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Attenuation–Crosstalk ratio. The value of attenuation, less the crosstalk value, both expressed in dB, at a particular frequency. A quality factor for cabling that expresses the relation of two important measured values.

Gigabits per second.


One billion bits of data. Abbreviated Gb.



See Asymmetric Digital Subscriber Line. GHz. A unit of frequency equal to 1 billion hertz.

Adapter, Optical Fibre


A passive coupling device that connects two male optical fibre connectors, aligning the light path. Graded index plastic optical fibre.

Analogue Signal

Ground Loop

An electrical signal that varies continuously, without discrete steps as with a digital signal. A condition whereby an unintended connection to ground is made through an interfering electrical conductance.


American National Standards Institute.


Approved Ground

Half Duplex

A building ground and or bonded earth connections that meet Health & Safety requirements and latest edition (16th) of Electrical Standards. A communications method where both transmitted and received signals are not simultaneously present, but alternate in presence (e.g., commercial two-way push-to-talk radio and standard, half-duplex Ethernet).

Asymmetric Digital Subscriber Line


ADSL. A high-speed, digital telecommunications technology offering fast downloads capabilities of 6Mbps, but much slower uploading speeds of 65Kbps. The unit of frequency, 1 cycle per second.


Horizontal Wiring

Asynchronous Transfer Mode. A transport protocol based on fast switching of 53 byte cells. With its high-speed operation, fast switching, and guaranteed delay times, ATM can transmit voice, data, and video efficiently along the same transmission path. Telecommunications (structured) wiring from the user station to the first termination point in the telecommunications room.



The decrease in magnitude of a signal as it travels through any transmitting medium, such as copper cable or optical fibre. Attenuation is measured as a ratio or as a logarithm or a ratio (dB). Optical fibre attenuation is measured in dB/Km. A device that is used to connects computers together on a LAN, typically in a star topology.

Audio Frequency


The range of frequencies within the range of human hearing. This range is generally as 20 to 20,000Hz, although few of us can detect sounds below 30Hz or above 16Hz. Heating, Ventilation, and air-conditioning units.

Average Power


The average level of power in a signal that varies with time. Abbreviation for hertz.



American Wide Gauge. An American wire diameter specification. The smaller the AWG number the larger the wire diameter.



Local Area Network. A computer network that typically exists within a single building or office or among a group of nearby buildings. Modern LAN’s may now interconnect various branches of a retail outlet spanning the United Kingdom and beyond.

Backbone Cable


Cable that connects distribution units in a single building or a group of buildings. A coherent source of light with a narrow beam. The word comes from ‘light amplification by stimulated emission of radiation’. Laser sources are normally used for Singlemode optical fibre transmissions. The laser source for most LAN connections is a semi-conductor laser diode.



An optical fibre term that refers to the scattering of light, in the opposite direction from which it was originally travelling. Light emitting diode.



A transforming device that matches an un-balanced circuit to a balanced circuit. An impedance matching device. Low Smoke Zero Halogen. Cable sheath type for preferred use in plenum rated areas.



The range of frequencies required for proper transmission of a signal, expressed as a difference in hertz (Hz). A continuous range from zero is said to be a baseband signal, while a range, which starts substantially above zero, is said to be broadband (or narrowband in the case of RF signals).


Media attachment unit. The transceiver in an Ethernet network; also a common name for the MSAU in a token-ring network



Audio and video signals sent over coaxial cable, typically used in CATV. Megabits per second. A bit is one unit of a digital signal.

Basic Link


The portion of a structured wiring cable connection between the cable termination at the horizontal cross-connect and the work area outlet connector. The length of a basic link is 90m. Note that the basic link now been replaced with the Permanent Link. Prefix meaning million.



The number of digital data signal-level transitions per second. For some common coding schemes, this would equate to bits per second, but this is not true for more complex coding schemes. Unit of frequency equal to 1 million hertz (1 million cycles per second).



A unit that represents the logarithm of the ratio of two power levels. See dB. Prefix meaning one-millionth.

Bend Loss


Increased attenuation in an optical fibre caused by an excessively small bend radius. Bend loss may be temporary or permanent if the micro-fractures caused by the bend attenuate the light signal through the affected area. One millionth of a farad.

Bend Radius


The radius of curvature of a bend in a cable. Cables may have transmission performance degradation from a bend radius that is below a certain amount. Millionth of a metre.



Bit Error Rate. The fraction or number of bits of digital data not transmitted or received fully. A single electromagnetic wave travelling in a wave-guide, such as optical fibre.


