"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.

Hi and thanks

Found firewall troubles on my end, 

I will be testing phone again soon

after firewall version upgrade; problem resolved