We have been noting the pattern of speed variation and disconnection for the past three to four years.
And what we found is that there is no pattern. Sometimes the connection would be fast and stable for 3-4 months straight, and sometimes it goes out almost the entire day. Most of the times, it's somewhere in between.
We have changed the entire computer, changed the OS, changed the wireless router, changed the modem, upgraded drivers, plugged the DSL modem in different phone jacks -- to no avail. Nothing seems to matter or affect the connection.
It's completely erratic.