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

"Benjamin M. Schwartz" <bmschwar@fas.harvard.edu> Sat, 03 April 2010 01:57 UTC

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Date: Fri, 02 Apr 2010 21:57:22 -0400
From: "Benjamin M. Schwartz" <bmschwar@fas.harvard.edu>
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Subject: Re: [codec] #5: Mention DTMF in requirements
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Michael Knappe wrote:
> I would agree with 'should'. 

I think DTMF should be ignored entirely as far as requirements.  If
someone wishes to perform tests, they are welcome to do so and present
results, but there is no need to require anything.

> Lot's of dtmf out there still, but also out of band options (rfc 2833 / 4733) that make in-band carriage less a concern for SIP telephony applications.

There are many different machine-to-machine communications systems that
have been designed to operate over channels that also carry audio.  We
should not attempt to support any of them.  The only purpose of this codec
should be to carry sounds to a human ear.

Any machine-to-machine communications SHOULD be decoded from the stream
prior to compression and transmitted independently.  Any system that
encodes using the IWAC has access to the input stream, and so can perform
any required decoding (of rotary clicks, DTMF, fax, DRM watermark, V.42,
ZX Spectrum cassette, etc.) at that time.

Decoders MAY do whatever they want with the output stream, but any use
other than listening by a human should be unsupported.

--Ben

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