Controlled Delay Active Queue Management
draft-ietf-aqm-codel-10

[Ballot comment]
Thanks for your work on this draft.  I have one question, it seems that problems with CoDel could lead to DoS attacks.  I understand that the goal here is reducing buffer bloat, so I would expect to see some discussion in the security considerations section that mentions improved availability from the Confidential, Integrity, Availability security principle discussed along with possible DoS considerations.  Please correct me if I'm wrong, otherwise it would be helpful to see some text added.

[Ballot comment]
Thank you for a clear and very well written document.  This was well worth staying up
past 1am to read fully.  I do have one primary comment and a couple minor points.

First, the document status is Experimental.  While encouraging experimentation, the
document doesn't really articulate what the concerns are or how experimentation might
determine that this should be changed to standards track.  While regrettably I haven't
personally followed the AQM work, I might assume that some of the issues to general
applicability might be tied to aspects around the challenges of applying CoDel to a
system architecture built around WRED AQM and enqueue complexity rather than dequeue
complexity.  Having a paragraph that gave context in the introduction for the questions
still to be explored would be helpful.

a) In Sec 3.4 :  "This property of CoDel has been exploited in
  fq_codel [FQ-CODEL-ID], which hashes on the packet header fields to
  determine a specific bin, or sub-queue, for each five-tuple flow,"
  For the general case of traffic, it would be better to focus on using a microflow's
  entropy information  - whether that is derived from a 5-tuple, the IPv6 flow label,
  an MPLS Entropy label, etc.  Tying this specifically to the 5-tuple is not ideal.
  Obviously I missed this for draft-ietf-aqm-fq-codel-06 - but even a slight rephrasing
to "for each microflow, identifiable via five-tuple hash, src/dest + IPv6 flow label, or
other entropy information" would encourage better understanding of micro-flow identification.
Of course, this is just a comment - so do with it what you will.

b) (Nit) In Sec 5.1: " We use this insight in the pseudo-code for CoDel later in the draft."
  The pseudo-code is actually earlier in the draft.  Also s/draft/document for publication.

[Ballot comment]
Same view as Warren point 1. I just wondered: why this section 5 as that position?
1: I found the overall structure of the document a little odd -- I'm assuming that this is an artifact of its history, or merging multiple documents into one, or similar. It starts off with a nice description of queuing and CoDel. It then gets all technical with the pseudo-code (which was really helpful). Where it feels a little odd is that it then suddenly goes back to being much more introductory feeling (Section 5 - ), and feels like it repeats some of the earlier material. Reformatting it all to address this seems like overkill, but perhaps a readers note to suggest people who want more background should skip ahead then come back.

[Ballot comment]
Glad to see this document progress.

From Fernando's Gen-ART review:

* Page 17:
  simulation that this result holds for Reno, Cubic, and
  Westwood[TSV84].

Missing space.

[Ballot comment]
Glad to see this document published.

From Fernando's Gen-ART review:

* Page 17:
  simulation that this result holds for Reno, Cubic, and
  Westwood[TSV84].

Missing space.

[Ballot comment]
The normative part of this document seems reasonably clear and I
believe I could implement it. Note: I have not attempted to assess the
technical quality of the algorithm described in this protocol.

I found the descriptive part a little hard to follow in places.
Specifically:

- It's a little hard to work out which things are informal terms
  and which are defined terms of art.
 
  "power" is used first on page 4 but it's only clear that
  it's a term of art in S 16. This could be fixed by a
  forward reference and a cite to Kleinrock.

  "target" and "interval" are constants in the algorithm,
  but this wasn't entirely clear to me in S 3.2. You could
  deal with this by stating in S 3 that the algorithm
  takes in two variables (TARGET and INTERVAL). Perhaps
  capitalize them. I see you also use "setpoint" and
  "target" and "target setpoint". I would stick to one
  if you can.

- It seems that the document went through some reordering
  because S 5.1. refers to the pseudo-code as coming later
  in the draft. Perhaps some of the rationale could come
  before the pseudo-code. Specifically, the intuition that
  the dropping happens only when you are able to send
  packets (dequeue) is kind of counter-intuitive.

- Following up on the above point, you must be able to
  drop packets when the queue is entirely full, but S
  4.4 doesn't seem to contemplate this. What is the impact
  of this? You just drop and ignore?

Finally, you seem a bit inconsistent about whether you are
capitalizing 2119 terms (see for instance the use of should
vs. SHOULD in the second graf of S 3.2).

