Network Topologies (Star, Bus, Mesh, Ring)
A network topology describes the layout or arrangement of devices (called nodes) and connections (called links) in a network. The topology affects the network's performance, reliability and cost.
You need to know four topologies for GCSE Computer Science: star, bus, mesh and ring.
Star Topology
In a star topology, every device is connected to a central switch or hub by its own dedicated cable. All data passes through the central device.
How it works
- Each device has a direct connection to the central switch.
- When Device A wants to send data to Device B, it sends the data to the switch, which then forwards it to Device B.
- The switch uses MAC addresses to direct data to the correct device.
Advantages of star topology
- Fault isolation — if one cable or device fails, the rest of the network continues to work. Only the affected device is disconnected.
- Performance — dedicated connections mean that data collisions are rare (especially with a switch rather than a hub).
- Easy to add devices — new devices can be connected to a spare port on the switch without disrupting the network.
- Centralised management — the switch provides a single point where network traffic can be monitored and managed.
Disadvantages of star topology
- Central point of failure — if the central switch fails, the entire network goes down.
- Cost — more cabling is required because every device needs its own cable to the switch. A switch is also needed, which adds to the expense.
- Cable length — each cable run must reach from the device to the switch, which can be long in large buildings.
Bus Topology
In a bus topology, all devices are connected to a single central cable called the backbone or bus. Each end of the backbone has a terminator to prevent signal reflection.
How it works
- Data is sent along the backbone in both directions.
- All devices on the network see the data, but only the intended recipient processes it.
- Terminators at each end absorb the signal so it does not bounce back.
Advantages of bus topology
- Low cost — uses less cabling than a star topology, and no central switch is needed.
- Simple to set up — easy to install for small networks.
- Easy to extend — additional devices can be connected along the backbone.
Disadvantages of bus topology
- Collisions — because all devices share one cable, data collisions are common, reducing performance as the network grows.
- Single point of failure — if the backbone cable breaks, the entire network fails.
- Limited scalability — performance degrades significantly as more devices are added.
- Difficult to troubleshoot — faults on the backbone can be hard to locate.
- Security — all data is visible to all devices on the bus.
Mesh Topology
In a mesh topology, devices are connected to multiple other devices, providing redundant paths for data.
There are two types:
- Full mesh — every device is connected to every other device.
- Partial mesh — some devices are connected to all others, but some are only connected to a few.
How it works
- Data can take multiple paths to reach its destination.
- If one link fails, data is automatically rerouted through an alternative path.
- Routing algorithms determine the best path for each piece of data.
Advantages of mesh topology
- High reliability — if one connection fails, data can be rerouted. There is no single point of failure.
- High performance — multiple paths mean data can be distributed across links, reducing congestion.
- Robust — the network can handle high volumes of traffic and node failures.
Disadvantages of mesh topology
- Expensive — a full mesh requires a very large number of connections. For n devices, a full mesh needs n(n-1)/2 connections.
- Complex — difficult to set up, manage and maintain.
- Cabling — the amount of cabling required is significant.
Where is mesh topology used?
- The internet uses a partial mesh topology — routers have multiple connections to provide redundancy.
- Military and emergency service networks where reliability is critical.
- Wireless mesh networks used in smart homes and IoT devices.
Ring Topology
In a ring topology, each device is connected to exactly two other devices, forming a closed loop or ring. Data travels around the ring in one direction (or both directions in a dual ring).
How it works
- Data is passed from device to device around the ring.
- Each device receives the data, checks if it is the intended recipient, and either processes it or passes it on.
- A token may be used to control access — only the device holding the token can transmit data (this is called token passing).
Advantages of ring topology
- Equal access — token passing ensures that every device gets a fair opportunity to transmit.
- Predictable performance — performance does not degrade as much as bus topology under heavy load.
- No collisions — the token-passing mechanism prevents data collisions.
Disadvantages of ring topology
- Single point of failure — if one device or cable in the ring fails, the entire network can go down (unless a dual ring is used).
- Difficult to add devices — the ring must be broken temporarily to add or remove a device.
- Slow — data may have to pass through many devices before reaching its destination.
- Troubleshooting — finding faults can be difficult because you have to check each node in sequence.
Comparing Topologies
| Feature | Star | Bus | Mesh | Ring |
|---|
| Central device | Switch/hub | None (backbone) | None | None |
| Fault tolerance | Good (except switch) | Poor | Excellent | Poor |
| Cost | Medium | Low | High | Medium |
| Scalability | Good | Poor | Good | Moderate |
| Performance | Good | Degrades with load | Excellent | Moderate |
| Complexity | Low | Low | High | Low |
Summary
- Star — devices connect to a central switch; most common in modern LANs.
- Bus — all devices share one backbone cable; cheap but unreliable.
- Mesh — devices have multiple connections; very reliable but expensive.
- Ring — devices form a loop; fair access but vulnerable to single failures.
Exam Tip: Be prepared to draw each topology and explain one advantage and one disadvantage of each. Star and mesh are the most commonly asked about.
Deeper dive: choosing a topology with worked examples