IƱaki Baz Castillo writes:
The client and the GW are UA's, but the proxy is just a proxy. As a proxy, I cannot decide which headers are mandatory and which ones can be dropped. The UAC (client) and UAS (gw) could decide to negotiate some SIP extension I'm not aware of, or I do know but it's transparent for me (the proxy), for example PRACK usage which involves new headers.
as i already said, then fix your gw to reply with '400 bad request'.
-- juha