It's been happening occasionally since we got Earthlink a few years ago. I always assumed they were doing maintenance.
We will get a good connection for a fairly long time.
Then, the PPPOE light will go off.
I will pull the power out of the Netopia modem for a minute.
Plug it back in.
Then the PPPOE light will come on for 15 seconds and then it will disappear again.
I'll have to keep doing that for a few minutes and then everything works again.
I can remember two occasions where it was past midnight, and it didn't start working again until I woke up.