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Re: Min DTMF Gap

From: Barry Dingle <btdingle@gmail.com>
Date: Sat, 18 Jan 2014 11:53:22 +1100
Message-ID: <CAN=GVAvHhmFG-C5XvY9BJYdn0kk16hn76bAG=2yZsEOsmPUBBQ@mail.gmail.com>
To: Gunnar Hellstrom <gunnar.hellstrom@omnitor.se>
Cc: "Cullen Jennings (fluffy)" <fluffy@cisco.com>, Mike Johns <m.johns@commsalliance.com.au>, "public-webrtc@w3.org" <public-webrtc@w3.org>
I have attached the Australian S002 Standard for reference.

In summary, Section 5.5.1.9 (e) states:

(i) *minimum duration* of DTMF burst (i.e. transmission)  shall be *50 ms*.

(ii) *minimum interval* between the transmission of digits shall be *70 ms*.


A Note says post answering DTMF signalling, digit duration should be
minimum 100 ms.

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> 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> 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 …
>>>>
>>>> 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 00:54:13 UTC

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