Network Topologies
A network topology describes how devices are physically or logically connected in a network. The topology affects performance, reliability, and cost. The Edexcel 4CP0 spec covers four topologies: bus, ring, star, and mesh.
Bus Topology
All devices connect to a single shared cable called the backbone. Data travels along the bus in both directions. Terminators at each end prevent signals from bouncing back.
- Advantage: Simple, cheap to set up — uses little cable
- Disadvantage: If the backbone cable fails, the entire network fails
- Disadvantage: All devices share the same bandwidth — performance degrades with more devices
- Disadvantage: Data collisions occur when two devices transmit simultaneously
- Largely obsolete in modern networks
Ring Topology
Each device connects to exactly two others, forming a closed loop. Data travels in one direction around the ring, passing through each device until it reaches the destination.
- Advantage: No data collisions — devices take turns to transmit (token passing)
- Advantage: Performance remains consistent as more devices are added
- Disadvantage: If any single device or connection fails, the whole network fails (unless dual-ring)
- Disadvantage: Adding or removing devices disrupts the ring
Star Topology
All devices connect to a central switch or hub. All data passes through the central device. This is the most common topology in modern LANs.
- Advantage: If one device or cable fails, only that device is affected — the rest of the network continues
- Advantage: Easy to add or remove devices without disrupting the network
- Advantage: Centralised management — easier to monitor and secure
- Disadvantage: If the central switch fails, the entire network fails
- Disadvantage: Requires more cable than bus topology; central switch adds cost
Mesh Topology
Every device connects directly to every other device (full mesh) or to several others (partial mesh). Used in WANs and high-reliability networks.
- Advantage: Highly reliable — multiple paths mean the network can reroute around a failure
- Advantage: No single point of failure
- Disadvantage: Expensive — requires a large amount of cable/connections
- Disadvantage: Complex to set up and manage
- Used in the internet's backbone infrastructure
Topology Comparison
| Topology | Single point of failure? | Cost | Ease of setup | Common use |
|---|
| Bus | Yes (backbone) | Very low | Easy | Obsolete |
| Ring | Yes (any node) | Low | Moderate | Some older LANs |
| Star | Yes (central switch) | Moderate | Easy | Modern school/office LAN |
| Mesh | No | High | Complex | Internet backbone, military |
📝 Exam Tip: Star topology is the most commonly examined. Know that a star network uses a central switch, not a hub. If the switch fails, the whole network fails — this is its main weakness. For a question asking which topology is most fault-tolerant, the answer is mesh.
⚠️ Common Mistakes
- Saying star topology has no single point of failure — the central switch is a single point of failure
- Confusing ring and bus — ring forms a loop (each device has two connections); bus is a single shared cable
- Saying mesh is cheap — full mesh is very expensive due to the large number of connections required