# Networks and topologies

> CIE A-Level Computer Science · 9618
> Source: https://www.owlsprep.com/study/cie-9618-u2-networks-and-topologies/

This module introduces core computer network concepts, classification by geographic scope, and common physical/logical network topologies. You will learn to compare properties of each topology for CIE exam questions.

**Prerequisites:** Basic understanding of computing hardware and communication devices

## Learning objectives

- Define a computer network and classify networks by geographic scope
- Distinguish between physical and logical network topologies
- Describe core features, advantages and disadvantages of common topologies
- Answer exam questions requiring recommendation and justification of network choice

## Core Definitions and Network Classification

**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.

**Worked example:** 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.

## Physical vs Logical Topology

**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.

**Worked example:** Distinguish between physical and logical topology in one clear sentence.

1. Step 1: Highlight the key difference, rather than just defining each term (required for 'distinguish' command term):
2. Physical topology describes the physical layout of cables and nodes in a network, while logical topology describes the path data travels between nodes.

## Common Topologies: Advantages and Disadvantages

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 |

**Worked example:** A bank wants a high-reliability network for its 10 central server nodes. Recommend a suitable topology and justify your answer.

1. Step 1: Align requirements to topology properties: The bank needs maximum reliability, so redundancy is a key priority.
2. Step 2: Eliminate unsuitable options: Bus, star and ring all have single points of failure that would take the network down.
3. 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.

## Exam Question Technique

**Exam command terms**

CIE uses common command terms for this topic, with specific marking expectations:

- **Distinguish** — Explicitly state the difference between two concepts, do not just define each *(Distinguish physical vs logical topology requires you to highlight how they differ)*

- **Compare** — State at least one similarity and two differences between the two topics *(Compare star and bus topology requires coverage of both similarities and differences for full marks)*

- **Justify** — Link your choice of topology/network to the specific requirements given in the scenario *(You must reference the scenario's needs (e.g. high reliability, low cost) to earn justification marks)*

**Check your understanding**

Test your understanding of core concepts:

1. 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

   *Why:* Correct! Logical topology describes how data flows, not physical arrangement.

2. What classification is a network connecting bank offices in New York, London and Singapore?

   - LAN
   - MAN
   - WAN
   - PAN

   *Why:* Correct! The network spans multiple countries, so it is a WAN.

## Common pitfalls

- **Wrong:** Confusing physical and logical topology, mixing up their definitions
  - Why it fails: This is the most common mistake on distinction questions, leading to lost marks
  - Correct: Remember: Physical = physical layout of cables, Logical = logical flow of data through the network
- **Wrong:** Claiming all mesh topology has no single point of failure
  - Why it fails: Only full mesh has no single point of failure; partial mesh can still fail if a key node/cable fails
  - Correct: Always explicitly specify full vs partial mesh when answering questions about redundancy
- **Wrong:** Stating star topology is cheaper than bus topology for the same number of nodes
  - Why it fails: Star requires more cable and a central switch/hub, so it is more expensive than bus
  - Correct: Correctly state that bus has lower installation cost, while star is easier to maintain and troubleshoot
- **Wrong:** Classifying a multi-building school campus as a WAN
  - Why it fails: WAN is classified by large geographic distance, not number of buildings. A single-site campus is never a WAN
  - Correct: Classify based on geographic span: WAN only applies to networks spanning multiple cities/countries

## 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 | >100km (multiple sites) | 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 |

## 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.

- [Protocols](https://www.owlsprep.com/study/cie-9618-u2-protocols/)
- [Wireless networking](https://www.owlsprep.com/study/cie-9618-u2-wireless-networking/)
- [Internet technologies](https://www.owlsprep.com/study/cie-9618-u2-internet-technologies/)

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