DSE ICT — Network Topologies and Transmission Media Guide for Tutors: Star versus Mesh, Media Choice and Transfer Time

2026-11-05

Tutor lesson-prep guides · Secondary ICT

Students can say that a star network is easier to manage, then go blank when asked how many cables 8 nodes need or how long 250 MB takes. This lesson turns topology and media into two formulas they can calculate with.

Objectives — Students can: (1) compare star and mesh for 8 nodes, stating cable counts (8 and 28) and the effect of a single link failure; (2) compare twisted pair, fibre and Wi-Fi on speed, distance and interference, with one campus scenario each; (3) compute 250 MB at 100 Mbps as 20 seconds and explain why the real time is longer.

01 Prerequisites (3-minute check)

If any of these fails, fix it before the lesson starts.

Skill	Quick check	Pass mark
Unit conversion	How many bits are in a byte?	Eight; one megabyte is eight megabits.
Network terms	What is the difference between bandwidth and latency?	Bandwidth is bits per second; latency is the delay before the first bit arrives.
Decimal prefixes	Is the M in 100 Mbps a power of two?	No, network bandwidth uses powers of ten.

02 Lesson flow (45 minutes)

Time	Stage	Tutor does	Student does
0-5 min	Prior knowledge check	Ask about bits and bytes, bandwidth and latency, the prefix M	Answer aloud; note errors
5-17 min	Act 1: topology is cost versus risk	Draw 8 nodes as star and mesh and count links live	Copy and count independently
17-32 min	Act 2: three media, three columns	Compare speed, distance and interference with campus examples	Fill the table and justify a choice
32-42 min	Act 3: bandwidth arithmetic	Model 250 MB at 100 Mbps and at 1 Gbps	Compute once and check units
42-45 min	Mixed practice	Hand out three items mixing topology, media and arithmetic	Write the formula, substitution and unit
45-45 min	Exit check	Ask the three exit questions and record answers	Answer aloud; misses become next lesson starters

03 Teaching script (read it out)

Scene 1: Act 1: topology is a trade between cost and risk

Draw 8 nodes. In a star, every node connects to a central switch, so links equal nodes: 8. In a mesh, every pair connects, so n(n-1)/2 gives 8 times 7 divided by two, which is 28.
Then ask about risk: a failed central switch stops the whole star network, while one failed mesh link leaves the rest working and affects only 25 percent of links. So the answer is always it depends on cost and reliability, never mesh is simply better.
Common misconception box: students assume every mesh node has a backup route; only a full mesh does.

Ask students to repeat: star links equal nodes, mesh links are n times n minus one over two.

Scene 2: Act 2: media are compared on three columns

Only three columns matter: speed, distance and interference. Twisted pair is cheap, limited to about 100 metres and picks up electromagnetic interference. Fibre is fast, runs for kilometres and ignores electromagnetic interference, but costs more and breaks easily. Wi-Fi is convenient, blocked by walls and shares bandwidth.
Campus cases: staff-room desktops use twisted pair, links between buildings use fibre, and a temporary hall connection uses Wi-Fi.
Common misconception box: students think Wi-Fi is always slower. Close up and alone it can be fast; the problem is sharing and interference.

Ask students to repeat: a media answer needs speed, distance and interference together.

Scene 3: Act 3: transfer time is one formula

Time equals data in bits divided by bandwidth in bits per second. 250 MB is 2000 megabits, which takes 20 seconds at 100 Mbps and 2 seconds at 1 Gbps.
At 60 percent utilisation the effective bandwidth falls to 60 Mbps and the time rises to 33.3 seconds before latency and retransmission are counted.
Common misconception box: dividing megabytes by megabits gives 2.5, which is eight times too small because the units never matched.

Ask students to repeat: convert megabytes to megabits before dividing.

04 Question types and worked steps

Type	Example	Steps	Answer
Link count	How many links does a full mesh of 8 nodes need?	Use n(n-1)/2, substitute, state links	28 links
Failure analysis	The central switch in a star network fails	Identify the scope, state the outage, suggest a spare	The whole network drops; a standby switch is needed
Media choice	Two buildings 800 metres apart	Compare with the 100-metre limit, choose fibre, cite interference	Fibre, because of distance and interference
Transfer time	250 MB at 100 Mbps	Multiply by eight, divide, state seconds	20 seconds

Sanity check (teach this): Sanity checks: a mesh always needs more links than a star (28 against 8), so a smaller number means the formula is wrong; transfer time must include the factor of eight, or the answer is eight times too small; a faster link must give a shorter time (2 seconds against 20), so a longer time means the divisor is wrong; a media answer without a reason earns little credit.

05 Independent practice (3 questions)

Question	Answer	What to watch
How many links do a star and a mesh of 8 nodes need, and what is the ratio?	8 and 28, a ratio of 3.5	Whether the formula, not counting, was used
Transfer time for 250 MB at 1 Gbps.	2 seconds	Whether the factor of eight appears
Choose a medium for two buildings 1.2 kilometres apart and give two reasons.	Fibre: beyond the 100-metre limit and immune to electromagnetic interference	Whether two reasons are given

06 Common mistakes and what to say

Mistake	Student writes	Say this
Dividing megabytes by megabits	250 divided by 100 gives 2.5 seconds.	Megabytes must become megabits first; without the factor of eight the answer is eight times too small.
Squaring the node count	8 squared gives 64 links.	Mesh links are n times n minus one over two; squaring double counts.
Assuming mesh always has redundancy	Every mesh node has two routes.	Only a full mesh gives complete redundancy; partial mesh nodes can hang on one link.
Choosing media only on speed	Fibre is fastest, so use fibre.	The reason fibre wins here is the 100-metre limit and interference, not raw speed.

07 Homework (paper, section and question numbers)

Redo this chapter — Redo the three items with formula, substitution and unit
ICT chapter index — Open the IP addressing chapter and compute subnets and usable hosts once
Formula card — Write the mesh link, transfer time and usable host formulas with one example each

08 Exit check (last 5 minutes)

Question	Answer	Decision
Link formulas for star and mesh	n for star (8), n(n-1)/2 for mesh (28)	If not, reteach Act 1
Time for 250 MB at 100 Mbps	20 seconds	If 2.5, reteach Act 3
Medium for a one-kilometre link and why	Fibre, beyond the 100-metre limit and immune to interference	If Wi-Fi, reteach Act 2

09 Tutor FAQ

Must the link formula be memorised?

Mesh n(n-1)/2 is examined often and star equals the node count; both are worth memorising.

Do wireless answers need interference?

Yes; naming interference and shared bandwidth earns credit.

Why is real time longer than theory?

Latency, retransmission and other users share the link, so the theoretical value is a lower bound.

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A TutorZone lesson-prep guide. Written by the TutorZone team; questions and lesson flow are original and are not taken from any school or publisher material.