Routers and more
If you go to your favorite electronics store and look at the aisle
that has routers, hubs, and switches in it, you'll notice that they
look about the same but hubs are cheaper. That's because hubs are
also the simplest option.
Hubs
In essence, a hub is like a car's radio: Everyone who's connected
to that channel (or section of network) can hear everything that's
being transmitted. Every computer that connects to a hub receives
all of the information that goes through the hub, and the hub depends
on the existence of a more advanced piece of network software (such
as a router) to work correctly. The hub can't assign network locations
to computers; it simply broadcasts whatever is fed into it.
Switches
A switch is a bit more complicated. A switch is like a two-way radio;
in a room full of people, only the person holding the other radio
can hear what's said. The switch keeps track of which computers are
connected to which ports, and when network traffic comes in, it sends
the information along to only that computer, rather than to all computers
on the network. It's both faster and more secure. But it's not as
powerful as a router; like a hub, a switch depends on the existence
of some more sophisticated piece of equipment to identify the computers
that are connected to it.
Routers
A router is like a telephone system. Each computer is given its own
unique number by the router. The information comes in, is identified
and processed, and then is sent along to the correct location. Along
the way, decisions take place behind the scenes in order to determine
which is the correct phone number (or computer) to connect with. There
are more control options built into a router than into a switch, including
networking equivalents of call screening and caller ID.
In practice
With the assistance of a typical broadband firewall-router from the
electronics store, you'll have a home network that's distinct from
the rest of the Internet. Your computers will be recognized by the
router, and the router will assign them IP addresses (the computer
version of a telephone number). Your computers can communicate with
each other within the private area that's "shielded" by
the router's firewall, and each computer can also make a connection
out to the Internet. But thanks to the firewall, external computers
won't be able to enter your local network and access your computers
without permission.
So when you open a file on Laptop and send it to Desktop's printer,
the network information never leaves your local network. The router
receives the network packets, recognizes that the packets are addressed
to the number it assigned to Desktop, and sends the packets on to
Desktop. Desktop receives the packets, recognizes that they're printing
instructions, and prints your file.

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