|Attachment Unit Interface (AUI)
Connector: Also called thicknet connector. The AUI
is a transceiver cable that provides a path between a
node's Ethernet interface and the Media Access Unit
|Bandwidth: The difference between
the highest and the lowest frequencies of a transmission
channel. A measure of the information capacity of the
transmission channel. Bandwidth is expressed in bits per
|BNC Connector: Acronym stands for
British Naval Connector. A standard connector from a
thin coaxial cable to a transceiver.
|Bridge: A device that
interconnects local or remote networks across all
higher-level protocols. Bridges form a single logical
network, centralizing network administration. Bridges
operate at the physical and link layers of the Open
Systems Interconnect (OSI) reference model.
|Cabling: The wire medium (usually
Shielded Twisted Pair, Cat 5, FTP 6) by which nodes on a
LAN are connected.
|CAD/CAM: Computer Aided
Design/Computer Aided Manufacturing.
|Client/Server: A common form of
distributed system in which software is split between
server tasks and user or client tasks. A client sends
requests to a server asking for information or action,
and the server responds. There may be either one
centralized server or several distributed ones.
|Coxial cable: A type of
electrical cable in which a solid piece of metal wire is
surrounded by insulation, which in turn is surrounded by
a metal tube. Coaxial cables have wide bandwidths and
carry many data, voice and video signals simultaneously.
|Collapsed Backbone: Network
Architecture under which the backplane of a device such
as a hub performs the function of a network backbone;
the backplane routes traffic between desktop nodes and
between other hubs serving multiple LANs.
|Duplexing: Duplexing has all the
benefits of mirroring but adds further protection
utilizing different disk channels to connect two drives
in a mirrored set. Often this is done using two SCSI
controllers, one to each SCSI drive.
|ECC (error checking and correction):
Detects errors in transmitted or stored data and
corrects them on the fly. The simplest form of error
detection is a single added parity bit or a cyclic
redundancy check. Multiple parity bits not only detect
that an error has occurred, but also which bits have
been inverted, and should therefore be re-inverted or
fixed to restore the original data.
|Ethernet: IEEE-standard data link
protocol that specifies how data is placed on and
retrieved from a common transmission medium. Data is
broken into packets, which are then transmitted using
the Carrier Sense Multiple Access/Collision Detect (CSMA/CD)
algorithm until they arrive at the destination without
colliding with any other. A node is either transmitting
or receiving at any instant. Bandwidth ~10Mbit/s.
Disk-Ethernet-Disk transfer rate with TCP/IP is
typically 30 kilobyte per second. The cable is a 50-ohm
coaxial cable with multiple shielding. Forms the
underlying transport vehicle used by several upper-level
protocols, including TCP/IP and XNS.
|Fault tolerance: Designed into
disk array subsystems to maintain data integrity and
data availability before, during and after a failure.
Fault tolerance implies that any component in a
subsystem can fail and the subsystem will remain
operational. In addition to the disks in any array
subsystem, the cabling, controllers, adapters, and power
supplies can have redundant capabilities.
|Fiber Distributed Data Interface (FDDI):
A 100 Mbit/s standard LAN architecture. The underlying
medium is fiber-optic cable (though it can be copper
cable, in which case it may be called CDDI) and the
topology is a dual-attached, counter-rotating token
FDDI rings are normally
constructed in the form of a "dual ring of
trees". A small number of devices, typically
infrastructure devices such as routers and concentrators
rather than host computers, are connected to both rings.
Host computers are then connected as single-attached
devices to the routers or concentrators. The whole dual
ring is typically contained within a computer room.
|Fiber optic cable: a transmission
medium that uses glass or plastic fibers, rather than
copper wire, to transport data or voice signals. The
signal is imposed on the fibers via pulses (Modulation)
or light from a laser or a light-emitting diode (LED).
Because of its high bandwidth and lack of susceptibility
to interference, fiber-optic cable is used in long-haul
or noisy applications.
|Gateway: Device that can
interconnect networks with different, incompatible
communications protocols. The gateway performs a layer-7
protocol-conversion to translate one set of protocols to
another. A gateway operates at Open Systems
Interconnection (OSI) layers up through the Session
|Hamming: Redundant bits added to
stored or transmitted data for the purposes of error
detection and correction.
|Hot Swap: The ability to replace
failed hardware without turning off the system. The
subsystem can remain operational and data is available
at all times even during service activities. An example
of hot swapping would be hard disks that can be added
and removed while a server is operational.
|Hub: A device connected to several
other devices, also called a repeater. Strictly, it is a
|JBOD: JBOD refers to several
disks in an array not set up as a RAID configuration.
