Subject: [MMUSIC] To share or not to share ports between "m=" lines

From: Flemming Andreasen <[email-masked]>
Date: Wed, 17 Sep 2003 10:49:41 -0400

At the last IETF, the issue of sharing a port between multiple "m="
lines, as exemplified in draft-ietf-mmusic-offer-answer-examples-01, was
raised but not resolved. The question here is whether it should be
allowed or not, and if so, what (if any) constraints should be placed on
it.

The advantage of allowing for sharing of ports between multiple "m="
lines is that it enables us to specify things we otherwise cannot in
SDP, for example asymmetric codecs, and alternative top-level MIME
types. The disadvantage is that RFC 2327, sdp-new, RFC 3264, etc. are
silent on this issue, and in general backwards compatibility with
existing implementations is unclear. It also raises a number of
questions that would have to be answered, e.g. can you specify different
transports, do you have to accept all of the shared "m=" lines or just a
subset, how do you use preconditions (RFC 3312), etc.

My personal opinion is, that while the functionality is desirable, there
are too many unknowns to endorse this mechanism, and hence it should not
be allowed.

Comments appreciated.

-- Flemming

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