Our FortiVoice FVC100 phone system sits behind a SonicWALL NSA240 for Internet connectivity. We recently setup SIP trunks via their FortiCall VoIP service. However, we are having trouble with some incoming calls not getting through. After working though a ticket with FortiNet support they gave me the following:
Thank you for having provided these additional log details. We've had the chance to look through the log data from today, along with speaking with our colleagues at Forticall, and have to diagnose this issue as being a firewall setup problem.
What's happening is that at the time you report you get an error on inbound calls, the Forticall server is sending the call to the phone system. However, the phone system is not getting the message at all.
Your report that you're able to make an outbound call, then follow it up with an inbound call successfully is corroborated in the log that you'd sent, and is classically an issue of port forwarding. More specifically, that a pinhole is being used by the firewall to dynamically open a SIP port for communication, that's automatically closed back down after a certain amount of time (usually 5 minutes or so).
Please ensure that your port forwarding is configured on your firewall. Ensure that there is an outbound rule as well as an inbound rule for your SIP traffic. Finally, you could contact Sonicwall to have them ensure that your SIP traffic travels through your configured port forwarding, rather than traversing the firewall via pinhole.
I have port forwarding configured, and the "firewall test" from the FVC100 passes no problem. Any ideas what else I should be doing?