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LAN - technical definition

A LAN is a packet network designed to interconnect host computers, peripherals, storage devices, and other computing resources within a local area, i.e., limited distance. LANs conform to the client/server architecture, a distributed computing architecture that runs applications on client microcomputers against one or more centralized servers, which are high-performance multiport computers with substantial processing power and large amounts of memory. A LAN might serve an office, a floor of a building, and entire building, or a campus area, but generally does not cross a public right-ofway such as a street.The distance limitation generally is in the range of a few kilometers, at most, although that is sensitive to the transmission media employed, which include coaxial cable, twisted pair, optical fiber, infrared (IR) light, and radio frequency (RF) systems. Raw bandwidth ranges up to 10 Gbps, although actual throughput generally is much less. LANs generally are private networks, although public wireless hotspots offering wireless Internet access currently are popular. Most LAN standards are set by the 802 Working Group of the Institute of Electrical and Electronic Engineers (IEEE), with examples being 802.3 (Ethernet) and 802.11a/b/g (Wi-Fi).A personal area network (PAN) such as Bluetooth, is much more limited in geographic scope than a LAN. LANs and LAN segments can be interconnected over a metropolitan area network (MAN) or wide area network (WAN). LANs operate at Layer 1, the Physical Layer, and Layer 2, the Data Link Layer, of the OSI Reference Model. See also 802.3, 802.5, 802.11, architecture, bandwidth, Bluetooth, client/server, coaxial cable, Data Link Layer, Ethernet, hotspot, IEEE, IR, MAN, optical fiber, OSI Reference Model, PAN, Physical Layer, RF, throughput, Token Ring, twisted pair, WAN, and Wi-Fi.

See LAN in Computer

(Local Area Network) A communications network that serves users within a confined geographical area. The "clients" are the user's workstations typically running Windows, although Mac and Linux clients are also used. The "servers" hold programs and data that are shared by the clients. Servers come in a wide range of sizes from Intel-based servers to mainframes. Printers can also be connected to the network and shared (see print server).

Thick and Thin Clients
In a LAN, the client machines are mostly Windows-based PCs that contain their own applications. These "thick" clients are the norm; however, some companies use "thin" clients, which are stripped-down machines. Some are diskless and floppy-only workstations that retrieve all software and data from the server. Windows terminals are also used, which are Windows PCs that act like input/output terminals. They perform no business processing and display only what comes from a central server. See thin client and Windows terminal.

The Network OS
The controlling software in a LAN is the network operating system in the server (Windows, Mac OS, Linux, Unix, NetWare). A component part resides in each client and allows the application to read and write data from the server as if it were on the local machine.

Client workstations can also function as a server, allowing users access to data on another user's machine. These peer-to-peer networks are often simpler to install and manage, but dedicated servers provide better performance and handle higher transaction volume. In large networks, multiple, dedicated servers are used.

The Transport
Data transfer over the network is managed by a transport protocol such as TCP/IP or IPX. The physical transmission is performed by the access method, almost exclusively Ethernet, which is on the motherboard or in the network adapter cards (NICs) plugged into the machines. The actual communications path is the twisted pair or optical fiber cable that interconnects each network adapter. See WAN, TCP/IP, Ethernet and client/server.

Clients and Servers in a LAN

This illustration shows one server for each type of service on a LAN. In practice, several functions can be combined in one machine and, for large volumes, multiple machines can be used to balance the traffic for the same service. For example, a large Internet Web site is often made up of several Web servers.