Dongle: ZTE MF825A
Assuming 192.168.0.1 is the IP of your dongle:
Connect
http://192.168.0.1/goform/goform_set_cmd_process?goformId=CONNECT_NETWORK
Disconnect
http://192.168.0.1/goform/goform_set_cmd_process?goformId=DISCONNECT_NETWORK
Configure to auto connect
http://192.168.0.1/goform/goform_set_cmd_process?goformId=SET_CONNECTION_MODE&ConnectionMode=auto_dial
Reference:
https://wiki.archlinux.org/index.php/ZTE_MF_823_(Megafon_M100-3)_4G_Modem