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Glossary of Terms

Champion ONE offers a comprehensive glossary of industry terms for your reference needs. We’ll update the glossary periodically so check back often.

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10BASE-2

A thin-coaxial-cable version of an IEEE 802.3 network

10BASE-5

A thick-coaxial-cable version of an IEEE 802.3 network; very similar to the original Ethernet specification.

10BASE-T

A twisted-pair cable version of an IEEE 802.3 network.

1U

Abbreviation for 'one unit.' 'U' = 1.75 inches.

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Absorption

That portion of optical attenuation in optical fiber resulting from the conversion of optical power to heat. Caused by impurities in the fiber such as hydroxyl ions.

AC (Alternation Current)

An electric current that reverses its direction at regularly recurring intervals.

Active Device

A device that requires a source of energy for its operation and has an output that is a function of present and past input signals. Examples include controlled power supplies, transistors, LEDs, amplifiers, and transmitters.

AD or ADC (Analog-to-Digital Converter)

A device used to convert analog signals to digital signals.

Add Drop Multiplexing

A multiplexing function offered in connection with SONET/SDH that allows lower level signals to be added or dropped from a high-speed optical carrier in a wire center. The connection to the add/drop multiplexer is via a channel to a central office port at a specific digital speed (DS3, DS1, etc.)

ADM (Add-Drop Multiplexer)

A device which adds or drops signals from a communications network.

ADSL (Asynchronus Digital Subscriber Line)

See DSL.

Amplifier

A device, inserted within a transmission path, that boosts the strength of an electronic or optical signal. Amplifiers may be placed just after the transmitter (power booster), at a distance between the transmitter and the receiver (in-line amplifier), or just before the receiver (preamplifier).

Analog

A continuously variable signal. Opposite of digital.

Angular Misalignment

Loss at a connector due to fiber end face angles being misaligned.

APC (Angled Physical Contact)

A style of fiber optic connector with a 5

APD (Avalanche Photodiode)

A photodiode that exhibits internal amplification of photocurrent through avalanche multiplication of carriers in the junction region.

Asynchronous

Data that is transmitted without an associated clock signal. The time spacing between data characters or blocks may be of arbitrary duration. Opposite of synchronous.

ATM (Asynchronous Transfer Mode)

A transmission standard widely used by the telecom industry. A digital transmission switching format with cells containing 5 bytes of header information followed by 48 data bytes. Part of the B-ISDN standard.

ATSC (ADVAnced Television Systems Committee)

A committee formed to establish technical standards for advanced television systems, including digital high definition television (HDTV).

Attenuation

The decrease in signal strength along a fiber optic waveguide caused by absorption and scattering. Attenuation is usually expressed in dB/km.

Attenuator

In optical systems, a passive device for reducing the amplitude of a signal without appreciably distorting the waveform.

Average Power

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

Axis

The center of an optical fiber.

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Back Channel

A means of communication from users to content providers. Examples include a connection between the central office and the end user, an Internet connection using a modem, or systems where content providers transmit interactive television (analog or digital) to users while users can connect through a back channel to a web site, for example.

Backscattering

The return of a portion of scattered light to the input end of a fiber; the scattering of light in the direction opposite to its original propagation.

Bandwidth-limited Operation

The condition in a fiber optic link when bandwidth, rather than received optical power, limits performance. This condition is reached when the signal becomes distorted, principally by dispersion, beyond specified limits.

Bend Radius

The smallest radius an optical fiber or fiber cable can bend before excessive attenuation or breakage occurs.

Bending Loss

Attenuation caused by high-order modes radiating from the outside of a fiber optic waveguide which occur when the fiber is bent around a small radius. See also macrobending, microbending.

BER (Bit Error Rate)

The fraction of bits transmitted that are received incorrectly.

Bi-Directional

Operating in both directions. Bi-Directional couplers operate the same way regardless of the direction light passes through them. Bi-Directional transmission sends signals in both directions, sometimes through the same fiber.

BIDI (Bi-Directional Transceiver)

A device that sends information in one direction and receives information from the opposite direction.

Bit

The smallest unit of information upon which digital communications are based; also an electrical or optical pulse that carries this information.

BR (Backreflection)

A term applied to any process in the cable plant that causes light to change directions in a fiber and return to the source. Occurs most often at connector interfaces where a glass-air interface causes a reflection.

Broadband

A method of communication where the signal is transmitted by being impressed on a high-frequency carrier.

Buffer

1) In optical fiber, a protective coating applied directly to the fiber (illustrated). 2) A routine or storage used to compensate for a difference in rate of flow of data, or time of occurrence of events, when transferring data from one device to another.

