Networking Dictionary                                                                       << back to main technical page

Here is a list of common words and terms used in Networking and computing along with definitions and meanings and is constantly being updated with new definitions and items.

A

Absorption
The loss of light energy in a fibre optic core resulting from impurities in the glass.

ADSL (Asymmetric Digital Subscriber Line)
A technology used to send data over existing copper telephone lines. ADSL supports data rates of 1.5 to 9 Mbps when receiving data and from 16 to 640 Kbps when sending data.

Application

A piece of software or a programor package that uses the operating system on a PC and manipulates data files. It allows a user to perform a specific job(such as accounting or word processing).

Armoured

The inner jacket of the cable is overlaid with a protective armouring. Two main types are Steel Wire Armoured (SWA) and Corrugated Steel Tape armoured (CST or STA). The armouring gives the best resistance against rodent attack or mechanical damage and provides high tensile strength and crush resistance.

Attenuation
This is the gradual loss in intensity of a signal through a medium. i.e. sunlight is attenuated by dark glasses. Attenuation affects the waves and signals in electrical and optical circuits. The light loss on an optical fibre is measured in dB/Km.

B

Backbone
A segment that connects two or more local area network(LAN) nodes thus providing a transmission path between them.

Backscatter
This is the reflection of light waves back to the direction in which they came. Measuring loss by the backscatter method is used for the fault finding and maintenance of optical fibres.

Bandwidth
The capacity of a cable to carry data. The higher the carrying capacity, the more data can travel down the cable.

Bend Loss
Attenuation to an optical signal that occurs when a fibre cable is bent around a tight radius. The light effectively spills out from the core and is lost in the cladding.

Bend Radius

Usually expressed as a minimum, this is the bend radius around which a fibre may be curved without the risk of damage, loss of light(See Bend Loss) or even breakage.

Breakout Cable
A cable with individually rugerdised fibres that are stranded together and bound with tape and sheathed with PVC or similar material. Each fibre can be terminated directly with a connector without the need for termination boxes and can be plugged directly into any equipment..

Buffering

This is the protective material directly on the fibre coating which protects it from the environment (also see tight-buffered).

Bus Topology

The Linear LAN used by Ethernet networks.

C

Chromatic Dispersion
This is the spreading of light pulses that are caused by the difference in refractive indices at different wavelengths. Also see Dispersion .

Cladding
This is the material that surrounds the core of an optical fibre. The cladding has properties that are less refractive in order to keep the light inside the core and prevent light loss.

Cleave
This is the process of scoring and breaking the optical fibre end in order to terminate a connector. A precision square cut is required to splice to cores together.

Connector
The end of a cable that plugs into an interface to connect one device to another. They come in a large number of different sizes and types to fit different types of cable.

Core

The centre light guiding part of an optical fibre. The refractive index is higher than that of the cladding to ensure propagation of optical signals.

Crosstalk
The unwanted transfer of energy from one circuit to another and it usually interferes with transmission. Usually occurs between adjacent cables or between pairs in one individual cable.

D

Dark Fibre
Fibre cores within a cable that are supplied without any optical signalling equipment in its path. Generally, they are sat there waiting to be utilised.

Data Centres

In simple terms, a data centre is a facility, room or building used to house computer systems and their associated equipment. They incorporate telecommunications, backup power supplies, data storage systems, data communications connections, air conditioning and fire suppression.

Decibel(dB)
The unit of measure used to express the strength of a signal. In Fibre Optics, the light lost from the transmitted end, to the received end of a fibre optic cable is expressed as the dB Loss.

Dispersion
This is the spreading or broadening of light pulses as they travel through the fibre optic core. The fibres raw make up and properties causing this effect is also called dispersion. The three fundamental types are Chromatic Dispersion, Modal Dispersion and Polarisation Mode Dispersion.

Duplex
A fibre cable with two cores, used for bi-directional transmission. Usually one core transmits and the other receives.

Dynamic Range

In Optoelectronics, this is the maximum operating power range expressed in dB.

E

Enclosure
A cabinet or box, usually used to organise and enclose cable terminations such as Fibre Optic splices. They can be used in main equipment rooms, entrances, in underground ducts, or on office walls. They usually have an IP (Ingress protection) rating and details of IP ratings can be found on the IP Ratings Page .

Entrance Facility

The entrance into a building for public and private network and service cables.

Epoxy
A thermosetting resin used to secure fibre cores with the connector when terminating connectors directly onto the fibre.

Ethernet
A local area network hardware standard that combines cable technology with a series of communication protocols. Generally, it is the primary communications system used in many  PC and mainframe networks.

