[rtcweb] DTMF resolution proposal

[Ted Hardie <[e-mail]>]

We've had about 60 or so messages on this topic, and the rough consensus
seems to be align this document with the limits set out in the W3C work
here:

https://www.w3.org/TR/webrtc/#rtcdtmfsender

However, there was also a proposal to slightly modify those limits.  They
are currently:

"The duration cannot be more than 6000 ms or less than 40 ms. The default
duration is 100 ms for each tone."

Based on Roman's note, a minimum of 40ms and a maximum 8000 ms to align
with the ITU and RFC2833.

To resolve this, I propose that we ask the WebRTC group to raise their max
to 8000 and, on receiving a positive response, publish this document with
40/8000 as the min and max.  If they give a negative response, we retain
40/6000.  This values alignment between the two documents higher than the
reference 2833, but that seems sensible in this context.

If you have an objection to this way forward, please send your reasoning to
the list by March 14th.

thanks,

Ted