Sending RTP Control Protocol (RTCP) Feedback for Congestion Control in Interactive Multimedia Conferences
RFC 9392

Received changes through RFC Editor sync (created alias RFC 9392, changed abstract to 'This memo discusses the rate at which congestion control feedback can be sent using the RTP Control Protocol (RTCP) and the suitability of RTCP for implementing congestion control for unicast multimedia applications.', changed pages to 17, changed standardization level to Informational, changed state to RFC, added RFC published event at 2023-04-26, changed IESG state to RFC Published)

[Ballot comment]
# GEN AD review of draft-ietf-rmcat-rtp-cc-feedback-11

CC @larseggert

Thanks to Linda Dunbar for the General Area Review Team (Gen-ART) review
(https://mailarchive.ietf.org/arch/msg/gen-art/IlQmtbncyGJ1B6qPc-IdbuGSqEA).

## Nits

All comments below are about very minor potential issues that you may choose to
address in some way - or ignore - as you see fit. Some were flagged by
automated tools (via https://github.com/larseggert/ietf-reviewtool), so there
will likely be some false positives. There is no need to let me know what you
did with these suggestions.

### Boilerplate

Document still refers to the "Simplified BSD License", which was corrected in
the TLP on September 21, 2021. It should instead refer to the "Revised BSD
License".

### Outdated references

Document references `draft-ietf-tcpm-RFC793bis`, but that has been published as
`RFC9293`.

### Grammar/style

#### Section 2, paragraph 6
```
e feedback and data packets are sent and the feedback is similar in size to
                                    ^^^^
```
Use a comma before "and" if it connects two independent clauses (unless they
are closely connected and short).

## Notes

This review is in the ["IETF Comments" Markdown format][ICMF], You can use the
[`ietf-comments` tool][ICT] to automatically convert this review into
individual GitHub issues. Review generated by the [`ietf-reviewtool`][IRT].

[ICMF]: https://github.com/mnot/ietf-comments/blob/main/format.md
[ICT]: https://github.com/mnot/ietf-comments
[IRT]: https://github.com/larseggert/ietf-reviewtool

[Ballot comment]
Thanks for an interesting read. One question --

### Section 3.2

I don't quite follow what you mean by "frame of packet" in

```
  Assume
  that video has constant bit rate and frame rate, and that each frame
  of packet has to fit into a 1500 octet MTU. 
```

Presumably "frame rate" means video frames, not network frames. But "frame of packet"?

[Ballot comment]
Thanks for this document, while I am not a transport person, it was readable and clearly written.

I can only regret the exclusive use of IPv4 in the tables, especially for VoIP where the larger IPv6 header could have a more negative impact.

Please do like in section 3.1 for the section 3.2 text "The RTCP SR packet contains the 28 octet header and sender" (i.e., specify IPv4 no IP options).

Regards

-éric

[Ballot comment]
Thank you to Linda Dunbar for the SECDIR review.

Section 3.1.  Per “A rate adaptive speech codec, such as Opus ...”, please provide a reference for “Opus”.

[Ballot comment]
It caught my attention that this document has no Normative references, which are documents "that must be read to understand...the technology in the new RFC" [1].

In this case, it looks like most of the RFCs cited in the Introduction should be Normative:

  The deployment of WebRTC systems [RFC8825] has resulted in high-
  quality video conferencing seeing extremely wide use.  ...

  To develop such congestion control, it is necessary to understand the
  sort of congestion feedback that can be provided within the framework
  of RTP [RFC3550] and the RTP Control Protocol (RTCP).  It then
  becomes possible to determine if this is sufficient for congestion
  control, or if some form of RTP extension is needed.

  This memo considers unicast congestion feedback that can be sent
  using RTCP under the RTP/SAVPF profile [RFC5124] (the secure version
  of the RTP/AVPF profile [RFC4585]).  This profile was chosen as it
  forms the basis for media transport in WebRTC [RFC8834] systems.
  Nothing in this memo is specific to the secure version of the
  profile, or to WebRTC, however.  It is also assumed that the
  congestion control feedback mechanism described in [RFC8888], and
  common RTCP extensions for efficient feedback [RFC5506], [RFC8108],
  [RFC8861], and [RFC8872] are used.



