IƱaki Baz Castillo writes:
Hi Juha, Referred-By header is not part of REFER specification but an extension (RFC 3892) and it's not mandatory:
2.1. Referrer Behavior
A UA sending a REFER request (a referrer) MAY provide a Referred-By header field value in the request.
if refer does not contain referred-by header, then there is no other choice than to refuse it. otherwise (unless you keep call state) you don't have any chance to know who sent the refer and what rights the sender might have.
-- juha