Subject: [tsvwg] FYI: Document writeup for draft-ietf-tsvwg-byte-pkt-congest

From: Gorry Fairhurst <[email-masked]>
Date: Wed, 15 Aug 2012 08:40:46 +0100

The following document has been revised after receiving WGLC comments.
No issues were found:

http://www.ietf.org/internet-drafts/draft-ietf-tsvwg-byte-pkt-congest-08.txt

This is now considered ready for publication. A copy o the writeup is
below, which will shortly be submitted to our TSV ADs.

Best wishes,

Gorry

---

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?

This document is intended as BCP. (This was discussed at IETF-81 and
that the status changed from Informational to BCP since it provides
guidance to implementors and people configuring routers and hosts).

(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 provides recommendations of best current practice
     for dropping or marking packets using active queue
     management (AQM) such as random early detection (RED) or pre-
     congestion notification (PCN).  We give three strong recommendations:
     (1) packet size should be taken into account when transports read and
     respond to congestion indications, (2) packet size should not be
     taken into account when network equipment creates congestion signals
     (marking, dropping), and therefore (3) the byte-mode packet drop
     variant of the RED AQM algorithm that drops fewer small packets
     should not be used. The document updates RFC 2309.

Working Group Summary

There was consensus to publish this as a WG document and agreement at
IETF-82 that the document was now complete.

Document Quality

Annexe A summarises a survey by the original authors showing deployment
of the techniques by router vendors. The recommendations are thought to
be in line with that of IETF groups, such as TSVWF, TCPM, PCN, and are
considered good advice for the general Internet.

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

I am the document shepherd, G Fairhurst.

(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 was presented at IEWTF-82 (Taipei), with a request for WGLC.
WGLC concluded with some discussion but no substantive changes on Friday
30th March 2012.

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

No - the original draft had a lot of background material, much of this
has been condensed or removed, resulting in a smaller document.

(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? 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.

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 IPR disclosures have been submitted directly on
draft-ietf-tsvwg-byte-pkt-congest.

(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 has WG support and there is consensus to publish. (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.) (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.

No. (12) Describe how the document meets any required formal review
criteria, such as the MIB Doctor, media type, and URI type reviews.
Not applicable. (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?

No.

(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.

(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.

One update is listed, RFC 2309, informational - replaced by this BCP.
It deprecates deliberate preferential treatment of small packets in AQM
algorithms.

(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).

Not applicable.

(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.

Not applicable.

---

From: John Leslie <[email-masked]>
Date: Wed, 15 Aug 2012 15:07:28 -0400

> The following document has been revised after receiving WGLC comments.

   The changes are mostly refreshing a document scheduled to expire this
month.

> No issues were found:

   Is that with WGC-hat-on?

   Neither my issues nor Philip Eardley's comments were addressed. In
fact, not even the changes Bob Briscoe mentioned on-list have been
included.

> ...

   Thank you for finally answering my question about BCP status.

>...

   Was that reviewed on-list?

>...

   Yes, I guess that is true; but ignoring substantive comments isn't
a good practice IMHO.

> has been condensed or removed, resulting in a smaller document.

   That is indeed what I basically asked for, but I don't see any
evidence of it:

- diff(07,08)  48 lines changed or deleted;  53 lines changed or added
- diff(06,07)   8 lines changed or deleted;  13 lines changed or added
- diff(05,06)  64 lines changed or deleted;  69 lines changed or added
- diff(04,05) 823 lines changed or deleted; 864 lines changed or added

(Need I go farther? That gets us back to March 2011...)

> The document has WG support and there is consensus to publish.

   This, IMHO, doesn't answer the question. :^(

   Does it represent the concurrence of a few individuals, or does the
WG as a whole understand and agree with it?