Bus Network

A network topology in which all terminals are attached to a transmission medium serving as a bus. Also called a daisy-chain configuration.

BW (Bandwidth)

The range of frequencies within which a fiber optic waveguide or terminal device can transmit data or information.

Bypass

The ability of a station to isolate itself optically from a network while maintaining the continuity of the cable plant.

Byte

A unit of eight bits.

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C-Band

The wavelength range between 1530 nm and 1562 nm used in some CWDM and DWDM applications.

Cable

One or more optical fibers enclosed, with strength members, in a protective covering.

Cable Assembly

A cable that is connector terminated and ready for installation.

Cable Plant

The cable plant consists of all the optical elements including fiber, connectors, splices, etc. between a transmitter and a receiver.

CATV (Community Antenna Television)

The term now typically refers to cable television.

CCTV (Closed-Circuit Television)

An arrangement in which programs are directly transmitted to specific users and not broadcast to the general public.

CDMA (Code-Division Multiple Access)

A coding scheme in which multiple channels are independently coded for transmission over a single wideband channel using an individual modulation scheme for each channel.

Center Wavelength

In a laser, the nominal value central operating wavelength. It is the wavelength defined by a peak mode measurement where the effective optical power resides (see illustration). In an LED, the average of the two wavelengths measured at the half amplitude points of the power spectrum.

Central Office (CO)

A common carrier switching office in which users' lines terminate. The nerve center of a communications system.

Channel

A communications path or the signal sent over that path. Through multiplexing several channels, voice channels can be transmitted over an optical channel.

Chromatic Dispersion

Reduced fiber bandwidth caused by different wavelengths of light traveling at different speeds down the optical fiber. Chromatic dispersion occurs because the speed at which an optical pulse travels depends on its wavelength, a property inherent to all optical fiber. May be caused by material dispersion, waveguide dispersion, and profile dispersion.

Cladding

Material that surrounds the core of an optical fiber. Its lower index of refraction, compared to that of the core, causes the transmitted light to travel down the core.

Coating

The material surrounding the cladding of a fiber. Generally a soft plastic material that protects the fiber from damage.

Coaxial Cable

1) A cable consisting of a center conductor surrounded by an insulating material and a concentric outer conductor and optional protective covering. 2) A cable consisting of multiple tubes under a single protective sheath. This type of cable is typically used for CATV, wideband, video, or RF applications.

Concatenation

The process of connecting pieces of fiber together.

Connector

A mechanical or optical device that provides a demountable connection between two fibers or a fiber and a source or detector.

Connector Plug

A device used to terminate an electrical cable (illustrated) or an optical cable.

Connector Receptacle

The fixed or stationary half of a connection that is mounted on a panel/bulkhead. Receptacles mate with plugs.

Connector Variation

The maximum value in dB of the difference in insertion loss between mating optical connectors (e.g., with remating, temperature cycling, etc.). Also called optical connector variation.

Core

The light-conducting central portion of an optical fiber, composed of material with a higher index of refraction than the cladding. The portion of the fiber that transmits light.

Coupler

An optical device that combines or splits power from optical fibers.

CPE (Customer Premises Equipment)

Terminal, associated equipment, and inside wiring located at a subscriber's premises and connected with a carrier's communication channel(s) at the demarcation point (demarc), a point established in a building or complex to separate customer equipment from telephone company equipment.

Cross-Connect

Connections between terminal blocks on the two sides of a distribution frame or between terminals on a terminal block (also called straps). Also called cross-connection or jumper.

CWDM (Coarse Wavelength-Division Multiplexing)

CWDM allows eight or fewer channels to be stacked in the 1550 nm region of optical fiber, the C-Band.

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Data Rate

The number of bits of information in a transmission system, expressed in bits per second (b/s or bps), and which may or may not be equal to the signal or baud rate.

dB

Decibel relative to Microwatt.

dB (Decibel)

A unit of measurement indicating relative power on a logarithmic scale. Often expressed in reference to a fixed value, such as dBm or dB

dBc

Decibel relative to a Carrier level.

dBm

Decibel relative to Milliwatt.

Demultiplexer

A module that separates two or more signals previously combined by compatible multiplexing equipment.

Detector

An opto-electric transducer used to convert optical power to electrical current. Usually referred to as a photodiode.

Digital

A signal that consists of discrete states. A binary signal has only two states, 0 and 1. Antonym of analog.

Digital Compression

A technique for converting digital video to a lower data rate by eliminating redundant information.

Digital Subscriber Line (DSL)

In an integrated systems digital network (ISDN), equipment that provides full-duplex service on a single twisted metallic pair at a rate sufficient to support ISDN basic access and additional framing, timing recovery, and operational functions. See also ISDN.

