Lesson video

Hello, my name is Mrs. Holborow, and welcome to "Computing." I'm so pleased you've decided to join me for the lesson today.

In today's lesson, we're going to be investigating why we need network models, and we're going to be looking at the Open Systems Interconnection model.

Welcome to today's lesson from the unit, "The internet and web technologies." This lesson is called "Network Models." And by the end of today's lesson, you'll be able to explain why network models are used and describe the Open Systems Interconnection, or OSI model.

Shall we make a start? We will be exploring these key words in today's lesson.

Let's take a look at them now.

OSI model, OSI model: A seven-layer model that describes how different computer systems can communicate over a network.

Encapsulation, encapsulation: When data is packaged with additional information as it moves down through the layers of a network model.

Decapsulation, decapsulation: When data is received and unpacked by a device as it moves up through the layers of the network model.

Look out for these keywords throughout today's lesson.

Today's lesson is broken down into two sections.

We'll start by explaining the requirements for network models, and then we'll move on to describe the Open Systems Interconnection model.

Let's make a start by explaining the requirement for network models.

Protocols are shared rules that allow billions of devices around the world to communicate, no matter who makes them.

All devices follow the same protocols, which ensures they can send and receive data correctly.

Network protocols organised data as it passes through a sequence of layers.

You can visualise these layers sitting on top of each other in a stack.

This is known as a protocol stack.

Different protocols operate at each layer.

The Open Systems Interconnection, or OSI model, is a seven-layer model developed by the International Organisation for Standardisation, the ISO, to create a universal standard for network communication.

This model is still used today.

While the OSI model is excellent for understanding network functions conceptually, the internet is actually built upon a different set of standards and network model, which we will be exploring in future lessons.

These protocol stacks allow devices made by different manufacturers to interact with each other and communicate effectively.

So long as these devices meet the necessary standards and use the appropriate protocols, the component will be able to interact with the other layers to communicate with other devices.

Time to check your understanding.

I have a true or false statement here.

"Protocol stacks allow devices made by different manufacturers to communicate with each other." Is this true or false? Pause the video whilst you have a think.

Did you select True? Well done, this layered structure helps organise how data is handled and communicated across networks.

When data is sent, it passes through the layers of the protocol stack.

Each layer accepts data from the layer above and adds extra information to help with delivery.

This process is called encapsulation.

Think of it like putting a letter in an envelope.

Each layer adds its own envelope with useful information such as addresses or delivery instructions.

The data is wrapped layer by layer until it is ready to be sent.

At the receiving device, the process is reversed.

Each layer takes off the extra information added by the layer above it gradually revealing the original data.

This process is called decapsulation.

Time to check your understanding.

I have a question for you.

"Why does each layer add its own specific information during encapsulation?" Is it A: to make the data much larger for storage, B: to help with the correct delivery and handling of the data at different network stages, or, C: to automatically translate the data into a different language? Pause the video whilst you think carefully about your answer.

Did you select B? Well done.

Each layer adds its own specific information to help with the correct delivery and handling of the data at different network stages.

Okay, we are moving on to our first task of today's lesson, task A.

For part one, I'd like you to explain why are network protocols organised into different layers known as a protocol stack? For part two, I'd like you to describe what happens to data as it moves through the layers of a protocol stack when it's being sent, and what happens as it moves back up through the layers when it's being received.

Pause the video whilst you complete the task.

How did you get on with the task? Let's have a look at a sample answer together.

For part one, you were asked, "Why are network protocols organised into different layers known as a protocol stack?" Network protocols are organised into layers to help manage all the different rules and functions needed for communication.

Visualising these layers as sitting on top of each other forms a stack, making the process of how data is handled clearer.

For part two, you were asked to describe what happens to data as it moves through the layers of a protocol stack, when it's being sent, and what happens as it moves back up through the layers when it's being received.

When data is sent, it passes down through the layers of a protocol stack.

At each layer, the data accepts information from the layer above and adds extra information to help with its delivery.

This process where data is wrapped layer by layer until it's ready to be sent is called encapsulation.

At the receiving device, the process is reversed.

As the data moves up through the layers, each layer removes its own added information.

This process where data is unwrapped layer by layer is called decapsulation, eventually revealing the original message.

Remember, if you want to pause the video to add any detail to your answer, or to go back and check through the previous slides, you can do that now.

