## Network Topology

The term topology in the context of communication network refers to the way the computers or workstations in the network are linked together.

Topology of a network is the geometric representation of relationship of all the links connecting the nodes.

The physical topology of a network refers to the configuration of cables, computers, and other peripherals.

Logical topology  is the method used to pass information between workstations

The study of network topology uses graph theory. Distances between nodes, physical interconnections, transmission rates, and/or signal types may differ in two networks and yet their topologies may be identical

According to the physical arrangements of workstations and nature of work, there are different  types of network topology

a) Star topology

A star topology is designed with each node connected directly to a central network hub or concentrator

There is bi-directional communication between various nodes.

Data on a star network passes through the hub or concentrator before continuing to its destination.

The hub or concentrator manages and controls all functions of the network that is  the central node controls all the activities of the nodes.

The advantages of the star topology are:

Easy to install and wire.

No disruptions to the network then connecting or removing devices.

Breakdown of one station does not affect any other device on the network.

Easy to detect faults and to remove parts.

The disadvantages of the star topology are:

The major disadvantage of star topology is that failure of the central node disables communication throughout the whole network.

Requires more cable length than a linear topology.

More expensive than linear bus topologies because of the cost of the concentrators

b)  Bus topology
A linear bus topology consists of a main run of cable with a terminator at each end .
All nodes are connected to the linear cable ,i.e. in bus topology all workstations are connected to a single communication line called bus.
In this type of network topology there is no central node as in star topology.
Transmission from any station travels the length of the bus in both directions and can be received by all workstations.
Without the termination, when the signal reaches the end of the wire, it bounces back and travels back up the wire. When a signal echoes back and forth along an unterminated bus, it is called ringing. The terminators absorb the electrical energy and stop the reflections.
Eg.  IEEE 802.4 standard

The advantages of the bus topology are
It is quite easy to set up.

Since the bus topology consists of only one wire, it is rather inexpensive to implement when compared to other topologies. Requires less cable length than a star topology.

If one station of the topology fails it does not affect the entire system.

Thus Bus is easy to use and understand and  inexpensive simple network

The disadvantages of the bus topology are that

The disadvantage of bus topology is that any break in the bus is difficult to identify.

Since only one cable is utilized, it can be the single point of failure. If the network cable breaks, the entire network will be down, since there is only one cable.

Terminators are required at both ends of the backbone cable.

c)  Ring topology

A ring topology connects the computers along a single path whose ends are joined to form a circle, so that the entire system is in the form of a ring.

In this topology data is transmitted in one direction only. Thus the data packets circulate along the ring in either clockwise or anti-clockwise direction.

Ring topologies typically utilize a token passing scheme, used to control access to the network. By utilizing this scheme, only one machine can transmit on the network at a time.

IEEE 802.5 standard

that any signal transmitted on the network passes through all the LAN stations.

One computer cannot monopolize the network.

The disadvantage of ring network is that the breakdown of any one station on the ring can disable the entire system. Adding and removing computers disrupts the network.

d)  Mesh Topology

This is one of the primitive ways of forming a computer network.

The computer network is formed in such a way that the computers are connected from one node to another.

Its not necessary, that every computer will have a direct connection to another computer.

In a mesh topology, each computer on network has redundant data paths

Diagram of a mesh network looks like a fishing net

Fully connected has n(n-1)/2  physical channels to connect n devices.

Robust bec  failure of any one computer does not bring down entire network

The mesh topology provides fault tolerance-if  some component fails, data can travel along an alternate path.

A mesh topology is most often used in large backbone networks in which failure of a single component can result in a large portion of the network going down.

Since every computer must be connected to every other computer installation is difficult. Cabling cost is more.

Reference

http://www.webopedia.com/DidYouKnow/Hardware_Software/mesh_topology.html

http://www.techterms.com/definition/networktopology

http://ninjacraze.hubpages.com/hub/Network-Topology-and-Types-of-Network-Topology

http://ninjacraze.hubpages.com/hub/Network-Topology-and-Types-of-Network-Topology