network-topologies

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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

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A bus topology has been replaced by much more efficient network topologies such as the star topology

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)

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

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)

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

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

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

Advantages	Disadvantages
Combines the strengths of multiple topologies (e.g. reliability of mesh, simplicity of bus)	Complex to design – needs careful planning to combine different topologies
Flexible – different parts of the network can be optimised for different needs	Expensive – more hardware and maintenance may be needed
Scalable – new segments (e.g. a new site or building) can be added without changing the whole setup	Troubleshooting can be harder – different parts use different systems and rules
Reliable – failures in one part don’t necessarily affect the rest of the network