Okay, so we've explained the requirements of network models.

Let's now move on to describe the Open Systems Interconnection model.

The seven layers of the OSI model, or Open Systems Interconnection model, are numbered from bottom to top.

Data moves up and down the stack as data is sent and received.

Additional data is added as it moves down the stack and data is removed on the way up.

So the first layer is the physical layer.

Layer two is the data link layer, layer three, the network layer, layer four, transport, layer five, session, layer, six presentation and layer seven, application.

Let's have a look now at each of these layers in a bit more detail.

The application layer handles software and apps like web browsers, email, and messaging.

It provides the tools for sending and receiving data.

For example, it's used when a web browser sends a request to load a webpage.

The presentation layer makes sure that the data is in a format that can be understood.

It handles file formats, encryption, and compression.

For example, it converts data to readable text, and encrypts it for secure transfer.

The session layer manages sessions or connections between two devices.

It opens, uses, and ends communication sessions.

For example, it keeps you logged into a website whilst you are browsing time.

To check your understanding.

I have a true or false statement here.

"As data moves down the protocol stack, information is added to it.

As it moves up, information is removed." Is this statement true or false? Pause the video whilst you have a think.

Did you select True? Well done.

This is the core principle of encapsulation, where information is added when data is sent down the stack.

And decapsulation is where information is removed when data is received up the stack.

The transport layer splits data into data packets for sending.

It makes sure all the packets arrive correctly and in the right order.

For example, it ensures your email arrives completely, not just a part of it.

The network layer handles routing, and decides the best path for data to travel across networks.

It uses IP addresses to identify the sender and receiver.

For example, it's used to send data to the correct location on the internet.

The data link layer creates a reliable link between two devices on the same network.

This layer handles error detection.

For example, it makes sure data can travel correctly from your laptop to your router.

The physical layer manages the actual hardware and physical connection.

It sends electrical signals or light pulses over cables or wireless.

For example, it's used by the Wi-Fi signal or ethernet cable carrying your data.

Okay, time to check your understanding.

I have a question for you.

Which layer handles routing and uses IP addresses to identify the send and receiver of data? Is it A: the transport layer, B: the network layer, or C: the data link layer? Pause the video whilst you have a think.

Did you select A: the transport layer? Well done.

Okay, we are moving on to our second task of today's lesson, task B.

You've done a fantastic job to get this far, so well done.

For part one, what is the Open Systems Interconnection, or OSI model, and why is it useful for understanding how computer networks communicate? For part two, describe what happens to data as it moves through the layers of the OSI model when it is being sent and when it is being received by another device.

For part three, name one layer of the OSI model and explain what that layer does.

Pause the video whilst you complete the task.

How did you get on with your questions? I'm sure you've done a fantastic job.

Let's have a look at some sample answers together.

For part one, you were asked, "What is the Open Systems Interconnection, or OSI model, and why is it useful for understanding how computer networks communicate?" The OSI model is a way to describe how network communication works by breaking it down into seven separate layers.

It helps us understand complex network processes by looking at smaller, more manageable parts.

It allows different types of devices and software to communicate by following a common structure.

For part two, you were asked to describe what happens to data as it moves through the layers of the OSI model when it is being sent and when it is being received by another device.

Encapsulation happens as data moves through the layers.

Each layer adds extra information to the data as it is sent.

Decapsulation happens as data moves up through the layers.

Each layer removes its corresponding extra information when it is received.

Finally, for part three, you are asked to name one layer of the OSI model and explain what that layer does.

We've chosen the application layer here.

The application layer is the layer closest to the user.

It provides network services directly to user applications.

For example, when you use a web browser or an email programme, these applications interact with the network through the application layer.

Other correct layers include the presentation layer, session layer, transport layer, network layer, data link layer, and the physical layer.

So if you've included those as part of your answer, you would also be correct.

Remember, if you want to pause the video now to add any extra detail to your answers, you can do that now.

Okay, we've come to the end of today's lesson, "Network Models," and you've done a fantastic job, so well done.

Let's summarise what we've learned in this lesson.

Network models are essential frameworks used to standardise communication between diverse devices across a network, so where devices may be made by different manufacturers.

The OSI model organises network communication into seven distinct layers, each with a specific role in managing the overall communication process.

I hope you've enjoyed today's lesson, and I hope you'll join me again soon, bye.