A collection of computers (servers, workstations, desktop PC's etc.), printers, and other devices (for example a serial hub) interconnected by means of network interface cards (NIC's), hubs, bridges, routers and switches. A LAN provides the means for computers to communicate with each other either on a peer to peer basis or via a server intermediary. A LAN also provides the means to share resources, such as, printers, fax modems, or Internet access portals.

A part of a LAN where data transmitted on it is broadcast to all of the devices on that segment but not to devices on another segment. Each segment may contain a single server or workstation, or multiple workstations that are connected to a hub. In the latter case two or more workstations can broadcast messages simultaneously, hence, the messages collide. That segment is a 'collision domain.' (The Ethernet protocol sorts this problem out with random timing rules for each workstation to re-broadcast its message.)

The cable distance between the farthest pair of computers in a LAN segment (Collision Domain.)

A circuit card that plugs into a computer to give that computer the ability to be attached to a LAN.

A device used to interconnect two like networks.

Router

A device used to interconnect two unlike networks.

A device that provides the means to interconnect multiple computers on a LAN using twisted pair wiring. Ethernet hubs come in 10 Mbps (10BASE-T) and the newer Fast Ethernet 100 Mbps (100BASE-T) varieties or 10/100 auto-sensing models in which each port adapts to the speed of the computer attached to it. With a hub, when any computer addresses any other computer on the network it broadcasts its message to all of the computers attached to the hub. Each computer looks for its address so that only the addressed computer accepts the message. Note: 100 Mbps hubs come in Class I and Class II varieties.

Note: Ethernet Switches are preferred over Ethernet Hubs.

Switches are used to segment a LAN. A switch is similar to an Ethernet hub in that it provides the means to interconnect multiple computers on a LAN using twisted pair wiring or fiber. Ethernet switches come in 10 Mbps (10BASE-T) and the newer Fast Ethernet 100MB/s (100BASE-T) varieties, or 10/100 auto-sensing models in which each port adapts to the speed of the computer or device attached to it. However, unlike a hub, when any computer addresses any other computer on the network the messages travel only between the two computers. Since messages between pairs of computers are NOT broadcast to the other computers on the switch, network traffic is greatly reduced. Switches can be used, in many applications instead of bridges and routers. Switches also allow networks to be extended indefinitely. When networks are based on Ethernet Hub technology the maximum distance between end stations is limited. For 10BASE-T, up to four hubs between any pair of devices is allowed. For 100Base-T the maximum is two. This is called the 'hop count.' A switch, however, turns the hop count back to zero. So partitioning a network into smaller and more manageable segments and linking them to the larger network using a switch removes these limitations.

Bi-directional communication between two network devices that takes place one direction at a time. Computers attached to an ordinary hub communicate with each other in a half-duplex fashion.

Bi-directional communication between two network devices that takes place both directions simultaneously. This doubles the throughput of that link so that a 100 Base-T, full-duplex link actually provides a 200 Mbps data rate. Servers or other computers attached to an Ethernet switch can be configured to communicate in a full-duplex manner. Links between two switches or a switch and a hub are full duplex. However, computers attached to the hub communicate in a half-duplex fashion.