[Ballot comment]
I think that this is a useful document - I also think that it would make a good introductory document to describe queuing for e.g a collage class.

I do have some readability suggestions to make it even better; these do not need any action, but if the authors happen to edit the document for any other reason, they may want to address them.

1: I found the overall structure of the document a little odd -- I'm assuming that this is an artifact of its history, or merging multiple documents into one, or similar. It starts off with a nice description of queuing and CoDel. It then gets all technical with the pseudo-code (which was really helpful). Where it feels a little odd is that it then suddenly goes back to being much more introductory feeling (Section 5 - ), and feels like it repeats some of the earlier material. Reformatting it all to address this seems like overkill, but perhaps a readers note to suggest people who want more background should skip ahead then come back.

2: Section 1.  Introduction
- "determined set point derived from maximizing the network power metric" -- I'd suggest referencing Section 5.2 where power is explained (or, if we assume readers understand this, section 5.2 can be dropped).

3: Section 3.  Overview of the Codel AQM
Sojourn time is a really important concept in this document, but it isn't really defined - Section 5.1 is closest to defining it, but still not great.

4: Section 3.1
"The MTU size can be set adaptively to the largest packet seen so far or can be read from the driver."
It was unclear what driver -- perhaps "interface driver" or simply "interface"?

5: Section 3.2 has an opening parens but no closing one ("known or measure (though ...").
This is a tiny nit, but set off my OCD tendencies :-)

6: Section 5.1
"We use this insight in the  pseudo-code for CoDel later in the draft.)
- earlier in the draft...

Section 5.2:
AIMD TCP could use a reference.

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

The IANA Services Operator has reviewed draft-ietf-aqm-codel-07.txt, 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
PTI

The following Last Call announcement was sent out:

From: The IESG
To: IETF-Announce
CC: wes@mti-systems.com, aqm@ietf.org, ietf@kuehlewind.net, draft-ietf-aqm-codel@ietf.org, aqm-chairs@ietf.org
Reply-To: ietf@ietf.org
Sender:
Subject: Last Call:  (Controlled Delay Active Queue Management) to Experimental RFC


The IESG has received a request from the Active Queue Management and
Packet Scheduling WG (aqm) to consider the following document:
- 'Controlled Delay Active Queue Management'
  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 2017-03-27. 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 document describes a general framework called CoDel (Controlled
  Delay) that controls bufferbloat-generated excess delay in modern
  networking environments.  CoDel consists of an estimator, a setpoint,
  and a control loop.  It requires no configuration in normal Internet
  deployments.




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

IESG discussion can be tracked via
https://datatracker.ietf.org/doc/draft-ietf-aqm-codel/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 is correctly indicated in the header. It is going as Experimental because there was not strong voice or reason for Standards Track, even though the WG charter permits it, and there are some issues for future research noted, though they are not believed to result in any unsafe conditions for the Internet.


(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

  Relevant content can frequently be found in the abstract
  and/or introduction of the document. If not, this may be
  an indication that there are deficiencies in the abstract
  or introduction.


  This document describes a general framework called CoDel (Controlled
  Delay) that controls bufferbloat-generated excess delay in modern
  networking environments.  CoDel consists of an estimator, a setpoint,
  and a control loop.  It requires no configuration in normal Internet
  deployments.  CoDel comprises some major technical innovations and
  has been made available as open source so that the framework can be
  applied by the community to a range of problems.  It has been
  implemented in Linux (and available in the Linux distribution) and
  deployed in some networks at the consumer edge.  In addition, the
  framework has been successfully applied in other ways.


Working Group Summary

  Was there anything in WG process that is worth noting? For
  example, was there controversy about particular points or
  were there decisions where the consensus was particularly
  rough?


CoDel was developed prior to the formation of the AQM working group.  It was widely felt to be a good part of the answer to the "bufferbloat" problem that the IETF was trying to figure out how to deal with.  The authors brought the specification of the algorithm to the working group after it was formed, and some clarifications and improvements to the description resulted from working group feedback.


Document Quality

  Are there existing implementations of the protocol? Have a
  significant number of vendors indicated their plan to
  implement the specification? 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? If
  there was a MIB Doctor, Media Type or other expert review,
  what was its course (briefly)? In the case of a Media Type
  review, on what date was the request posted?

There are multiple existing implementations, in simulators (e.g. ns-2, ns-3) and real operating systems (e.g. Linux, FreeBSD).  The quality of the document is high in terms of being able to write new implementations, as it contains significant amounts of pseudo-code to describe the algorithm, along with textual descriptions of its design facets.


