There is an option in the PPP application that automatically disconnects services when the dial up services are idle for a designated period of time. This feature saves long distance telephone charges or reduces idle use of PPP server telephone lines.
If you don't need this feature active it can be turned off in Apple Remote Access. Other dial up applications may have a similar option. Here is how to change the setting in Apple Remote Access:
1. Open the Remote Access control panel.
2. Select the "Options..." button.
3. Uncheck the reminder "disconnect if idle for ten minutes."