Cambridge Syllabus Notes

4. Networks and the Effects of Using Them

Objective

Know and understand the differences and similarities between an extranet, intranet and the Internet, and be able to describe the key network devices, topologies, IP concepts, wireless technologies, cloud services, network types, performance metrics, security issues and electronic‑conferencing tools required by the Cambridge IGCSE ICT (0417) syllabus.

Key Definitions

Internet – The worldwide public network that interconnects millions of private, academic, business and government networks. It uses the TCP/IP protocol suite and is accessible to anyone with an appropriate connection.
Intranet – A private network that uses the same protocols as the Internet (TCP/IP, HTTP/HTTPS, DNS) but is restricted to members of an organisation. It supports internal communication, document sharing and business applications.
Extranet – A controlled extension of an intranet that gives selected external users (partners, suppliers, customers) limited access to specific resources. Access is secured by VPNs, firewalls and strong authentication.

Network Devices

These are the building blocks of any LAN, WLAN or WAN.

Network Interface Card (NIC) – Provides the physical link between a computer and a network (wired or wireless).
Hub – Layer 1 device that repeats incoming signals to all ports; creates a single collision domain.
Switch – Layer 2 device that forwards frames only to the destination port; each port has its own collision domain.
Bridge – Layer 2 device that connects two LAN segments and filters traffic by MAC address.
Router – Layer 3 device that forwards packets between different networks (e.g., LAN ↔ WAN) and performs IP addressing and routing.
Firewall – Can be hardware, software or a combination; inspects traffic and applies rules (packet‑filtering, stateful inspection, DMZ creation) to protect the internal network from unauthorised access.

Typical LAN layout showing NICs, hub, switch, router and firewall — Typical LAN layout – NICs connect to a switch, which links to a router and a firewall.

Network Topologies

Understanding the physical layout helps to predict performance and fault tolerance.

Star – All devices connect to a central switch or hub; easy to manage, a single cable failure isolates only one device.
Bus – All devices share a single backbone cable; simple but a break in the backbone disables the whole network.
Mesh – Devices are interconnected with multiple paths; high reliability but expensive and complex.

Simple star, bus and mesh topologies — Star, bus and mesh LAN topologies.

Basic IP Addressing

IP addresses are written as four octets (e.g., 192.168.12.45).
Public IP – Unique on the Internet; assigned by an ISP.
Private IP – Used inside organisations; not routable on the public Internet. Common ranges: 10.0.0.0 – 10.255.255.255, 172.16.0.0 – 172.31.255.255, 192.168.0.0 – 192.168.255.255.
Subnet mask (e.g., 255.255.255.0) determines which part of the address identifies the network and which part identifies the host.

Core Network Services

DNS (Domain Name System) – Translates human‑readable domain names (e.g., www.bbc.co.uk) into IP addresses.
DHCP (Dynamic Host Configuration Protocol) – Automatically assigns IP addresses, subnet masks, gateways and DNS servers to devices on a network.
File/Print Services – Centralised servers that store files and manage printers for LAN users.

Wireless Technologies

Wi‑Fi (WLAN) – Based on IEEE 802.11 standards (a/b/g/n/ac/ax). Used in schools, homes and cafés.
Security: WPA2‑Personal (PSK) for small networks; WPA2‑Enterprise (or WPA3‑Enterprise) with 802.1X authentication for larger organisations.
Bluetooth – IEEE 802.15.1, short‑range (≤10 m) for peripherals (headsets, keyboards, mice). Security relies on pairing codes and device authentication.

Cloud Computing

Services delivered over the Internet, accessed through a web browser or thin client.

Cloud Storage – Files are stored on remote servers (e.g., Google Drive, OneDrive, Dropbox). Users upload, download and share documents.
Software‑as‑a‑Service (SaaS) – Complete applications run on the provider’s servers (e.g., Google Workspace, Microsoft 365, Salesforce). Users interact via a browser; no local installation required.
Advantages – Low upfront hardware cost, easy scalability, access from any device with Internet.
Disadvantages – Dependence on Internet connectivity, ongoing subscription fees, data‑security and data‑sovereignty concerns (organisation must know where the data is physically stored).

Network Types

Network Type	Typical Scale	Common Uses	Examples
Local Area Network (LAN)
LAN	Single building or campus	File sharing, printers, internal web sites	School computer lab, office floor
Wireless LAN (WLAN)
WLAN	Same as LAN but uses Wi‑Fi	Mobile device access, flexible seating	School Wi‑Fi, coffee‑shop hotspot
Wide Area Network (WAN)
WAN	Geographically dispersed sites	Connect multiple branches, remote access	Company offices in different cities, Internet
LAN‑WAN Link
LAN‑WAN link	LAN connected to a WAN via a router	Enable Internet access, inter‑site communication	School LAN ↔ ISP router ↔ Internet

Network Performance Metrics

Bandwidth – Maximum amount of data that can be transferred per second (measured in Mbps or Gbps).
Latency – Time taken for a packet to travel from source to destination (measured in milliseconds).
Jitter – Variation in latency; important for real‑time applications such as video conferencing.

