Re: [codec] #5: Mention DTMF in requirements

This is all wonderful, but what seems to be missing here is any type of
standard test for DTMF tone detection. We have a number of tests for things
that should not be detected as DTMF (various talk-off tapes), but there is
no test with samples of valid DTMF signals. In real world you get quite a
variety of tones that different handsets or telephone devices generate when
a digit is pressed. Some of those tones are almost at border line conditions
for a valid DTMF tone.

Second issue, which was already mentioned here, would be performance of DTMF
tone detector in the presence of packet loss or time stretching caused by
jitter buffer. Those things, even if they do not prevent DTMF detection, are
almost guaranteed to split a single long tone in two.

Finally, we seemed to concentrate on DTMF tones only, but in reality all the
signaling/special tones are quite important. Fax Send/Receive tones come to
mind almost immediately as tones that are typically detected inband (very
few gateways encode those tones using RFC 4733/2833)

I think we should formulate this requirement not in terms of DTMF tone but
in terms of accuracy of reproduction of  periodic signals in specified
frequency ranges. To be honest, the most robust solution would be to
incorporate RFC4733/4744 as a part of the codec in a manner similar to
comfort noise frames.
_____________________________
Roman Shpount - www.telurix.com

On Fri, Apr 2, 2010 at 1:34 PM, Christian Hoene <hoene@uni-tuebingen.de>wrote:

> Hi Stephan,
>
> Comments inline:
>
>
> ---------------------------------------------------------------
> Dr.-Ing. Christian Hoene
> Interactive Communication Systems (ICS), University of Tübingen
> Sand 13, 72076 Tübingen, Germany, Phone +49 7071 2970532
> http://www.net.uni-tuebingen.de/
>
> From: stephen botzko [mailto:stephen.botzko@gmail.com]
> Sent: Friday, April 02, 2010 4:50 PM
> To: Christian Hoene
> Cc: Michael Knappe; stpeter@stpeter.im; codec@ietf.org
> Subject: Re: [codec] #5: Mention DTMF in requirements
>
> (a) "MUST NOT" means that it must fail.  Perhaps you meant "need not" or
> "might not"?
>
> CH: Yes, I meant need not (or the German „muss nicht“)
>
> (b) SHOULD is commonly used in establishing requirements, and it certainly
> was used in MARTINI and other working groups at IETF77 in
> requirements presentations with no confusion. It has a clear meaning in the
> requirements context (desirable but not essential) and I
> see no reason to avoid its use at this phase.  There will certainly be
> other things that are "nice to have", and it is appropriate
> to track them and consider them in the selection/standardization process.
>
> CH: Better? "The codec SHOULD support the transmission DTMF at most
> transmission conditions."
>
> I agree that language about DTMF might not need to be in the final RFC.
> Though if DTMF quality is known to be inadequate, it
> probably makes sense to tell people that.
>
> CH: Agreed. The limits of the codec shall be clearly stated.
>
> I also agree to the obvious comment that DTMF detection methods are out of
> scope.
>
> CH: Agreed.
>
> CH: Isn't time to include the MUST requirement for DTMF testing and SHOULD
> requirement for transmission support into the
> requirements document.
> Then, we could close issue #5 and continue with other things.
>
>  Christian
>
>
>
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