[Serusers] ser and client behind nat,no audio...urgent

I really need to sort out my nat situation with ser as soon as possible....Im beginning to believe its not doable. SER is behind nat and clients are behind nat (one on the same lan as ser) and the other on a totally different nat. Both clients register with a public address and port forwarding the nat router forwards the sip traffic to ser. I know this situation is horrible but I cant do anything about it. I have setup nathelper and rtpproxy on ser. Now if a client behind nat (which is on the same lan as ser) rings another client behind nat (on same lan as ser), then everything works fine and the audio flows. However if a lcient behind (on the same lan as ser) rings a client on behind on nat on DIFFERENT network to ser, then no audio flows. I realise this is because of that fact that they both have internal IP addresses and a middle man is needed. That is why I set up rtpproxy. But will rtpproxy work when its also behind nat??.... I've did an ethereal sniff of remote client and also of ser when calling from my client on ser lan to the remote client and the results are below. My config was a jumble of various emails from the mailing list so Im going to start from scratch and say my ser.cfg is just like the basic one included in the below link. http://www.informatik.uni-bremen.de/~prelle/terena/cookbook/Cookbook_D 2/ch04s07.html#d0e5091 Please, Please give me guidance. I know this is a horrible nat situation but i just cant figure out how to solve it or if it can be solved. Thanks, Aisling ethereal sniff of remote client (not on same lan as ser, but behind nat)xxx.xxx.xxx.xxx is my public address SIP INVITE xxx.xxx.xxx.xxx. -> 10.0.1.21 (internal address of remote client) 100 trying 10.0.1.21 -> xxx.xxx.xxx.xxx 180 ringing 10.0.1.21 -> xxx.xxx.xxx.xxx 200 ok 10.0.1.21 -> xxx.xxx.xxx.xxx rtp 10.0..1.21 -> xxx.xxx.xxx.xxx ethereal sniff of ser (with nathelper and rtpproxy) but behind nat INVITE 172.16.3.28 (internal address of client on same lan as ser) -> xxx.xxx.xxx.xxx invite xxx.xxx.xxx.xxx.172.16.3.15(internal address of ser) 100 trying 172.16.3.15 -> xxx.xxx.xxx.xxx invite 172.16.3.15 -> 157.190.70.231(public address of remote client) 100 xxx.xxx.xxx.xxx -> 172.16.3.28 100 trying 157.190.70.231 -> 172.16.3.15 icmp 172.16.3.15 -> 157.190.70.231 dest unreachable same happens for 180 ringing and 200 ok. -------------------Legal Disclaimer--------------------------------------- The above electronic mail transmission is confidential and intended only for the person to whom it is addressed. Its contents may be protected by legal and/or professional privilege. Should it be received by you in error please contact the sender at the above quoted email address. Any unauthorised form of reproduction of this message is strictly prohibited. The Institute does not guarantee the security of any information electronically transmitted and is not liable if the information contained in this communication is not a proper and complete record of the message as transmitted by the sender nor for any delay in its receipt.