I want to cofig ser as a outbound server to resolve all nat problem. The follow picture is the system architecture. uac--nat-->outboud1(ser1+nathelper+rtpproxy)------------->ser(main) uac--nat-->outboud2(ser2+nathelper+rtpproxy)-------------| uac--nat-->outboud3(ser3+nathelper+rtpproxy)-------------| Can someone know if ser can rewrite the uac's contact as itself ip address and forward to main ser? Nathelper can rewrite sdp ip/port to it own ip/port. But it only rewrite contac with nat's ip and port.