Elwell, John wrote:
-----Original Message-----From: sip-bounces at ietf.org [mailto:sip-bounces at ietf.org] On Behalf Of Dale.Worley at comcast.netHowever... If we change the sequence of operations a bit, so that the UAS sends a 183 with a Contact carrying a specific header parameter carrying a crypto-random value, and we get B2BUAs to pass it through (attaching it to the Contact they use in the 183 they emit on the other side), then if the UAS does a non-filtered dialog event SUBSCRIBE, it can check the returned NOTIFY to see if it carries the Contact header parameter that it created. That's a reasonably good test that the UAC of the INVITE can be reached via the From value that the UAS received.[JRE] Unless a B2BUA fails to play according to the rules and acknowledges the SUBSCRIBE without carrying out the same test on the next hop.
That's kind of the point of Juri's draft, though -- semantically, the recipient of the SUBSCRIBE doesn't need to know that this is an identity check. So the B2BUA would have no obligation to do anything towards the calling party.
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