RFC 4733, "RTP Payload for DTMF Digits, Telephony Tones, and Telephony Signals", December 2006Source of RFC: avt (rai)
Errata ID: 3451
Publication Format(s) : TEXT
Reported By: Xavier Marjou
Date Reported: 2013-01-11
Rejected by: Gonzalo Camarillo
Date Rejected: 2013-04-04
Section 2.1 says:
Named telephone events are carried as part of the audio stream and MUST use the same sequence number and timestamp base as the regular audio channel to simplify the generation of audio waveforms at a gateway.
It should say:
Named telephone events are carried as part of the audio stream and MUST use the same SSRC (therefore the same timing and sequence number space) and the same timestamp clock rate as the regular audio channel to simplify the generation of audio waveforms at a gateway.
RFC4733 was written in a way to avoid the multiple clock-rate problem by mandating the use of the same SSRC for DTMF and audio. However it's not explicitly written, which brings an ambiguity. It was commented that RFC4733 needs to be updated. (c.f. http://tools.ietf.org/wg/avtext/minutes?item=minutes-85-avtext.html)
Discussions around this erratum resulted in the updated 3489 erratum.