A tape of thread used for holding groups of pairs together within a cable. Multi-pair cables often bind in pair’s in-groups of 25 and 100 pairs.  


Modal Dispersion

One binary digit. A bit may assume a binary value of 0 or 1. See Dispersion.



A coaxial cable connector that uses a ‘bayonet’ style turn-and-lock mechanical mating method. Multi-station Attachment Unit. The device for interconnecting station lobe cables to from a ring in the token-ring network.


Multimode Optical Fibre

The method used to produce good electrical contact between metallic parts. In the wiring context, bonding describes electrical connection of grounding bars and straps within a building to the central approved ground. A fibre wave-guide that supports the propagation of multiple modes. Multimode fibre may have a typical core diameter of either 50ìm or 62.5ìm with a refractive index that is graded or stepped. It allows the use of inexpensive LED light sources and connector’s alignment and coupling is less critical than with Singlemode fibre. Distances of transmission and transmission bandwidth are less than Singlemode fibres because of dispersion of the light signal.



A network hardware device that connects LAN segments together.



One-thousandth of one-millionth.
A very high-speed data transmission system, capable of supporting large transfers of media such as sounds, video, and other data.


Butt Set

(nm) One-billionth of a meter.
A telephone-testing device resembling an oversized handset that is used for temporary connection and operation of a telephone line. See also telephone cable termination 



One-billionth of a second.
Commonly believed to be a group of 8 bits, although in fact a byte may be as much as 10 bits although only 8 will be used for data.



A synthetic rubber that has good resistance to chemicals and flame. The chemical is polychloroprene.



An acronym for cable television. The term was derived from Community Antenna Television. Near-end crosstalk. Crosstalk between two twisted pair measured at the same end of the cable as the signal source.



A fixed-length data packet transmitted in certain digital systems such as ATM. See nominal velocity of propagation.

Central Office

Nominal Velocity of propagation

An American telecommunications phrase that refers to either a telephone company facility for switching signals among local telephonic circuits or another used as another term for a PABX, although generally a large voice switch that is able to handle in excess of 1000 users. The speed of signal propagation through a cable, expressed as a decimal fraction of the speed of light in a vacuum. Considered being ‘nominal’ because variations in geometry along a cable may produce absolute variations in the value. The NVP is used in reflectometry to closely estimate the length of a cable by the formula length = ½t X NVP x c, where t is the transit time for the reflected pulse and c is the speed of light in a vacuum. NVP is sometimes given as a percentage, but must be converted to a decimal fraction to be used in the formula.



The entire structured cabling wiring connection between equipment in the telecommunications room to the work area equipment, including all users cords, patch cords and jumper wires. Total length is referred to as 90m (permanent link) + 10m (patch cords etc).


The electrical unit of resistance. The value of resistance through which a potential difference of 1 volt will cause a current flow of 1 ampere.

Characteristic Impedance

A value of impedance (resistance and reactance) of a transmission line measured over a frequency range that would exist if the line were infinite in length. A transmission line of finite length will have perfect power transmission, allowing for absorptive transmission losses, if driven and terminated by exact conjugates matching load impedance. An exact match will cause reflections that increase transmission loss.


A break in the circuit or wiring.

Optical Fibre

A thin filament of glass used for the transmission of information-bearing light signals.

Coaxial Cable


A type of cable consisting of a conductor contained inside a tubular conducting shield, separated by a dielectric A version of the TDR intended for use with optical fibre cables.
material and covered with an insulating jacket. The shield may be foil, wire, braid, or solid metal, and is typically at ground potential.




Reducing the number of bits required too encode a digital signal. This is generally achieved by eliminating long strings of identical bits or bits that do not change in format. A group of bits grouped serially in defined format, containing a command or data message over a network.

Consolidation Point

Patch Panel

A location between a telecommunications room and user work areas at which multiple station cables are brought together for cross-connection or interconnection and consolidation. Typically used in modular offices as a permanent point of termination between the telecommunications room and the movable office modules. A panel containing jacks or connectors that is used to connect or provide access to telecommunications or data circuits.


Permanent Link

The light transmitting central portion of an optical fibre. The core is surrounded with a cladding that has a higher refractive index and thus helps channel the light along the core, as a wavelength. The portion of a structured wiring connection between the cable termination at the horizontal cross-connect and the work area outlet connector, excluding the test cables entirely. The permanent link total length is 90m.



Customer main earthing terminal Prefix meaning one-millionth.

