A Call Control and Multi-Party Usage Framework for the Session Initiation Protocol (SIP)
draft-ietf-sipping-cc-framework-12

[Ballot comment]
Two very minor editorial nits:

First sentence of section 2.7.1: expansion of acronyms "SIPS"?

Renumber/reorganize sections 2.6.2-2.6.7 to indicate that these sections  all describe "Media Inermediaries", while sections 2.7 through 2.9 discuss other topics?

[Ballot comment]
- Abstract states "This framework also describes other goals that embody
the spirit of SIP applications as used on the Internet" - it would have
been useful if this sentence at least had identified a few of these goals.

- Section 2.3: "peers can take advantage of end-to-end message integrity
or encryption" - I would say this applies only when certain conditions are
met and hence perhaps something like "peers may take advantage..." or
similar would be better.

- Section 2.6.7.2: Acronym "IVR" introduced without explanation. An early
"Acronyms" section would be useful.

- Section 3: The sentence "One means of accomplishing this is through the
ability to define and obtain URIs for these actions as described in
section ." seems to be missing the final section reference.


From Gen Art...

Nits/editorial comments:
- in Abstract page 2: SIP -> Session Initiation Protocol (SIP)

- ToC page 3: Far fork -> Far-fork (or Near-fork -> Near fork but
fixing the far branch seems better)

- Toc page 4: Acknowledgements -> Acknowledgments
(IETF/RFC Editor spelling)

- 2.3 page 10: the UA abbrev should be introduced (and IMHO far before)

- 2.4.2.1 page 12: large- scale -> large-scale

- 2.6.7.2 page 17: the IVR abbrev must be introduced

- 3.3.2 page 26: from controller) -> from controller):

- 3.3.2 page 26: i.e. -> i.e.,
(same for other i.e. and e.g.)

- 3.3.5 page 28: a central mixer) -> a central mixer).

- 3.3.8 page 29 (title): Far fork -> Far-fork

- 3.2.8 page 30: forked-media -> forked media ?

- 4 page 30: The class ... include -> includes ?

- 6.31 page 39: (ex: -> (e.g.,

- 7 page 39 (title): Acknowledgements -> Acknowledgments

[Ballot discuss]
Magnus is out for a bit so I am going to hold his review ....

Although brief, the Security Considerations section reads well (a more
comprehensive trust/threat model analysis for the proposed framework would
have been nice though). It could be useful to add a sentence or two on
anonymity aspects in the context of the proposed framework. The body of
the text mentions this aspect in passing once (2.6.4) but there is no
mentioning in the Security Considerations section.

In the sixth paragraph, an explicit method for replay attack prevention is
recommended (lower-case "should"). I am not sure about the reason for this
and could potentially see other ways to mitigate such attacks. Hence, one
suggestion could be to replace the current "In the case of features
initiated by a former participant, these should be protected against
replay attacks by using a unique name or identifier per invocation" with:
"In the case of features initiated by a former participant, these should
be protected against replay attacks, e.g. by using a unique name or
identifier per invocation."

For clarity, I also suggest changing this section's last sentence to:
"These credentials may for example need to be passed transitively or
fetched in an event body."

A question: The third paragraph in the Security Considerations section
refers to Section 3.2 - might this be Section 2.3?

[Ballot comment]
It seems to me that SIP is getting closer and closer to needing to make routing decisions as multi-segment SIP calls are established, and as SIP servers discover each other and the capabilities of other servers.

Although not specific, I would like to urge the SIP experts to consult with the Routing Area in order to see whether there is helpful cross-fertilisation that can take place.

[Ballot comment]
The flexibility offered by this model is incredible. But I am wondering
what it means for interoperability in practice. Are systems employing
this model in use, and what do we know of their interoperability across
vendors and across potentially different ways to handle calls?

[Ballot comment]
Comments
--------

Although brief, the Security Considerations section reads well (a more
comprehensive trust/threat model analysis for the proposed framework would
have been nice though). It could be useful to add a sentence or two on
anonymity aspects in the context of the proposed framework. The body of
the text mentions this aspect in passing once (2.6.4) but there is no
mentioning in the Security Considerations section.

In the sixth paragraph, an explicit method for replay attack prevention is
recommended (lower-case "should"). I am not sure about the reason for this
and could potentially see other ways to mitigate such attacks. Hence, one
suggestion could be to replace the current "In the case of features
initiated by a former participant, these should be protected against
replay attacks by using a unique name or identifier per invocation" with:
"In the case of features initiated by a former participant, these should
be protected against replay attacks, e.g. by using a unique name or
identifier per invocation."

