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- Alternating current. A signal that alternates its
polarity between positive and negative with respect to an
earth ground. Dynamic signals such as audio, radio waves and
utility power are typically AC.
- Abbreviation for the Acknowledge response in data
- Analog to Digital Converter.
- The method of labeling, identification,
documentation and usage needed to implement moves, additions
and changes of the telecommunications infrastructure.
- Attenuation to Crosstalk Ratio. ACR is a comparison of
signal strength to noise interference and is used as a
- Attenuation is the degradation of signal level along the
cable due to losses in the cable. It measured in dB and
calculated as follows: Attenuation = 10 log Received
Voltage/Transmitted Signal Voltage. See also OPTICAL LOSS.
AUTOTEST - A
series of tests performed by a LAN Cable Tester activated by
the AUTOTEST key. The content of a test series and the test
limits are predefined by the selection of a Standard (e.g.
Category 6), or a cable manufacturer's test suite, or may be
constructed by the test unit's user.
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BACK REFLECTION - Light
reflected from the cleaved or polished end of a fiber caused
by the difference of the refractive indices of air and
glass. Back Reflectance is typically 4% of the incident
light. It is expressed in dB relative to incident power.
- A facility (e.g. pathway, cable or conductors) between
telecommunications rooms, or floor distribution terminals,
the entrance facilities, and the equipment rooms within or
BACKSCATTERING - The scattering of light in a fiber back
toward the source. This backscattered light is used to make
Optical Time Domain Reflectometer (OTDR) measurements.
- Balance is the ratio of the differential signal output
at either end of any pair to a common mode
- A passive line matching transformer designed to
match the impedance of a transmission medium referenced to
ground such as coaxial cable to transmission media whose
signals are differential, or referenced to each other, such
as TV antenna twin lead. Frequently used to connect twisted
pair media to coaxial cable.
- The range of electrical frequencies that an
electronic device or transmission system can effectively
handle. For LAN's, it describes the maximum data rate for a
given topology. The best bandwidth indicator of a cabling
system is Attenuation Crosstalk Ratio (ACR), and one should
strive for 7-10 dB ACR at the highest frequency level of
transmission. The higher the ACR, the stronger the signal.
Crosstalk Ratio (ACR)).
- The use of the entire bandwidth of the network cable
to transmit a single digital signal. The frames are applied
directly to the cable in digital form without modulation or
multiplexing. Ethernet and Token Ring are Baseband
transmissions because they use only one protocol.
BASEBAND VIDEO - An application that defines
transmission characteristics up to 862 MHz.
BASIC LINK - A testing configuration that appeared in
older editions of the ANSI/TIA/EIA-568-A Standard. It has
been replaced by Permanent Link test configuration in the
568-B Standard that replaced 568-A. See
- The most basic unit of data transmission speed, one
baud represents one signal state change per second. It is
often confused with bits per second (bps) because they were
at one time very similar. By using current data compression
and modulation techniques, many times the baud rate in bits
per second can be achieved.
BENDING RADIUS - The minimum allowed curvature of any
piece of cable (fiber or metallic). It is absolutely
critical that the bending radius be maintained so that
neither the cable's impedance (metallic) nor refractive
index (fiber optic) is affected.
- Bit Error Rate. The ratio of received error bits of
data to the total number of bits transmitted.
- Information contained in one of two states, either 0
(zero) or 1 (one). Digital computers are designed to respond
to streams or groups of binary information. By combining and
manipulating this information, these machines can be
instructed to perform useful tasks. All information, whether
alpha or numeric, must be converted into a binary equivalent
to be processed by these systems. It forms the basis of the
Binary digIT or BIT. Eight bits together form a BYTE. (Four
bits form a NIBBLE).
BINARY SYNCHRONOUS COMMUNICATIONS - BCS or BISYNC.
Developed by IBM as a form of communications between their
mainframes and other devices. This protocol depends on
synchronization between transmitter and receiver via timing
- Binary Digit. The smallest unit of data (and most
basic) for data communications. It can have a value of a one
(mark) or a zero (space).
BIT RATE - The number of bits passing a given point in a
measured period of time. Usually expressed as bits per
second (bps), thousands of bits per second (Kbps), or
millions of bits per second (Mbps).
- A group of transmitted data, typically framed with
control characters and having a fixed size, such as 256,
512, 4096, etc.
- The Bayonet-Neill-Concelman connector. Widely used in
10BASE2 and other thin coaxial applications.
- Bits Per Second. (See also
- The stranded shield found on most types of axial
metallic media and some types of twisted pair, such as IBM
- In the LAN arena, it is a device used to connect two
physically separate networks.
- To send a message to two or more receiving devices
at the same time.
BROADCAST STORM - In a NETBIOS based network, devices
broadcast their addresses when queried. When several or all
devices broadcast their addresses, the network slows down
with the excess traffic.
- A combination bridge and router, performing the
functions of both in a single device. See also
BUNDLED CABLE - An assembly or two or more cables
continuously bound together to form a single unit.
- An electrical connection tying two or more points
together. A bus can be serial or parallel and can carry both
dynamic signals or DC voltage.
BUS NETWORK - A topology based on all communicating
devices being attached to a common medium. Various access
methods are used including CSMA/CD and Token Passing.
Typically bus networks carry data in the millions of bits
per second data rate.
- Eight data bits or two nibbles.
BYTE COUNT - The number of bytes in a given message or
block of data.
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- An assembly of one or more conductors within an
enveloping sheath, constructed so as to permit use of the
conductors singly or in groups.
CABLE RISER - Vertically installed cable connecting
floors of a building. Cable tested to UL 1666 is "riser"
rated. Typically multi-pair copper and fiber.
CABLE RUN - A
length of installed media who may include other components
along its path.
CABLE SHEATH - A covering over the optical fiber or
conductor assembly that may include one or more metallic
members, strength members or jackets.
CABLE SHIELD - A conductive layer of material located
just under the cable's outer sheath which is designed to
increase the cable's immunity to outside electrical noise
interference. It may be constructed of metal foil or braided
- A combination of all cables, jumpers, cords and
CAMPUS - The
buildings and grounds having legal contiguous
- The measured ability of an electronic component to
store an electrical charge. Capacitance is rated in units
called FARADS. Common divisions of farads include
microfarads (mF = X 10 6 ), nanofarads (nF = X 10
) and picofarads (pF = X 10 12 ).
CARRIER SENSE MULTIPLE ACCESS/COLLISION DETECTION (CSMA/CD)
- The most common form of access control found in an
Ethernet environment. It is used to avoid data collisions in
a logical bus topology, such Ethernet.
CARRIER SIGNAL - A continuous signal, upon which is
modulated the data or other signal that is to be
CATEGORY 3 (CAT 3) - 4-pair UTP cable and associated
connecting hardware whose transmission characteristics are
specified up to 16 MHz. (SEE ISO 11801 CLASSES A, B, C)
CATEGORY 4 (Cat 4) - 4-pair UTP cable and associated
connecting hardware whose transmission characteristics are
specified up to 20 MHz. (SEE ISO 11801 CLASSES A, B, C)
CATEGORY 5 (CAT 5) - 4-pair UTP cable and associated
connecting hardware whose transmission characteristics are
specified up to 100 MHz.
