Christer Holmberg wrote:
Hi,
One of the PRACK related issues presented in SFO is whether we should
change the requirement to include SDP offer in the first reliable
provisional response, if the INVITE does not contain SDP.
Two use-cases, which the current requirement affect, were presented:
1. H.323/SIP interworking, where an empty INVITE may have been received
and an SDP offer is not available when the first reliable 18x is to be
sent (please see meeting slides for details).
This is the issue I hear complaints about.
2. Call fowarding, when a 181 provisional is sent. The 181 may be sent
by an intermediate, and if the INVITE did not contain SDP a reliable 181
would be required to contain an SDP offer.
This is only an issue if the INVITE contained Require:100rel. (And AFAIK
that is rarely the case. If it was the case the 181 could simply be
omitted.)
Otherwise, an unreliable 181 can be sent, which needn't have SDP.
Another possibility would be to send a 181 with bogus SDP. For instance
it could have c=0 and port=0 for all the media. That could work even
reliably. And it wouldn't affect any real answers because it will have a
unique to-tag.
It was indicated that there may be backward compability issues. That of
course depends on the number of deployments where INVITE without SDP is
sent AND a reliable 18x without SDP offer would cause an error.
Some people indicated concern, so I would like to ask what people think?
Would changing the rules cause problems in existing deploymentnts?
I'll have to ask around.
Paul
Regards,
Christer
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