Across the internet

Classroom resources

Load these into Waypoints Prepare: choose Load URL and paste the copied address, or download the file and import it. In Prepare, the worksheet's Teacher edition shows the answers; the student copy hides them.

• Slides Download Copy address for Prepare Present from the browser, or export to PowerPoint or PDF.
• Worksheet Download Copy address for Prepare Print the student copy; the Teacher edition has the answers.

Students will be able to

• 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.

Timing

Predict and Try 8 min · Worked example 10 min · Vary 10 min · Practise and Make 12 min

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

1. Predict: students who chose the router hold Sam's misconception; ask what Eve on the Wi-Fi would see.
2. Try: pause after each log line and name the lesson it comes from.
3. Worked example: ask where most of the internet's cables are (including under the sea).
4. Vary: link each experience (slow page, gap) to its cause.
5. 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

Answers to the checks

1. where is it encrypted?: Your card number travels from your laptop to an online shop. Where does it get encrypted?
   On your laptop, by the browser (HTTPS), before it leaves. Anywhere later would leave the first part of the trip, including the Wi-Fi, readable.
2. Try: buy something: Press Send and read the log as it fills in. Where was the data encrypted, and what happened to the lost packet?
   
   Encrypted on the laptop first, split into packets, sent over Wi-Fi then fibre, routed, one packet sent again by TCP, put back in order and decrypted by the shop.
3. Follow the purchase: Which part of this journey is wireless?
   Laptop to the home router (Wi-Fi)
   Only the first hop is wireless here. Most of the internet is cables and fibre, including under the sea.
4. Find the mistake: Sam describes how the card number is protected. Click the line where it first goes wrong.
   line 3
   Line 3: the browser encrypts the data on the laptop (HTTPS) before it is sent. If the router did it, the packets would cross the Wi-Fi as plain text, where anyone nearby could copy them.
5. HTTPS off: With HTTPS **off**, who could read the card number?
   Anyone on the Wi-Fi or any network along the way
   Without encryption, every link and router on the way handles readable packets.
6. HTTPS off: Switch HTTPS off and send. What does Eve see?
   
   The card number crosses the Wi-Fi in plain text, so Eve reads it.
7. HTTPS on: Switch HTTPS back on and send.
   
   Eve sees only scrambled text; the shop decrypts it.
8. Slow at the far end: The page takes ages to load at the far end of the house. Which part of the journey is most likely to blame?
   The Wi-Fi hop: distance and walls
   A weak Wi-Fi link loses packets and adds delay, so TCP has to keep resending.
9. Without TCP: Without TCP, what would the shop receive when a packet is lost?
   A card number with a piece missing
   A gap: that is why orders and payments use TCP.
10. Mobile video: You watch a video on the school bus on mobile data. Which part of the trip is wireless?
    Phone to the mobile tower
    Phone to tower is wireless; from the tower onwards it is mostly fibre.
11. Which protocol?: Which protocol puts a web page's packets back in order and asks for lost ones?
    TCP
    TCP numbers, acknowledges and resends packets.
12. Review: decrypt: Review: a message was encrypted with key 2. You receive **JK**. What did it say?
    HI
    J → H and K → I: HI.
13. put the journey in order: Put the journey of an online purchase in order. One line doesn't belong.
    see the program below
    Encrypt on the laptop, split into packets, Wi-Fi, cables and fibre, routers, TCP, put back in order, decrypt at the shop. The router never encrypts it: by then it would already have crossed the Wi-Fi.

    You press Buy, and your browser encrypts the card number (HTTPS).
    The encrypted data is split into numbered packets.
    The packets cross the Wi-Fi to your home router.
    They travel by cable and fibre to your internet provider.
    Routers pass each packet on, by different routes.
    The shop's computer confirms each packet; a lost one is sent again (TCP).
    The packets are put back in order by number.
    The shop decrypts the card number with its key.
    

Solutions

One possible solution for each task. Other correct programs are fine.

Vary: change one thing › HTTPS off

Open task: any program that does what the step asks.

Vary: change one thing › HTTPS on

Open task: any program that does what the step asks.

Vary: change one thing › Slow at the far end

Open task: any program that does what the step asks.

Vary: change one thing › Without TCP

Open task: any program that does what the step asks.

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.

Exit ticket

Describe the journey of a password from your phone to a website in four steps, naming where encryption, packets and TCP each come in.

Encrypted on the phone (HTTPS); split into packets; sent over wireless then wired links through routers, with TCP resending lost packets; put back in order and decrypted by the website.

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.

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.