CATEGORY 5e (CAT 5e) - 4-pair UTP cable and associated
connecting hardware whose transmission characteristics are
specified up to 100 MHz. It has approximately 3 dB stronger
signal strength than standard CAT 5. Category 5e includes
additional tests (Headroom, PSACR, PSELFEXT, PSNEXT, and
ACR) to ensure that Gigabit Ethernet can run over unshielded
Twisted Pair (UTP) cabling. (SEE ISO 11801 CLASS D)
CATEGORY 6 (CAT 6) - a proposed addition, in draft form,
to the ANSI/EIA/TIA-568-B.2 and ISO 11801 Standards
specifying testing transmission characteristics for 4-pair
STP and UTP cabling and connectors up to 250 MHz (See ISO
CLASS E). Additionally, tests for Capacitance, Resistance and
Impedance are required in addition to all tests required for
Category 5e. Approval is expected in early 2002.
CATEGORY 7 (CAT 7) - an anticipated addition to the
ANSI/EIA/TIA-568-B.2 Standard specifying testing
transmission characteristics for 4-pair STP cabling and
connectors up to 600 MHz (See ISO 11801
CLASS F). Approval of the ISO 11801 Standard is possible
in late early 2002 with an ANSI/EIA/TIA Standard following
at some future date.
- Community Antenna TeleVision or Cable TeleVision. CATV
is Broadband transmission effected by multiplexing multiple
channels on one medium.
- Controlled Access Unit. A type of semi-intelligent
central wiring concentrator for the Token Ring environment.
Used in conjunction with LAM's.
- International Telephone and Telegraph Consultative
Committee. An international standards setting body for the
telecommunications industry. In 1985, the CCITT chartered
the TIA/EIA with drafting the 568 Standards we use today.
- Copper Distributed Data Interface. A standard describing
100 Mbps data transmission on metallic cable.
CENTRALIZED CABLING - A cabling configuration from the
work area to a centralized cross-connect using pull-through
cables, an interconnect or splice in the telecommunications
CHANNEL LINK - The Channel Link includes up to 90 m (295
ft) of horizontal cable, a work area patchcord, a
telecommunications outlet/connector, an optional transition
point or consolidation connector, and two connections in the
telecommunications room. When a maximum horizontal length of
90 m is used, then the total length of the patchcords shall
not exceed 10 m (33 ft). For other lengths of horizontal
cabling, refer to ANSI/EIA/EIA-568-B.2.
CONNECTING HARDWARE - A device providing mechanical
cable terminations between two cable ends.
- Central Processing Unit. The portion of a computer
which performs all arithmetic and logic manipulation in
addition to instruction interpretation and processing.
- Color Graphics Adapter.
CHANNEL SERVICE UNIT - A device that interfaces a
digital telephone line to a multiplexer or other digital
device for high-speed communications.
- A combination of binary digits representing an
- Characteristic Impedance is the measure of a
transmission medium's impedance throughout its length and
over a swept frequency spectrum. When terminating
transmission media, it is important to match its
Characteristic Impedance so as to minimize reflections.
CHARACTER ORIENTED PROTOCOL - A communications protocol
that responds to special control characters as opposed to
individual bit values for function control.
- Slang for 10BASE-2, also Thinnet, Thinwire Ethernet
using a 50 ohm coax cable. (also see THIN ETHERNET)
- Customer Interface Control System. An IBM user
interface designed for mainframe interaction and job
- The low refractive index optical coating surrounding the
core of a fiberoptic cable that prevents light from escaping
the core. The cladding guides light along the core.
CLASS D - An approved ISO 11801 Standard specifying
testing transmission characteristics for 4-pair STP and UTP
cabling and connectors up to 150 MHz (also see Category 6).
Approval is expected in late 2001.
CLASS E - A
proposed addition, in draft form, to the ISO 11801 Standard
specifying testing transmission characteristics for 4-pair
STP and UTP cabling and connectors up to 250 MHz (also see
Category 6). Approval is expected in early 2002.
CLASS F - An
anticipated addition to the ISO 11801 Standard specifying
testing transmission characteristics for 4-pair STP cabling
and connectors up to 600 MHz (Category 7). Approval of the
ISO 11801 Standard is expected in early 2002 with an
ANSI/TIA/EIA Category 7 Standard following at some future
CMIP - Common
Management Information Protocol. One of many network
management information exchange protocols. The current
favorite is SNMP.
COAXIAL CABLE - A cable constructed of an insulated
center conductor surrounded by a shield. 10 BASE-5 and 10
BASE-2 require different types of 50-ohm coax cables.
- The event that occurs when data from two devices
attached to a common bus are placed on the bus at the same
time. In Ethernet this typically generates a
COMMUNICATIONS PROTOCOL - The rules that govern the
behavior and attributes of both hardware and software as
they apply to data communications.
COMMUNICATIONS SERVER - A device which acts as a gateway
to communication lines outside normal building boundaries or
to a different communicating device. The server may allow
access to several lines by any number of users on a network.
Sometimes called a modem pool.
- A device used in LAN applications to attach several
nodes to one AUI or bus attachment point. Often this term is
used mistakenly in place of hub.
CONNECTING BLOCK - An interconnecting device used in
telecommunications and LAN applications consisting of
multiple points for wire attachment. Some common connecting
blocks are the 66 block, 110 block, the BIX block and the
(also see Cross-Connect)
CONSOLIDATION POINT - A location for interconnection
between horizontal cables extending from a
telecommunications room and horizontal cables extending to
- The central light carrying part of a fiberoptic cable.
It has a higher index of refraction than that of the
- An optical device that splits or combines light from
more than one fiber.
- Characters Per Second.
- Central Processing Unit
- Cyclic Redundancy Check. A common form of error
checking for data communications and other situations where
blocks of data are moved from one location to another. All
bits in a block are divided by a predetermined binary number
and the result is compared with what the actual number
- A facility enabling the termination of cable elements
and their interconnection or cross-connection.
- A connection scheme between cabling runs, subsystems and
equipment using patch cords or jumpers that attach to
connecting hardware on each end.
- Crosstalk is the measure of noise induced to one
pair by another pair of conductors. Crosstalk measured from
the near end is "NEXT" and Crosstalk measured from the far
end is "FEXT". Crosstalk is expressed in dB and the smaller
the number, the greater the inductive noise effect.
ANSI/TIA/EIA-568-B.2 requires bidirectional NEXT
measurements to verify performance in both directions.
- Carrier Sense Multiple Access/Collision Detection (an
Ethernet Media Access Mechanism).
CSU - See
CHANNEL SERVICE UNIT -
- Clear To Send
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- A sort of status line in the ISDN arena. A 16 Kbps line
carrying control signals and call data in the BRI interface.
A 64 Kbps line in the PRI interface.
D TYPE - A description for the 9, 15 and 25 pin
connectors widely used for data communications and
microcomputer peripherals. It looks very loosely like a "D"
when viewed vertically.
- Directly Accessible Storage Device. IBM's term for
local hard disk.
DATA GRADE CIRCUIT - A telephone line capable of
carrying high-speed data. The line is specially conditioned
to accommodate this.
DATA SERVICE UNIT - DSU. A device for transmitting data
on digital transmission facilities. Sometimes incorporated
with a CSU.
DATA SET - Another term for modem.
- the abbreviation for decibel. A unit of measurement
to compare an output signal to an input signal. A relative
term. (See also text on ATTENUATION for more information)
- Direct Current. A steady state voltage, either
positive or negative with respect to ground, but not both.
Batteries are a source of DC.
DC RESISTANCE - Provides an effective check on cable and
connector integrity. Both cabling and connectors have
inherent DC resistance. Loop resistance is the combined
resistance of each individual wire in a two-wire pair. It is
tested for each pair by placing a known DC voltage on one
wire in the pair, shorting the Remote Handset and reading
the voltage loss at the Display Handset. DC loop resistance
testing is essential to isolating poor connector punch
downs, cable damage and shorts.
