Please bear with my n00bness regarding networking. Relatives of mine live above their workplace. They have got 2 phone lines, let's call them line A and line B. Downstairs, at the workplace, they have a modem and a router and they use line B for the phone, and line A for the internet. At home, on the floor above, they use line A both for Internet and for phone. They also have another router and modem there upstairs, because the router down below isn't powerful enough to cater for both floors. Now here are the issues: 1) If the "upstairs" router and modem are switched on, they cut off the "downstairs" internet signal. I was thinking it's because you can't have more than one modem on the same phone line (A) but I want to confirm this. 2) It's always the downstairs internet access which quits. If the downstairs is connected there's no way it can "win" over the upstairs signal. Why? 3) When phoneline A is used for a normal land-line phone call, the downstairs internet signal also quits, even if neither upstairs router or modem are switched on. Why? 4) Downstairs the internet connection is 'nearly' what they're paying for, checked it with Speedtest. Whereas upstairs they are getting slightly less than half the speed they're paying for. They can't even view online streaming or a youtube video without endless buffering making it not worth even trying. This happens whether the router and modem downstairs are switched on or off. So, any clues where I might start here?