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Re: Min DTMF Gap

From: Gunnar Hellstrom <gunnar.hellstrom@omnitor.se>
Date: Sat, 18 Jan 2014 07:45:46 +0100
Message-ID: <52DA231A.4030506@omnitor.se>
To: public-webrtc@w3.org
On 2014-01-18 01:53, Barry Dingle wrote:
> I have attached the Australian S002 Standard for reference.
Good,
>
> In summary, Section 5.5.1.9 (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.
>
> 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?

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

/Gunnar
>
> I _cannot_ find a reference to a minimum 125 ms tone + gap time Or to 
> a maximum 'signalling rate' of 8 digits per sec (that equals 125 ms).
>
>
> Cheers,
> /Barry
>
> Barry Dingle
> "Australia"
>
> On Sat, Jan 18, 2014 at 8:39 AM, Gunnar Hellstrom 
> <gunnar.hellstrom@omnitor.se <mailto:gunnar.hellstrom@omnitor.se>> wrote:
>
>     On 2014-01-17 18:35, Cullen Jennings (fluffy) wrote:
>
>         I’m fine with lower limits allowing people to shoot themselves
>         in the feet but I want the defaults to be safe for most cases.
>
>         So the way I think we should set this is to set the default to
>         be "safe" for all major deployments world wide.  And have the
>         minimum values allow you set it to be as low as is usable in
>         any any major deployment world wide. With that strategy, and
>         the information folks provided in this email thread, I think
>         we get to the following.
>
>         How about this for a proposed change:
>
>         We change the min tone time to 40 ms.
>
>         We change the min gap time to 30 ms.
>
>         We change the default gap to 70 ms (this meets Australia AS/CA
>         S0020)
>
>         We leave the default tone duration at 100 ms.
>
>     Why this long tone? All columns show minimum 40 ms for duration.
>
>     If you want to guarantee the minimum total length of tone + gap to
>     be 125 ms as required by Australia, it would make more sense to
>     set the default tone to 55 ms.
>     Then default tone + default gap is 125 ms, and this is also very
>     close to the maximum rate set by Japan and Brazil.
>
>     Regarding all problems with misbehaving echo cancellers in VoIP
>     gateways, I think it is good to not push these figures to its
>     extremes.
>
>     So, my proposals for default figures are 55 ms tone and 70 ms gap.
>
>     And minimums as Cullen's proposal.
>
>     /Gunnar
>
>
>         Does that change look OK to folks?
>
>
>
>
>         On Jan 17, 2014, at 6:26 AM, Barry Dingle <btdingle@gmail.com
>         <mailto:btdingle@gmail.com>> wrote:
>
>             Thanks for helpful reply Gunnar.
>
>             The Australian DTMF specification in included in AS/CA
>             S002. The current version of S002 'still' states that DTMF
>             tones should have a minimum 70 ms gap. The min DTMF Gap
>             value has not changed because of PSTN network equipment
>             and some older Customer Equipment including IVR.
>
>             I have informed the organisation (Communications Alliance)
>             that reviews S002 of the WebRTC interest in setting
>             consistent DTMF tone and gap durations and that it might
>             impact operation involving Australian approved equipment.
>
>             Barry Dingle
>             "Australia"
>
>
>             On Fri, Jan 17, 2014 at 6:11 PM, Gunnar Hellstrom
>             <gunnar.hellstrom@omnitor.se
>             <mailto:gunnar.hellstrom@omnitor.se>> wrote:
>             On 2014-01-17 01:43, Roman Shpount wrote:
>
>                 I was the person who asked for this change.
>
>                 Based on http://www.itu.int/rec/T-REC-Q.24-198811-I/en
>                 Annex A, valid tone duration is 40 ms and up. Valid
>                 gap duration is 30 ms (minimal for Japan) and up to 70
>                 ms minimum in Australia. So, my suggestion was to keep
>                 defaults at their current values but allow to set
>                 minimal values to minimal possible legal values (40 ms
>                 tone and 30 ms gap). My justification is that DTMF is
>                 a legacy interop feature and it should be able
>                 reproduce any legal DTMF string which can occur in the
>                 wild by modifying the JavaScript parameters.
>
>             The same table in Q.24 has a value for signal velocity,
>             that is the minimal sum of a tone and a gap. Figures are
>             between 93 and 125 ms, with 93 for USA, 100 ms for Europe,
>             120 for Japan and Brazil and 125 for Australia.
>             That would require for example 50 tone and 50 pause to
>             cover USA and Europe, and 50 tone and 75 pause to cover all.
>
>             Since RFC 4733 should be used for the transmission and
>             detection of DTMF, one could expect to rely on RFC 4733
>             for the timing. In section 3.1 it refers to Q.24 and
>             points out 40/40 but a limit of 8 to 10 digits per second.
>              That would be accomplished for example by 50 tone and 70
>             pause.
>
>             It would be interesting to know if there are any
>             international experience from setting parameters for RFC
>             4733 usage that we could use.
>
>             We should also remember that Q.24 is talking about timing
>             for detection at the receiving end. So, some tolerance
>             should be given at the generating end.
>
>             So, it seems that 50 tone and 50 pause would be good
>             timing for transmission except for Australia, Brazil and
>             Japan ( if the Q.24 limits are still valid in these
>             countries ).
>
>             Gunnar
>
>
>
>                 _____________
>                 Roman Shpount
>
>
>                 On Thu, Jan 16, 2014 at 7:19 PM, Cullen Jennings
>                 (fluffy) <fluffy@cisco.com <mailto:fluffy@cisco.com>>
>                 wrote:
>
>                 This has been sitting on the editors todo list for a
>                 long time and I wanted to try and sort it out …
>
>                 The gap between DTMF digits is currently specified at
>                 50ms. Long ago someone requested we change this to 40 ms.
>
>                 Does anyone remember why people wanted to make this
>                 change? Thought on if it should be 40 or 50?
>
>                 Thanks, Cullen
>
>
>
>
>
>
>
>
Received on Saturday, 18 January 2014 06:46:24 UTC

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