DEAD ZONE - In OTDR measurements, if a subsequent event
occurs at a distance less than the pulse width generated by
the OTDR, the subsequent event will not be "seen" by the
OTDR because it occurs within a "dead zone."
DELAY SKEW - Also known as Propagation Delay/Delay Skew.
Delay Skew is a measurement of the signaling delay
difference from the fastest pair to the slowest. Delay Skew
is calculated from Propagation Delay measurements.
DENSE WAVELENGTH DIVISION MULTIPLEXING (DWDM) - A method
of increasing the amount of data that can be transmitted
over an optical fiber.
- The conversion of an analog or continuous signal
into a data stream of binary digits.
- Distributed Office Support System by IBM.
DISTRIBUTED PROCESSING - A system or network whereby the
processing is done at each individual workstation and not at
a central device. A LAN is an example of distributed
- Direct Memory Access.
- Digital Equipment Corporation's Network
- An area including all peripherals and nodes under
control of a single computer or server in a network.
- LAN Cable Testers perform this function using a Time
Domain Reflectometer (TDR) that samples and analyzes the
impedance of a link. Relative Impedance is measured as a
function of length and each cable can be viewed in graphical
format along its length to ascertain where the anomalies are
located, whereas Characteristic Impedance is usually
measured in a laboratory with complex test equipment such as
an expensive network analyzer. The TDR measures relative
impedance in the field to find crimps, kinks and/or
stretched cable that would show up as a blips, peaks or
valleys on the otherwise flat line graph of a good link.
(also see FAULT FIND)
DRAIN WIRE - In a cable, it is an uninsulated wire
included in the sheath with the insulated wires. Typically
used for grounding.
DROP CABLE -A cable connecting a workstation or
peripheral to the main network cable.
- Digital Service Level 0, a 64 Kbps digitized voice line.
- Digital Service Level 1, a 1.544 Mbps line carrying 24
- Digital Service Level 1C, a 3.152 Mbps line also called
- Digital Service Level 2, a 6.312 Mbps line also called
- Digital Service Level 3, a 44.736 Mbps line also called
- Digital Service Level 4, a 273 Mbps line also called
DUAL NEAR END CROSSTALK - Near end Crosstalk (NEXT) is
the amount of transmitted signal on one pair that is induced
electromagnetically onto adjacent pairs. High levels can
cause excessive retransmission rates. An AutoTest generates
swept signals for NEXT from 1 to 250 MHz for Category
6/CLASS E and it measures the induced noise on adjacent
pairs at precise intervals. The AutoTest performs Dual NEXT
tests from both ends.
DWDM - See DENSE WAVELENGTH DIVISION MULTIPLEXING
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- Extended Binary Coded Decimal Interchange Code. An 8-bit
code developed by IBM for data transfer between their
- Electronis Industry Association. A trade
organization of manufacturers which sets and defines
standards for its members. This group works with the TIA on
standards pertaining to both industries. The originator of
the "RS" series of interfaces (RS232, RS-449, etc.)
- Extended Industry Standard Architecture. An
independent alternative to IBM's Micro-channel for 32 bit
- See EQUAL LEVEL FAR-END CROSSTALK.
- Electromagnetic Interference.
- Erasable Programmable Read Only Memory.
EQUAL LEVEL FAR-END CROSSTALK (ELFEXT) - A measure of
the unwanted signal coupling from a transmitter at the
near-end into a neighboring pair measured at the far-end
relative to the received signal level measured on that same
EQUIPMENT CABLE CORD - A cable or cable assembly used to
connect telecommunications equipment to horizontal or
- Enhanced Small Device Interface.
- A LAN operating under the guidelines of the IEEE
802.3 document defining physical and data link layer
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- A device similar to a concentrator in that it
provides multiple access to a single backbone tap.
- A unit for measuring capacitance. One farad is a
one-coulomb charge with one-volt potential difference
between the plates. A 50-volt, one farad capacitor is
roughly the size of a quart milk container. (also see CAPACITANCE)
LOSS (FEXT) - A measure of the unwanted signal coupling
from a transmitter at the near-end into a neighboring pair
measured at the far-end.
- File Allocation Table. The location of all names and
addresses of data files stored on a disk.
FAULT FIND - A diagnostics feature on the IDEAL LAN
Testers that allows you to determine where in a link a fault
is located. (also see DOWNLINE IMPEDANCE)
- Federal Communications Commission.
FC CONNECTOR - A connector type used primarily for
Singlemode fiberoptic cable. It offers precise alignment of
the cable with respect to the transmitter and detector.
Using a threaded receptacle and a locator notch, once
installed the position is maintained with absolute accuracy.
- Frame Check Sequence. An error-checking field found
in bit oriented protocols.
- Fiber Distributed Data Interface. A dual
counter-rotating ring topology based on fiber optics
operating at 100 Mbps.
- Frequency Division Multiplexing. A technique in
which several signals are transmitted on the same cable
simultaneously at different frequencies. Used in Broadband.
- An abbreviation for Full Duplex transmission.
Gigabit Ethernet will use full duplex transmission on all
four pairs. This is analogous to being on an 8-lane highway
and any car can go any direction, at any time!
- Front End Processor. A preprocessor for devices
attached to a larger, faster computer.
-The component of a connector that holds a fiberoptic
cable in place and maintains its alignment. Cylindrical in
shape with a hole in the middle, the ferrule is sometimes
described as a sleeve.
FEXT - See FAR END CROSSTALK.
- A thin filament of glass capable of carrying information
in the form of light.
FIBEROPTICS (FO) - Light transmission through flexible
fibers for communications or lighting.
FIBEROPTIC TEST PROTOCOLS - A series of test procedures
defined by the FO 6.2 committee of TIA. The procedures cover
a wide number of situations, for example, verification by
manufacturers of cable specifications, cable bend radius,
connector manufacturing, fire rating, and field testing of
fiber optic installations.
FIBEROPTICS LAN SECTION - Known as FOLS, a group
operating within the trade association operation of TIA.
FOLS is dedicated to promoting the common interests of TIA
members involved in fiberoptic telecommunications.
FILE SERVER - A device found on local area networks
which sends requested files and programs to requesting nodes
and stores files sent from nodes.
- Operating instructions for a processor permanently
stored in devices such as EPROM's, and ROM's which are
FLASH MEMORY - Flash Erasable Programmable Read-only
Memory is a form of computer semiconductor storage. It
allows data in electronic format to be held without loss
(unlike RAM) for an indefinite period (like ROM), and for
the contents to be changed. It is a popular type of
removable storage used for transporting data between
recording devices and a PC.
FO-2, FO-6 - See TIA/IEEE STANDARDS COMMITTEES
FOLS - See FIBEROPTICS LAN SECTION
FOTP - See FIBEROPTIC TEST PROTOCOL
- A transmission circuit using a transmit pair and a
receive pair, or four wires altogether.
- The rate, at which an electrical current alternates,
usually measured in Hertz, or cycles per second, which are
- File Transfer Protocol. A file sharing protocol often
used in conjunction with TCP/IP. It operates in layers 5
through 7 of the OSI network model.
FULL DUPLEX - The ability of a circuit to carry signals
in two directions simultaneously. (also see
and GIGABIT ETHERNET)
FUSION SPLICER - An instrument that splices fiber by
fusing or welding the fibers, typically by an electric arc.
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- For LAN's, a connection between two dissimilar network
topologies, i.e., Token-Ring and Ethernet.
