Edexcel GCSE Computer Science Topic 4 Networks: LANs and WANs, the internet, wired and wireless, protocols, TCP/IP layers, topologies and network security

What Topic 4 actually demands

Networks is the connectivity topic. You must explain why computers are networked and the LAN versus WAN distinction, how the internet is structured with IP addressing and routers, how wired and wireless connections affect performance (and how to calculate transmission time), the purpose of the named protocols and which TCP/IP layer each belongs to, the three topologies, and how networks are kept secure.

This guide ties together the six dot-point pages for Topic 4.

Networks, the internet and performance

Computers are networked to share resources (hardware, internet connection), share files, communicate and be managed centrally. A LAN covers a small owned site; a WAN covers a large leased area, and the internet is the largest WAN, a global network of networks. Every device has an IP address (a unique identifier), and routers forward packets between networks using those addresses. Wired connections give higher, more consistent bandwidth and lower latency; wireless is convenient but affected by range, interference and walls. Network speed is in bits per second, and transmission time is file size divided by rate.

Protocols and the TCP/IP model

A protocol is a set of rules for communication. Ethernet and Wi-Fi govern wired and wireless LANs; TCP/IP packages, addresses and routes data; HTTP and HTTPS transfer web pages (HTTPS encrypted); FTP transfers files; SMTP sends email while POP3 and IMAP retrieve it. The four-layer TCP/IP model organises this: application (protocols), transport (packets and reliable delivery), internet (addressing and routing) and link (the physical connection).

Topologies and security

Topologies describe how devices are connected: a bus uses one shared cable (cheap but a single point of failure); a star connects all devices to a central switch (reliable per device, easy to extend); a mesh interconnects devices with multiple paths (very resilient, no single point of failure). Network security matters because networks hold valuable data; vulnerabilities are found by penetration testing and ethical hacking, and networks are protected by access control, physical security and firewalls.

Check your knowledge

A mix of recall, calculation and applied questions covering Topic 4. Attempt them, then check against the solutions.

1. State what LAN and WAN stand for. (1 mark)
2. State what an IP address is. (1 mark)
3. State the role of a router. (1 mark)
4. A 24 megabit file is sent at 6 megabits per second. Calculate the transmission time. (2 marks)
5. State which email protocol sends email. (1 mark)
6. State which TCP/IP layer adds IP addresses and routes packets. (1 mark)
7. State one advantage of a mesh topology. (1 mark)
8. State one method of protecting a network from unauthorised access. (1 mark)