Lesson video

Hello, my name's Ben and welcome to lesson three of this year five Oak Academy Computing Systems and Networks unit.

This lesson is all about transferring information.

You'll need somewhere quiet, free of distractions, a pen and a piece of paper will be handy.

So when you're ready, let's begin.

In this lesson you will recognise how information is transferred across the internet.

You will recognise that data is transferred using agreed methods.

You will explain that digital devices have an address and explain that data is transferred over networks in packets.

Let's start with a quick recap of the previous two lessons.

What word can be used to describe many parts working together successfully? Hopefully you've remembered, the answer is of course system.

In the last two lessons, we've looked at various systems, some human-based and some computer-based and some combining the two.

In this lesson, we're going to look at a communication system using computers.

Before we look at a communication system, let's have a think about how we communicate with someone successfully.

Imagine you're in a face-to-face scenario, what helps good communication? Pause the video while you have a think about that and complete your task.

Resume the video when you're ready.

Here are some of the things you could have thought about for face-to-face communication.

So to be able to communicate between two people, you need to have a message, which you're communicating.

The message needs to be from someone to someone.

Traditionally, you might think of that as a speaker and a listener although communication doesn't always have to be sound-based.

It could be using signs or many different ways.

To communicate effectively, it's useful to take turns.

So one person communicates the other listens, the other communicates, and then the other listens.

It's also useful if there is understanding between the two people in the communication process and traditionally that will involve using the same language.

So how does that compare with communicating over the computer? It's very similar.

For computers to communicate with each other they again, need a message to be communicated between them.

It needs to go from someone to someone, It needs to happen in turns, and just like face-to-face communication, a common language needs to be used between the computers.

When you send a message, it's important that it gets to the right place.

To make that point, Let's have a look at six postcards, which have been addressed in different ways.

On your handout, You've got each of these six postcards and what I'd like you to do is put them in order from the least to the most likely to get to the right place.

Pause the video while you complete that task and then we'll have a look at the order you might've chosen.

The first thing to say here is this is probably the least likely to the most likely order.

Not definitely as with many things, some of the order here is open to interpretation.

So possibly the least likely to get to its destination is this one.

This one is just addressed to J Smith 256 High Street.

There are many streets in the country called High Street, so it's very unlikely this would get to its intended recipient.

The next one at least has the town on it although the street is misaddressed.

It just has 256 High rather than 256 High Street.

Although it does have the name of the person that the postcard is addressed to.

This next one actually has less information or fewer lines than the previous one, but it does have the postcode.

And the postcode may isolate it down to fewer properties than just having 256 High.

The next one has the postcode and the town and it has High Street, but this time it doesn't have the house number.

This could get to the intended recipient if the person delivering the postcode knows the name of the person that lives in that property.

So they could make an assumption that it's for 256, although Smith being quite a common name, this might not be the case.

The next one, 256 High Street and then the postcode.

So this would or could get to the correct address.

However it's not got the name of the person who it's actually intended for on it.

So the J Smith is not on this one.

That could be a problem, if there are lots of people living in that property, so that may or may not get to its intended recipient.

And then finally we have J Smith 256 High Street Bigton and the postcode.

This is the only one that would definitely get to its intended recipient.

It's got the name of the person, the full address and the postcode.

So when you're sending messages between two people, it's important that they are addressed properly.

Before we look in detail, at how you send messages between computers, there's a few things we need to understand.

There's quite a lot of new information on this slide so don't worry if you can't take it all in now, we will be coming back to these points later on in the lesson.

So first of all, you need to understand that a group of connected computers is a network.

To be able to send messages over the internet, a computer must be connected to a network.

Messages between computers are sent using agreed protocols.

This is a word we'll have a look at later in the lesson.

Each computer has a unique IP address.

Messages are split into small packets when they are sent.

They are directed to their destination by routers.

And finally within the message, there are instructions to make sure that it goes to the right place and it can be put back together again successfully when it gets to the recipient.

Let's have a look at how addressing is dealt with when we are using computers.

What we have here is what's known as an IP address.

So an IP address is always a sequence of four combinations of numbers up to three digits each separated by dots.

So in this case, we would read the IP address as 192.

168.

1.

200 so what do these numbers mean? The first part of an IP address is always the network ID.

So that is the identification of the network to which the computer is attached.