[1] https://www.ietf.org/about/groups/iesg/statements/normative-informative-references/

(Via drafts-lastcall@iana.org): IESG/Authors/WG Chairs:

The IANA Functions Operator has reviewed draft-ietf-rmcat-rtp-cc-feedback-10, which is currently in Last Call, and has the following comments:

We understand that this document doesn't require any registry actions.

While it's often helpful for a document's IANA Considerations section to remain in place upon publication even if there are no actions, if the authors strongly prefer to remove it, we do not object.

If this assessment is not accurate, please respond as soon as possible.

For definitions of IANA review states, please see:

https://datatracker.ietf.org/help/state/draft/iana-review

Thank you,

Michelle Thangtamsatid
IANA Services Specialist

The following Last Call announcement was sent out (ends 2022-08-09):

From: The IESG
To: IETF-Announce
CC: Zaheduzzaman.Sarker@ericsson.com, anna.brunstrom@kau.se, draft-ietf-rmcat-rtp-cc-feedback@ietf.org, rmcat-chairs@ietf.org, rmcat@ietf.org
Reply-To: last-call@ietf.org
Sender:
Subject: Last Call:  (Sending RTP Control Protocol (RTCP) Feedback for Congestion Control in Interactive Multimedia Conferences) to Informational RFC


The IESG has received a request from the RTP Media Congestion Avoidance
Techniques WG (rmcat) to consider the following document: - 'Sending RTP
Control Protocol (RTCP) Feedback for Congestion Control in
  Interactive Multimedia Conferences'
  as Informational RFC

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
last-call@ietf.org mailing lists by 2022-08-09. 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 memo discusses the types of congestion control feedback that it
  is possible to send using the RTP Control Protocol (RTCP), and their
  suitability of use in implementing congestion control for unicast
  multimedia applications.




The file can be obtained via
https://datatracker.ietf.org/doc/draft-ietf-rmcat-rtp-cc-feedback/



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

# Document Shepherd Writeup

## Document History

1. Does the working group (WG) consensus represent the strong concurrence of a
  few individuals, with others being silent, or did it reach broad agreement?
 
There seems general, but not overwhelming, consensus from the working group that an informational document describing the ways the congestion control feedback can be sent can provide useful guidance for developers. 

2. Was there controversy about particular points, or were there decisions where
  the consensus was particularly rough?
 
No, there has been no controversy or disagreement around the document.

3. 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 publicly available.)

No, no one has threatened an appeal or otherwise indicated extreme discontent.

4. For protocol documents, are there existing implementations of the contents of
  the document? Have a significant number of potential implementers indicated
  plans to implement? Are any existing implementations reported somewhere,
  either in the document itself (as [RFC 7942][3] recommends) or elsewhere
  (where)?
 
N/A, it is not a protocol document.

### Additional Reviews

5. Does this document need review from other IETF working groups or external
  organizations? Have those reviews occurred?
 
During its development, the document was presented to and reviewed by members of the avtcore wg, in addition to the members of the rmcat wg. No need for additional review from other IETF working groups or external organizations has been identified.

6. Describe how the document meets any required formal expert review criteria,
  such as the MIB Doctor, YANG Doctor, media type, and URI type reviews.
 
N/A. The content of the document does not relate to any formal review criteria.

7. If the document contains a YANG module, has the final version of the module
  been checked with any of the [recommended validation tools][4] for syntax and
  formatting validation? If there are any resulting errors or warnings, what is
  the justification for not fixing them at this time? Does the YANG module
  comply with the Network Management Datastore Architecture (NMDA) as specified
  in [RFC 8342][5]?
 
N/A. The document does not contain a YANG module.

8. Describe reviews and automated checks performed to validate sections of the
  final version of the document written in a formal language, such as XML code,
  BNF rules, MIB definitions, CBOR's CDDL, etc.
 
N/A. The document does not use formal language.

### Document Shepherd Checks

9. Based on the shepherd's review of the document, is it their opinion that this
  document is needed, clearly written, complete, correctly designed, and ready
  to be handed off to the responsible Area Director?
 
The document shepherd has performed a detailed review of the text in the document and also checked part of the calculations presented in the document. The document shepherd believes that the document is useful, correct and generally well written. The smaller issues found during shepherd review relate to the presentation only, no technical issues were found. The documents is forwarded in its current version, as the editorial issues detected during shepherd review can be resolved along with any comments from the AD review.

