Re: [rtcweb] Fwd: Last Call: <draft-ietf-rtcweb-audio-10.txt> (WebRTC Audio Codec and Processing Requirements) to Proposed Standard

[Harald Alvestrand <[e-mail]>]

Den 03. mars 2016 17:06, skrev Roman Shpount:
> On Thu, Mar 3, 2016 at 6:49 AM, Harald Alvestrand <[e-mail]
> <mailto:[e-mail]>> wrote:
> 
>     You've made this argument before. I cannot see that anything new has
>     been brought to the table that is likely to alter the WEBRTC WG
>     consensus to have these enforced limits.
> 
> 
> Am I correct to understand that WEBRTC WG decided that there should be
> limits on DTMF tone generation and it is up to this group (IETF rtcweb)
> to decide the exact values of these limits?

Formally, the RTCWEB group can advise the WEBRTC group about appropriate
values, but in practice, the result is indistinguishable from your
formulation :-)

> In this case, as I have stated before, the maximum tone duration should
> be 8000 ms to match possible tone duration for RFC 2833 DTMF tone. RFC
> 2833 was in use for the past 15 years and no one reported any issues
> with this limit.
> 
> Minimum tone duration of 40 ms and minimum gap duration of 30 ms are
> minimum physically required to transmit DTMF tone as 8 KHz audio signal
> and still satisfy the talk-off specifications. These limitations have
> not caused any practical issues for the past 50 years. I would like to
> mention that shorter tones are used during call setup since it can be
> guaranteed that no audio signal is present and talk-off requirements are
> relaxed. Furthermore VoIP only networks, which use RFC 2833/RFC 4733
> tones, can support tones and gaps of anything from 0 ms and up. This is
> why I initially advocated for 0 ms min duration. On the other hand if
> the group decides that removing one more potential foot gun is more
> important, I will not be too upset.
> 
> If anybody can come up with the practical example where tones longer
> then 8 sec or shorter then 40 ms with less then 30 ms gaps are used,
> please report them to the list. Otherwise, let's document what is in W3C
> TR and move on.

Sounds good.