[Users] STUN still mandatory ?

Hi, Is the use of a STUN server or any other solution of this type (another daemon) still mandatory to solve NAT problem since I have set up correctly a media proxy and the netHelper module in my configuration file ? If it's not the case which type of configuration is out of the scope if my server is in this configuration ? For example for this network configuration, is a STUN server with UA compatible mandatory ? UA1 --- [openSER+MediaProxy+FW wiht NAT] --- [ Internet ] --- [ FW/NAT ] --- UA2 If it the case, which module(s) must be used with openSER and which STUN server (open source/free) can be used ? I already tested that this network configuration is working without any STUN server UA1 --- [openSER+MediaProxy+FW wiht NAT] --- [Internet] --- [FW] --- UA2(softphone on PC with direct access on internet) Thanks, Christophe