Equipment Room

This is often called a Comms room and is a dedicated centralised room for housing the networking equipment and the termination room for telecoms cabling.

F 

FDDI

Fibre Distributed Data Interface. This is a standard for a 100Mbps Fibre Optic local area network.

Ferrule
The rigid prong in a fibre optic plug that aligns the fibre with the socket. Usually made from ceramic, plastic and stainless steel.

Frequency

This is a unit of measurement of bandwidth. The number of cycles per second measured in Hertz(Hz) where 1 hertz is 1 cycle per second.

Fresnal Reflection

This is the reflection of light at the end of an optical fibre caused by the difference in refractive index between the fibre core and the media (often air) with which it is interfacing. 

Fusion Splice
Method of joining of two fibre ends by applying heat to fuse or melt the ends together to forming a continuous fibre. A Fusion Splicer is required for the process.

G

Gigabit Ethernet
A high-speed network standard, that provides a data transfer rate as high as 1000 Mbps. Sometimes known as 1000Base-T.

Graded-Index
This is the design where the refractive index of the core is lower towards the outside of the fibre core and increases toward the middle of the core. It bends the light rays inward and allows them to travel faster in the lower index of refraction region. Graded index fibre provides higher bandwidth for multimode fibre transmission.

H

Half-Duplex
A data transmission method where data is transmitted in both directions but not at the same time.

Hard Clad Fibre

An optical fibre with a hard plastic cladding surrounding a step index silica core.

Hertz (Hz)
The measure of frequency or bandwidth. One Hertz is equivalent to one cycle per second.

Horizontal Cabling
Another name for the structured cabling connecting the data outlets to the network cabinet or wiring closet.

Horizontal Cross Connect

A cross connect of horizontal cabling to other cabling such as backbone, equipment, Horizontal etc.

Hub

Hybrid Cable

A fibre Optic cable consting of two or more different fibre types i.e. singlemode and multimode within the same cable.

I

Index Matching Material

Normally a gel or liquid with a refractive index which is almost equal to the core index. Normally used to reduce reflections at a fibre end face.

Index Profile

Curve of the refractive index over the cross section of an optical waveguide.

Index of Refraction (IOR)
This is the ratio of light velocity in a vacuum to its velocity in a given transmission medium.

Infrared

This is the band of electromagnetic wavelengths between 700nm to approximately 1µm. The transmission of light in glass optical fibres is most efficient in the infrared at wavelengths from 850nm to 1100nm.

Impedance
The resistance to the flow of current in a circuit or cable.

Internal/External (Int/Ext)
Fibre Cable that is suitable for both indoor and outdoor applications. The cable construction usually uses a gel filled loose tube containing the fibres.

Insertion Loss
This is the loss of light caused by the insertion of a component into an optical system. 

ISDN

Integrated Services Digital Network. A public network in which a single subscriber interface provides a variety of communication services for voice and data.

ISO (International Standards Organisation)
Worldwide body promoting the development of worldwide standards.

J

Jack
This is socket used with a plug to make a connection between communication circuits. They are the female component of a jack/plug connector or the socket that the plug marries up with.

Jumper Wire
Wire of twisted pairs without connectors and usually two cores used to join telecommunications circuits and links at the cross connect. Used by telecomms engineers to “Jumper” extensions from the telephone switch onto the building wiring.

K

KB: Kilobyte
A Kilobyte(KB) is a unit of measurement of data and is approximately 1,000 bytes.

Key/Keying
A mechanical feature of a connector that assures the correct orientation and alignment of a connector into its socket.

Kevlar
Kevlar is the strong material that offers tensile strength, providing support and protection of the fibre cores in a fibre cable. Kevlar® is a actually a brand of Aramid Yarn.

L

Laser

Light Amplification by Stimulated Emission of Radiation. In Fibre Optics, Laser Diodes are used as light emitters, especially in Singlemode and long haul systems.

LC

This is a small form Fibre Optic connector. Developed by Lucent Technologies, LC stands for Lucent Connector. The LC has good performance and is favoured for Singlemode and high volumes, such a Data Centres.

Local Area Network (LAN)
A computer network that occupies a small area. Usually they are found in a single building or group of buildings. LANs connect PCs and office equipment, enabling users to communicate, share files, and access remote hosts or other networks.

Loose Tube (L/T)
This is the protective tube surrounding one or more fibres and is usually found in cables used for outdoor installations. The protective tube loosely surrounds the optical fibre cores and is often filled with protective gel.

