[Serusers] Creating a test scenario to test NATing..

hi all, I wanna simulate a test scenario in which the sip clients are behind NAT (whether same or different NAT, in some private network), and the SER and MediaProxy are running on some public IP. My question is, in this case the client is not able to communicate with the server through the Firewall / NAT. My SIP messages are being dropped at the Firewall itself. Can anybody tell me, what could be the reason behind that????? I'm totally stuck at this point..... plz revert asap... thanx in advance.. The information contained in this e-mail message is intended only for the use of the individual or entity to which it is addressed. If you are not the intended recipient, you should return it to the sender immediately. Please note that while we scan all e-mails for viruses we cannot guarantee that any e-mail is virus-free and accept no liability for any damage caused by any virus transmitted by this email.