In some conditions, we use a primary server and a backup server to maintain the system stability. The IP phone will register to the primary server first, when the primary server is down, the backup server will take over and serve as the working server. When the primary server recovers, it returns to be the working server.

Configurations on the Phone

1. Go to SIP Account > Line1 settings page, configure the Outbound Server and the Backup Outbound Server, the Outbound Server is the primary server, and the Backup Outbound Server is the backup server.

2. Go to the SIP Advanced Setup page, and set up the following settings. 

Register Refresh Interval (sec): The phone will initiate registration with the half-time of this value, it is 1800 by default.

Primary Server Detect Interval: The SIP option interval to detect the primary server activity. It is 0 by default.

Max Detect Fail Count: The fail count for the primary server to respond to the phone’s SIP option. When exceeding this value, the phone will switch to the backup server. It is 3 by default.

Prefer Primary SIP Server: With this option enabled, the phone will switch back to the primary server when it detects the primary server recovers.