The Benefits of Using Explicit Congestion Notification (ECN)
draft-ietf-aqm-ecn-benefits-08

Received changes through RFC Editor sync (created alias RFC 8087, changed title to 'The Benefits of Using Explicit Congestion Notification (ECN)', changed abstract to 'The goal of this document is to describe the potential benefits of applications using a transport that enables Explicit Congestion Notification (ECN).  The document outlines the principal gains in terms of increased throughput, reduced delay, and other benefits when ECN is used over a network path that includes equipment that supports Congestion Experienced (CE) marking.  It also discusses challenges for successful deployment of ECN.  It does not propose new algorithms to use ECN nor does it describe the details of implementation of ECN in endpoint devices (Internet hosts), routers, or other network devices.', changed pages to 19, changed standardization level to Informational, changed state to RFC, added RFC published event at 2017-03-07, changed IESG state to RFC Published)

[Ballot comment]
The document fails to note that devices exist which still are or can be configured to use the tos byte as part of a hash key and therefore may induce extremely odd behavior including reordering or due to hashing to a stateful device, connection resets in the face of ecn capability signaling.

While we see these are rare they nevertheless still exist.

The canonical example of a network device doing this probably being junos enhanced hash key  which still supports this in contemporary code.

[Ballot comment]
In this text:

  The authors would like to thank the following people for their
  comments on prior versions of this document: Bob Briscoe, David
  Collier-Brown, Colin Perkins, Richard Scheffenegger, Dave Taht, Wes
  Eddy, Fred Baker, Mikael Abrahamsson, Mirja Kuehlewind, John Leslie,
  and other members of the AQM and TSV Working Groups.
 
At the risk of making the name redundant, the ack probably needs to go to the TSVWG working group.

[Ballot comment]
- The discard of packets serves
  as a signal to the end-to-end transport that there may be congestion
  on the network path being used.

Why not?
  The discard of packets serves
  as a signal to the end-to-end transport that there is congestion
  on the network path being used.



- Section 3.5.  Bleaching and Middlebox Requirements to deploy ECN

Sligthly confused by ECT(0) is different the zero codepoint

  When ECN-capable IP packets, marked as ECT(0) or ECT(1), are remarked
  to non-ECN-capable (i.e., the ECN field is set to zero codepoint),

  ...
 
  A network device must not change a packet with a CE mark to a zero
  codepoint, if the network device decides not to forward the packet
  with the CE-mark,

I had to look up https://tools.ietf.org/html/rfc3168

      +-----+-----+
      | ECN FIELD |
      +-----+-----+
        ECT  CE        [Obsolete] RFC 2481 names for the ECN bits.
        0    0        Not-ECT
        0    1        ECT(1)
        1    0        ECT(0)
        1    1        CE

If you had one or two sentences to introduce the codepoints, that would avoid the confusion and would ease the readability.

And below is Dan Romascanu's OPS DIR review:
The following three comments are editorial in nature, triggered by difficulties in understanding some of the information (otherwise clearly presented):



1.      It would be useful to break the definition of ‘ECN-capable’ in two separate definitions for ‘ECN-capable packet’ and ‘ECN-capable network device’. It also would be good to copy or refer the definition of ECN codepoint from RFC 3168.

2.      Section 2.5 uses both CE-marking and ECN-marking terms. They are meant to be synonymous, so chosing one of them would make the text more clear

3.        Sections 4.3 and 5 uses the following phrase about endpoints – ‘it can … conservatively react to congestion’. Please explain what this means.

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

IANA has reviewed draft-ietf-aqm-ecn-benefits-06, which is currently in Last Call, and has the following comments:

We understand that this document doesn't require any IANA 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, IANA does not object.

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

The following Last Call announcement was sent out:

From: The IESG
To: IETF-Announce
CC:
Reply-To: ietf@ietf.org
Sender:
Subject: Last Call:  (The Benefits of using Explicit Congestion Notification (ECN)) to Informational RFC


The IESG has received a request from the Active Queue Management and
Packet Scheduling WG (aqm) to consider the following document:
- 'The Benefits of using Explicit Congestion Notification (ECN)'
  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
ietf@ietf.org mailing lists by 2015-10-15. 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


  The goal of this document is to describe the potential benefits when
  applications use a transport that enables Explicit Congestion
  Notification (ECN).  The document outlines the principal gains in
  terms of increased throughput, reduced delay and other benefits when
  ECN is used over a network path that includes equipment that supports
  ECN-marking.  It also discusses challenges for successful deployment
  of ECN.  It does not propose new algorithms to use ECN, nor does it
  describe the details of implementation of ECN in endpoint devices
  (Internet hosts), routers or other network devices.




