Re: [Technical Errata Reported] RFC4028 (1681)

On Tue, 2009-02-10 at 11:56 -0500, Bob Penfield wrote:
> The text in 8.1.3.5 means that the From and To headers in the new
> INVITE should have the same value including tags as the rejected
> INVITE. If it was an initial (out-of-dialog) INVITE, there will be no
> to-tag in the To, and thus the re-submitted request will not have a
> to-tag either. There is no need to change the Call-ID or the from tag
> because no dialogs were created.
>  
> If it is an in-dialog request, it must have the same tags otherwise it
> will not match the dialog. This could happen if authentication is
> required for in-dialog requests and the UAC did not include the
> credentials, or the credentials are stale.
>  
> From an implementation point of view, it is simpler if the procedures
> for re-submitting requests for repairable 4xx errors are the same for
> in-dialog and out-of-dialog requests.
>  
> I see no reason to change the Call-ID or from tag.

All of the above matches my understanding and the discussions that I've
seen here.
 
> As for the question "If the From tag doesn't change, can the UAS
> retrain the same To tag as well?", I would say that UAS should not use
> the same to-tag for a new request.

I'm sure that the UAS should not use the same to-tag in its response to
the new request -- the first request did not establish a dialog, so the
second request could not be part of that dialog.  And indeed, it would
be difficult to build a UAS that did use the same to-tag, as it would
have to remember the to-tag it used in the first request and use it in
the second -- but nonetheless, if it received two copies of the first
INVITE and rejected both, it would have to use different to-tags for the
two error responses.

Dale


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