A Level Computer Science: Communication (Cambridge 9618)

Topic 2 Communication is AS Level content in Cambridge International AS & A Level Computer Science (9618), following Topic 1 Information Representation. The whole topic consists of one dense sub-topic, 2.1 Networks including the internet, which covers everything from how a LAN is physically built to how a URL locates a specific resource on the web. It is examined on Paper 1 alongside the rest of the “Computer systems” content.

Networking devices, LANs and WANs

You need to understand the purpose and benefits of networking devices, and the characteristics that distinguish a LAN (local area network) from a WAN (wide area network) – broadly, geographic scope and who owns the infrastructure.

Network models: client-server, peer-to-peer, thin/thick client

Two network models are examined in detail:

• Client-server: dedicated server computers provide services (file storage, authentication, printing) to client computers on the network.
• Peer-to-peer: computers on the network have equal status, each able to act as both client and server.

For both, you need to know the roles of the different computers involved (including subnetwork models), and the benefits and drawbacks of each, since exam questions typically ask you to justify which model suits a given situation rather than just define the two. A related distinction is thin-client versus thick-client: a thin client relies heavily on a server for processing, while a thick client performs most processing locally.

Network topologies

You need to understand the bus, star, mesh and hybrid topologies, including how packets are transmitted between two hosts for a given topology, and be able to justify the use of a specific topology for a given situation. A star topology, for example, routes all traffic through a central switch, making it easier to isolate a single faulty connection than a bus topology, where all devices share one communication line.

Cloud computing

This covers public and private clouds, and the benefits and drawbacks of cloud computing generally – weighing accessibility and reduced local infrastructure needs against dependence on internet connectivity and third-party data hosting.

Wired and wireless media, and LAN hardware

You need to understand the differences between, and implications of using, wired versus wireless networks, and be able to describe the characteristics of the specific media named in the syllabus: copper cable, fibre-optic cable, radio waves (including WiFi), microwaves and satellites.

The hardware that supports a LAN is also named explicitly: switch, server, network interface card (NIC), wireless network interface card (WNIC), wireless access points (WAP), cables, bridge and repeater. You also need to describe the role and function of a router specifically, since it operates differently from the other named devices (directing traffic between networks rather than within one).

Ethernet and collision handling

You need to show understanding of Ethernet and how collisions between transmissions are detected and avoided, specifically using Carrier Sense Multiple Access / Collision Detection (CSMA/CD) – the mechanism by which a device checks whether the shared medium is free before transmitting, and detects and recovers from a collision if two devices transmit simultaneously.

Bit streaming

This covers the two named methods of bit streaming – real-time and on-demand – and the importance of bit rate and broadband speed to how well bit streaming performs. This content connects back to Topic 1’s coverage of sound sampling: a higher sampling rate and resolution produce better audio quality but require a higher bit rate to stream smoothly.

The internet, IP addressing and DNS

The final block distinguishes the World Wide Web (WWW) (the system of linked documents and resources accessed via HTTP) from the internet (the underlying global network infrastructure the web runs on) – a distinction often confused in casual use but tested precisely here. You also need to know the hardware that supports the internet (modems, the Public Switched Telephone Network (PSTN), dedicated lines, cell phone networks).

IP addressing is covered in detail: the format of an IP address including IPv4 and IPv6, the use of subnetting, how an IP address is associated with a device on a network, the difference between a public and a private IP address (and the security implications of each), and the difference between a static and a dynamic IP address.

Finally, you need to explain how a Uniform Resource Locator (URL) is used to locate a resource on the WWW, and the role of the Domain Name Service (DNS) in translating a human-readable URL into the IP address a network actually uses to route the request.

How to approach it

Because this topic packs a large amount of named terminology into one sub-topic, organise your revision around the same structure used above – devices, models, topologies, media, and internet-specific concepts – rather than trying to hold the whole sub-topic as an undifferentiated list. The “justify the use of X for a given situation” instruction appears repeatedly across models, topologies and cloud computing, so practise writing short justification answers (two or three sentences, weighing a specific benefit against a specific drawback for the scenario given) for each, since this is the exam skill Cambridge is explicitly building toward throughout the sub-topic. Keep the WWW/internet distinction and the static/dynamic and public/private IP address distinctions especially sharp, since these pairs of similar-sounding terms are common sources of confused or reversed answers under exam pressure.

Official syllabus

Cambridge International, Cambridge International AS & A Level Computer Science (9618) syllabus for examination in 2026: official syllabus PDF, Subject content, section 2 “Communication”. Verified 2026-09-02.