Cut It Up and Send It: Packets and Addresses

We are learning to explain how a message is split into numbered, addressed packets, routed by different paths, and reassembled, with lost packets sent again.

Before you startAbout 65 minutes · what success looks like · notes for the helper

About 65 minutes. It's fine to stop after the Quick Check and come back another day: the lesson opens where you left it, at the Quick Check.

You'll know you've got it when

I can split a message into numbered packets and write a header on each with a sender address, a receiver address and the packet's place in the sequence
I can explain what a router does and why packets of one message can take different paths and arrive out of order
I can reassemble a jumbled set of packets using their numbers
I can describe how a receiver detects a missing packet and what happens next

For the helperhow to sit beside this lesson, and what this step is for

This step: Spark

Start with the question at the top and chat about it. There is no wrong answer here: it gets your learner thinking about what they already know.

Getting ready: A few strips of paper or index cards, a pencil, and two or three other rooms or willing people who can act as routers. A short message of about 24 characters, counting spaces, is plenty. The packet-size choice needs a calculator or a confident head for multiplication. The lesson is about 65 minutes, and running the network with people takes time to set up, so it can spread over two sittings.
What understanding sounds like: You might listen for your learner writing a full header (to, from, 'n of total', a check) on every packet, saying that the numbers are what let the receiver rebuild the message, that the address tells a router where to send it rather than where it sits in the message, and that a missing number is asked for again, never guessed.
A likely mix-up, and something that helps: A likely belief is that packets must arrive in order, or that one lost packet means starting the whole message again. One way in is to hand over the packets shuffled and ask, 'What would you need written on each one to rebuild this?'
If it comes easily: A good puzzle for a quick learner: how big should a packet be, weighing what tiny packets waste against what a huge packet costs when it has to be sent again?
If it's a struggle: If it is a struggle, one way is to start with three short packets and a single route, and add the second route only after the first rebuild works. Header, payload and router are new words doing a lot of work; pointing at the strip of paper while naming each part, in the family's home language too if that helps, makes them concrete. If your learner has had enough, one message cut up and rebuilt from its numbers is a fair place to stop.

Step 1 of 6 · Spark

Lesson 1 of 5 · How Messages Cross the World and Stay Private

A novel posted one page at a time

For the helper

Start with the question at the top and chat about it. There is no wrong answer here: it gets your learner thinking about what they already know.

Suppose you had to post a whole novel to a friend in Perth, but the post office would only accept envelopes holding a single page. You would tear out each page, number it, and write the same destination on every envelope. Some envelopes would go by one truck and some by another. A few would arrive days apart, and one might be lost entirely. Your friend would still be able to read the novel in order. This is close to what happens to every message you send, including this page as it reached you. Before you read on, say what you would have to write on each envelope, and what your friend should do when page 112 is missing.

One page per envelope, numbered, all addressed to the same place. Different trucks, different days, one readable book.