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In the last years the number of computers is very increased; this fact is the result of peopleís desire to be connected between each other.

The growth of connectivity would make the whole world closer to the users than in the past.

A computer network is a connection between many computers that could exchange information whit one another.

The networks could be differentiated in two ways:

_by topologies

_by extent

A topology is the way in which the different terminals (called nodes) could be linked.

The different kinds of topologies are basically three: star, ring, and bus, but a network could be produced by hybrid combinations of these topologies.

In the star topology there is a host computer connected to every other computer system: these smaller computer systems communicate whit other ones through the host and share the host computerís database.

The disadvantage is that if the host computer is damaged, the whole system will be blocked.

The ring topology is the connection between computers of the same size: every computer is connected to the previous and the following.

A information pass, in the way of a message, computer by computer all over the circle until it reaches its destination.

The disadvantage is that there is a fault in a part of the ring, all the nodes will be blocked.

In bus topologies every node is connected to a common cable: a message is spread to all computer systems but only the destination node respond to the signal.

The advantage is that if a node is damaged, the others wonít be blocked.

The networks differentiated by extent could be of two types: LAN (local area network) and WAN (wide area network).

A LANphysically links the different computers to each other, so could cover a small area.

Every computer must have a NIC (network interface card).

If a data or a program isnít on the internet it might be stored on a file server, a specialized computer whit a large hard-drive.

In WANthe computers connected are placed over a large area, even the whole world.

The communication could be made in many different ways: microwave, satellite, telephone.

Advantages of a Linear Bus Topology

        Easy to connect a computer or peripheral to a linear bus.

        Requires less cable length than a star topology.

Disadvantages of a Linear Bus Topology

        Entire network shuts down if there is a break in the main cable.

        Terminators are required at both ends of the backbone cable.

        Difficult to identify the problem if the entire network shuts down.

        Not meant to be used as a stand-alone solution in a large building.

Advantages of a Star Topology

        Easy to install and wire.

        No disruptions to the network then connecting or removing devices.

        Easy to detect faults and to remove parts.

Disadvantages of a Star Topology

        Requires more cable length than a linear topology.

        If the hub or concentrator fails, nodes attached are disabled.

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

Advantages of a Tree Topology

        Point-to-point wiring for individual segments.

        Supported by several hardware and software venders.

Disadvantages of a Tree Topology

        Overall length of each segment is limited by the type of cabling used.

        If the backbone line breaks, the entire segment goes down.

        More difficult to conure and wire than other topologies.


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