Computer network, often simply referred to as a network, is a collection of computersand devices interconnected by communications channels thatfacilitate communications among users and allows users to share resources. . A computer network allows sharing of resources and information among interconnected devices. In the 1960s, the Advanced Research Projects Agency ( ARPA) started funding the design of the Advanced Research Projects Agency Network (ARPANET) for the United States Department of Defense. Development ofthe network began in 1969, based on designs developed during the 1960s. The ARPANET evolved into the modern Internet.
PURPOSEComputer networks can be used for a variety of purposes:Facilitating communications. Using a network, people cancommunicate efficiently and easily via email, instant messaging,chat rooms, telephone, video telephone calls, and videoconferencing.Sharing hardware. In a networked environment, each computeron a network may access and use hardware resources on thenetwork, such as printing a document on a shared networkprinter.Sharing software. Users connected to a network may runapplication programs on remote computers.Information preservation.Security.Speed up.
Types of networksCommon types of computer networksmay be identified by their scale.Personal Area Network(PAN)Local Area Network(LAN)Metropolitan Area Network(MAN)Wide AreaNetwork(WAN)
Personal area networkA Personal area Network (PAN) is a computer networkused for communication among computer anddifferent information technological devices close toone person. Some examples of devices that are usedin a PAN are personal computers, printers, faxmachines, telephones, PDAs, scanners, and evenvideo game consoles. A PAN may include wired andwireless devices. The reach of a PAN typicallyextends to 10 meters. A wired PAN is usuallyconstructed with USB and Firewire connections whiletechnologies such as Bluetooth and infraredcommunication typically form a wireless PAN.
Local area networkA Local area Network (LAN) is a network thatconnects computers and devices in a limitedgeographical area such as home, school,computer laboratory, office building, or closelypositioned group of buildingsThe defining characteristics of LANs, in contrastto WANs (Wide Area Networks), include theirhigher data transfer rates, smaller geographicrange, and no need for leasedtelecommunication lines.
Metropolitan area networkA Metropolitan area Network(MAN) is alarge computer network that usually spansa city or a large campus.Special devices like routers, switches andhubs are connected to create a MAN.
Wide area networkA Wide area Network (WAN) is a computernetwork that covers a large geographic areasuch as a city, country, or spans evenintercontinental distances, using acommunications channel that combines manytypes of media such as telephone lines, cables,and air waves. A WAN often uses transmissionfacilities provided by common carriers, such astelephone companies
TWISTED PAIRTwisted Pair wire is the most widely used medium fortelecommunication. Twisted-pair cabling consist ofcopper wires that are twisted into pairs. Ordinarytelephone wires consist of two insulated copper wirestwisted into pairs.Computer networking cabling consist of 4 pairs ofcopper cabling that can be utilized for both voice anddata transmission. The use of two wires twistedtogether helps to reduce crosstalk andelectromagnetic induction. The transmission speedranges from 2 million bits per second to 100 millionbits per second.
COAXIAL CABLE• Coaxial Cable is widely used for cable television systems, office buildings, and other worksites for local area networks.• The cables consist of copper or aluminum wire wrapped with insulating layer typically of a flexible material with a high dielectric constant, all of which are surrounded by a conductive layer. The layers of insulation help minimize interference and distortion. Transmission speed range from 200 million to more than 500 million bits per second.
OPTICAL FIBEROptical Fiber cable consists of one or morefilaments of glass fiber wrapped in protectivelayers. It transmits light which can travel overextended distances. Fiber-optic cables are notaffected by electromagnetic radiation.Transmission speed may reach trillions of bitsper second. The transmission speed of fiberoptics is hundreds of times faster than forcoaxial cables and thousands of times fasterthan a twisted-pair wire.