Re: [Sip] Contact header in 1xx responses/updates remote target or not?

["Christer Holmberg" <christer.holmberg at ericsson.com>]

Hi,

I agree with Paul's conclusion. But, I still think that is somethin that
we should somehow document and clarify. This is a common reason for
interop problems, so just agree on a mailing list and leave it there is
not a good thing to do.

IF (To-tag && Contact) THEN dialog 

And, it IS allowed to update the Contact in subsequence provisional
responses. But, as Paul said: it is asking for trouble, so it should not
be done unless you have a really good reason for it.

I also think that updating the Contact in a re-INVITE/UPDATE is asking
for trouble. At least you also there need to be prepared to receive
requests on both the new and old contact for a period of time.

Regards,

Christer

> -----Original Message-----
> From: Paul Kyzivat [mailto:pkyzivat at cisco.com] 
> Sent: 28. helmikuuta 2008 19:47
> To: Rockson Li (zhengyli)
> Cc: Christer Holmberg; sip at ietf.org
> Subject: Re: [Sip] Contact header in 1xx responses/updates 
> remote target or not?
> 
> No, I don't think we have an answer, though I do have an opinion. :-)
> 
> Are you asking about whether the contact may be omitted? Or 
> if it may be changed?
> 
> AFAIK there is nothing normative that *forbids* the contact 
> from being changed in subsequent provisional responses. But 
> doing so is *asking* for trouble, so you shouldn't do it. 
> Perhaps you could get away with it in a *reliable* 
> provisional, but then you would still have a bunch of messy 
> cases. The likelihood of it working is slim. Doing it with
> *unreliable* provisionals is going to cause trouble because 
> they can be lost. Even with reliable provisionals, you will 
> have to be prepared to receive on both addresses for some 
> period of time.
> 
> It seems clear that a contact may be omitted in a 100, since 
> it is hop by hop, and presumably must be omitted in the 100 
> responses from proxies. Some other 1xx responses may be 
> returned by proxies (notably
> 181) and presumably they should also not contain a contact in 
> those cases.
> 
> A 1xx that establishes an early dialog must contain a contact 
> or else you really don't have a dialog. I think it is 
> ambiguous whether:
> - the first 1xx with a particular to-tag *does* establish an early
>    dialog and so *must* contain a contact,
> 
> - OR a 1xx with a new to-tag, but without a contact, simply doesn't
>    establish a dialog, but is legal.
> 
> I would split the difference and say that the UAS MUST 
> include a contact in the first 1xx it returns with a 
> particular to-tag, but a UAC should accept a 1xx with new 
> to-tag and without a contact and simply treat it as not 
> establishing an early dialog. (Don't establish the dialog 
> until you get enough info to do so.)
> 
> 	Paul
> 
> Rockson Li (zhengyli) wrote:
> > Paul , Christer and all,
> >  
> > I am following the email thread as in subject above 
> > http://www.ietf.org/mail-archive/web/sip/current/msg19322.html
> >  
> > However, I do not find the definite answer to Christer's 
> question, Do 
> > we have the answer now?
> >  
> > Thanks a lot
> > 
> > Regards,
> > Rockson Li
> > 
> > Cisco R&D Center, Shanghai, PRC
> > 
> >  
> 
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