Duplication Grouping Semantics in the Session Description Protocol
draft-ietf-mmusic-duplication-grouping-04

[Ballot comment]
3.1:


  The "a=group:DUP" semantics MUST be used to group the redundant
  streams except when the streams are specified in the same media
  description, i.e., in the same "m" line (See Section 3.2).

Don't you mean "is" instead of "MUST be"? I don't understand what the MUST means in this context other than "is".

3.1 & 3.2:

  ...the order of the listed redundant streams does
  not strictly indicate the order of transmission, although it is
  RECOMMENDED that the stream listed first is sent first, with the
  other stream(s) being the (time-delayed) duplicate(s).

Is there any downside to doing them out of order (or any upside to doing them in order)? If yes, why isn't it a MUST? If no, why the RECOMMENDation?

[Ballot discuss]
Section 3.3:
"(1) with an answer that ignores the grouping attribute ... In the first case ..."

How does the sender recognize that the grouping attribute has been "ignored"?  Do you mean to say that the answer will *omit* the grouping attribute?  That would be something the sender could recognize and act on.

[Ballot comment]
In his OPS-DIR review, Fred summarizes pretty well the operational impacts stemmed from this specification.
I would be worth the extra couple of paragraphs IMHO. A new section "operational impact" would be ideal.
For completeness, Fred's review is included below:

The operational impacts of the duplication mechanism (which is in use operationally, if I'm not mistaken) are three-fold:
- impact on total traffic load
- impact on routing
- impact on receiving system

The impact on traffic load is obvious: if I duplicate every packet among a set of packets, I double its total traffic load.

The impact on routing is somewhat glossed over by the document, although it is hinted at in comments about using different addresses and so preferring different routes in at least parts of the path. Sending separate packet streams that use the same route subjects all of the traffic streams to the same set of potential failures; if a packet from stream 1 is subject to loss at a congested interface or a place where routing is unstable, so will its counterpart in stream 2. If a given interface en route is heavily loaded, doubling a component of its service load won't reduce that. An important characteristic of these separate streams, therefore, is disjoint routing, and ideally routing along paths unlikely to experience simultaneous failures (e.g., using different lambdas in the same fiber doesn't help if the fiber is cut).

The impact on the receiving system is that something one might consider architecturally unusual, such as duplication or reordering of packets and the implied processing, suddenly becomes normal. Duplication is obvious. Reordering would happen when traffic on one stream consistently arrives earlier than that another, and a packet is lost on the first. The arriving packet on the second stream will be perceived as a packet out of order. One can hopefully expect RTP's application to recognize the matter and resolve it, but it would be nice if that could happen as early in packet processing as possible. So one has an increased interrupt and processing load on the receiving system, and the algorithms used to deal with duplicated or reordered traffic may need tuning.

I don't know that I would request any changes to the document. If I did, it would be to highlight these issues and point to other RFCs or operational procedures that could be used to mitigate them.

[Ballot comment]
-- Section 3.3 --

  (1) with an answer that ignores the grouping attribute or (2) with a
  refusal to the request (e.g., 488 Not Acceptable Here or 606 Not
  Acceptable in SIP).

SIP?  Or should that be "SDP"?

IESG/Authors/WG Chairs:

IANA has reviewed draft-ietf-mmusic-duplication-grouping-03.  Authors should review the comments and/or questions below.  Please report any inaccuracies and respond to any questions as soon as possible.

IANA's reviewer has the following comments/questions:

IANA understands that, upon approval of this document, there are two actions which IANA must complete.

First, in the Semantics for the "group" SDP Attribute registry in the Session Description Protocol (SDP) Parameters page at

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

a new semantic will be registered as follows:

Semantics Token Reference
------------------------------------- ------ --------------
Duplication DUP [ RFC-to-be ]

Second, in the Semantics for the "ssrc-group" SDP Attribute registry in the Session Description Protocol (SDP) Parameters page at

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

a new semantic will be registered as follows:

Token Semantics Reference
------- ----------------------------- --------------
DUP Duplication [ RFC-to-be ]

IANA understands that these two actions are the only ones required 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.

