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Data communications refers to the exchange of data between two devices using a transmission medium, such as a wire cable, while networking indicates the interconnection of devices capable of communication.

In order to achieve data communication, the two computers must be part of a communications system, which includes both hardware and software. Effective data communications require that data be delivered to the correct destination by the communications system, and received by the receiving computer. The data must be delivered accurately and without alteration, in order for it to be useful.

Data may be represented by text, ASCII, Unicode, ISO, numbers, images, audio, or video.

The two components, data communication, and networking, are required in order to transfer meaningful information between several computer systems.

A network refers to a group of computers or other devices that are connected by communication links. Each device can be referred to as a node and may be a computer, a printer, or another device that is capable of sending data transmitted or generated by another node on the network.

The performance of a network is measured by its transit time and response time. The transit time is the amount of time that it takes for data to travel from one node to another. The response time is the time an enquiry by the receiver, and a response from the sender. Other variables that can affect the performance of a network include the number of users, the transmission media type, the performance of the connected hardware, and the software in use by the network.

The reliability of a network is determined by the frequency of failure, as well as by network security issues.

A network is represented by two or more devices connected through links. A link is a communications pathway used to transfer data from one node to another. A link might be seen as a line drawn between two points in the network and, for communication to occur, these two points must be connected to the same link at the same time.

This might be accomplished through a point-to-point connection, which is a dedicated link between two devices, usually through a wire or cable, but it might be done through a satellite link.

Another type of connection is known as a multipoint connection, which is one in which more than two devices share the same link. In this type of connection, the capacity of the channel is shared by whatever devices are part of the connection. This might be a spatially shared connection, in which several devices can use the link simultaneously, or a timeshared connection, where users must take turns.

In a mesh topology, each device has a dedicated point-to-point link to every other device on the network. A dedicated link carries traffic only between the two nodes that it connects. A mesh topology is robust and secure, but it requires a large investment in cabling.

With a star topology, every node on the network has a dedicated point-to-point link to a central controller, known as a hub. As the nodes are not linked to one another, the hub serves as an exchange and as a relay point. A star topology is less expensive than a mesh topology, but it is entirely dependent upon the hub.

A bus topology is a multipoint connection, in which one long cable acts as a backbone, linking all of the nodes in the network. Backbone cable is laid along the most efficient path, then connected to the nodes by drop lines of various lengths.

A ring topology uses a dedicated point-to-point connection with only the two devices on either side of it. Data is passed along the ring in one direction, from node to node, until it reaches its destination. A disadvantage is that a break anywhere in the ring can disable the entire network.

Network types include local area networks (LAN), metropolitan area networks (MAN), and wide area networks (WAN). A LAN is confined to a single office, building, or campus, while a MAN generally covers an entire city, such as in a cable television network, and a WAN represents the long-distance transmission of data, voice, images, and video over a large geographical area, which may be a country, a continent, or the entire world. It is unusual to find a LAN or a WAN in isolation today, as they are generally connected to one another in what is known as an internet, which may be private or public.



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