Thanks for help, but i have tried it already and its is not working.
Any more ideas?
If you have just one external IP address, You should define the rules that way :
From Uplink ANY ----> external public IP ---> Translate to ---> Internal IP : port
if You have multiple public addresses, You have to specify Source Nat rules in addition to the above.
From Asterisk box ---> Uplink ANY [ Any service ] ---> NAT to a specific external IP.
Hope this helps..