[SR-Users] Nat issue

hello dears when i'm using kamailio 5.2 as IMS i'm facing the following NAT issue : * when p-cscf handle a call from user1 to user2 that pre-registered on private address "192.X.X.X" (on another LAN) the user can't receive the invite message . in another word: proxy ip : 10.192.X.X user1 ip : 10.X.X.X user2 ip : 192.X.X.X the call scenario : user1 ---invite----> user2 (not arrived) * when p-cscf handle a call from user2 that pre-registered on private IP "192.X.X.X" (on another LAN) to user1 the user receive the invite message . the call scenario : user2 ---invite----> user1 (arrived) * when both of the user on different LANs the message 200 OK doesn't arrive to proxy :\ so based on that does any one has an experiment with NAT handling & nathelper module and how to configure it on P-cscf . thanks in advance