We recommend best practise by setting a short registration timeout trunk setting to make best use of our auto-failover facility so we recommend that you set the ‘registration expiry timeout’ setting (often shown as 'Time between registration attempts', 'Server Expires' or simply 'Timeout' in your PBX settings) to be equal to 5 minutes (300 seconds) on both on the trunk and for good measure on all end devices also via your phone system’s device profiles / device settings.

Please also refer to DNS Record Settings.