Network Topologies (Edexcel GCSE Computer Science)

What is a network topology?

• A network topology is the arrangement of devices in a network

• It defines how the network hardware will be arranged to create the network

• Three popular topologies to understand for the exam are:

  • Bus topology

  • Star topology

  • Mesh topology

Bus

What is a bus topology?

• A bus topology is all devices connected by one single ‘bus’ cable, terminated at each end

• The terminators stop the signal bouncing back and causing errors

• A bus topology works by each device:

  • ‘Listening’ to electrical signals

  • Checking data packets for their specific address

  • Ignoring data packets it does not recognise

• A bus topology has been replaced by much more efficient network topologies such as the star topology

What are the advantages of a bus topology?

• Easy and cheap to set up as only one cable is required

• Does not rely on any other network hardware such as a central server/switch

What are the disadvantages of a bus topology?

• Low security as data is seen by all devices on the network

• Slow data transfer and prone to data collisions

• If the cable breaks, the whole network is affected (central point of failure)

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Star

What is a star topology?

• A star topology has a central switch which all other devices connect to

• A switch is an intelligent device which ensures that traffic only goes to the intended device

• A star topology is commonly seen in most homes, businesses, organisations and schools

What are the advantages of a star topology?

• If any single cable stops working, the rest of the network will continue to work

  • An example you may have experienced would be in school when one computer won't log on to the network, but all other classmates can get logged on

• This is important because in other topologies if a cable was broken, all computers on the network would stop working which would have a negative impact on learning in schools and businesses completing their daily tasks

What are the disadvantages of a star topology?

• The central switch is a single point of failure

• This means that if the switch stops working, all of the devices connected to it will not be able to connect to the network or any of its facilities and resources

Mesh

What is a mesh topology?

• A mesh topology allows all computers to be connected to all other computers

• This is known as a full mesh network topology

• LANs can make use of mesh networks however, they are more commonly seen in IoT devices such as wearable technology and smart home devices

What are the advantages of a full mesh topology?

• If any single cable stops working, the rest of the network will continue to work as the data can find a different route to get to its destination

• In the example below you can see that one cable has been marked as not working and that that data can simply use an alternate route

What are the disadvantages of a full mesh topology?

• The topology requires a lot of hardware, cables and switches to set up

• This means there is a higher cost for setting up the network

• Adding new devices is not as easy as in a star topology, making it more challenging to scale the network

• The solution to these disadvantages is called a ‘Partial Mesh Topology’

What is a partial mesh topology?

• A partial mesh topology is very similar to a full mesh, with the difference being that each device is not connected to every other device directly

• This means 

  • Less cables and hardware are required

  • Multiple routes still exist between devices

  • It is a compromise solution to reduce the amount of hardware needed

• The diagram below is an example of how the backbone structure of the Internet appears