For reference, my comments included:
] 
] When I previously skimmed this document, I believed it contained only
] common ground: that AQM should drop/mark packets without favoring small
] packets, and that to whatever extent packet size _is_ considered, that
] should be a transport-layer responsibility.
]     
] Alas, when I read it carefully this week, I find that Bob is actually
] saying that transport-layer should _only_ consider "congested bytes", not
] "congested packets".
]     
] In fact, Bob openly endorses replacing TCP congestion-control with an
] algorithm which calculates "fair-share bytes" and doesn't back off at all
] (even in the presence of 20% packet loss) unless you're already sending
] more than this "fair-share".
]     
]    I do not believe that is the consensus of this WG; and I believe if   
] that were the consensus it would exceed our charter.
]     
] The draft contains a number of things I _do_ support; and I'd be happy
] to support a considerably shorter draft which concentrates on the AQM
] recommendation, omitting any suggestions of modifying TCP congestion
] control.

and Philip's comments included:
] 
] S2.2 I thought the numbered bullets could be better phrased, something like
] +this:-
] 
]   1.  AQM algorithms such as RED SHOULD use packet-mode drop, ie they SHOULD NOT
] +use byte-mode drop. The latter
] is more complex,
]        it creates the perverse incentive to fragment segments into tiny
]        pieces and it is vulnerable to floods of small-
]        packets.
] 
]    2.  If a vendor has implemented byte-mode drop, and an operator has   
]        turned it on, it is RECOMMENDED to turn it off, after establishing if
] +there are any implications on
] the relative performance of
]        applications using different packet sizes.
]    
]   3.  RED SHOULD NOT be turned off. Without RED, a drop tail
]        queue biases against large packets.
] 
] Nit - the following paragraph shouldn't be indented (Note well that RED's...)
]    
] S3.3
] The section could be slightly clearer. Starting with the second para, where you
] +start talking about something you don't recommend (ie you have to remember that
] +you're talking about the consequences of not following your recommendation).
] 
] S3.3
]    o  Also, if the network biases congestion notification by packet size
]       it has to assume a baseline packet size--all proposed algorithms
]       use the local MTU.  Then transports have to guess which link was   
]       congested and what its local MTU was, in order to know how to
]       tailor their congestion response to that link.
] So you're saying that for byte-mode drop, the network element has to compare the
] +size of the current pkt with the MTU, and if it's 25* smaller then reduce the
] +pkt loss probably by 25*? And if the MTU was bigger, then the current pkt would
] +be dropped with greater probability? And both of these things are hard to do.
]     
] S3.4 (& knock-on effect on 3.3)
] I think this could be better.
] I agree with your arguments in S3.1 & 3.2 that dropping or marking should be
] +independent of pkt size.
] You now go into a couple of pages, which I think could be boiled down to a
] +paragraph, saying something like:-
] * the overall system (network + transport) has to be packet-size dependent in   
] +order to drive out the right amount of traffic so the resource becomes
] +uncongested (since we assume all resources are in practice byte rather than
] +packet limited)
] * from S3.1 and S3.2 the IETF is convinced that the network should notify
] +independent of packet-size.
] * therefore the transport must act dependent on packet-size.
] 
] It seems to me this is a necessary consequence of your earlier assumptions
] +/arguments.
] 
] [On the other hand, if someone disagrees with the arguments and thinks that the
] +network should notify dependent on packet-size, then it follows that the
] +transport can act independent of packet-size.]
] 
] I think in S3.3 you're trying to make another argument (?):-
] * we can either do packet-size biasing in the network element or on the end host
] +transport (see argument above)
] * packet-size biasing in the network is quite tricky, because then both the
] +network element & the transport have to make some guesses about MTU - whereas
] +with packet-size biasing in the transport, neither network element nor
] +transport needs to know what the MTU is.
] * it is also easier to implement packet-size biasing in the transport than in
] +the network.   
]        
] On the last bullet, I didn't really follow your argument in S3.5. Might be
] +easier to follow if S3.5 also talked about how a network element would take
] +account of pkt size? Also, does the following argument also apply?:
] * if pkt-size biasing is done in the transport, then the work (to do the 
] +biasing) is spread over many end hosts,
] * whereas if pkt-size biasing is done in the network, then the work is
] +concentrated in just the congested network element, which has to operate on all
] +the traffic at line speed.

   (Has there perhaps been some confusion about what went into the -08
version?)

--
John Leslie <[email-masked]>