Subject: [AVT] RFC4733/2833 related: Should volume field value be used in regenerating DTMF tone?

From: "HE Bing" <[email-masked]>
Date: Fri, 22 Oct 2010 08:59:57 +0800

Hello Mr Schulzrinne, et. all

We got a different understanding from our DSP vendor regrading the DTMF
relay based on NTE packet defined in RFC 2833 and later 4733, thus we
need your help for clarification.

Our DSP vendor uses a hardcoded power level instead of the valid value
carried by the volume field in NTE packet and declare this does not
violate RFC 2833 and RFC 4733 due to no explicit statement telling that
value SHALL or SHOULD be used.

We can say nothing bu we do think the volume field value SHALL be used
in generating DTMF tone as long as it is valid. Each DSP vendor may have
different implementation, but if support of RFC 2833 or 4733 is
declared, use of volume field has to be supported at least as an option.
We already run into problem in a customer project where the terminal
expect DTMF signal with power level higher than the hardcoded value.

Could you share with your opinion? If the volume field is not used in
reconstructing the relayed DTMF and other tone, then any other
motivation to design such a field within NTE packet?

Thanks a lot for your clarification!
Best regard.
He Bing