For some network topology complex, for example Modem Switch in a room, another switch in a part of the house (upstairs) and another switch in another part of the house (ground floor), the downside is when the modem is disconnected from the Internet happens. Then you have to go and reset the modem hardware because from intranet says reboot, but do nothing ...
The problem is that to get to restart it is to open 3 doors and cross the yard, either night and day, cold, heat, rain, meteorites and other ...
The idea is as follows, by a single Ethernet cable UTP cat-5 or Level-5, passing the connection IEEE over the telephone line, as the Ethernet standard requires 4 connections TX +, TX-, RX + and RX- 4 pins left over and most of which take two and added the phone connection, so I have a By-Pass in the part where I had the modem before and then hooked the phone, the switch (as it was before) and UTP which flows to another plant where I have By-Pass the other taking the Ethernet and phone connection to power the modem.
Here is the diagram:
