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Shepherd writeup
draft-ietf-tsvwg-l4s-arch

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?

Informational.  This is indicated properly and is the proper type of RFC since
this describes the architecture for L4S, while other Experimental RFCs describe
the transport behaviors for use of the L4S identifier and DualQ that is one of
the possible queueing options compatible with this architecture.

(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 document describes the L4S architecture, which enables Internet
   applications to achieve Low queuing Latency, Low Loss, and Scalable
   throughput (L4S).  The insight on which L4S is based is that the root
   cause of queuing delay is in the congestion controllers of senders,
   not in the queue itself.  With the L4S architecture all Internet
   applications could (but do not have to) transition away from
   congestion control algorithms that cause substantial queuing delay,
   to a new class of congestion controls that induce very little
   queuing, aided by explicit congestion signalling from the network.
   This new class of congestion controls can provide low latency for
   capacity-seeking flows, so applications can achieve both high
   bandwidth and low latency.

   The architecture primarily concerns incremental deployment.  It
   defines mechanisms that allow the new class of L4S congestion
   controls to coexist with 'Classic' congestion controls in a shared
   network.  These mechanisms aim to ensure that the latency and
   throughput performance using an L4S-compliant congestion controller
   is usually much better (and rarely worse) than performance would have
   been using a 'Classic' congestion controller, and that competing
   flows continuing to use 'Classic' controllers are typically not
   impacted by the presence of L4S.  These characteristics are important
   to encourage adoption of L4S congestion control algorithms and L4S
   compliant network elements.

   The L4S architecture consists of three components: network support to
   isolate L4S traffic from classic traffic; protocol features that
   allow network elements to identify L4S traffic; and host support for
   L4S congestion controls.

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.

Document Quality:

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.

Personnel:

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?

No concerns.

(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 transport, congestion control, packet marking,
and 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, discussed in question 9 below.

(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.

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

No.

(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 even wider than normal support for going
forward with this work; spanning industry, including vendors, network
operators, and congestion control researchers.

There were very specific technical concerns and disagreements with the other 2
L4S drafts (on the ECN usage and DualQ).  Specific concerns related to the
content of those drafts are discussed in their writeups. - In this particular
document there were some early objections related to use of the term "classic"
for traditional non-L4S transports and queues, though no superior term was able
to be agreed on, and only a small number of people seemed unhappy with
"classic". - More substantially, there were concerns raised about the overall
state of development and study of the combined L4S architecture elements,
particularly the compliant transport protocols.  The TCP Prague reference code
had some issues discovered (and fixed), and some of the working group
participants did not feel like it was mature enough nor were the results of
tests encouraging enough for them to support L4S advancing.  Note that other
L4S transports beyond just TCP Prague have been under development by other
groups, who reviewed the L4S drafts and reported on their capabilities to meet
L4S requirements with their transports. - The selection of the L4S identifier
(in the companion ecn-l4s-id document) is not specific to this architecture
draft, but is at the root of a great deal of the lack of unanimous support. 
Since the beginning of this work, it was well understood that enhancing ECN
involves tradeoffs in the choice of header encodings selected, since there are
limited options in terms of the header bits, codepoints, and other fields like
DSCP that can be leveraged.  The working group went through a process of
assessing the pros and cons of all of the options that were put on the table. 
The different weights that participants attach to the importance of these
tradeoffs seems to be a major source of the inability to unanimously agree on
the particular L4S usage of ECT1 (and CE).  It was remarked in one WG meeting
that we ideally would have 5 codepoints, but unfortunately need to live with 4
and engineer within that.  As a possible supplement for the limited ECN
codepoints, the working group considered pros and cons of different means of
using DSCP values, multiple times over the life of these documents.  Some
participants preferred approaches relying on DSCP, based on their view of the
tradeoffs. - Some of the objecting participants have proposed another
technology (SCE) to enhance ECN differently, and incompatibly with L4S and this
architecture.  After careful consideration and a focused interim, the working
group strongly supported the use of ECT(1) as an input to classification as in
L4S to enable low latency traffic identification.  SCE proponents propose that
their alternative approach also can control latency, but make use of ECT(1) as
an output to indicate finer-grained levels of congestion.

One potential mitigation for some of these concerns is that the TSVWG plans to
be an open forum for experimenters to continue to present data and other
findings, where the WG can ask questions, explore whether specific concerns
have manifested, and discuss potential further development and advancement of
L4S along the Standards Track.

(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 to consider an appeal.

(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.

N/A.

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

Yes - all are 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?

No.

(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.

No.

(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.

N/A.

(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 8126).

There are (correctly) 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.

N/A.

(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  - there are no formal languages used.

(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
RFC8342?

N/A.
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