Notes

The Internet

3 min read

The Internet

Internet vs World Wide Web

These are not the same thing:

InternetWorld Wide Web
What it isThe physical infrastructure, cables, routers, hardwareA service that runs on top of the internet
How accessedAny networked deviceWeb browser
ContainsAll internet-based services (web, email, FTP, etc.)Web pages and websites only

The internet is the motorway. The World Wide Web is one type of vehicle that travels on it.

How the Internet Is Structured

   Your Device
       │
       ▼
  Home Router ──── connects to ────▶ ISP (Internet Service Provider)
                                           │
                                           ▼
                              DNS Servers + Internet Backbone
                                           │
                          ┌────────────────┼────────────────┐
                          ▼                ▼                ▼
                     Web Servers      Other ISPs        Routers
  • ISP (Internet Service Provider): Your broadband/mobile provider; connects your home network to the internet
  • Internet backbone: High-speed fibre optic cables connecting major network hubs globally
  • Web servers: Computers that host websites and are always available online (hosting)

IP Addresses

An IP address is a unique number that identifies a device on a network.

  • Every device on the internet has an IP address
  • Allows routers to direct data to the correct destination
  • Example (IPv4): 192.168.1.1
  • Example (IPv6): 2001:0db8:85a3:0000:0000:8a2e:0370:7334

Domain Name System (DNS)

Humans remember domain names (e.g., google.com), not IP addresses. The DNS translates between them.

Process:

  1. You type www.example.com in your browser
  2. Your device asks a DNS server: “What is the IP address for www.example.com?”
  3. The DNS server responds: 93.184.216.34
  4. Your browser uses that IP address to contact the web server

Without DNS, every user would need to memorise IP addresses to visit websites.

Packets

Data sent across the internet is broken into packets.

Each packet contains:

  • Header: Source IP address, destination IP address, sequence ID (packet number), error-checking data
  • Payload: A chunk of the actual data being sent

Why Packets?

  • Allows data to travel across multiple routes simultaneously
  • If one route is congested, packets can take a different path
  • Packets may arrive out of order, they are reassembled at the destination using the sequence ID
Message: "Hello World"
  │
  ├── Packet 1: [Header: from A, to B, seq=1] [Data: "Hello"]
  └── Packet 2: [Header: from A, to B, seq=2] [Data: " World"]
  
At destination: reassembled in order → "Hello World"

Web Hosting

  • Websites are stored on web servers
  • Servers are always on and connected so websites are accessible at any time
  • Companies or individuals pay for hosting, renting server space

Exam Questions

Q: What is the difference between the internet and the World Wide Web?

The internet is the global hardware infrastructure (cables, routers) that connects devices worldwide. The World Wide Web is a service that runs on the internet, used to access web pages through a browser.

Q: What is the purpose of a DNS server?

A DNS server converts a domain name (URL) into an IP address so that routers can locate the correct web server.

Q: Explain how packets are used to send data over the internet.

Data is split into packets, each containing header information (sender address, destination address, sequence ID) and a portion of the data. Packets can travel different routes and may arrive out of order, but are reassembled correctly at the destination using the sequence IDs.

Exam Tip

The internet ≠ the World Wide Web. The internet is the infrastructure; the WWW is a service. This distinction is a common exam question.

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