10. Several IETF Areas have assembled [lists of common issues that their
    reviewers encounter][6]. Do any such issues remain that would merit specific
    attention from subsequent reviews?

No, no such issues remain.

11. What type of RFC publication is being requested on the IETF stream (Best
    Current Practice, Proposed Standard, Internet Standard, Informational,
    Experimental, or Historic)? Why is this the proper type of RFC? Do all
    Datatracker state attributes correctly reflect this intent?

The RFC is requested as Informational. This is the proper type, as the document does not provide a protocol specification, but rather information that can help protocol implementers. More specifically, it provides information on the types of congestion control feedback that can be used with the RTP Control Protocol when implementing congestion control for unicast multimedia applications. The Datatracker correctly indicate the document as informational.

12. Has the interested community confirmed that any and all appropriate IPR
    disclosures required by [BCP 78][7] and [BCP 79][8] have been filed? If not,
    explain why. If yes, summarize any discussion and conclusion regarding the
    intellectual property rights (IPR) disclosures, including links to relevant
    emails.

The author has confirmed that he does not know of any IPR relating to this draft.

13. Has each Author or Contributor confirmed their willingness to be listed as
    such? If the number of Authors/Editors on the front page is greater than 5,
    please provide a justification.

Yes.

14. Identify any remaining I-D nits in this document. (See [the idnits tool][9]
    and the checkbox items found in Guidelines to Authors of Internet-Drafts).
    Simply running the idnits tool is not enough; please review the entire
    guidelines document.

Informational references to other drafts should be updated to the latest version before publication. No other ID nits were identified.

15. Should any informative references be normative or vice-versa?

No, all references are correctly indicated as informative.

16. List any normative references that are not freely available to anyone. Did
    the community have sufficient access to review any such normative
    references?

The document does not contain any normative references.

17. Are there any normative downward references (see [RFC 3967][10],
    [BCP 97][11])? If so, list them.

No, the document does not contain any downward normative references.

18. Are there normative references to documents that are not ready for
    advancement or are otherwise in an unclear state? If they exist, what is the
    plan for their completion?

No, the document does not contain any normative references.

19. Will publication of this document change the status of any existing RFCs? If
    so, does the Datatracker metadata correctly reflect this and are those RFCs
    listed on the title page, in the abstract, and discussed in the
    introduction? If not, explain why and point to the part of the document
    where the relationship of this document to these other RFCs is discussed.

No, publication of this document does not change the status of any existing RFCs.

20. Describe the document shepherd's review of the IANA considerations section,
    especially with regard to its consistency with the body of the document.
    Confirm that all aspects of the document requiring IANA assignments are
    associated with the appropriate reservations in IANA registries. Confirm
    that any referenced IANA registries have been clearly identified. Confirm
    that each newly created IANA registry specifies its initial contents,
    allocations procedures, and a reasonable name (see [RFC 8126][12]).

As indicated in the IANA considerations section, the document does not involve any IANA actions.

21. List any new IANA registries that require Designated Expert Review for
    future allocations. Are the instructions to the Designated Expert clear?
    Please include suggestions of designated experts, if appropriate.

N/A. The document does not involve any IANA actions.

# Document Shepherd Writeup

## Document History

1. Does the working group (WG) consensus represent the strong concurrence of a
  few individuals, with others being silent, or did it reach broad agreement?
 
There seems general, but not overwhelming, consensus from the working group that an informational document describing the ways the congestion control feedback can be sent can provide useful guidance for developers. 

2. Was there controversy about particular points, or were there decisions where
  the consensus was particularly rough?
 
No, there has been no controversy or disagreement around the document.

3. 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 publicly available.)

No, no one has threatened an appeal or otherwise indicated extreme discontent.

4. For protocol documents, are there existing implementations of the contents of
  the document? Have a significant number of potential implementers indicated
  plans to implement? Are any existing implementations reported somewhere,
  either in the document itself (as [RFC 7942][3] recommends) or elsewhere
  (where)?
 
N/A, it is not a protocol document.

### Additional Reviews

5. Does this document need review from other IETF working groups or external
  organizations? Have those reviews occurred?
 
During its development, the document was presented to and reviewed by members of the avtcore wg, in addition to the members of the rmcat wg. No need for additional review from other IETF working groups or external organizations has been identified.

6. Describe how the document meets any required formal expert review criteria,
  such as the MIB Doctor, YANG Doctor, media type, and URI type reviews.
 
