RTP Header Extension for the RTP Control Protocol (RTCP) Source Description Items
draft-ietf-avtext-sdes-hdr-ext-07

[Ballot comment]

Thanks for handling my DISCUSS point.

--- OLD COMMENTS below, I didn't check 'em

- So this one confused me for a bit but I was thinking
about RFC4568 - shame about that acronym collision;-)
It'd have helped this reader to say that this is not
about sending keys in header fields:-) But I'm probably
not the intended reader, so it's fine that you didn't.

- I wonder if confidentiality protection of these header
fields is likely? Is that more or less likely to be
deployed than some security for RTCP? If there's a
significant difference then I think that ought be called
out. Just pointing at rfc6904 doesn't seem entirely
sufficient to me if nobody ever does it.

- Has someone done an analysis of the privacy
implications of moving values from one context (RTCP) to
another (RTP) over the range of likely deployments? Note:
I'm not asserting that there is a significant privacy
exposure here, I don't know if there is or not. So I'm
just asking if folks have thought about that and e.g.
whether or not some data exposed in this header field
could allow easier re-identification or correlation or
some similar and possibly subtle privacy issue.

[Ballot comment]

think these were addressed by 06

I have reviewed this document (draft-ietf-avtext-sdes-hdr-ext-05) as part of the
Operational directorate's  ongoing effort to review all IETF documents being
processed by the IESG.  These comments were written with the intent of improving
the operational aspects of the IETF drafts. Comments that are not addressed in
last call may be included in AD reviews during the IESG review.  Document editors
and WG chairs should treat these comments just like any other last call comments.

I am not an expert on the details of RTP thus treat my comments are not really on the technical side of the document. I found the document fine and have no concerns with it.

The IDnits comments can be ignored. They are to be fixed by RFC editor when the
RFC numbers are known.

I have few minor comments:

o Line 180 at the beginning of the paragraph starts “That document also..” Since this is the start of the new paragraph I would recommend setting up the context and explicitly say what “that document” is.

o Line 304 "extension word aligned, thus in total 36 bytes.” seems to assume a word is 32 bits. Due historical reasons to avoid confusion I would explicitly state that a 32 bit alignment is what ‘word aligned’ means.

o Line 458 "shall be applied, i.e. discard items that can be determined to be”
          ^^^^^^ although it is not strictly required but I would use the familiar uppercase format here and probably also use more typical MUST here..

- Jouni
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[Ballot discuss]

I'd like to check if there's a small hole in the
security/privacy properties here. If there is I hope that
a little re-wording will handle it.

You say: (1) "In RTP sessions where any type of
confidentiality protection is enabled for RTCP, the SDES
item header extensions MUST also be protected." And then
you say: (2) "The security level that is applied to RTCP
packets carrying SDES items SHOULD also be applied to
SDES items carried as RTP header extensions."

My concerns are that the SHOULD in (2) isn't really well
motivated (for me) - you just seem to say that someone
who doesn't follow the SHOULD has to say why, but I don't
think that's likely a run-time concept.  Secondly, (1)
doesn't say that the new stuff has to be protected in the
same way, e.g. with the same endpoints having the keys,
and not e.g. where the RTCP data has e2e protection but
the new header field just has hop-by-hop protection.

Are my concerns justified? (If not, that's fine you'll
tell me and we're done:-)

If these are justified concerns, I think we can easily
get around them by (a) closing that potential loophole in
(1) and (b) s/SHOULD/MUST/ in (2) or else (c) better
specify an exception to the SHOULD that makes sense at
coding time or at run time.

[Ballot comment]

- So this one confused me for a bit but I was thinking
about RFC4568 - shame about that acronym collision;-)
It'd have helped this reader to say that this is not
about sending keys in header fields:-) But I'm probably
not the intended reader, so it's fine that you didn't.

- I wonder if confidentiality protection of these header
fields is likely? Is that more or less likely to be
deployed than some security for RTCP? If there's a
significant difference then I think that ought be called
out. Just pointing at rfc6904 doesn't seem entirely
sufficient to me if nobody ever does it.

- Has someone done an analysis of the privacy
implications of moving values from one context (RTCP) to
another (RTP) over the range of likely deployments? Note:
I'm not asserting that there is a significant privacy
exposure here, I don't know if there is or not. So I'm
just asking if folks have thought about that and e.g.
whether or not some data exposed in this header field
could allow easier re-identification or correlation or
some similar and possibly subtle privacy issue.

[Ballot comment]
Editorial

OLD:
First, some requirements language and terminology are defined. The following section motivates why this header extension is sometimes required or at least provides a significant improvement compared to waiting for regular RTCP packet transmissions of the information.

NEW:
First, some requirements language and terminology are defined. The section 3 motivates why this header extension is sometimes required or at least provides a significant improvement compared to waiting for regular RTCP packet transmissions of the information.

