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Re: Min DTMF Gap

From: Roman Shpount <roman@telurix.com>
Date: Sun, 19 Jan 2014 13:53:10 -0500
Message-ID: <CAD5OKxv4ONsyzQNXeeYBfCqtLgy9g4Qq-LRQGzS1hcAcHWzEDQ@mail.gmail.com>
To: Gunnar Hellstrom <gunnar.hellstrom@omnitor.se>
Cc: "public-webrtc@w3.org" <public-webrtc@w3.org>
On Sat, Jan 18, 2014 at 1:45 AM, Gunnar Hellstrom <
gunnar.hellstrom@omnitor.se> wrote:

> In summary, Section (e) states:
>  (i) *minimum duration* of DTMF burst (i.e. transmission)  shall be *50
> ms*.
> And ETSI ES 201 235-2 section 4.2.4 requires 65 to75 ms.
>  (ii) *minimum interval* between the transmission of digits shall be *70
> ms*.
> And ETSI ES 201 235-2 section 4.2.4 requires at least 65 ms and a note
> requiring not more than 75 ms.
If you read ETSI ES 201 235-2 carefully you would realize that this
recommendation covers interactions between telephone terminal and telephone
switch or PBX. In other words it covers DTMF before the call answer. This
is not the most common scenario for WebRTC so this specification does not
necessarily apply.

>   A Note says post answering DTMF signalling, digit duration should be
> minimum 100 ms.
> How do you interpret this. Is it tone duration that should be 100 ms or
> tone + gap that should be 100 ms?

This is 100 ms minimal tone which is from my experience is the safe default.

> I guess that all our use of DTMF will be "post answering".

Most but not all. You still get applications that connected a VoIP call to
a dial tone in the remote location and allow caller to dial the number.
This is "post answering" on the origination side but end up being
pre-answering on the remote side.

Roman Shpount
Received on Sunday, 19 January 2014 18:53:40 UTC

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