Security Considerations

Security measures differ for Internet, Intranet and Extranet, but the underlying principles are the same.

Authentication – Strong, unique passwords; two‑factor authentication (2FA); for Wi‑Fi, WPA2‑Enterprise/802.1X.
Encryption – SSL/TLS (HTTPS) for web traffic; VPNs for remote or extranet connections; WPA2/WPA3 for wireless.
Anti‑malware – Reputable antivirus/anti‑spyware on all devices; keep signatures up to date.
Firewalls – Hardware firewalls at network edges; host‑based firewalls on individual computers; can create a DMZ for public services.
VPN (Virtual Private Network) – Creates an encrypted tunnel for remote users or extranet partners.
e‑Safety – Awareness of phishing, social engineering, safe browsing habits and reporting suspicious activity.

Good‑Practice Checklist (Student Level)

Use a password manager to generate and store complex passwords.
Enable automatic updates for the operating system and applications.
Connect to Wi‑Fi only if it uses WPA2‑Personal, WPA2‑Enterprise or WPA3.
Never share login details with anyone outside the authorised group.
Log out of cloud services when finished, especially on shared computers.
Report any suspicious email or link to a teacher/IT staff immediately.

Electronic Conferencing

Video conferencing – Real‑time two‑way video and audio (e.g., Zoom, Microsoft Teams). Requires webcam, microphone and stable Internet.
Audio conferencing – Voice‑only calls, often via telephone or VoIP (e.g., Skype, Google Meet audio‑only).
Web‑conferencing – Shared screen, whiteboard, chat and file sharing within a browser (e.g., Google Meet, Cisco Webex).
Classroom example – A virtual lesson where the teacher shares a PowerPoint, students ask questions via chat, and the session is recorded for later review.

Comparison of Internet, Intranet and Extranet

Feature	Internet	Intranet	Extranet
Scope of users	Public – anyone worldwide	Private – employees and authorised internal staff	Restricted – internal staff plus selected external parties (partners, suppliers, customers)
Access control	None at network level – security is site‑specific (HTTPS, firewalls on individual servers)	Strong – firewalls, authentication, internal security policies	Strong – VPN, firewalls, user‑level permissions, often a separate DMZ zone
Typical uses	Web browsing, email, social media, cloud services, public information	Internal portals, HR systems, file servers, internal email, intranet news	Supplier portals, customer support sites, joint project workspaces, B2B applications
Network infrastructure	Public service providers, backbone routers, DNS root servers	Organisation’s LAN/WAN, internal routers, private DNS, dedicated firewall	Organisation’s LAN/WAN plus secure gateway (VPN concentrator, DMZ, external firewalls)
Security concerns	High – exposure to malware, phishing, DDoS attacks	Medium – insider threats, accidental data loss, internal malware spread	Medium‑high – must protect internal data while allowing external access; risk of mis‑configured permissions
Cost of implementation	Low for end‑user (subscription); high for ISPs and backbone providers	Moderate – hardware, software licences, maintenance, staff training	Higher – additional security devices, VPN licences, monitoring tools, higher maintenance overhead

Similarities

All rely on the same core protocols (TCP/IP, HTTP/HTTPS, DNS).
Data is transmitted in packets through routers and switches.
Encryption (SSL/TLS) can be applied to any of them.
Each can host web‑based applications and services.

Advantages and Disadvantages

Network Type	Advantages	Disadvantages
Internet	Universal access Vast amount of information and services Low cost for end users	High security risk (malware, phishing, DDoS) Uncontrolled content Potential bandwidth congestion
Intranet	Secure environment for sensitive data Improved internal communication and collaboration Customised applications for the organisation	Limited to internal users only Requires ongoing maintenance and IT support Risk of information silos if not integrated with other systems
Extranet	Facilitates collaboration with external partners Reduces need for physical meetings and travel Can improve supply‑chain and customer‑service efficiency	Complex security management Higher implementation and maintenance cost Risk of data leakage if permissions are mis‑configured

Key Points to Remember

Internet, intranet and extranet all use the same core technologies but differ in scope, access control and security requirements.
An intranet is completely internal; an extranet is a controlled bridge between internal and selected external users.
Effective use of an extranet requires robust authentication, encryption (VPN/SSL) and regular monitoring.
Choosing the right network type depends on the organisation’s need for openness versus control, cost considerations and security policies.

Venn diagram showing overlap of users and services among Internet, Intranet and Extranet — Venn diagram illustrating the shared and unique users/services of the Internet, Intranet and Extranet, with arrows indicating data flow and security boundaries.

Know and understand the differences and similarities between an extranet, intranet and the internet