The acronym stands for "just a bunch of
|Local Area Network (LAN): A data
communications network that is geographically limited
allowing easy interconnection of workstations and
servers within adjacent buildings. Ethernet and FDDI are
examples of standard LANs.
Because the network is known to cover only a small
area, optimizations can be made in the network signal
protocols that permit data rates up to 100Mb/s.
|Metropolitan Area Network (MAN):
A data network intended to serve an area the size of a
|Mirror: Disk mirroring provides
and identical twin of all data written to the primary
disk. Total usable disk space is 50% of all drives in
the mirrored set. If one disk fails, the system uses the
complete data from the other disk.
|Network Interface Card (NIC):
Also called an adapter card. A board installed in a
computer to provide a physical connection to and from
that computer system.
|Network Operating System (NOS):
The software that controls the operation of the network.
A NOS enables users to communicate and to share files
and peripherals. It provides the user interface to the
LAN and communicates with the LAN hardware or network
interface card (NIC).
|Open Systems Interconnection (OSI):
OSI is the umbrella name for a series of non-proprietary
protocols and specifications. The OSI architecture is
split between seven layers, from lowest to highest:
Physical layer: this layer determines how
signals are transmitted on the network cabling.
Data Link: incorporates the logical link (LLC)
and the media access control (MAC) sublayers. The
data link layer transmits data groups into frames
using the Ethernet or Token ring access methods.
Network layer: handles the routing of data in
packets using the networking protocols.
Transport layer: ensures error free data
Session layer: establishes and maintains
connection between nodes according to the
Presentation layer: handles data encoding and
formatting; provides data compression.
Application layer: provides the means for
application processes to use the network services;
the interface to user database, file and email
software often implemented with API's (application
Each layer uses the layer immediately below it and
provides a service to the layer above.
|Parity: Error checking procedure
in which the number of 1s in a binary sequence must
always be the same, either odd or even, for each group
of bits transmitted. ECC adds correcting function to
|Protocol: A set of formal rules
describing how to transmit data, especially across a
network. Low-level protocols define the electrical and
physical standards to be observed, bit- and
byte-ordering and the transmission and error detection
and correction of the bit stream. High-level protocols
deal with the data formatting, including the syntax of
messages, the terminal to computer dialogue, character
sets, sequencing of messages etc.
|Redundant Array of Independent
(/Inexpensive) Disks (RAID): A technology using a
software or hardware controller with several disk drives
to allow varying degrees of either increased performance
or data integrity. Levels of redundancy or data security
are dependent on the number of drives in the array, as
well as the way the data is stored across the drives.
|Repeater: A device which
propagates electrical signals from one cable to another.
Less intelligent than a bridge, gateway or router.
|Router: A device which forwards
packets between networks. The forwarding decision is
based on network layer information and routing tables,
often constructed by routing protocols.
|Server: A Computer that provides
service for other computers connected to it via a
network. The most common example is a file server that
has a local disk and services requests from remote
clients to read and write files on that disk using the
Network File System (NFS) protocol or network operating
|Shielded Twisted Pair (STP):-Common
transmission medium that consists of a receive (RX) and
a transmit (TX) wire twisted together to reduce
crosstalk. The twisted pair is shielded by a braided
|Striping: Combines area of
multiple disks into one large logical drive. Data is
distributed evenly over drives in a stripe set. All
drives in a stripe set work to perform the same
functions done by a single drive in a normal
configuration. Allows concurrent I/O. Striping requires
at least 2 drives.
|Thinnet: 10BASE2 standard cable.
Also called cheapernet in reference to this less
expensive, thinner version of traditional Ethernet
|Token Ring (TR): A communication
methods that uses a token to control access to the LAN.
The difference between a token bus and a token ring is
that a token ring LAN does not use a master controller
to control the token. Instead, each computer knows the
address of the computer that should receive the token
next. When a computer with the token has nothing to
transmit, it passes the token to the next computer in
|Topology: A network topology shows
the hosts and the links between them. A network layer
must stay abreast of the current network topology to be
able to route packets to their final destination.
|Unshielded Twisted Pair (UTP):
Normal telephone wire (in the U.S.). It may be used for
computer-to-computer communications. It is much less
expensive than standard Ethernet cable.
|Wide Area Network (WAN): Public or
private computer network serving a wide geographic area.
|Workstation: A general-purpose
computer designed to be used by one person at a time.