Subject: [MMUSIC] Prelim copy of comedia-02 available

From: "David Yon" <[email-masked]>
Date: Tue, 2 Apr 2002 14:16:24 -0500

http://www.dialout.net/public/ietf/draft-ietf-mmusic-sdp-comedia-02.txt

The above link is an unofficial copy that I've posted for discussion
purposes.  The following changes have been made since comedia-01:

	- The assumption now is that media only ever needs a single
	  connection, which simplifies the semantics of
"direction:both".

	- A method to reduce the probability that "direction:both"
	  will result in an extra connection is discussed (section 2.4).

	- Rohan Mahy's text about UDP and RTP/AVP is incorporated
	  (sections 2.6 and 5.4).

	- "direction:reuse" has been removed.  Section 4.3 covers 
	  the scenarios that reuse intended to address.

	- A discussion of listener and connection lifetime has been 
	  added (section 4).

	- The BNF has been checked for compatibility with SDPnew.

I've gone through and made sure that comedia meets the SDP requirements
discussed in Jeorg's slides in Minneapolis (session setup, session
pause, session resume, session redirect, session parameter renegotiate,
session teardown).  At this point I don't see anything missing.
Pause/resume/redirect/renegotiate are directly addressed in section 4.

Modulo any showstopper issues brought up in the list, I'm ready to
submit this as the official comedia-02 at any time. 

Everyone is encouraged to review and provide feedback as soon as
possible.  We'd like to get this into Last Call in the next week or two.

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---

From: Colin Perkins <[email-masked]>
Date: Fri, 05 Apr 2002 18:52:20 -0500

>possible.  We'd like to get this into Last Call in the next week or two.

This looks pretty good. A few comments:

 - The Protocol Identifiers section may want to point to the discussion of 
   m= in SDP, which specifies that the identifiers are MIME subtypes for
   audio/video/application media types. This is implicit in the examples,
   and explicit in SDP, but not noted in this draft.
 
 - Section 2.2 ("Semantics of direction:active") could go with an SDP
   fragment, showing exactly where the source and destination address 
   and port are specified (i.e. an SDP fragment including c=, m= and
   a=direction lines).
 
 - How specific is this to SDP used with offer/answer? It's probably
   appropriate to have a section explaining how comedia is used with
   SIP (i.e. offer/answer), RTSP, MEGACO and perhaps SAP.

 - Section 2.6 says that you MUST NOT send media on a passive port until 
   a packet has been received. Does this include not sending RTCP? 

 - In section 3, how is the source address useful given that it can't be
   trusted? More explanation of how it can be used is probably needed.

 - Section 4.1: the time window is the t= line?

 - The possible race when both parties select diraction:both concerns me,
   but I'm not sure I can see a better alternative (unless there's some
   trick to make one side win deterministically, for example the lowest
   IP address wins).

Editorial comments:

 - The section numbering needs to start with the introduction as section 1.
 - The introduction and motivation sections could easily be combined. Add a
   couple of sentances to the end of the combined section saying that "this
   memo defines two new protocol identifies, TCP and TLS, along with the
   syntax and semantics of the a=direction attribute".
 - Move the terminology section after the combined introduction/motivation
 - A couple of instances of non-ASCII characters need to be fixed.
 - A couple of places say "the a= line" but mean "the a=direction:" line 
   (e.g. end of section 2.2, second paragraph of section 2.3, ...)

Regards,
Colin