Network topology

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What does "topology" mean?

A computer network is made of computers which are linked to one another with communication lines (network cables, etc.) and hardware elements (network adapters, as well as other equipment for ensuring that data travels correctly). The physical arrangement — that is, the spatial configuration of the network — is called the physical topology.


Network Topology

A network consists of multiple computers connected using some type of interface, each having one or more interface devices such as a Network Interface Card (NIC) and/or a serial device for PPP networking. Each computer is supported by network software that provides the server or client functionality.

The hardware used to transmit data across the network is called the media. It may include copper cable, fiber optic, or wireless transmission.

( The standard cabling used for the purposes of this document is 10Base-T category 5 ethernet cable. This is twisted copper cabling which appears at the surface to look similar to TV coaxial cable. It is terminated on each end by a connector that looks much like a phone connector. Its maximum segment length is 100 meters. )

Network Categories
There are two main types of network categories which are:
• Server based
• Peer-to-peer

• In a server based network, there are computers set up to be primary providers of services such as file service or mail service. The computers providing the service are are called servers and the computers that request and use the service are called client computers.
  
• In a peer-to-peer network, various computers on the network can act both as clients and servers. For instance, many Microsoft Windows based computers will allow file and print sharing. These computers can act both as a client and a server and are also referred to as peers. Many networks are combination peer-to-peer and server based networks. The network operating system uses a network data protocol to communicate on the network to other computers. The network operating system supports the applications on that computer. A Network Operating System (NOS) includes Windows NT, Novell Netware, Linux, Unix and others

Computer network topologies can be categorized in the following categories.

* Bus topology
* Star topology
* Ring topology
* Tree topology
* Mesh topology

Hybrid networks are the complex networks, which can be built of two or more above mentioned topologies.

• The logical topology, as opposed to the physical topology, refers to way that data travels along communication lines. The most common logical topologies are Ethernet, Token Ring and FDDI.

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Bus topology

Bus topology is the simplest way a network can be organised. In bus topology, all computers are linked to the same transmission line by using a cable, usually coaxial. The word "bus" refers to the physical line that joins all the machines on the network.



The advantages of this topology are that
it is easy to implement and functions easily;
on the other hand, it is highly vulnerable, since if one of the connections is defective, the whole network is affected.

Star topology

In star topology, the network computers are linked to a piece of hardware called a hub. This is a box which contains a certain number of sockets into which cables coming out of the computers can be plugged. Its role is to ensure communications between those sockets.



Unlike networks built with bus topology, networks which use star topology are much less vulnerable, as one of the connections can easily be removed by disconnecting it from the hub, without paralysing the rest of the network.

The critical point in this network is the hub, as without it, communication between the computers on the network is no longer possible.

However, a star topology network is bulkier than a bus network, as additional hardware is required (the hub).

Ring Topology

In a ring-topology network, computers each take turns communicating, creating a loop of computers in which they each "have their turn to speak" one after another.



In reality, ring topology networks are not linked together in loops. They are actually linked to a distributor (called a MAU, Multistation Access Unit) which manages communication between the computers linked to it, by giving each of them time to "speak."


distributor

The two main logical topologies which use this physical topology are Token ring and FDDI.

Tree Topology
Tree topologies are comprised of the multiple star topologies on a bus. Tree topologies integrate multiple star topologies together onto a bus. Only the hub devices can connect directly with the tree bus and each Hub functions as a root of a tree of the network devices. This bus/star/hybrid combination supports future expandability of the computer networks, much better than a bus or star.





Mesh Topology

Mesh topology work on the concept of routes. In Mesh topology, message sent to the destination can take any possible shortest, easiest route to reach its destination.

In the previous topologies star and bus, messages are usually broadcasted to every computer, especially in bus topology.

Similarly in the Ring topology message can travel in only one direction i.e clockwise or anticlockwise. Internet employs the Mesh topology and the message finds its route for its destination. Router works in find the routes for the messages and in reaching them to their destinations.The topology in which every devices connects to every other device is called a full Mesh topology unlike in the partial mesh in which every device is indirectly connected to the other devices.

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just for clearing concept