Incompatibility The second most common cause of disconnects is modem incompatibilities, again typically related to re-trains. Get the latest firmware revision for your modem. The statement 'my modem has no problems with Joe's Internet Service' is not particularly meaningful. Every modem will be compatible with someone, but we have yet to see the modem that is compatible with everyone. As modems become faster they also become more complex.
Some modems have a way to record the reason why a connection failed.
Another common cause of disconnects is line noise. Also unplug your laser printer and microwave oven from the AC wall outlet. We have learned that many telephone line surge protectors or noise filters will seriously impair your phone line. The modem should be the ONLY thing connected to your phone lines. If the problem goes away, then you have something in your house causing you to disconnect.