- A prefix for one billion.
GIGABIT ETHERNET - Gigabit Ethernet is defined by three
standards generated by IEEE 802.3 working groups.
Ã‚Â· 1000Base-T supports Gigabit Ethernet over 100 meters of
Category 5e balanced copper cabling.
1000BASE-SX supports the use of short wavelength Vertical
Cavity Side-Emitting Lasers (VCSELs) to transmit data over
fiber optic cable. The lasers specified by the Standard
operate over Multimode Fiber in the wavelength range of 770
to 860 nanometers.
1000BASE-LX supports the use of long wavelength lasers to
transmit data over fiber optic cable. The lasers specified
by the Standard operate over either Multimode or Singlemode
Fiber in the wavelength range of 1270 to 1355 nanometers.
GROUND LOOP -
This occurs when a segment is grounded at more than one
point. It creates a situation for a potential voltage
difference between the grounds, causing the network cable to
conduct unwanted electricity. A bad thing.
- Pronounced "gooey", it's the abbreviation for
Graphical User Interface
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HALF DUPLEX - The ability of a
circuit to carry signal in one direction at a time. Ethernet
and Fast Ethernet use half duplex with one pair transmitting
and the other pair receives.
- A generic term describing all computing and peripheral
- A permanent connection between two devices, usually
not easily disconnected.
- A cable adapter used to change an Amphenol type 50
pin Telco connector into multiple RJ-45's or RJ-11's.
- High Level Data Link Control. A bit oriented
protocol developed by the International Standards
- Headroom is the sum of the natural margin, or ACR,
of the cabling and the additional margin between the worst
case NEXT and the limit for NEXT. Headroom is calculated
using a power sum ACR on the worst pair after the
attenuation for that pair has been normalized to 100 meters
HERTZ (Hz) - An equivalent to cycles per second for
- Slang for an induced electrical impulse. (also see
HOME RUN - A cable run going from a workstation or
office directly back to a wiring closet with no other
connections. Physical star topologies consist exclusively of
HORIZONTAL CABLING - The cabling between and including
the telecommunications outlet-connector and the horizontal
- Term describing a Host computer. A central computer
responsible for the control of time-share terminals and
other peripherals. Usually associated with minicomputers and
- 1. A central point of connection for several
circuits. 2. A device which electrically converts a logical
topology to a different physical topology. An ARCNET hub
enables physically star-wired nodes to be seen as a logical,
token-passing bus. Hubs can be active (powered), or passive
(non-powered). Active hubs sometimes are capable of allowing
longer cabling lengths than passive units.
HUB ACTIVATION - Hub activation tests transmit a signal
to a 10 BASE-T hub to verify it is operational.
HYBRID CABLE - An assembly of two or more cables, of the
same or different types or categories, covered by one
- See Hertz.
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- A collection of those telecommunications components,
excluding equipment that together provide the basic support
for the distribution of all information within a building or
I/O CHANNEL - A high-speed bus used to interconnect
peripherals with the CPU.
I/O CONTROLLER - A device that arbitrates the I/O
channel and controls data transfer between devices attached
to the channel.
IBM TOKEN RING - A token passing network topology that
conforms to the IEEE 802.5 definition and documents.
Operating at 4 Mbps or 16 Mbps, it is the chief topology
used to interconnect small and mid-size equipment from IBM
and other vendors.
- Insulation Displacement Connector. A type of connector
in which the insulated wire is pushed down between two sharp
blade-like pieces of metal so that the conductor touches the
connector and there is no exposed bare wire. Modular
telephone plugs (RJ series) are examples of insulation
- Intermediate Distribution Frame as it was called
previous to being changed to "IC" or intermediate
cross-connect in TIA/EIA 568-A. Also known as a wiring
closet, the IDF is a cross connection point for horizontally
attached devices to riser media. Provides the wiring
interface between the end-user and the Main Distribution
Frame. The MDF was change to "MC", which stands for main
- Institute of Electrical and Electronic Engineers. A
standards setting and publishing body responsible for such
guidelines as the 802 series for LAN's.
IEEE 802.X - Guidelines describing the physical and data
link layers of the OSI network model for various topologies.
- The complex opposition to current flow dynamically in a
transmission medium. Including components of resistance,
capacitance and inductance when driven by a voltage source.
CHARACTERISTIC IMPEDANCE for more detailed information)
IMPEDANCE MATCHING - An operation to assure maximum
transfer of signal power over the operating frequency range
by proper selection of all elements of a transmission
system. A properly impedance matched system transfers
maximum signal power to the load with no signal distortion.
IMPULSE NOISE - Intermittent, short, high frequency,
high amplitude pulses that are induced into a transmission
line. Can cause data corruption and in some cases hardware
- The tendency for an electrical current to build a
magnetic field around a conductor and cause a portion of
that current to be induced or generated on an adjacent
conductor. (also see
INSERTION LOSS - The signal loss resulting from the
insertion of a component, or link, or channel, between a
transmitter and receiver (often referred to as attenuation).
- A non-conductive material used to separate conductors to
prevent electrical short circuits. Cables are insulated and
rated for different applications. Plenum rated cables can be
used anywhere inside a building and riser rated cables are
only used between floors.
INTELLIGENT TERMINAL - A computer terminal or personal
computer/workstation having the ability to process data
independently from the host computer.
- A connection scheme that employs connecting hardware for
the direct connection of a cable to another cable without a
patch cord or jumper.
- The point at which two different items come
together. They might be mechanical, electronic or software.
INTERNET PROTOCOL (IP) - Used at OSI Level 3 and above
to connect networks through gateways.
- The connection of multiple networks for data
interchange. This is normally accomplished with interface
devices such as bridges, brouters and gateways.
- Initial Program Load. A fancy term for "booting" a
- Interrupt ReQuest. A form of peripheral
prioritization for microcomputers.
- International Standards Organization. Based in
Paris, this body develops open industry standards for the
world. A key standard is the Open Systems Interconnection
Network Model (OSI model) which forms a general definition
for all LAN's. ISO 11801 is similar to ANSI/EIA/TIA/568-B
but uses different terms and values in some instances.
to the top
JABBERING, JABBER - The
continuous transmission of meaningless data, usually due to
a failure of some sort. The network slows tremendously when
burdened with this excess traffic.
- A receptacle for a modular device. Mates with a
- The outer protective sheath of a cable.
- The skewing of a transmitted pulse so as to cause
its edge to become poorly defined and difficult to correctly
- An assembly of twisted pairs without connectors, used to
join telecommunications circuits/links at the cross-connect.
to the top
- A short form for the metric "Kilo" or 1000. Often
appended to measurements of things like frequency (KHz),
storage (KBytes), and bit rate (Kbps).
- The mechanical feature of a connector system that
guarantees correct orientation of a connection or prevents
the connection to a jack or to an optical fiber adapter of
the same type intended for another purpose.
to the top
- Local Area Network. A
distributed processing environment usually located within
the confines of a single building.
LAUNCH CABLE - A known good fiber optic jumper cable
attached to a source and calibrated for output power used
for loss testing. This cable must be made of fiber and
connectors of a matching type to the cables being tested.
- From cable manufacturing. A term describing the
length of one conductor in a twisted pair in making one
- A subdivision of a complete model comprising
software and/or hardware elements to complete a specific and
related set of tasks.
- Liquid Crystal Display.
- See LONGITUDINAL CONVERSION LOSS.
LCTL - See LONGITUDINAL CONVERSION TRANSMISSION LOSS.
