Problem behind router

Hi ive got installed asterisk behind a dlink router. i put the ip of the pc with asterisk under DMZ config in the router, everithing is ok. the soft and hard phones register ok. but when somebody make a call, nobody can hear.

when i put the pc with asterisk directly coneected to the adsl modem, everything work fine.

i need help configuring asterisk behind my router

and please sorry my english =$