Network topologies: bus, star, ring, mesh, tree, hybrid and the hierarchical model
In short: A topology is the layout of a network. The physical topology is how devices are cabled; the logical topology is how data actually flows. Star and tree (hierarchical) layouts dominate today because they are easy to manage and grow.
What is a topology?
A network topology describes how devices are connected and how data moves between them. It applies to computers in a LAN, routers in a WAN or links between sites. There are two views:
- Physical topology: how the cables and devices are actually laid out.
- Logical topology: the path the data takes, which can differ from the physical layout. See Ethernet, VLANs and Token Ring.
Bus
All devices share one cable. Each end has a terminator that absorbs the signal so it doesn't bounce back. Because everyone shares the cable, devices must take turns (Ethernet used CSMA/CD for this). One failed PC doesn't affect the others, but a break in the main cable stops everyone. Cheap, but obsolete for LANs.
Star
Every device connects to a central device, today a switch. It is the most common LAN layout: adding a device needs only one more cable, faults are easy to isolate and one broken cable affects only one device. The weakness is the centre: if the switch fails, everything connected to it loses connectivity. An extended star connects several stars together.
Ring
Each device connects to exactly two neighbours, forming a circle; data passes through the devices in between to reach its destination. Adding a device needs one extra cable, but in a simple ring one failure breaks the whole ring. A dual ring adds a second ring in the opposite direction as a backup, a design still used in some fibre and industrial networks.
Mesh
Devices have point-to-point links to several or all other devices and can relay traffic for each other.
- Full mesh: every device links to every other. It is the most reliable design, but the number of links grows fast: n(n − 1) ÷ 2. For 5 devices that's 10 links; for 20 devices, 190.
- Partial mesh: only the important devices get extra links. A common choice for WAN cores and data centres.
Tree (hierarchical)
A tree joins several stars in levels branching from a root, combining star and bus ideas. It is the most common layout in organisations today. If a higher-level link fails, everything below it is cut off, which is why important links are doubled.
Campus networks are usually built in three layers:
- Access layer: switches and access points that end devices connect to.
- Distribution layer: joins access switches, routes between VLANs and applies policies.
- Core layer: a high-speed backbone joining the distribution layer and the data centre.
Smaller sites often merge core and distribution into a collapsed core.
Hybrid
A hybrid combines two or more topologies, for example star-wired offices joined by a fibre ring between buildings. Most large networks are hybrids.
| Topology | Strength | Weakness |
|---|---|---|
| Bus | Very little cable | Cable break stops all; collisions |
| Star | Easy to add devices and find faults | Central switch is a single point of failure |
| Ring | Orderly, predictable traffic | One failure can break the ring (unless dual) |
| Mesh | Most reliable, many paths | Expensive, many links |
| Tree | Scales well, easy to manage in layers | Upper links are critical |
Practice
How many links does a full mesh of 6 devices need?
Which topology is used in almost every office LAN today, and what is its weak point?
Name the three layers of the hierarchical model.
Key takeaways
- Physical topology is the cabling; logical topology is how data flows.
- Bus and ring are mostly historical for LANs; star and tree dominate today.
- Full mesh needs n(n−1)/2 links; partial mesh protects only key devices.
- Real networks use the access, distribution and core hierarchy, with redundant links.
Original content written by Mohamed Fayas for FM TecHub. © 2026 FM TecHub. You're welcome to share a link to this page; please don't copy the text elsewhere without permission.