Computer Networks I

A computer network consists of two or more computing devices connected by a medium allowing the exchange of electronic information. These computing devices can be mainframes, workstations, PCs, or specialized computers; they can also be connected to a variety of peripherals, including printers, modems, and CD-ROM towers. Most networks are supported by a host of specialized software and hardware that makes these connections possible, including routers, bridges, and gateways, which help accommodate traffic between unlike systems.

Many different types of computer networks exist. Some, such as local area networks (LANs), metropolitan area networks (MANs), and wide area networks (WANs), are defined by their geographic layout and the differing technologies that support such layouts. LANs are by far the most common, and in most cases, the fastest. Networks may be public, such as the Internet; semi-public, such as subscription networks (including subscription-based Internet service providers and other content-based networks); or private, such as internal corporate LANs, WANs, intranets, and extranets. Most networks are private, but of course the relatively few public ones, like the Internet, support a very large user base. Networks may also be open, or linked to other networks, or closed, which means they are self-contained and do not allow connectivity with outside resources. Most modern corporate networks are somewhere in between; they often allow access to the outside, but tightly restrict access from the outside. "Open" can also describe whether network technology is based on widely accepted standards that multiple hardware/software vendors support, versus a closed or proprietary system that is dependent on a single developer (or very few).