Here is a bunch of technical stuff about routing, switches and gateways from Cisco, one of the largest router manufacturers. A UPS is the generic term for Uninterruptible Power Supply. It is a battery connected to the wall with a built in charger. Computer equipment plugs into it. Should the power fail, or some other electrical problem occur, the devices connected to it will keep running off of the battery.
Batteries usually last a few years.
The units vary in price depending on the load which they handle. Smaller facilitates have small systems. Larger companies have generators operated by huge diesel engines with banks of car batteries connected to voltage inverters to keep the computers running until the generators can start and take over for the power grid. A UPS on your home computer will safeguard your machine against a power failure. Most UPS devices connect to your computer with a cable.