A network connects computers, or other devices (like printers and fax machines) together either by cables or wirelessly by radio or infrared signals. The purpose of a network is to make information at one point available at another. A network doesn't have to be only for computers. The analog telephone system is a network. The Internet is an abbreviation for interconnection of networks. The Internet is itself a type of network.
Types of Networks
Engineers categorize networks by the geographical area they cover. Most networks are Local Area Networks (LANs). Other categories are Personal Area Networks, which include home networks and entertainment system; Metropolitan Area Networks and Wide Area Networks. The division between each category is vague. A LAN covers a limited area, like an office, and is controlled by one organization. A Wide Area Network is also controlled by one body, but will reach out to satellite branches. This includes linking far flung offices together in the same network. The connecting sections between satellites may cross public networks. In this instance, it is usual to protect that traffic by creating a Virtual Private Network, which encrypts all data packets as they cross the common media. A Metropolitan Area Network is usually run by a utility company or local government. It has a large, but contiguous geographical area.
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The Wide Area Network often utilizes resources owned by different organizations. The Internet is the biggest example in the world of a Wide Area Network. The Internet was started in defense research and across academic institutions. The forerunner of the Internet was called DARPANET. This takes its name from DARPA, the US Defense Advanced Research Projects Agency.
One big difference between networks and the Internet is how they handle addressing and routing. On a private network, the network administrator can use any system for these tasks. All devices and software are controlled by one authority. It is important that all nodes, and especially routers, in a network use the same protocols. Otherwise the receiver will not be able to decipher the sender's instructions. As there is no overall owner of the Internet, a number of conventions have evolved to ensure compatibility. There is only one routing protocol used for the Internet and that is the Border Gateway Protocol.
Private networks interconnect through the Internet. This enables the sharing of information and eases commerce through the transaction of processes like ordering and payment. Academics and engineers are better able to collaborate and share information by connecting their networks together over the Internet. Private networks enable companies to encourage collaboration within the organization without making proprietary data publicly available.