I am using ubuntu 11.10 LTS. when I switch on my lappy, the network connections i have created works fine, but after sometime (not always) they disappear and no connection lefts available for use. the default wired connection also disapprears along with DSL connection i have created. I restart my PC and again start using network but the same thing happens again. Sometimes network connections work smooth sometime continuously same problem gets repeated without any reason. I only browse internet on Mozilla when such thing happens, no other network tool or other any other software is running when this problem occurs. So it is not triggered by other software or network tool, it happens automatically. This time I am using DSL connection for more than 1 hour and its working smoothly. before this i switched off my lappy several times and then again started up again problem occurred again switched off.... .. . dont knw what is wrong with this...I am using HP Laptop intel core i 5.
I think you should should reconnect the modem (or anything you use) whenever you log in your account. It is because of the reason that linux does not identify the modem when you log in ....... It needs a booster dose !!