Communication and the internet: Edexcel IGCSE Computer Science Complete Notes

Networks and the internet form the connective tissue of modern computing. Whether you are sending an email from London to Lagos, streaming a lesson from Berlin, or syncing files between devices in Tokyo, the same underlying principles govern how data travels. The edexcel igcse computer science communication and the internet section covers all of them.

This section contains three topics: networks, network security, and the internet and the world wide web. The communication and the internet edexcel igcse content is tested with notable regularity across both papers. These edexcel igcse computer science revision notes for the 4CP0 course cover each objective with the international perspective that this inherently global subject demands.

Networks

Why computers are networked

Computers are connected in networks to share resources (printers, internet connections, storage), communicate (email, messaging, video calls), and centralise data management (backups, user access control). A school that networks its computers can share a single internet connection among hundreds of devices, store student work on a central server, and manage software updates from one location.

Types of network

Network type	Coverage	Example
PAN (Personal Area Network)	Within a few metres of one person	Bluetooth connection between a phone and wireless earbuds
LAN (Local Area Network)	A single building or campus	A school's internal network connecting classrooms and offices
WAN (Wide Area Network)	Across cities, countries or continents	The internet itself is the largest WAN

Network models

Client-server: A central server provides services (file storage, email, web hosting) to client devices. The server manages access, security and backups centrally. Most school and business networks use this model.
Peer-to-peer: Every device on the network has equal status. Each computer can share files and resources directly with any other. Simpler to set up for small networks, but harder to manage and secure at scale.

Wired and wireless connectivity

Wired connections (Ethernet cables) offer higher speeds and greater reliability with less interference. Wireless connections (Wi-Fi, Bluetooth) offer mobility and convenience but are susceptible to interference, signal degradation over distance, and security risks such as eavesdropping.

Network data speeds are measured in bits per second. Typical units include Mbps (megabits per second) and Gbps (gigabits per second). Note the lowercase 'b' for bits, distinguishing from bytes (uppercase B).

Network protocols

A protocol is an agreed set of rules governing how data is transmitted across a network. The igcse 4cp0 communication and the internet specification requires knowledge of several:

Protocol	Purpose
Ethernet	Standard for wired LAN connections
Wi-Fi	Standard for wireless LAN connections
TCP/IP	Suite of protocols that governs how data is addressed, packaged, transmitted and received across the internet
HTTP	Transfers web pages from server to browser (not encrypted)
HTTPS	Encrypted version of HTTP; protects data in transit
FTP	Transfers files between computers on a network
POP3	Downloads emails from a mail server to a single device (removes from server)
IMAP	Synchronises emails across multiple devices (keeps on server)
SMTP	Sends outgoing emails from client to server or between servers

Packet switching and the TCP/IP model

Data transmitted across a network is broken into packets. Each packet contains a portion of the data, plus a header with the source address, destination address, and sequence number. Packets may take different routes through the network and arrive out of order. The receiving device reassembles them in the correct sequence using the packet numbers.

The TCP/IP model organises network communication into four layers:

Application layer: Protocols that interact with the user (HTTP, FTP, SMTP, IMAP)
Transport layer: Manages end-to-end communication and ensures packets arrive correctly (TCP)
Network layer: Handles addressing and routing of packets across networks (IP)
Data link layer: Manages the physical transmission of data on the local network (Ethernet, Wi-Fi)

The layered approach matters. Each layer handles a specific aspect of communication and only interacts with the layers directly above and below it. This means you can change the technology at one layer (for example, switching from Ethernet to Wi-Fi at the data link layer) without affecting the layers above it. The exam may ask you to explain the benefit of this layered structure.

Network topologies

Topology	How it works	Key advantage	Key disadvantage
Bus	All devices share a single central cable (backbone)	Cheap and simple to set up	If the backbone fails, the entire network goes down
Ring	Each device connects to two others, forming a closed loop	Data flows in one direction, reducing collisions	A break in the ring disrupts the whole network
Star	All devices connect to a central switch or hub	One device failure does not affect others	If the central switch fails, all connections are lost
Mesh	Every device connects to every other device	Highly fault-tolerant; many alternative routes	Expensive due to the number of connections required

Mobile communication standards

The specification covers 3G, 4G and subsequent generations of mobile network standards. Each generation offers increased data speeds and bandwidth compared to its predecessor. 3G enabled mobile web browsing; 4G enabled streaming video; 5G and beyond support even higher speeds and lower latency, enabling applications such as real-time remote control and the Internet of Things.

