OCR J277 · Component 1 · Topic 1.3.1d

Star & Mesh Network Topologies

What Is a Topology? · Star Topology · Mesh Topology · Advantages & Disadvantages · Exam Scenarios

CSZone OCR GCSE Computer Science J277

Learning Objectives

By the end of this video you will be able to...

Explain what a network topology is, and why the choice of topology matters

Describe a star topology: its structure and how it works

Describe a mesh topology: its structure and how it works, including the difference between full and partial mesh

State the advantages and disadvantages of both star and mesh topologies

Apply knowledge of topologies to recommend a suitable topology for a given scenario, justifying your answer

⚡ This is part 4 of 4 covering 1.3.1 — Networks and topologies.

Network Topology

How devices are arranged and connected

DEFINITION

A network topology describes the arrangement of devices (nodes) and the connections between them in a network — both the physical layout and how data flows.

The choice of topology affects performance, cost, reliability and ease of management. Different topologies suit different scenarios and network sizes.

The two topologies required for OCR J277 are star and mesh. You need to be able to recognise each from a diagram, describe it, and compare advantages and disadvantages.

⚡ "Topology" simply means "shape" or "arrangement." Star and mesh describe the shape of how the network is wired up.

Star Topology

All devices connect to a central switch or hub

STAR TOPOLOGY

In a star topology, every device connects individually to a central switch (or hub). Data travels from a device to the switch, which then forwards it to the intended recipient.

Because each device has its own dedicated cable to the central switch, devices do not share cables with each other — they communicate independently.

⚡ The switch is the heart of a star network. All communication passes through it.

Star Topology

Advantages & Disadvantages

✓

Easy to add new devices — a new device is simply connected to the central switch with a cable. The rest of the network is not disrupted.

✓

Fault isolation — if one device or its cable fails, only that device is affected. The rest of the network continues to work normally.

✓

Good performance — devices do not share cables, so there is less collision of data and the network can handle traffic efficiently.

✗

Single point of failure — if the central switch fails, the entire network goes down, as all devices depend on it.

✗

Cable cost — each device needs its own dedicated cable to the switch, which can be expensive in a large network.

⚡ The key disadvantage examiners look for: the central switch is a single point of failure — if it breaks, the whole network stops working.

Mesh Topology

Devices connect directly to each other

MESH TOPOLOGY

In a mesh topology, devices connect directly to each other. In a full mesh, every device is connected to every other device. In a partial mesh, only some devices are directly connected.

Data can travel along multiple different paths between devices. If one connection fails, data is automatically rerouted along an alternative path, keeping the network running.

⚡ The key strength of a mesh: no single point of failure. Multiple paths mean the network is highly resilient.

Mesh Topology

Advantages & Disadvantages

✓

Highly reliable / no single point of failure — if one connection or device fails, data is rerouted via an alternative path. The network keeps working.

✓

Multiple paths — data can travel via the most efficient route, which can improve speed and reduce bottlenecks.

✓

Scalable — adding new devices simply requires connecting them to one or more existing nodes; no central point needs to change.

✗

Expensive and complex to install — in a full mesh, every device needs a connection to every other device. The number of cables required grows rapidly as more devices are added.

✗

Difficult to manage — with many interconnections, troubleshooting and maintaining the network becomes more complex.

⚡ Key advantage: highly resilient with no single point of failure. Key disadvantage: expensive due to the large number of cables needed.

Star vs Mesh

Comparing the two topologies

	Star	Mesh
Single point of failure?	Yes — the switch	No

Cable cost

Moderate — one cable per device

High — every device to every device

Reliability

Good — isolated faults

Excellent — multiple paths

⚡ Exam tip: the star's main weakness is the switch as a single point of failure. The mesh's main weakness is cost and complexity. Use these to justify your recommendation in a scenario question.

