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 1 November 2019.
(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 is the proper type of RFC, and is indicated in the title
page header. The technology described is intended for experimental use in
conjunction with L4S transports that are an active area of research.
(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: (from Abstract)
This specification defines a framework for coupling the Active Queue
Management (AQM) algorithms in two queues intended for flows with
different responses to congestion. This provides a way for the
Internet to transition from the scaling problems of standard TCP
Reno-friendly ('Classic') congestion controls to the family of
'Scalable' congestion controls. These are designed for consistently
very Low queuing Latency, very Low congestion Loss and Scaling of
per-flow throughput (L4S) by using Explicit Congestion Notification
(ECN) in a modified way. Until the Coupled DualQ, these L4S senders
could only be deployed where a clean-slate environment could be
arranged, such as in private data centres. The coupling acts like a
semi-permeable membrane: isolating the sub-millisecond average
queuing delay and zero congestion loss of L4S from Classic latency
and loss; but pooling the capacity between any combination of
Scalable and Classic flows with roughly equivalent throughput per
flow. The DualQ achieves this indirectly, without having to inspect
transport layer flow identifiers and without compromising the
performance of the Classic traffic, relative to a single queue. The
DualQ design has low complexity and requires no configuration for the
Working Group Summary:
The working group largely supports and is enthusiastic about L4S technology,
which this document is a part of. It was last called along with 2 other L4S
documents. There is a wider than normal level of support that has been
expressed for this work, but it is not unanimous. There are also some WG
participants who have concerns about L4S or prefer an alternative approach.
The working group had many long email threads and conducted several interim
meetings focused on L4S, its goals, technical challenges, and concerns with the
approach and potential impact on Internet safety. Full agreement was not
obtained in all cases, but significant work was done to address the issues that
were agreed upon, and each concern was considered in detail by the working
group, even if some resolutions were not unanimously agreed with.
There are multiple existing implementations of the technology described, and
around 25 vendors and operators have indicated intentions to experiment with
the overall L4S technology.
Wesley Eddy is the document shepherd, and Martin Duke is the responsible AD.
(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.
I have reviewed the document myself, and believe it is ready for publication.
In addition, both other TSVWG co-chairs have closely reviewed and commented on
earlier revisions of the document.
(4) Does the document Shepherd have any concerns about the depth or breadth of
the reviews that have been performed?
(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.
Since the document deals with queuing behavior, there can be security,
operations, internet, and routing area interests. There has been a healthy mix
of academic, industry/vendor, and operator participation in this work, and a
breadth of reviews have been incorporated.
(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.
There are no personal concerns of my own. However, there have been concerns
raised in the working group (explained further in response to Question 9
below). These have been discussed at length in meetings and on the list. One
summary of concerns was assembled after the working group last call and posted
to the list via David Black:
those concerns, I believe all have been understood and adequately worked
through by the working group. As noted in that email, the chairs agreed that
some of the items specific to this DualQ document should not impact its
publication as Experimental at this time.
(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?
(8) Has an IPR disclosure been filed that references this document? If so,
summarize any WG discussion and conclusion regarding the IPR disclosures.
Yes. There is IPR filed in the tracker linked to this document. It was
discussed at length in the working group both on-list and in meetings. Draft
authors have actually discussed ways implementations can avoid the IPR claims,
and there seems to be good agreement that between this and the terms, the
situation is acceptable for going forward. Although there was one participant
that still may have a concern with this, it does not appear to be shared by
(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?
There was a combined last call for this and the other two main L4S documents.
During that last call, it was clear that while a majority strongly supports the
work and is eager to experiment with the technology, there are still also a
number of participants who have concerns and/or prefer alternatives to L4S.
The working group devoted considerable time, including multiple focused interim
meetings in order to understand objections and try to address or mitigate all
concerns. It is clear that while there are still some technical disagreements,
there is a great deal of support and an even wider than typical energy level to
go forward that spans the industry, including vendors, network operators, and
congestion control researchers.
Regarding this DualQ document specifically, there are other queueing approaches
that can work within the L4S architecture (as described in the architecture
I-D), so an implementer with any particular concern about DualQ has
Likely based on a mistaken experimental setup, a concern was raised at the WGLC
about potential for non-L4S traffic to abuse the L-queue for a "throughput
bonus". This was discussed following the WGLC in an interim, and then further
on the mailing list in the thread started here:
Multiple experimental results and analysis from several participants on the
list suggest that the concern stems from inadvertently disabling the congestion
response in the original experiment.
- Reference to results directly demonstrating this:
- In summary, there has been substantial work and experiments towards
addressing this concern, and the working group as a whole does not seem to find
it as an issue, though it hasn't been explicitly retracted by those that
originally raised the concern.
One participant specifically asked to have their disagreement noted in this
shepherd writeup, and indicated that they do not think L4S is ready for
advancement based on the achieved results so far. They stated in email to the
chairs: "I do not think that L4S (as currently designed, implemented and
described in the drafts) is the best solution for the whole internet, but it
pretty much tailored to make the already pre-ratified low latency DOCSIS (LLD)
compliant with IETF RFCs." Some other participants agree with this point,
though it is believed by the chairs to be "in the rough".
(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.)
Some participants may feel strongly enough against L4S in general to consider
(11) Identify any ID nits the Document Shepherd has found in this document.
(See http://www.ietf.org/tools/idnits/ and the Internet-Drafts Checklist).
Boilerplate checks are not enough; this check needs to be thorough.
There are very minor ID nits that can be corrected during publication. These
are the instances reported of non-ASCII characters and the outdated references
to the other L4S documents.
(12) Describe how the document meets any required formal review criteria, such
as the MIB Doctor, YANG Doctor, media type, and URI type reviews.
(13) Have all references within this document been identified as either
normative or informative?
(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 a normative reference to the L4S identifier document, which is
advancing to be published in parallel to this one.
(15) Are there downward normative references (see RFC 3967)? If so, list these
downward references to support the Area Director in the Last Call procedure.
(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.
(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
The document correctly states there are no IANA considerations.
(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.
(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, YANG modules, etc.
N/A - The document does contain pseudocode, but it is not a formal language.
(20) If the document contains a YANG module, has the module been checked with
any of the recommended validation tools
(https://trac.ietf.org/trac/ops/wiki/yang-review-tools) 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