[Ballot comment]
I too was confused about why MID was not being registered here, but then saw that it is being registered in draft-ietf-mmusic-sdp-bundle-negotiation. I think the text in Section 3 should make this more clear.

I also gather that in some previous version of this draft it may have been registering both, and so there is language in 5.2 and 5.3 ("Initial assignments," "SDES Items") indicating that multiple things are being registered. I think these should be made singular.

[Ballot comment]
The first mention of UTF-8 needs a reference.

I am agreeing with Mirja about registering MID, as the document argues that it would be a good idea.

[Ballot comment]
This is a very clear and well written doc. Thanks. Two minor comments:

1) The calculation for the number of transmission N seems slightly over-complicated: "N is selected so that the header extension target delivery probability reaches 1-P^N, where P is the probability of packet loss." Does a new participant already know the loss probably e.g. at the time of joining? Is it correct that if it is assumed to be p=0 that one will send the extension header only once? Should there be a minimum...?

2) Should this doc also register MID?

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

IANA has completed its review of draft-ietf-avtext-sdes-hdr-ext-05.txt. If any part of this review is inaccurate, please let us know.
Upon approval of this document, IANA will complete two actions.

First, in the RTP Compact Header Extensions registry at http://www.iana.org/assignments/rtp-parameters, IANA will register the following:

Extension URI: urn:ietf:params:rtp-hdrext:sdes
Description: Reserved as base URN for RTCP SDES items that are also defined as RTP Compact header extensions.
Contact: Authors of [RFCXXXX]
Reference: [RFCXXXX]

This registration must be approved by the designated expert for this registry. IANA will initiate this review.

Second, IANA will create the following sub-registry under the RTP Compact Header Extensions registry, with the same format:

Registry Name: RTP SDES Compact Header Extensions
Registration Procedure(s): Expert Review
Expert(s): Unassigned
Reference: [RFCXXXX]

Extension URI: urn:ietf:params:rtp-hdrext:sdes:cname
Description: Source Description: Canonical End-Point Identifier (SDES CNAME)
Contact: Authors of [RFCXXXX]
Reference: [RFCXXXX]

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 Specialist
ICANN

The following Last Call announcement was sent out:

From: The IESG
To: "IETF-Announce"
CC: ben@nostrum.com, avtext@ietf.org, jonathan@vidyo.com, avtext-chairs@ietf.org, "Jonathan Lennox" , draft-ietf-avtext-sdes-hdr-ext@ietf.org
Reply-To: ietf@ietf.org
Sender:
Subject: Last Call:  (RTP Header Extension for RTCP Source Description Items) to Proposed Standard


The IESG has received a request from the Audio/Video Transport Extensions
WG (avtext) to consider the following document:
- 'RTP Header Extension for RTCP Source Description Items'
  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 2016-03-18. 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


  Source Description (SDES) items are normally transported in RTP
  control protocol (RTCP).  In some cases it can be beneficial to speed
  up the delivery of these items.  Mainly when a new source (SSRC)
  joins an RTP session and the receivers needs this source's identity,
  relation to other sources, or its synchronization context, all of
  which may be fully or partially identified using SDES items.  To
  enable this optimization, this document specifies a new RTP header
  extension that can carry SDES items.




The file can be obtained via
https://datatracker.ietf.org/doc/draft-ietf-avtext-sdes-hdr-ext/

IESG discussion can be tracked via
https://datatracker.ietf.org/doc/draft-ietf-avtext-sdes-hdr-ext/ballot/


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

Hi,

Here is my AD evaluation of draft-ietf-avtext-sdes-hdr-ext-02. I have a few questions and comments that I would like to resolve prior to IETF last call, as well as some editorial comments that can be handled whenever is convenient:

Thanks!

Ben.

=== Substantive:

- 4.2.1, last paragraph:
The guidance about RTP middleboxes seems to apply to header extensions in general. Is this not already documented somewhere else?

- 4.2.6, 2nd paragraph: "... issues can be avoid by performing ..."

Do you mean "... the receiver performing..."?

- 5.1:

Please elaborate on what you mean by sub-space. I don't think RFC 5285 contemplated this idea. How would IANA indicate that things in this sub-space have additional rules beyond those of 5285? Or more concretely, how do we indicate that urn:ietf:params:rtp-hdrext:sdes:cname is bound by the rules for urn:ietf:params:rtp-hdrext:sdes?

Paragraph 2 says "preferably in a publically available reference." I think that's a hard requirement in 5285. This seems to relax that--I assume that is not the intent. Security considerations are also already required by 5285 (but there is no mention of privacy considerations.)

-6, general:

The requirements here are pretty abstract. Would it make sense to say something to the effect of "If you SRTP it you MUST encrypt the RTP extension header"?

