[Serusers] SER + RTPProxy and Client behind NAT

[Kanakatti Mahesh Subramanya]

I'm having a strange problem with getting  SER+RTPProxy to work when the 
UA is behind NAT
Setup is as follows


UA --> NAT1 --> SER+RTPProxy --> NAT2 --> Asterisk

I've got RTPProxy running in "bridge" mode, gatewaying 'tween Asterisk 
and the Public Internet

SIP traffic all routes perfectly.  STUN enabled clients work perfectly.

The problem is that if the outbound port on NAT1 for the RTP stream is 
*different* from the outbound port from the UA, then RTPProxy persists 
in sending the packets to the UA port, *not* the NAT1 port.

e.g.
if the SDP payload from the UA contains

            c=IN IP4 192.168.5.100
            m=audio 16396 RTP/AVP....

but NAT1 sends the RTP stream out on port 64003, then rtpproxy sends the 
media from Asterisk back to port 16393 at NAT1, instead of to port 64003 
at NAT1!

Is it supposed to do this?  Am I missing something really obvious?


The relevant section from ser.cfg is as follows

 if (nat_uac_test("3")) {
    if (method == "REGISTER" || ! search("^Record-Route:")) {
      fix_nated_contact(); # Rewrite contact with source IP of signalling
      if (method == "INVITE") {
        fix_nated_sdp("1"); # Add direction=active to SDP
      };
      setflag(6);    # Mark as NATed
    };
  };

 rewritehostport("........");
  if (force_rtp_proxy("FEI")) {
    t_on_reply("4");
  };
.
.
.
onreply_route[4] {
  if (!(status=~"183" || status=~"200")) {
   break;
  };
  fix_nated_contact();
  force_rtp_proxy("F");
   break;
}


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