Network security

Network security protects systems, data and users from unauthorised access, damage and theft. The edexcel igcse computer science explained content divides this into threats, vulnerabilities and defences.

Cyber attacks

Phishing: Fraudulent messages (often emails) designed to trick the recipient into revealing personal information or clicking malicious links.
Shoulder surfing: Physically observing someone entering sensitive information (passwords, PINs).
Pharming: Redirecting a legitimate website's traffic to a fake site, often by corrupting DNS records.
Unpatched software: Exploiting known vulnerabilities in software that has not been updated.
USB devices: Introducing malware through infected removable storage.
Eavesdropping: Intercepting data as it travels across a network, particularly on unencrypted wireless connections.

Identifying vulnerabilities

Penetration testing: Authorised attempts to break into a system to identify weaknesses before attackers do.
Ethical hacking: Similar to penetration testing but broader in scope; ethical hackers simulate a range of attack methods.
Commercial analysis tools: Software that scans networks and systems for known vulnerabilities automatically.
Review of network and user policies: Examining who has access to what, and whether policies enforce strong passwords, regular updates and appropriate access levels.

Defences

Access control: Restricting who can access which resources through user accounts, passwords and permission levels.
Physical security: Locks, biometric scanners, CCTV and secure server rooms.
Firewalls: Software or hardware that monitors and filters network traffic, blocking unauthorised connections.
Encryption: Encoding data so that intercepted information is unreadable without the decryption key.
Secure coding practices: Writing software that validates inputs, handles errors gracefully, and does not expose vulnerabilities.
Audit trails: Logs that record who accessed what, and when, enabling investigation after an incident.

The internet and the world wide web

The internet vs the world wide web

These are not the same thing. The internet is a global network of interconnected computer networks. The world wide web (WWW) is a collection of web pages and resources accessed via the internet using HTTP/HTTPS. The web runs on the internet, but the internet also supports email, FTP, streaming and many other services.

IP addressing

Every device on the internet has a unique IP address. Two standards exist:

IPv4: Uses 32-bit addresses, written as four groups of numbers separated by dots (e.g., 192.168.1.1). Supports approximately 4.3 billion unique addresses, which is no longer sufficient given the number of connected devices worldwide.
IPv6: Uses 128-bit addresses, written as eight groups of hexadecimal values separated by colons (e.g., 2001:0db8:85a3:0000:0000:8a2e:0370:7334). Supports a vastly larger address space.

DNS (Domain Name Service)

DNS translates human-readable domain names (www.example.com) into IP addresses that computers can use. Without DNS, you would need to memorise numerical addresses for every website you visit.

Components for internet access

Component	Function
Modem	Converts digital data to analogue signals (and vice versa) for transmission over telephone lines
Router	Directs data packets between networks, choosing the best route
Switch	Connects devices within a LAN, forwarding data only to the intended recipient device
Wireless Access Point (WAP)	Allows wireless devices to connect to a wired network

In a typical home setup, these components are often combined into a single device (a wireless router that includes a modem, switch and WAP), but the exam expects you to describe each function separately.

Common mistakes in this section

Confusing the internet and the WWW. The internet is the physical infrastructure (cables, routers, servers). The WWW is a service that runs on it. Email is another service on the internet but is not part of the WWW.
Mixing up POP3 and IMAP. POP3 downloads emails and typically removes them from the server. IMAP keeps emails on the server and synchronises across devices. If the question mentions accessing email from multiple devices, the answer is IMAP.
Describing topologies without naming the disadvantage. Every topology has trade-offs. A full answer names both the advantage and the limitation.
Forgetting that HTTPS is encrypted. HTTP transmits data in plaintext. HTTPS encrypts it using TLS/SSL. The exam rewards this distinction.

Self-check questions

Work through these edexcel igcse computer science practice questions using your edexcel igcse computer science notes as a reference only after attempting each one.

Explain the difference between a LAN and a WAN. Give one example of each.
Describe how data is transmitted across the internet using packet switching. Include the role of packet headers and reassembly.
A company has 200 employees working in a single office building. Recommend a network topology and justify your choice.
Explain two methods an organisation can use to protect its network from cyber attacks.
Describe the role of DNS in accessing a website. What would happen if DNS were unavailable?

Networks connect the world. The questions in this section test whether you understand not just what each component does in isolation, but how they work together to move data reliably and securely from one point to another. Precision in terminology and awareness of the broader context are what separate strong answers from adequate ones.