A network is a group of computers and devices that are interconnected by communications channels. These channels facilitate communications among users and allow them to share resources. Many different characteristics can be used to classify a network.

There are several purposes for networks. One of the most common uses of a network is for communication purposes. With a network, people can communicate efficiently and easily through email, instant messaging, chat rooms, video telephone calls, and video conferencing. Also, multiple computers can use networks to share data, software, and hardware. In a networked environment, every computer on the specific network may access and use the documents, files, storage devices, and applications that are in the network.

Networks have many different important attributes. Computer networks use different connection methods for different purposes. These methods may include optical fiber, Ethernet, Wireless LAN, or Power line communication. Computers must use different devices and cords to connect to networks. A twisted pair wire is the most commonly used tool for telecommunication. Twisted-pair wires are regular telephone wires that have two insulated copper wires twisted into pairs. The use of two wires twisted together helps to reduce crosstalk and electromagnetic induction. Coaxial cables are widely used for cable television systems, office buildings, and other worksites for local networks. These cables consist of copper or aluminum wire covered with insulating layer of flexible material with a high dielectric constant and a conductive layer. The layers of insulation help minimize interference and distortion. An optical fiber cable containing one or more filaments of glass fiber wrapped in protective layers. It broadcasts light which can travel over extended distances. Fiber-optic cables are not affected by electromagnetic radiation. Computer networks can also be classified by the network topology that the network is based on, such as bus network, star network, ring network, mesh network. Network topology is the specific arrangement of devices in the network.

Common types of computer networks may be identified by their scale. A personal area network (PAN) is a computer network used for communication between computers and different information technological devices in similar proximities, such as printers, fax machines, telephones, and scanners. A local area network (LAN) is a network that connects computers and devices in a limited space, such as a home or business office. Each computer or device on the network is a node. The defining characteristics of LANs are their higher data transfer rates and smaller geographic range. A home area network (HAN) is a residential LAN which is used for communication between digital devices generally organized in the home, such as a small number of personal computers, printers, and mobile computing devices. A wide area network (WAN) is a computer network that covers a large geographic area, such as a city or county, using a communication channel that combines several types of media such as telephone lines, cables, and air waves. A campus network is a computer network made up of an interconnection of local area networks within a limited location. For example, a university campus-based network is likely to link a variety of campus buildings together. A virtual private network (VPN) is a computer network that uses open connections and virtual circuits in larger networks to link nodes together. Finally, a global area network (GAN) is a network used for supporting mobile communications across a random number of wireless LANs and satellite coverage areas.

In relation to networks, the internet is very important. It is a global system of interconnected academic, community, corporate, governmental, and private computer networks. It is based on the networking technologies of the Internet Protocol Suite and is the successor of the Advanced Research Projects Agency Network. The Internet is also the fundamental base for communications in the World Wide Web (WWW).

Furthermore, intranets and extranets are parts or extensions of a computer network, usually a local area network. An intranet is a set of networks that is controlled by a single administrative entity. An extranet is a network that is limited to a single organization and has limited connections to the networks of other companies. An overlay network is a virtual computer network that is built on top of another network. Overlay nodes are connected by virtual links that correspond to certain paths in the underlying network.

There are several basic hardware components that are the building blocks for networks. A network card is a piece of computer hardware that allows computers to communicate through a computer network. It provides the physical access to a networking device and often provides a low-level addressing system. A repeater is an electronic device that receives a signal, cleanses it of unnecessary noise, regenerates it, and retransmits it at a greater power level so that the signal can cover longer distances without degradation. A network hub contains multiple ports that copy information without modifying it. A network switch is a device that forwards and filters OSI layer 2 datagrams between cables, based on their addresses. A switch is distinct from a hub in that it only forwards the frames to the specific ports involved in the communication instead of all the ports connected. A router is an internetworking device that forwards packets between networks by processing information in the packet. Routers use routing tables to determine what boundary is needed to forward packets.

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