Personnel

  Who is the Document Shepherd? Who is the Responsible Area
  Director?

Wesley Eddy (wes@mti-systems.com) is the document shepherd.  Mirja Kuhlewind is the 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 multiple times and it is ready for publication.


(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.

No additional special reviews are needed.


(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 or issues.


(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.

There are no known IPR disclosures.

Note that there is dual-licensed BSD/GPLv2 code in the document.



(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? 

WG consensus was strong to adopt and publish this document. 


(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 https://www.ietf.org/tools/idnits/ and the Internet-Drafts
Checklist). Boilerplate checks are not enough; this check needs to be
thorough.

There are nits on references [6] and [7] that should be fixed in a later update (e.g. bundled with other fixes that result from IESG review).

Nits on RFC 896 and 2309 are spurious, as these are explicitly used as historic references.  The nit on RFC 2581 can be bundled with other updates and made a reference to 5681.


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

None.

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

References are properly split into normative and informative sections.  The RFC Editor may choose to handle the "URIs" reference section in some other way, if needed.


(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 concerns.


(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.

No downrefs are present, as this is an Experimental document.


(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 changes to other document status are made.


(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).

There are no required IANA actions.


(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.  There is C++-like pseudocode in the document.  There are references to C code from the Linux kernel.

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 is correctly indicated in the 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

  Relevant content can frequently be found in the abstract
  and/or introduction of the document. If not, this may be
  an indication that there are deficiencies in the abstract
  or introduction.


  This document describes a general framework called CoDel (Controlled
  Delay) that controls bufferbloat-generated excess delay in modern
  networking environments.  CoDel consists of an estimator, a setpoint,
  and a control loop.  It requires no configuration in normal Internet
  deployments.  CoDel comprises some major technical innovations and
  has been made available as open source so that the framework can be
  applied by the community to a range of problems.  It has been
  implemented in Linux (and available in the Linux distribution) and
  deployed in some networks at the consumer edge.  In addition, the
  framework has been successfully applied in other ways.


Working Group Summary

  Was there anything in WG process that is worth noting? For
  example, was there controversy about particular points or
  were there decisions where the consensus was particularly
  rough?


CoDel was developed prior to the formation of the AQM working group.  It was widely felt to be a good part of the answer to the "bufferbloat" problem that the IETF was trying to figure out how to deal with.  The authors brought the specification of the algorithm to the working group after it was formed, and some clarifications and improvements to the description resulted from working group feedback.


Document Quality

  Are there existing implementations of the protocol? Have a
  significant number of vendors indicated their plan to
  implement the specification? 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? If
  there was a MIB Doctor, Media Type or other expert review,
  what was its course (briefly)? In the case of a Media Type
  review, on what date was the request posted?

There are multiple existing implementations, in simulators (e.g. ns-2, ns-3) and real operating systems (e.g. Linux, FreeBSD).  The quality of the document is high in terms of being able to write new implementations, as it contains significant amounts of pseudo-code to describe the algorithm, along with textual descriptions of its design facets.


Personnel

  Who is the Document Shepherd? Who is the Responsible Area
  Director?

Wesley Eddy (wes@mti-systems.com) is the document shepherd.  Mirja Kuhlewind is the 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 multiple times and it is ready for publication.


(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.

No additional special reviews are needed.


(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 or issues.


(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.

There are no known IPR disclosures.

Note that there is dual-licensed BSD/GPLv2 code in the document.



(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? 

WG consensus was strong to adopt and publish this document.  It is going as Experimental because there was not strong voice or reason for Standards Track, even though the WG charter permits it, and there are some issues for future research noted, though they are not believed to result in any unsafe conditions for the Internet.



(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 https://www.ietf.org/tools/idnits/ and the Internet-Drafts
Checklist). Boilerplate checks are not enough; this check needs to be
thorough.

There are nits on references [6] and [7] that should be fixed in a later update (e.g. bundled with other fixes that result from IESG review).

Nits on RFC 896 and 2309 are spurious, as these are explicitly used as historic references.  The nit on RFC 2581 can be bundled with other updates and made a reference to 5681.


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

None.

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

References are properly split into normative and informative sections.  The RFC Editor may choose to handle the "URIs" reference section in some other way, if needed.


(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 concerns.


(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.

No downrefs are present, as this is an Experimental document.


(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 changes to other document status are made.


(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).

There are no required IANA actions.


(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.  There is C++-like pseudocode in the document.  There are references to C code from the Linux kernel.