Buying something online uses everything at once: your browser encrypts the data (HTTPS), it is split into packets, the packets cross Wi-Fi and then cables, routers pass them on by different routes, TCP gets any lost packet sent again, and the shop puts them in order and decrypts them.
You press Buy. Less than a second later, a shop on the other side of the world has your order, and nobody on the way could read your card number. What happened in between?
Each lesson in this course showed one part of how the internet works: links, packets, TCP and encryption. A single purchase online uses all of them at once. The board shows the trip from your laptop to an online shop, with a step-by-step log of what happens.
Predict: Read the problem and decide what you think before you try anything. A wrong guess is fine: it shows you what to look for.
Try: Try it on the board and compare the result with your prediction.
Investigate: Work out why it happens, one step at a time.
Modify: Change the problem on purpose and see what happens.
Practise: A few on your own, to check you have it.
Make: Make your own problem using what you have learned. Expect a few tries; that is normal.
Make your prediction first. Help opens once you've locked it in.
PredictRead the problem and decide what you think before you try anything. A wrong guess is fine: it shows you what to look for.
Where is it encrypted?
TryTry it on the board and compare the result with your prediction.
Try: buy something
Was your prediction right? Which parts of the trip were wireless, and which wired?
Try it yourselfYour edits are saved in this browser.
Press Send and read the log as it fills in. Where was the data encrypted, and what happened to the lost packet?
Use the board. This ticks when you get there.
InvestigateWork out why it happens, one step at a time.
Worked example: the whole chain
Worked exampleBefore each step, say what you think comes next.
encrypt (HTTPS)On the laptop, before anything is sent (Who can see your data?).
split into packetsNumbered packets (Packets).
Wi-Fi, then fibreWireless first, then wired links (Wired or wireless).
routers, different routesEach packet is passed on towards the shop.
lost packet sent againTCP: the shop never confirmed it, so it was resent.
reorder, decryptThe shop rebuilds the message by number and decrypts it with its key.
Now pick out the wireless part.
Sam describes how the card number is protected. Click the line where it first goes wrong.
ModifyChange the problem on purpose and see what happens.
Vary: change one thing
Try it yourselfYour edits are saved in this browser.
Switch HTTPS off and send. What does Eve see?
Use the board. This ticks when you get there.
Switch HTTPS back on and send.
Use the board. This ticks when you get there.
PractiseA few on your own, to check you have it.
The internet
MakeMake your own problem using what you have learned. Expect a few tries; that is normal.
Put the journey in order
Then: which steps would change if you used mobile data instead of home Wi-Fi?
Put the journey of an online purchase in order. One line doesn't belong.
Pieces (click to add)
Your program
For teachers
Students follow an online purchase from laptop to shop on a board and its step log, connecting wired and wireless links, packets, TCP and HTTPS encryption into one end-to-end account, then put the journey in order themselves (AC9TDI8K02 node 5). About 40 minutes.
I can describe the journey of data across the internet.
I can say where packets, a protocol and encryption each play a part.
I can point out which parts of the trip are wired and which are wireless.
Before class
Try the board yourself and read the log.
The integration node: everything from this course in one scenario (the kit's example is an online purchase). The board simplifies: one home Wi-Fi hop, one fibre hop, two routes; real trips cross many networks, and HTTPS uses a key agreed when the page loads (Secret messages lesson 6 shows how keys can be agreed in public).
Years 9–10 (AC9TDI10K01) takes this further: addresses, domain names, routing, and public key encryption.
Running the lesson
Predict: students who chose the router hold Sam's misconception; ask what Eve on the Wi-Fi would see.
Try: pause after each log line and name the lesson it comes from.
Worked example: ask where most of the internet's cables are (including under the sea).
Vary: link each experience (slow page, gap) to its cause.
Make: ask why the extra line is wrong.
The hard part (on purpose)
Holding the whole chain at once. Use the board's log as the scaffold and have students say which earlier lesson each line comes from.
When students get stuck
A student puts encryption at the router (Sam's mistake). Ask: What travels over the Wi-Fi if the router encrypts? Fix: Plain text, readable by anyone nearby. Encrypt on the device.
A student thinks the whole internet is wireless. Ask: How does data get between countries? Fix: Mostly fibre, including undersea cables; wireless is usually just the first hop.
Stretch and support
Stretch: Look up a map of undersea internet cables. Which ones connect Australia to the rest of the world?
Support: Give the eight journey steps on cards to order before the board.
Where it leads
Next: Network capture the flag (the course challenge).
Next (Years 9–10): Security and privacy (addresses and routing, passwords and hashing, public key encryption). Code links: Secret messages.
What each step is for
where is it encrypted?: Committing to where the card number is encrypted tests the integration: encryption must happen on your device, before the first link, or every link after it is exposed.
Try: buy something: Sending with HTTPS on and reading the log settles the prediction and lays out the whole chain in order.
Worked example: the whole chain: Labelling each stage of the journey with the idea from earlier lessons models the integration. Sam encrypts at the router, the misconception planted after the method.
Vary: change one thing: Each task changes one setting of the journey: HTTPS off, HTTPS on again, then which property or protocol is responsible for each experience.
the internet: Spotting where each idea appears in everyday internet use, and a review of encryption.
put the journey in order: Ordering the whole journey from scratch reverses the board: students rebuild the chain themselves, with one wrong step left out.
Now you can
Describe the journey of data across the internet.
Say where packets, a protocol and encryption each play a part.
Point out which parts of the trip are wired and which are wireless.