[Serusers] Asterisk inside a NAT, client inside ANOTHER NAT

[C.K]

Hello,

By looking at this section from the link
http://www.voip-info.org/wiki-Asterisk+SIP+NAT+solutions

9. Asterisk inside a NAT, client inside ANOTHER NAT

In this case, we need a middle man to even find each
other, an outbound SIP proxy that handles the SIP
transaction and is reachable by all parties. To get
media streams from point to point we need another
middle man, a media server. Asterisk could be that
media server, that could add media codec conversion.
Portaone's rtpproxy works together with SIP Express
router as a media server in this situation. 

Could anyone share the configuration on how to do this
? I could only succeed if I put on port forwarding on
the UA's end.

Regards, C.K