Network Topologies

What is a Topology?

There are two main types of topologies – physical and logical topologies. The physical topology of a network has to do with the configuration of computers, cables and other computer peripherals. On the other hand logical topology is the system used to pass information between computers.

Basic Types of Physical Topologies

Below are four basic types of physical topology:
Bus
Star
Ring
Mesh

Bus Topology

A bus topology is sometimes called a linear bus topology; this is because it consists of one major run of cable or a communication line. All the nodes are connected to this one cable by the means of drop lines which are shorter cables that connect each device to the bus cable or the backbone. At each end of the major cable is a terminator which serves as a resister, which absorbs signals from bouncing back on the network, thereby preventing reflections. The physical and the logical topology of a bus behave in the same way.

Star Topology

Data on the star network passes through the hub or the switch. Each node on a star is connected directly to the central hub or switch. The physical and the logical topology of the star behave in the same way. The topology looks like a star and behaves like a star.

Ring Topology

The ring topology is also known as the Cambridge ring. The nodes are connected to a single circle of cable, data flows around the ring in one direction. The signal travels around the circle or ring.

The physical and the logical ring behave in the same way. A variation to this is the IMB token ring. The physical and the logical topology of an IMB token ring do not behave in the same way.

The physical topology is a star topology, in which case all the devices attached to the network are connected a device called MAU (Multistation Access Unit), the token is however passed internally using a logical ring.

Mesh Topology

In a Mesh topology, each node is connected physically to another by a separate cable. This provides multiple paths through the network. If one cable breaks there is always another way for data to be transferred over the network.

Number of Cable links in a Topology

Bus

The number of cable links in a bus topology may be calculated using n, where:
n = number of device(s) connected to the network.

This may be calculated as:

The number of links = 1(bus) + n drop lines
If a network with a bus topology has six devices connected to it then

Number of links = 1(bus) + 6 drop lines. 

Star

The number of cable links in a star topology may be calculated using n, where:
N = number of devices connected to the network.
Unlike the bus, the star has no central cable; all devices are connected to a hub.

The number of cable links in a star topology = n

If n = 6 then the number of cable links is simply 6

Ring

The number of cable link in a ring topology is calculated in the same way as the Star, this is similar because a ring those not have a central cable.

The number of cable links in a ring topology = n

If n = 6 then the number of cable links is simply 6

Mesh

The number of cable links in a Mesh topology may be calculated using n, where:
n = number of device(s) connected to the network.

All the devices in a mesh network are connected to the other; however, the links are dedicated in that the link only transmits traffic between the two devices it is connected to.

The formula becomes n (n-1)/2 physical channels.
Where n = number of devices on the network,
n-1 input/output (I/O) ports with 2 physical channels linking to n.
If 6 devices are connected to the network, then:
N= 6
The number of cable links = 6(6-1)/2 = 6(5)/2 = 15 cable links