"The best business telephones in the world."

Hello and Thanks

Cisco Spa504g at same remote office as snoms below work perfectly.

Snom 320 821 in use at remote office disconnect after 31 seconds.

Both are behind sonicwall firewall.

Both use session border controller to connect to 3cx server.

Both show same error in SBC log  no RTP session

This change occurred since upgrading from v14 to v15 of 3cx.

Neither phone was taken to office for provisioning.

Both show provisioned on 3cx console.

Hello Morris,

We will need to investigate more, I converted this topic in a support ticket.

You will be contacted soon for the next steps,

Regards,

Hi and thanks

Found firewall troubles on my end, 

I will be testing phone again soon

after firewall version upgrade; problem resolved

I've got the same problem with Snom phones behind a Sonicwall with the latest firmware SonicOS Enhanced 6.5.2.1-31n

The Snom phones which range from 720, 760 to 725s only purchased last month and all on 8.9.3.88 (3CX preferred version) all exhibit the same issue where calls disconnect with "Network Failure"