For the last two decades, there has been a tremendous growth in the field of communication, called networking. Networking allows the sharing of computers, peripherals, software, and network devices through transmission media. Networks have a physical layout similar to a city in which transmission media are analogous to streets or roads, and computers, peripherals or network devices are analogous to houses or buildings.

The best way to understand a network is through its topology. Network topology defines the connectivity arrangement of cables and network devices (e.g. computers, printers, patch panels, hubs, bridges, switches and routers) that make up a network. Network topology comprises the following two topologies:

• Physical topology: It defines the actual layout of the transmission media used to connect the network.

• Logical topology: It defines the actual path followed by a signal when it passes through the transmission media and network devices.

Physical topology versus Logical topology

The best way to remember the distinction between these two topologies is that a physical topology describes the way the network looks and a logical topology defines the way the data travels through the network devices.

Most Common Network topologies
The most common network topologies are listed below:

•  Bus topology
•  Star topology
•  Ring topology
•  Mesh topology
•  Hybrid topology

It is important to note that a network may have one type of physical topology but a different type of logical topology. For example, Ethernet 10base-T networks use a star physical topology but they use a bus logical topology. On the other hand, Token Ring networks use a star physical topology and a ring logical topology.


A bus topology is best described as common and shared cable to which all devices connect to make a network as shown in figure. This shared cable is sometimes called backbone cable.

Most common network architecture named Ethernet uses bus topology as a physical topology in 10base-2 or 10base-5 networks and as a logical topology in the most popular 10base-T Ethernet networks.


A star physical topology allows all the computers and network devices to be connected to a central device like hub or MAU through transmission media. However, path followed by data while passing through the central device (the logical topology) depends on the design of the central device. Inter-connection of star topology networks forms a topology called extended star network topology. Star topology is shown in following figure


Ring topology connects network devices and transmission media in a circle. Each device is connected to its neighbours on both sides and data passes along the ring only in one direction. Ring topology networks require central devices like Multi-station Access Units (MAUs) or concentrators. That’s why it is more expensive to implement than the bus topology. The ring topology is usually implemented as a logical topology. Token ring is a first token-passing network that uses logical ring topology. It connects all the devices to a central device (physical star), but data travels along a logical ring. Ring Topology is shown in the following figure

In mesh topology, each device is directly connected to all the other devices on the network. To add a new device to the network, a connection to all existing devices must be made. This is the main advantage of mesh topology, as it provides a great deal of fault tolerance. If any transmission media breaks, data can be transferred through alternative paths. However, the disadvantage of this topology is that it needs more cables and most expensive to implement. The following figure shows Mesh topology:



The topology that combines more than one topology is called hybrid topology. This topology is used to connect a network that is divided into smaller sections also known as segments. You may need to use a reliable topology for one particular segment and an inexpensive topology for the rest of the segments. In this case you can implement a hybrid topology. Most commonly, hybrid topology is the combination of star and ring topologies. Another example of hybrid topology is the combination of star and bus topologies where hubs of each star topology are connected together using bus topology. The following figure describes hybrid topology: