June 17, 2026 • Internet

What is the Internet?

Introduction

In a very brief and summarized way, the Internet is a group of computers and other devices (cell phones, smart devices, self-driving cars, etc.) connected to each other. They are capable of exchanging information, generally using a communication protocol. There are several types of protocols that we will see later.

Why was the Internet created?

The Internet began to be developed during the Cold War in the 1960s. The US, fearing some kind of attack that could leave them without communication (such as a Nuclear War), decided to invest in the ARPA (Advanced Research Projects Agency) initiative.

Soon after, it became DARPA (Defense Advanced Research Projects Agency) and gave rise to ARPANET. This network is considered the embryonic version of the Internet we have today, allowing communication between universities, research centers, and government agencies.

The Project’s Founders

Below are some names of the founders of this great project, along with some references for you to dive deeper:

  • J.C.R. Licklider: The man who had the great idea to create a global network of computers.
  • Robert Taylor: Led the ARPANET project within ARPA.
  • Larry Roberts: The project’s principal architect.
  • Paul Baran: Developed the fundamental concepts of distributed networks and packet switching.
  • Leonard Kleinrock: Led the team that sent the first ARPANET message in 1969.

Given this proper introduction, we can say that today the Internet is in almost every part of the globe, playing a fundamental role in various aspects of our lives:

  • In the way we communicate;
  • In the way we study and stay updated;
  • In shopping, at work, and in our homes.

All of this is done through computers, cell phones, and smart devices.

Main Internet Protocols

Now let’s learn a little more about how all of this works (of course, just a brief introduction, otherwise this would turn into a book!).

As I said earlier, the Internet is a conglomerate of computers and devices connected through protocols and technologies. Below is a list of the most well-known ones:

  • IP (Internet Protocol): Protocol responsible for identifying and locating devices on a network.
  • TCP (Transmission Control Protocol) e UDP (User Datagram Protocol): Transport protocols responsible for taking data from one application to another across the network. Briefly, TCP could be compared to a registered letter with delivery confirmation (prioritizes reliability), while UDP would be the guy who is tired of handing out flyers on the street and decides to just throw the remaining flyers in the air at the end of the day (prioritize speed).
  • HTTP (Hypertext Transfer Protocol): Application layer protocol used for transferring data on the web, such as pages and APIs.
  • HTTPS (Hypertext Transfer Protocol Secure): Protocol used for secure (encrypted) communication between browsers and web servers, using a process called the TLS Handshake.
  • FTP (File Transfer Protocol): Protocol responsible for transferring files between computers. Detail: this protocol does not contain encryption, making it unsafe to use today.
  • SFTP (SSH File Transfer Protocol): Protocol responsible for the secure transfer of files between computers.
  • SMTP (Simple Mail Transfer Protocol): Protocol used to send emails.
  • POP3 (Post Office Protocol version 3): Protocol used to download and, optionally, remove emails from the server.
  • IMAP (Internet Message Access Protocol): Protocol used to manage and synchronize emails on the server.
  • DNS (Domain Name System): Responsible for converting domain addresses (like URLs) into IP addresses.
  • TLS (Transport Layer Security): It is the modern security protocol on the Internet. SSL (Security Socket Layer) is its predecessor and is considered obsolete today.

What happens under the hood when you type a URL in your browser?

🌐 Step-by-step process

1) Browser interprets the URL The browser breaks the URL into parts:

It understands: “I need to access a web server securely”

2) Cache check (fast) Before hitting any network, the browser checks:

  • DNS Cache
  • Page Cache
  • TLS Connection Cache

If everything is recent, it can skip parts.

3) DNS Resolution (discovering the IP) The browser needs to find out: What is the IP of www.example.com? It does this using the Domain Name System. Typical flow:

  1. Checks local cache
  2. Asks the router/ISP’s DNS
  3. If it doesn’t know, queries global DNS servers

It receives something like: 93.184.216.34. Now it knows where the server is.

4) Connection to the server (TCP) The browser opens a connection with the server IP. It uses the Transmission Control Protocol (TCP). Here happens the famous 🔁 Three-way handshake:

  • SYN → “can we talk?”
  • SYN-ACK → “yes, we can”
  • ACK → “ok, let’s talk”

Now there is a reliable connection.

5) Security (TLS handshake - HTTPS) Since it is HTTPS (Transport Layer Security), the browser and the server:

  • negotiate encryption
  • validate digital certificate
  • create secure keys

👉 From here on, everything is encrypted

6) HTTP Request Now the browser sends something like this (Hypertext Transfer Protocol):

GET / HTTP/1.1
Host: www.example.com
User-Agent: Chrome

7) Server processing The server receives the request and:

  • identifies the / route
  • fetches data (database, APIs, files)
  • builds the HTML page
  • prepares the response

8) HTTP Response is sent back The server responds:

HTTP/1.1 200 OK
Content-Type: text/html

And sends the page’s HTML.

9) Browser receives and processes HTML Now the browser:

  • reads the HTML
  • identifies CSS
  • identifies JavaScript
  • builds the DOM (page structure)

10) Additional downloads (parallel) The browser realizes it needs images, CSS, JS, fonts. It opens new HTTP/HTTPS requests for each resource.

11) Page rendering Finally:

  • CSS styles
  • JS executes
  • layout is calculated
  • pixels are drawn on the screen

👉 The page appears to the user

🧠 One-line summary URL → DNS → TCP → TLS → HTTP → server processes → HTTP response → browser renders

Sequence Diagram (The Complete Flow)

sequenceDiagram
    autonumber
    actor U as User
    participant B as Browser
    participant C as Local Cache
    participant D as DNS
    participant S as Web Server<br/>(93.184.216.34)
    
    U->>B: Types the URL<br/>(https://www.example.com/)
    
    Note over B: 1) Interprets the URL<br/>(HTTPS, Domain, Path)
    
    B->>C: 2) Checks Cache (DNS, Page, TLS)
    C-->>B: No valid cache (Example)
    
    B->>D: 3) DNS Resolution: IP for www.example.com?
    D-->>B: IP: 93.184.216.34
    
    Note over B,S: 4) TCP Connection (Three-way handshake)
    B->>S: SYN ("can we talk?")
    S-->>B: SYN-ACK ("yes, we can")
    B->>S: ACK ("ok, let's talk")
    
    Note over B,S: 5) Security (TLS Handshake)
    B->>S: ClientHello (negotiates encryption)
    S-->>B: ServerHello & Digital Certificate
    B->>S: Finalizes TLS (Everything encrypted)
    
    Note over B,S: 6) HTTP Request
    B->>S: GET / HTTP/1.1 (Host: www.example.com)
    Note over S: 7) Server Processing<br/>(Routing, Data, HTML)
    
    Note over B,S: 8) HTTP Response
    S-->>B: HTTP/1.1 200 OK (Content-Type: text/html)
    
    Note over B: 9) Processes HTML & Builds DOM
    B->>S: 10) Additional Downloads (CSS, JS, Images)
    S-->>B: Returns Resources (In parallel)
    Note over B: 11) Page Rendering<br/>(Styles, executes JS, draws screen)
    B-->>U: Page appears to the user!
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