What is a Network Topology?

When we talk about a topology, we are simply talking about the physical layout or shape of a network. If you look at the computers in your classroom, they are all connected together, but how are those cables actually arranged behind the walls?

To understand this, it helps to think of a computer network like a busy city. There are two ways to think about the layout of this city:


For the rest of this lesson, and whenever you are designing modern networks, we will be focusing purely on the Physical Topology - where we actually plug the cables in and to what! Network Engineers have four main shapes to choose from when building their physical topologies. Let's explore each one.

The History Books

In the early days of computing, hardware and cables were extremely expensive. Network engineers had to find ways to connect computers using as little wire as possible. This led to two topologies that are now largely obsolete and rarely seen in modern practice.

The Bus Topology


In a physical Bus network, all nodes are connected to a single, main central cable called the backbone. In the 1980s, thousands of UK schools used the BBC Micro computer, connected together using a famous system called the Acorn Econet, which was a classic Bus topology. It was incredibly cheap to install, but if that single main cable was cut, the entire classroom's network went down!

The Ring Topology


In a Ring network, each computer is connected to exactly two other computers, forming a closed physical loop. A famous example was the IBM Token Ring, heavily used in corporate offices in the 1980s and 1990s. Data travelled in one direction around the circle. The major flaw? If you turned off one computer, or unplugged one cable, the physical circle was broken and the whole network crashed.

Because of these massive reliability issues, engineers stopped building Bus and Ring networks. They have been replaced by the modern champions: Star and Mesh.

The Modern Standards: Star and Mesh

Today, almost every network you will ever encounter uses either a Star or a Mesh physical topology.

The Star Topology


In a Star network, every single node (computer, printer, etc.) is connected directly to a central piece of hardware, usually a switch. This is what you have in your home and in your school! It requires a lot of cable, but it is incredibly reliable. If one cable breaks, only that specific computer loses its connection; the rest of the school carries on working.

The Mesh Topology


A Mesh network is all about redundancy (having backup routes). In a Full Mesh, every single node is connected directly to every other node - the ultimate design for reliability. If a cable breaks, the data simply routes itself down a different path. Whilst wiring a full wired mesh is too expensive and complicated for most domestic and business situations, it is the underlying concept behind the Internet itself, and the principle is heavily used in modern wireless mesh networks.

Topology Comparison Analysis

As a network architect, you need to know the strengths and weaknesses of all four shapes, even the legacy ones!