Lesson video

Hello, my name is Mrs. Holborow, and welcome to Computing.

I'm so pleased you've been able to join me for the lesson today.

In today's lesson, we're going to be identifying the uses of network protocols and investigating the layers of the TCP/IP model.

Welcome to today's lesson from the unit "The internet and web technologies." This lesson is called "The TCP/IP model." And by the end of today's lesson, you'll be able to explain the TCP/IP model and common network protocols.

Shall we make a start? We will be exploring these keywords throughout today's lesson.

Let's take a look at them now.

Layer, layer, a level in a model that describes how data is transmitted across a network.

TCP/IP model, TCP/IP model, a conceptual four-layer model and set of protocols for internet communications.

Look out for these keywords throughout today's lesson.

Today's lesson is broken down into two parts.

We'll start by describing the four layers of the TCP/IP model, and then we'll move on to identify uses and layers of network protocols.

Let's make a start by describing the four layers of the TCP/IP model.

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

You can visualise these layers sitting on top of each other in a stack, which is known as a protocol stack.

Different protocols operate at each layer of the stack.

As the internet developed, the internet community defined new standards and simplified a seven-layer model, or the OSI model, by merging some layers.

The Transmission Control Protocol/Internet Protocol, or TCP/IP, has four layers, which are the main protocols used for communication between computers on the internet.

Each layer performs a series of tasks before packaging up the data and sending it to the next layer.

Time to check your understanding.

I have a true or false statement here.

As the internet developed, the original seven-layer model became more complex as new layers were added.

Is this statement true or false? Pause your video whilst you have a think.

Did you select false? Well done.

It's actually the opposite.

The internet community simplified the seven-layer model by merging some layers.

They didn't add new ones.

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

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

This process is called encapsulation.

The top layer of the TCP/IP model is the application layer.

This layer is used by applications such as web browsers.

The application layer has protocols for preparing data and sending.

Protocols are also used to decode any receiving data into a meaningful form for the end user.

The next layer is the transport layer.

The transport layer accepts messages from the application layer as application data.

It takes this data and splits it into segments.

Each segment is given a header that contains information, such as the segment number and the total number of segments.

The transport layer also states the port number used for sending and receiving data.

Ports aren't just physical things that are seen on the side of PCs, laptops, and other devices.

They can be logical too.

The operating system allocates ports for applications to use so that the data knows where it needs to go.

The third layer in the TCP/IP stack is the internet layer.

This is sometimes referred to as the network layer.

The internet layer receives segments from the transport layer and packages them up into IP packets.

IP packets include the sender and receiver's IP addresses.

This is so that the packets can be distributed to the correct location.

The fourth layer is the link layer.

The link layer is responsible for transporting the IP packets across each individual links that make up the path between the client and the server.

The protocols that are used at this layer will depend on the technology being used to transmit the data.

The technology may change many times as it travels from the client to the server.

For example, Wi-Fi might be used to transmit data from a device to a home router, and then Ethernet might be used to transmit the data on the next step of its journey.

At the link layer, a header is attached that includes the physical location of the next node on the network.

The physical location is known as the media access control address, or MAC address.

Time to check your understanding.

I have a question for you.

What is the main task of the internet layer in the TCP/IP model? Is it A, to provide user applications, B, to package data into IP packets, or C, to manage physical hardware connections? Pause the video whilst you think carefully about your answer.

Did you select B? Well done.

The main task of the internet layer in the TCP/IP model is to package data into IP packets.

At the receiving device, the process is reversed.

When the data is received by an end device, it is processed back up the TCP/IP layers.

So you can see, the arrows in the diagram indicate the flow of data.

So, at the sending end, we start at the application layer and move down to transport, then internet, and then link.

And then at the receiving end, we do the opposite.

So we move up the layers, so we start at the link layer, then the internet layer, then the transport layer, ending at the application layer.

At the receiving end, each layer takes off the extra information added by the layer above it, gradually revealing the original data.

This process is called decapsulation.

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

For part 1, I'd like you to answer the question, what is the overall purpose of the TCP/IP model? And then for part 2, I'd like you to describe the four layers of the TCP/IP model, explaining what happens at each layer.

Remember to pause the video whilst you complete the task.

How did you get on with the questions? Did you manage to write some responses? Well done.