Now I've highlighted it as the first two parts of the IP address.

It could be either the first one part, two parts or even three parts, but it's always at the beginning of the IP address.

Following on from the network ID, we have the host ID.

So this is the address of the individual computer or device you're accessing the network through.

So in this example again, it's the last two parts of the IP address, but it could be the last.

just the last part, the last two parts or the last three parts.

Again it's always at the end, so the network ID is always before the host ID.

So let's have a look at what this looks like when you are sending messages between computers.

So we've got an example here of a, from IP address, 193.

168.

1.

200 and a to IP address 192.

168.

1.

21 What I want you to think about it now is why we need a from and a to IP address.

Pause the video while you consider that.

The answer to why we need a from and a to address is really quite simple.

It's so that the message can be replied to, if the message only had a to address, the person receiving the message, wouldn't know where the message had come from and wouldn't be able to reply to it.

Now we're going to have a look at protocols and packets.

Two words which were mentioned in one of the previous slides.

So a packet will contain the sender and the receivers address, which packet it is and the contents of the packet.

And if you remember, packets are used to break messages down into small chunks.

So they're easier to send, the one we see below, the example of the packet below is the first of two packets in this message.

So let's go across from the left and see what's in there.

So we have a two and a from, and we've used these as kind of shortened IP addresses.

So it's from computer 10 to computer eight.

It is message one of two in total.

And it's the letters, H-E-L-L-O W-O the whole structure of the message is the protocol.

So each message on this computer will be in this format.

So to and from message X of Y, and then the contents of the message itself.

The receiving computer will know to expect the message in this format, and we'll be able to understand the protocol.

It's just like if you're talking to one of your friends, you would both expect to be speaking the same language so you can both understand each other.

Using this protocol what I'd like you to do is on your handout, complete the second packet, so that the full message reads, hello world.

Pause the video now and complete your task.

This is what the full message should look like.

So we've got the first packet from before from the previous slide.

So from computer 10 to number eight message one of two, hello w-o and the second packet, which you should have filled in, again is from computer 10 to computer eight, this time it's message two of two, and it's the remaining letters of world.

So R-L-D with the exclamation mark, I've put in underscores to show parts of the packet, where there is no information.

If you just left that blank, that's absolutely fine.

We mentioned earlier on that routers direct information around the internet.

So we're now going to simulate the role of a router to direct a message from one computer to another.

So our message is going to go from computer number 10, to computer number seven over here.

So I want you to think about now, which routes it could be used for our message to get from number 10 to number seven.

And each one of these empty boxes in the middle is a router.

So they will direct the message onto the next router.

In a minute, I'm going to ask you to pause the video and fill in the route for the message to get from computer number 10, to computer number seven.

Pause the video now and complete your task.

There are lots of routes you could have chosen.

This is just one example.

So in this example, we have gone from computer 10 over here, following this route to computer seven.

Any route which gets from computer 10 to computer seven is valid.

So there are lots of possibilities you could have chosen.

Let's see what happens if some of the routes are blocked.

So now I've put an X for these three routers in the middle.

The message can no longer follow this route.

So which route could you follow now to get from computer 10 to computer number seven? Pause the video and do that on your handout now.

Let's look at one potential route, you could've chosen with these three routes blocked.

So again, it starts off at computer 10 and follows this route, avoiding the block route in the middle, all the way to computer seven and this simulates what would happen in the real world.

If certain routers were out of action or a message couldn't follow a particular route.

So this is the way information flows around the internet.

Earlier on in the lesson, I mentioned that packets have to be put back together again by the computer receiving the message.

On your handout there are five packets which make up one message.

This message is a bit different to the one you've seen before.

It's not texts and messages are not always texts.

The message could be a picture or video or audio.

Use the message to make an image on the grid provided on your handout.

If the square has a one shade it in, if it has a zero leave it blank.

What does the message show? Pause the video now, while you complete that task.

If you showed it in the message correctly, you should see the number eight in the format shown on the grid.

Each square which is shaded had a one in it, each square which has left blank, had a zero in it.

If you've managed to get the number eight, you've managed to reassemble a number of packets to form a message.

Well done.

Thank you for taking part in this computing lesson with Oak National Academy.

If you'd like to show your work, please ask your parents or carer to share it on Facebook, Instagram, or Twitter, tagging @OakNational and #LearnwithOak.