N/A. The content of the document does not relate to any formal review criteria.

7. If the document contains a YANG module, has the final version of the module
  been checked with any of the [recommended validation tools][4] for syntax and
  formatting validation? If there are any resulting errors or warnings, what is
  the justification for not fixing them at this time? Does the YANG module
  comply with the Network Management Datastore Architecture (NMDA) as specified
  in [RFC 8342][5]?
 
N/A. The document does not contain a YANG module.

8. Describe reviews and automated checks performed to validate sections of the
  final version of the document written in a formal language, such as XML code,
  BNF rules, MIB definitions, CBOR's CDDL, etc.
 
N/A. The document does not use formal language.

### Document Shepherd Checks

9. Based on the shepherd's review of the document, is it their opinion that this
  document is needed, clearly written, complete, correctly designed, and ready
  to be handed off to the responsible Area Director?
 
The document shepherd has performed a detailed review of the text in the document and also checked part of the calculations presented in the document. The document shepherd believes that the document is useful, correct and generally well written. The smaller issues found during shepherd review relate to the presentation only, no technical issues were found. The documents is forwarded in its current version, as the editorial issues detected during shepherd review can be resolved along with any comments from the AD review.

10. Several IETF Areas have assembled [lists of common issues that their
    reviewers encounter][6]. Do any such issues remain that would merit specific
    attention from subsequent reviews?

No, no such issues remain.

11. What type of RFC publication is being requested on the IETF stream (Best
    Current Practice, Proposed Standard, Internet Standard, Informational,
    Experimental, or Historic)? Why is this the proper type of RFC? Do all
    Datatracker state attributes correctly reflect this intent?

The RFC is requested as Informational. This is the proper type, as the document does not provide a protocol specification, but rather information that can help protocol implementers. More specifically, it provides information on the types of congestion control feedback that can be used with the RTP Control Protocol when implementing congestion control for unicast multimedia applications. The Datatracker correctly indicate the document as informational.

12. Has the interested community confirmed that any and all appropriate IPR
    disclosures required by [BCP 78][7] and [BCP 79][8] have been filed? If not,
    explain why. If yes, summarize any discussion and conclusion regarding the
    intellectual property rights (IPR) disclosures, including links to relevant
    emails.

The author has confirmed that he does not know of any IPR relating to this draft.

13. Has each Author or Contributor confirmed their willingness to be listed as
    such? If the number of Authors/Editors on the front page is greater than 5,
    please provide a justification.

Yes.

14. Identify any remaining I-D nits in this document. (See [the idnits tool][9]
    and the checkbox items found in Guidelines to Authors of Internet-Drafts).
    Simply running the idnits tool is not enough; please review the entire
    guidelines document.

Informational references to other drafts should be updated to the latest version before publication. No other ID nits were identified.

15. Should any informative references be normative or vice-versa?

No, all references are correctly indicated as informative.

16. List any normative references that are not freely available to anyone. Did
    the community have sufficient access to review any such normative
    references?

The document does not contain any normative references.

17. Are there any normative downward references (see [RFC 3967][10],
    [BCP 97][11])? If so, list them.

No, the document does not contain any downward normative references.

18. Are there normative references to documents that are not ready for
    advancement or are otherwise in an unclear state? If they exist, what is the
    plan for their completion?

No, the document does not contain any normative references.

19. Will publication of this document change the status of any existing RFCs? If
    so, does the Datatracker metadata correctly reflect this and are those RFCs
    listed on the title page, in the abstract, and discussed in the
    introduction? If not, explain why and point to the part of the document
    where the relationship of this document to these other RFCs is discussed.

No, publication of this document does not change the status of any existing RFCs.

20. Describe the document shepherd's review of the IANA considerations section,
    especially with regard to its consistency with the body of the document.
    Confirm that all aspects of the document requiring IANA assignments are
    associated with the appropriate reservations in IANA registries. Confirm
    that any referenced IANA registries have been clearly identified. Confirm
    that each newly created IANA registry specifies its initial contents,
    allocations procedures, and a reasonable name (see [RFC 8126][12]).

As indicated in the IANA considerations section, the document does not involve any IANA actions.

21. List any new IANA registries that require Designated Expert Review for
    future allocations. Are the instructions to the Designated Expert clear?
    Please include suggestions of designated experts, if appropriate.

N/A. The document does not involve any IANA actions.