Hi,
>I am still confused by the distinction between Target and P-CPI. > >I agree that you have described rules for updating Target >that are different from those for updating P-CPI. But it >seems to me that is a distinction without a significant >difference. For the recipient of the request, the two are >used the same way, toward the same end. If anything I would >view the rules for Target to be just a bug fix on P-CPI. You don't update P-CPI. It's inserted by the home proxy, and nothing else. The headers have differenct semantics. I don't see that as a bug. Maybe we could try to change the semantics of P-CPI, and re-define the header, but that was never my intention when I proposed to use P-CPI. Regards, Christer > Paul > > Christer Holmberg wrote: > > Hi John, > > > >> 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? > > > > I am not sure what you mean by "earlier" target. > > > > Target, if present, always represents the current target. A > receiving > > entity that receives a request without a Target header has > to assume > > that the Request-URI represents the current target. When no Target > > header is available on the request then the Target is > inserted when a > > reroute is performed. > > > > P-CPI is ONLY used to maintain the R-URI which is rewritten by the > > contact of the UAS. I.e. by the home proxy which is usually > at the end > > of a chain of proxies. > > > > When both Target and P-CPI are used: Target always represents the > > current target. P-CPI always represents the AOR received by > the home > > proxy which may in some cases be the same as the current > target but it > > may also be the last route (not equal to the current > target) taken to > > deliver the request. > > > >> 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. > > > > Yes, we agree with your analysis regarding History-Info. The > > UA-loose-draft discusses further issues with using History-Info. > > > >> 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. > > > > Target always represents the current target. See above. > > > > P-CPI does not represent the current target in all cases. See above. > > > >> 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. > > > > In the next version of the draft I will remove as much as possible > > about P-CPI, in order not to cause confusion. I will only keep some > > text where I describe the semantical difference between > Target and P-CPI. > > > > I also do agree with one of your previous comments, that we should > > clarify the meaning of all the URIs we're using - and that > should be > > done no matter if we adopt Target or not. > > > > Regards. > > > > Christer > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >>> -----Original Message----- > >>> From: Christer Holmberg [mailto:[EMAIL PROTECTED] > >>> Sent: 15 January 2008 08:48 > >>> To: Francois Audet > >>> Cc: [email protected]; 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:[EMAIL PROTECTED] > >>>>> Sent: Monday, January 14, 2008 03:56 > >>>>> To: Audet, Francois (SC100:3055) > >>>>> Cc: [email protected]; 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 > >>>>> > >>>>> > > > _______________________________________________ Sip mailing list https://www1.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
