Rockson Li (zhengyli) wrote:
Paul and Christer,
IMHO, I don't like the first-reliable-provisional-resp-with-sdp rule.
Implementation are required to accept first reliable response without
sdp by customer,
While must be prepared to follow this rule sending resp in case any
criticism of non-compliance from other vendors,
Which makes implemenation more complex.
BTW, what's the history on making this rule,could you please share with
me?
I don't know the reason for this rule. It seems excessively prescriptive
to me. Absent an understanding of *why* it was imposed, I wish it hadn't
been.
But whether it should be changed now is a different question.
There are pros (for devices that have difficulty following this rule)
and cons (backward compatibility with any devices that might depend on
it working this way.) I think we hear frequently from those in favor. I
haven't really heard from anyone who might be negatively impacted by the
change. That could be because nobody would be negatively impacted, or
that some would and just haven't responded.
Thanks,
Paul
Thanks
Regards,
-Rockson
-----Original Message-----
From: sipping-bounces@xxxxxxxx [mailto:sipping-bounces@xxxxxxxx] On
Behalf Of Paul Kyzivat (pkyzivat)
Sent: Tuesday, March 31, 2009 4:55 AM
To: Christer Holmberg
Cc: sipping@xxxxxxxx
Subject: Re: PRACK: Change MUST requirement to include SDP
offer in first reliable provisional response
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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