The Internet: HTTP and HTML
I'm Jasmine and I'm a program manager on the XBOX One engineering
team. One of our biggest features is called XBOX Live. It's an online service that connects
gamers from all around the world, and we rely on the internet to make that happen. This
is no easy task and there are a lot of things happening behind the scenes. The internet
is totally changing how people interact and connect. But how does it work? How do the
computers all across the world actually communicate with each other? Let's look at web browsing.
First, you open a web browser. It's the app you use to access the web pages. Next, you
type in the web address, or URL, which stands for Uniform Resource Locator of the website
you want to visit like tumblr.com. Hi, I'm David Karp, the founder of Tumblr and we're
here today to talk about how those web browsers we use everyday actually work. So you've probably
wondered what actually happens when you type an address into your web browser and then
hit enter. And it really is about as crazy as you can imagine. So in that moment your
computer starts talking to another computer, called a server, that's usually thousands
of miles away. And in milliseconds your computer asks that server for a website, and that server
starts to talk back to your computer in a language called HTTP. HTTP stands for HyperText
Transfer Protocol. You can kind of think of it as the language that one computer uses
to ask another computer for a document. And it's actually really pretty straightforward.
If you were to intercept the conversation between your computer and a web server on
the internet, it's mainly made up of something called "GET" requests. Those are really very
simply the word GET and the name of the document that you're requesting. So if you try to log
into Tumblr and load our login page, all you're doing is sending a GET request to Tumblr's
server that says GET /login. And that tells Tumblr's server that you want all of the HTML
code for the Tumblr login page. So HTML stands for Hyper Text Markup Language and you can
think of that as the language you use to tell a web browser how to make a page look. If
you think about something like Wikipedia, which is really just a big simple document
and HTML is the language that you use to make that title big and bold, to make the font
the right font, to link certain text to certain other pages, to make some text bold, to make some
text italic, to put an image in the middle of the page, to align the image to the right,
to align the image to the left. The text of a web page is included directly in the HTML,
but other parts like images or videos are separate files with their own URLs that need
to be requested. The browser sends separate HTTP requests for each of these and displays
them as they arrive. If a web page has a lot of different images, each of them causes a
separate HTTP request and the page loads slower. Now sometimes when you browse the web, you're
not just requesting pages with GET requests. Sometimes you send information like when you
fill out a form or type a search query. Your browser sends this information in plain text
to the web server using an HTTP POST request. Let's say you log in to Tumblr. Well the first
thing you do is you make a POST request, that is a POST to Tumblr's login page that has
some data attached to it. It has your email address, it has your password. That goes to
Tumblr's server. Tumblr's server figures out that okay, you're David. It sends a web page
back to your browser that says, Success! Logged in as David. But along with that web page,
it also attaches a little bit of invisible cookie data that your browser sees and knows to save.
And it's really important because it's really the only way that a website can remember who
you are. All that cookie data really is, is an ID card for Tumblr. It's a number that
identifies you as David. And your web browser holds on to that number and the next time
you refresh Tumblr, the next time you go to Tumblr.com, your web browser knows to automatically
attach that ID number with the request that it sends over to Tumblr's servers. So now
Tumblr's servers sees the request coming from your browser, sees the ID number, and knows
"Ok, this is a request from David." Now, the internet is completely open. All
of its connections are shared and information is sent in plain text. This makes it possible
for hackers to snoop on any personal information that you send over the internet. But safe
websites prevent this, by asking your web browser to communicate on a secure channel
using something called Secure Sockets Layer and its successor Transport Layer Security.
You can think of SSL and TLS as a layer of security wrapped around your communications
to protect them from snooping or tampering. SSL and TLS are active when you see the little
lock that appears in your browser address bar, next to the HTTPS. The HTTPS protocols
ensure that your HTTP requests are secure and protected. When a website asks your browser
to engage in a secure connection, it first provides a digital certificate. Which is like
an official ID card proving that it's the website it claims to be. Digital certificates
are published by certificate authorities, which are trusted entities that verify the
identities of websites and issue certificates for them. Just like a government can issue
IDs or passports. Now if a website tries to start a secure connection without a properly
issued digital certificate, your browser will warn you. That's the basics of web browsing!
The part of the internet we see day to day. To summarize, HTTP and DNS manage the sending
and receiving of HTML, media files, or anything on the web. What makes this possible under
the hood are TCP/IP and router networks that break down and transport information in small
packets. Those packets themselves are made up of binary, sequences of 1s and 0s that
are physically sent through electric wires, fiber optic cables, and wireless networks.
Fortunately, once you've learned how one layer of the internet works, you can rely on it
without remembering all the details. And we can trust that all those layers will work
together to successively deliver information at scale and with reliability.