SACK-IMMEDIATELY Extension for the Stream Control Transmission Protocol
RFC 7053

[Ballot comment]
I have no objection to the publication of this document.

Curiously, after reading it I cam to enter this position and found two other ADs had already made the point I wanted to make. Clearly, if the receiver is a legacy implementation, it will ignore the I bit, and perhaps this is the point. Since this document updates 4960, the behaviour on receipt of the I bit becomes normative, so making the behaviour somewhat optional (via SHOULD) seems a good way to get off the hook.

However, the wording in section 5.2 does leave this all a bit ambiguous.

[Ballot comment]
I had the same reaction to Pete.  Under what circumstances would the receiver choose to delay (i.e., not obey the SHOULD)?  If none exist, then it should be a MUST.

[Ballot comment]
I had the same reaction to Pete.  Under what circumstances would the receiver choose to delay (i.e., not obey the SHOULD).  If none exist, then it should be a MUST.

[Ballot comment]
Section 5.2 invites the question: Why shouldn't the receiver delay and, more importantly, under what circumstances is it reasonable for the receiver to delay and when is it not reasonable? Might be handy to give some advice here.

IESG/Authors/WG Chairs:

IANA has reviewed draft-ietf-tsvwg-sctp-sack-immediately-03.  Authors should review the comments and/or questions below.  Please report any inaccuracies and respond to any questions as soon as possible.

We received the following comments/questions from the IANA's reviewer:

IANA understands that, upon approval of this document, there is a single action which IANA must complete.

In the DATA Chunk Flags subregistry of the Stream Control Transmission Protocol (SCTP) Parameters registry located at:

http://www.iana.org/assignments/sctp-parameters

a new DATA Chunk flag will be registered as follows:

Chunk Flag Value: 0x08
Chunk Flag Name: I Bit
Reference: { RFC-to-be ]

IANA understands that this is the only action required to be completed upon approval of this document.

Note:  The actions requested in this document will not be completed
until the document has been approved for publication as an RFC.
This message is only to confirm what actions will be performed.

Michael and I continued to talk about a question I had on explaining why this capability matters after I requested IETF Last Call. Michael suggested the following text. When I ballot "yes", I'll add it as a Comment.

  In specific situations the delaying of SACKs results in reduced
  performance of the protocol:

  1.  If such a situation can be detected by the receiver, the
      corresponding SACK can be sent immediately.  For example,
      [RFC4960] recommends the immediate sending if the receiver has
      detected message loss or message duplication.

  2.  However, if the situation can only be detected by the sender of
      the DATA chunk, [RFC4960] provides no method of avoiding a delay
      in sending the SACK.  Examples of these situations include ones
      which require interaction with the application (e.g. applications
      using the SCTP_SENDER_DRY_EVENT, see Section 4.1) and ones which
      can be detected by the SCTP stack itself (e.g. closing the
      association, hitting window limits or resetting streams, see
      Section 4.2).

  To overcome the limitation described in the second case, this
  document describes a simple extension of the SCTP DATA chunk by
  defining a new flag, the I-bit.  The sender of a DATA chunk indicates
  by setting this bit that the corresponding SACK chunk should not be
  delayed.

The following Last Call announcement was sent out:

From: The IESG
To: IETF-Announce
CC:
Reply-To: ietf@ietf.org
Sender:
Subject: Last Call:  (SACK-IMMEDIATELY Extension for the Stream Control Transmission Protocol) to Proposed Standard


The IESG has received a request from the Transport Area Working Group WG
(tsvwg) to consider the following document:
- 'SACK-IMMEDIATELY Extension for the Stream Control Transmission
  Protocol'
  as Proposed Standard

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 2013-08-26. 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 updates RFC 4960 by defining a method for the sender of
  a DATA chunk to indicate that the corresponding SACK chunk should be
  sent back immediately and not be delayed.  It is done by specifying a
  bit in the DATA chunk header, called the I-bit, which can get set
  either by the SCTP implementation or by the application using an SCTP
  stack.  Since unknown flags in chunk headers are ignored by SCTP
  implementations, this extension does not introduce any
  interoperability problems.




The file can be obtained via
http://datatracker.ietf.org/doc/draft-ietf-tsvwg-sctp-sack-immediately/

IESG discussion can be tracked via
http://datatracker.ietf.org/doc/draft-ietf-tsvwg-sctp-sack-immediately/ballot/


No IPR declarations have been submitted directly on this I-D.

(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 a PS.

(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 updates RFC 4960 by defining a method for the sender of
a DATA chunk to indicate that the corresponding SACK chunk should be
sent back immediately and not be delayed. It is done by specifying a
bit in the DATA chunk header, called the I-bit, which can get set
either by the SCTP implementation or by the application using an SCTP
stack. Since unknown flags in chunk headers are ignored by SCTP
implementations, this extension does not introduce any
interoperability problems.


Working Group Summary:

There was consensus to adopt this as a WG document, review by the WG,
and agreement by the WG to finally publish this.


Document Quality:

This document is seen as ready to publish.

FreeBSD supports this extension since FreeBSD 7.2, released May 2009.
The Linux kernel supports it also (accessibility by a the user was added
recently to netinet/sctp.h).


Personnel:

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

I am the document shepherd, G Fairhurst, .
The responsible AD is: Spencer Dawkins


(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.

WGLC Announcement sent draft-ietf-tsvwg-sctp-sack-immediately-02 on 19th
March 2013 and concluded Friday 5th April 2013 with comments from 6
people provided. These have been addressed in the present version.

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

No.

(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.

As far as I know, no IPR disclosures have been submitted.

(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 initial discussion of whether this mechanism was needed -
especially since no equivalent method exists in TCP. After use-cases
were provided there was strong support for this work and no objections.
There was review of the work within the WG, and consensus to publish. No
objections were noted.

(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.

None.

(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?

Yes, this OK.

(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 external dependencies.

(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.

Updates: 4960 - it is a backwards-compatible SCTP update.

(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).

OK, normal SCTP allocation.

(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.