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Definition: LAN


(Local Area Network) A communications network that is typically confined to a building or premises. A LAN is a local network, whereas a WAN is a wide area network that spans long distances (see WAN). Every wireless router has four LAN ports, which creates a small local network in the home or office (see wireless router).

The "clients" in a LAN are the user's computers running Windows, Mac or Linux, while the "servers" hold programs and data shared by the clients. Servers come in a wide range of sizes from PC-based servers to mainframes (see server).

The Transport
Data transfer over a LAN is managed by the TCP/IP transport protocol, and the physical transmission is handled by Ethernet over twisted pair or optical fiber cables. Using Wi-Fi, Ethernet's wireless counterpart, laptops and mobile devices connect without cables. See twisted pair, optical fiber, TCP/IP and Ethernet.

Thick and Thin Clients
In a company LAN, the client machines are mostly Windows PCs; however, Macs are also widely used. Each PC or Mac contains a variety of installed applications. These "thick" clients are the norm; however, some organizations use "thin" clients, which perform limited business processing. For example, a Windows PC can be turned into an input/output terminal to a server (see Remote Desktop Services). See thin client and client/server.

The Network OS
The software that enables data sharing is the network operating system in the servers, typically running Windows, Linux or Unix. In large organizations, multiple dedicated servers are used. A component part resides in each client operating system, which allows the application in the client to read and write data from the server.

Client machines can also function as a server, allowing other users access to data in folders configured as "sharable." These "peer-to-peer" networks are easier to manage, but dedicated servers provide better performance and handle high transaction volume.




Clients and Servers in a LAN
This shows the private employee-facing side and the public-facing site. In large companies, multiple servers are used for each type of service. Today, it is uncommon to see a remote access server for dial-up connections.






Software in a Network Client
These are examples of common applications found in a user's machine. Printers may be connected to clients or servers wired or wireless (see print server).






Software in a Network Server
These are the common services in a network server.