[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:02.76,0:00:08.50,Default,,0000,0000,0000,,The Internet | Wires, Cables, and Wi-Fi
Dialogue: 0,0:00:08.50,0:00:12.78,Default,,0000,0000,0000,,My name is Tess Winlock, I'm a software engineer
Dialogue: 0,0:00:12.78,0:00:17.74,Default,,0000,0000,0000,,at Google. Here's a question: How does a picture,\Ntext message, or email get sent from one device
Dialogue: 0,0:00:17.74,0:00:25.05,Default,,0000,0000,0000,,to another? It isn't magic, it's the Internet.\NA tangible, physical system made to move information.
Dialogue: 0,0:00:25.05,0:00:29.66,Default,,0000,0000,0000,,The Internet is a lot like the postal service,\Nbut the physical stuff that gets sent is a
Dialogue: 0,0:00:29.66,0:00:36.91,Default,,0000,0000,0000,,little bit different. Instead of boxes and\Nenvelopes, the Internet ships binary information.
Dialogue: 0,0:00:36.91,0:00:41.36,Default,,0000,0000,0000,,Information is made of bits. A bit can be\Ndescribed as any pair of opposites: on or
Dialogue: 0,0:00:41.36,0:00:49.33,Default,,0000,0000,0000,,off, yes or no. We typically use a 1 meaning\Non, or a 0 meaning off. Because a bit has two
Dialogue: 0,0:00:49.33,0:00:56.15,Default,,0000,0000,0000,,possible states we call it binary code. 8\Nbits strung together makes 1 byte. 1000 bytes
Dialogue: 0,0:00:56.15,0:01:01.70,Default,,0000,0000,0000,,all together is a kilobyte. 1000 kilobytes\Nis a megabyte. A song is typically encoded
Dialogue: 0,0:01:01.70,0:01:07.94,Default,,0000,0000,0000,,using about 3-4MB. It doesn't matter if it's\Na picture, a video, or a song, everything
Dialogue: 0,0:01:07.94,0:01:12.86,Default,,0000,0000,0000,,on the Internet is represented and sent around\Nas bits. These are the atoms of information.
Dialogue: 0,0:01:12.86,0:01:16.82,Default,,0000,0000,0000,,But it's not like we're physically sending\N1s and 0s from one place to another or one
Dialogue: 0,0:01:16.82,0:01:22.20,Default,,0000,0000,0000,,person to another. So what is the physical\Nstuff that actually gets sent over the wires
Dialogue: 0,0:01:22.20,0:01:25.92,Default,,0000,0000,0000,,and the airways? Well, let's look at a small\Nexample here of how humans can physically
Dialogue: 0,0:01:25.92,0:01:30.75,Default,,0000,0000,0000,,communicate to send a single bit of information\Nfrom one place to another. Let's say that
Dialogue: 0,0:01:30.75,0:01:36.59,Default,,0000,0000,0000,,we can turn on a light for a 1 or off for\N0. Or use beeps or similar sorts of things
Dialogue: 0,0:01:36.59,0:01:42.00,Default,,0000,0000,0000,,to Morse code. These methods work but they're\Nreally slow, error prone, and totally dependent
Dialogue: 0,0:01:42.00,0:01:46.61,Default,,0000,0000,0000,,upon humans. What we really need is a machine.\NThroughout history, we've built many systems
Dialogue: 0,0:01:46.61,0:01:51.21,Default,,0000,0000,0000,,that can actually send this binary information\Nthrough different types of physical mediums.
Dialogue: 0,0:01:51.21,0:02:00.25,Default,,0000,0000,0000,,Today, we physically send bits by electricity,\Nlight, and radio waves. To send a bit via electricity,
Dialogue: 0,0:02:00.25,0:02:04.80,Default,,0000,0000,0000,,imagine that you have two lightbulbs connected\Nby a copper wire. If one device operator turns
Dialogue: 0,0:02:04.80,0:02:09.28,Default,,0000,0000,0000,,on the electricity then the lightbulb lights\Nup. No electricity, then no light. If the
Dialogue: 0,0:02:09.28,0:02:14.14,Default,,0000,0000,0000,,operators on both ends agree that light on\Nmeans 1 and light off means 0, then we have
Dialogue: 0,0:02:14.14,0:02:19.60,Default,,0000,0000,0000,,a system for sending bits of information from\None person to another using electricity. But
Dialogue: 0,0:02:19.60,0:02:24.100,Default,,0000,0000,0000,,we have kinda a small problem, if you need\Nto send a 0 five times in a row, well how
Dialogue: 0,0:02:24.100,0:02:29.99,Default,,0000,0000,0000,,can you do that in such a way that either\Nperson can actually count the number of 0s?
