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

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
jdrosen@cisco.com
http://www.jdrosen.net                         PHONE: (408) 902-3084
http://www.cisco.com

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