[Ballot comment]
One thought to explore if it hasn't been already: If an attacker can inject post-repair reports and also induce loss of the RTP, then the processing at the sending endpoint could be convinced that no remedial changes are necessary (due to loss) when, in fact, they should be made. This would only be effective if no other feedback exposed the problem.

[Ballot comment]
1. It is not clear to me what item in the AVT WG charter this document is covering. I see that two new metric blocks are to be defined, one for  high resolution measurements of audio and speech quality and the second for quality of video, but it is not clear where does this document and a number of other of this WG I-Ds fit.

2. It would be useful to clarify whether the applicability statements defined in RFC 3611 for packet-by-packet reporting blocks fully apply to the new block defined in this document and what are the differences if there are such differences. What is the applicability for network monitoring purposes?

[Ballot discuss]
This is a minor point I would like to see fixed before I recommend approving of this document:

4.  Session Description Protocol Signaling

  A new parameter is defined for the Post-repair Loss RLE Report Block
  to be used with Session Description Protocol (SDP) [RFC4566].  It has
  the following syntax within the "rtcp-xr" attribute:

This doesn't specify what kind of syntax is used for the definition. I think you meant RFC 5234. This would need to become a normative reference.

      rtcp-xr-attrib = "a=rtcp-xr:" [xr-format *(SP xr-format)] CRLF

This just seem to be repeating the definition from Section 5.1 of RFC 3611.

            xr-format = "post-repair-loss-rle" ["=" max-size]

This rule should be using the "=/" ABNF rule, as it is adding another choice. (At least this is my understanding.)

            max-size  = 1*DIGIT ; maximum block size in octets
            DIGIT    = %x30-39
            CRLF      = %d13.10

(Comment) There is no need to define DIGIT/CRLF, they are defined in RFC 5234.

[Ballot discuss]
The Gen-ART Review by Brian Carpenter posted on 15-Dec-2008 raised a
  question that I think should be answered in the document.

  The document says:
  >
  >  o  thinning (T):  4 bits
  >      The amount of thinning performed on the sequence number space.
  >
  And, Brian asks:
  Is there any value in suggesting that T should be identical for
  Pre-repair and Post-repair Loss RLE Reports?  That would seem to
  make pre- and post- comparisons more meaningful.
 
  The authors respond:
  While having an identical T value in both pre- and post-repair reports
  would simplify the comparison, it seems a better idea to me not to
  mandate it.  Depending on the scenario, different T values may be
  needed and/or be more useful in pre- and post-repair reports.  At the
  end, using identical T values is still perfectly OK.

[Ballot discuss]
1. It is not clear to me what item in the AVT WG charter this document is covering. I see that two new metric blocks are to be defined, one for  high resolution measurements of audio and speech quality and the second for quality of video, but it is not clear where does this document and a number of other of this WG I-Ds fit.

2. It would be useful to clarify whether the applicability statements defined in RFC 3611 for packet-by-packet reporting blocks fully apply to the new block defined in this document and what are the differences if there are such differences. What is the applicability for network monitoring purposes? Are there any supplementary concerns about bandwidth usage and do the methods for limitation described in RFC 3611 apply?

[Ballot comment]
During the fall we had a discussion about the issue of RTP sequence number wrap around. I did accept the decision to not expand the numberspace. However, I think there still should be a warning about this issue, and the need for senders to take care of this issue. Can you please add a paragraph or so about it?

[Ballot discuss]
I think Tim's comment should be elavated to a Discuss due to that there are clear differences on what information the RTCP XR report block type provide. There is clear differences if the regular loss RLE is present or not. I think both usages has its point.

Because of the potential for different security solutions for RTP it is important that extensions clearly express the threats and requirements on any security solution that protects a RTP session with this extension in use. I would also recommend (not mandate) the usage of SRTP if that fulfills the requirements.

[Ballot comment]
The security considerations are a one sentence pointer to RFC 3611.  While the RFC 3611
considerations do apply, it would be helpful if this document noted any considerations
unique to this report block, as with the security considerations for the Loss RLE report block
in RFC 3611.  Without this information, the reader might infer that the security considerations
are the same as for Loss RLE, which I don't think is true...

