 on the SIP trunk to the CUBE

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Hi Dennis,

Hi Dennis,

Thank you for the quick response.

Yeah its true that OOB utilizes SIP Notify messaging. However, my concern is that what will happen in situation when SIP trunk is configured as either below:

No Preference


oob and rfc2833

Note: Party 1 supports OOB while Party 2 supports rfc2833

thanks in advance...

VIP Advisor

well I have had a scenario

well I have had a scenario where an inbound call from an MGCP gateway going to CUCM, then  onto a SIP trunk got connected after about 40 seconds because the was no 3 way SIP handshake, this was caused by DTMF going from inband to OOB.


no preference :  SIP TRunk will use SIP notify

RFC2833:  SIP trunk will use in band signalling, through SIP SDP

OOB and RFC 2833: what I understand from it, is that it is capable of supporting both, but unclear of this requires MTP on the SIP trunk or not.

I am not sure of this answers your question

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Re: well I have had a scenario

My experiece with setting both on the trunk was an MTP was still needed, I have a TAC case open and I am waiting on confirmation.

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