A Real-time Transport Protocol (RTP) Header Extension for Client-to-Mixer Audio Level Indication
draft-ietf-avtext-client-to-mixer-audio-level-06

[Ballot comment]
This new text " or could dominate a conference (by seizing its
speaker-selection algorithm) without actually speaking."
misses the issue I was pointing to just a little. I would
expect the speaker to actually be speaking, but asking his
endpoint to exaggerate (perhaps all the time) when indicating
how much energy he's speaking with, so that speaker selection
algorithms will always choose him. Please consider adjusting
this text to call that potential out.

[Ballot discuss]
Updating now that I've heard why we don't need the pre5378 boilerplate:

Several paragraphs in this document are heavily influenced by RFC3389.

One bit of borrowed text speaks of expressing audio level "relative to the overload point of the system". Even though that text exists in 3349, I'm not sure it's as clear as it needs to be. What is "the system" in this context, and where are its boundaries?

The first full paragraph on page 5 (beginning "The audio level header extension only carries the level of the audio in...) works well for payload formats that are a sequence of samples, but I'm not sure the description works as well for encodings that are more intricate. Are implementations expected to reconstruct the equivalent of a PCM encoding from whatever encoding is in use to calculate this level value? The section later talks about how redundant data (2198) wouldn't affect the level measure. Shouldn't it also say something about error correcting bits or information used in some encodings for loss concealment also not affecting the measure?

[Ballot comment]
The Security Considerations section sketches a scenario where an attacker sends high level indications, but encoded audio that is actually silent to suppress other participant's audio. A more likely attack is one that sends high level indications just to seize any speaker-selection algorithm used by a conference system.

[Ballot discuss]
Several paragraphs in this document are heavily influenced by RFC3389 (some of the sentences are direct copies, others are copies with minor edits). Should this document use the pre5378 boilerplate?

One bit of borrowed text speaks of expressing audio level "relative to the overload point of the system". Even though that text exists in 3349, I'm not sure it's as clear as it needs to be. What is "the system" in this context, and where are its boundaries?

The first full paragraph on page 5 (beginning "The audio level header extension only carries the level of the audio in...) works well for payload formats that are a sequence of samples, but I'm not sure the description works as well for encodings that are more intricate. Are implementations expected to reconstruct the equivalent of a PCM encoding from whatever encoding is in use to calculate this level value? The section later talks about how redundant data (2198) wouldn't affect the level measure. Shouldn't it also say something about error correcting bits or information used in some encodings for loss concealment also not affecting the measure?

[Ballot comment]
"A malicious endpoint could choose to set the values in this header
  extension falsely, so as to falsely claim that audio or voice is or
  is not present.  It is not clear what could be gained by falsely
  claiming that audio is not present, but an endpoint falsely claiming
  that audio is present could perform a denial-of-service attack on an
  audio conference, so as to send silence to suppress other conference
  members' audio.  "

... you could also dominate the conversation by always claiming that you have strong audio present.

=======

This security  consideration from the mixer to client looks like it might be applicable

2.  Furthermore, the fact that audio level values would not be
      protected even in an SRTP session might be of concern in some
      cases where the activity of a particular participant in a
      conference is confidential.  Also, as discussed in
      [I-D.perkins-avt-srtp-vbr-audio], an attacker might be able to
      infer information about the conversation, possibly with phoneme-
      level resolution.

[Ballot comment]
"A malicious endpoint could choose to set the values in this header
  extension falsely, so as to falsely claim that audio or voice is or
  is not present.  It is not clear what could be gained by falsely
  claiming that audio is not present, but an endpoint falsely claiming
  that audio is present could perform a denial-of-service attack on an
  audio conference, so as to send silence to suppress other conference
  members' audio.  "

... you could also dominate the conversation by always claiming that you have strong audio present.

[Ballot comment]
(1) If vad can expose encrypted vbr, then why don't the security
considerations here say "if encrypting vbr and doing vad then you
MUST use apply commensurate protection to both"? I don't get the
logic in the current section 6 where it says "if encrypting vbr
and doing vad then you SHOULD use some additional mechanism" -
what's the exceptional case that justifies the SHOULD there and
why would you ever do something appreciably weaker or stronger?

(2) Is the alternative to srtp-encrypted-header-ext to use IPsec or
TLS or what? It'd be better to reference those since if you don't
then I don't get how srtp-encrypted-header-ext isn't a normative
reference? I'd suggest adding a reference to either TLS or IPsec,
whichever is more likely to be used.

IANA understands that, upon approval of this document, there is a single
IANA Action which must be completed.

In the RTP Compact Header Extensions sub-registry of the Real-Time
Transport Protocol (RTP) Parameters registry, located at:

http://www.iana.org/assignments/rtp-parameters

a new registration will be made as follows:

Extension URI: urn:ietf:params:rtp-hdrext:ssrc-audio-level
Description: Audio Level
Contact: jonathan@vidyo.com
Reference: [ RFC-to-be ]

IANA understands that this is the only actions required to be completed
upon approval of this document.

