4.1.8 Network topologies
What Is a Network Topology?
A network topology describes the physical or logical arrangement of devices and the connections between them. The topology chosen affects the network's performance, cost, reliability and ease of management. Three topologies are required at GCSE: bus, star and mesh.
In a bus topology, all devices connect to a single shared cable — the backbone. Data travels in both directions along the backbone; all devices receive every transmission and ignore messages not addressed to them. The ends of the bus are terminated with a resistor to prevent signal reflection.
- Advantages: simple and cheap — only one cable needed; easy to add devices
- Disadvantages: if the backbone cable fails, the entire network goes down; all devices share the same bandwidth — more devices = slower network; data collisions can occur when multiple devices transmit simultaneously; not used in modern LANs
In a star topology, every device connects to a central switch (or hub). All data passes through the central switch, which forwards it only to the intended recipient. This is the standard topology for modern wired and wireless LANs.
- Advantages: if one device or cable fails, only that device is affected — the rest of the network continues; each device has a dedicated connection to the switch (no collisions); easy to add or remove devices; easy to diagnose faults
- Disadvantages: if the central switch fails, the entire network goes down; requires more cable than bus (one cable per device to the switch); cost of the switch
In a mesh topology, every device connects to every other device (full mesh) or multiple devices (partial mesh). There is no single central point — data can be routed via multiple paths.
- Advantages: highly resilient — if one connection or device fails, data reroutes via another path; no single point of failure; good for critical infrastructure
- Disadvantages: very expensive — large amounts of cabling (n devices require n(n−1)/2 connections for full mesh); complex to manage and configure; impractical for large numbers of devices
- Use: internet backbone routing (partial mesh between major routers); wireless mesh networks for extending Wi-Fi coverage
Comparison
| Property | Bus | Star | Mesh |
|---|---|---|---|
| Cable needed | Low | Medium (one per device) | Very high |
| Single point of failure | Backbone cable | Central switch | None (full mesh) |
| Device failure impact | Minor | Minor (only that device) | None |
| Cost | Low | Medium | High |
| Common use | Obsolete in LANs | Standard modern LAN | Internet backbone, critical infrastructure |
Key Takeaways
- Bus: single backbone cable; cheap; backbone failure = entire network down; obsolete.
- Star: central switch; most common modern LAN; switch failure = network down; individual device failures isolated.
- Mesh: multiple redundant paths; no single point of failure; very expensive; used in critical infrastructure.