Network Topologies

= Network Topologies =

The topology is the physical and logical network layout. The physical topology define the way the computer are connected, the logical one define the way the data travel in the network. They are some common topologies: bus, ring, star, mesh and wireless.

The bus topology
This bus topology consists of a linear cable called a trunk to which all the computers on the network connect. Data is sent to all the computers. Each computer examines every packet on the wire to determine who the packet is for and accepts only messages addressed to them. The advantages of the topology is cheap, easy to implement and to extend. There are less number of cable than for other topology. However, the topology becomes slow when there is a lot of device because networks do not coordinate with each other to reserve times to transmit.

The ring topology
In this configuration, the computers are connected on a single circle of cable. Each computer, when he receives a message, acts as repeater. That keeps the signal strong. One device cannot monopolize the network. The network

continue to function after the capacity is exceeded but the speed will be slow. There are some disadvantages. Indeed, the failure of one device can affect the whole network and then it’s difficult to troubleshoot. Adding and removing devices disrupts the network.

The star topology
Star is a basic computer network topology. Here, the devices are connected with a connection point-to-point to a centralized device, called hub. The hub acts like a signal repeater. This topology is used by the Wi-Fi/IEEE 802.11- based products.

There are some advantages for this topology:

-         The failure of a single device doesn’t bring down the entire network

-         The topology is easy to design and to implement

-         It is simple to add a node

-         The centralized networking equipment can reduce costs in the long run by making network management much easier

There also are disadvantages:

-         If the central device has a problem, it causes the whole network failure

The mesh topology
Each computer connect to every other. There are so a high level of redundancy. In this case, all the nodes relay data in the network. The network can be expanded without disruption to current uses. There are two types of network: a fully connected network and a partially connected network. The wireless mesh networks have a relatively stable topology except for the occasional failure of nodes or addition of new nodes.

=== The fully connected network === It’s a network topology characterized by direct links between all pairs of nodes. If the network has n nodes, it has n*(n-1)/2 direct links. It’s an expensive network. Indeed, there are a lot of connections but you have a high degree

of reliability. It is nearly impossible to do this with a large network.

=== The partially connected mesh topology === In this configuration, a number of nodes is connected to exactly one other node, others are connected to two or more nodes with a point-to-point connection. It uses some of the redundancy of mesh topology which is fully connected,

without its expense and its complexity. That reduces the chance to lose a connection.