[AVT] DTMF interoperability: In-band, RFC 2833 or SIP INFO

["Murat Artun" <artunmurat at gmail.com>]

Hello all,

I want to ask about the interoperability issues for DTMF sending.

There exist three ways for DTMF sending: In-band (I use this term
meaning in audio as a voice data), RFC 2833 (currently 4733 obsoletes,
but no change to previous procedure exists) and SIP INFO.

Among these three ways, I know that only RFC 2833 is announced in the
SDP of a VoIP application when it is ready to receive DTMF events as
RFC 2833 packets.

I have a few points to be clarified in the sense of interoperability issues:

- Is it preferred that DTMF is also sent in-band and as SIP INFO when
the remote VoIP application announces that it is ready to receive RFC
2833 packets?

- What if the remote VoIP application does not announce that it is
ready to receive RFC 2833 packets? Which method should be preferred,
In-band or SIP INFO, or both for reliability purposes?

- I have observed that sending DTMF as RFC 2833 packets is mostly
preferred considering that sending DTMF In-band requires the remote
VoIP application to perform tone detection in RTP level which requires
considerable processing overhead as RFC also states. Is there a known
issue about SIP INFO method for DTMF sending?

Thanks in advice...

--
M u r at  A r t u n, MSc.
  Design Engineer

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