Network Topologies

Network Topologies

First of all I want to describe what a network topology is. A network topology is a structure of connections between computers.

There are three standard topologies:
à BUS - topology
à STAR - topology
à RING - topology

and one structure with which I can mix the standard topologies:
à TREE - topology

BUS - TOPOLOGY

A BUS - topology is the easiest and most common structure. There exists one main cable which is called "Backbone" or "Bus". Every computer in the network is connected to the "Bus" with a so called T - component. At the two ends of the "Bus" are end resistants for the termination. That is important because if a computer signal comes to the end of the bus it would be reflected and the other signals would be overlapped.

Data transmission:
One computer wants to send a message two another computer. It sends the message package and destination address of the computer which sends the message, over the bus. Each computer compares the destination address with his own address. If the address is the same the computer knows that the message is for him. One important fact is that just one computer can send at the same time.

Advantages:
à a BUS - topology is easy to administer

low cable consumption

Disadvantage:
à if the main cable is broken the network breaks down
à just one message can be sent at the same time

STAR - TOPOLOGY

A STAR - topology consists of one central node (e.g. mainframe, HUB) and the workstations. If today someone use a STAR - topology he will use a HUB because it is cheaper than a mainframe. A HUB is a central linking up station which sends the data to terminals. The central point, the heart, of the network is the HUB and each terminal or computer has a connection to the HUB.

Data Transmission:
If one computer sends a message to another computer the transmitter sends the message package with the destination address to the HUB. The HUB is intelligent enough to send the message to the correct computer.

If one computer breaks down it doesn’t affect the other computers and the network doesn’t break down. Only if the HUB breaks down the network can’t work.

Advantage:
à the network doesn’t break down if one computer has a failure

Disadvantages:
à high cable consumption
à if the HUB has a failure the network breaks down

RING - TOPOLOGY

The computers are connected with one cable to a ring - like network. The RING - topology is similar to the BUS - topology because it also has just one cable. There are only differences in the data transmission.

Data Transmission:
If one computer sends a message to another computer the transmitter sends the message with the destination address. Every computer checks the destination address with his own address. If it isn’t the same the computer amplifies the computer signal and sends it to the next computer in the ring structure (in a BUS - topology the computer doesn’t amplifies the signal). If a computer amplifies a computer signal we speak from a active topology. Otherwise, for example the BUS - topology is a passive topology.

Advantage:
à it’s very good for large networks

Disadvantage:
à if one computer has a failure the network breaks down

DOUBLE - RING - TOPOLOGY

This topology is an improvement of the RING - topology. There are two different RING - Topologies, one primary ring and one secondary ring. If one computer has a failure the primary ring and the secondary ring will be connected to on big RING - topology. If a second computer has a failure the two ring systems will be connected like before. Now you have two independent ring systems which are able two work.

TREE - TOPOLOGY

The TREE - topology is used for very large networks. I want to describe this topology with an example of a school network.

The root of the tree is a distributor (e.g. HUB, ...), which connects the various departments in the school. This first connection is called primary connection. Within a department you divide the network, e.g. in floors. This is called secondary connection.
Here I have two possibilities:

Collapsed Backbone: that means that each floor is connected with the building distributor Distributed Backbone: that means that each floor has is own distributor which are connected. Just one distributor is connected to the building distributor

Each floor can be divided in various computer rooms. That’s the tertiary connection.

Advantage:
à you can mix different topologies in one TREE - topology

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