Network Topologies: Advantages And Disadvantages

Network topology is the layout pattern (or structure) of the interconnection of the various elements (software and hardware) of the network.

There are two types of topologies

* The physical topology

* Logical Topology

 In this particular lesson, we will focus our attention on the physical topology

II-Physical Topology

I I-1 Definition

The physical topology refers to the physical design of the network, its physical layout or the geometric arrangement of the nodes and the links

There are five basic physical topologies:

*The bus topology

*  The star topology

* The ring topology

* The mesh topology

* The tree topology

a)      The Bus topology

Diagram

As we can see from the diagram, here each node is connected to a single cable which is the bus, also referred to as the backbone.

The T-connectors is used by computers to connect to the main cable.

Explanation

In this network organization, any device which wants to communicate sends the broadcast message to all the devices (through the main cable), but only the intended receiver actually accepts and processes the message. A terminator connected at each end of the main cable eliminates any incoming signal to avoid the reverberation problem.

Advantages

·         It is  topology is not  expensive

·         Easy to setup

 Disadvantages

·          The entire network shuts down if there is any break on the main cable

·         It is very difficult to diagnose a problem when the network shuts down.

b)      The Star Topology

Diagram

It is the most commonly used topology in the LAN.  All the computers are connected at the central point which can be a switch or a hub.

Explanation

In this network organization, any device which wants to communicate sends the broadcast message to the central point which will either forward it to the intended computer (case of the switch) or to all the computers (case of hub).

Advantages

·         It very easy to setup

·         The adding, the removing or the malfunctioning of a computer does not affect the rest of the network

·         It easy to diagnose and maintain

Disadvantages       

·          If the central point has a problem, all the computer are disconnected

·         It requires more cables and extra devices and is therefore expensive

c)      The tree topology

Diagram

 

This is the network pattern that combines the characteristics of a bus and star topology.

Advantages

·          It allows for the expansion of an existing network

·         It is supported by several software and hardware vendors

Disadvantages

·         If the backbone  line breaks, the entire segment goes down

·         It is difficult to configure and wire

d)      The Ring topology

Diagram

This is a network topology whereby all devices are connected to one another in the shape of closed loop (ring) so that each device is directly connected to two others devices, one on either side.

Explanation

Messages flow in one direction. Since there is only one path way between two nodes and the message is conveyed through a token ring.

Advantages

·          The transfer of data is fairly simple since it travels only in one direction.

·         No data collision

·         Very high transmission rates are possible

·         Extra computer can be added without any little disturbance of the network, but it must shut down.

Disadvantages

·         If a single link fails, the entire network is disrupted.
(This problem is solved by adding a second ring)

·         The downfall of a single node causes the downfall of the whole network

·         Data must pass through every computer until it reaches the destination

·         Difficult to troubleshoot

 Line topology - This rare topology works by connecting every host to the host located to the right of it. Most networking professionals do not even regard this as an actual topology, as it is very expensive (due to its cabling requirements) and due to the fact that it is much more practical to connect the hosts on either end to form a ring topology, which is much cheaper and more efficient.

Diagram

e) The Mesh topology

Diagram

 It is view as the combination of the above (bus, star, ring)

Advantages

·         If any cable fails, there are many other ways for two nodes to communicate

·         Mesh topology are installed where fault tolerance is important

Disadvantages

·         It is very expensive to wire up

·         It is difficult to install