State changed to In Last Call from Last Call Requested.

The following Last Call Announcement was sent out:

From: The IESG
To: IETF-Announce
CC:
Reply-To: ietf@ietf.org
Subject: Last Call:  (A Real-Time Transport Protocol (RTP) Header Extension for Client-to- Mixer Audio Level Indication) to Proposed Standard


The IESG has received a request from the Audio/Video Transport Extensions
WG (avtext) to consider the following document:
- 'A Real-Time Transport Protocol (RTP) Header Extension for Client-to-
  Mixer Audio Level Indication'
  as a Proposed
Standard

The IESG plans to make a decision in the next few weeks, and solicits
final comments on this action. Please send substantive comments to the
ietf@ietf.org mailing lists by 2011-10-04. Exceptionally, comments may be
sent to iesg@ietf.org instead. In either case, please retain the
beginning of the Subject line to allow automated sorting.

Abstract


  This document defines a mechanism by which packets of Real-Time
  Transport Protocol (RTP) audio streams can indicate, in an RTP header
  extension, the audio level of the audio sample carried in the RTP
  packet.  In large conferences, this can reduce the load on an audio
  mixer or other middlebox which wants to forward only a few of the
  loudest audio streams, without requiring it to decode and measure
  every stream that is received.




The file can be obtained via
http://datatracker.ietf.org/doc/draft-ietf-avtext-client-to-mixer-audio-level/

IESG discussion can be tracked via
http://datatracker.ietf.org/doc/draft-ietf-avtext-client-to-mixer-audio-level/


No IPR declarations have been submitted directly on this I-D.

Proto writeup for "A Real-Time Transport Protocol (RTP) Header
Extension for Client-to-Mixer Audio Level Indication", draft-ietf-
avtext-client-to-mixer-audio-level-04 as proposed standard

  (1.a) Who is the Document Shepherd for this document? Has the
        Document Shepherd personally reviewed this version of the
        document and, in particular, does he or she believe this
        version is ready for forwarding to the IESG for publication?

Keith Drage is the document shepherd. The document has had extensive
review and is ready for forwarding to the IESG for publication.

  (1.b) Has the document had adequate review both from key WG members
        and from key non-WG members? Does the Document Shepherd have
        any concerns about the depth or breadth of the reviews that
        have been performed? 

The history of the document is as follows:

- draft-lennox-avt-rtp-audio-level-exthdr-00 was submitted 17th
June 2009 and expired 19th December 2009.
- draft-lennox-avt-rtp-audio-level-exthdr-00 was submitted 20th
October 2009 and expired 23rd April 2010.
- draft-lennox-avt-rtp-audio-level-exthdr-02 was submitted 11th
July 2010 and expired 12th January 2011.
- draft-ietf-avtext-client-to-mixer-audio-level-00 was
submitted 18th February 2011 and expires 22nd August 2011.
- draft-ietf-avtext-client-to-mixer-audio-level-01 was
submitted 14th March 2011 and expires 15th September 2011.
- draft-ietf-avtext-client-to-mixer-audio-level-02 was
submitted 2nd June 2011 and expires 4th December 2011.
- draft-ietf-avtext-client-to-mixer-audio-level-03 was
submitted 5th July 2011 and expires 6th January 2012.
- draft-ietf-avtext-client-to-mixer-audio-level-04 was
submitted 27th August 2011 and expires 28th February 2012.

The document was originally targetted at the AVT working group, and
with the split of the charter of AVT into 4 new groups, fell within
the scope of the AVTEXT working group.

The document was adopted by the AVTEXT working group on 14th February
2011. WGLC was initiated 6th July 2011 to complete 20th July 2011 on -
03 version as proposed standard. Working group last call comments
were received from Keith Drage, Magnus Westerlund, Kevin Fleming.
Indications were received from the following that they had read the
document and that it was ready to go: Stephan Wenger, John Elwell,
Peter Musgrave. An indication was also taken in the AVTEXT face to
face meeting and 10 - 15 people identified they had read and were OK
with the WGLC version.

There are no concerns about the depth or breadth of review.

  (1.c) Does the Document Shepherd have concerns that the document
        needs more review from a particular or broader perspective,
        e.g., security, operational complexity, someone familiar with
        AAA, internationalization or XML?

The document contains an SDP extension that has been reviewed by
experts from the MMUSIC working group (specifically Miguel Garcia).