Dialogue: 0,0:02:29.99,0:02:34.60,Default,,0000,0000,0000,,Well the solution is to introduce a clock\Nor a timer. The operators can agree that the
Dialogue: 0,0:02:34.60,0:02:38.77,Default,,0000,0000,0000,,sender will send 1 bit per second and the\Nreceiver will sit down and record every single
Dialogue: 0,0:02:38.77,0:02:43.98,Default,,0000,0000,0000,,second and see what's on the line. To send\Nfive 0s in a row, you just turn off the light,
Dialogue: 0,0:02:43.98,0:02:48.20,Default,,0000,0000,0000,,wait 5 seconds, the person at the other end\Nof the line will write down all 5 seconds.
Dialogue: 0,0:02:48.20,0:02:53.91,Default,,0000,0000,0000,,For five 1s in a row, switch it on, wait 5 seconds,\Nwrite down every second. Obviously we'd like
Dialogue: 0,0:02:53.91,0:02:57.63,Default,,0000,0000,0000,,to send things a little bit faster than one\Nbit per second, so we need to increase our
Dialogue: 0,0:02:57.63,0:03:04.26,Default,,0000,0000,0000,,bandwidth - the maximum transmission capacity\Nof a device. Bandwidth is measured by bitrate,
Dialogue: 0,0:03:04.26,0:03:08.84,Default,,0000,0000,0000,,which is the number of bits that we can actually\Nsend over a given period of time usually measured
Dialogue: 0,0:03:08.84,0:03:13.98,Default,,0000,0000,0000,,in seconds. A different measure of speed is\Nthe latency, or the amount of time it takes
Dialogue: 0,0:03:13.98,0:03:21.74,Default,,0000,0000,0000,,for one bit to travel from one place to another,\Nfrom the source to the requesting device.
Dialogue: 0,0:03:21.74,0:03:26.56,Default,,0000,0000,0000,,In our human analogy, one bit per second was\Npretty fast but kinda hard for a human to
Dialogue: 0,0:03:26.56,0:03:31.42,Default,,0000,0000,0000,,keep up with. Let's say that you actually\Nwant to download a 3MB song in 3 seconds,
Dialogue: 0,0:03:31.42,0:03:37.08,Default,,0000,0000,0000,,at 8 million bits per megabyte that means\Na bit rate of about 8 million bits per second.
Dialogue: 0,0:03:37.08,0:03:40.95,Default,,0000,0000,0000,,Obviously, humans can't send or receive 8\Nmillion bits per second but a machine could
Dialogue: 0,0:03:40.95,0:03:45.37,Default,,0000,0000,0000,,do that just fine. But now there's also the\Nquestion of what sort of cable to send these
Dialogue: 0,0:03:45.37,0:03:50.06,Default,,0000,0000,0000,,messages over and how far the signals can\Ngo. With an ethernet wire, the kind that you
Dialogue: 0,0:03:50.06,0:03:55.94,Default,,0000,0000,0000,,find in your home, office, or school you see\Nmeasurable signal loss or interference over
Dialogue: 0,0:03:55.94,0:04:01.06,Default,,0000,0000,0000,,just a few hundred feet. For the Internet\Nto work all around the world, we need to have
Dialogue: 0,0:04:01.06,0:04:06.14,Default,,0000,0000,0000,,an alternative method to send bits really\Nlong distances. We're talking like across
Dialogue: 0,0:04:06.14,0:04:11.40,Default,,0000,0000,0000,,oceans. So what else can we use? What do we\Nknow that moves a lot faster than just electricity
Dialogue: 0,0:04:11.40,0:04:17.72,Default,,0000,0000,0000,,through a wire? Light. We can actually send\Nbits as light beams from one place to another
Dialogue: 0,0:04:17.72,0:04:22.55,Default,,0000,0000,0000,,using a fiber optic cable. A fiber optic cable\Nis a thread of glass engineered to reflect
Dialogue: 0,0:04:22.55,0:04:27.09,Default,,0000,0000,0000,,light. When you send a beam of light down\Nthe cable, light bounces up and down the length
Dialogue: 0,0:04:27.09,0:04:31.24,Default,,0000,0000,0000,,of the cable until it is received on the other\Nend. Depending on the bounce angle, we can
Dialogue: 0,0:04:31.24,0:04:36.09,Default,,0000,0000,0000,,actually send multiple bits simultaneously,\Nall of them traveling at the speed of light.