Loss

This is the attenuation of an optical signal. It is usually measured in dB and is used to measure the light lost in an optical fibre cable, splices, connector etc.

Loss Budget

A calculated amount of signal attenuation that a system will tolerate between two points. It is used to establish the total amount of tolerable loss attributable to the propagated signal through splices, connectors and the cable.

Low Smoke Zero Halogen (LS0H/LSZH)
Much of the cable currently in use in the world contains halogens. Halogens are gases such as fluorine, chlorine, iodine, or bromine. These halogens give off toxic fumes that harm the eyes, nose, lungs, and throat when exposed to flames. Many different manufacturers now make low-smoke, zero-halogen (LSZH or LS0H) cables that are designed to emit no toxic fumes and produce little or no smoke when exposed to flames. Many new buildings now specify this grade of cable to be installed.

M

Macrobend
This is a large cable bend that can be seen with the unaided eye and is often reversible.

Mechanical Splice
Method of joining two fibre ends together by a temporary or permanent mechanical means in order to maintain continuous signal transmission. Usually with a crimp tool and crimp style connectors.

Metropolitan Area Network (MAN)
A network found in an area such as a town or city. MANs are larger than LANs, but smaller than WANs.

Micron (µm)
One micrometer or one millionth of a meter. Used to express the dimensions of fibre optic cores.

Microbend
This is a small, microscopic bend that is often caused by the cabling installation process such as mechanical stress by water in the cable during repeated freeze and thaw cycles or even packaging.

Modal Dispersion
This is the spreading of light pulses along the length of the fibre optic cable caused by the different optical paths taken in multimode fibre. See Multimode.

This is a small form Fibre Optic connector. It is small in size and houses two fibre cores.

Multimode
Multimode fibre carries multiple light rays or modes concurrently, each at a slightly different reflection angle within the fibre core. Multimode fibre has a larger core than single mode and is typically either 50µ (Micron) or 62.5µ (Micron) in diameter. Multimode fibre transmission is used for relatively short distances because the modes tend to disperse over longer lengths. The maximum distances of the cable depends on the application the cable is being used for. To run Gigabit over Multimode, a guideline of 550 Metres maximum for 50/125 cable and 220 Metres maximum for 62.5/125 cable should be used. For longer distances, Singlemode fibre is used. The most common application for Multimode is LAN's(Local Area Network).

N

Nanometer (nm)
One billionth of a metre. The wavelengths of light used in Fibre Optics are measured in nanometers. (See Wavelength).

Network
An number of devices that are connected together and used to store, retrieve, and share information. A network lets a group of computers/users communicate with each other and share other devices on the network (such as printers).

Node
A Node, is an connection point in a network or a junction common to two or more lines in a network. Nodes, are usually can be interconnected by links or cables, and are control points on the network.

NVP (Nominal Velocity of Propagation)
The speed at which a signal propagates through a cable. It is expressed as a decimal fraction of the speed of light in a vacuum.

O

OTDR (Optical Time Domain Reflectometer)
A piece of test equipment that measures the optical transmission characteristics by sending pulses of light down fibre cores and observing backscattered light. It is used to measure fibre attenuation and evaluate optical transmission at splices and connectors by calculating losses in light on the fibre core.

Outlet
A connecting device in the work area onto which a horizontal cable(UTP) terminates. Usually in the form of an RJ45 faceplate and module.

Outside Vapour Deposition (OVD)

This is a manufacturing process that is patented and used by corning using three steps: Laydown, Consolidation & Draw.

P

Packet
A unit of information by which the network communicates. Each packet contains the identities of the sending and receiving stations, information about how to handle the request, error-control information, a request for services, and of course, any necessary data needs to be transferred.

Patch Cord or Patch Lead
A specific length of cable with connectors on each end. Used for connecting patch panels, outlets, equipment and devices on a network.

Patch Panel
A device, allowing Horizontal Cabling (UTP) to terminate to, and holds the connectors that allow circuit arrangements by simply plugging and unplugging patch cords/leads. Usually rack mounted inside wiring closets(Cabinets), they allow patching/unpatching to make horizontal cabling outlets live with either a data signal or telephone extension.

Peer-to-Peer Network
A network in which each node  or computer has both client and server capabilities. Communication and data sharing occurs directly between nodes.

Pigtail
A short length of fibre cable(Single core) with a connector at one end and the other is free to be spliced to another fibre core. Used when Fusion splicing.

Ping
A network program that determines whether a machine is attached to the network. It sends a packet to a network address and waits for a reply. It is usually used to troubleshoot network connections.

