My original setup was probably far from ideal now that I look at it: a cable run from the main phone point to the stairs, a female/female RJ11 connector, an RJ11 splitter one side connected to DSL microfilter and phone and the other to another long cable run upstairs to the router beside the desktop PC. Basically all the connections and cable runs could feasibly have introduced flakiness causing the router to disconnect from time to time. I need to monitor it a bit more but it looks like moving the router to nearer the main phone point has helped.