Network Topologies

A network topology is the physical or logical arrangement in which the computers and devices of a network are connected together — the "shape" or layout of the network. The choice of topology affects the cost of cabling, the speed, and what happens if one link or computer fails. The common topologies are bus, star, ring, mesh, and tree.

1. Bus topology. In a bus topology all computers are connected to a single main cable called the backbone, with a terminator at each end. Data sent by any computer travels along the backbone, and the computer it is addressed to picks it up. It uses the least cable and is cheap and easy to set up for a small network, but if the backbone cable breaks, the whole network fails, and performance drops as more computers are added.

2. Star topology. In a star topology every computer is connected by its own separate cable to a central device — a hub or a switch. All data passes through this central device. A star is easy to set up and manage, and if one cable or computer fails, the rest keep working; but it needs more cable, and if the central device fails, the whole network fails. The star is the most common topology in modern LANs.

3. Ring topology. In a ring topology the computers are connected in a closed loop, each joined to the next, so data travels around the ring in one direction from computer to computer until it reaches its destination. It can handle steady traffic well, but a break in the ring or the failure of one computer can disturb the whole network (unless a double ring is used).

4. Mesh topology. In a mesh topology every computer is connected directly to every other computer. This gives many alternative paths for data, so it is very reliable — if one link fails, data can take another route — and secure. Its drawback is that it needs a very large amount of cabling and is expensive and complex, so it is used mainly where reliability matters most.

5. Tree topology. A tree topology is a hierarchy shaped like a tree: a central root node connects to several hub nodes, and each of those connects to further computers, combining features of the star and bus. It suits large networks that need to be organised in levels, but if a higher-level node fails, the whole branch below it is cut off.