LED -See LIGHT-EMITTING DIODE.
LENGTH - The
distance of a communications link measured by a tester with
a TDR. For TIA/EIA 568-B.2, the Permanent Link is limited to
90 meters of horizontal cabling embedded in the walls and
ceiling plenum. Length is one of the ANSI/EIA/TIA-568-B.2
required tests for a Category 5e UTP cable limited to a
total distance of 100 meters including the Permanent Link of
90 meters + 10 meters allowance of line cords, patch cords
and up to two cross-connects in a link. (also see
NOMINAL VELOCITY OF PROPAGATION)
LIGHT-EMITTING DIODE (LED) - A semiconducting device
that emits light when stimulated by an electrical current.
Used in transmitters for multimode fiber links.
- A term used loosely to describe a connection between
two communicating devices.
- A term referring to the termination pinout pairs of
cable. (also see
LINE SPEED - The maximum rate of data transfer for a
- A transmission path between two points, not including
terminal equipment, work area cables, and equipment cables.
- Logical Link Control. A protocol developed by the
IEEE for end-system addressing and error checking. Operates
in Layer 2 of the OSI model.
- Equipment included in a list published by an
organization, acceptable to the authority having
jurisdiction, that maintains periodic inspection of
production of listed equipment, and whose listing states
either that the equipment or material meets appropriate
standards or has been tested and found satiable for use in a
LOCAL DISTRIBUTION FRAME - LDF. Another name for an
Intermediate Distribution Frame or "IC" as the
ANSI/EIA/TIA-568-B.2 standard specifies.
LONG WAVELENGTH -
A commonly used term for light in the 1300 and 1550 nm
CONVERSION LOSS - A ratio expressed in dB, of measured
differential voltage relative to the common mode voltage on
a conductor pair applied at the same end.
CONVERSION TRANSMISSION LOSS - A ratio expressed in dB,
of measured differential voltage relative to the common mode
voltage on a conductor pair applied at the opposite end.
LOSS BUDGET -
Sometimes known as dB LOSS BUDGET, it is the amount of light
available to overcome attenuation in a fiberoptic link and
maintain performance specifications.
- Longitudinal Redundancy Check. Another term for parity
to the top
- Short form of the metric "Mega" or 1,000,000. Used
as a prefix for frequency (MHz), storage (MBytes) and line
- Representation of the metric "milli" or 1/1000th
- Media Access Control. A control protocol designed
for specific media with variations for different media.
Works in conjunction with LLC.
MACHINE LANGUAGE - The binary digits that the computer
hardware processes without interpretation. Also called
MAIN DISTRIBUTION FRAME - the MDF has been changed to
"MC" (main cross-connect) in ANSI/EIA/TIA-568-B.2. The MC is
the point at which outside service lines interface to inside
service and then to IC's or to TC's.
- A large computer system.
- Metropolitan Area Network. A Network operating
within the confines of a single city or community.
MANCHESTER ENCODING - An encoding method which involves
a digital state change (0 to 1 or vice versa) for every bit
representation occurring in the middle of the transmitted
bit. Useful in local area networks because it is
self-clocking. The receiver can develop the data clock from
the transmitted data stream. Used in Token Ring and Ethernet
systems. Standard Ethernet uses Manchester encoding which
results in 10 Mbps throughput at 10 MHz frequency
- The act of associating logical representations with
their physical counterparts.
- Media Access Unit. Another name for an Ethernet
transceiver. MAU was also the abbreviation for a Token Ring
Multi-station Access Unit. This has been changed recently to
MSAU to avoid confusion.
- Micro-Channel Architecture. IBM's 32-bit peripheral
bus for microcomputers.
- Main Distribution Frame,
which has been changed to "MC" (main cross-connect) by
ANSI/EIA/TIA-568-B. The connecting point in a building where
outside services interface to internal services. All
networking components are "star-wired" back to the MC.
MECHANICAL SPLICE - A semi-permanent connection between
two fibers, made with an alignment device and refractive
index matching fluid or adhesive.
MEDIA (Telecommunications) - Wire, cable or conductors
used for telecommunications.
- Material used for the transmission of signals.
- Management Information Base. An information database
used in conjunction with the Simple Network Management
MICRO (Ã‚Âµ) - Prefix for one millionth. Used as a
prefix for capacitance.
MICROFARAD (Ã‚Âµf) - One millionth of a farad.
- Millions of Instructions per Second. A speed rating
for computers and workstations.
- Modular Jack. A term describing plug-in IDC
connectors used in telephone and data communications. The
connectors usually are configured with 4, 6 or 8 pins.
- Modified Modular Jack. Developed by Digital
Equipment Corp. (DEC), it is an RJ-12 (6 pin) modular jack
with the bottom-locking tab offset to one side.
MODAL DISPERSION - The temporal spreading of a pulse in
an optical waveguide caused by modal effects.
- MOdulator DEModulator. A device which converts
digital data to a modulated form which can be transmitted
over telephone lines and reverses the process when
MODULAR PLUG - A series of connectors designed for ease
of use and flexibility. They are characterized by locking
plastic tabs on the bottom and typically appear in three
configurations: RJ-11 (4-conductor), RJ-12 (6-conductor) and
- Multi-Station Access Unit. The new abbreviation for
a Token Ring wiring center. The units can be active or
passive. They typically have eight ports for device (or
lobe) attachment and a RI (ring-in) and RO (ring-out) port
for network attachment.
- Microsoft NETworks. The predecessor to LAN Manager.
First introduced in MS-DOS version 3.1.
- Mean Time Between Failures. The average operational
time of a device.
MULTIMODE FIBER - A fiber with a core diameter (commonly
50 or 62.5 microns) much larger than the wavelength of light
transmitted that allows many modes of light to propagate.
Commonly used with LED light sources for lower speed, short
distance links. More recently used with VCSEL laser light
sources for Gigabit Ethernet.
MULTIMODE PROPAGATION - A method of introducing a light
pulse with multiple light rays (modes) into an optical
fiber. Multimode is typically used for short-haul
applications of less than 2 KM using relatively inexpensive
light sources usually operating at a 850 or 1300 nanometer
wavelength. Gigabit Ethernet uses an 850 VCSEL laser while
most other applications use Light Emitting Diode (LED) light
- The ability of a system to run two or more processors
- A device which causes two or more signals to use the
same communications medium. Multiplexing can occur in either
the frequency or the time domain.
MUTUAL CAPACITANCE - The capacitance between two
conductors with all other conductors shorted to ground.
- A short form slang of multiplex. Also MUXED, MUXING.
to the top
- No Acknowledgment. A data
communications negative response.
NEAR-END CROSSTALK (NEXT) - The coupling of power from
the transmitted signal pair to an adjacent pair at the same
transmitting end of the LAN cable.
- Network Basic Input/Output System.
- A network management offering from IBM.
- A popular network operating system from Novell Inc.
NETWORK ADDRESS - A number giving a specific
identification to a network attached device.
NETWORK INTERFACE CARD - NIC. A circuit card providing
the hardware interface between a network device and the
NETWORK OPERATING SYSTEM - NOS. The software component
of a network. The NOS contains all instructions pertinent to
data transfer, file manipulation and services and
NETWORK TOPOLOGY - The physical layout and
interconnection of a network.
- See NEAR-END CROSSTALK.
- A connection point into a network. The node may
perform several functions (i.e., file server, workstation,
print server, bridge, etc.).
