We are using Check Point firewall I configured this server to allow both way in/out and NATED with public IP. For testing purpose I kept all ports opened in the firewall, for this particular server. I don�t why I am not able to register it.
Might take a closer look at the Checkpoint to see if it is doing Port Address Translation (PAT) in addition to NAT. If I recall correctly, the older versions of Checkpoints software did PAT, which caused folks problems when an app wanted to use specific tcp/udp port numbers (for example, when trying to use an non-checkpoint VPN box on the inside of the checkpoint).
Which is better PSTN gateway. We are looking at 1 to 2 FXS port at this time for testing purpose.
? FXS is a PSTN-phone-2-IP gateway, isn't it? The most popular is cisco's ata.
Think the FXS is a Foreign Exchange interface intended to tie a ser-accessible gateway to a telephone/pbx line (not to a telephone instrument).