The Network module owns the data connection to the nRF91M1 Serial Modem. It brings the PPP link up and down through Zephyr's connection manager and reports connectivity to the rest of the application so that no other module needs to know how the link is established.
By default the module connects on startup and keeps the connection for the lifetime of the application. The connection can also be controlled from the application or from the shell, see Configurations and Shell commands.