Network topologies

A network's topology is the arrangement of its computers, devices and cables. Each arrangement has its strengths and weaknesses.

• Mesh: every node is linked directly to every other node. With n nodes, this needs n(n − 1)/2 cables. It is very reliable and secure (if one link fails, data takes another route), but costly and complicated to wire.
• Ring: each node is linked to its two neighbours, forming a circle, and data travels around it in one direction. A break anywhere can stop the network.
• Bus: all nodes connect to one shared cable, the backbone. It is cheap and easy to install, but less reliable: a fault in the backbone stops everything, and only one node can send at a time.
• Star: every node connects to a central hub or switch. If one node fails, the others are unaffected, and faults are easy to find. But if the centre fails, the whole network stops.
• Tree (or hybrid): branches of stars, rings or buses joined into a hierarchy. It is used to build large networks such as WANs.

To compare topologies, count the cables needed, and find the weak point: the one failure that would bring the network down.