Local area network

Local area network (LAN), any communication network for connecting computers within a building or small group of buildings. A LAN may be configured as (1) a bus, a main channel to which nodes or secondary channels are connected in a branching structure, (2) a ring, in which each computer is connected to two neighbouring computers to form a closed circuit, or (3) a star, in which each computer is linked directly to a central computer and only indirectly to one another. Each of these has advantages, though the bus configuration has become the most common. 

computer

computer: Local area networks

Local area networks (LANs) connect computers within a building or small group of buildings. A LAN may be configured as (1) a bus, a main channel to which nodes or secondary channels are connected in a branching structure, (2) a ring, in…

Even if only two computers are connected, they must follow rules, or protocols, to communicate. For example, one might signal “ready to send” and wait for the other to signal “ready to receive.” When many computers share a network, the protocol might include a rule “talk only when it is your turn” or “do not talk when anyone else is talking.” Protocols must also be designed to handle network errors.
The most common LAN design since the mid-1970s has been the bus-connected Ethernet, originally developed at Xerox PARC. Every computer or other device on an Ethernet has a unique 48-bit address. Any computer that wants to transmit listens for a carrier signal that indicates that a transmission is under way. If it detects none, it starts transmitting, sending the address of the recipient at the start of its transmission. Every system on the network receives each message but ignores those not addressed to it. While a system is transmitting, it also listens, and if it detects a simultaneous transmission, it stops, waits for a random time, and retries. The random time delay before retrying reduces the probability that they will collide again. This scheme is known as carrier sense multiple access with collision detection (CSMA/CD). It works very well until a network is moderately heavily loaded, and then it degrades as collisions become more frequent.
The first Ethernet had a capacity of about 2 megabits (millions of bits) per second (mbps), and today 10- and 100-mbps Ethernet is common, with gigabit-per-second (billions of bits per second; gbps) Ethernet also in use. Ethernet transceivers (transmitter-receivers) for personal computers are inexpensive and easily installed.
A standard for wireless Ethernet, known as Wi-Fi, has become common for small office and home networks. Using frequencies from 2.4 to 5 gigahertz (GHz), such networks can transfer data at rates up to 600 mbps. Early in 2002 another Ethernet-like standard was released. Known as HomePlug, the first version could transmit data at about 8 mbps through a building’s existing electrical power infrastructure. A later version could achieve rates of 1 gbps. Another standard, WiMax, bridges the gap between LANs and wide area networks (WANs).
David Hemmendinger

Learn More in these related Britannica articles:

  • computer
    computer: Local area networks
    Local area networks (LANs) connect computers within a building or small group of buildings. A LAN may be configured as (1) a bus, a main channel to which nodes or secondary channels are connected in a branching structure, (2) a ring, in…
  • The basic organization of a computer.
    computer science: Network protocols
    …over short distances to form local area networks (LANs) or via telephone lines, television cables, or satellite links to form wide-area networks (WANs). By the 1990s, the Internet, a network of networks, made it feasible for nearly all computers in the world to communicate. Linking computers physically is easy; the…
  • Jacquard loom, engraving, 1874At the top of the machine is a stack of punched cards that would be fed into the loom to control the weaving pattern. This method of automatically issuing machine instructions was employed by computers well into the 20th century.
    automation: Communications
    …automation in communications systems include local area networks, communications satellites, and automated mail-sorting machines. A local area network (LAN) operates like an automated telephone company within a single building or group of buildings. Local area networks are generally capable of transmitting not only voice but also digital data between terminals…
  • Structure of organizational information systemsInformation systems consist of three layers: operational support, support of knowledge work, and management support. Operational support forms the base of an information system and contains various transaction processing systems for designing, marketing, producing, and delivering products and services. Support of knowledge work forms the middle layer; it contains subsystems for sharing information within an organization. Management support, forming the top layer, contains subsystems for managing and evaluating an organization's resources and goals.
    information system: Telecommunications
    Local area networks (LANs) join computers at a particular site, such as an office building or an academic campus. Metropolitan area networks (MANs) cover a limited densely populated area and are the electronic infrastructure of “smart cities.” Wide area networks (WANs) connect widely distributed data…
  • A simple closed telecommunications networkNetwork switches, or nodes, enable users (stations) to link to any number of network users through communications channels.
    telecommunications network: Broadcast network
    A wired local area network (LAN), for example, may be set up as a broadcast network, with one user connected to each node and the nodes typically arranged in a bus, ring, or star topology, as shown in the figure. Nodes connected together in a wireless LAN…

Leave a Reply

Your email address will not be published. Required fields are marked *