-6, paragraph 2:
- "In RTP sessions where any type of confidentiality protection is
  enabled for RTCP, the SDES item header extensions MUST also be
  protected per default. "

Why “per default”? That tells me that an implementation would, if not configured otherwise, protect the header extension if it protected RTCP. Do you intend to allow the “configured otherwise” loophole?

- "users of SRTP need to implement encrypted header extensions"
Do you mean to say “implementers must also implement” or “users must also use”? Or both?

- "Commonly, it is expected that the same security level is
  applied to RTCP packets carrying SDES items, and to an RTP header
  extension containing SDES items. "

The phrase “Commonly, it is expected…” seems to water down the guidance. Any reason not to say SHOULD or MUST here?

- 6, paragraph 3:
- "there SHOULD be strong
  requirements on integrity and source authentication"

What needs to have that strong requirement? The specs for extensions in the sub-space? Or does this mean to say that "there SHOULD be strong integrity protection and source authentication"?

=== Editorial:

- General: There's a fair number of instances of noun/verb agreement issues. I will point out the ones I found, but there's enough that I would suggest proofreading for more.

- 1, 2nd paragraph:

--"Some SDES items performs binding or identifies synchronization context"
Singular/plural disagreements among [items, performs, identifies, context]

-- "No use case has identified where this information is required at the same time as the first RTP packets arrive."
I think it would be helpful to mention that this extension actually allows information deliver in the first RTP packets in the first paragraph. Leaving it to an in-passing remark here sort of buries the lede.

-1, last paragraph:
With the heavy use of passive voice in this paragraph, it was not immediately obvious to me that it talked about the following sections of the document itself. Please consider something more of the form of “Section 2 defines requirements language and terminology…”

-3, 2nd paragraph: "because an end-point is adding"
s/is adding/adds

-3, 3rd paragraph: "Thus an RTP header extension for carrying SDES items like CNAME is a powerful combination..."
What combination do you have in mind? When in combination with 6051? Or do you just mean to say it's a powerful tool?

-3, 4th paragraph:
s/does provide/provides

-3, 2nd to last paragraph:

You mean to say that that the MID spec already defines the header extension, not that _this_ draft defined it, right?

-4.2.2, 2nd paragraph:"If the packet expansion cannot be taken into account..."
Do you mean "... is not taken into account..."?

-5, first bullet:
Consider reordering this a bit: “… the URN sub-space…for SDES items”"

-5.1, first paragraph:"some additional considerations are provided here that needs to be considered"
noun/verb disagreement (considerations is plural, needs is singular)

- 5.1, 2nd paragraph: "security and privacy consideration"
s/consideration/considerations

-6, 2nd paragraph:
"If the security level is different,
  it is important to consider the security properties as the worst in
  each aspect for the different configurations."

I find this sentence hard to understand. I _think_ you are saying that the protection of the SDES item is equal to the protection of RTCP or that of the RTP header extension, whichever is lower?

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; a new family of RTP header extensions is defined,
for which interoperability will be necessary.

(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

  Source Description (SDES) items are normally transported in the RTP
  control protocol (RTCP).  In some cases it can be beneficial to
  speed up the delivery of these items.  Mainly when a new source
  (SSRC) joins an RTP session and the receivers needs this source's
  identity, relation to other sources, or its synchronization
  context, all of which may be fully or partially identified using
  SDES items.  To enable this optimization, this document specifies a
  new RTP header extension that can carry SDES items.

Working Group Summary

  The document went through working group last call.  Several people
  commented during last call that they had read the document but had
  no issues with its content.

Document Quality

  The document got good reviews from AVText members.  The document
  generalizes a mechanism which is used by the SDP BUNDLE mechanism,
  which required for all WebRTC implementations.

Personnel

  The document Shepherd is Jonathan Lennox.  The Responsible Area
  Director is 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 read the submitted version of the document
fully, as well as reviewing and commenting on several earlier versions
of the document.

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

This document got good review by multiple people from AVText and all
comments were addressed.

(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 broader reviews are needed.

(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.

All the authors have indicated they no of know relevant IPR on this
document.

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

No IPR Disclosures have 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 group's most active (and expert) participants have
indicated agreement with the document.  No disagreement was
indicated.


(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.

http://tools.ietf.org/idnits?url=http://tools.ietf.org/id/draft-ietf-avtext-sdes-hdr-ext-02.txt

Later versions of several informatively-cited documents have been
released since this version of this draft was published.  None of
the changes in these versions alter their use in this document; the
versions can be updated after IETF Last Call or by the RFC Editor.

(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 needed.

(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.

No.

(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 document provides additional constraints for a subspace of the
existing RTP Compact Header Extensions registry.  This registry is
Expert Review required, and thus this provides additional guidance to
that registry's experts.  The new requirements are clearly specified.
No new registries are defined.


(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.

No new registries are defined.

(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.

No formal language is used in the document.