What happens when you open a page

Type an address into your browser and tap Go. About a second later, a page appears. In that second your phone traded messages with computers that may be thousands of kilometers away, and it did so dozens of times.

This lesson walks the whole trip once, quickly. The rest of the course slows down at each stop.

Press Play to follow a page request, or Step to inspect one stage. This is a simplified TCP path; QUIC combines setup differently.

Step 1: get onto the network

Your phone talks over Wi-Fi to a small box in your home, the router. The router connects to your internet provider, the company you pay each month. Your provider connects to other networks, and those connect to others still. "The internet" is the name for all those networks agreeing to carry each other's traffic. Nobody owns it, and no single computer runs it.

Step 2: turn the name into a number

Computers on the internet find each other by numeric address, called an IP address. One looks something like 203.0.113.7. The name you typed, say wikipedia.org, means nothing to the machines that move your data. So your phone first asks the Domain Name System, or DNS, which number goes with that name. Usually the answer is already saved somewhere nearby and comes back in a few milliseconds.

Step 3: open a conversation

Your phone contacts that address and sets up a connection. Then it runs a second setup for encryption, so that nobody between you and the server can read what follows. Each setup is a quick exchange of messages there and back. Every round trip costs time, which is why a faraway server feels slow even on fast Wi-Fi.

Step 4: ask for the page

Now your browser sends the actual request, in the language browsers and web servers share, called HTTP. In older versions of HTTP, the request was plain text you could read:

GET / HTTP/1.1
Host: wikipedia.org

That says "send me the main page of wikipedia.org." Newer versions pack the same information into a more compact form, but the idea hasn't changed.

Step 5: the answer comes back in pieces

The server replies with the page's HTML, broken into small chunks called packets. The HTML lists everything else the page needs, like images, fonts, and scripts. A busy news page can ask for a hundred files or more, often from several different servers. Your browser fetches many at once and draws the page as they land, which is why text often shows up before the pictures.

The big idea

Each step is handled by a separate layer that ignores the others. Wi-Fi doesn't know it's carrying a web page. Routers don't look at what's inside the packets they pass along. Your browser doesn't care whether the packets crossed an ocean. That separation is the internet's best design decision. It's why the same network carries video calls, email, and games, even though it was built for none of them in particular.