For clarity, I also suggest changing this section's last sentence to:
"These credentials may for example need to be passed transitively or
fetched in an event body."

A question: The third paragraph in the Security Considerations section
refers to Section 3.2 - might this be Section 2.3?

General/editorial:

- Abstract states "This framework also describes other goals that embody
the spirit of SIP applications as used on the Internet" - it would have
been useful if this sentence at least had identified a few of these goals.

- Section 2.3: "peers can take advantage of end-to-end message integrity
or encryption" - I would say this applies only when certain conditions are
met and hence perhaps something like "peers may take advantage..." or
similar would be better.

- Section 2.6.7.2: Acronym "IVR" introduced without explanation. An early
"Acronyms" section would be useful.

- Section 3: The sentence "One means of accomplishing this is through the
ability to define and obtain URIs for these actions as described in
section ." seems to be missing the final section reference.

-- Magnus

[Ballot discuss]
This is a good document, it reads well, and provides a nice overview of the requirements for
multi-party control of SIP.

However, the Security Considerations need to be enhanced to cover some of the complexities
of multi-party control, especially those introduced by the peer-to-peer approach. 

Implementing authentication, authorization, and policy in a peer-to-peer model for
establishing conversation spaces seems to introduce new problems:
(1) If authentication is being performed by "mutually untrusted participants" (bullet eight
in the Introduction), then ensuring that consistent levels of authentication were performed
becomes very difficult.
(2) It will be difficult to convey which forms of authentication credentials are acceptable,
since different participants may have different capabilities.  That is, Alice may be able to
validate certificate credentials while Bob can only handle shared keys (or whatever the
other possibilities are in SIP).
(3) Communicating how a participant was authenticated and by whom, in addition to the
list of participants, may be important.
I also believe that the same types of issues will apply with authorization and policy.

I don't believe the issues are new (I seem to recall this discussion with respect to the
conferencing framework), but they are more complicated in the peer-to-peer model.
Perhaps we can refer to security considerations in other documents and note that the
issues are exacerbated by the pee-to-peer model.

Magnus Nystrom posted a secdir review on June 14.  I believe many of his comments have
merit  and would like to discuss one on the call.  I have appended the remainder as
comments, and request that the authors include Magnus in any discussion of his comments.

From the secidr review:

    Background
    ----------
    This document describes a framework for call control and multi-party usage
    of SIP (while the abstract also talks about requirements, I did not see
    any strong requirements - at least there are no normative statements in
    the RFC 2119 sense in the document).

There are some firm protocol requirements in this document, but I wonder if they
are prominent enough without the use of 2119 language.  I also recall that use of
2119 language in this type of document is controversial...  does anyone else think
that a mechanism of some sort to highlight the requirements is needed?

[Ballot comment]
The Gen-ART Review by Francis Dupont raised a few editorial comments
  that ought to be considered:

  - in Abstract page 2: SIP -> Session Initiation Protocol (SIP)
  - ToC page 3: Far fork -> Far-fork (or Near-fork -> Near fork but
    fixing the far branch seems better)
  - ToC page 4: Acknowledgements -> Acknowledgments
    (IETF/RFC Editor spelling)
  - 2.3 page 10: the UA abbrev should be introduced (and IMHO far before)
  - 2.4.2.1 page 12: large- scale -> large-scale
  - 2.6.7.2 page 17: the IVR abbrev must be introduced
  - 3.3.2 page 26: from controller) -> from controller):
  - 3.3.2 page 26: i.e. -> i.e.,  (same for other i.e. and e.g.)
  - 3.3.5 page 28: a central mixer) -> a central mixer).
  - 3.3.8 page 29 (title): Far fork -> Far-fork
  - 3.2.8 page 30: forked-media -> forked media ?
  - 4 page 30: The class ... include -> includes ?
  - 6.31 page 39: (ex: -> (e.g.,
  - 7 page 39 (title): Acknowledgements -> Acknowledgments

[Ballot comment]
6.16.  Do Not Disturb

  In Do Not Disturb, Alice selects the Do Not Disturb option.  Calls to
  her either ring briefly or not at all and are forwarded elsewhere.
  Some variations allow specially authorized callers to override this
  feature and ring Alice anyway.  Do Not Disturb is best implemented in
  SIP using presence [RFC3264].

Should this be referencing [RFC3856]?

[Ballot comment]
From Gen Art...