Dialogue: 0,0:04:36.09,0:04:41.03,Default,,0000,0000,0000,,So fiber is really really fast. But more importantly\Nthe signal doesn't really degrade over long
Dialogue: 0,0:04:41.03,0:04:45.48,Default,,0000,0000,0000,,distances. This is how you can go hundreds\Nof miles without signal loss. This is why
Dialogue: 0,0:04:45.48,0:04:50.26,Default,,0000,0000,0000,,we use fiber optic cables across the ocean\Nfloors to connect one continent to another.
Dialogue: 0,0:04:50.26,0:04:56.36,Default,,0000,0000,0000,,In 2008 there was a cable that was actually\Ncut near Alexandria, Egypt which really interrupted
Dialogue: 0,0:04:56.36,0:05:00.55,Default,,0000,0000,0000,,the Internet for most of the Middle East and\NIndia. So we take this Internet thing for
Dialogue: 0,0:05:00.55,0:05:05.21,Default,,0000,0000,0000,,granted but it's really a pretty fragile,\Nphysical system. And fiber is awesome but
Dialogue: 0,0:05:05.21,0:05:09.11,Default,,0000,0000,0000,,it's also really expensive and hard to work\Nwith. For most purposes, you're going to find
Dialogue: 0,0:05:09.11,0:05:16.97,Default,,0000,0000,0000,,copper cable. But how do we move things without\Nwires? How do we send things wirelessly? Radio.
Dialogue: 0,0:05:16.97,0:05:21.13,Default,,0000,0000,0000,,Wireless bit sending machines typically use\Na radio signal to send bits from one place
Dialogue: 0,0:05:21.13,0:05:27.93,Default,,0000,0000,0000,,to another. The machines have to actually\Ntranslate the 1s and 0s into radio waves of
Dialogue: 0,0:05:27.93,0:05:32.37,Default,,0000,0000,0000,,different frequencies. The receiving machines\Nreverse the process and convert it back into
Dialogue: 0,0:05:32.37,0:05:37.52,Default,,0000,0000,0000,,binary on your computer. So wireless has made\Nour Internet mobile. But a radio signal doesn't
Dialogue: 0,0:05:37.52,0:05:41.78,Default,,0000,0000,0000,,travel all that far before it gets completely\Ngarbled. This way you can't really pick up
Dialogue: 0,0:05:41.78,0:05:48.08,Default,,0000,0000,0000,,a Los Angeles radio station in Chicago. As\Ngreat as wireless is, today it still relies
Dialogue: 0,0:05:48.08,0:05:52.19,Default,,0000,0000,0000,,on the wired Internet. If you're in a coffee\Nshop using wifi, then the bits get sent to
Dialogue: 0,0:05:52.19,0:05:56.17,Default,,0000,0000,0000,,this wireless router and then are transferred\Nthrough the physical wire to travel the really
Dialogue: 0,0:05:56.17,0:06:01.05,Default,,0000,0000,0000,,long distances of the Internet. The physical\Nmethod for sending bits may change in the
Dialogue: 0,0:06:01.05,0:06:06.10,Default,,0000,0000,0000,,future, whether its lasers sent between satellites,\Nor radio waves from balloons, or drones, but
Dialogue: 0,0:06:06.10,0:06:10.97,Default,,0000,0000,0000,,the underlying binary representation of information\Nand the protocols for sending that information
Dialogue: 0,0:06:10.97,0:06:15.13,Default,,0000,0000,0000,,and receiving that information have pretty\Nmuch stayed the same. Everything on the Internet,
Dialogue: 0,0:06:15.13,0:06:20.58,Default,,0000,0000,0000,,whether it's words, emails, images, cat videos,\Npuppy videos, all come down to these 1s and
Dialogue: 0,0:06:20.58,0:06:25.85,Default,,0000,0000,0000,,0s being delivered by electronic pulses, light\Nbeams, radio waves, and lots and lots of love.