I have been selected as the General Area Review Team (Gen-ART) reviewer
for this draft (for background on Gen-ART, please see
http://www.alvestrand.no/ietf/gen/art/gen-art-FAQ.html).
Please resolve these comments along with any other Last Call comments
you may receive.

Document: draft-ietf-mmusic-decoding-dependency-05.txt
Reviewer: Brian Carpenter
Review Date: 2008-02-03
IETF LC End Date: 2009-02-09
IESG Telechat date: (if known)

Summary: Almost ready.
--------

Comments:
---------

This draft defines a retro-fit to SDP to allow for the progression from
simple layered encoding to more complex mechanisms, where different components 
of the endcoded stream depend on each other in a directed graph. The simple 
layered hierarchy could be directly deduced whereas more complex dependencies 
need to be signaled. The Motivation section does a pretty good job of explaining
this and the draft as a whole is clear and well written.

I have not checked the examples in detail.

Major issues:
-------------

> 6.1. Usage with the SDP Offer/Answer Model
...
>    Depending on the implementation, a node that does not understand DDP
>    grouping (either does not understand line grouping at all, or just
>    does not understand the DDP semantics) SHOULD respond to an offer
>    containing DDP grouping either (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).

This may be my ignorance of SDP, but how does the sender of the offer
know that the responses (2) are caused by DDP rather than by some other
part of the offer?

Minor issues:
-------------

I found the Abstract quite hard to understand until after I read the
Introduction and Motivation. I don't have any specific suggestions for
improvement; the subject is quite complex for a newcomer.

> 1.   Introduction
...
>    When drafting
>    [I-D.ietf-avt-rtp-svc], it was observed that the aforementioned lack
>    in signaling support is one that is not specific to SVC, 

Actually this is the first time that the problem is identified as a lack
of signaling, so I suggest deleting "aforementioned", which is confusing.

> 5.2.1.    SDP grouping semantics for decoding dependency
>
>    This specification defines a new grouping semantic
>    Decoding Dependency "DDP":

DDP is the acronym for Direct Data Placement (RFC 4296). If you could find
a non-clashing acronym, that might be better.