Networks

Computer networks enable communication between devices. A-Level covers the principles of how data is transmitted, routed, and secured across local and wide-area networks, as well as the protocols and models that govern these processes.

Topics Covered

Network Fundamentals

• LAN, WAN, WLAN — classification by geography and technology
• Client-server vs. peer-to-peer — architecture models and their trade-offs
• Topologies — star, bus, ring, mesh, hybrid; advantages and disadvantages of each
• Transmission media — copper (twisted pair, coaxial), fibre optic, wireless; bandwidth and latency trade-offs

The OSI and TCP/IP Models

• OSI 7-layer model — Physical, Data Link, Network, Transport, Session, Presentation, Application
• TCP/IP 4-layer model — Link, Internet, Transport, Application
• Protocol mapping — where HTTP, TCP, IP, Ethernet sit in each model
• Encapsulation — how data is wrapped with headers at each layer

Protocols

• TCP — reliable, connection-oriented; three-way handshake, flow control
• UDP — unreliable, connectionless; when speed matters more than reliability
• IP addressing — IPv4 (dotted decimal), subnet masks, CIDR notation
• HTTP/HTTPS — request-response model, status codes, TLS encryption
• DNS — domain name resolution, hierarchical lookup
• DHCP — automatic IP address assignment

Network Security

• Firewalls — packet filtering, stateful inspection
• Encryption — symmetric vs. asymmetric; TLS/SSL handshake
• Authentication — passwords, biometrics, multi-factor authentication
• Malware and attacks — viruses, worms, trojans, phishing, DDoS, SQL injection

Web Technologies

• HTML, CSS, JavaScript — structure, presentation, behaviour
• Client-side vs. server-side processing — where computation happens and why

Study Tips

1. Draw the OSI and TCP/IP models side by side — memorise which protocols operate at which layer.
2. Trace a packet from application layer through to physical — describe what headers are added at each layer (encapsulation).
3. Compare TCP and UDP with specific use cases — e.g., TCP for web browsing, UDP for video streaming.
4. Practise IP subnetting — calculating network address, broadcast address, and host range from an IP and subnet mask.
5. Link security concepts to real-world scenarios — exam questions often describe a situation and ask which protection to apply.

How to Use These Notes

Start with network fundamentals and the OSI model, then move to protocols and security. Each page provides definitions, diagrams, worked examples, and exam-style problems.