Plastic Fibre
An optical fibre core made from plastic rather than the usual glass.

Polarisation Mode Dispersion(PMD)
This type of dispersion comes from slight asymmetries in fibre optic cores and the speed of light varies with polarisation.

Polishing Paper
Paper with a fine grit used to remove imperfections in the fibre end surface that may exist after cleaving. Fibre ends terminated with a connector are polished flush with the end of the ferrule. Also known as lapping film.

Protocol
This is a set of rules that network devices must follow in order to communicate.

Q

R

Raceway
A channel or containment that is designed for holding or routing wires and cables. Raceways can be metallic or non-metallic and may totally or semi-enclose the wiring. Examples of Raceways are conduit, trunking, traywork, cable sleeves and basket tray.

Receiver (RX)
An opto-electronic device that converts optical signals into electrical signals.

Refraction
The bending of light as it passes between materials of different refractive index.

Refractive Index
Also called the Index of Refraction. This is the ratio of speed of light in a vacuum to the speed of light in a material.

Remote Access
A feature that enables remote users of PC's to dial into a network and access all available resources including files, databases and e-mail services.

Repeater
A type of transceiver that converts an optical signal to electronic and back to optical.

Return Loss
The power returned down a fibre after reflection from a component. This is expressed in dB.

Ribbon Fibre
These are Primary coated fibres of around four or more in quantity. They are layered next to each other between layers of tape. This ribbon is usually incorporated into other cable constructions. Specialist tooling is needed for terminating and splicing. They are usually compact in construction and used in high fibre counts by telecoms companies.

Ring Topology
A network topology where terminals are connected in a point-to-point serial fashion in an unbroken circular configuration.

Riser
A cable route for cables to pass between floors in buildings.

Riser Cable
A type of cable used in vertical building shafts and risers. It usually has more mechanical strength than general use cable via a central strength member and has an intermediate fire protection rating. Often Low Smoke Zero Halogen (See LS0H).

RJ45 (Registered Jack-45)
A USOC code which identifies an 8-pin modular plug or jack(socket) used with unshielded twisted pair(UTP) cable. An eight-wire connector used to connect a computer onto a LAN. Generally plugs into an RJ45 network outlet on a Structured Cabling network.

S

SC

This is a Fibre Optic connector with a push-pull latch mechanism providing quick insertion and removal. The connector is square in shape.

Server
A computer on a network that responds to client requests for services. Services range from file, print and email services to complex applications.

Singlemode
Singlemode fibre is designed for the transmission of a single ray or mode of light as a carrier over long-distance signal transmission. Singlemode fibre has a much smaller core than multimode fibre, between 8µ and 10µ (micron). Singlemode cable can carry Gigabit upto 5,000 Metres. Singlemode provides greater bandwidth than multimode.

Spectral Width
The range of Wavelengths emitted by a source.

Speed of Light
The speed that light travel. Aproximately 2.998x10⁸ Metres per second (In a Vacuum).

Splice
A method of joining two optical fibre ends. Fusion splicing and mechanical splicing are the two types.

Splice Closure
A container used to house and protect splice trays and splices.

Splice Loss

This is the loss of light on the Fibre core at a splice. The level of loss can depend on a number of variables, some of which are due to the Fibre cable characteristics and some of which relate to the method or device being used to splice the Fibre cores.

Splice Tray
A container used to hold, organise and protect spliced Fibre Optic cores.

Star Topology
A network configuration whereby each node is connected with a separate link, and all links lead back to the same central location.

Star Wired Ring Topology
A network configuration that contains links that allows information to pass from one device to another in a circle or ring and also includes a link back to a central location. This is a ring and star topology combined.

ST

This is a Fibre Optic connector which uses a plug and socket system which is locked in place with a bayonet lock. The connector is round in shape.

STP (Shielded Twisted Pair)
Twisted four pair cable with intertwined cores that is wrapped in a metal sheath which provides extra protection from external interference.

Step Index Fibre

A Fibre in which the refractive index of the core is uniform across its diameter.

Strength Member
Part of optic cable that increases the cable's tensile strength and bears the load. It can be made of Kevlar, fiberglass filament, or steel strands.

Switch
A network device that selects a path for sending a unit of data to its destination on a network.

T

Telecommunications
This term relates to both voice and data communications in the form of signals transmitted over media.

Termination
The act of attaching a connector to bare cabling. Data cabling “terminations” must be in accordance with industry standard wiring codes. An ST style Fibre connector may be said to be “terminated” onto a fibre core. This would be defined as ST style “ termination ”. An example of a termination method is fusion splicing. This is the method of “ terminating” the connector to the cable.