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

For part 1, you were asked, what is the overall purpose of the TCP/IP model? The TCP/IP model organises how data travels across networks using four important layers.

For part 2, you were asked to describe the four layers of the TCP/IP model, explaining what happens at each layer.

The application layer is the top layer, handling data directly from user applications like web browsers or email.

It prepares this data for network transfer and provides application services.

The transport layer is responsible for breaking the data into smaller pieces called segments and ensuring it is delivered reliably.

It uses protocols like TCP and User Datagram Protocol, UDP, to manage the connection between devices.

The internet layer is responsible for routing data.

It uses IP addresses to send data packets across different networks, determining the best path for delivery.

Finally, the link layer handles the physical transmission of data over the network.

It includes hardware addresses like MAC addresses and manages communication between devices on the same local network.

So, we've described the four layers of the TCP/IP model.

Let's now identify some uses and layers of network protocols.

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.

So, for example, my laptop, which may be made by one manufacturer, will be able to communicate with maybe somebody else's smartphone, which is made by another manufacturer, on the other side of the world.

Different protocols are used in different layers of the TCP/IP model.

Let's have a look at some of these protocols in a bit more detail.

In the application layer, the following protocols are used: so, we have HTTP, HTTPS, and IMAP.

HTTP stands for Hypertext Transfer Protocol.

It's used for requesting and transferring web pages from web servers.

HTTPS is Hypertext Transfer Protocol Secure.

So this is very similar to HTTP, although it's used for secure web browsing, so it adds a layer of encryption.

IMAP stands for Internet Message Access Protocol, and it's used for accessing email on a server.

Here are some more protocols that are used in the application layer.

So, SMTP is Simple Mail Transfer Protocol.

This is used for sending emails from one server to another.

POP stands for Post Office Protocol.

This is used for downloading emails to a device, like a laptop or a smartphone.

And then finally, FTP, or File Transfer Protocol, is used for uploading and downloading files between computers.

In the transport layer, the following protocols are used: TCP, Transmission Control Protocol.

This is used for reliable data transfer that ensures data is delivered in order and without errors.

This is used for web browsing and email.

UDP, User Datagram Protocol, is faster than TCP but less reliable.

So, it's used for things like streaming online games and video calls where perhaps a missed packet isn't quite as crucial.

In the internet layer, the following protocols are used: IP, Internet Protocol.

This assigns unique addresses to devices and routes data across networks.

ARP, Address Resolution Protocol, matches an IP address to a device's physical MAC address on a local network.

In the link layer, the following protocols are used: Ethernet, this hasn't got an abbreviation, so it's just Ethernet.

This is used for wired networking that sends data via cables.

And then Wi-Fi, which stands for Wireless Fidelity.

This is used for wireless networking that sends data using radio signals.

Addresses are used throughout the TCP/IP stack to help deliver data to the correct place.

The two key types of address are the MAC address and the IP address.

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

So, MAC addresses.

This is a device's physical address, which is built into the hardware.

It's used to deliver data within a local network, and it's used at the link layer of the TCP/IP stack.

IP addresses are a device's logical address, which are assigned by the network, and these can change.

IP addresses are used to deliver data between different networks, and these are used at the internet layer of the TCP/IP stack.

Time to check your understanding.

Have a true or false statement here.

In the TCP/IP model, a single protocol handles all of the tasks across the four layers.

Is this statement true or false? Pause the video whilst you have a think.

Did you select false? Well done.

But why is it false? Each layer in the TCP/IP model has its own specific set of protocols that perform particular tasks, working together to enable communication.

We're now going to see how these protocols operate when we try to access a website.

A request to access the Raspberry Pi Foundation website begins when raspberrypi.

org is entered into a web browser's address bar.

The request then travels from the web browser, across the internet, to the web server application at the Raspberry Pi Foundation.

The application layer includes many protocols that prepare data so both the sender and receiver can understand it.

Different types of applications use different protocols.

These are built into software as small programmes.

The web browser uses HTTP to talk to the application layer on a web server.

At the transport layer, two main protocols are used: TCP and UDP.

Web browsing needs complete and reliable data, so it uses TCP.

Data from the application layer, like a HTTP request, is broken into smaller pieces called segments.