Applying to a Scenario

Choosing the right topology

SCENARIO A

"A school wants to network 30 computers in a computer room. Cost is a concern, but it must be easy to add new computers and faults must be easy to isolate."

Recommendation: Star. It's cost-effective (only one cable per device), easy to expand (just connect new devices to the switch), and faults on individual devices are isolated — they don't affect others.

SCENARIO B

"A hospital's network must remain operational at all times. No single failure can be allowed to bring the whole network down."

⚡ Recommendation: Mesh. There is no single point of failure — if one connection breaks, data is rerouted via another path, keeping the network running. The higher cost is justified by the critical nature of the network.

Decision Guide

When to choose star vs mesh

CHOOSE STAR WHEN...

Cost is a concern and a simpler setup is preferred

Ease of adding devices matters more than resilience

Network downtime from a switch failure is acceptable

CHOOSE MESH WHEN...

Reliability is critical and downtime cannot be tolerated

The network needs to handle failure without disruption

Budget is available to cover the higher cabling cost

⚡ Always justify your choice: link the topology feature to the requirement stated in the scenario. E.g. "I would recommend a mesh topology because there is no single point of failure, which means the network will continue to work even if one connection breaks."

Putting It Together

Star & Mesh — the big picture

STAR

All devices → central switch. Easy to add devices. Single point of failure = switch.

STAR ADV / DIS

✓ Fault isolation, easy to expand, good performance.
✗ Switch = single point of failure. Cabling cost.

MESH

Every device → every other device (full). Multiple paths. No single point of failure.

MESH ADV / DIS

✓ Highly reliable, multiple paths, no single point of failure.
✗ Expensive, complex to install and manage.

⚡ Always link your topology choice to the scenario: cost, reliability, and ease of management are the three key factors to weigh up.

Exam Practice

Exam-Style Questions — Topologies

Question 1 · 2 marks

State one advantage and one disadvantage of a star topology.

2 marks

ANS

Advantage: If one device fails, it does not affect the rest of the network (fault isolation) / easy to add new devices.
Disadvantage: If the central switch fails, the entire network stops working (single point of failure) / requires a dedicated cable for each device.

Question 2 · 2 marks

Explain why a mesh topology is more reliable than a star topology.

2 marks

ANS

In a mesh topology, there are multiple paths between devices, so if one connection fails, data can be rerouted via an alternative path. In a star topology, all data passes through the central switch, so if it fails the entire network goes down.

Question 3 · 3 marks

A business has offices across several sites that must stay connected at all times. Recommend and justify a suitable network topology for this business.

3 marks

Common Mistakes

Four mistakes that cost marks in the exam

1

Saying a star topology has "no" single point of failure. It does — the central switch. If the switch fails, all devices lose their connection. This is the most common topology mistake in the exam.

2

Confusing "fault isolation" with "no single point of failure." In a star, an individual device failure is isolated (other devices keep working). But that doesn't mean there's no single point of failure — the switch itself still is one.

3

Describing mesh as "every device connected to one central device." That's a star, not a mesh. In a mesh, devices connect directly to each other, not to a single central node.

4

Recommending a topology without justifying it with the scenario. Always link your choice to a specific feature of the scenario — e.g. "reliability is critical, so I'd choose mesh because there is no single point of failure."

Summary

1.3.1d — Star & Mesh Topologies

STAR

Central switch. One cable per device. Easy to expand. Switch = single point of failure.

STAR: USE WHEN

Cost matters, network is straightforward, brief downtime is acceptable.

MESH

Device-to-device connections. Multiple paths. No single point of failure. More expensive.

MESH: USE WHEN

Reliability is critical, network cannot go down, budget available for cabling.

⚡ Exam tip: always justify your topology choice by linking a topology feature to the scenario's specific requirement.

CSZone.co.uk

That's 1.3.1 complete!

Next up: 1.3.2a — Wired & Wireless Networks

Full quiz, marked worksheet and slides at CSZone.co.uk