I’m currently setting up a Sipura SPA1001 at my home office to connect to an asterisk server over the internet. The * will actually provide a gateway connection to an analog extension on our Nortel KSU through a FXO port (Digium TDM).
From an inbound call to the Nortel system, as well as dialing the extension from in the office, the * server correctly routes the call to the Sipura adapter, and the phone rings. But there is no audio on either end. Also, * server has to be restarted before another attempt can be made.
Both sides of the connection are behind NAT.