Re: [MMUSIC] SDP offer/answer question from SIPit

["Christer Holmberg" <christer.holmberg at ericsson.com>]

Hi,
 
Since the port is zero, does it really matter?
 
As long as the transport types etc match for the non-zero port m- lines, the offerer should be ok.
 
Regards,
 
Christer

________________________________

From: mmusic-bounces at ietf.org on behalf of Robert Sparks
Sent: Thu 17/09/2009 20:33
To: mmusic at ietf.org
Subject: [MMUSIC] SDP offer/answer question from SIPit



Can somebody point quickly to some existing text that answers this 
question?
(If none exists, perhaps we should think about creating some)

When you reject an m-line that has something in it you've never heard 
of before,
(say someone sent you m=application 50000 TCP/TLS/BFCP *) you return a
corresponding m-line with a port of 0 as below, the question is, as 
you are building
that response:

m=application 0 ????what goes here????

One sane answer is to just copy the bits from the offer without trying 
to attribute any
meaning to them:

m=application 0 TCP/TLS/BFCP *

But remember that the rejector probably doesn't know TCP/TLS/BFCP
from NEVER/USE/THIS. Section 6 of 3264 has this language:
"To reject an offered
    stream, the port number in the corresponding stream in the answer
    MUST be set to zero.  Any media formats listed are ignored.  At 
least
    one MUST be present, as specified by SDP."

Now, media-field is this in SDP:
    media-field =         %x6d "=" media SP port ["/" integer]
                          SP proto 1*(SP fmt) CRLF

So the text from 3264 could be read to be talking only the fmt field.
Should the proto field also be ignored at this point?

Would it be ok to return

m=application 0 RTP/AVP 0

for example?

If not, what text makes it clear?
(It might exist, but the testing is furious today and I'm not spotting 
it quickly).

RjS
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