It seems that this extension is intended for use in addition to the Loss RLE Report Block.  I also
assume that the Loss RLE and Post Repair Loss RLE report blocks are protected by the same
security mechanisms.  In this case, the only additional information that is revealed is the
overall effectiveness of the loss repair mechanisms.  That is, unlike the Loss RLE report
block, this extension does not facilitate multicast inference of network characteristics (MINC)
since any useful information has already been revealed.

The open question is whether knowledge of the effectiveness of repair mechanisms on a
particular system is helpful to an attacker.  (I would guess that it could be useful, but I will
leave that up to the RTCP experts.)

[Ballot comment]
It would be nice if the security considerations noted any considerations unique to this
report block, as in RFC 3611.

It seems that this extension is intended for use in addition to the Loss RLE Report Block.  I also
assume that the Loss RLE and Post Repair Loss RLE report blocks are protected by the same
security mechanisms.  In this case, the only additional information that is revealed is the
overall effectiveness of the loss repair mechanisms.  That is, unlike the Loss RLE report
block, this extension does not facilitate multicast inference of network characteristics (MINC)
since any useful information has already been revealed.

The open question is whether knowledge of the effectiveness of repair mechanisms on a
particular system is helpful to an attacker.  (I would guess that it could be useful, but I will
leave that up to the RTCP experts.)

IANA comments:

Action 1:

Upon approval of this document, IANA will make the following
assignments in the "RTP Control Protocol Extended Reports (RTCP
XR) Block Type Registry" at
http://www.iana.org/assignments/rtcp-xr-block-types/rtcp-xr-block-types.xhtml

BT Name Reference
-- ---- ---------
TBD(10) Post-repair Loss RLE Report Block [RFC-avt-post-repair-rtcp-xr-04]


Action 2:

Upon approval of this document, IANA will make the following
assignments in the "RTP Control Protocol Extended Reports (RTCP
XR) Session Description Protocol (SDP) Parameters Registry" at
http://www.iana.org/assignments/rtcp-xr-sdp-parameters/rtcp-xr-sdp-parameters.xhtml

Parameter Reference
--------- ---------
rtcp-xr [RFC-avt-post-repair-rtcp-xr-04]


We understand the above to be the only IANA Actions for this document.

    (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?

The document shepherd is Roni Even. I have reviewed the document, 
and believe it is ready 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?

This document defines a new report block type within the framework of  RTP
Control Protocol (RTCP) Extended Reports (XR) (RFC 3611). The document went
through a long WGLC. It was reviewed by assigned reviewers including authors
of RFC3611 and the latest revision was given sufficient time for review. The
document shepherd has no concerns about the review process.

    (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?

No concerns. The document defines a new report block type to RFC3611.

    (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.

No concerns. There is no disclosed IPR on this document.

    (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 good consensus from the WG.

    (1.f)  Has anyone threatened an appeal or otherwise indicated 
          extreme discontent?  If so, please summarize 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.)

No.

    (1.g)  Has the Document Shepherd personally verified that the
          document satisfies all ID nits?  (See
          http://www.ietf.org/ID-Checklist.html 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?

The document does not have the new boiler plate required from December 16,
2008.

No other nits.

    (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].

References have been split. There are no normative references to 
internet-drafts, and no normative down-references.

    (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 [RFC2434].  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 IANA considerations exist, and are consistent with the document.

    (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?

No such sections.

    (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.

This document defines a new report block type within the framework of RTP
Control Protocol (RTCP) Extended Reports (XR).  One of the initial XR report
block types is the Loss Run Length Encoding (RLE) Report Block.  This report
conveys the information regarding the individual Real-time Transport
Protocol (RTP) packet receipt and loss events experienced during the RTCP
interval preceding the transmission of the report.  The new report, which is
referred to as the Post-repair Loss RLE Report, carries the information
regarding the remaining lost packets after all loss-repair methods are
applied.  By comparing the RTP packet receipts/losses before and after the
loss repair is completed, one can determine the effectiveness of the
loss-repair methods in an aggregated fashion.  This document also defines
the signaling of the Post-repair Loss RLE Report in the Session Description
Protocol (SDP). 

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?

The document has been reviewed by the AVT working group to ensure
consistency with RTCP XR.

            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?

There are implementations of RTCP-XR and this draft adds a new report type.
The document was reviewed by Alan Clark and Geoff Hunt, both have been
involved with the RTCP-XR work.

          Personnel
              Who is the Document Shepherd for this document?  Who is 
              the Responsible Area Director?

Roni Even is the document shepherd.