Star Topology

In this Star Topology the computers which are there in the computer network are connected to a central point. This central point can be a network device like Hub or Switch. Any computer whichever wants to send some data packet, send the packet to the central location and then it is distributed to the destination computer/s. If Hub is used at the central location then it will not filter the network traffic and it sends the packet to all the computers which are connected to it. But only that machine whose address matches with the destination address came along with the packet accepts that packet.

Animation Lesson on Star Topology

What is this address and who places it in the Packet?

When you want to send some letter to some one you write the 'To' and 'From' address. Similrly when a packet of data is sent out by a computer on the network it places the address of the destination machine and it's own address in the packet. A computer network which follows TCP/IP standard to send and receive the data packets uses two different addresses which are placed in the packet which is sent out on the network. One is IP (Internet Protocol) address placed by the Network Layer and other is the MAC (Media Access Control) address placed by the Data Link layer. IP address is the logical address and MAC is the physical address present in the Network Interface card.

When a packet sent by one computer reaches the Central point, say we have Hub there then the packet is sent to every computer which is connected to the Hub. Each of the machines receive the packet and check it's MAC address with destination MAC address which has come along with the packet and if matches then the packet is sent to the next layer that is the Network Layer. Here it checks whether it's IP address matches with the destination IP address came along with the packet and if so the machine understands that the packet is for it and it accepts. If any one or none of the address match, the packet is rejected by the machine. Thus only that machine accepts the packet whose physical as well as logical address has matched.

You can see in this Star Topology animation that when the packet color is green that means the packet belongs to that machine and it accepts and all other machines rejects it.

The advantage in this Star Topology is that all the machines in the network need not be up and running all the time for the network to work. The network fails if the central networking device fails.

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