Require DTMF Reception Explanation

[tpfrankli]

I've seen numerious postings on this but have yet to get a nice clear understanding of what it does. Under a phones settings there is the Require DTMF Reception checkbox. What exactly does this do, given the following situation. The phone is SCCP and is connecting to a device over a SIP trunk.

Thanks.

[Bruno Rangel · Accepted solution]

Hi tpfrankli

Let me try clarify that

Depending on your environment and what SIP provider offers you might need to leverage an MTP or transcoder for DTMF reception. Transcoders or an MTP will required for DTMF reception if they use signals DTMF in-band and not via the Named Telephone Event (NTE) system.

The RFC 2833 Dual-Tone Multifrequency (DTMF) Media Termination Point (MTP) Passthrough feature passes DTMF tones transparently between Session Initiation Protocol (SIP) endpoints that require either transcoding or use of the RSVP Agent feature. (An RSVP agent is a Cisco IOS-based Resource Reservation Protocol [RSVP] proxy server that registers with CUCM or CUCME as a media-termination point or a transcoder device.).

So, on Cisco Unified Communications Manager Administration, check the Require DTMF Reception checkbox for each registered Cisco Unified SIP Phone 3911. Cisco Unified Communications Manager will verify transcoder support for RFC 2833 and allocate its own MTP resource as necessary.

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[tpfrankli]

So I think I'm following. Basically this only applies in the case of using a SIP endpoint (phone) with a SIP provider service that uses out-of-band DTMF instead of RFC 2833 NTE. So in my case I'm using SCCP devices going to a SIP trunk that uses RFC 2833 NTE.

Thus the only time MTP resources come in to play for me are for SCCP devices that only do out-of-band DTMF and don't support RFC 2833. Now of course since I'm not on 8.x of CUCM (soon) I have to check require MTP on my SIP trunks to cover any devices not compatible with RFC 2833 and also as a result even those that do will end up allocating an MTP resource.

Am I wrapping my head around this correctly?

[Bruno Rangel]

You are right buddy !!!

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[Ayodeji Okanlawon]

NB: You dont need to check require MTP on the sip trunk for DTMF purposes. CUCM automatically insert MTP when its needed. Just ensure that you have an MTP available in the MRG assigned to the MRGL of the sip trunk

Have a look at the CUCM 8.X SRND. The section on MTP is really good.

http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/srnd/8x/media.html#wp1046314

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[tpfrankli]

That's correct and in the future is how I plan to configure it. But it's my understanding that on CUCM 7.x which I'm running that is not the case.

[Ayodeji Okanlawon]

That is not correct. This behaviour is the same on cucm 7.X

Here is the excerpt from CUCM 7.x SRND

DTMF Conversion

DTMF tones are used during a call to signal to a far-end device for purposes of navigating a menu system, entering data, or other manipulation. They are processed differently than DTMF tones sent during a call setup as part of the call control. There are several methods for sending DTMF over IP, and two communicating endpoints might not support a common procedure. In these cases, Unified CM may dynamically insert an MTP in the media path to convert DTMF signals from one endpoint to the other. Unfortunately, this method does not scale because one MTP resource is required for each such call. The following sections help determine the optimum amount of MTP resources required, based on the combination of endpoints, trunks, and gateways in the system.

If Unified CM determines that an MTP needs to be inserted but no MTP resources are available, it uses the setting of the service parameter "Fail call if MTP allocation fails" to decide whether or not to allow the call to proceed. The default value of this setting is False, which lets the call continue.

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"'Nature is too thin a screen, the glory of the omnipresent God bursts through it everywhere"-Ralph Waldo Emerson

[andersonmanueltomas]

Good day Everyone,

I´m facing issue regarding the DTMF. im using 8861 cisco phone and my Manager asked me to assist with DTMF.

i double check on CUBE and i can see the DTMF is well configured ant its working when call to call center for whatever sites.
my concern is how can i activate on the phone via CUCM to allow use DTMF.
i know this uses MTP and it should be happen automatically.

happy to ear your experience.

Regards.