Coupled Congestion Control for RTP Media
draft-ietf-rmcat-coupled-cc-09

[Ballot comment]
Editorial:

age 1:    The first sentence: “When multiple congestion controlled RTP sessions...”. 

I suggest expanding the “RTP”, like Real-time Transport Protocol (RTP), since it first appear in the document.



Page 1:    The last sentence: “It specifies how to apply the method for the NADA congestion control...”. 

I suggest expanding the “NADA”, like Network-Assisted Dynamic Adaptation (NADA). The reason same to above item.



Page 3:    The first paragraph: “sometimes the rate is increased further, until packets are ECN-marked or dropped.”

            I suggest adding a reference to help the readers understanding “ECN-marked”.


Page 3:    Suggest adding a term definition: “Flow State Identifiers (FSIs)” which be used in section 4 but not be introduced in the section 2 Definitions.



Page 11:    6.1 NADA -- " Network-Assisted Dynamic Adapation (NADA) [I-D.ietf-rmcat-nada] is a congestion control scheme for rtcweb."

I suggest adding a reference or some sentence to help the readers understand the “rtcweb”.





A run of idnits revealed there were 0 error, 3 warning and 2 comments:



  Miscellaneous warnings:

  ----------------------------------------------------------------------------



  -- The document date (March 28, 2017) is 140 days in the past.  Is this

    intentional?



  -- Found something which looks like a code comment -- if you have code

    sections in the document, please surround them with '' and

    '' lines.





  Checking references for intended status: Experimental

  ----------------------------------------------------------------------------



  == Outdated reference: A later version (-04) exists of

    draft-ietf-rmcat-nada-03



  == Outdated reference: A later version (-05) exists of

    draft-ietf-rmcat-eval-test-04



  == Outdated reference: A later version (-08) exists of

    draft-ietf-rmcat-sbd-04





    Summary: 0 errors (**), 0 flaws (~~), 3 warnings (==), 2 comments (--).



    Run idnits with the --verbose option for more detailed information about

    the items above.

[Ballot comment]
I'm really glad to see this draft going forward. I do have comments, but they're mostly about clarity.

It would be good to expand NADA as "Network-Assisted Dynamic Adapation (NADA)" in the Abstract.

In the first paragraph of the Introduction,

  When there is enough data to send, a congestion controller must
  increase its sending rate until the path's capacity has been reached;
  depending on the controller, sometimes the rate is increased further,
  until packets are ECN-marked or dropped.  This process inevitably
  creates undesirable queuing delay when multiple congestion controlled
  connections traverse the same network bottleneck.
 
I'm not sure about "must increase its sending rate", but ignoring that, I think this paragraph is really saying

  When there is enough data to send, a congestion controller attempts to
  increase its sending rate until the path's capacity has been reached.
  Some controllers detect path capacity by increasing the sending rate
  further, until packets are ECN-marked or dropped, and then decreasing
  its sending rate until that stops happening. This process inevitably
  creates undesirable queuing delay when multiple congestion-controlled
  connections traverse the same network bottleneck, and each connection
  overshoots the path capacity as it determines its sending rate.
 
Do the right thing, of course.

I'm wondering if https://tools.ietf.org/html/rfc7478 is the right reference for rtcweb in the Introduction, since even the Abstract of that RFC says (paraphrasing) "this is what we thought about RTCWeb early in the process, and the document hasn't been updated as we worked on RTCWeb". I know that https://datatracker.ietf.org/doc/draft-ietf-rtcweb-overview/ has been in "Revised I-D Needed" substate for some time, but that might be more appropriate.

Do the right thing, of course.

I understand why "Shared bottlenecks do not change quickly:" is a limitation, but I'm not sure I understand why "Sender-side only:" is listed as a limitation in Section 3 - I've seen "sender-side only" as a strength for most of the time I've worked in TSV. It's worth pointing out as an attribute, and maybe even as a design goal, but that's not the way it's presented here.

I'm a little bit confused by

  This document describes both
  active and passive versions, however the passive version is put into
  the appendix as it is extremely experimental. 
 
in an Experimental RFC. Perhaps the point is that the passive version is less mature, or has received less analysis, or something? But I'm not sure from reading this whether you want people to experiment with the passive version, which would be the point of including it in an Experimental RFC.

And ... when I make it all the way to Appendix C, I find

  While the passive algorithm works better for congestion
  controls with RTT-independent convergence, it can still produce
  oscillations on short time scales.  The algorithm described below is
  therefore considered as highly experimental and not safe to deploy
  outside of testbed environments. 
 
which would have been good information to include in Section 4!

At a minimum, s/the appendix/Appendix C/, because there are multiple appendices ...

