Computer networks and how the internet works

Aysel types a website address into her browser and presses Enter, and in less than a second a page arrives from a server that may be in another country. In that short moment her request passes through dozens of devices, the address is turned into numbers, and the page travels back in pieces. Let's follow that journey step by step.

What is a computer network?

The internet is the largest wide area network, joining millions of networks around the world — a “network of networks”. Your home network is connected to the internet by a router. Routers pass data from one network to another and choose a good path for it. Most things on the internet follow the client–server model: your browser (the client) sends a request, and the computer that hosts the website (the server) sends back a response.

IP addresses and packets

Every device on a network has an IP address — like a postal address, it tells where data should be delivered. In the widely used IPv4 format an address is four numbers separated by dots, for example 192.168.1.10. Each number is one byte, so it ranges from 0 to 255, and the whole address is 32 bits.

A large file or page does not travel across the network in one piece: it is split into small parts called packets. Each packet carries the IP addresses of the sender and the receiver. Packets may take different routes, and at the destination the TCP protocol puts them back in the right order and asks again for any lost ones.

DNS: the internet's phone book

People remember names better than numbers, so websites have domain names like www.example.com. DNS (the Domain Name System) turns a name into an IP address: your computer asks a DNS server “what is the address for this name?” and gets an IP address in reply. The rightmost part of the name is the top-level domain: .com, .org, or country domains such as .az (Azerbaijan), .tr (Türkiye) and .ru (Russia).

HTTP and HTTPS: how a browser talks to a server

A protocol is a set of agreed rules that lets devices understand each other. Web pages are delivered with the HTTP protocol: the browser sends the server a request (for example, GET /index.html), and the server returns the page together with a status code. HTTPS is the secure version of the same protocol: the data is encrypted, so nobody along the way can read or change it.

Now let's put all the pieces together. Here is what happens when a website opens:

1. 1
   You enter the address

   Aysel types https://www.example.com into the browser.

2. 2
   DNS lookup

   The computer asks a DNS server for the IP address of www.example.com.

3. 3
   Connection

   The browser opens a TCP connection to the server at that IP address; with HTTPS, encryption keys are then agreed on.

4. 4
   HTTP request

   The browser asks for the page with a GET request.

5. 5
   Response

   The server sends back the code 200 OK and the page's HTML in packets.

6. 6
   Building the page

   The browser reads the HTML, loads the images and style files in the same way and shows the page on the screen.

const url = new URL('https://www.example.com/lessons/informatics?lang=az');
console.log(url.protocol);
console.log(url.hostname);
console.log(url.pathname);
console.log(url.searchParams.get('lang'));

https:
www.example.com
/lessons/informatics
az