Digi X2 - Manual (Page 156)

C o n f i g u r a t i o n t h r o u g h t h e w e b i n t e r f a c e
1 5 6
A server-initiated connection works the opposite way. The Connectware Manager server
opens a TCP connection, and the Digi device must be listening for the connection to the
Connectware Manager server to occur. An advantage of server-initiated connections is
that you are not charged for sending the keep-alive bytes that are used in client-initiated
connections. A disadvantage is that there is no way of knowing whether the devices
displayed in the device list at the Connectware Manager server are offline or connected.
The device list shows all the devices as disconnected until the Connectware Manager
server does something to interact with them. In addition, server-initiated connections
cannot be used if Digi devices have private IP addresses and are behind a NAT.
Last Known Address (LKA)
Changes to the IP address for a Digi device present a challenge in server-initiated
connections, because the Connectware Manager server needs to locate the Digi device by
its new IP address. Digi Cellular Family devices handle address changes by sending a Last
Known Address (LKA) update to the Connectware Manager server. This permits the
Connectware Manager to connect back to the Digi device, or to dynamically update a
DNS with the IP address of the device.