Subject: [tsvwg] [Technical Errata Reported] RFC3390 (4583)

From: RFC Errata System <[email-masked]>
Date: Wed, 6 Jan 2016 10:54:38 -0800 (PST)

The following errata report has been submitted for RFC3390,
"Increasing TCP's Initial Window".

--------------------------------------
You may review the report below and at:
http://www.rfc-editor.org/errata_search.php?rfc=3390&eid=4583

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Type: Technical
Reported by: Joe Touch <[email-masked]>

Section: 1.

Original Text
-------------
   This increased initial window is optional: a TCP MAY start with a
   larger initial window.  However, we expect that most general-purpose
   TCP implementations would choose to use the larger initial congestion
   window given in equation (1) above.

Corrected Text
--------------
   This increased initial window is optional: a TCP MAY start with a
   smaller initial window.  However, we expect that most general-purpose
   TCP implementations would choose to use the larger initial congestion
   window given in equation (1) above.

Notes
-----
The MAY allows use of values smaller than this document allows, not larger.

Instructions:
-------------
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RFC3390 (draft-ietf-tsvwg-initwin-04)
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Title               : Increasing TCP's Initial Window
Publication Date    : October 2002
Author(s)           : M. Allman, S. Floyd, C. Partridge
Category            : PROPOSED STANDARD
Source              : Transport Area Working Group
Area                : Transport
Stream              : IETF
Verifying Party     : IESG

---

From: Mark Allman <[email-masked]>
Date: Wed, 06 Jan 2016 14:09:32 -0500

This is clearly a correction to the document.  The intent of the
authors and the WG was never to allow the initial window to be
higher than given in the document.  (It was hard enough to get folks
to accept an initial window of 2-4 segments.  It'd have been
impossible to get the community to agree to leave an explicit escape
hatch for larger values.)

This error also applies to RFC 2414 (where the text originated).

allman

> Title: Increasing TCP's Initial Window
> Author(s): M. Allman, S. Floyd, C. Partridge
> Category: PROPOSED STANDARD
> Source: Transport Area Working Group
> Area: Transport
> Stream: IETF
> Verifying Party     : IESG

---

From: Joe Touch <[email-masked]>
Date: Wed, 6 Jan 2016 11:19:10 -0800

> This error also applies to RFC 2414 (where the text originated).

Agreed, but since 2414 is obsoleted by 3390, do we also need an errata
there too?

Joe

---

From: Mark Allman <[email-masked]>
Date: Wed, 06 Jan 2016 14:28:33 -0500

> Agreed, but since 2414 is obsoleted by 3390, do we also need an errata

Someone else more pedantic that I can decide that.  If we're going
to the trouble it seems like it is low cost to flag it for RFC 2414,
too.  But, I for damn sure will not fight about it.

allman

---

From: Joe Touch <[email-masked]>
Date: Wed, 6 Jan 2016 11:40:42 -0800

Well, the text in RFC2414 actually has the opposite intent:

   This increased initial window is optional: that a TCP MAY start with
   a larger initial window, not that it SHOULD.

I.e., in that text it really is an admission that there's no forced
restriction limiting the IW. However, in the case of 3390, that text may
have been imported but I agree that was probably not the intent at that
time.

So, IMO, we should leave 2414 as it is.

Joe

---

From: Mark Allman <[email-masked]>
Date: Wed, 06 Jan 2016 14:48:53 -0500

> I.e., in that text it really is an admission that there's no
> forced restriction limiting the IW. However, in the case of 3390,
> that text may have been imported but I agree that was probably not
> the intent at that time.

FWIW.

RFC3390 replaces ", not that it SHOULD" with this sentence:

   However, we expect that most general-purpose TCP implementations
   would choose to use the larger initial congestion window given in
   equation (1) above.

I think the intent was these things were the same, but we explained
it a bit more in RFC3390.  I think it is clear that in both cases
s/larger/smaller/ applies.

(And, am sort of at a loss for how this wasn't caught given all the
times we were over this document and how many people reviewed the
thing.  Oh Well.)

allman

---

From: Joe Touch <[email-masked]>
Date: Wed, 6 Jan 2016 11:53:37 -0800

> times we were over this document and how many people reviewed the

Hmm. I can see it being interpreted either way in 2414 - i.e.,:

	(A) not that you should use a larger window than recommended

	(B) not that you should use a smaller window than recommended

In 3390, the intent is more clear (i.e., (B))

I'm happy to submit the errata to 2414 if we all think the intent there
was also (B) and not (A).

Joe

---

From: <[email-masked]>
Date: Thu, 7 Jan 2016 01:07:36 +0000 (UTC)

someone more pedantic observes that it's 'an erratum'. 

like data/datum.

Given that the RFCs are archival and on the web,
listing applicable errata even once the RFCs are obsoleted
is helpful. I'd also want 'obsoleted by' to be listed at 
the top of all errata just to make it more visible.
 Lloyd Wood [email-masked] http://about.me/lloydwood 

----- Original Message -----
From: Mark Allman <[email-masked]>
To: Joe Touch <[email-masked]>
Cc: [email-masked]; [email-masked]; [email-masked]; [email-masked]; [email-masked]; RFC Errata System <[email-masked]>
Sent: Thursday, 7 January 2016, 6:28
Subject: Re: [tsvwg] [Technical Errata Reported] RFC3390 (4583)

allman

---

From: Joe Touch <[email-masked]>
Date: Wed, 6 Jan 2016 17:45:30 -0800

> someone more pedantic observes that it's 'an erratum'. 

See the usage note here:

http://dictionary.reference.com/browse/errata

Note that even the RFC Editor page refers to the entry as an "errata",
e.g., see the button on this page:
https://www.rfc-editor.org/errata.php

> is helpful.

Isn't "Obsoleted by" the ultimate errata (in total or as a group,
whatever you prefer)?

> I'd also want 'obsoleted by' to be listed at

The errata applies to the RFC; to find out anything useful about the RFC
requires looking at the RFC itself anyway.

Joe

---

From: Anna Brunstrom <[email-masked]>
Date: Thu, 7 Jan 2016 10:22:43 +0100

The text is unclear, but needs to be interpreted in context I think. In 
the context of where it is written (discussion of the new upper bound 
for the initial window size, and expanding on "This increased initial 
window is optional"), I would interpret the text as:

A TCP MAY start with a larger initial window as specified in this 
document, but can still use a value of one segment if it wants. (RFC 2414)

A TCP MAY start with a larger initial window as specified in this 
document, but can still use a value of one or two segments if it wants. 
We expect most implementations to use an initial window as specified in 
this document. (RFC 3390)

The "a larger initial window" in the text relates to the MSS dependence 
as I interpret it. This would be consistent with the believed intent of 
the documents.

s/larger/smaller/ in RFC 3390 as suggested would make the text clearer I 
think.
s/larger/smaller/ in RFC 2414 would not make the text clearer I think.

Anna