[SIPForum-discussion] RFC2833 dtmf with inband dtmf

[Jastak, Eric]

Hi Chet,

That's a very common scenario.  The advantage of sending both rfc2833 dtmf events (out of band) and the dtmf imbedded in the rtp stream (in-band) is redundancy.  If the rtp stream terminates on a gateway that doesn't support rfc2833 dtmf events, then the in-band dtmf will be used by the receiving device.  Of course, this only works with g711 codec.  In-band dtmf with g729, for example, would not be useable because of poor fidelity.  So, you are completely dependent on rfc2833 for dtmf when using  lower bandwidth codecs like g729.

Eric



On Dec 12, 2012, at 7:39 PM, "Chet Curry" <ccurry at telovations.com<mailto:ccurry at telovations.com>> wrote:

I have searched the RFC's but I have not found the answer to my question.

Is it normal to transmit inband dtmf (audio frequencies) while also using RFC 2833 DTMF events?

I am receiving calls from Level 3 with both being used.

--
Chet Curry
Sr. Network Architect

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