Subject: [rtcweb] Comments on draft-ietf-rtcweb-audio-03

From: Magnus Westerlund <[email-masked]>
Date: Wed, 22 Jan 2014 16:28:57 +0100

WG and Authors,
(As Individual)

I have reviewed this draft and have some comments.

1. Section 3:
 o  G.711 PCMA and PCMU with one channel, a rate of 8000 Hz and a
      ptime of 20 - see section 4.5.14 of [RFC3551]

Especially in regards to amount of data packetized in each RTP payload
this is fairly narrow definition. Wouldn't the interoperability gain to
at least require wider receiver capabilities?

2. Section 3:
 o  Telephone Event - [RFC4733]

Maybe one should be more explicit about which RTP payload format one is
expected to support. As RFC 4733 contains two. Do I assume correctly
that only audio/telephone-event is to be supported?

In addition considering that this payload format can carry any of the
events listed in the event registry:
http://www.iana.org/assignments/audio-telephone-event-registry/audio-telephone-event-registry.xhtml#audio-telephone-event-registry-1

I think the events that an endpoint shall be capable of generating and
consume needs to be explicitly listed.

3. Section 4:

   AUTHORS' NOTE: The idea of using the same level as what the ITU-T
   recommends is that it should improve inter-operability while at the
   same time maintaining sufficient dynamic range and reducing the risk
   of clipping.  The main drawbacks are that the resulting level is
   about 12 dB lower than typical "commercial music" levels and it
   leaves room for ill-behaved clients to be much louder than a normal
   client.  While using music-type levels is not really an option (it
   would require using the same compressor-limitors that studios use),
   it would be possible to have a level slightly higher (e.g.  3 dB)
   than what is recommended above without causing interoperability
   problems.

The WG needs to resolve this Author's note before we can go to WG last
call. I would hope that we would be able to go to WG last call after the
next update. Thus, anyone have feedback on this? If no one have input, I
would suggest that we remove the note and leave the recommendation as it
is.

4. Section 8.

Can you please be more specific to what is relevant for this document in
regards to the security considerations. I assume confidentiality, source
authentication are the two main issues. Anything else that needs to be
included?

5. Section 10.

[I-D.ekr-security-considerations-for-rtc-web] needs to be updated to the
latest version.

Cheers

Magnus Westerlund

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From: Jean-Marc Valin <[email-masked]>
Date: Mon, 27 Jan 2014 17:33:07 -0500

Hi Magnus,

We just posted a new version of the draft, see
http://tools.ietf.org/html/draft-ietf-rtcweb-audio-04

See more below.

> at least require wider receiver capabilities?

Changed this to "any ptime up to 120 ms" to match Opus.

> consume needs to be explicitly listed.

This part was clarified. Let us know if there's any more issue.

> would suggest that we remove the note and leave the recommendation as it

Note removed. I haven't heard of anyone disagreeing so far.

> authentication are the two main issues. Anything else that needs to be

Added a link to RFC6562 on the VBR issue and made it clear that
encryption and authentication were out of scope here.

> [I-D.ekr-security-considerations-for-rtc-web] needs to be updated to the

Removed the reference since it wasn't relevant to this draft.

Cheers,

	Jean-Marc