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Re: Min DTMF Gap

From: Cullen Jennings (fluffy) <fluffy@cisco.com>
Date: Fri, 17 Jan 2014 17:35:15 +0000
To: Barry Dingle <btdingle@gmail.com>, Mike Johns <m.johns@commsalliance.com.au>, Gunnar Hellstrom <gunnar.hellstrom@omnitor.se>
CC: "public-webrtc@w3.org" <public-webrtc@w3.org>
Message-ID: <44EB8709-0C6D-4CC2-B3A0-0FAF63C25320@cisco.com>

Iím 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. 

Does that change look OK to folks? 




On Jan 17, 2014, at 6:26 AM, Barry Dingle <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> 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> wrote:
>> 
>> This has been sitting on the editors todo list for a long time and I wanted to try and sort it out Ö
>> 
>> 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 Friday, 17 January 2014 17:35:44 UTC

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