  (1.d) Does the Document Shepherd have any specific concerns or
        issues with this document that the Responsible Area Director
        and/or the IESG should be aware of? For example, perhaps he
        or she is uncomfortable with certain parts of the document,
or
        has concerns whether there really is a need for it. In any
        event, if the WG has discussed those issues and has indicated
        that it still wishes to advance the document, detail those
        concerns here. Has an IPR disclosure related to this document
        been filed? If so, please include a reference to the
        disclosure and summarize the WG discussion and conclusion on
        this issue.

There are no specific concerns or issues with this document.

No IPR disclosures have been made against this document or its
predecessors.

  (1.e) How solid is the WG consensus behind this document? Does it
        represent the strong concurrence of a few individuals, with
        others being silent, or does the WG as a whole understand and
        agree with it? 

The document has WG concensus and appears to be well supported.

  (1.f) Has anyone threatened an appeal or otherwise indicated
extreme
        discontent? If so, please summarise the areas of conflict in
        separate email messages to the Responsible Area Director. (It
        should be in a separate email because this questionnaire is
        entered into the ID Tracker.)

There has been no issues for appeal or otherwise discontent
identified during the discussion.

  (1.g) Has the Document Shepherd personally verified that the
        document satisfies all ID nits? (See the Internet-Drafts
Checklist
        and http://tools.ietf.org/tools/idnits/). Boilerplate checks
are
        not enough; this check needs to be thorough. Has the document
        met all formal review criteria it needs to, such as the MIB
        Doctor, media type and URI type reviews?

Apart from the MMUSIC review already mentioned, no other external
reviews have been identified as necessary for this document.

The document was checked with idnits 2.12.12 and no issues were
identified. There is one outdated reference to a document which is
proceeding in parallel to this document.

  (1.h) Has the document split its references into normative and
        informative? Are there normative references to documents that
        are not ready for advancement or are otherwise in an unclear
        state? If such normative references exist, what is the
        strategy for their completion? Are there normative references
        that are downward references, as described in [RFC3967]? If
        so, list these downward references to support the Area
        Director in the Last Call procedure for them [RFC3967].

The document has split its references into normative and informative
references, and these references have been checked to be in the
appropriate group.

There is an informative reference to an unpublished document, draft-
lennox-avtcore-srtp-encrypted-header-ext, and the final publication
of this document should be held until this document receives an RFC
number. Similarly draft-ietf-avtext-client-to-mixer-audio-level
should also receive an RFC number before this document is published.
Publication should not wait for other unpublished documents.

  (1.i) Has the Document Shepherd verified that the document IANA
        consideration section exists and is consistent with the body
        of the document? If the document specifies protocol
        extensions, are reservations requested in appropriate IANA
        registries? Are the IANA registries clearly identified? If
        the document creates a new registry, does it define the
        proposed initial contents of the registry and an allocation
        procedure for future registrations? Does it suggest a
        reasonable name for the new registry? See [RFC5226]. If the
        document describes an Expert Review process has Shepherd
        conferred with the Responsible Area Director so that the IESG
        can appoint the needed Expert during the IESG Evaluation?

The document makes one entry to the RTP Compact Header Extensions
subregistry of the Real-Time Transport Protocol (RTP) Parameters
registry and this is defined in the document in an IANA
considerations section. The registration requirement for this
registry is Expert Review which may be considered to have already
occurred, AVTEXT and MMUSIC being the appropriate expert working
groups.

  (1.j) Has the Document Shepherd verified that sections of the
        document that are written in a formal language, such as XML
        code, BNF rules, MIB definitions, etc., validate correctly in
        an automated checker?

The document contains no formal language to validate.

  (1.k) The IESG approval announcement includes a Document
        Announcement Write-Up. Please provide such a Document
        Announcement Write-Up? Recent examples can be found in the
        "Action" announcements for approved documents. The approval
        announcement contains the following sections:
    Technical Summary
        Relevant content can frequently be found in the abstract
        and/or introduction of the document. If not, this may be
        an indication that there are deficiencies in the abstract
        or introduction.
    Working Group Summary
        Was there anything in WG process that is worth noting? For
        example, was there controversy about particular points or
        were there decisions where the consensus was particularly
        rough?
    Document Quality
        Are there existing implementations of the protocol? Have a
        significant number of vendors indicated their plan to
        implement the specification? Are there any reviewers that
        merit special mention as having done a thorough review,
        e.g., one that resulted in important changes or a
        conclusion that the document had no substantive issues? If
        there was a MIB Doctor, Media Type or other expert review,
        what was its course (briefly)? In the case of a Media Type
        review, on what date was the request posted?

This document defines a mechanism by which packets of Real-Time
Transport Protocol (RTP) audio streams can indicate, in an RTP header
extension, the audio level of the audio sample carried in the RTP
packet.  In large conferences, this can reduce the load on an audio
mixer or other middlebox which wants to forward only a few of the
loudest audio streams, without requiring it to decode and measure
every stream that is received.

The document is a product of the AVTEXT working group.

Vidyo has a working implementation of this internet-draft.