Subject: RE: [Sipping] refer and pstn

From: "Christer Holmberg (LMF)" <[email-masked]>
Date: Wed, 11 Jun 2003 09:20:08 +0200

Hi,

>>Exactly what information do you want the protocol to provide?
>as i mentioned earlier, for example, the gw would like to know if
>referred-by can be trusted and that the party doing the refer has the
>right the forward a call to the refer-to number.

That is if the gw cares. The who-is-allowed-to-call-who handling can also be done by a proxy, but that of course require that all INVITEs are sent via that proxy. And, one of your concerns was that the gw doesn't send the INVITE to that proxy, but directly to the new UAS. However, if your network has that kind of functionality in the network, eg in a proxy, I guess you would have to configure that proxy as default outbound proxy, and send all INVITEs (also those triggered by REFER, I'd assume) to that proxy.

Regards,

Christer Holmberg
Ericsson Finland
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From: Juha Heinanen <[email-masked]>
Date: Wed, 11 Jun 2003 10:30:26 +0300

Christer Holmberg (LMF) writes:

 > That is if the gw cares. The who-is-allowed-to-call-who handling can
 > also be done by a proxy ...

exactly, so lets focus on the proxy instead.  as i have asked before,
how does the proxy know if referred-by has been checked upstream or how
can it indicate to downstream if it itself has verified referred-by.
that is, what is the equivalent of remote-party-id for referred-by?

also, lets assume that the uri in refer-to contains a telephone number.
if so, the proxy must make enum query on it.  where in the request does
the proxy store the result of the enum query?

-- juha

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From: Rohan Mahy <[email-masked]>
Date: Wed, 11 Jun 2003 15:46:50 -0700

> that is, what is the equivalent of remote-party-id for referred-by?

I sense another "trusted network" p-header discussion looming ahead.  
If you want to be really sure, then you use an authentication identity 
body.  If you are just using the transitive trust model, then your 
proxy would need to do a number of gross things including verify that 
the Referred-By header in a REFER matches the identity of the sender. 
Gateways and other "trusted" UAs would also need to reject any REFER 
requests which did not arrive through their proxy with a 305 Use Proxy.

> the proxy store the result of the enum query?

the proxy retargets the Request-URI in the triggered INVITE, not the 
Refer-To URI

thx,
-r