Content-ID Header Field in the Session Initiation Protocol (SIP)
draft-ietf-sipcore-content-id-10

[Ballot comment]
I've checked whether this is consistent with email use and it seems to be.

Note that RFC 2392 says:

  The Content-ID of a MIME body part is required to be globally unique.

and this document only requires it to be unique within a message.

I don't think the difference in restrictions makes any real world difference, because I don't think applications enforce uniqueness of Content-IDs between different messages.

[Ballot comment]
I'm a little surprised that the document didn't end up with any text detailing the historical context for formally adding this mechanism.

I would expect to see some discussion explaining that the use of Content-ID as a SIP header field has been inferred as acceptable for years, and that so many IETF participants had taken it as given that Content-ID was *already* a registered SIP header field that it appears in examples in (for example) RFCs 5368 and 6080.

While I think the document would serve its intended purpose as-is, I believe that more explanatory text in the Introduction section to clarify that this is an attempt to formalize already-assumed (and likely deployed) behavior -- rather than simply casting it as a minor optimization -- would go a long way towards dealing with Eric's concerns.

[Ballot discuss]
This document really needs some discussion of the interoperability implications of this change. Assuming I understand correctly, it is not possible to use this mechanism with any existing content type, because receiving implementations will expect to see a multipart and thus refuse to accept the message. Is that correct? If so, it seems like a limitation which needs to be called out explicitly

[Ballot comment]
This document seems rather gratuitous to me. I agree it's somewhat of a misfeature not to be able to have Content-ID in the SIP headers, but as the examples in this document make clear, there's a straightforward workaround. It's unclear to me that there is actually sufficient benefit to this mechanism to publishing a standards track document with this change.

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

The IANA Services Operator has completed its review of draft-ietf-sipcore-content-id-06.txt. If any part of this review is inaccurate, please let us know.

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

In the Header Fields registry on the Session Initiation Protocol (SIP) Parameters registry page located at:

https://www.iana.org/assignments/sip-parameters/

a single, new Header Field is to be registered as follows:

Header Name: Content-ID
Compact:
Reference: [ RFC-to-be ]

The IANA Services Operator 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.

Thank you,

Sabrina Tanamal
IANA Services Specialist
PTI

The following Last Call announcement was sent out:

From: The IESG
To: IETF-Announce
CC: ben@nostrum.com, Jean Mahoney , sipcore-chairs@ietf.org, sipcore@ietf.org, mahoney@nostrum.com, draft-ietf-sipcore-content-id@ietf.org
Reply-To: ietf@ietf.org
Sender:
Subject: Last Call:  (Content-ID header field in Session Initiation Protocol (SIP)) to Proposed Standard


The IESG has received a request from the Session Initiation Protocol Core WG
(sipcore) to consider the following document: - 'Content-ID header field in
Session Initiation Protocol (SIP)'
  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 2017-06-27. 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 specifies the Content-ID header field for usage in the
  Session Initiation Protocol (SIP).  The document also updates RFC
  5621, to enable a Content-ID URL to reference a complete message-body
  and metadata provided by some additional SIP header fields.




The file can be obtained via
https://datatracker.ietf.org/doc/draft-ietf-sipcore-content-id/

IESG discussion can be tracked via
https://datatracker.ietf.org/doc/draft-ietf-sipcore-content-id/ballot/


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

This is my AD evaluation of draft-ietf-sipcore-content-id-05. I have some points I would like discuss before going to IETF last call.

Note: I plan to request an Art-Art review on this draft to focus on the MIME usage aspects.

-----

Discussion Points:

- I have some difficulty seeing the difference between "the body and related metadata" and "the SIP message". I realize you have the more MIME-specific header fields in mind when you say "metadata". But any SIP header field could be considered metadata.

The main point of that question is, as used in MIME, Content-Id is intended to label a body part. Message-Id is used to label the whole message. Aren't we talking about the whole message here?

- Is there an expectation for the SIP Content-ID header field value to be referenced from outside the SIP message? If so, what are the uniqueness expectations? Note that for MIME, Content-ID is expected to be globally unique. Is that the case here?