I'm struggling a bit with this text:

  Implementations can
  take various forms: for instance, all the elements in the figure
  could be implemented within a single application, thereby operating
  on flows generated by that application only.  Another alternative
  could be to implement both the FSE and SBD together in a separate
  process which different applications communicate with via some form
  of Inter-Process Communication (IPC).  Such an implementation would
  extend the scope to flows generated by multiple applications.  The
  FSE and SBD could also be included in the Operating System kernel.
 
because I'm reading ahead to Section 5.3, which says

  Below, two example algorithms are described.  While other algorithms
  could be used instead, the same algorithm must be applied to all
  flows. 
 
so, I'm wondering if there's a similar restriction that applies to how many implementations can co-exist with good results - if some of my flows are using an implementation that is specific to an application, others are using an implementation that's in a separate process, and still others are using an implementation within the OS kernel, is that supposed to work well? If not, that's worth mentioning in Section 4.

I'm not sure what "the latter method" is in this text:


  1.  From multiplexing: it can be based on the simple assumption that
      packets sharing the same five-tuple (IP source and destination
      address, protocol, and transport layer port number pair) and
      having the same values for the Differentiated Services Code Point
      (DSCP) and the ECN field in the IP header are typically treated
      in the same way along the path.  The latter method is the only
      one specified in this document: SBD MAY consider all flows that
      use the same five-tuple, DSCP and ECN field value to belong to
      the same FG. 
     
Did I miss other methods being previously mentioned? It looks like this is referring to "2.  Via configuration" and "3.  From measurements", but they haven't been mentioned at this point - so, "the latter method" probably isn't what you want to say. "This method" might be clearer.

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

The IANA Services Operator has reviewed draft-ietf-rmcat-coupled-cc-06, 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.

Thank you,

Sabrina Tanamal
IANA Services Specialist

The following Last Call announcement was sent out (ends 2017-08-28):

From: The IESG
To: IETF-Announce
CC: rmcat-chairs@ietf.org, Colin Perkins , rmcat@ietf.org, draft-ietf-rmcat-coupled-cc@ietf.org, ietf@kuehlewind.net, csp@csperkins.org
Reply-To: ietf@ietf.org
Sender:
Subject: Last Call:  (Coupled congestion control for RTP media) to Experimental RFC


The IESG has received a request from the RTP Media Congestion Avoidance
Techniques WG (rmcat) to consider the following document: - 'Coupled
congestion control for RTP media'
  as Experimental 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
ietf@ietf.org mailing lists by 2017-08-28. 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


  When multiple congestion controlled RTP sessions traverse the same
  network bottleneck, combining their controls can improve the total
  on-the-wire behavior in terms of delay, loss and fairness.  This
  document describes such a method for flows that have the same sender,
  in a way that is as flexible and simple as possible while minimizing
  the amount of changes needed to existing RTP applications.  It
  specifies how to apply the method for the NADA congestion control
  algorithm, and provides suggestions on how to apply it to other
  congestion control algorithms.




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

IESG discussion can be tracked via
https://datatracker.ietf.org/doc/draft-ietf-rmcat-coupled-cc/ballot/


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

As required by RFC 4858, this is the current template for the Document
Shepherd Write-Up.

Changes are expected over time. This version is dated 24 February 2012.

(1) What type of RFC is being requested (BCP, Proposed Standard,
Internet Standard, Informational, Experimental, or Historic)?  Why
is this the proper type of RFC?  Is this type of RFC indicated in the
title page header?

  Experimental.

  This matches the working group milestone, and is appropriate since the
  proposed mechanisms have been evaluated in simulations and are believed
  safe, but have not yet been widely tested in real networks. See Section
  7 of the draft for discussion.

  The intended status is mentioned in the title page header.


(2) 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

  The RMCAT working group is developing congestion control schemes for use
  with RTP. When multiple such congestion controlled RTP flows traverse the
  same network bottleneck, combining their controls can improve the total
  on-the-wire behavior in terms of delay, loss and fairness.  This document
  describes such a method for flows that have the same sender, in a way
  that is as flexible and simple as possible while minimizing the amount of
  changes needed to existing RTP applications. It specifies how to apply
  the method for the NADA congestion control algorithm, and provides
  suggestions on how to apply it to other congestion control algorithms.

Working Group Summary

  The draft has been under development in the working group for some years.
  Much of the time was taken waiting for the candidate congestion control
  algorithms to stabilise, mapping the algorithms to the mechanisms given
  in this draft, and deciding which congestion control algorithms should be
  supported. The coupled congestion control algorithm itself has proved
  reasonably stable.
 
  The draft discusses how to apply coupled congestion control to NADA and
  Google Congestion Control. The mapping to NADA is in the main body of the
  draft, since NADA is nearing working group last call and believed stable.
  The mapping for Google Congestion Control is in an appendix, since Google
  Congestion Control is not yet finalised. There is no mapping for SCReAM
  at this time, but one could be added later if there was interest in doing
  so (nothing in SCReAM should prevent this).

