Maybe the looby is brooken?
Incidentally, if it only happens "all on a saturday night" then you may need to refer to a book of nineteenth century verse for the answer.
Alternatively, check that your PS3's connection has priority on the required ports and get your phone company to check the signal/noise ratio on your line.
Having a 20Mbps connection etc. etc. is no advantage online - you can play on dialup if your line is solid. If the connection's dropping then its either your PS3>Router connection suffering a problem or your Router>World connection.