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

From: "DRAGE, Keith \(Keith\)" <[email-masked]>
Date: Tue, 4 Dec 2007 16:27:02 +0100

(As WG chair)

We have a couple of milestones that we generated as a result of
discussion of 

http://www.ietf.org/internet-drafts/draft-rosenberg-sip-ua-loose-route-0
1.txt

Dec 2007    Delivering request-URI and parameters to UAS via proxy to
WGLC  
Feb 2008    Delivering request-URI and parameters to UAS via proxy to
IESG (PS)  

This work is currently stalled and the editor needs input.

The document contains various example scenarios where a solution is
required, for which there appears to be no dispute that a solution is
needed.

The document proposes one solution to resolve these example scenarios,
but this solution is not gaining consensus. At least one other solution
has been talked about, but there is no documentation on the table.

This mail is to identify a deadline for other solutions to the example
scenarios to be documented as internet drafts, showing how the solution
works for those scenarios. This deadline is:

	January 11th 2008

It is appropriate fo these documents to identify any other scenarios
where such a solution is appropriate. Any other input is also welcome in
identifying other scenarios.

If we have no such internet-drafts by this deadline, we will proceed
with completing the solution we have.

Regards

Keith

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---

From: "Christer Holmberg" <[email-masked]>
Date: Tue, 4 Dec 2007 18:58:25 +0100

Hi,
 
In order to think about documenting "alternative solutions", I have a question for clarifications regarding the scope of the problem we are trying to solve.
 
The MECHANISM part of the draft says that a UA supporting the mechanism would indicate it to the registrar, and the registrar would only use the mechanism in case the UA has indicated support for it (that is also shown in the example in the draft). It has also been claimed that this would be backward compatible with an MGC which uses the R-URI to map to ISUP Called Party number, because the MGC does not register so the mechanism would not be used towards it. 
 
My question is: does this mean that the only entity allowed to use this mechanism is the registrar, since the mechanism is used based on whether the UA supports it or not? 
 
When reading the USE-CASE part of the draft, I would say that the answer is "no". Because, as I understand the text, there could be non-registrar entities in the path, which today normally would re-write the R-URI, but would now instead use this mechanism. Is my understanding correct?
 
If so, my next question is: these non-registrar entities have no clue about whether the terminating UA supports the mechanism or not, or whether the call will be routed towards an MGC. So, what happens if the request is routed towards an UA that has not indicated support, or towards an MGC? The MGC may not be able to map the R-URI.
 
Regards,
 
Christer

________________________________

Lähettäjä: DRAGE, Keith (Keith) [mailto:[email-masked]]
Lähetetty: ti 4.12.2007 16:27
Vastaanottaja: [email-masked]
Aihe: [Sip] Delivering request-URI and parameters to UAS via proxy

(As WG chair)

        January 11th 2008

Regards

Keith

---

From: Jonathan Rosenberg <[email-masked]>
Date: Wed, 05 Dec 2007 17:03:16 -0500

Christer Holmberg wrote:
> Hi,
> 
> In order to think about documenting "alternative solutions", I have a
> question for clarifications regarding the scope of the problem we are
> trying to solve.
> 
> The MECHANISM part of the draft says that a UA supporting the
> mechanism would indicate it to the registrar, and the registrar would
> only use the mechanism in case the UA has indicated support for it
> (that is also shown in the example in the draft).

For when a proxy is talking to a registered UA, yes.

> It has also been
> claimed that this would be backward compatible with an MGC which uses
> the R-URI to map to ISUP Called Party number, because the MGC does
> not register so the mechanism would not be used towards it.

That is not the intent.

The idea is, any proxy that is translating a request-URI, is doing so 
based on some kind of mapping table. There are many ways that this 
mapping table can get into the proxy:

1. dynamically through register
2. provisioned
3. through an enum query
etc.

If we take provisioning as an example (i.e., someone enters phone number 
routing rules via prefix matching rules), when those rules are 
provisioned, they would include a flag which says whether the 
destination is loose-route compliant. If they are loose route compliant, 
the proxy uses a Route header, else it uses r-uri translation as is 
currently done.

> 
> My question is: does this mean that the only entity allowed to use
> this mechanism is the registrar, since the mechanism is used based on
> whether the UA supports it or not?

As above, no.

> 
> When reading the USE-CASE part of the draft, I would say that the
> answer is "no". Because, as I understand the text, there could be
> non-registrar entities in the path, which today normally would
> re-write the R-URI, but would now instead use this mechanism. Is my
> understanding correct?

Yes.

> 
> If so, my next question is: these non-registrar entities have no clue
> about whether the terminating UA supports the mechanism or not, or
> whether the call will be routed towards an MGC. So, what happens if
> the request is routed towards an UA that has not indicated support,
> or towards an MGC? The MGC may not be able to map the R-URI.

Hopefully the above paragraph answers your question.

-Jonathan R.

-- 
Jonathan D. Rosenberg, Ph.D.                   499 Thornall St.
Cisco Fellow                                   Edison, NJ 08837
Cisco, Voice Technology Group
[email-masked]
http://www.jdrosen.net                         PHONE: (408) 902-3084
http://www.cisco.com

---

From: "Christer Holmberg" <[email-masked]>
Date: Wed, 12 Dec 2007 13:41:27 +0100

Hi,
 
I have had an off-line discussion with Jonathan about this, but I'll let everyone else know too.
 
One issue with Jonathan's proposed mechanism is that it is assumes that the entity/proxy who wants to use it (instead of modifying the R-URI value) KNOWS whether the next hop device also supports the mechanism or not. I think that assumption makes the usability of the proposed solution extremely limited and "undynamic", and services which rely on the mechanism will be dependent on whether intermediates (which have nothing to do with the service as such) support the mechanism
 
Also, assuming that one or more entities/proxies in the path have already used the mechanism, and now an entity/proxy realizes that the next hop device does NOT support it. This most likely means that that entity/proxy now will have to "fix" the INVITE (e.g put the "correct" URI back into the R-URI etc), in order for the next hop to be able to deal with it correctly (at least the home proxy of the terminating user would need the "fix" in order to find the registered contact, and an MGC to correctly map the called party number).
 
And, yes, I AM thinking about an alternative solution, and my intention IS to submit a draft before the deadline.
 
Regards,
 
Christer

Lähettäjä: Jonathan Rosenberg [mailto:[email-masked]]
Lähetetty: ke 5.12.2007 23:03
Vastaanottaja: Christer Holmberg
Kopio: [email-masked]; DRAGE, Keith (Keith)
Aihe: Re: VS: [Sip] Delivering request-URI and parameters to UAS via proxy

That is not the intent.

As above, no.

Yes.

-Jonathan R.

--
Jonathan D. Rosenberg, Ph.D.                   499 Thornall St.
Cisco Fellow                                   Edison, NJ 08837
Cisco, Voice Technology Group
[email-masked]
http://www.jdrosen.net <http://www.jdrosen.net/>                          PHONE: (408) 902-3084
http://www.cisco.com <http://www.cisco.com/>