Internet
Summary: A global network of interconnected computers and networks that communicate using standardised protocols (TCP/IP). Provides the infrastructure for services like the World Wide Web, email, VoIP, and file transfer. Data travels in packets via packet switching across routers worldwide. Tags: igcse computer-science Created: 2026-05-08T14:03:00Z Last Updated: 2026-07-16
What is the Internet?
The Internet is a global system of interconnected computer networks — a “network of networks.” It links billions of devices worldwide using the TCP/IP protocol suite, a standard set of communication rules that allows different types of computers and networks to exchange data.
The Internet is not owned or controlled by any single organisation. It is a distributed network maintained through cooperation between Internet Service Providers (ISPs), network operators, and standards bodies (such as the IETF and ICANN).
Internet vs World Wide Web
A critical distinction for IGCSE:
| Internet | World Wide Web (WWW) | |
|---|---|---|
| What it is | The physical/electronic infrastructure — cables, routers, switches, satellites, and the TCP/IP protocols | A service that runs on top of the Internet |
| Analogy | The road network (roads, traffic lights, road rules) | The delivery trucks that drive on the roads |
| Created | 1960s (ARPANET) | 1989 (Tim Berners-Lee at CERN) |
| Uses | Many services: WWW, email (SMTP), file transfer (FTP), VoIP, online gaming, streaming | One specific service: accessing hyperlinked web pages via HTTP/HTTPS |
The Internet existed for ~20 years before the World Wide Web was invented. You can use the Internet without using the Web (e.g., sending email via SMTP, or using a messaging app that does not use HTTP).
How Data Travels: Packets
Data sent over the Internet is broken into small chunks called packets. Each packet is typically 64—1500 bytes.
Packet Structure
Every packet contains two main parts:
| Part | Contents |
|---|---|
| Header | Source IP address, destination IP address, sequence number (packet order), protocol, time-to-live (TTL) |
| Payload | A portion of the actual data being transmitted |
Why Packets?
- Efficiency: If one packet is corrupted or lost, only that packet needs to be resent — not the entire file
- Sharing: Packets from many different users and applications can share the same network lines
- Resilience: Packets can take different routes if one path is congested or broken
Packet Switching
Packet switching is the method by which data travels across the Internet:
- The sending computer breaks the data into packets
- Each packet is sent to a router (the first “hop”)
- The router reads the destination IP address from the header and decides which neighbouring router to forward the packet to
- Each packet travels independently — different packets may take different routes
- At the destination, packets are reassembled into the original order using the sequence numbers
Advantages of Packet Switching
- No dedicated connection: Unlike circuit switching (traditional phone calls), packet switching does not require a dedicated physical path
- Robust: If one route fails, packets can be rerouted dynamically
- Efficient use of bandwidth: The network carries packets from many sources simultaneously
Disadvantages
- Packets may arrive out of order (must be reassembled)
- Latency (delay) can vary — problematic for real-time applications like VoIP and gaming
- Packets can be lost and must be retransmitted
Key Internet Protocols (TCP/IP Stack)
| Layer | Protocol | Purpose |
|---|---|---|
| Application | HTTP, HTTPS, FTP, SMTP, DNS | Services that applications use |
| Transport | TCP, UDP | End-to-end communication, error checking (TCP), or speed (UDP) |
| Internet | IP (IPv4, IPv6) | Addressing and routing packets across networks |
| Network Access | Ethernet, Wi-Fi, fibre | Physical transmission of bits |
TCP (Transmission Control Protocol): Ensures reliable delivery — packets are acknowledged, lost packets are retransmitted, and data arrives in order. Used for web pages, email, file downloads.
UDP (User Datagram Protocol): No guarantee of delivery or ordering. Faster but less reliable. Used for streaming, VoIP, online gaming where speed matters more than perfect accuracy.
Sources
- BBC Bitesize GCSE Computer Science — Internet and Networking, BBC (free educational resource)
- Cambridge IGCSE Computer Science 0478 — The Internet and Its Uses, Cambridge Assessment International Education
- CK-12 Computer Science — Networking, CK-12 Foundation (free, CC BY-NC 3.0)
Related Notes
- World Wide Web — The web of hyperlinked pages built on top of the Internet
- HTTP — Protocol for transferring web pages
- HTTPS — Secure, encrypted version of HTTP
- DNS — Translates domain names to IP addresses
- IP Address — Numerical label that identifies each device on the Internet
- Data Packet — Structure and contents of a network packet in detail
- Packet Switching — How packets are routed across the Internet
- URL — Uniform Resource Locator for web addresses
- Web Browser — Software used to access the World Wide Web
- CS-Index
Common Misconceptions
| Misconception | Reality |
|---|---|
| ”The Internet and the World Wide Web are the same thing” | The Internet is the infrastructure; the Web is a service on top of it. Email, VoIP, and online gaming use the Internet but are not part of the Web. |
| ”The Internet is stored somewhere — like a big server” | The Internet is a network of networks, not a central repository. It has no single physical location. |
| ”Packets from the same message all take the same route” | Each packet is routed independently. Different packets of the same message can (and often do) take entirely different physical paths. |
| ”The Internet was invented by one person” | It evolved from multiple projects (ARPANET, packet switching research). Many people contributed. Tim Berners-Lee invented the World Wide Web, not the Internet. |
| ”Wi-Fi is the Internet” | Wi-Fi is a wireless local network technology. It connects devices to a router, which may (or may not) be connected to the Internet. |