Re: [rtcweb] Support DTMF "codec" or expose DTMF in signaling? (Re: DTMF usecase before DTMF API)

[Iñaki Baz Castillo <[e-mail]>]

2011/11/18 Matthew Kaufman <[e-mail]>:
>> In case
>> http://tools.ietf.org/html/draft-kaplan-dispatch-info-dtmf-package-00
>> becomes a standard, there is no need to send DTMF over the media
>> stream (when interoperating with SIP networks). Since this just
>> concerns the in-the-wire signaling it becomes up to the application
>> developer.
>>
>>
> Are you advocating that we not put DTMF-in-media support in browsers (in
> which case I have a good argument against), or are you simply making an
> observation about an alternative that may also become available?


I'd would like not to make the WebRTC API ugly just due to
interoperability with legacy networks, and DTMF is something that, for
sure, is so far from the concept of "Web innovation".

So if such DTMF can be emulated via the free in-the-wire signaling we
avoid adding it to the WebRTC API and also avoid browsers vendors
having to deal with DTMF duration, volume and other pure legacy
telephony stuff.

Even in modern SIP networks, sending DTMF's over RTP is undesired in
many cases and forces some non optimal architectural designs. For
example, it's very common the use case in which a SIP PBX system
brigdes a call between two phones/endpoints and offers "on-demand"
recording service. For this, the user (which just has a common/legacy
SIP phone) must enter some specific DTMF tones during the call. In
order the PBX to intercept these DTMF codes, the RTP must pass through
the PBX. If not, DTMF's must be sent over the signaling path so the
PBX is aware of them and can react.

So sending DTMF's over the signaling path is just better than sending
them over the media stream, IMHO for all the possible cases. This is
the reason of the use of INFO for carrying DTMFs (even if it has never
been standarized and its usage has real drawbacks).

Said that, I would strongly propose the above if
http://tools.ietf.org/html/draft-kaplan-dispatch-info-dtmf-package-00
was already a standard, unfortunatelly it's not the case.


-- 
Iñaki Baz Castillo
<[e-mail]>