Crossed Pair


A wring error in twisted pair cabling where both conductors of one pair are incorrectly exchanged for conductors of another pair at one end of the cable. Pairs in Metal Foil (a type of STP cable).



The coupling of unwanted signals from one pair within a cable to another pair. Any space, whether closed or open that is used for air circulation. For example, air ducts, return ducts, airshafts, and above ceiling air return spaces. Workspaces are not generally considered plenum spaces.


Plenum Cable

Carrier Sense Multiple Access with Collision Detection. The access method used by Ethernet. Cable that has been certified by the manufacturer as meeting accepted standards for installation in plenum spaces without enclosing in metallic conduit. Plenum cable is generally fire resistant and has low emissions of smoke and toxic fumes in contact with a flame.


Polyvinyl Chloride

Dark Fibre

Installed optical fibre without a transmitter or receiver. Typically installed to offer expansion capacity.

PVC. A general-purpose thermoplastic used for wire and cable installation and jackets. PVC is known for its high flexibility. Often used in non-plenum wire and cable installations.



Decibel abbreviation. A logarithmic unit of measure expressing the ratio between two power levels. The value is 10 times the value in Bels (named after Alexander Graham Bell). Power Sum. A term that indicates that a measured parameter includes the sum of contributions from all pairs in a cable, excluding the pair under test, with no other pairs excited simultaneously.



Polyvinyl Chloride.

Demarcation point. The point of telecommunications termination by a telecommunications carrier within a building or residence. The user (subscriber) has the responsibility for circuit operation beyond the demarcation point.




An insulating material between two conductors. Abbreviation for radio frequency.

Digital Signal


An electrical signal that uses two or more discrete physical layers or signal phases to transmit information. For example, the conversion of a voice waveform to a digitally encoded representation of the waveform produces a data stream in which instantaneous amplitude samples of the voice are represented by a binary value. The data stream may then be transmitted as discrete elements and decoded at the far end to reproduce the original signal. A device whose purpose is to capture transmitted signal energy and converts that energy for useful functions.

Digital Subscriber Line


A service offered by telecommunication service providers that transmits digital signals to homes at speeds exceeding 100 kilobits (up to 10 megabits per second) over twisted-pair cabling – Reaching higher frequency rates that voice signals. A return of electromagnetic energy that occurs at an impedance mismatch in a transmission line, such as LAN cable. Reflections in an operating system are undesirable and may result from a physical problem, such as crushing, or untwist, or from an electrical connectivity problem, such as a short or open circuit.



The phenomenon in an optical fibre whereby light photons arrive at a distant point in different phase than they entered the fibre. Modal dispersion occurs when elements of the optical signal take slightly different paths along the fibre and the different path lengths cause the received signal to lose definition. Chromatic dispersion is caused by differing transmission times of different wavelengths of light, which are refracted differently, according to each wavelength. Dispersion causes light signals distortion that ultimately limits the bandwidth and usable length of the optical fibre link. A device that connects two segments in an Ethernet network, or two portions of a token-ring network ring so as to extend and regenerate the LAN signal.

Drain Wire

Reversed Pair

An un-insulated wire in contact with the shield braid of foil along its length. At terminating points of the cable, the drain wire may be used to connect to the shield. A wiring error in twisted pair cabling where the conductors of a pair are reversed between connector pins at each end of the cable.



See digital subscriber line.



A metallic foil or multi-wire screen mesh that is used to prevent electromagnetic fields from penetrating or exiting a transmission cable. Also called ‘screened’.
Digital television.



A near-zero-resistance connection between two wires of a circuit. A short is usually unintended and considered as a failure.
Consisting of two parts, bi-directional transmission. Duplex optical fibre cable consists of two fibre strands that are separately jacketed and joined together.


  The information conveyed through a communication system.

Singlemode Optical Fibre



A term for zero-referenced ground.

A fibre wave-guide in which only one mode will propagate. Singlemode fibre has a very small core diameter of 8.3ìm. It allows signal transmission for long distances with relatively high bandwidths.


Skin Effect

European community


Electronic Industry Association. A membership association of manufacturers and users that establishes standards and publishes test methods (see TIA).

The tendency of alternating current to travel on the surface of a conductor as frequency increases. As much as 63% of a signal can move away from the copper core of twisted pair when the frequency rate exceeds 1Mhz and above.

