The Internet: Wires, Cables & Wifi - YouTube 이중 자막

The Internet: Wires, Cables & Wifi - 이중 자막

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 place to another?

It isn't magic.

It's the internet, a tangible physical system that was 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 like boxes and envelopes, the internet ships binary information.

Information is made of bits.

A bit can be described as any terror of opposites on or off.

Yes or no.

We typically use a one, meaning on or a zero, meaning off.

Because a bit has two possible states, we call it binary code.

Eight bits strung together, makes one.

1,000 bytes altogether is a kilobyte, 1,000 kilobytes is a megabyte, a song is typically encoded using about 3 to 4 megabytes.

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 ones and zeros from one place to another one person to another.

So what is the physical stuff that actually gets sent over the wires in 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.

So say that we could turn on a light for a one or off for zero,

or use beeps or similar sort of things of like Morse code.

These methods work, but they're really slow, air-prone, totally dependent upon humans.

We really need as a machine.

So 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 light bulbs connected by a copper wire.

If one device operator turns on the electricity, then light bulb lights up.

No electricity, no light.

If the operators on both ends agree that light on means one and light off means zero,

then we have a system for sending bits of information from one person to another using electricity.

But we have a problem.

Let's say that we want to send five zeros in a row.

Well, how can you do that in such a way that either person can actually count the number of zeros?

Well, the solution is to introduce a clock or a timer.

The operators can agree that the sender will send one bit per second,

and receiver will sit down and record every single second and see what's on the line.

To send five zeros in a row, you just turn off the light.

Wait five seconds,

the person on the other end of the line will write down all five seconds,

say zero, zero, zero, and for ones, do the opposite, turn on the light.

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 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.

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 kind of hard for a human to keep up with.

So let's say that you want to actually download a three megabyte song in like three seconds.

At eight million bits per megabyte, that means a bit rate of about eight million bits per second.

Obviously, humans can't send or receive eight million bits per second but a machine can do that just fine.

But now there's also a 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 or office or school, you see really measurable signal loss over just a few hundred feet.

So, if we really want this internet thing to work over the entire world, we need a different

way of sending this information really long distances.

I like, of course.

So what else can we use?

Well, what do we know that moves a lot faster than just like electricity through a wire?

Is, well, 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 fun.

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

In 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 move things without wires?

How do we send things wirelessly?

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

The machines have to actually translate the ones and zeros into radio waves of different frequencies.

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

So wireless has made our internet mobile, but a radio signal doesn't travel all that far before it completely gets garbled.

This is why you can't really pick up a Los Angeles radio station in Chicago.

As great as wireless is, today it's still relies on the wired internet.

If you're in a coffee shop using Wi-Fi then the bits get sent through this wireless router

and then are transferred to the physical wired to travel the really long distances of the internet.

The physical method for sending bits may change in the future whether it's laser sent between satellites or radio waves from balloons or drones,

but the underlying binary representation of information and the protocols for that information and receiving that information have pretty much stayed the same.

Everything on the internet,

whether it's word,

emails, images, cat puppy all kinds of

and zeros being delivered by electronic pulses, light beams, radio waves, and, you know, lots and lots of vlogs.

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