Re: FW: I-D Action:draft-kaplan-sip-session-id-00.txt
Robert Sparks <[email protected]>
| Newsgroups | gmane.ietf.sip |
|---|---|
| Message-ID | <[email protected]> |
From tags exist because we put the response-to-forked-request disambiguator in the To-tag and needed to be able later to send a request in the other direction - and we needed to do this in a way that was backward compatible with the 2543 (and a few slightly pre-2543) things around at the time. If I remember things correctly, there was a rev of bis briefly that defined to-tags but didn't have from-tags in it at all. And I _vaguely_ remember discussing the alternative of putting this info on the Call-ID in the response instead of To, but that fell away to some backwards-compatibility problems (but I could be misremembering). RjS On Dec 15, 2008, at 10:18 AM, Dale Worley wrote: > On Tue, 2008-12-09 at 10:04 +0000, Michael Procter wrote: >>> The to-tag we needed to identify forked responders generating >> unique early-dialogs with a common Call-ID, but why did we need the >> UAC to generate a from-tag? (I'm feeling dumb that I can't figure out >> the answer) >>> >> >> In the reverse direction, the presence of a to-tag in a request >> indicates an in-dialog request. Therefore, requiring a from-tag >> ensures >> that requests in the reverse direction can have a to-tag, and thus be >> correctly treated as in-dialog. > > I'm looking at the code in sipX that works with tags to determine the > status of a SIP message, and though the from-tag is not logically > necessary, it does make the code simpler, as the To and From URIs are > handled more symmetrically. > > In addition, it allows the SIP element to extract and compare only the > tags, rather than having to compare the To/From URIs (as is required > in > RFC 2543), which is always fraught with problems. > > Dale > > > _______________________________________________ > Sip mailing list https://www.ietf.org/mailman/listinfo/sip > This list is for NEW development of the core SIP Protocol > Use [email protected] for questions on current sip > Use [email protected] for new developments on the application of sip _______________________________________________ Sip mailing list https://www.ietf.org/mailman/listinfo/sip This list is for NEW development of the core SIP Protocol Use [email protected] for questions on current sip Use [email protected] for new developments on the application of sip