[Users] sip contact relay/forward/rewrite?

[Paul Smith]

Hi,
I am new to openser and trying to use it as a proxy i.e. I have a
phone behind NAT, and another SIP server with all our
account/registrar/routing details, I want to try mediaproxy as a far-end
nat traversal solution to allow us to install phones without doing much
(or anything) to the NAT firewalls....  The idea is that I set up phones
to use Openser as Outbound proxy, and use symmetric RTP, and tell
openser to nathelper to do regular keep alive pings.  Then the phone
should open SIP port to openser when registering, and OpenSER forwards
the registration to the current sip server.  Later invites from the
current server should go back through Openser to the phone over the
still open ip:port pair.  MediaProxy on the openser should handle the
RTP traffic between phone and old sip server.

I have got ser and mediaproxy running and outgoing calls are fine.  The
problem is that incoming calls are not going through the proxy... the
phone registers via the openser proxy, but when initiating an incoming
call to the phone the registrar server sends the SIP invite straight to
the NAT firewall, which rejects it...

What do I need to do so that openSER tells the registrar to route SIP
INVITES back through the openser server?

I realise that at present I am looking at a very insecure open relay -
I'll add more auth and domain checking when I get the basic outbound
relay / media proxy bit working.

PHONE ---- NAT ---- SER ----- SIP registrar Server with user details etc.

Thanks.