What is the internet? — Internet fundamentals (TCP/IP)

More than just websites

The internet is not the web. The web (websites, HTML, browsers) is just one application that runs on top of the internet. The internet is the global network infrastructure that connects billions of devices: and it's the foundation everything else is built on.

As a Rails developer, understanding how the internet works at a fundamental level helps you debug network issues, configure servers, and build applications that work reliably across the globe.

A brief history

The internet wasn't invented in a single moment. It evolved over decades:

Year	Milestone
1969	ARPANET: First message sent from UCLA to the Stanford Research Institute (it crashed after two letters: "LO")
1974	TCP/IP proposed by Vint Cerf and Bob Kahn: the protocols that still power the internet today
1983	ARPANET switches to TCP/IP: the "birthday" of the modern internet
1989	World Wide Web invented by Tim Berners-Lee at CERN
1991	First website goes live
1995	Commercial internet explodes: Amazon, eBay launch
2004	Ruby on Rails released by DHH
Today	~6 billion internet users (ITU, 2025), over a billion websites

The internet is decades older than the web. Email, file transfer (FTP), and remote login existed long before anyone had a browser.

The physical internet

The internet feels magical and invisible, but it's built on very physical things:

Cables

The backbone of the internet is fiber optic cables: thin glass strands that carry data as pulses of light, at about two thirds of light's speed in a vacuum.

flowchart TB
  A["Your computer"] -->|"Ethernet / WiFi"| B["Home router"]
  B -->|"Copper or fiber"| C["ISP local exchange"]
  C -->|"Fiber optic"| D["ISP regional hub"]
  D -->|"Fiber optic backbone"| E["Internet exchange point (IXP)"]
  E -->|"Submarine cables, across oceans"| F["Another country's network"]

There are over 500 submarine cables crossing the oceans right now, some stretching thousands of kilometers across the Atlantic and Pacific. When you visit a website hosted in another country, your data physically travels through these cables.

Data centers

Web applications (including Rails apps) run on servers in data centers: warehouses full of computers with redundant power, cooling, and network connections.

When you deploy a Rails app to a hosting provider, your code runs on a physical server in one of these data centers.

Internet exchange points (IXPs)

IXPs are physical locations where different networks connect to each other. They're like highway interchanges: they allow traffic to flow between networks efficiently without going through unnecessary hops.

How devices connect: ISPs and the network of networks

The internet is not one single network: it's a network of networks. These networks are connected through a hierarchy:

Tier 1: the backbone

A handful of massive networks (like AT&T, NTT, Lumen) that form the internet's backbone. They connect directly to each other through peering agreements: no one pays anyone; they just agree to exchange traffic.

Tier 2: regional networks

Larger ISPs that buy transit from Tier 1 networks and sell to smaller providers and businesses.

Tier 3: local ISPs

Your home internet provider. They buy connectivity from Tier 2 networks and sell it to consumers.

flowchart TB
  subgraph T1["Tier 1 backbone"]
    ATT["AT&T"] <-->|"peering"| NTT["NTT"]
    LUM["Lumen"] <-->|"peering"| TEL["Arelion"]
  end
  T1 --> R1["Tier 2: regional ISP"]
  T1 --> R2["Tier 2: regional ISP"]
  R1 --> Y["Tier 3: your ISP"]
  R2 --> S["Tier 3: their ISP"]
  Y --> PC["Your PC"]
  S --> SRV["Their server"]

When you visit a website, your data may travel through several of these networks to reach its destination.

Packets: how data travels

The internet doesn't send data as a continuous stream. Instead, it breaks data into small packets: like cutting a long letter into numbered postcards.

Original data: "Hello, I am learning Rails and TCP/IP!"

Packet 1: "Hello, I a"     → Sequence #1
Packet 2: "m learning"     → Sequence #2
Packet 3: " Rails and"     → Sequence #3
Packet 4: " TCP/IP!"       → Sequence #4

Each packet contains:

Source address: Where it came from
Destination address: Where it's going
Sequence number: Its position in the original data (TCP adds this)
Payload: The actual data chunk
Checksum: Error detection

Why packets?

Advantage	Explanation
Efficiency	Multiple conversations share the same wires simultaneously
Resilience	If one path is congested, packets can take different routes
Error recovery	If one packet is lost, only that packet needs to be resent
Fairness	No single transfer can monopolize the network

This is called packet switching, and it's the fundamental design choice that makes the internet work. Before the internet, telephone networks used circuit switching: a dedicated line for each call. Packet switching is far more efficient.

Protocols: the rules of communication

For all these devices and networks to communicate, they need agreed-upon rules. These rules are called protocols.

Think of protocols like human communication conventions:

Language: Both parties must speak the same language
Turn-taking: Don't talk over each other
Acknowledgment: Nod or say "uh-huh" to confirm you're listening
Error handling: "Could you repeat that?"

The internet uses a stack of protocols, each handling a different concern:

flowchart TB
  A["Application layer — what to send<br>HTTP, HTTPS, FTP, SMTP, DNS<br>your Rails app lives here"]
  T["Transport layer — how to deliver<br>TCP, UDP<br>reliable or fast delivery"]
  I["Internet layer — where to send<br>IP (IPv4, IPv6)<br>addressing and routing"]
  L["Link layer — the physical medium<br>Ethernet, WiFi<br>the actual wires and signals"]
  A --> T --> I --> L

This is the TCP/IP model: we'll explore each layer in detail throughout this course.

The internet vs. the web vs. other services

The internet is the infrastructure. Many services run on top of it:

Service	Protocol	What It Does
World Wide Web	HTTP/HTTPS	Websites and web apps (Rails!)
Email	SMTP/IMAP/POP3	Sending and receiving email
File Transfer	FTP/SFTP	Uploading/downloading files
DNS	DNS	Translating domain names to IPs
Streaming	RTMP/HLS	Video and audio streaming
Gaming	UDP-based	Real-time game communication
SSH	SSH	Secure remote server access

As a Rails developer, you'll primarily work with HTTP/HTTPS, but you'll also use SSH (to access servers), DNS (to configure domains), and SMTP (to send emails from your app).

Why this matters for Rails development

Every Rails concept is built on internet fundamentals:

Internet Concept	Rails Connection
IP addresses	`request.remote_ip`, server binding
Packets	Every HTTP request/response is broken into packets
TCP connections	Puma manages TCP connections for your app
Ports	Rails dev server runs on port 3000
Protocols	HTTP is the protocol Rails speaks
DNS	Your domain name points to your server's IP

When something goes wrong (a timeout, a connection refused, a DNS error) understanding these fundamentals helps you diagnose the problem instead of guessing.

Summary

Concept	Key Point
The internet	A global network of networks, not the same as the web
Physical infrastructure	Fiber optic cables, data centers, submarine cables
ISP tiers	Backbone (Tier 1) → Regional (Tier 2) → Local (Tier 3)
Packets	Data broken into small numbered chunks for efficient delivery
Packet switching	Multiple conversations share the same wires
Protocols	Agreed-upon rules for communication (TCP/IP stack)
TCP/IP model	Four layers: Link, Internet, Transport, Application
Web vs Internet	The web (HTTP) is just one service running on the internet