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 are going to be describing, and comparing, some common network topologies.

But what is a network topology? Welcome to today's lesson from the unit Network Fundamentals.

This lesson is called Network Topologies, and by the end of today's lesson, you'll be able to describe and compare different network topologies, including their advantages and disadvantages.

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

Let's take a look at them now.

Star, star.

The arrangement, usually physical, of a network where devices are connected through a central point.

Bus, bus.

A network where all devices are connected to a single shared communication line that transmits data to every device on the network.

Mesh, mesh A network where each device is connected to one or more others, allowing multiple data paths.

Look out for these key words throughout today's lesson.

Today's lesson is split into two sections.

We'll start by describing common network topologies, and then we'll move on to compare network topologies.

Let's make a start by describing some common network topologies.

There are many different arrangements for network engineers to choose from.

These arrangements are called topologies, so the word topology basically means how is the network arranged? Graphs are sometimes used to represent the different topologies or arrangements.

The nodes, or dots in this case, illustrate a component in the network, like maybe a computer or a printer, and the edges or lines represent how they are connected to each other.

Time to check your understanding.

I have a true or false statement for you.

Networked topologies are the different arrangements network engineers can choose from for a network.

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

Did you say true? Well done.

But why is it true? Remember, topologies describe how devices are physically or logically connected in a network.

This is a graph for the star topology.

The arrangement has one central node, with all the other nodes connected to it.

The central node would typically be a hub or a switch that transfers data between nodes.

When a hub is the central device in a network, it sends or broadcast data to all connected devices, not just the intended recipient.

Broadcasting means transmitting data to every device on the network, rather than just targeting just one.

If a hub is the central node, then it will broadcast the data to all nodes connected to it.

Note, the red crosses indicate that the message has been ignored because it wasn't addressed to that location.

If a switch is the central node, then it will transfer the data to the required location.

This is the graph for a bus topology.

In this arrangement, each node is connected to a single cable, which is known as the bus.

When data is sent from one node to another, it is sent in both directions.

Terminators are placed at the end of the cable to stop signals being reflected back down the cable.

In a bus topology, the data is sent to all nodes connected to the bus.

It is only accepted by the node that requires it.

Time to check your understanding.

I have a question for you.

What is the key difference of a star topology compared to a bus topology? Is it, A, star connects to one main cable, whereas bus connects to a central hub, B, star connects to a central node, whereas bus connects to one main cable, or C, star uses terminators, whereas bus uses a central switch? Pause the video whilst you think carefully about your answer.

Did you select B? Well done? Star connects to a central node, whereas bus connects to one main cable, which is referred to as the bus.

This is the graph for a mesh topology.

In this arrangement, there are multiple ways for data to transfer from one node to another.

In a mesh network, each node is connected to at least one other node.

It is more common for them to be connected to multiple other nodes.

In a mesh network, the most efficient route is typically calculated before transferring the required data.

This can help reduce transmission time and network traffic.

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

I'd like you to describe three common network topologies, explaining how each arrangement connects devices and how data travels with it.

If it's useful, you might want to sketch out the topology as well.

Pause the video here whilst you complete the task.

How did you get on with the task? Did you manage to describe some common network topologies? Well done.

Let's have a look at a sample answer together.

You were asked to describe three common network topologies, explaining how each arrangement connects devices and how data travels within it.

A star topology connects all devices to a central node, such as a switch, which directs data.

A bus topology connects all devices to a single main cable, sending data both ways to all nodes, but only the intended one accepts it.

In a mesh topology, devices have multiple connections, and data travels via the most efficient path.

Remember, if you'd like to pause the video here and make any amendments to your answer, you can do that now.

Okay, so we've described some common network topologies.

Let's now go on and compare some of these common network topologies.

We're going to look at the benefits and drawbacks of some of the common topologies we've looked at so far in this lesson.

Let's start with the star topology.

So the benefits.

A damaged link only affects the attached node.

It doesn't affect the whole network.

You can also easily add new nodes to the network without any disruption.

It works well when there are lots of users on the network at the same time.

The drawbacks.

The central node is a single point of failure, so if that central node stops working, then the whole network will be affected.

