Introduction to Topologies

To make networks you can use either of the two connections:
Point-to-point connection
It is a one to one connection where only two devices share a connection.
As there can only be two devices which can share the connection so a level of bandwidth is assured to the user.

Multipoint connection
It is connection where three or more than three computers share the connection and is also called as multi-drop connection.
The bandwidth available for each user depends upon the number of computers on the network accessing the resources and changes drastically depending on the load.
Physical and Logical Topologies
The structure or the layout of the network is called as the topology of the network.
Network Topology is divided into two types:
Physical Topology
It explains the actual physical layout of the network.
Logical Topology
It explains the logical flow of the data through the network.

Star Topology
This is a network in which each PC is connected to a central device like hubs or switches via a point-to-point link.
When a PC sends any data on the network then the central device receives the signals and sends the signals to all the PC's on network which is connected to the central device.
For example star topology is very similar to an EPABX telephone system which is used by most of the corporate companies.
Star Topology

Advantages
It is a commonly used technology and has been previously used in telephone systems.
It is very easy to configure and reconfigure the network settings.
As all the data is sent to a central device it is very easy to manage and maintain the system while at the same time making it easy to locate any problem in the network.
Any problems in the media NIC or workstation are automatically detected and isolated.


Disadvantages
As the network is depended on a central device if the device fails the whole network fails.
You need to keep a spare hub because of this single point of failure (SPOF) of the central device.
It takes up a lot of time to install because you need to install and check each connection point.
Compared to other network topologies it requires more cables.
Star Topology

Backbones
You need backbones when you want to interlink more than one hub together using a single cable.
The backbone cable needs to be capable of higher data transfer speeds than the rest of the network so that the performance of the system is maintained and does not slow down.
For example for a network made up of UTP cables you can use fiber optic cable to maintain the bandwidth as fiber optic cable supports much better transfer speeds than UTP.
It is commonly used to interlink hub situated in different floors of a building or in completely different buildings.

Cascading hubs
It is one of the commonly used methods for using multiple hubs.
The multiple hubs can be linked together by:
Twisted-pair crossover cables - Crossover cables are typically used to connect hubs together but they can also be used for directly connecting two computers together without using a hub.
Some standalone switches have a button on the hub to effect the crossover at a particular point. This allows you to connect to another switch or a hub without using a crossover cable.

Bus Topology
It is a topology in which all nodes are attached directly to the main or backbone cable in a linear method.
The bus needs to be terminated at both ends of the cable so that the signal is reflected back when it has gone through all the devices connected on the network in one direction.
In this network the signal travels in both the direction of the cable.

Advantages
It follows the common standards and is easy to install.
Compared to other network topologies it requires the least amount of network cable.
It is the cheapest of all network topologies.
It is not dependent on any one device for its functioning and works well even if only two computers are running

Disadvantages
Compared to other topologies it is relatively hard to reconfigure.
The signal quality deteriorates with increasing number of PCs thus limiting the no of PCs which can be connected to the network using this topology.
There is also a minimum length limitation of the cable used to connect the PC's otherwise it might create a bottleneck on the network.
It is difficult to troubleshoot cable problem because it can be there anywhere on the segment of the cable.
Unlike star network topology all the other networks share the same problem of media fault as start network which provides terminated network between each device and the hub.

Ring Topology
In this topology the PCs are connected in a circle in a series of point-to-point links between each device.
You can attach the computer directly to the ring or through an intermediary device like Multi-Station Access Unit (MSAU).
In this network a signal generated by one computer is passed from one device to another in a single direction and the signal is regenerated each time at each device.
This topology has been commonly implemented as IBM's token ring and Fiber Distributed Data Interface (FDDI) or Copper Distributed Data Interface (CDDI).
Ring Topology

Advantages
It uses the least amount of cable for networking after Bus Topology.
It is relatively simple to install.
You can make a fault tolerance network by using two ring systems via dual counter rotating rings.
The dual counter rotating rings allow the PCs to avoid a break in the ring.

Disadvantages
Adding or removing a device can affect the network making it difficult to reconfigure the network.
All devices will be affected by media or device failure on the network.
It is difficult to troubleshoot any problems in this topology.
Other Topology

Hybrid-star bus and star ring
You can take the advantage of two different topologies by making a hybrid topology of two different topologies.
You can see the below images to understand how two different topologies can be combined together.
Star Bus
Star Ring

Other Topology

Hierarchical or tree - stars nested with other stars
It is common to use hierarchical topology when the star network grows beyond a certain limitation.
You can see the layout of the topology after it has been put in a hierarchical format.

Mesh
It is the most commonly used topology in Wide Area Networks (WANs) and is often seen in public networks like Internet.
According to mesh network theory every device needs to have a point-to-point connection with every other device on the network.
But in practice this network is used in a hybrid approach with only the most important devices interconnected in the mesh.
This is so because it is impractical to do so in normal condition.
These networks can be used for critical applications like important servers as other computers can take over through other routes using intermediary devices if one of the servers fail.