Networks and topologies
CIE A-Level Computer ScienceΒ· 15 min read
1. Core Definitions and Network Classificationβ β ββββ± 5 min
Computer Network
A collection of two or more independent computing devices connected via communication links, enabling resource sharing (data, printers, internet access) and communication between users.
Networks are classified by their geographic scope, a common topic for short answer and multiple choice CIE exam questions.
PAN (Personal Area Network): Covers up to 10 meters, used for connecting personal devices e.g. Bluetooth headphones to a mobile phone.
LAN (Local Area Network): Covers a single site (e.g. school, office building), typically owned and managed by one organisation.
MAN (Metropolitan Area Network): Covers a city or large university campus, larger than a LAN but smaller than a WAN.
WAN (Wide Area Network): Covers large geographic areas spanning multiple countries/continents; the internet is the world's largest WAN.
A university has 5 connected buildings on a single campus within the same city. What network classification best describes this setup?
- 1
Step 1: Check the geographic span of the network: The campus is within one city, larger than a single building LAN but smaller than a cross-country WAN.
- 2
Step 2: Match to the correct classification: This fits the definition of a MAN (Metropolitan Area Network). If the campus was very small it could be classified as a LAN, but MAN is the best fit for a multi-building city campus.
2. Physical vs Logical Topologyβ β ββββ± 4 min
Network Topology
Describes the structure of a network, split into two distinct categories: physical topology is the actual physical arrangement of nodes and cables. Logical topology describes the path that data takes through the network between nodes, regardless of physical layout.
Example:
A physical star topology can sometimes behave as a logical bus topology.
CIE exams regularly ask to distinguish between physical and logical topology, so this distinction is critical for full marks.
Distinguish between physical and logical topology in one clear sentence.
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Step 1: Highlight the key difference, rather than just defining each term (required for 'distinguish' command term):
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Physical topology describes the physical layout of cables and nodes in a network, while logical topology describes the path data travels between nodes.
3. Common Topologies: Advantages and Disadvantagesβ β β βββ± 6 min
The most common topologies tested in CIE 9618 are bus, star, full/partial mesh, ring, and tree. The table below summarises their core properties, which you will need to recall for exam questions.
Topology | Key Description | Main Advantages | Main Disadvantages |
|---|---|---|---|
Bus | All nodes connected to a single backbone cable | Low cable cost, simple to install | Backbone failure takes entire network down; hard to troubleshoot |
Star | All nodes connected to a central switch/hub | Easy to add new nodes, simple fault isolation | Central switch failure takes entire network down; higher cable cost |
Full Mesh | Every node connected directly to every other node | Maximum redundancy, very high reliability | Very high installation/cable cost, complex to manage |
Partial Mesh | Some nodes connected to multiple other nodes (not all) | Balances redundancy and cost | More complex than star, may still have single points of failure |
Ring | Nodes connected in a closed loop, data passes around the ring | Low cable cost, no data collisions | One node/cable failure breaks the entire network |
A bank wants a high-reliability network for its 10 central server nodes. Recommend a suitable topology and justify your answer.
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Step 1: Align requirements to topology properties: The bank needs maximum reliability, so redundancy is a key priority.
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Step 2: Eliminate unsuitable options: Bus, star and ring all have single points of failure that would take the network down.
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Step 3: Select and justify: A full mesh topology is the best choice. Every server is connected to every other server, so there is no single point of failure, meeting the bank's high reliability requirement.
4. Exam Question Techniqueβ β β βββ± 3 min
Test your understanding of core concepts:
Which of the following is a correct definition of logical topology?
The physical arrangement of cables
The path data takes between nodes
The number of nodes in the network
The type of network cable used
Reveal answer
The path data takes between nodes βCorrect! Logical topology describes how data flows, not physical arrangement.
What classification is a network connecting bank offices in New York, London and Singapore?
LAN
MAN
WAN
PAN
Reveal answer
WAN βCorrect! The network spans multiple countries, so it is a WAN.
5. Common Pitfalls
Wrong move:
Confusing physical and logical topology, mixing up their definitions
Why:
This is the most common mistake on distinction questions, leading to lost marks
Correct move:
Remember: Physical = physical layout of cables, Logical = logical flow of data through the network
Wrong move:
Claiming all mesh topology has no single point of failure
Why:
Only full mesh has no single point of failure; partial mesh can still fail if a key node/cable fails
Correct move:
Always explicitly specify full vs partial mesh when answering questions about redundancy
Wrong move:
Stating star topology is cheaper than bus topology for the same number of nodes
Why:
Star requires more cable and a central switch/hub, so it is more expensive than bus
Correct move:
Correctly state that bus has lower installation cost, while star is easier to maintain and troubleshoot
Wrong move:
Classifying a multi-building school campus as a WAN
Why:
WAN is classified by large geographic distance, not number of buildings. A single-site campus is never a WAN
Correct move:
Classify based on geographic span: WAN only applies to networks spanning multiple cities/countries
6. Quick Reference Cheatsheet
Category | Name | Key Property | Main Advantage | Main Disadvantage |
|---|---|---|---|---|
Network Type | PAN | <10m | Personal use | Low range |
Network Type | LAN | <1km (single site) | High speed, low cost | Limited geographic size |
Network Type | MAN | 1-100km (city) | Covers urban areas | Higher cost than LAN |
Network Type | WAN |
| Global connectivity | Lower speed, higher cost |
Topology | Bus | Single backbone cable | Low cost | Backbone failure = full outage |
Topology | Star | All nodes connected to central switch | Easy troubleshooting | Central switch failure = full outage |
Topology | Full Mesh | All nodes connected to each other | Maximum reliability | Very high cost |
Topology | Ring | Nodes in closed loop | Low cable cost | One failure = full outage |
When this came up on past exams
AI-estimated based on syllabus patterns β cross-check with official past papers for accuracy. Use only as revision-focus signals.
- 2022 Β· 12
Compare star vs bus topologies
- 2023 Β· 11
Classify network by geographic scope
- 2024 Β· 12
State advantages of mesh topology
Going deeper
What's Next
This sub-topic is the foundation for all further network topics in CIE 9618 Unit 2. Understanding topologies helps you learn about network hardware like routers and switches, network security, the TCP/IP stack, and client-server vs peer-to-peer networks. You will apply topology concepts when answering network design questions, a common long answer question in Paper 1. Mastering the advantages and disadvantages of each topology prepares you for both multiple choice and extended response questions across all network units.