RE: [Sip] RE: Delivering request-URI and parameters to UAS via proxy

"Elwell, John" <john.elwell@siemens.com> Tue, 15 January 2008 09:20 UTC

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Date: Tue, 15 Jan 2008 09:20:01 +0000
From: "Elwell, John" <john.elwell@siemens.com>
Subject: RE: [Sip] RE: Delivering request-URI and parameters to UAS via proxy
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To: Christer Holmberg <christer.holmberg@ericsson.com>, Francois Audet <audet@nortel.com>
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Christer,

I guess what still confuses me is, when both Target and P-CPI are used,
which comes first, i.e., which represents the earlier target? When I
read the draft, I thought Target was earlier. From various clarifying
emails I now get the impression that Target is later. Can you confirm?

Picking up on Francois' point about History-Info, with the introduction
of Target and P-CPI we do indeed have a lot of URIs, and of course
History-Info can already convey all these URIs and any others. The
difference is that History-Info does not give particular semantics to
each of the URIs it conveys - they are simply a succession of targets.
With Target and P-CPI we are aiming to define specific semantics. I am
concerned whether we will be able to define these semantics tightly
enough to ensure consistent implementations. The more URIs we try to
define, the harder it will be to assign each one a clearly
distinguishable meaning. I hope the next draft will help.

John

> -----Original Message-----
> From: Christer Holmberg [mailto:christer.holmberg@ericsson.com] 
> Sent: 15 January 2008 08:48
> To: Francois Audet
> Cc: sip@ietf.org; DRAGE, Keith (Keith); Paul Kyzivat; Elwell, John
> Subject: RE: [Sip] RE: Delivering request-URI and parameters 
> to UAS via proxy
> 
> 
> Hi, 
> 
> P-CPI could probably be useful in some cases, in addition to Loose
> Route/Target. And, as the draft says, P-CPI will still have to be used
> in IMS, because there are procedures defined for it.
> 
> However, again, the purpose of the draft was to provide an alternative
> to the Loose Route alternative, and that alternative is Target only. 
> 
> I am working on an updated version of the draft to make that 
> more clear.
> 
> Regards,
> 
> Christer
> 
> 
> 
> 
> 
> >Hum. I guess then P-Called-ID would then be useful with 
> >Loose-route as well (although now I'm thinking that 
> >History-Info covers it).
> > 
> >I think explaining all that in great and precise details, 
> >with a concrete example would be very useful.
> > 
> >And then we could compare P-Target with Loose-route. 
> 
> 
> 
> 
> 
> > 
> > > -----Original Message-----
> > > From: Christer Holmberg [mailto:christer.holmberg@ericsson.com]
> > > Sent: Monday, January 14, 2008 03:56
> > > To: Audet, Francois (SC100:3055)
> > > Cc: sip@ietf.org; DRAGE, Keith (Keith); Paul Kyzivat; Elwell, John
> > > Subject: RE: [Sip] RE: Delivering request-URI and 
> parameters to UAS 
> > > via proxy
> > > 
> > > 
> > > Hi Francois,
> > > 
> > > >I think what you meant by Target was more the "Current" 
> > > >target as opposed to the Initiatl Target.
> > > 
> > > Yes.
> > >  
> > > >And if that's the case, then I don't see why it is 
> different from 
> > > >P-Called-ID (although I might be missing something with what the 
> > > >P-Called_ID is supposed to be).
> > > 
> > > In the draft we try to explain the difference. But, we are 
> > working on 
> > > the text to make it more clear.
> > > 
> > > The P-CPI is inserted when the R-URI is rewritten by the Contact 
> > > address of the UAS. RFC3455 calls that operation 
> > "retargeting", but we 
> > > don't think that is the definition for retarget used in the 
> > > ua-loose-route draft, which says:
> > > 
> > > "When a home proxy receives a request and accesses a 
> > location service, 
> > > the resulting contact(s) obtained from the location service are 
> > > considered the last hop in the route towards the entity 
> > addressed by 
> > > the Request-URI.  Since that target, almost by definition, 
> > can claim 
> > > the identity of the URI prior to translation, the operation 
> > is one of 
> > > routing and not retargeting."
> > > 
> > > So, if we follow the definitions in the ua-loose-route 
> draft, P-CPI 
> > > would be inserted due to a reroute - not retarget.
> > > 
> > > But, no matter whether we call it retarget or reroute, 
> the point is 
> > > that the P-CPI is inserted when the R-URI is rewritten with the 
> > > Contact address of the UAS. The scope of Target is wider 
> than that, 
> > > and can be used in any retargeting situation.
> > > 
> > > Regards,
> > > 
> > > Christer
> > > 
> > > 
> > 
> 


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