NOMINAL VELOCITY OF PROPAGATION - "NVP" is the relative
speed a signal travels on a conductor that is proportionate
to the speed of light in a vacuum. Length measurements are
determined by sending a signal down a line and measuring the
reflected signal that comes back and factoring in the amount
of time that it took to make the return trip. (also see
c and LENGTH)
to the top
- A cable adapter that
transforms a 25-pair feeder into individual modular plugs.
ODD PARITY - An error checking method in which binary
1's or zeroes are added to a character so that the number of
1's is always odd.
- A measure of resistance. One ohm allows one ampere
of current to flow across a one volt potential.
OPEN CIRCUIT - An incomplete circuit. A cable connected
at one end only is an example of an open circuit. The
opposite of a short circuit.
OPEN OFFICE - A floor space division provided by
furniture, moveable partitions or other means instead of by
OPERATING SYSTEM - A software program or collection of
programs that manage the computer's hardware and provide an
interface to that hardware for the end-user.
OPTICAL LOSS TEST SET - A measurement instrument for
optical loss that includes both a meter and a light source.
OPTICAL POWER - The amount of radiant energy per unit
time expressed in linear units of Watts or on a logarithmic
scale in dBm (where 0 dB equals 1 mWatt) or dB* (where 0 dB
= 1 microwatt).
OPTICAL RETURN LOSS (ORL) - Light reflected from the
cleaved or polished end of a fiber caused by the difference
of refractive indices of air and glass.
OPTICAL TIME DOMAIN REFLECTOMETER (OTDR) - A device that
uses an emitted light pulse of known power and width and
measuring the light that is scattered back from events along
the length of the fiber. Distance to splices, connectors,
faults and the end of the cable can then be calculated and
- Abbreviation for Operating System.
- Open Systems Interconnect. A seven layer model
defining the different levels of data communications in a
network environment. Developed by the International
Standards Organization. Cables comprise the Physical Layer
of the OSI model.
OTDR - See OPTICAL TIME DOMAIN REFLECTOMETER.
- A metallic or nonmetalic box mounted within a wall,
floor or ceiling and used to hold telecommunications
outlets/connectors or transition devices.
- A cable placed in a residential unit extending directly
between the telecommunications outlet/connector and the
(Telecommunications) - A connecting device in the work
area on which horizontal or outlet cable terminates.
- Telecommunications infrastructure designed for
installation exterior to buildings.
to the top
- A group of data in an
organized form with a distinct header, control information
and a destination address.
PACKET SWITCHING - The transmission of packetized data
through a network. Each packet has information linking it to
the rest of the total message or file as well as the
destination address. This form of communication is efficient
because each packet can take a different route if necessary
to maximize throughput.
PACKET SWITCHING NETWORK - A network constructed to move
data packets. An X.25 network is an example of a packet
- Two wires, usually twisted around each other.
PAIRED CABLE - Cable in which all conductors are
arranged in color-coded pairs usually twisted around each
other and then surrounded by a sheath.
PARALLEL DATA - Multiple bits of data transmitted each
on its own line simultaneously.
PARITY CHECK - The addition of a bit to a character to
aid in error checking.
PATCH CORD - A Length of cable with a plug on one or
PATCH PANEL - A
cross-connect system of mateable connectors that facilitates
- Public Data Network.
- Premise Distribution system.
PEER-TO-PEER NETWORK - A network in which all devices
have equal status and abilities for file transfer, printer
PERMANENT LINK - The Channel Link includes up to 90 m
(295 ft) of horizontal cable and one connection at each end
and may also include an optional transition/consolidation
point connection. The permanent link configuration excludes
both the cable portions of the test cord and the connection
to the testing device.
PHYSICAL LAYER - The bottom layer of the OSI model,
concerning physical interconnect hardware and electrical
interface between devices.
- 1 X 10 -12 . Used as a prefix usually for
capacitance (pF) values.
(pF) - One-trillionth (10 -12)
of a farad. A common unit used in measuring mutual
capacitance in cable.
PLENUM CABLE - Cable that can meet the UL 910 (Steiner
Tunnel) test by using fire retardant insulation that
inhibits fire propagation and toxic fumes. These cables can
be used in horizontal runs in open air ceiling returns and
will be clearly indicated with a "P" suffix (such as CMP) as
certified by UL, ETL or other third party testing firms. It
is typically coated with TEFLONÃ‚Â®.
- In LAN applications, it is a query to a node looking
for information to be transferred on the network.
POLYVINYL CHLORIDE - PVC. A common insulation material
sheathing many types of paired and axial cable. Emits very
toxic gases when burned so it may not be used in free-air
plenums or risers in premises applications. (also see also PLENUM CABLE)
- Plain Old Telephone Service. Slang term to describe
unknown, older, generic telephone wire.
POWER BUDGET - The difference (in dB) between the
transmitted optical power (in dBm) and the receiver
sensitivity (in dBm).
POWER METER (Fiberoptic) - An instrument that measures
optical power emanating from the end of a fiber.
POWER SUM - Pair-to-Pair measurements are used to
measure one pair against another. Power Sum measurements
select a pair and then measure the disturbances from other
pairs within the same sheath. This can be used in a 4-Pair
or other high pair count (25, 50, 100 and up) to determine
the effects of all the cables (of course testers only test
4-Pair at a time). Power Sum ACR, ELFEXT, and bidirectional
NEXT measurements are made with the LT8000 Series. In
general, this results in an approximately 3-dB loss limit
when compared to pair-to-pair test values.
ATTENUATION TO CROSSTALK RATIO (PSACR) - A ratio
expressed in dB, determined by subtracting the insertion
loss from the POWER SUM NEAR-END CROSS TALK LOSS.
POWER SUM EQUAL
LEVEL FAR-END CROSSTALK (PSELFEXT) - A computation of
the unwanted signal coupling from multiple transmitters at
the near-end into a pair measured at the far-end relative to
the received signal level on that same pair.
POWER SUM NEAR-END
CROSSTALK LOSS (PSNEXT) - A computation of the unwanted
signal coupling from multiple transmitters at the near-end
into a pair measured at the near-end.
PREMISES DISTRIBUTION SYSTEM - A multifunction wiring
system designed by AT&T for integration of voice, data,
video and graphics. It includes cables, adapters, electronic
modules, wall jacks and protective covers. It is scalable
from a single floor to a campus environment.
PRIMARY RATE INTERFACE (PRI) - An ISDN service
consisting of either 23 B-channels + 1 D-channel (1.544
Mbps) or 30 B-channel + 1 D-channel (2.048 Mbps). (also see B-CHANNEL and D-CHANNEL) .
PROPAGATION DELAY - Propagation Delay is the time it
takes for a signal to propagate from one end of a conducting
pair in cabling, cables or connecting hardware to the
opposite end of that pair. (also see
- The speed at which electricity travels in a transmission
medium. Expressed as a percentage of the speed of light that
is represented as a lowercase "c".
- A set of rules governing all aspects of communicated
PROTOCOL ANALYZER - A device capable of capturing,
monitoring, decoding and analyzing various communications
protocols. A high level troubleshooting and analysis tool.
- See POWER SUM ATTENUATION TO CROSSTALK RATIO.
PUNCH-DOWN BLOCK - A device used to terminate and
cross-connect premises wiring. (also see also CONNECTING BLOCK)
PULL STRENGTH - See
- The pulling force that can be applied to a cable.
PVC - See POLYVINYL CHLORIDE.
to the top
- A metal or plastic trough
used to guide and carry installed cabling.
- Any device which receives communications. The opposite
of a transmitter.
(Optical) - A device containing a photodiode and signal
conditioning circuitry that converts light into an
electrical signal in fiberoptic links.
