Network Topologies (Cambridge (CIE) A Level Computer Science) : Revision Note
What is a network topology?
A network topology is the physical structure of the network
It defines how the network hardware will be arranged to create the network
Topologies to understand for the exam are:
Star topology
Bus topology
Mesh topology
Hybrid 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A bus topology has been replaced by much more efficient network topologies such as the star topology
Bus topology - advantages vs disadvantages
Advantages | Disadvantages |
|---|---|
Easy and cheap to set up – only one cable is needed | Low security – data is visible to all devices |
Does not rely on other network hardware (e.g. central server or switch) | Slow data transfer – prone to data collisions |
If the cable breaks, the whole network is affected (central point of failure) |
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
Traffic (packets) on a star topology is handled differently depending on the device used as the central node
A hub will send traffic to all devices on the network, if the address in the packet matches a device it will be accepted, otherwise it is ignored
A switch will only send traffic to devices on the network where the address in the packet is a match
Star topology - advantages vs disadvantages
Advantages | Disadvantages |
|---|---|
If one cable fails, the rest of the network still works | The central switch is a single point of failure |
A problem with one device (e.g. a school computer) won’t affect others | If the switch stops working, all devices lose connection to the network and its resources |
More reliable than other topologies like bus or ring | Can be expensive to install due to the switch and extra cabling (not mentioned but useful add-on) |
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
Traffic (packets) on a mesh topology can follow two different methods:
Routing - devices are given routing logic (act like a router) to ensure packets are sent to the correct device in the shortest route
Flooding - all packets are sent to all devices using no routing logic, this can lead to network flooding causing performance issues
Mesh topology - advantages vs disadvantages
Advantages | Disadvantages |
|---|---|
If one cable fails, the network still works – data can use an alternate route | Requires lots of hardware, cables, and switches |
Provides high fault tolerance – multiple paths for data to travel | High cost to set up due to the amount of equipment needed |
Very reliable – good for critical systems | Hard to scale – adding new devices is more complex than in a star topology |
A partial mesh topology is often used as a more practical and cost-effective alternative |
Hybrid
What is a hybrid topology?
A hybrid topology is a mix of two of more different network topologies
For example, bus & star, star & mesh etc
A typical use of a hybrid topology would be when there is a need to join different networks together
Imagine a large education trust takes over three schools: School A, School B, and School C.
School A uses a bus topology to connect classroom computers with a simple shared cable
School B uses a star topology to link all devices to a central switch in the IT room
School C uses a mesh topology to make sure every building (e.g. science block, library) stays connected, even if one cable fails
When the trust wants to connect all three schools into a single network, it uses a hybrid topology
This allows:
Each school to keep its own existing setup (bus, star, or mesh)
The schools to be linked together efficiently
Easy expansion, such as adding a new school or admin office without changing everything
The network to be more flexible and reliable, using the strengths of each topology
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