Subject: [MMUSIC] Some issues with draft-ietf-mmusic-sctp-sdp-02

From: Paul Kyzivat <[email-masked]>
Date: Mon, 03 Dec 2012 15:29:28 -0500

While commenting on some related discussions I had occasion to look at 
this draft again and I found a few issues:

First, some very specific ones::

Section 4.1 says:

    If the <port> sub-field is 'SCTP' or ...

This is a typo. s/port/proto/

But the major issue is that this draft doesn't explain the semantics of 
the <port> field. The only things I can find that touch on this are:

- section 10.1 refers to "SCTP port 54111" and then shows an m-line
   with: m=application 54111 SCTP 0 1 2
   But this is just an example, not normative text.

- section 4.1 says:

    [OPEN ISSUE 3] do we need also an attribute to specify the SCTP port
    number for the SCTP over DTLS scenario? that can be useful in the
    case where multiple association are running on top of the same DTLS
    session.

   This implies that the SCTP port number is *not* what is in the port
   field in this case. Presumably because the UDP port number is in
   that field.

ISTM that there needs to be a clear discussion of all the required port 
numbers for each case, and how they are specified. When there is more 
than one (namely in the SCTP/DTLS and DTLS/SCTP cases), *one* of them 
can be in the m-line and the other one must be somewhere else. And if 
the one that is not in the m-line is optional, then I guess there must 
be a default.

	Thanks,
	Paul