Each segment gets a header with a sequence number to keep track of the order.

A checksum is added to help detect errors in the data.

The internet layer, which is also sometimes called the network layer, receives these segments from the transport layer.

It wraps these segments into IP packets.

Each data packet gets a header with important information, including the sender and receiver's IP addresses.

This helps the packets be routed to the correct destination, like the Raspberry Pi Foundation web server.

The link layer, which is sometimes known as the data link layer, manages the physical transfer of packets.

Devices connect to networks using technologies like Ethernet, Wi-Fi, and Bluetooth.

The appropriate link layer protocol is used depending on the connection type.

For example, with Ethernet, IP packets are wrapped in Ethernet frames for local network transmission.

An IP packet can be wrapped and unwrapped multiple times while travelling across the internet.

Each time the packet moves to a new link, it is wrapped in a frame suited for that link's technology.

Each frame includes the address of the next device on the path.

This address is called the media access control, or MAC, address.

The packets containing the HTTP request reach their final destination, the Raspberry Pi Foundation web server.

Each frame is unpacked as it arrives.

The IP packets are passed from the link layer to the internet layer.

At the internet layer on the web server, each IP packet is unpacked.

The TCP segment inside the packet is passed up to the transport layer.

At the transport layer on the web server, each segment is checked.

If any segments arrive out of order, they are put back into the correct sequence.

The server sends back acknowledgements for each segment.

If any segments are missing, they are sent again.

Once complete, the full HTTP request is passed to the application layer.

At the application layer on the web server, the request for the webpage is received.

The web server gathers the data needed to show the webpage.

It formats the data as a HTTP response.

The response is passed down to the transport layer so it can begin the journey back to the client, the user's device in this case.

Eventually, the data will be received back at the application layer on the client side and displayed to the user.

And it's amazing to think how quickly all of this happens, because you don't have to wait long for a website to appear in your web browser, do you? Time to check your understanding.

Which application layer protocol is used for sending emails between servers? Is it A, IMAP, B, POP, C, SMTP, or D, FTP? Pause the video whilst you think carefully about your answer.

Did you select C, SMTP? Well done.

SMTP is specifically used for sending emails between mail servers.

IMAP and POP are both email protocols, but they're used for accessing and downloading emails, and FTP is used for file transfer.

Okay, we're moving on to our next task of today's lesson, Task B.

For part 1, explain the differences between an IP address and a MAC address.

For part 2, which layer of the TCP/IP model primarily uses IP addresses, and which layer primarily uses MAC addresses? And then for part 3, describe the path a web request takes as it moves down through the application, transport, internet, and link layers of the TCP/IP model on the client's device before it leaves the local network.

Pause the video here whilst you complete the task.

How did you get on with the tasks? Did you manage to write a response for each question? Well done.

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

Remember, whilst we're going through the sample answers, you might want to make any additional notes or make any changes to your responses.

For part 1, you were asked to explain the difference between an IP address and a MAC address.

An IP address is like the postal address for your device on a network.

It helps identify your device and makes sure data is sent to the right place, even across different networks.

Your IP address can change if you connect to a different network.

A MAC address is like a name tag that is built into your device.

It is unique and never changes.

The MAC address is used to identify your device when it's communicating within the same network.

For part 2, you were asked, which layer of the TCP/IP model primarily uses IP addresses, and which layer primarily uses MAC addresses? The internet layer uses IP addresses for routing data across different networks.

The link layer uses MAC addresses for managing the physical transfer of packets between devices on the same local network.

For part 3, you were asked to describe the path a web request takes as it moves down through the application, transport, internet, and link layers of the TCP/IP model on the client's device before it leaves the local network.

The application layer first prepares the web request.

This request then passes to the transport layer, where it is broken down into smaller segments.

The internet layer wraps these segments into IP data packets, adding the sender and receiver's IP addresses.

Finally, at the link layer, these IP packets are wrapped into frames, which makes them ready for sending.

Okay, we've come to the end of today's lesson, "The TCP/IP model." And you've done a fantastic job, so well done.

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

The TCP/IP model is the foundational network model for the internet, comprising four distinct layers.

Each layer is responsible for a different aspect of network communication.

Common network protocols operate at specific layers, serving defined purposes in the successful transmission and reception of data.

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