Internet Connection Problem. Poor and fluctuating signal from supplier causes frequent disconnection and subsequent unavailability of device. 'nmcli nm' shows STATE as being disconnected with both WWIFI and WWAN H/W and S/W enabled, and 'nmcli dev' does not show device ttyUSB0. How do I reactivate the device so that it can be seen by 'nmcli dev' and change STATE to connected? 'nmcli con up id i[id]' does not work as device does not register with 'nmcli dev'. Currently, have to unplug/re-plug device, but even that does not work sometimes. Also, is there a way of connecting /talking to a modem as with the Hayes command set? Is there a way of directly activating the PPP connection?
Also, a command that lists all Linux/network commands would be helpful. IBM AIX used to have 'lscmd' command (I think) that showed all commands, hopefully there is an equivalent under Linux.

I regard myself as an absolute beginner although I have gone through some tutorials and looked for answers in books etc.