- The blockage or obstruction of current flow. A
property of all conductors, it is measured in ohms.
RETURN LOSS - A measure of impedance mismatch
indicated by a return echo signal reflection. It is often
referred to as "RL" and it measures the ratio between the
transmitted signal strength and the signal reflected back to
the transmitting end. Like attenuation, excessive return
loss indicates reduced signal strength at the receiver end
and it can indicate a mismatched impedance at some point
along the cable link. Return Loss is reported as a dB value
for each pair, from each end. A value of 20 dB or higher for
UTP is very good and a value below 10 dB causes a large
reflection of signal back to the source and is not good. The
IDEAL LT8000 Series provides this measurement.
REVERSED PAIR - See also SPLIT PAIR and TRANSPOSED PAIR.
A situation that occurs when the one end of a twisted pair
has its connections reversed. This condition is detected by
a LAN Cable Tester's
Wiremap test. (also see SPLIT PAIR and TRANSPOSED
- The path between floors of a building carrying
cables which interconnect the floors.
- A device used to connect LAN's utilizing different
communications protocols. It directs traffic within networks
and offers security by restricting access to those that
don't belong. Routers require intensive programming
instructions and are used mostly for WAN (wide area network)
interface to outside services.
- A standard developed by the EIA defining signal levels
and pin assignments for serial data communications. Much
misused and modified, it no longer represents a standard,
but a general guideline to follow when interfacing DTE and
to the top
- Systems Application
Architecture. Specifications designed by IBM to insure
compatibility at the application (highest) level between all
newly developed software packages.
- The downward curvature of a wire or cable due to its
weight. The TIA/EIA 569 Pathways and Spaces Standard
requires Category 5 cable to be supported at 48" to 60"
intervals and the sag cannot exceed 12" between supports.
SC CONNECTOR - The SC (Subscriber Carrier) fiber optic
connector is one of three connectors (the other two are ST
and SFF) approved by ANSI/TIA/EIA 568-B.3. The SC
Connector's main advantage is polarization since the
connectors can be paired and keyed.
SCATTERING - The change of direction of light after
striking small particles that causes loss in optical fibers.
- An element of a cable formed by a shield
- Small Computer Systems Interface. A high-speed
semi-intelligent peripheral interface for microcomputers.
- Synchronous Data Link Control. A bit oriented
synchronous communications protocol developed by IBM for use
- A cable run. Its maximum length is determined by the
topology. A 10BASE2 segment may be up to 605 feet long. A
10BASE-T segment may be up to 328 feet long.
SERIAL TRANSMISSION - The sending of multiple data bits
down a single line in a stream.
- A network device which provides a service to other
network devices. Services include file, printer,
communications or gateway.
SESSION LAYER - The fifth layer of the OSI model dealing
with network processing, linking and unlinking users from
their chosen service.
SFF CONNECTOR - See
SMALL FORM FACTOR CONNECTOR.
SHORT WAVELENGTH -A commonly used term for light in the
665, 790, and 850 nm ranges.
SINGLEMODE FIBER - A fiber with a small diameter
(commonly 8-10 microns) core, only a few times the
wavelength off light transmitted that only allows one mode
of light to propagate. Commonly used with laser sources for
high-speed, long-distance links.
SMALL FORM FACTOR CONNECTOR (SFF) - The SFF CONNECTOR is
a term used to describe a group (rather than a single) of
fiberoptic connectors approved by ANSI/TIA/EIA 568-B.3
(along with ST and ST Connectors). They are not presently
used for Singlemode connections. They are designed to reduce
the size of patch panels, thereby reducing the number and
cost of telecommunication closets to make
fiber-to-the-desktop more competitive with copper. Popular
SFF connectors include SC/DC, LC, MT-RJ, Volition and Fiber
SHARED LOGIC - The simultaneous use of resources in a
computer by several users.
SHEATH - See
SHIELD - A
metallic layer placed around a conductor or group of
SHIELDED PAIR - A pair of wires, twisted together and
covered with a conductive material to provide any
potentially induced noise a quick path to ground.
SINGLEMODE PROPAGATION - A method of introducing a light
pulse into a single light ray (mode) into an optical fiber.
Singlemode is typically used for long-haul applications of 2
to 50 kilometers using relatively expensive laser light
sources usually operating at a 1310 or 1550 nanometer
SHORT CIRCUIT - A condition that exists when two
conductors are connected ahead of where they normally should
be in a circuit. This causes reduced resistance and
sometimes the undesirable side effects.
SIGNAL GROUND - A common point of reference for all
other signals in a communications interface.
SIGNAL TO NOISE RATIO - (SNR) The ratio of received
signal to existing system noise. In LAN applications it is
the attenuation to NEXT ratio. Both are expressed in
SILVER SATIN - Flat, untwisted cable used typically as a
telephone extension cord. It should never be used in a Local
- Transmission in one direction only.
Ã¢â‚¬â€œ See DELAY SKEW.
- Systems Network Architecture. Developed by IBM as a
path to interconnect all of its computer products. Very
common and very successful.
- Simple Network Management Protocol. A popular
network management protocol that is incorporated into many
intelligent hubs and concentrators. Originally designed for
TCP/IP, it now functions independently and with most
topologies and network operating systems.
- Synchronous Optical NETwork.
SOURCE - A laser diode or LED used to inject an optical
signal into a fiber.
- Another name for a binary "0" in data
- A splice describes the connection of two fibers in a
permanent joint. A splice may be formed by "fusion
splicing," wherein the two fibers are welded together,
usually with an electric arc. Alternatively, a splice may be
formed by "mechanical splicing" that uses a mechanical
alignment fixture and a matching gel or epoxy to minimize
SPLIT PAIR - A situation that occurs when a twisted pair
is misconnected so that it becomes Ã‚Â½ of two separate
pairs. The noise immunity of the twists is lost and an
impedance mismatch is created. This wiring error will not
show up as an error on a Wiremap, but will be indicated by
very high NEXT. (also see also
REVERSED PAIR and
ST CONNECTOR - The ST (Straight Through or alternatively
Straight Terminus) fiber optic connector is one of three
connectors (the other two are SC and SFF) approved by
ANSI/TIA/EIA 568-B.3. The ST Connector is the most widely
used connector for Multimode fiberoptic cable.
STAR TOPOLOGY - A physical layout in which each device
is wired back to a central point.
START BIT - In asynchronous communications, a start bit
and stop bit delimits each character to indicate to the
receiver the character's location.
START/STOP TRANSMISSION - Another term for Asynchronous
STOP BIT - The trailing bit in an asynchronous character
- Shielded Twisted Pair. Cable constructed of pairs of
insulated wire twisted around each other surrounded by
shielding material made of foil or braid or both. The entire
group of wires may have a common shield or as found in
Category 7 cables, each pair may be shielded individually
with another shield around the entire group just under the
STRANDED CONDUCTOR - A wire or cable constructed of
several small strands of conductor instead of one larger
solid piece. This configuration provides for more
flexibility in certain applications. Patch cords are made
out of stranded conductors and the NEXT values are degraded
up to 20% to allow for them in a link.
SURFACE EMITTER LED - An LED that emits light
perpendicular to the semiconductor chip. Most LEDs used in
data communications are surface emitters.
- Multi-port device used to connect a quasi-exclusive
10/100/1000 Mbps connection between any two-end systems
using the source and destination addresses of the packet via
the internal bus. Switches work at the MAC (Media Access
Control) Layer and above and use either "store and forward"
or "cut-through" technology. Switches are "plug-and-play "
devices that can be used to segment a network when it starts
to slow down. Each port can function at the rated speed of
the switch and some are auto-sensing for 10/100 Mbps.
