Kamailio SBC using RTPproxy

Dear Kamailio community,

I am currently developing a VoIP system using 2 instances of Kamailio. One as SBC and one as SIP server.
The SBC is configured to work in bridge mode (one NIC on the public side, one NIC on the private side).
The SIP server works as expected.

But the SBC server seems to have some difficulties to route the RTP traffic.
I am using RTPproxy to handle NAT traversals.

Currently, I handled the following situations:

  *   Internal to internal call
  *   External (both NAT and CG-NAT) to internal call
  *   Internal to external (both NAT and CG-NAT) call

The situation that does not work is the following:

  *   External (both NAT or CG-NAT) to External (both NAT or CG-NAT)

The SBC seems to always translate the IN IP4 field from external to internal (as desired when calling from external to internal), but this seems not to be desired when calling from external to external.
This way, both external devices try to send the RTP data to the internal (inaccessible) address of the SBC.
How can I configure the SBC to stop translating the IN IP4 field when both devices are external?

I have the following configuration that talks to the RTPproxy service:

==========================
    if(nat_uac_test("8")) {
        if($Ri == "MY_PUBLIC_IP") {
            rtpproxy_manage("coiew");
        } else {
            rtpproxy_manage("faei");
        }
    } else {
        rtpproxy_manage("cor");
    }
==========================


Also, is this the desired way to handle NAT traversal with RTPproxy?

Kind regards
Ibe Van de Veire
System Engineer

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