[Freeswitch-users] DTMF SIP Info or rfc2833 (rfc 4733)

[Mimiko]

On 05.01.2017 19:01, Anthony Minessale wrote:
> The 4733 is just an update to 2833 and its basically the same in terms
> of our usage so you can consider the names interchangeable.
> There is no way to negotiate SIP INFO DTMF so you can enable it as needed.
> If you want to send INFO DTMF you can set the variable dtmf_type=info in
> the outbound dial string.
>
> INFO is the most reliable when used with TCP, 2833 is more reliable over
> UDP.
> INFO traverses the signaling patch where 2833 traverses the media so
> there are considerations to make.  There is no best.

Oh, my project does not allow to flow rtp directly between clients, so 
SIP info is ok, also I use UDP so rfc2833 is needed. As I understand FS 
will catch SIP info and rfc2833 in same leg using that option.

Well, found some interesting info:

http://sip-implementors.cs.columbia.narkive.com/0VSY8gy9/is-rfc-2833-a-must-in-sending-dtmf

> Remember that SIP and RTP sometimes travels different paths. For many
> applications, it is important that DTMF is timed with the rest of the
> audio. Sending DTMF without timestamps and in a different signalling
> path totally removes the relation to the audio stream.
>
> My experience is that very few carriers now support SIP Info.

> Well, arguably not much relation to audio stream is really needed for
> DTMF applications. Relative events ordering, not absolute timestamps, is
> what important here and it is provided reliably by the CSeq in SIP INFO.
>
> I think technically SIP INFO delivery method is superior to RFC2833
> (DTMF is a signaling, not media after all, so that it should take
> signaling path), however, as it has been correctly mentioned here, there
> is no common standard and much weaker support across different
> implementations.

> The only upside I see is that it's easier to debug DTMF in the SIP
> channel than deep down in RTP.
> Otherwise, RFC2833 is the way to go.

I think info from the post should be reflected at 
https://freeswitch.org/confluence/display/FREESWITCH/DTMF

-- 
Mimiko desu.