[SR-Users] loose_route security

[Iñaki Baz Castillo]

2011/4/17 Juha Heinanen <jh at tutpro.com>:
> lets say that a sip ua has dialog established with pstn gw and the sip
> ua sends refer to pstn gateway for the purpose of transferring the call
> to another pstn destination.  in that case, referred-by uri is used for
> accounting of the new pstn leg.

I've never seen a PSTN gw properly handling a REFER, neither I think a
PSTN gw should handle it (but a B2BUA/PBX) between the UA and the PSTN
gw(s).

The REFER with "Referred-by" headers tells the receipt of such REFER
to generate an INVITE with destination indicated in "Refer-To" header
and mirroring the "Referred-By" header (so the UAS receiving the
INVITE knows that it arrives from user in From header but is a
transfer from user in "Referred-By").

Honestly I can imagine how a PSTN gw is supposed to assert the value
of "Referred-By". Perhaps it just allows the REFER if it contains a
Referred-By matching the From URI header?

Cheers.

-- 
Iñaki Baz Castillo
<ibc at aliax.net>