It also requires more cables than a bus, which can become expensive.

Let's now have a look at the bus topology.

The benefits of a bus topology are, a bus network is cheap because it uses minimal cables.

A bus network is simpler to set up than other arrangements, and it works well for very small networks.

Some drawbacks.

If the main cable or bus fails, then the whole network will fail.

It isn't very secure, because data is sent to all nodes on the network.

As more nodes are connected, the network performance reduces significantly.

Let's now look at the mesh topology.

The benefits.

There is no central node, so there is no single point of failure.

The data uses the most efficient route, making data transfer faster, and it works well under heavy network load.

That means lots of network traffic.

Drawbacks.

The increased cabling required for a wired network makes it expensive.

A wired mesh is far more complicated to manage and maintain than other topologies, and for this reason, quite often a mesh topology is implemented as a wireless network.

A couple more benefits of a mesh topology.

If a node breaks, then the new route can be found for the data.

New nodes can also be added without shutting down the whole network.

Time to check your understanding.

I have a true or false statement for you.

A drawback of the bus topology is that if the main cable fails, the entire network fails.

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

That's right, it's true.

Well done.

The main cable is a single point of failure in a bus topology, meaning that a break in it will disrupt all communication on the network.

There are several key differences between star and bus topologies.

Star is more reliable, as a cable failure only affects one device.

Bus is fragile.

If the main cable fails, the whole network fails.

Star performs well under heavy use, especially when using a switch.

Bus slows down as more devices connect to the network.

Bus is cheaper to instal, because it uses less cabling.

Star is more expensive to set up due to the greater amount of cabling and the cost of the central device.

Let's have a look at how star and mesh topologies compare.

Star has a single point of failure, which is the central hub or switch.

Mesh is fault-tolerant, because data can find new routes if one path fails.

Star is easier to set up and manage.

Mesh is more complex to configure and maintain.

Both are scalable, which means that they can get bigger easily.

But mesh allows for new nodes to be added without network downtime.

Bus and mesh topologies also have some important differences.

Bus is less secure, because all data is sent to every connected device on the network.

Mesh is more private, with data travelling directly to the destination.

Bus is simple and inexpensive to instal.

Mesh is costly and requires more cabling.

Mesh performs well under heavy network load, whereas bus struggles when lots of devices are connected.

Okay, time to check your understanding.

I have a question for you.

Which of the following statements correctly compares the reliability of a star topology and a mesh topology? A, star can keep working despite component failure.

Mesh has a single point of failure.

Star has a single point of failure.

Mesh can keep working despite component failure.

Or C, both have a single point of failure.

Pause the video whilst you think about your answer.

Did you select B? Well done? Star has a single point of failure.

Mesh can keep working despite component failure.

Okay, we've come to our second task of today's lesson, Task B.

I'd like you to compare and contrast the star, bus, and mesh network topologies.

Pause the video here whilst you complete the activity.

How did you get on comparing the network topologies? I'm sure you've done a fantastic job.

Well done.

Let's have a look at a sample answer together.

So you were asked to compare and contrast the star, bus, and mesh network topologies.

A star topology connects all devices to a central point, making it more reliable than a bus topology, where a single main cable connects everything, causing the whole network to fail if that cable breaks.

Bus is typically cheaper and simpler to set up than star, which requires more cabling and a central device.

When compared with mesh topology, star has a single point of failure, the central hub or switch, whereas mesh is highly fault-tolerant due to its multiple connections, allowing data to find new routes if one path fails.

Mesh networks are generally more complex and costly to manage than both star and bus.

In terms of performance under heavy use, mesh excels, handling heavy loads better than star, and significantly outperforming bus, which slows down as more devices connect.

Did you have a similar response? Remember, if you'd like to pause your video here and add any extra detail to your answer, or go back and have a look through the slides, you can do that now.

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

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

A star topology connects all devices directly to a central hub or switch.

A bus topology links all devices to a single shared cable.

A mesh topology creates connections where each device is linked to several others.

Each of these topologies has distinct benefits and drawbacks which impact the network's overall performance, cost, and reliability.

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

Bye.