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How do networks connect computers, and what roles do topologies, protocols and the internet play in moving data?

Describe networks and topologies, transmission media and methods, protocols and the TCP/IP stack, and how the internet works.

A focused answer to WJEC A-Level Computer Science Unit 1 communication, covering LANs and WANs, network topologies, transmission methods, protocols and the TCP/IP stack, packet switching, and how the internet works.

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  1. What this dot point is asking
  2. The answer
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What this dot point is asking

WJEC wants you to describe networks (LAN and WAN), the common topologies, transmission media and methods, the role of protocols and the TCP/IP stack, packet switching, and how the internet works. Networking links the hardware of Unit 1 to the security topic that follows and to the deeper transmission content of Units 3 and 4. Expect questions on packet switching, on LAN versus WAN, and on the purpose of protocols.

The answer

Networks: LAN and WAN

The distinction is mostly about geographic scale and who owns the infrastructure: a LAN's cabling belongs to the organisation, while a WAN typically leases long-distance links from providers.

Topologies and transmission

A star topology is robust (one failed cable affects only one device) and is the common choice for modern LANs, whereas a mesh gives resilience through redundant paths, which is why the internet's core is mesh-like.

Packet switching

In packet switching, a message is divided into packets, each carrying the destination address and a sequence number. Packets travel independently, possibly by different routes, and are reassembled in order at the destination. This uses shared links efficiently and is resilient: if a route fails, packets take another.

Protocols and the internet

Examples in context

Example 1. Why a star LAN suits a school
A school wires every room to a central switch. If one classroom's cable fails, only that room loses connection, and faults are easy to isolate. This robustness and ease of maintenance is why the star topology dominates real LANs, whereas a single bus cable would take the whole network down if it broke.
Example 2. Packet switching keeps a video call going
During a video call, packets are sent continuously and routed independently. If one link gets congested or fails, packets reroute and the call continues, perhaps with a brief glitch. A circuit-switched call would drop entirely if its reserved path failed, which shows the resilience advantage of packet switching.
Example 3. IP and TCP doing different jobs
Downloading a file, IP gets each packet to the right machine by address, while TCP checks every packet arrived and reorders them, requesting resends for any lost. The file arrives intact because the two protocols split the work: addressing and routing versus reliable, ordered delivery, a division examiners expect you to explain.

Try this

Q1. State what a network topology describes. [1 mark]

  • Cue. How the devices on a network are arranged or connected.

Q2. State the purpose of the sequence number added to each packet in packet switching. [1 mark]

  • Cue. So the packets can be reassembled into the correct order at the destination.

Exam-style practice questions

Practice questions written in the style of WJEC exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

WJEC 20194 marksExplain what is meant by packet switching and give one advantage of it over circuit switching.
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Describe how packet switching moves data, then give a genuine advantage.

In packet switching, a message is split into small packets, each labelled with its destination address and sequence number. The packets travel independently across the network, possibly by different routes, and are reassembled in order at the destination.

Advantage over circuit switching: the network is used more efficiently because no single dedicated path is reserved for the whole conversation. Many communications share the same links, and if a route fails, packets can be sent by an alternative route, giving resilience.

Markers reward splitting into addressed packets, independent routing and reassembly, and a valid advantage such as efficient shared use of links or resilience to a failed route.

WJEC 20214 marksDescribe the difference between a local area network (LAN) and a wide area network (WAN), and give one example of each.
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Contrast the geographic scale and ownership, then give an example of each.

A LAN connects computers over a small geographic area, such as a single building or site, and is usually owned and managed by one organisation using its own cabling or wireless. Example: a school or office network.

A WAN connects computers over a large geographic area, such as between cities or countries, typically using infrastructure leased from telecommunications providers. Example: the internet, or a bank's network linking branches nationwide.

Markers reward the small-area versus large-area distinction, the ownership difference, and a valid example of each.

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