Many Internet service providers offer combined modem/router units, but a modem isn’t the same thing as a router. Understanding exactly what a modem is is important so you can buy your own modem and stop paying £15-£20 a month to rent one from your Internet service provider.
A router and modem are really two separate devices. If you’re purchasing your own modem, you might need to also purchase a router if you don’t already have one.
What a Router Does
The router then connects to the Internet through the modem and the router itself receives a single public IP address on the Internet. Servers on the Internet communicate with your router, and the router routes that traffic to the appropriate devices on your home network.
But, with just a router, you can’t actually connect to the Internet. The router must be plugged into the Internet via an Ethernet cable. You need a modem to do so.
What a Modem Does
Your modem communicates with your Internet service provider’s network. If it’s a cable modem, it plugs into your cable provider’s infrastructure via a coaxial cable. If it’s a DSL modem, it plugs into your telephone line.
The modem communicates with your Internet service provider, and you’ll need the correct type of modem that will work with your ISP’s infrastructure.
The modem plugs into whatever type of infrastructure you have — cable, telephone, satellite, or fiber — and gives you a standard Ethernet cable output that you can plug into any router (or a single computer) and get an Internet connection.
Combined Routers and Modems
Some Internet service providers offer a modem and router in a single box. That box has the electronics and software in it to provide both functions, acting as a modem that communicates with your ISP and functioning as a router to create a home Wi-Fi network.
ISPs like offering all-in-one devices like these, but there’s no reason you have to use one in the same box.
