The Internet: Wires, Cables, & Wifi

This educational video introduces how the physical infrastructure of the Internet moves information.

See more at Code.org/educate/csp

Presented by Tess Winlock / Software Engineer at Google

Special Thanks:
Tess Winlock,
Abby Huang
Bemnet Assefa
Saloni Parikh
archive.org
wikimedia
submarinecablemap.com
Google Earth
Wikipedia

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The Internet | Wires, Cables, and Wi-Fi

My name is Tess Winlock, I'm a software engineer

at Google. Here's a question: How does a picture,
text message, or email get sent from one device

to another? It isn't magic, it's the Internet.
A tangible, physical system made to move information.

The Internet is a lot like the postal service,
but the physical stuff that gets sent is a

little bit different. Instead of boxes and
envelopes, the Internet ships binary information.

Information is made of bits. A bit can be
described as any pair of opposites: on or

off, yes or no. We typically use a 1 meaning
on, or a 0 meaning off. Because a bit has two

possible states we call it binary code. 8
bits strung together makes 1 byte. 1000 bytes

all together is a kilobyte. 1000 kilobytes
is a megabyte. A song is typically encoded

using about 3-4MB. It doesn't matter if it's
a picture, a video, or a song, everything

on the Internet is represented and sent around
as bits. These are the atoms of information.

But it's not like we're physically sending
1s and 0s from one place to another or one

person to another. So what is the physical
stuff that actually gets sent over the wires

and the airways? Well, let's look at a small
example here of how humans can physically

communicate to send a single bit of information
from one place to another. Let's say that

we can turn on a light for a 1 or off for
0. Or use beeps or similar sorts of things

to Morse code. These methods work but they're
really slow, error prone, and totally dependent

upon humans. What we really need is a machine.
Throughout history, we've built many systems

that can actually send this binary information
through different types of physical mediums.

Today, we physically send bits by electricity,
light, and radio waves. To send a bit via electricity,

imagine that you have two lightbulbs connected
by a copper wire. If one device operator turns

on the electricity then the lightbulb lights
up. No electricity, then no light. If the

operators on both ends agree that light on
means 1 and light off means 0, then we have

a system for sending bits of information from
one person to another using electricity. But

we have kinda a small problem, if you need
to send a 0 five times in a row, well how

can you do that in such a way that either
person can actually count the number of 0s?

Well the solution is to introduce a clock
or a timer. The operators can agree that the

sender will send 1 bit per second and the
receiver will sit down and record every single

second and see what's on the line. To send
five 0s in a row, you just turn off the light,

wait 5 seconds, the person at the other end
of the line will write down all 5 seconds.

For five 1s in a row, switch it on, wait 5 seconds,
write down every second. Obviously we'd like

to send things a little bit faster than one
bit per second, so we need to increase our

bandwidth - the maximum transmission capacity
of a device. Bandwidth is measured by bitrate,

which is the number of bits that we can actually
send over a given period of time usually measured

in seconds. A different measure of speed is
the latency, or the amount of time it takes

for one bit to travel from one place to another,
from the source to the requesting device.

In our human analogy, one bit per second was
pretty fast but kinda hard for a human to

keep up with. Let's say that you actually
want to download a 3MB song in 3 seconds,

at 8 million bits per megabyte that means
a bit rate of about 8 million bits per second.

Obviously, humans can't send or receive 8
million bits per second but a machine could

do that just fine. But now there's also the
question of what sort of cable to send these

messages over and how far the signals can
go. With an ethernet wire, the kind that you

find in your home, office, or school you see
measurable signal loss or interference over

just a few hundred feet. For the Internet
to work all around the world, we need to have

an alternative method to send bits really
long distances. We're talking like across

oceans. So what else can we use? What do we
know that moves a lot faster than just electricity

through a wire? Light. We can actually send
bits as light beams from one place to another

using a fiber optic cable. A fiber optic cable
is a thread of glass engineered to reflect

light. When you send a beam of light down
the cable, light bounces up and down the length

of the cable until it is received on the other
end. Depending on the bounce angle, we can

actually send multiple bits simultaneously,
all of them traveling at the speed of light.

So fiber is really really fast. But more importantly
the signal doesn't really degrade over long

distances. This is how you can go hundreds
of miles without signal loss. This is why

we use fiber optic cables across the ocean
floors to connect one continent to another.

In 2008 there was a cable that was actually
cut near Alexandria, Egypt which really interrupted

the Internet for most of the Middle East and
India. So we take this Internet thing for

granted but it's really a pretty fragile,
physical system. And fiber is awesome but

it's also really expensive and hard to work
with. For most purposes, you're going to find

copper cable. But how do we move things without
wires? How do we send things wirelessly? Radio.

Wireless bit sending machines typically use
a radio signal to send bits from one place

to another. The machines have to actually
translate the 1s and 0s into radio waves of

different frequencies. The receiving machines
reverse the process and convert it back into

binary on your computer. So wireless has made
our Internet mobile. But a radio signal doesn't

travel all that far before it gets completely
garbled. This way you can't really pick up

a Los Angeles radio station in Chicago. As
great as wireless is, today it still relies

on the wired Internet. If you're in a coffee
shop using wifi, then the bits get sent to

this wireless router and then are transferred
through the physical wire to travel the really

long distances of the Internet. The physical
method for sending bits may change in the

future, whether its lasers sent between satellites,
or radio waves from balloons, or drones, but

the underlying binary representation of information
and the protocols for sending that information

and receiving that information have pretty
much stayed the same. Everything on the Internet,

whether it's words, emails, images, cat videos,
puppy videos, all come down to these 1s and

0s being delivered by electronic pulses, light
beams, radio waves, and lots and lots of love.