Subject: RE: [Sipping] refer and pstn

From: "Christer Holmberg (LMF)" <[email-masked]>
Date: Wed, 11 Jun 2003 08:11:39 +0200

Hi,

>>Now, I think it's a pure implementation issue how the gw 
>>handles all these cases, ie if it decides to accept the responses/requests or
>>not.
>yes, but the protocol must provide enough information for the 
>gateway to make its decision and i'm not sure if that is the case with refer.

Exactly what information do you want the protocol to provide?

Regards,

Christer Holmberg
Ericsson Finland
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From: Juha Heinanen <[email-masked]>
Date: Wed, 11 Jun 2003 10:08:22 +0300

> 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.

-- juha

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From: Alan Johnston <[email-masked]>
Date: Wed, 11 Jun 2003 16:28:34 -0500

>right the forward a call to the refer-to number.

The GW uses the same approach for a REFER that it uses to 
authenticate/authorize a BYE - using standard SIP means.

The transferee does not need to trust the Referred-By header - it can 
authenticate the REFER.  That is a requirement of the transfer target which 
receives the triggered INVITE which may contain the Referred-By header.  If 
the transfer target is unable to verify the Referred-By header (using the 
cryptographic means discussed in the draft) and the target is screening 
calls, then the target should reject the INVITE.

A PSTN gateway is just a normal SIP UA - the main difference with respect 
to REFER is that a PSTN gateway can not in general initiate a transfer due 
to the user interface limitations of phones, unless there is some mid-call 
DTMF string that the gateway recognizes.

Thanks,
Alan Johnston
MCI