The following Last Call announcement was sent out:

From: The IESG
To: IETF-Announce
CC:
Reply-To: ietf@ietf.org
Sender:
Subject: Last Call:  (Duplication Grouping Semantics in the Session Description Protocol) to Proposed Standard


The IESG has received a request from the Multiparty Multimedia Session
Control WG (mmusic) to consider the following document:
- 'Duplication Grouping Semantics in the Session Description Protocol'
  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 2013-09-24. 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


  Packet loss is undesirable for real-time multimedia sessions, but can
  occur due to congestion, or other unplanned network outages.  This is
  especially true for IP multicast networks, where packet loss patterns
  can vary greatly between receivers.  One technique that can be used
  to recover from packet loss without incurring unbounded delay for all
  the receivers is to duplicate the packets and send them in separate
  redundant streams.  This document defines the semantics for grouping
  redundant streams in the Session Description Protocol (SDP).  The
  semantics defined in this document are to be used with the SDP
  Grouping Framework.  SSRC-level (Synchronization Source) grouping
  semantics are also defined in this document for RTP streams using
  SSRC multiplexing.




The file can be obtained via
http://datatracker.ietf.org/doc/draft-ietf-mmusic-duplication-grouping/

IESG discussion can be tracked via
http://datatracker.ietf.org/doc/draft-ietf-mmusic-duplication-grouping/ballot/


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

PROTO Writeup for draft-ietf-mmusic-duplication-grouping-03

(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. The title page notes the document as Standards Track.


(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

  Packet loss is undesirable for real-time multimedia sessions, but
  can occur due to congestion, or other unplanned network outages.
  This is especially true for IP multicast networks, where packet loss
  patterns can vary greatly between receivers.  One technique that can
  be used to recover from packet loss without incurring unbounded
  delay for all the receivers is to duplicate the packets and send
  them in separate redundant streams.  This document defines the
  semantics for grouping redundant streams in the Session Description
  Protocol (SDP).  The semantics defined in this document are to be
  used with the SDP Grouping Framework [RFC5888].  SSRC-level
  (Synchronization Source) grouping semantics are also defined in this
  document for RTP streams using SSRC multiplexing.


Working Group Summary

  There is WG consensus behind this draft. All issues raised during
  and before WGLC have been addressed.


Document Quality

  The document has received multiple reviews from working group
  participants and the document shepherd.  There is currently
  at least one vendor implementing this mechanism and various
  other vendors have expressed interest for this technique.


Personnel

Who is the Document Shepherd? Who is the Responsible Area
Director?

  Ari Keranen is the Document Shepherd, and the Responsible Area
  Director is Gonzalo Camarillo.


(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 has reviewed the past three versions of the
document and believes the document is ready for publication.


(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.

No need for any such review.


(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 specific 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.

Yes, the shepherd has received confirmation from all authors.


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

There are no filed IPR disclosures for this document.


(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? 

  There seems to be good consensus on the current document by the WG,
  which seems to understand and agree with it.


(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 http://www.ietf.org/tools/idnits/ and the Internet-Drafts
Checklist). Boilerplate checks are not enough; this check needs to be
thorough.

The document has been checked by idnits and the I-D Checklist and no
nits have been found (apart from references to this document that
will be fixed by RFC editor).


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

  The document provides extensions to SDP only and as such the
  necessary review has already been done by the MMUSIC WG.


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

Yes, all references are classified 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?

  There is no such dependency.


(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.

  There are no downward normative references.


(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.

  The publication of this document will not change the status of any
  existing RFC.


(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 has been reviewed and no issues found.


(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.

  There are no new IANA registries defined by this document.


(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.

  There is no such formal language in the draft.