# Network Topology

A topology is the physical structure of the network using different types of connection. In this article, you will learn about network topologies such as mesh, star, ring, and bus topology.

A network is two or more devices connected through links where the link transfers data from one device to another.

The link connects the devices and they are of two types:

## Point-to-point connection

This type of connection has a dedicated link between two devices. The devices use the entire capacity of the link.

Example,

TV remote control use infrared to control TV.

## Multipoint or Multidrop connection

More than two devices are connected to the link. The capacity of the link is either spatially shared(simultaneously connected) or time-shared (take a turn to use the link).

## Network Topologies

A network topology defines the physical structure of the network. Here is a list of network topologies.

1. Mesh
2. Star
3. Bus
4. Ring
5. Hybrid

### Mesh Topology

The mesh topology consists of a point-to-point connection between every device using a dedicated link. If there are n nodes in the network, then it makes n (n-1) / 2 duplex links.

• If one link fails in a mesh that will not cause the whole network failure. Only that link is affected.
• The point-to-point connection makes fault identification easier and ensures the proper delivery of the packets.

• The mesh network uses too many ports that make it expensive.
• Too many cables make it difficult to implement this network, therefore, a mesh is only required when the network is closed or requires high availability. Example, telephone regional offices are connected through the mesh.

### Star Topology

The star topology makes a point-to-point connection to a hub device. The hub exchange data on behalf of the devices.

The star topology is not expensive because of less number of cables and ports required as compared to mesh.
A failure of one link in star topology does not fail the whole network. Only that link is failed.
The number of ports on devices is also less as compared with a mesh topology.

If the hub device goes down or becomes faulty, the entire network goes down.

Example,

This type of topology is used in LAN (Local Area Network).

### Bus Topology

The bus topology uses a multipoint connection, and all devices are connected to a backbone link in the network. The backbone is one long cable to which nodes are connected using droplines and taps. A dropline is a connection between the device and the backbone. A Tap is a connector that creates contact with the metallic core of the backbone.

• A bus topology is easy to install. It uses less cabling because only backbone and droplines are required.
• A new device installation requires changing backbone because it may not be of sufficient length.

• The backbone signals become weaker and weaker towards the other end of the cable as it travels some distance.
• There is a limit to the number of devices a bus topology can support due to backbone capacity.
• Failure at any point in the network can cause complete failure of the network.
• Fault isolation is difficult.

Example, early LANs were bus topology networks.

### Ring Topology

A ring topology appears like a ring where a single device is connected using point-to-point on either side. A single pass from one direction in the ring until it reaches its destination.

Each device has a repeater, if the message intended for another device, then the repeater regenrates it and passes it to the next device. Otherwise, it accepts it.

• Easy installation and fewer cables.
• In a ring topology, fault isolation is easy. When a repeater not working an alarm can alert a network administrator with a location.
• Adding new device is easy because you only need two connections on either side of the device.

• The only difficulty with ring topology is that a single device failure can cause the whole network to go down.

### Hybrid Topology

A hybrid topology is made of a combination of two or more network topologies.

Consider the above example, star topology and each connection of star can be a bus network.