RE: [Sip] RE: Delivering request-URI and parameters to UAS via proxy -new version of the draft-holmberg-sip-target-uri-delivery draft

"Christer Holmberg" <christer.holmberg@ericsson.com> Tue, 29 January 2008 21:57 UTC

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Subject: RE: [Sip] RE: Delivering request-URI and parameters to UAS via proxy -new version of the draft-holmberg-sip-target-uri-delivery draft
Date: Tue, 29 Jan 2008 22:57:45 +0100
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From: "Christer Holmberg" <christer.holmberg@ericsson.com>
To: "Jonathan Rosenberg" <jdrosen@cisco.com>, "Elwell, John" <john.elwell@siemens.com>
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Hi Jonathan,

>Sorry for jumping in late here. Trying to clarify some points 
>here and there.
> 
>The UA-loose mechanism needs to know that the entity which 
>would have previously been reached by the DNS/IP forwarding 
>based on the R-URI, is now prepared for a request which 
>reaches it with that target in the Route header field.
> 
>In the case of a UA registering through a chain of 
>Path-inserting proxies, it means that only the *UA* has to 
>support UA-loose route. 
>Thats because of the assumption that the intermediate 
>path-inserting proxies weren't being targeted based on the 
>R-URI previously; they were (and still will) forward the 
>request based on Route.
>
>The 'next hop' use case that Christer is referring to are 
>cases where we would have done a R-URI translation without a 
>registration. For example, lets say a proxy receives an 
>INVITE with sip:12345@proxy.com, and its using some 
>number-prefix based routing rules, which have been CONFIGURED 
>into the proxy, to determine a next-hop gateway. The UA loose 
>route rules would say that, since this is a routing operation 
>and not a retargeting, the request looks like:
> 
>INVITE sip:12345@proxy.com
>Route: sip:ip-of-gateway
> 
>whereas current rules would require:
> 
>INVITE sip:12345@ip-of-gateway
> 
>in this use case, the entity which was previously being 
>reached by the R-URI *is* the next hop.
> 
>And so, the main limitation that I see of the UA loose route 
>mechanism is, in cases where the next-hop is being reached 
>via a configured routing rule, or by some other 
>non-registration means, and said operation is a re-route and 
>not retarget, the UA_loose-route requires that this 
>configured routing rule include information about whether the 
>next hop uses UA loose routing, and if so, what URI to use in 
>the Route header.
> 
>This is a limitation, I agree. Whether its significant or not 
>is debatable.
> 
>I will note that, it is possible to separate these concerns. 
>We could define UA loose route to strictly be used for the 
>registration cases, since that is the specific problem at hand.
> 
>I agree CHrister's mechanism does not have this configuration 
>limitation, and that this aspect of it is better. My main 
>beef, as others have commented, is that it leaves us with 
>nearly half-dozen header fields which are all awfully similar 
>(To, P-C-ID, Route, History-Info, and now Target). I was 
>hoping to reduce the set and include only the minimum. In 
>that way, I think UA loose route is architecturally better 
>since it gives some clarity to this.

I don't think a solution with the configuration limitation is
architecturally better.  

However, there is also a possibility to merge both solution proposals:
UA-loose-route would be used from the home proxy towards the UE (giving
Request-URI the same semantics as P-Called-Party-ID has today), and
Target to convey the current target. Yes, we would have another header.
But, the new header would have clear semantics, and we would get rid of
the configuration limitation. (Another possibility that does not require
a new header is to fix the semantics of the To header and allow it to be
modified, but that may have unwanted backward compatibility issues.)

The merged solution would probably also solve the issues raised by
Youssef - eventhough the "intermediate entity" (being a B2BUA) he is
talking about could as well map the Target header into a R-URI. However
we think it would be good to additionally cover the use case that is
behind this in the UALR work to justify such a combined solution.

