[Users] how to correctly handle NAT on inbound call from another SIP-proxy?

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 hi list, we have some trouble handling NAT correctly when receiving a call from another SIP-proxy. the mediaproxy-module does not seem to rewrite SDP when it finds another proxy's record-route header, though it invokes mediaproxy and sends uncorrected SDP to the other SIP-server resulting in one-way-audio as the provided c=-field includes the RFC1918-address of the client. when receiving calls through our Cisco AS5350 everything is fine ('cause it does not add the record-route). the addition of the header cannot be circumvented bacause the other provider wants to bill calls (obviously) and therefor needs to be in the SIP-dialog. is there a neat solution to this problem or do we have to get a session-border-controller or some B2BUA-config for handling the received calls? and by the way, how do i distinguish external INVITEs destined for one of our clients (uri==myself) from the INVITEs being sent out to the callee upon an external INVITE? if there was a way we could invoke mediaproxy from there? how is the recommended setup? brgds, g.feiner