Applying Signaling Compression (SigComp) to the Session Initiation Protocol (SIP)
RFC 5049

[Ballot discuss]
This document should discuss how it interacts with RFC 3749 compression.

When SIP-TLS is used, if both this and RFC 3749 are implemented, which
should be used for interoperability?

draft-ietf-lemonade-compress has text resulting from Cullen's discuss on this topic.

[Ballot discuss]
3320 section 8.7 (Decompression failures)

"If a decompression failure occurs when decompressing a message then
  the UDVM informs the dispatcher and takes no further action.  It is
  the responsibility of the dispatcher to decide how to cope with the
  decompression failure.  In general a dispatcher SHOULD discard the
  compressed message (or the compressed stream if the transport is
  stream-based) and any decompressed data that has been outputted but
  not yet passed to the application.
"

and in this draft there is no mention of how SIP should handle decompression failures.


2007.07.18:
NOTE: I have been in contact w/ the authors and they agree to add wording to clear this up.

From: Carsten Bormann
Subject: sigcomp-sip: David Ward's DISCUSS
Date: Wed, 18 Jul 2007 09:12:57 +0200
To: rohc@ietf.org
...snip ...
" ...the discussion of NACK in the draft only relates to SigComp 
state; it could mention that NACK (now being mandatory) is the 
general way to handle decompression failure.

All of this is editorial, I think, but I also think it would be nice 
not to entirely rely on the reader making the connections.
Any opinions?  I could go ahead and draft some text.

Gruesse, Carsten
"

Most likely his text will clear my discuss.

[Ballot comment]
The Security Considerations section indicates that keeping SigComp states does not pose
additional security risks for two reasons.  I believe the second reason,

  "b) this is on a voluntary basis and a SigComp endpoint can choose not to offer it"

is irrelevant.  I suggest deleting b).

[Ballot comment]
The Security Considerations section indicates that keeping SigComp states does not pose
additional security risks for two reasons.  I believe the second reason,

  "b) this is on a voluntary basis and a SigComp endpoint can choose not to offer it"

is irrelevant.  I suggest deleting b).

[Ballot discuss]
3320 section 8.7 (Decompression failures)

"If a decompression failure occurs when decompressing a message then
  the UDVM informs the dispatcher and takes no further action.  It is
  the responsibility of the dispatcher to decide how to cope with the
  decompression failure.  In general a dispatcher SHOULD discard the
  compressed message (or the compressed stream if the transport is
  stream-based) and any decompressed data that has been outputted but
  not yet passed to the application.
"

and in this draft there is no mention of how SIP should handle decompression failures.

[Ballot discuss]
3320 section 8.7 (Decompression failures)

"If a decompression failure occurs when decompressing a message then
  the UDVM informs the dispatcher and takes no further action.  It is
  the responsibility of the dispatcher to decide how to cope with the
  decompression failure.  In general a dispatcher SHOULD discard the
  compressed message (or the compressed stream if the transport is
  stream-based) and any decompressed data that has been outputted but
  not yet passed to the application.
"

and in this draft there is no mention of how SIP should handle decompression failures in this doc.

[Ballot comment]
I'm glad the authors thought carefully about the Identifier Comparison Rules (section 9.2), but I'm worried this could still be a can'o'worms.  One problem could be with URNs that may also be IRIs.  If the original URN has extended characters, they can get canonicalized or otherwise changed in transit, and then the comparison may not work even though the generating application always initially provides the same URN. 

Is it still possible to limit the kinds of identifiers?  Perhaps recommend UUID URNs at a SHOULD level and note the difficulties in equality comparisons for other kinds of URNs?

IANA Last Call Comment:

Action #1:
Upon approval of this document, the IANA will make the
following assignments in the "Session Initiation Protocol (SIP)
Parameters" registry located at

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

sub-registry "Header Field Parameters and Parameter Values -
per [RFC3968]"

Predefined
Header Field Parameter Name Values Reference
---------------------------- --------------- --------- ---------

Via sigcomp-id No [RFC-rohc-sigcomp-
sip-06]


Action #2:
Upon approval of this document, the IANA will make the following
assignments in the "Session Initiation Protocol (SIP) Parameters"
registry located at

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

sub-registry "SIP/SIPS URI Parameters - per [RFC3969]"

Parameter Name Predefined Values Reference
-------------- ----------------- ---------
sigcomp-id No [RFC-rohc-sigcomp-sip-06]


We understand the above to be the only IANA Actions for
this document.

PROTO Write-up

(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?

I (Lars-Erik Jonsson) am the Document Sheperd for this document, and I have personally reviewed this version of the document, which I believe is ready for publication.

(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?

The document has been reviewed by both key WG members and by key non-WG members, and I am confident with the depth and breadth of the reviews.

(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 concerns!

(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.

No concerns!

(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?

There is strong consensus behind this document within the ROHC WG.

(1.f)  Has anyone threatened an appeal or otherwise indicated extreme
      discontent?

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?

I have reviewed the document, and believe it satisfies all criterias.

(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].

References are split into normative/informative. There is one pending normative reference to draft-ietf-sip-outbound-07.

(1.i)  Has the Document Shepherd verified that the document IANA
      consideration 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 suggested a
      reasonable name for the new registry?  See
      [I-D.narten-iana-considerations-rfc2434bis].  If the document
      describes an Expert Review process has Shepherd conferred with
      the Responsible Area Director so that the IESG can appoint the
      needed Expert during the IESG Evaluation?

The IANA registrations requested are well specified and should be fine.

(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?

There are no such sections.

(1.k)  The IESG approval announcement includes a Document
      Announcement Write-Up.  Please provide such a Document
      Announcement Writeup? 


Technical Summary

  This document describes some specifics that apply when Signaling
  Compression (SigComp) is applied to the Session Initiation Protocol
  (SIP), such as default minimum values of SigComp parameters,
  compartment and state management, and a few issues on SigComp over
  TCP.  Any implementation of SigComp for use with SIP must conform to
  this document, in addition to SigComp and support of the SIP and
  Session Description Protocol (SDP) static dictionary.

Working Group Summary

  This document has been in the workings for several years, and it has
  been given the time needed to make it mature. The document has
  been carefully reviewed by both the WG and various other SIP and
  SigComp experts, and there is WG consensus that the document
  should now be published as an RFC.

Document Quality

  There are several independent implementers of SigComp, and they
  have collectively developed the content of this specification, based
  on running code experience.

Personnel
       
  Document Sheperd for this document is Lars-Erik Jonsson, and Magnus
  Westerlund is the Responsible Area Director.