Lesson video

Hi, I'm Allen Heard, this is lesson four of six, and this one is all about the Internet.

For this lesson you will need a pen and paper or something to write on or something to write with.

Make sure all distractions are out of the way and notifications are turned off on your mobile phones, when you're ready, we can get started.

Okay.

So in this lesson, we'll describe what the internet is, we'll explain how data travels between devices on the internet, we'll explain packets and addressing.

So let's start with the internet and see if we can have some thoughts on this question.

What is the internet and what can it be used for? You can pause the video, write down some answers as to what you think it is and what it can be used for, and come back when you are done.

Okay, so put simply, the internet is a collection of networks connected globally and information can travel within and between these networks.

But how are they connected? So if you were to think about networks in the UK and networks in the United States, if I were to send a message for instance, or ask for a website, how might those networks be connected? Have a think about that second, pause the video and resume when you're ready.

Well, if you take a look at this picture, this picture shows Oceanic cables and how countries are connected together by cables that go underneath the sea.

This isn't generally what we think of when we think of the internet and how things are connected.

We tend to think of satellites and things going through the air and this term of the cloud, but actually things are connected with cables that go under the oceans.

The first one was laid in 1851 to connect the telephones.

99% of the world's internet data travels through these cables that go under the sea.

And they can be damaged by anchors and trawlers and fishing ships and then the like, and quite a lot of them get bit by sharks too.

So just as you have an address for your house, all devices that are connected to the internet have their own address, this is called an IP address or Internet Protocol address.

These are made of four groups of numbers between nothing and 255 and they're separated by dots, and these are unique for every device on the internet.

Typically, if you're connecting to the internet from your home, you'd have one IP address which would be the router of your main connection, which is what the IP address that other people would see.

But internally all your devices would have an individual IP address within your house.

You can find out your IP address if you want to, you can ask a parent or carer to help you type in what is my IP address into a search engine, and it will actually tell you what your IP address is that is going out to everyone else.

So given that in 2019 there were 27 billion devices connected to the internet, how does the message find its way from one device to another? Well, let's imagine we're after a web address.

So we take the URL into our browser or Uniform Resource Locator, and then your computer sends that request, you know, like a virtual envelope, including the information of where it's from and where it's going to, and with the site you're looking for.

We call this information a packet.

So this packet with your request for a web address travel its way through a telephone cable out of your house, underground through the copper wires, and it continues through regional networks until it reaches the internet hub in the UK.

So it's TeleHouse North in London.

It then goes out under the sea.

So in one of those Oceanic cables that we just talked about, and then it arrives at another internet hub.

So if it was the United States, it would arrive here, at 60 Hudson Street, New York.

This hub would then send it through some more regional networks until it arrives at the server of the web address you're looking for, and the server would look up that information.

Now a website's too large to send in one packet or in one chunk, so the Transfer Control Protocol or TCP, splits up the information into thousands of small packets of information.

And then when they arrive at the internet hub for outward delivery, the hub checks the traffic and again, sends the packets out in order under the sea, back through regional networks.

Finally, your computer receives all of these packets, it may not necessarily receive them in the right order, even though they're originally sent in the right order.

And the TCP puts them back into the correct sequence and is able to make up that information, what you were requesting for, and displays the website on your screen.

All of that happens in about a second.

So from you typing in the web address in and pressing enter, going out under the sea, out of your house back again, all of that happens in under a second.

So packets can arrive in the wrong order as I said in the last slide, but the packet header contains the sender IP, the destination IP and the sequence.

Those sequence number are one of three in this one, in this example, for instance.

And the packet payload contains the information itself.

So you can see an example of a packet there on the screen.

You can see it's got sender IP destination up here and that says one of three, and the payload which the information in this case says, hello.

So at this point you have a task to complete it's on the worksheet.

It's task one, packets of information.

You're required to send a message using four packets.

Open the task and fill in the gaps.

Okay, so how did you find that task? Well, on each of the package, you can see they've got a sender IP address and the destination IP address, and they're going to be the same across all of them.

So in this example of our sender IP address is 1.

1.

1.

1 and the receiver address is 2.

2.

2.

2.

Each packet has a sequence number.

So some of those were filled in for you and some of them weren't.

And I guess that the important thing here is splitting up the payload or splitting up the information you want to send and making sure the sequence number for that specific piece of information is correct, because otherwise it could end up being jumbled up at the other end.

So one of four is what, two of four is, is, three or four, your and four of four is name.

So no matter what order they will receive them, you could look at those sequence numbers and you could rearrange it into the right order.

Okay, so packets and routers.

Well a router is used to connect networks together across the internet, and they forward these packets along from sender to receiver.

There are millions of these on the internet.

And packets can take different routes on their way to their destination.

So imagine you were sending some information from the top left house to the one on the bottom right.

It can go through that network in any order it chooses or depending on traffic and which way it's sent.

But looking at this diagram, which internet routers will all packets pass through? So you can pause the video and have a think about that for a second.

Which internet routers will all of the packets pass through? You can pause the video and complete the task.

Okay, so hopefully looking at this diagram, you should have realised that all information must travel from the house through to IR1 for definite, because that's how it gets its initial connection to the network, and then as it travels its way through the network, whichever way it decides to go, it will then definitely go through IR4, the internet route of four because that's the last connection to get to the house on the bottom right.

Don't forget there is a quiz at the end of this lesson to complete, to assess what you've learned during the lesson.

We'd love you to also to share your work with Oak National, so if you'd like to, please ask your parent or carer to share your work on Instagram, Facebook or Twitter.

Tag in @OakNational and #LearnwithOak.

I really enjoyed teaching that lesson, see you next time.