The keep-alive function is configured in the Remote sites list.
If the short hold time is set to 0 seconds, the connection is not actively terminated by the device. This setting thus prevents disconnection if no data is transferred over a longer period. With this setting, however, a disconnect at the remote site is not automatically re-established.
With a holding time of 9,999 seconds the connection is always re-established after any disconnection. Additionally, the connection is re-established after booting the device ('auto reconnect').