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152 Glossary
Glossary
L LAN
Local Area Network. A computer network that spans a relatively small
area. Most LANs are confined to a single building or group of buildings.
However, one LAN can be connected to other LANs over any distance
via telephone lines and radio waves. A system of LANs connected in this
way is called a wide-area network (WAN).
Most LANs connect workstations and personal computers. Each node
(individual computer) in a LAN has its own CPU with which it executes
programs, but it also is able to access data and devices anywhere on the
LAN. This means that many users can share expensive devices, such as
laser printers, as well as data. Users can also use the LAN to
communicate with each other, by sending e-mail or engaging in chat
sessions.
There are many different types of LANs, Ethernets being the most
common for PCs. Most Apple Macintosh networks are based on Apple's
AppleTalk network system, which is built into Macintosh computers. The
following characteristics differentiate one LAN from another:
topology: The geometric arrangement of devices on the network. For
example, devices can be arranged in a ring or in a straight line.
protocols: The rules and encoding specifications for sending data. The
protocols also determine whether the network uses a peer-to-peer or
client/server architecture.
media: Devices can be connected by twisted-pair wire, coaxial cables, or
fiber optic cables. Some networks do without connecting media
altogether, communicating instead via radio waves.
LANs are capable of transmitting data at very fast rates, much faster than
data can be transmitted over a telephone line. However, the distances
are limited and there is also a limit on the number of computers that can
be attached to a single LAN.
lock
A state that prohibits other users from accessing a resource, such as a
device or interface.
logical unit
A logical unit is a number associated with an interface. In Agilent SICL, a
logical unit uniquely identifies an interface. Each interface on the
controller must have a unique logical unit.