If the Content-ID is _not_ expected to be referenced from outside of the SIP message that contains it, then we have a sort of degenerate case where it always identifies _this_ message regardless of the value. Does that value ever need to change? Does that suggest any guidance on how to construct values?

Specific comments:

1.4 and children: These examples seem like fairly weak motivation, since I assume in both cases one could still have just put a single body-part inside a multipart envelope. That seems more an "inconvenience" than a "problem". Are there any known use-cases where that would not be possible? (This is certainly not a show stopper; we are allowed to solve inconveniences. But if there are any stronger motivations that could be documented, they might save questions down the road.)

3.2, 2nd note: How has the msg-Id been simplified, and why?

3.4 and children: An example or two would be extremely helpful.


Editorial:

1.1, 3rd paragraph: Citation to RFC5621 is not a link in the PDF version.

1.2 and 1.3: A sentence or two that more strongly contrasts "body part" vs "message-body" would be helpful. I think that some people will think of a message-body as still a body-part.

1.5, Note: Seems like the note belongs in the problem statement more than the solution.

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?

  Proposed Standard, which is indicated in the header. This
  draft updates RFC 5621, which is Proposed Standard, and
  registers the Content-ID header field, which requires
  standards action.


(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 specifies the Content-ID header field for
  usage in the Session Initiation Protocol (SIP) to identify
  a complete message-body of a SIP message. The document also
  updates RFC 5621, to enable a Content-ID URL to reference
  a complete message-body and metadata provided by some 
  additional SIP header fields.

Working Group Summary

  Discussions about the Content-ID header field started in the
  ECRIT working group when the group identified cases where a
  request with a single message body also needs to include a
  Content-ID header field in the SIP message header to refer to
  the MIME entity, but the Content-ID header field was not actually
  a SIP header field, surprising some working group members. The
  authors brought the issue to the SIPCORE working group. There
  was consensus that this was an oversight in SIP. There was a
  discussion about perhaps adding all the Content-* MIME header
  fields as SIP header fields for completeness (SIP already has
  extended the some of the MIME header fields), but the working
  group decided to focus only on Content-ID since there wasn't a
  clear need for some of the others like Content-Transfer-Encoding.

Document Quality

  This short document received detailed review from a handful 
  of working group participants. The authors incorporated received
  feedback.

  Although the Document Shepherd is not aware of implementations,
  the Content-ID header field will be useful when transporting
  data for location conveyance and emergency calls. There may be
  implementations of Content-ID as a SIP header field since
  RFC 5368 shows Content-ID as a SIP header field in its examples.


Personnel

  Jean Mahoney is the document shepherd. Ben Campbell is
  the responsible area director.


(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 shepherd thoroughly reviewed the last versions of the draft.
  The document is ready to be 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.


(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.

  The document requires no specialized expertise beyond that
  possessed by regular participants in the SIPCORE working group.


(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.


(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.

  Each author has confirmed conformance with BCPs 78 and 79.


(8) Has an IPR disclosure been filed that references this document?
If so, summarize any WG discussion and conclusion regarding the IPR
disclosures.

  No disclosure has been filed.


(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? 

  Most of the regular WG participants reviewed the document,
  (although SIPCORE is not large), and there were no dissent.
  There was consensus that a lack of a Content-ID header field
  was an oversight in SIP.


(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.

  idnits 2.14.01 was run, and no issues were found.
  The Shepherd checked the draft against
  http://www.ietf.org/id-info/checklist.html.
  No issues were found with the draft.


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

  No formal review requirements are triggered by this document,
  aside from any required by IANA process.


(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.

  This document updates RFC 5621, and this is captured in
  the header, abstract and introduction.


(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).

  The IANA Considerations section clearly identifies the
  "Header Fields" sub-registry within the "Session Initiation
  Protocols" registry, and provides the values for a new row
  in that sub-registry.


(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.

  This document adds a new entry to an existing IANA registry.
  The registration procedure is Standards Action, which this
  document is following.


(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.

  Chris Newman's ABNF Validator, available at
  http://www.apps.ietf.org/content/tools, was run.
  The tool complained about undefined rules. However,
  those rules are defined in RFC 5322 and RFC 3261, and
  the document references those rules.