First off all it is crucial to understand both features run as separate services on the CloudGate although their output is heavily linked.
In essence the connection priory feature is responsible to make sure the CloudGate is connected to the best available communications link. Connection Persistence however is ensuring that the service required for proper operation is reachable.
The CloudGate will first attempt to connect to the highest priority network selected in the connection priority table. In case after 15 seconds this does not yield in a connected state the next interface will be started to try and connect in parallel to the primary interface. If after an additional 15 seconds none of the previously started interfaces is in connected state the next interface in line will be started. It is important to understand Cloudgate will keep checking higher priority interfaces for their connection status.
Example: Connection priority is configured in following order: 1. Ethernet; 2. WLAN; 3. 3G interface. At startup CloudGate will check is the Ethernet is connected, if not the WLAN interface will be started; at that point Cloudgate will check both WLAN and Ethernet. When WLAN is in a connected state Cloudgate will keep checking the Ethernet interface in the background and will switch back to the Ethernet interface incase the state is changed to connected.
When the connection persistence feature is enable the CloudGate will in addition to checking for a connected state, monitor the result of connection persistence on the current and higher priority interfaces. In case a higher priority interface is connected but the connection percistence service has detected the required service is unreachable the interface next in line will be started and checked for connectivity in parallel.
Example: Connection priority is configured in following order: 1. WLAN; 2. Ethernet; 3. 3G interface. The WLAN interface reports it is connected although connection persitence reports it cannot resolve the requested destination address. (e.g. Cloudgate is connected to a WLAN network with a captive portal active). CloudGate will start the Ethernet interface. When Ethernet is connected and connection persistence reports the link is accepted Cloudgate will start using the Ethernet interface
The 3G interface has additional reset options: When connection persistence detects the 3G interface is not connected to its appropriate service the interface will initially get a soft reset as all the other interfaces can get but if this is unsuccessfull the 3G interface will be rebooted without having to rebooting the CloudGate.