Regards,

Christer









> 
> Elwell, John wrote:
> > Christer,
> > 
> > I don't think the entity using the mechanism needs to know 
> about next 
> > hop support for the loose route mechanism - only whether the UAS 
> > supports it. If the UA registers, then the loose route 
> draft provides 
> > an automatic mechanism. If the UA does not register, support would 
> > need to be indicated by provisioning. I am not sure this ranks as a 
> > significant limitation, since a certain amount of 
> provisioning needs 
> > to be done anyway for UAs such as gateways that do not register.
> > 
> > John
> > 
> >> -----Original Message-----
> >> From: Christer Holmberg [mailto:christer.holmberg@ericsson.com]
> >> Sent: 16 January 2008 11:51
> >> To: Elwell, John; sip@ietf.org
> >> Cc: Paul Kyzivat; DRAGE,Keith (Keith); Francois Audet
> >> Subject: RE: [Sip] RE: Delivering request-URI and 
> parameters to UAS 
> >> via proxy -new version of the 
> draft-holmberg-sip-target-uri-delivery 
> >> draft
> >>
> >>
> >> Hi,
> >>
> >>> I hear what you are saying, but I don't really see that the
> >> points you
> >> raised in section 4 are real limitations of the loose 
> route mechanism.
> >>
> >> I think it is a limitation that an entity using the 
> mechanism has to 
> >> know whether the the next hop supports it or not, and that the 
> >> mechanism can only be used if the subsequent hops support it.
> >>
> >> Regards,
> >>
> >> Christer
> >>
> >>
> >>
> >>
> >>>> -----Original Message-----
> >>>> From: Christer Holmberg [mailto:christer.holmberg@ericsson.com]
> >>>> Sent: 16 January 2008 11:06
> >>>> To: Elwell, John; sip@ietf.org
> >>>> Cc: Paul Kyzivat; DRAGE, Keith (Keith); Francois Audet
> >>>> Subject: [Sip] RE: Delivering request-URI and parameters
> >> to UAS via
> >>>> proxy - new version of the draft-holmberg-sip-target-uri-delivery
> >>>> draft
> >>>>
> >>>>
> >>>> Hi John,
> >>>>
> >>>>> Thanks for this revision, which makes things somewhat
> >>> clearer. I do
> >>>>> have a couple of comments:
> >>>>>
> >>>>> 1. I am not sure I agree with the assertions in section 4
> >>> concerning
> >>>>> issues with the mechanisms in loose-route. Taking 
> example 1, the 
> >>>>> Route header field should contain enough entries to get
> >> you to the
> >>>>> registered contact, not just to an intermediate proxy. 
> >>> Therefore this
> >>>>> situation should not arise with a correctly implemented
> >>> home proxy. 
> >>>>> It is not clear to me how example 2 could arise either,
> >>> for similar
> >>>>> reasons. The MGC case can be resolved by taking into 
> account the 
> >>>>> option tag in the REGISTER request, or if it is permanently 
> >>>>> registered, through provisioning.
> >>>> The examples are not meant to show bugs in the loose-route
> >>> mechanism.
> >>>> They are meant to help people understand the limitations 
> with the 
> >>>> loose-route mechanism.
> >>>>  
> >>>>> 2. Comparing the mechanism proposed with the loose-route
> >>> mechanism,
> >>>>> my understanding is:
> >>>>> a)When retargeting occurs, the loose-route mechanism
> >>> places the new
> >>>>> target in the Request URI. Your proposal places the new
> >> target in
> >>>>> both the Request-URI and the Target header field.
> >>>>> b) When rerouting, the loose-route mechanism places the
> >> new route
> >>>>> (i.e., the registered contact) in the Route header field. Your 
> >>>>> proposal places the new route in the Request-URI (the
> >>> latter as per
> >>>>> RFC 3261).
> >>>>> So the two mechanisms solve exactly the same problems using a 
> >>>>> slightly different mechanism. Correct?
> >>>> Yes. The two solutions intend to solve the same problem.
> >>>>  
> >>>>> 3. How P-Called-Party-ID fits into this is not really
> >>> relevant from
> >>>>> an IETF perspective - it seems there are some 3GPP-specific 
> >>>>> situations where the contents of P-Called-Party-ID will
> >>> not equal the
> >>>>> contents of Target. Correct?
> >>>> Correct.
> >>>>
> >>>>> 4. If my suggestion in point 1 above that the loose-route
> >>> mechanism
> >>>>> does not suffer from the problems suggested, then each
> >>> mechanism will
> >>>>> work and each addresses the same problem.
> >>>>> So it is just down to a beauty contest between the two. Correct?
> >>>> See question 1.
> >>>>
> >>>> We believe that our solution does not have the same
> >>> limitations as the
> >>>> loose-route solution. But, again, both solutions intend to
> >>> solve the
> >>>> same problem.
> >>>>
> >>>> Regards,
> >>>>
> >>>> Christer
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>>> -----Original Message-----
> >>>>>> From: Christer Holmberg
> >> [mailto:christer.holmberg@ericsson.com]
> >>>>>> Sent: 16 January 2008 08:41
> >>>>>> To: sip@ietf.org
> >>>>>> Cc: DRAGE, Keith (Keith); Paul Kyzivat; Elwell, John;
> >>> Jeroen van
> >>>>>> Bemmel; Francois Audet
> >>>>>> Subject: Delivering request-URI and parameters to UAS via
> >>>>> proxy - new
> >>>>>> version of the draft-holmberg-sip-target-uri-delivery draft
> >>>>>>
> >>>>>>
> >>>>>> Hi,
> >>>>>>
> >>>>>> We've uploaded a new version (-01) of the Target draft.
> >>>>>>
> >>>>>> We've tried to make things more clear. I've also
> >>> removed all text
> >>>>>> about P-Called-Party-ID, except from one chapter where
> >>> we try to
> >>>>>> explain the semantical difference between Target and P-CPI.
> >>>>>>
> >>>>>> You can also find the draft from:
> >>>>>> http://users.piuha.net/cholmber/drafts/draft-holmberg-sip-targ
> >>>>>> et-uri-del
> >>>>>> ivery-01.txt
> >>>>>>
> >>>>>> Regards,
> >>>>>>
> >>>>>> Christer
> >>>>>>
> >>>>
> >>>> _______________________________________________
> >>>> Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
> >>>> This list is for NEW development of the core SIP Protocol Use 
> >>>> sip-implementors@cs.columbia.edu for questions on 
> current sip Use 
> >>>> sipping@ietf.org for new developments on the application of sip
> >>>>
> >>>
> >>> _______________________________________________
> >>> Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
> >>> This list is for NEW development of the core SIP Protocol Use 
> >>> sip-implementors@cs.columbia.edu for questions on current sip Use 
> >>> sipping@ietf.org for new developments on the application of sip
> >>>
> > 
> > 
> > _______________________________________________
> > Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
> > This list is for NEW development of the core SIP Protocol Use 
> > sip-implementors@cs.columbia.edu for questions on current sip Use 
> > sipping@ietf.org for new developments on the application of sip
> > 
> 
> -- 
> Jonathan D. Rosenberg, Ph.D.                   499 Thornall St.
> Cisco Fellow                                   Edison, NJ 08837
> Cisco, Voice Technology Group
> jdrosen@cisco.com
> http://www.jdrosen.net                         PHONE: (408) 902-3084
> http://www.cisco.com
> 


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