LAN

A local area network (LAN) is a computer network covering a local area, like a home, office or small group of buildings such as a college.
When using ethernet the computers are usually wired to a hub or to a switch. This constitutes the physical layer.
A layout known as a spanning tree protocol is often used to maintain a loop free network topology within a LAN, particularly with ethernet.
A number of network protocols may use the basic physical layer including TCP/IP. In this case DHCP is a convenient way to obtain an IP address rather than using fixed addressing. LANs can be interlinked by connections to form a Wide area network. A router is used to make the connection between LANs.
LANs are distinguished from other kinds of networks by three characteristics: (1) their size, (2) their transmission technology, and (3) their topology.