Tight Buffered
A protective coating (usually 900 µm) that is used to "buffer" the primary coating of fibres. Provides strength, durability, easy handling and termination.

Topology
The physical interconnection pattern of a network. Can be shown in diagrammatic format(See Ring Topology, Star Topology and Star Wired Ring Topology).

Traffic
The volume of data that is transmitted over a cable at any given time. It is generated by the devices and software applications running on the network. Excessive traffic can impair the performance of the cable and the LAN.

Transceiver
A device that transmits and receives signals, usually on a local area network.

Transmission Loss
This is the total loss suffered by a lightwave through a system due to the attenuation created by the fibre core, connectors and splices etc.

Transmitter (TX)
An opto-electronic device that converts an electrical signal to an optical signal.

U

Ultraviolet Light
Electromagnetic waves with wavelengths around 100 to 400nm. The wavelength is shorter than that of visible light but longer than x-rays. Ultraviolet light can be found in sunlight.

UPS (Uninterruptible Power Supply)
A back-up power unit that provides continuous power even when the normal power supply is interrupted. Some small UPS's provide 5-10 minutes of back-up, which enables users to power down any equipment properly in the event of a power cut, thus minimizing lost data.

Upstream
An Upstream is the direction of data flow from a users workstation to the network. Traffic on networks flows in both upstream and downstream directions at the same time.

UTP (Unshielded Twisted Pair)
Twisted four pair cable with intertwined cores that is not shielded. This is the most common type of wiring used in LAN's.

V

Visible Light
Electromagnetic radiation that is visible to the human eye with wavelengths around 400 to 700nm. The wavelength is shorter than that of visible light but longer than x-rays. Ultraviolet light can be found in sunlight.

Voice

Anything relating to telephone services. i.e. voice cabling transmits voice signals.

VoIP or Voice Over IP
Voice over IP (VOIP) refers to technologies that use Internet Protocol (IP) to transmit voice as packets over a network. Voice communications can be achieved on any IP network.  Benfits of VoIP are: very low cost, integrated data, voice and video on the same network, simplified management.

W

Wide Area Network (WAN)
Two or more LANs that are in separate geographic locations connected by a remote link. They can be a very long distance apart.

Wavelength
The length of a wave measured from any point on one wave to the corresponding point on the next. The wavelengths of light used in Fibre Optics are measured in Nanometers. Common wavelengths are 850, 1300, 1310, 1550 nm.

Windows

With reference to Fibre Optics, the windows are the 1^st 2^nd and 3^rd, which are 850nm, 1310nm and 1550nm respectively. These are the most commonly used wavelengths.

Wiring Closet
A Wiring Closet refers to the room containing the individual network connections for the devices in a network. This is a US term. In the UK we often call it a Comms Room.

Workgroup
A workgroup is a group of computers on a local area network (LAN) sharing common resources such as printers and storage devices. 

Workstation
A Workstation is a computer for an individual user and usually connected to a LAN. Usually in the form of a PC or thin client on a network.

X

Y

Z

Zero Dispersion Wavelength

The wavelength at which the chromatic dispersion of an optical fibre is zero and occurs when waveguide dispersion is cancelled out material dispersion.

Zip Cord

A Zip Cord is a two core Fibre cable consisting of two single Fibre cables that have their jackets joined by a strip of jacket material.

#

10Base-2
Adaptation of the Ethernet standard that uses thin coaxial cable, providing data transfer rates of up to 10 Mbps. The maximum effective distance for 10Base-2 is 185 metres. Also  known as thinnet.

10Base-5
The original Ethernet standard that uses thick coaxial cable, providing data transfer rates of up to 10 Mbps. The maximum effective distance for 10Base-5 is 500 meters. Also known as thicknet.

10Base-F
Adaptation of the Ethernet standard that uses optical fibre cable, providing data transfer rates of up to 10 Mbps. 10Base-F can transmit data over very long distances with little loss of data integrity.

10Base-T
An Ethernet standard that runs over unshielded twisted pair(UTP) cabling providing data transfer rates of 10 Mbps.

10 Gigabit Ethernet
An emerging high-speed network standard that will use high-capacity cabling to provide data transfer rates up to 10,000 Mbps.

100Base-T (Fast Ethernet)
A high-speed network standard, based on Ethernet, providing data transfer rates as high as 100 Mbps.

1000Base-T (Gigabit Ethernet)
A high-speed network standard, based on Ethernet, providing data transfer rates as high as 1000 Mbps.