Network Topologies: Bus, Star, Ring, Tree and Mesh

Hello students, welcome to Kwickprep. In one office, a single broken cable stops every computer. In another office, nobody even notices. Why? The answer is topology. Today we will learn bus, star, ring, tree and mesh, what happens when a link fails, and how to choose one.

First, the meaning. A topology is the layout, or the shape, in which the devices of a network are connected. A node is any device on the network, like a computer or a printer. A link is the cable or wireless path joining two nodes. So topology is simply the pattern of nodes and links.

Let us draw the first shape, the bus. In a bus topology, every node is attached to one long main cable, called the backbone. A small device called a terminator sits at each end, so the signal does not bounce back. Data sent by one node travels along the whole cable, and every node sees it, but only the right node accepts it. Picture houses along one village road, all sharing the same road.

The second shape is the star. In a star topology, every node has its own separate cable to one central device. That central device is a hub or a switch, which passes data between nodes. This is the most common layout in school labs and offices today. Picture the spokes of a bicycle wheel, all meeting at the centre.

The third shape is the ring. In a ring topology, each node is connected to exactly two neighbours, one on each side. The links form a closed circle. Data travels around the ring from one node to the next, until it reaches the right one. Picture children in a circle playing passing the parcel.

The fourth shape is the tree, also called hierarchical topology. It joins several star networks in levels, like the branches of a tree. A central device at the top, the root, connects to smaller stars below it. To grow the network, you simply add a new branch. Picture a school: the principal at the top, then departments, then classes under each department.

The fifth shape is the mesh. In a mesh topology, nodes are joined by many links, so data has many possible paths. In a full mesh, every node is linked directly to every other node. Each of four computers links to the other three, that is twelve links. But each link is counted twice, so a full mesh of four needs six links. Picture roads that join every city directly to every other city.

Let us see all five together. Bus is one straight line, and everything depends on the backbone cable. Star looks like spokes, and depends on the hub or switch. Ring is a circle with no centre. Tree is branches, with a root device at the top. Mesh is a web of links, also with no centre.

Now the big question: what happens when something fails? If the backbone of a bus breaks, the whole bus network stops. In a star, one broken cable cuts off just one node. But if the central hub fails, the whole star stops. In a simple ring, one broken link stops data going around, so the ring stops. In a tree, a cut branch disconnects only the nodes below it. In a mesh, data simply takes another path, so the network keeps working.

Pause and predict. A star network has ten computers, and the cable of one computer is cut. How many computers can still talk to each other? The answer is nine, because in a star, each computer has its own cable, so only that one computer is cut off.

Now let us weigh advantages and disadvantages. A bus uses the least cable, so it is cheap, but a fault in the backbone stops everything. It is easy to add a node to a bus, but it slows down when many nodes send data. A star makes faults easy to find, but if the hub fails, the whole network fails. In a star, adding or removing a node is easy, but it needs more cable than a bus.

Here are the other three. A ring avoids data collisions, which means two signals clashing, because data moves in order, but one break can stop the whole ring. A tree is easy to expand branch by branch, but if the root fails, the branches cannot reach each other. A mesh is very reliable, because there are many paths, but it needs the most cable and is costly. Mesh links can also be private between two nodes, but setting it up is hard.

Now let us choose a topology for a situation. For a school computer lab, choose star, because faults are easy to find and computers are easy to add. For a small, temporary setup with little budget, a bus uses the least cable. For a company with many floors or departments, choose tree, because each floor becomes a branch. For links between bank data centres, choose mesh, because the network must never stop.

In exam case studies, ask three questions before choosing. First, how much money is available, because more cable costs more. Second, how many nodes are there, and will the network grow later? Third, how serious is a breakdown, since a hospital or bank cannot afford to stop.

Let us revise what we learned today. A bus uses one backbone, and a break in it stops everything. A star uses a central hub, and one cut cable affects only one node. A ring is a closed circle, where one break can stop the whole network. A tree joins stars in levels, and a cut branch is isolated from the rest. A mesh has many paths, so it is the most reliable, but also the most costly.