The file can be obtained via
https://datatracker.ietf.org/doc/draft-ietf-aqm-ecn-benefits/

IESG discussion can be tracked via
https://datatracker.ietf.org/doc/draft-ietf-aqm-ecn-benefits/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)?

Informational RFC

Why is this the proper type of RFC?

The document does not standardize or provide guidance on best current practise
of the use of ECN. It summarizes the potential benefits of finally deploying
ECN for transport protocols.


Is this type of RFC indicated in the title page header?

Yes



(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:

This document is mostly a list of demonstrated and expected benefits to
transport protocols by using ECN. It highlights points that are most
visible to the application layer within the end-points. It then goes on
discussing specific deployment scenarios of ECN in a network, and the
internet at scale.

The key benefits of running ECN are summarized as
o) Improved throughput                               
o) Reduced Head-of-Line blocking                     
o) Reduced probability of RTO Expiry                 
o) Applications that do not retransmit lost packets   
o) Making incipient congestion visible               
o) Opportunities for new transport mechanisms         


Working Group Summary:

The document was brought to the working group to highlight and underline the
many benefits ECN can have, if deployed at scale. During the WG discussions, the
character of the draft changed slightly, from looking only at the positive
implications to also describe potential drawbacks and pitfalls.

The intention of this document though is less technical in nature, and instead is
intended as a reference as to why deploying ECN at this time would be sensible.
It aims to be a manifest that can be shown to decision-makers who quickly need
to understand the key benefits of ECN, with a high level of technical guidance.

Document Quality:

Are there existing implementations of the protocol?

The document is agnostic of any specific implementation, and rather argues
about the architectural model (well, as supported by the IP protocol) to use
ECN. Implementations of ECN in TCP (RFC3168) are in wide-spread use, but with
the ECN capabilities disabled, or only passively enabled. Arguably, the document
helped to persuade decision-maker at a large vendor to actively start deploying
ECN.



Have a significant number of vendors indicated their plan to implement the
specification?

The document aims to achieve just that - to drive the adoption rate of a well
known and available protocol by vendors up.


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?

There were lively discussions in the AQM working group around this document.
First, to not only speak exclusively about the positive aspects, but also
mention potential issues. Second, that document had widespread support in the WG
as it preaches to the choir - but word has to be spread about ECN to a larger
audience.

Personnel:

Who is the Document Shepherd?

Richard Scheffenegger, AQM WG co-chair


Who is the Responsible Area Director?

Martin Stiemerling, Transport 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.

The document had thorough discussions in the WG sessions. Both content and
wording have been honed, as witnessed also by the sheperd. There are no
unresolved issues which would preclude this from being forwarded to the
IESG.


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

No; the final few iterations were all about word-smithing, and to put the
document into a form that is expected to have the most impact at the
intended audience.


(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.

No;


(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?

None.


(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 is strong concensus on the document, as the entire WG strongly
thinks ECN will allow the internet to further improve. But as ECN requires
multilateral support to play out, it was found that the time is now for a
high level overview document like this to become a referencable RFC.


(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.


(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.

Some references need updating (some in RFC editor queue) as they are in
".bis" state, or pre-RFC references.

There is one intentional downref reference to RFC1349 - as some devices appear to
still be running code that does not comply with RFC2474.



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

No formal reviews necessary.


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

Yes, all references are accounted for, and are split in normative and
informative, as appropriate.

(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?

Yes - some references are in ".bis" state (one has become RFC already). As
the document does not standardize new protocols, but rather encourage the
deployment of existing mechanisms, the document may not need to be delayed
until these references have been posted as full RFCs.



(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.

RFC1349 - as an example where existing gear has not been updated to comply
with the current RFC2474 (both are in the same paragraph).


(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.

No.



(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).

No IANA actions required, no protocol updates are part of the document.


(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.

This RFC does not have any sections containing formal language, thus this is
not applicable.