Re: 199 Open Issue: UAS sending 199

> 1. UAS never sends 199: 
>
> In this case only forking proxies/B2BUA 
> would send 199. 

I prefer the goal of option 1.  B2BUA (which is a UAS) or proxy sends
199 whenever it desires to indicate termination of a dialog and sending
a final INVITE response is not yet appropriate.  The subsequent INVITE
final response SHOULD contain a different To tag than those sent within
199s.  A device which does not trigger more than 1 To tag (i.e. fork or
simulate forking interaction) for an INVITE, SHOULD NOT generate a 199
since it needs to generate subsequent final failure response with the
same To tag.

<snip>


> Robert S also raised an issue on what Require: 199 means.

It means the UAS is required to support the RFC.

Depending upon RFC (working group decision), "Require: 199" means UAS
MAY, SHOULD, or MUST send 199 for early dialogs containing To tags
different than the INVITE's subsequent final response To tag; I prefer
MAY.

Depending upon RFC (working group decision), "Require: 199" also means
UAS MAY, SHOULD, MUST, or SHOULD NOT send 199 for early dialog
containing To tag which is the same as the INVITE's subsequent final
response To tag; I prefer SHOULD NOT.  If MUST is preferred, I would
desire usage of a different option-tag such as "failure-reason" or
"termination-reason".
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