A topology is the shape in which machines (nodes) are wired together. The wiring decides the journey every message takes — and the central trade-off is always the same: more links buy fault tolerance, but cost more cabling and complexity.
The four classic shapes
1Bus — every node taps one shared backbone cable. A signal is a broadcast: all nodes hear it, but only the addressee keeps the frame. Cheap, but the shared medium causes collisions and a break in the backbone can split the network.
2Star — every node connects to a central hub (or switch). Easy to wire and add to, but the hub is a single point of failure: if it dies, the whole network goes with it.
3Ring — each node links to two neighbours, forming a loop; messages pass hop by hop around it. A single break can sever the ring unless it's a dual ring.
4Mesh — in a full mesh every node links directly to every other. Maximum fault tolerance from redundant paths, but the cabling explodes.
Count the links
For *n* nodes: a bus needs roughly n − 1 taps, a star needs n links (one per node to the hub), a ring needs n links, and a full mesh needs n(n − 1) / 2. Mesh growth is quadratic — 10 nodes already need 45 links.
How to choose
If cost dominates and a central device is acceptable, a star wins — it's why almost every office LAN is a star around a switch. If survivability dominates and money doesn't, a mesh wins, which is why network backbones and the internet's core are heavily meshed. Bus and pure ring are mostly historical, undone by their shared-medium and single-break weaknesses.
Watch the single point of failure
A star concentrates all risk in the hub. The convenience is real, but so is the blast radius — one hub failure takes down every attached node at once.