Ethernet switches are offered as standalone systems or as
modules for existing hubs.
SYNCHRONOUS TRANSMISSION - Transmission between devices
with a common clock. Data can be sent at a much higher speed
because there is no need to frame each character.
to the top
T CONNECTION - A connector
fanning out in three directions and looking like a "T".
Commonly used is a BNC T connector for 10BASE2 applications.
- An electrical connection to a bus to enable access.
A tap may be invasive (requiring a cable splice), or
non-invasive (a "vampire" tap).
- Transmission Control Protocol/Internet Protocol. A suite
of protocols designed by the Department of Defense to enable
communications between dissimilar computer systems. Now
widely used by the commercial and academic sectors.
- Time Domain Reflectometer. A piece of test equipment
used to measure metallic cable length and impedance.
- Any transmission, emission, and reception of signs,
signals, writings, images and sounds, that is information of
any nature by cable, radio, optical or other electromagnetic
TELECOMMUNICATIONS INDUSTRY ASSOCIATION - Known as TIA,
this association is made up of two autonomous parts. The
first operates as a traditional trade association structured
to promote the common interests of its members. The second
operates as the Standards Development organization for the
telecommunications industry in North America.
TERMINAL SERVER - A device that allows connection of
several terminals and multiplexes them onto a LAN cable.
- To connect a wire or wires to a device or a matching
- Another term for IEEE 802.3 10BASE-5 systems.
THIN ETHERNET - Normally describes a 10BASE-2 system.
Also called Cheapernet.
TIA - See TELECOMMUNICATIONS INDUSTRY ASSOCIATION.
- A unique combination of bits that passes from station to
station in a token passing network. When a station has the
token, it may communicate with the network.
TOKEN BUS - A bus topology that uses token passing as
its contention method.
TOKEN PASSING - Moving a special combination of bits
from station to station in a ring or bus when there is no
traffic. When a workstation has the token, it may then use
the network channel for communications.
TOKEN RING - A logical ring topology that passes a token
in one direction around the ring. A given device must
possess the token to communicate with any other device. If
it does not gain control of the token as it passes, it must
wait until the token goes around the ring.
- The geometric form describing a network's logical and
- See TIA/IEEE STANDARDS COMMITTEES.
- A measure of the activity on a network at a given
time. Network analyzers can monitor traffic and when
Ethernet segments start to exceed 30% to 40% utilization,
they run much slower and need to be segmented with switches.
- A device which can transmit and receive information,
typically to a workstation from a network connection.
TRANSFER IMPEDANCE - A measure of shielding performance
determined by the ratio of the voltage on the conductors
enclosed by a shield to the surface currents on the outside
of the shield.
TRANSPORT LAYER - Level 4 of the OSI model, this layer
deals with end-to-end control of the transmitted information
and provides results to the session layer.
TRANSPOSED PAIR - A transposed pair occurs when the ends
of two twisted pairs are interchanged. This condition is
detected by a LAN Cable Tester's Wiremap test. (also see
SPLIT PAIR and REVERSED PAIR).
TRANSVERSE CONVERSION LOSS - A ratio expressed in dB, of
measured common mode voltage on a pair relative to the
differential mode voltage on the same pair applied at the
TSB - 67, TSB - 95 - Technical Service Bullets that
augmented the ANSI/EIA/TIA-A Standard. TSBs were
incorporated into the body of ANSI/EIA/TIA-B, and further
updates are issued as updated Standards.
TWINAXIAL CABLE - Cable constructed of two insulated
center conductors surrounded by a braided shield. Widely
used in midrange IBM systems (AS 400's).
TWISTED PAIR - Two insulated wires twisted around each
other at regular intervals. May be shielded or unshielded.
The number of twists per foot directly relates to the
relative noise immunity of the pair.
to the top
- See UNDERWRITERS LABORATORIES.
UNDERWRITERS LABORATORIES (UL) - A testing body formed
primarily to certify fire safety of electrical equipment
dealing with voltages greater than 48 VAC or DC. UL has the
most recently assumed the responsibility for certification
of data grade unshielded twisted pair media for conformance
to EIA/TIA and NEMA specifications. The cable categories III
through V from the EIA/TIA TSB 36 document serve as the
basis for UL cable LEVELS 2 through 5. Cable certified by
the UL to meet these standards would bear a marking
UNIVERSAL SERVICE ORDERING CODE - USOC. A wiring
standard for telephone service to an individual phone. In a
modular plug, the two center conductors are the primary
pair, and supplementary pairs radiate out concentrically.
For example, in an RJ-45 (eight pin) plug, pins 4,5 are the
primary pair with pins 3,6 - 2,7 - 1,8 forming the
supplementary pairs. Note that this is not compatible with
TIA/EIA 568-A's recommendation of T-568A or T-568B.
UNIVERSAL SYSTEMS BUS (USB) - A bus for transmitting
data between computing devices. Rated at 11 Mbits per
second, it offers about 100 times the throughput of a Serial
- Universal Synchronous/Asynchronous Receiver Transmitter.
- See UNIVERSAL SYSTEMS BUS.
- Unshielded Twisted Pair. Cable constructed of
typically multiple twisted pairs of wires, unshielded in a
PVC- or plenum-rated sheath.
- Microvolt. One millionth of a volt.
- A "micro-meter" equals one millionth of a meter.
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VAMPIRE TAP - A tap system for 10BASE5 systems that does
not require cutting and splicing the cable. This system uses
a sharp pin that pierces the insulator and contacts the
center conductor of the thick 10BASE5 cable.
VCSEL - See VERTICAL CAVITY SIDE-EMITTING LASER
VERTICAL CAVITY SIDE-EMITTING LASER (VCSEL) - A type of
light source usually operating at 850 nm and used for
Gigabit Ethernet applications.
VOICE GRADE - A designation for a facility capable of
carrying signals with a frequency range of 200 - 4000 Hertz.
- The potential difference in energy between two
- Virtual Telecommunications Access Method. A software
suite designed by IBM for their 370 line to manage remote
communications for the host and users.
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- Wide Area Network. A
network typically spanning a continent or the globe and
connected by routers.
- Wide Area Telecommunications Service.
WAVELENGTH DIVISION MULTIPLEXING - WDM is a method
encoding data for transmission over an optical fiber.
- See WAVELENGTH DIVISION MULTIPLEXING.
WIRING CLOSET - Typically called a telecommunications
closet (TC). It is a central point for horizontal floor
wiring to connect to vertical riser cable or to backbones
running to an IC or MC.
- A test performed in the suite of ANSI/EIA/TIA-B.2
requirements that determines the pinout configuration of the
wiring pairs. This is the first test a Category 5 tester
runs and it looks for opens, shorts, reversals, split pairs
and any other miswiring. TIA/EIA 568-B.2 specifies that all
four pairs are terminated for Category 5 UTP. Each
respective protocol has different pinouts as shown by the
WIREMAP test results. Ethernet uses pins 1,2 and 3,6 and
Token Ring uses 3,6 and 4,5. (also see LINEMAP)
- The number of bits transmitted in parallel on a data
WORK AREA (work
- A building space where the occupants interact with
telecommunications terminal equipment.
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- A basic form of information flow control for data
communications, the receiving device would issue an X-OFF to
the transmitter while it emptied its buffer to disk or
performed another operation. When the receiver was ready for
more data, it would then issue an X-ON.
- Abbreviation for cross-connect.