Topology refers to the way in which the network of computers is connected. Each topology is suited to specific tasks and has its own advantages and disadvantages. The choice of topology is dependent upon type and number of equipment being used, planned applications and rate of data transfer required, response time, and cost. Topology can also be defined as the geometrically interconnection pattern by which the stations (nodes/computers) are connected using suitable transmission media (which can be point-to-point and broadcast).There is four basic topologies as follows:

Basic Topologies

Other than above there are Tree and Hybrid Topology

1. Mesh Topology: In this topology, every device has a dedicated point to point link to every other device.

Advantages:

• It eliminates traffic problems that occurs when links must be shared by multiple devices
• It is robust and makes fault identification and fault isolation easy.

Disadvantages:

• Installation and reconnection are difficult.
• The share bulk of wiring can be greater than the available space can accommodate
• The hardware required to connect each links (I/O ports and cable) can be prohibitively expensive.

2. Star Topology: In this topology, each device has a dedicated point-to-point link only to a central controller usually called a hub. Unlike a mesh topology a star topology does not allow direct traffic between devices, Controller acts as on Exchange.

Advantages:

• Less expensive than mesh topology as it requires less cabling
• Easy to install and reconfigure

Disadvantages:

• More cabling required as compared to bus or ring topology
• One of the biggest disadvantages of a star topology is the dependency of the whole topology on one single point, the hub, if the hub goes down, the whole system is dead.

3. Bus Topology

i. Bus Topology is by far the simplest topology used. There is a common linear transmission medium called the Bus to which all the stations attach as shown in Figure

ii. In bus topology, all nodes connect through a hardware interface called Tap. Drop lines provide connectivity between the common linear communication medium, the Tap and the nodes.

iii. Bus topology supports Full- Duplex mode of transmission. The nodes communicate with other nodes in the network through the Tap.

iv. Taps allow data transmission from the nodes to the bus and from the bus to the nodes. A transmission from a node propagates throughout the entire length of the medium. A transmission from a node reaches all other nodes in a bus network. A terminator is located at both the ends of the linear medium.

Advantages:

• Fault isolation and identification is easy
• Easy to re-configure.

Disadvantages:

• Data intended for a node reaches all the other nodes in the network before reaching the destination.

  A mechanism must be in place to regulate traffic.