Depends on where the fault lies. Let me outline those I have personally experienced:
In the case where, say, my Ethernet cable was faulty, then I would get disconnected whenever the contact between the cable and the modem, or the cable and the Ethernet card was bad. I solved this problem simply by buying another Ethernet cable.
If the outage is due to, say, a tree falling and shorting out the cable line outside, then it's another matter.
If it's due to some screwup in the ISP's servers (once, for some unknown reason they lost my MAC address), then you can call tech support and ask them to check.
All these situations will result in disconnection, and Windows (2K, which is what I am running) will notify that your cable connection is disconnected. Obviously if your cable is disconnected, you are disconnected from the Internet.
Also, firmware version should not affect connection, though there are times when disconnecting all cables and power supply, and reconnecting them and then rebooting the entire system will restore the connection. Weird.