Electromagnetic Field


The combined electric and magnetic fields caused by electron motion in conductors. EM fields may exist at great distances from conductors; however, near-field effects are of more concern in wiring. Simple Network Management Protocol. A remote management protocol this is part of the TCP/IP suite of protocols. Devices that support SNMP can be monitored and controlled remotely over a network.


The electrical charge that exists when the charge is at rest.


Synchronous optical network. SONET is an optical fibre technology that is used to transport telecommunications at 155Mbps and greater. It is the physical level for several ATM implementations.

Electromagnetic Interference

Step-Index Optical Fibre

An interfering electromagnetic signal. Networks wiring and equipment can be susceptible to EMI and emit EMI as well. An optical fibre in which the core is of a uniform refractive index with a sharp decrease in the index of refraction at the core-cladding interface.



Equal-level FEXT (see FEXT) Screened Twisted Pair.

Equipment Room


ER. An area that contains telecommunications or LAN equipment. An ER may be collocated within a telecommunications (wiring) room. Shielded twisted pair.



See electromagnetic interference.

Erbium-Doped Optical Fibre Amplifier
An optical fibre doped with the rare earth element Erbium, which can amplify light at 1530 to 1565nm when pumped by an external light source.

A network device that can filter and forward data across segments of a LAN. Often used to connect different types of LAN technologies (such as 10BaseT and 100BaseT LAN segments). Switching is done on the mechanical level, as opposed to bridges that use slower software switching. The term switch may also be used to describe a PABX




A LAN topology and access method that uses CSMA/CD transmission method. Ethernet may be used with two types of coax cable, twisted pair, or optical fibre. Transmission Control Protocol/Internet Protocol. A protocol used in the interconnection of computers. Although TCP/IP is actually a single protocol, the term is generally used to refer to a suite of closely related protocols for networking. The TCP/IP protocol is used extensively in the Internet.




A tube within an optical fibre connector that contains the core of an optical fibre.


Fibre Distributed Data Interface. A LAN topology and access method that passes tokens over dual counter-rotating optical fibre rings.


Functional Earth

Time Domain Reflectometry. A technique for measuring cable lengths by timing the period between a test pulse and the reflections of the pulse from an impedance discontinuity on the cable. The returned waveform reveals many undesirable cable conditions, including shorts, opens, and transmission anomalies due to excesses bends or crushing. The length to any anomaly, including the un-terminated cable end, may be computed from the relative time of the wave return and the nominal velocity of propagation of the pulse through the cable (see nominal velocity of propagation).



Fluorinated ethylene propylene. A thermoplastic with excellent dielectric properties, which is often used for conductor insulation in fire-rated cables. Telecommunications Industry Association.



Far-end crosstalk. Crosstalk between two twisted pairs, measured at the opposite end of the cable from the signal source. The physical or logical interconnection pattern of a LAN.


Twisted Pair

Material that prevents the passage of flame or smoke through an opening in a wall or floor.


A device that examines each data packet’s source address. If that address is on an approved list, the packets gain entry. If not, they are rejected.

A communications cable using one or more pairs of wires that are twisted together. When a pair is balanced (twisted), the twisting reduces the susceptibility to external interference and the radiation of signal energy (see skin effect).


Optical fibre inter-repeater link. An Ethernet optical fibre connection method intended for connection of repeaters. FOIRL is standardised as 10BaseFL and is defined in IEEE/ISO 8802-3 (IEEE 802.3).



Underground Cable


Cable that is intended to be placed beneath the surface of the ground (often referred to as UG) in ducts or conduit.
The number of times a periodic action occurs in a unit of time. The unit measure is the Hertz, abbreviated Hz. One hertz equals 1 cycle per second.


Frequency Response


A range of frequencies within which a device operates within expectations. The limits are usually given as the frequencies for which the normal signal transfer of a device falls 3dB below the nominal level of 20-20 000Hz, while a telecommunications circuit may have a frequency response of 300-3000Hz. Wide Area Network. Anextension of a local computer network (a LAN) over data communications lines provided by telecommunications common carriers. A typical WAN connects one or more remote office sites to the central corporate site over dedicated analogue or digital circuits.



Foil Twisted Pair. The amplitude of a signal over time.

Full Duplex


A communications method where both transmitted and received signals are simultaneously present (e.g., the common telephone instrument and full-duplex Ethernet. The physical distance between successive peaks of a wave in a transmission medium. Wavelength may be calculated from the frequency of a signal and the nominal velocity of propagation. In a vacuum, the NVP is simply the speed of light (300 000Km/s).


  Symbol for impedance.


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