A network is a group of two or more computer systems linked together.

A topology is a usually schematic description of the arrangement of things in a location.

Network topology is the layout of computer, cables and other component on a network. There are many different types of topology and a network may be built using multiple topologies. The different type of a network layout are as follows:

BUS TOPOLOGY

A bus topology use a cable known as a main trunk (backbone, segment) to connect all system together. Bus topology is very easy to set up and requires no additional hardware such as a hub. With bus topology, when a computer send signals, it travels around the cable length in both direction from the send computer. When the signal reaches the end of the cable length, it bounces back and returns to where it comes from. This is known as signal bounce signal bounce is a problem because if another signal is sent on the same cable length, at the same time the signal will COLLIDE and be destroyed and then must be re-transmitted.To prevent this, there is a cable terminator to absorb the signal when it reaches the end to prevent signal bounce.

There are two types of bus topology: Linear Bus Topology and Distributed Bus Topology. In Linear Bus Topology, all nodes of the network are connected to a common transmission medium which has exactly two endpoints. Distributed Bus in which all of the nodes of the network are connected to a common transmission medium which has more than two endpoints that are created by adding branches to the main section of the transmission medium.

Bus topology uses less cable compared to mesh, ring, or the star topology. Making it less costly and also its very Easy to install or set up such a network. The main disadvantage of the bus topology is that it is difficult to troubleshoot, when the network goes down, usually due to break in the network cable segment.

STAR TOPOLOGY

With the star topology all the computers are connected through a central device such as a Hub or a Switch. Each workstation has a cable that goes from the network card to the centralized device. 

One advantage of star topology is the scalability and ease of adding another system to the network thus, connecting that system to an unused port on the centralized device. Another benefit is that if there is break in the cable it affects only the system that is connected to the cable, but does not affect the entire network.

 Some demerits of these topology is that, failure from the centralized device, brings the entire network down and since a centralized device must be present, and also every node needs its own cable to be connected to the network, it makes establishing such networks quite costly.

MESH TOPOLOGY

The mesh topology is not very common in computer networks today. In mesh topology every workstation has a connection to every device present on the network. The mesh network topology employs two schemes called full mesh and partial mesh. In the full mesh topology, each workstation is connected directly to each of the others. In the partial mesh topology, some workstations are connected to all the others, and some are connected only to those other nodes with which they exchange the most data.

Fault tolerance is the main merit of the mesh topology. If there is a break in a cable segment, traffic can be rerouted through a different pathway because there is multiple path way to send data from the system to another. This also makes it impossible for the network to go down due to cable fault.

Mesh topology is very costly due to the connection of cables to every device on the network and the interface to create a multiple pathway between each system. Mesh topology is very hard to administer because of numerous connections.

RING TOPOLOGY

In the ring topology all computers are connected via a cable that loops in a ring or circle. Terminators are not necessary in the ring topology.

Signal degeneration is very low because, each workstation is responsible for regenerating or boosting the signal. With other topologies, as the signal travels the wire, it gets weaker and weaker as a result of outside interference, eventually it becomes unreadable if the destination system is too far away.

In this topology, if one computer fails or the cable link is broken, the entire network will go down, and also cable change to the network or moving a workstation briefly or disconnection can interrupt or bring down the entire network.

HYBRID TOPOLOGY

Hybrid topology is a mixture of other topologies, for example, a very popular hybrid topology is a star-bus topology, in which a number of star topologies are connected by a central bus, as shown in a figure.

 WIRELESS TOPOLOGY

Wireless topology is the one in which few cables are used to connect the systems. The network is made up of transmitters that broadcast the packet using radio frequencies. The network contains special transmitters called cells or wireless access point. This bubble can extend to multiple rooms and possible floor in a building. The PCs and the network has a specials transmitter receiver which allows them to receive broadcast and transmit requested data back to the access point. The access point is connected to a physical network by a cable which allows it, and any wireless client, to communicate with the system on the wired network.

PCs connected to this type of network are mobile due to less cable use. Also troubleshooting failed devices and cells are very easy. Failed components are easy to find and replace.

Disadvantages of wireless topology is a greater chance of signal interference, other devices and machinery that emit radio frequencies or “noise” can cause interference the signal from the access point, and also Blockage can occur in structures that are made of thick stones or metal, which do not allow radio frequencies to pass through them easily there affecting the signal. Another major disadvantage is the signal interception, which means unwanted third parties can intercept wireless without physically being on the premises.

  

These are the types of network topologies we have, there are other types of  topologies for example tree topology,hierarchical topology etc but ,looking at their structures, you would realize that they all fall under hybrid topology.