Nits/editorial comments:
- in Abstract page 2: SIP -> Session Initiation Protocol (SIP)

- ToC page 3: Far fork -> Far-fork (or Near-fork -> Near fork but
fixing the far branch seems better)

- Toc page 4: Acknowledgements -> Acknowledgments
(IETF/RFC Editor spelling)

- 2.3 page 10: the UA abbrev should be introduced (and IMHO far before)

- 2.4.2.1 page 12: large- scale -> large-scale

- 2.6.7.2 page 17: the IVR abbrev must be introduced

- 3.3.2 page 26: from controller) -> from controller):

- 3.3.2 page 26: i.e. -> i.e.,
(same for other i.e. and e.g.)

- 3.3.5 page 28: a central mixer) -> a central mixer).

- 3.3.8 page 29 (title): Far fork -> Far-fork

- 3.2.8 page 30: forked-media -> forked media ?

- 4 page 30: The class ... include -> includes ?

- 6.31 page 39: (ex: -> (e.g.,

- 7 page 39 (title): Acknowledgements -> Acknowledgments

(1.a) Who is the Document Shepherd for this document? Has the
Document Shepherd personally reviewed this version of the
document and, in particular, does he or she believe this
version is ready for forwarding to the IESG for publication?

Gonzalo Camarillo is the document shepherd. He has reviewed this
document and believes it is ready to be published.

(1.b) Has the document had adequate review both from key WG members
and from key non-WG members? Does the Document Shepherd have
any concerns about the depth or breadth of the reviews that
have been performed?

There have been extensive discussions on this document on the SIPPING
list. The current revision of the draft addresses all the reviews received.

(1.c) Does the Document Shepherd have concerns that the document
needs more review from a particular or broader perspective,
e.g., security, operational complexity, someone familiar with
AAA, internationalization, or XML?

No.

(1.d) Does the Document Shepherd have any specific concerns or
issues 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. Has an IPR disclosure related to this document
been filed? If so, please include a reference to the
disclosure and summarize the WG discussion and conclusion on
this issue.

No.

(1.e) 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?

After long discussions, all the WG was behind this effort.

(1.f) Has anyone threatened an appeal or otherwise indicated extreme
discontent? If so, please summarize the areas of conflict in
separate email messages to the Responsible Area Director. (It
should be in a separate email because this questionnaire is
entered into the ID Tracker.)

No.

(1.g) Has the Document Shepherd personally verified that the
document satisfies all ID nits? (See
http://www.ietf.org/ID-Checklist.html and
http://tools.ietf.org/tools/idnits/.) Boilerplate checks are
not enough; this check needs to be thorough. Has the document
met all formal review criteria it needs to, such as the MIB
Doctor, media type, and URI type reviews? If the document
does not already indicate its intended status at the top of
the first page, please indicate the intended status here.

Yes, the draft passes ID nits.

(1.h) Has the document split its references into normative and
informative? 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
strategy for their completion? Are there normative references
that are downward references, as described in [RFC3967]? If
so, list these downward references to support the Area
Director in the Last Call procedure for them [RFC3967].

The document only has Informative references.

(1.i) Has the Document Shepherd verified that the document's IANA
Considerations section exists and is consistent with the body
of the document? If the document specifies protocol
extensions, are reservations requested in appropriate IANA
registries? Are the IANA registries clearly identified? If
the document creates a new registry, does it define the
proposed initial contents of the registry and an allocation
procedure for future registrations? Does it suggest a
reasonable name for the new registry? See [RFC2434]. If the
document describes an Expert Review process, has the Document
Shepherd conferred with the Responsible Area Director so that
the IESG can appoint the needed Expert during IESG Evaluation?

The document contains a no-op IANA Considerations Section.

(1.j) Has the Document Shepherd verified that sections of the
document that are written in a formal language, such as XML
code, BNF rules, MIB definitions, etc., validate correctly in
an automated checker?

No formal language is used in the document.

(1.k) 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.

This document defines a framework and requirements for call control
and multi-party usage of SIP. To enable discussion of multi-party
features and applications we define an abstract call model for
describing the media relationships required by many of these. The
model and actions described here are specifically chosen to be
independent of the SIP signaling and/or mixing approach chosen to
actually setup the media relationships. In addition to its dialog
manipulation aspect, this framework includes requirements for
communicating related information and events such as conference and
session state, and session history. This framework also describes
other goals that embody the spirit of SIP applications as used on the
Internet.

Working Group Summary
Was there anything in the WG process that is worth noting?
For example, was there controversy about particular points
or were there decisions where the consensus was
particularly rough?

Consensus was reached among all interested parties before requesting the
publication of this document.

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?

Some of the features in this document are widely implemented.

Personnel
Who is the Document Shepherd for this document? Who is the
Responsible Area Director? If the document requires IANA
experts(s), insert 'The IANA Expert(s) for the registries
in this document are .'


The document shepherd is Gonzalo Camarillo. The responsible AD is Jon
Peterson.