Powerline

Have the network extended via the power cords. If new cable routing is not possible, it can be a solution to use EoP (ethernet over powerline). In practice, this means that you put a module in an electrical outlet, e.g. by your router and connects it to your router with a network cable. This sends the network via the power cord to the place where they put the 2nd module. Module no. 2 A network cable is also inserted, such as leads to a switch or an access point and voila - then the network is extended.

The 2 (or more) sockets used for modules should be on the same phase. Your electrician can help you with this if you are in doubt.