Broadband modem: A broadband modem is the box that should be connected to the cable that runs through your wall. If you have a DSL connection, it will be a phone line. If you have a cable connection, it will be...well, a cable. And if you have a fiber-based setup, it will be another cable. The box communicates with your Internet Service Provider. If it's switched off, no Internet for you (unless you're leeching it from your neighbor's Wi-Fi network). If a support person tells you to "reset your modem" by unplugging it, this is the box to unplug.
A broadband modem generally has several lights—some of which will blink. They include a power light, a status light, and a LAN (local area network) light. Get to know what these lights look like when your connection is working properly. If a green light suddenly turns red, you have a problem.
Router: A router is your local network's traffic cop. If you have a Mac, iPhone, iPad, Apple TV, and smart TV connected to your network, the router ensures that the right data gets sent to and from the right device. In most cases it handles this task by assigning individual addresses to each device. Routers can be wireless or wired. An AirPort Base Station, for example, is a wireless router.
"But wait!" you interject. "I don't have two boxes, I have just one. And my network works perfectly well!"
Correct. And it does so because you have a modem that additionally includes a router. Not all of them do.
Network switch: Suppose that your cable company has supplied you with a modem/router combo box. This box has a single ethernet output port, which you can use to connect your Mac to the network. But wait—you also have an Apple TV and a smart TV that you'd like to use with that ethernet connection. What do you do?
You purchase a network switch (in this case, an ethernet switch). The switch also functions as a traffic cop: If the router sends information to a particular address—the address of your Apple TV, say—that information goes only to the Apple TV and not to the rest of your gear. (An ethernet hub, a device rarely seen these days, does something similar; however, it doesn't perform any traffic-routing duties. All data sent to the hub's input gets transmitted to everything attached to the hub. This makes for slower communication, along with the occasional data collision.)
Switches come in various configurations—from four to umpteen ports—and speeds. Most of today's switches support 10/100/1000-mbps connection speeds. Apple's AirPort Extreme Base Station includes a built-in switch that handles the three LAN ports.
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