Networks and Topologies
What Is a Computer Network?
A computer network is formed whenever two or more devices are connected so they can communicate. Networks are everywhere — your school uses one to share printers and the internet connection; hospitals use them to access patient records; banks rely on them to process transactions in real time. Understanding how networks are structured is a core part of GCSE Computer Science.
Characteristics of Networks
All networks share a common set of characteristics that define how they work and what they can do:
- Shared resources — devices on a network can share hardware (printers, scanners), software (licences), and internet connections, reducing cost.
- Communication — users can send messages and files directly to each other through email, messaging apps and shared drives.
- Centralised storage — files saved to a network server can be accessed from any device on the network, making collaboration easier.
- Security management — a network administrator can apply security policies, manage user accounts and monitor activity across all connected devices from one place.
The main advantages of networking are shared resources (hardware and internet), centralised data storage, easier communication between users, and the ability to apply security policies across all devices from one central point.
Network Topologies
A network topology describes the layout of a network — how devices are physically connected and how data travels between them. The four topologies you must know for your exam are star, mesh, ring and bus.
Star Topology
In a star topology, every device connects directly to a central switch or hub. Data from any device travels to the switch first, which then forwards it to the correct destination.
Advantages of star topology:
- If one cable or device fails, the rest of the network keeps working — the fault is isolated.
- Performance is consistent because each device has a dedicated link to the switch; one device’s traffic does not slow down another’s.
- Adding new devices is straightforward — just plug another cable into the switch.
Disadvantages of star topology:
- The central switch is a single point of failure — if it breaks, the entire network goes down.
- More cabling is needed than in some other topologies, which increases cost.
- The switch itself represents an additional hardware cost.
Star topology is the most common choice for modern wired networks in schools, offices and homes.
Mesh Topology
In a mesh topology, every device connects to multiple other devices, creating redundant paths for data. A full mesh connects every device to every other device; a partial mesh connects most devices but not all.
Advantages of mesh topology:
- Highly reliable — if one path fails, data is automatically rerouted through another path.
- There is no single point of failure, making mesh networks ideal for critical systems.
- Data can travel across multiple routes simultaneously, increasing throughput.
Disadvantages of mesh topology:
- Very expensive to install — a full mesh of ten devices requires 45 cables.
- Complex to manage and configure, especially as the network grows.
Star topology relies on a central switch and is easy to manage but has a single point of failure at the switch. Mesh topology is highly reliable with no single point of failure but is expensive to cable and complex to manage.
In a ring topology, devices are connected in a closed loop. Data travels around the ring in one direction (or both directions in a dual ring), passing through each device until it reaches its destination.
Advantages of ring topology:
- Data flows in an orderly manner — each device gets a turn to transmit, preventing collisions.
- Performance is predictable and degrades gradually rather than suddenly as more devices are added.
Disadvantages of ring topology:
- If one device or cable in the ring fails, the entire network is disrupted (unless a dual ring is used).
- Adding or removing a device requires temporarily breaking the ring, causing downtime.
- Data must travel through every intermediate device before reaching its destination, which can be slow on large networks.
Ring topology is rarely used in modern networks but remains a common exam topic.
In a bus topology, all devices connect to a single shared cable called the backbone. Data broadcast by any device travels along the entire cable and is read by all other devices, but only the intended recipient processes it. Terminators at each end of the cable absorb signals and prevent them from bouncing back.
Advantages of bus topology:
- Simple and cheap to install — uses a single backbone cable.
- Easy to extend by adding more devices to the backbone.
Disadvantages of bus topology:
- If the backbone cable fails, the entire network stops working.
- All devices share the same cable, so only one device can transmit at a time — heavy traffic causes collisions and slows the network significantly.
- Performance degrades quickly as more devices are added.
Bus topology was common in early Ethernet networks but has been replaced by star topology in most modern installations.
Comparing the Four Topologies
When exam questions ask you to compare topologies, focus on three criteria: fault tolerance, cost and scalability.
| Topology | Fault tolerance | Cost | Scalability |
|---|---|---|---|
| Star | High (switch fail only) | Medium | Good |
| Mesh | Very high | High | Poor (cabling) |
| Ring | Low (one break halts all) | Low–medium | Poor (needs downtime) |
| Bus | Low (backbone break halts all) | Low | Poor (collisions increase) |