Subject: [Sip] changing of media types allowed in offer/answer and SIP open issu e #24

From: Jonathan Rosenberg <[email-masked]>
Date: Wed, 5 Dec 2001 12:11:28 -0500

Folks,

draft-rosenberg-mmusic-sdp-offer-answer-00.txt currently says:

 The media type (audio, video, etc.) for a stream MAY be changed. This
   is particularly useful for changing between voice and fax in a single
   stream, which are both separate media types. To do this, the offerer
   creates a new media description, with a new media type, in place of
   the description in the previous SDP which is to be changed. The IP
   address and port for the stream MAY change, or MAY remain the same.
   However, the list of payload type numbers for the new codecs MUST be
   different than any used previously for this stream.

This is somewhat linked to the current sip open issue #24 about whether or
not you can reuse a media stream "slot" which has been previously disabled
with port=0. After all, changing the media type is really the same, more or
less, as using a new media stream in place of where an old one was. I think
leaning of consensus in the sip group was to disallow such reuse (although I
can't remember at this moment what the reasoning was), and that would argue
for removing the above capability. 

Comments or thoughts on this?

-Jonathan R.

---
Jonathan D. Rosenberg, Ph.D.                72 Eagle Rock Ave.
Chief Scientist                             First Floor
dynamicsoft                                 East Hanover, NJ 07936
[email-masked]                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com

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From: Paul Kyzivat <[email-masked]>
Date: Thu, 06 Dec 2001 11:44:15 -0500

I think the restriction is silly. 

I don't see why any piece of code that can keep track of the positional
assignments, including media that have been refused, should have any
trouble reusing a previous slot for a new purpose. And changing the
media type in one step is more or less the same thing.

So why not allow those slots to be reused? 
We may yet see applications where there are enough reinvites with
changes in media that recycling of slots is important.

	Paul