  Overall, the working group process has been relatively smooth, although
  not rapid. The main issue of contention was the choice of congestion
  control algorithm to which the mechanism should be applied - based on
  the maturity of the candidate congestion control algorithms, and the
  relative importance the authors of the candidates placed on coupled
  congestion control.


Document Quality

  The algorithm has been implemented in simulations and emulated testbeds.
  This is appropriate for an experimental protocol of this type, and meets
  the usual community evaluation standards for transport protocol research.
  The draft has been reviewed by some authors of each candidate congestion
  control algorithm, with Xiaoqing Zhu and Stefan Holmer providing detailed
  reviews and advice on integration with the congestion control proposals.
  The draft is well written, and the mechanism is clearly specified.

  There is no need for MIB Doctor, Media Type, or other expert review,
  since the proposed mechanism relies only on common RTP features and
  parameters that can be directly measured by the end-point using the
  mechanism.


Personnel

  The document shepherd is Colin Perkins.
  The responsible AS is Mirja Kuehlewind.


(3) Briefly describe the review of this document that was performed by
the Document Shepherd.  If this version of the document is not ready
for publication, please explain why the document is being forwarded to
the IESG.

  The shepherd conducted a detailed review to ensure consistency in
  terminology, and to clarify a few points. See https://mailarchive.ietf.org/arch/msg/rmcat/H7E2agZrv-7BDqMrGyoWtZ_ZtbQ/?qid=b6b2bf182bd5a8c93a97c5695a6f0780
  and the follow-up discussion. The draft was in good shape after working
  group last call, and few issues were noted.


(4) Does the document Shepherd have any concerns about the depth or
breadth of the reviews that have been performed?

  No - the reviews and evaluation have been appropriate for an
  experimental proposal.


(5) Do portions of the document need review from a particular or from
broader perspective, e.g., security, operational complexity, AAA, DNS,
DHCP, XML, or internationalization? If so, describe the review that
took place.

  This is a heavily transport related draft, being focussed entirely
  on details of congestion control. Security considerations are adequate,
  although they will likely need elaboration for a future standards-track
  revision of this work in the light of operational experience. The draft
  says little about operational complexity, and the risks of cheating and
  poor quality implementations, but this will depend on the experiences
  with the protocol, and cannot effectively be done without experimentation
  and controlled deployment experience.


(6) Describe any specific concerns or issues that the Document Shepherd
has 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.

  No concerns.


(7) Has each author confirmed that any and all appropriate IPR
disclosures required for full conformance with the provisions of BCP 78
and BCP 79 have already been filed. If not, explain why.

  Yes - no disclosures required.

(8) Has an IPR disclosure been filed that references this document?
If so, summarize any WG discussion and conclusion regarding the IPR
disclosures.

  No IPR disclosures have been submitted.

(9) 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 been been widely reviewed. There seems general, but not
  overwhelming, consensus from the working group that the mechanism is
  useful and applicable to the candidate congestion control algorithms.


(10) 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 publicly available.)

  No such issues.


(11) Identify any ID nits the Document Shepherd has found in this
document. (See https://www.ietf.org/tools/idnits/ and the Internet-Drafts
Checklist). Boilerplate checks are not enough; this check needs to be
thorough.

  Some references are to slightly outdated versions of other working group
  documents (the changes in the latest version of those documents do not
  affect this).

  Pseudo code is not surrounded by and , but I
  do not believe it appropriate to do this.
 

(12) Describe how the document meets any required formal review
criteria, such as the MIB Doctor, media type, and URI type reviews.

  None needed.

(13) Have all references within this document been identified as
either normative or informative?

  Yes.

(14) 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 plan for their completion?

  There is one reference to an Internet-draft (draft-ietf-rmcat-nada),
  but this draft is in working group last call.


(15) Are there downward normative references references (see RFC 3967)?
If so, list these downward references to support the Area Director in
the Last Call procedure.

  None.


(16) Will publication of this document change the status of any
existing RFCs? Are those RFCs listed on the title page header, listed
in the abstract, and discussed in the introduction? If the RFCs are not
listed in the Abstract and Introduction, explain why, and point to the
part of the document where the relationship of this document to the
other RFCs is discussed. If this information is not in the document,
explain why the WG considers it unnecessary.

  This does not update or change the status of any existing RFCs.


(17) 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 protocol extensions that the document makes
are associated with the appropriate reservations in IANA registries.
Confirm that any referenced IANA registries have been clearly
identified. Confirm that newly created IANA registries include a
detailed specification of the initial contents for the registry, that
allocations procedures for future registrations are defined, and a
reasonable name for the new registry has been suggested (see RFC 5226).

  The shepherd agrees the draft makes no request to IANA.


(18) List any new IANA registries that require Expert Review for future
allocations. Provide any public guidance that the IESG would find
useful in selecting the IANA Experts for these new registries.

  None.

(19) Describe reviews and automated checks performed by the Document
Shepherd to validate sections of the document written in a formal
language, such as XML code, BNF rules, MIB definitions, etc.

  None needed.