[OpenSER-Users] Please help in Openser behind NAT design

Hi All I'm a new member and trying to use Openser as my VOIP "router" I plan to make following configuration: UA <---> Openser <---> Firewall/NAT <--INTERNET--> Firewall/NAT <---> UA a.a.a.a/24 x.x.x.x y.y.y.y b.b.b.b/24 a.a.a.a and b.b.b.b is internal IP not internet route-able x.x.x.x and y.y.y.y is Firewall/NAT external IP number I know there is mediaproxy and RTPProxy to solve the UA b.b.b.b that behind NAT but I don't know if my decision to put Openser behind NAT is correct or not. How to archive the above diagram with Openser ? If above Openser location is wrong, where should the Openser reside in the diagram? Install in Firewall/NAT or in INTERNET (dedicated server) Thank you for your help and sorry if my question is too newbie Halomoan