Line noise is sometimes enough to cause your link to drop. If you ever notice "crackly" noises on normal voice calls, you will most probably experience connection problems.
If you get disconnected from your ISP without warning and too often, try adding "S10=50" (without the quotes) to the initialisation string of the modem. This should extend the time period a little before the modem "hangs up".
In Win 95/98 open the Control Panel, click on the Modems icon, click your modem's Properties button, select the Connection tab, then click the Advanced button. In the Extra settings field, enter "S10=50" without the quotes.
In Win XP open the Control Panel, click on Phone and Modems options, then select the Modems Tag. Select the Modem you want to use then click the Properties button, select the Advanced tab. In the Extra settings field, enter "S10=50" without the quotes.
Please Note: If you have more than one entry in your Extra Settings field, each should be separated by a single space.