Secondary 3 ICT | Networks and Internet Safety: Tutor Lesson Prep Guide | Bandwidth conversion, IP and packets, four common mistakes

2026-11-11

Tutor lesson-prep guides · Secondary ICT

When a student says the internet is slow so they should pay for more, they have usually never separated bandwidth from latency. This lesson locks down the Mbps to MB relationship first, then builds safety judgement on top of numbers students can check.

Objectives — By the end students can: (1) explain the difference between LAN and WAN and work out that 100 Mbps downloads 500 MB in 40 seconds, which is 12.5 MB/s; (2) state that an IP address is four parts totalling 32 bits, that data travels as packets, and that bandwidth and latency are different things; (3) explain that HTTPS only encrypts the connection and a padlock does not make a site trustworthy, and list three protective habits on public Wi-Fi.

01 Prerequisites (3-minute check)

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

Skill	Quick check	Pass mark
Bits and bytes	How many bits are in one byte?	8 bits, so b and B differ by a factor of 8
Division	What is 500 divided by 12.5?	40, because 12.5 times 40 is 500
Shape of an IP address	How many number groups does an IP address have?	Four groups, each from 0 to 255

02 Lesson flow (60 minutes)

Time	Stage	Tutor does	Student does
0-6 min	Diagnose the guess	Write “slow means pay more” and ask which kind of slow they actually meet	Describe one time their connection stalled
6-16 min	Draw LAN and WAN	Draw the home router and the internet, marking the LAN and WAN boundary	Mark which side their phone sits on
16-36 min	Three scripts	Teach LAN and WAN, bandwidth conversion, safety judgement; stop after each for recall	Say back that Mbps is divided by 8 to get MB/s
36-46 min	Four question types	Model download time, unit conversion, IP and packets, safety judgement; one each	Do one of each and explain the steps
46-55 min	Error contrast	Put the four common mistakes on the board and have students correct them	Correct each sentence and give the reason
55-60 min	Exit check	Collect the three answers and judge on the spot	Complete three questions alone

03 Teaching script (read it out)

Scene 1: Script 1: LAN is indoors, WAN is outdoors

“Everything in your home connects to the same router. That is the LAN, the family talking inside the house without stepping out. The router then runs a line to the broadband provider, and that side is the WAN, the internet. So if the question asks whether two phones in the same home need the internet to swap files, the answer is not necessarily: inside one LAN the router passes it directly. Bandwidth is how many bits per second the line carries; latency is how long one packet takes to go and come back.”

Do two devices on the same LAN need the internet to exchange a file?

Scene 2: Script 2: divide Mbps by 8 to get MB/s

“100 Mbps means a hundred million bits every second, not 100 MB. One byte is 8 bits, so divide by 8 and you get 12.5 MB/s. A 500 MB file is 500 divided by 12.5, which is 40 seconds. The usual misconception is dividing 500 by 100 and writing 5 seconds. The units differ, so convert first.”

How many MB per second is 100 Mbps?

Scene 3: Script 3: a padlock encrypts the pipe, not the owner

“HTTPS and the padlock only mean the channel between you and that site is encrypted. They say nothing about who runs the site; phishing pages can have padlocks too. Ask three questions: is the address spelled correctly, is the page demanding a password right now, and is the public Wi-Fi asking you to install a certificate. If any answer feels wrong, stop.”

Does the padlock mean the site is trustworthy, or only that the connection is encrypted?

04 Question types and worked steps

Type	Example	Steps	Answer
Download time	How long does a 500 MB file take on a 100 Mbps line?	(1) 100 Mbps divided by 8 gives 12.5 MB/s. (2) 500 divided by 12.5. (3) Write the unit seconds.	40 seconds
Unit conversion	How many MB per second is a 24 Mbps upload?	(1) Divide Mbps by 8. (2) 24 divided by 8. (3) Write MB/s.	3 MB/s
IP and packets	How many bits are in one IP address?	(1) Four groups. (2) Eight bits each. (3) Multiply.	32 bits
Safety judgement	A padlocked site asks for online banking details immediately. What do you do?	(1) Check the address spelling. (2) Ask whether a password is really needed now. (3) Close the page and use the official app.	Stop, close the page, use the official app or call the bank

Sanity check (teach this): Sanity check: a 24 Mbps line caps at 3 MB/s, so 24 MB/s means the division by 8 was skipped. 500 MB at 12.5 MB/s takes 40 seconds, so 5 seconds means Mbps was never converted. A 1.2 GB upload at 24 Mbps takes 409.6 seconds, about 6.83 minutes, so 6.8 seconds means GB was never converted to MB.

05 Independent practice (3 questions)

Question	Answer	What to watch
How long does 500 MB take on a 100 Mbps line?	40 seconds	Whether 12.5 MB/s appears before dividing
How long does a 1.2 GB upload take at 24 Mbps?	409.6 seconds, about 6.83 minutes	Whether GB was converted to MB and multiplied by 8 first
How strong is an 8-character random password from 62 symbols in bits?	About 47.63 bits	Whether they take log base 2 of 62 to the eighth power

06 Common mistakes and what to say

Mistake	Student writes	Say this
Treating Mbps as MB/s	“500 MB divided by 100 is 5 seconds”	“100 Mbps needs dividing by 8, that is 12.5 MB/s. 500 MB takes 40 seconds.”
Thinking a padlock makes a site trustworthy	“If it has HTTPS it cannot be a fake site”	“The padlock encrypts the pipe. It says nothing about the owner. Check the address spelling yourself.”
Logging into online banking on public Wi-Fi	“The hotel Wi-Fi has a password so it is safe”	“Use a VPN or mobile data on public Wi-Fi, and never log into banking on the spot.”
Adding a digit and calling it strong	“Pa55word is strong enough”	“Length matters most. Eight random characters is about 47.6 bits, and two digits barely move it.”

07 Homework (paper, section and question numbers)

ICT chapter index: revise bandwidth calculations in the Networks chapter — Chapter 05 Networks and the Internet
ICT chapter index: revise bits and bytes in Data Representation — Chapter 02 Data Representation

08 Exit check (last 5 minutes)

Question	Answer	Decision
How long does 500 MB take on 100 Mbps?	40 seconds	Wrong: reteach bandwidth conversion from script 2
Does a padlock mean the site is trustworthy, or only that the connection is encrypted?	Encrypted connection only	Wrong: reteach safety judgement from script 3
How many bits are in one IP address?	32 bits	Wrong: reteach network addressing from script 1

09 Tutor FAQ

Is this guide enough for Secondary 3?

Yes. Secondary 3 network work centres on bandwidth conversion, LAN versus WAN and basic safety awareness, and this lesson covers all three.

How should 60 minutes be split?

About six to seven minutes per script, ten minutes on question types and nine on error contrast. Teach the safety script slowly, because students answer that one by feeling.

Is there practice material?

Yes. The homework row links to the ICT chapter index; choose Networks and the Internet plus Data Representation, which match this lesson.

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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.