Re: [rtcweb] The DTMF API [Was: Traffic should be encrypted. (Re: Let's define the purpose of WebRTC)]

On Wed, Nov 16, 2011 at 2:46 AM, Randell Jesup <randell-ietf@jesup.org>wrote:

> On 11/16/2011 1:38 AM, Hadriel Kaplan wrote:
>
>> On Nov 16, 2011, at 1:13 AM, Justin Uberti wrote:
>>
>>  [Local]MediaStreamTrack.**sendDTMF(in DOMString tones, in optional long
>>> duration)
>>>
>>> ex:
>>> sendDTMF("1")  // plays tone 1 for 50 ms
>>> sendDTMF("2", 200)  // plays tone 2 for 200 ms
>>> sendDTMF("123")  // plays tones 1, 2, 3 in succession, each for 50 ms
>>> sendDTMF("456", 200)  // plays tones 4, 5, 6 in succession, each for 200
>>> ms
>>>
>> Sounds good to me, but supporting a multi-digit-string as you did above
>> reminds me that I'll have to check with some experts if this is ok - it
>> reminded me there have been issues with DTMFs being too close to each other
>> in time, but I am not an expert in that and it may not be an issue at all.
>>  (there were issues in PSTN when multiple DTMFs were generated back-to-back
>> from a saved address-book contact-entry type thing, but it may have only
>> been a problem for using in-band DTMF which won't be an issue here)
>>
>
> Typically you need an on-time and an off-time when sending a stream.  I
> think typical minimums are around 70ms on, 40ms off, but that's
> off-the-cuff from old neurons.  I think the minimum is around 45ms on, but
> that will see problems with decoders.
>
> http://nemesis.lonestar.org/**reference/telecom/signaling/**dtmf.html<http://nemesis.lonestar.org/reference/telecom/signaling/dtmf.html>
> indicates 50ms min on, 45ms min off, 100ms min cycle duration. I wouldn't
> want to run too close to those numbers, though.
>
> "It should be mentioned that Radio Shack, one of the worlds largest
> retailers of consumer telephone equipment, requires that all telephone
> devices it sells generate DTMF tones of no less than 70 msec of duration.
> Radio Shack developed this number based on real-life use of their equipment
> on telephone networks throughout North America and the finding that shorter
> tones are more likely to cause dialing troubles."

If I read this right, sounds like this means we enforce a minimum tone
length of 100 ms and a minimum gap of 50 ms.

>
>
> --
> Randell Jesup
> randell-ietf@jesup.org
>
>
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