Re: Min DTMF Gap

On Fri, Jan 17, 2014 at 12:44 PM, Roman Shpount <roman@telurix.com> wrote:

> On Fri, Jan 17, 2014 at 12:35 PM, Cullen Jennings (fluffy) <
> fluffy@cisco.com> 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.
>>
>> Does that change look OK to folks?
>>
>>
> This looks perfect to me.
>
>
After I thought about this a little bit more I would suggest that tone and
gap generation should take the packet ptime into account. The reason is
that WebRTC will switch between RFC 4733 tone and audio codec during the
pause. This means for 70 ms pauses and most common ptime of 20 ms we will
end up with a 10 ms audio packet. Packets of duration other then ptime have
a tendency to cause interop issues. In our implementations of similar DTMF
generation code we would round up gap and tone duration to the next ptime
interval, so that with 20 ms ptime you can set the gap to 40, 60, 80, 100
ms (etc) and tone duration to 40, 60, 80, 100 ms (etc). With 30 ms ptime it
would be 30, 60, 90 ms (etc) for the gap and 60, 90, 120 ms (etc) for the
tone.
_____________
Roman Shpount