Why do we need network topology? Explain star topology along with its merits and demerits.

A network topology is the arrangement of devices (nodes) and links in a network. It is needed because it decides:

• how devices are connected and how data travels between them,
• the cost of cabling and equipment,
• how the network performs and scales as devices are added,
• how easy it is to find and fix faults, and how a failure affects the rest of the network.

Common topologies are bus, ring, star, mesh, tree and hybrid.

Star topology

In a star topology every device is connected by its own cable to a central device, a hub or (today) a switch. Devices never talk to each other directly: all traffic passes through the centre.

        PC1
         |
 PC4 -- SWITCH -- PC2
         |
        PC3

Merits

• Easy to install, and a new device is added by running one cable to the switch.
• The failure of one cable or device affects only that device.
• Faults are easy to find, because each link can be checked on its own.
• With a switch, performance is good because devices do not share one cable.
• Centralised management and monitoring.

Demerits

• The whole network depends on the central device: if the hub or switch fails, every device is cut off.
• Needs more cable than a bus topology.
• Extra cost for the hub or switch.
• The number of devices is limited by the ports on the central device.

It is the most common topology in LANs, such as a college computer lab.