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Shepherd writeup

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?

Informational, which is reflected correctly on the title page header. This
document updates RFC 5502, which is also Informational. While RFC 5502 was AD
sponsored, the SIPCORE WG adopted this as a working group item.

The header field P-Served-User is used only in 3GPP IMS mobile networks.
Because of this, the Document Shepherd expects that during Last Call at least
one person will ask why this document did not go to the Independent stream. RFC
3113 covers the 3GPP-IETF standardization collaboration. Work on SIP extensions
that are needed for 3GPP networks occurs in the IETF. There was no pushback
against adopting this draft in the SIPCORE working group.

(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.

Within 3GPP-specified mobile networks, the SIP header field P-Served-User
[RFC5502] conveys the identity of the served user, his/her registration state,
and the session case between a SIP proxy known as a Serving Call Session
Control Function (S-CSCF) and a SIP Application Server (AS). Any calls that a
user places (originates) or receives (terminates) pass through the user's
assigned S-CSCF. Each user has a user profile that informs the S-CSCF of which
action to perform depending on the session direction (originating or
terminating) and the user state (registered or not). RFC 5502 covers basic
originating and terminating session cases, but does not cover the case of call
diversion services (CDIV) when the session is re-targeted. Without a session
case for originating after CDIV, a S-CSCF cannot trigger an originating service
for the diverting user nor can an AS execute the procedures for this particular
session case.

This document defines a new P-Served-User header field parameter, "orig-cdiv",
which conveys the session case of an originating session after CDIV services
have been invoked. This document also fixes the ABNF in RFC5502 and provides
more guidance for using the P-Served-User header field.

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

This document started out in the DISPATCH working group. During discussions on
list, the DISPATCH working group found issues with RFC 5502's ABNF for the
P-Served-User header field, so this draft captures that feedback. While this
draft was being discussed in DISPATCH, the SIPCORE charter was expanded
slightly, and the DISPATCH chairs felt that this document should go SIPCORE to
see if the WG wanted to take it on (originally the draft was going to go the
AD-sponsored route). The WG accepted the work with lots of +1s to adopt. It
received thorough feedback from a few of the participants, all of which was

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?

This addition to the P-Served-User header field will be implemented in 3GPP
mobile networks, so multiple vendors will be implementing this draft.

The document's Acknowledgments section thanks reviewers who had significant
feedback, and all feedback was addressed.

Since the document updates the Header Fields sub-registry of the SIP Parameters
registry by adding a reference, the designated expert Adam Roach looked at it
and had no issues.


  Who is the Document Shepherd? Who is the Responsible Area

Document Shepherd: Jean Mahoney

Responsible Area Director: Ben Campbell

(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 shepherd checked that all feedback provided on both the DISPATCH
and SIPCORE lists was incorporated or otherwise addressed in document updates.
This 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?


(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.


(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.

The Document Shepherd has no specific concerns or issues with the draft.

(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.

The author confirmed that she had no IPR to declare on this draft.

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

None 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?

The draft was adopted by the working group with lots of +1s. It received
thorough feedback from a handful of WG participants in both DISPATCH and

(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 and the Internet-Drafts
Checklist). Boilerplate checks are not enough; this check needs to be

idnits 2.15.01 was run, and no issues were found. The Shepherd checked the
draft against  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.

According to RFC 5727, documents that specify Informational SIP header fields
pass through an Expert Review system. Adam Roach, as designated expert for SIP
header fields, reviewed the draft and had no issues with it.

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


(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?


(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.


(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 5502. This information is clearly 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 and shows
how to modify the row in the subregistry with the new reference to this

The IANA Considerations section clearly identifies the "Header Field Parameters
and Parameter Values" sub-registry within the "Session Initiation Protocols"
registry, and provides the values for 3 new rows 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 does not define any new IANA registries.

(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.

This document corrects errata filed against the ABNF in RFC 5502
(, The updated ABNF received feedback
on the SIPCORE WG mailing list.

Chris Newman's ABNF Validator, available at, was run. The tool complained about
undefined rules. However, those rules are defined in RFC 3261, and the document
references those rules.