Diode

An electronic device that lets current flow in only one direction. Semiconductor diodes used in fiber optics contain a junction between regions of different doping. They include light emitters (LEDs and laser diodes) and detectors (photodiodes).

Diode Laser

Synonymous with injection laser diode.

Diplexer

A device that combines two or more types of signals into a single output. Usually incorporates a multiplexer at the transmit end and a demultiplexer at the receiver end.

Directional Coupler

A coupling device for separately sampling (through a known coupling loss) either the forward (incident) or the backward (reflected) wave in a transmission line.

Dispersion

The temporal spreading of a light signal in an optical waveguide caused by light signals traveling at different speeds through a fiber either due to modal or chromatic effects.

Dispersion-Compensating Fiber (DCF)

A fiber that has the opposite dispersion of the fiber being used in a transmission system. It is used to nullify the dispersion caused by that fiber.

Dispersion-Compensating Module (DCM)

This module has the opposite dispersion of the fiber being used in a transmission system. It is used to nullify the dispersion caused by that fiber. It can be either a spool of a special fiber or a grating based module.

Dispersion-Shifted Fiber (DSF)

A type of single-mode fiber designed to have zero dispersion near 1550 nm. This fiber type works very poorly for DWDM applications because of high fiber nonlinearity at the zero-dispersion wavelength.

Distortion

Nonlinearities in a unit that cause harmonics and beat products to be generated.

Distributed Feedback Laser (DFB)

An injection laser diode which has a Bragg reflection grating in the active region in order to suppress multiple longitudinal modes and enhance a single longitudinal mode.

Distribution System

Part of a cable system consisting of trunk and feeder cables used to carry signals from headend to customer terminals.

DSx

A transmission rate in the North American digital telephone hierarchy. Also called T-carrier.

Dual In-Line Package (DIP)

An electronic package with a rectangular housing and a row of pins along each of two opposite sides.

Dual Ring (FDDI Dual Ring)

A pair of counter-rotating logical rings.

Duplex Cable

A two-fiber cable suitable for duplex transmission.

Duplex Transmission

Transmission in both directions, either one direction at a time (half-duplex) or both directions simultaneously (full-duplex).

DWDM (Dense Wavelength-Division Multiplexing)

The transmission of many of closely spaced wavelengths in the 1550 nm region over a single optical fiber. Wavelength spacings are usually 100 GHz or 200 GHz which corresponds to 0.8 nm or 1.6 nm. DWDM bands include the C-Band, the S-Band, and the L-Band.

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Electromagnetic Spectrum

The range of frequencies of electromagnetic radiation from zero to infinity.

EMI (Electromagnetic Interference)

Any electrical or electromagnetic interference that causes undesirable response, degradation, or failure in electronic equipment. Optical fibers neither emit nor receive EMI.

EMR (Electromagnetic Radiation)

Radiation made up of oscillating electric and magnetic fields and propagated with the speed of light. Includes gamma radiation, X-rays, ultraviolet, visible, and infrared radiation, and radar and radio waves.

Enterprise Systems Connection (ESCON)

A duplex optical connector used for computer-to-computer data exchange.

EO

Abbreviation for electrical-to-optical converter. A device that converts electrical signals to optical signals, such as a laser diode.

Erbium-Doped Fiber Amplifier (EDFA)

Optical fibers doped with the rare earth element, erbium, which can amplify light in the 1550 nm region when pumped by an external light source.

Error Correction

In digital transmission systems, a scheme that adds overhead to the data to permit a certain level of errors to be detected and corrected.

Error Detection

Checking for errors in data transmission. A calculation based on the data being sent; the results of the calculation are sent along with the data. The receiver then performs the same calculation and compares its results with those sent. If the receiver detects an error, it can be corrected, or it can simply be reported.

Ethernet

A standard protocol (IEEE 802.3) for a 10-Mb/s baseband local area network (LAN) bus using carrier sense multiple access with collision detection (CSMA/CD) as the access method. Ethernet is a standard for using various transmission media, such as coaxial cables, unshielded twisted pairs, and optical fibers.

Extinction Ratio

The ratio of the low, or OFF optical power level (PL) to the high, or ON optical power level (PH)

Eye Pattern

A diagram that shows the proper function of a digital system. The openness of the eye relates to the BER that can be achieved.

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FCPC

See FC. A threaded optical connector that uses a special curved polish on the connector for very low backreflection. Good for single-mode or multimode fiber.

FDM

See frequency-division multiplexing.

Ferrule

A rigid tube that confines or holds a fiber as part of a connector assembly.

Fiber Channel

An industry-standard specification that originated in Great Britain which details computer channel communications over fiber optics at transmission speeds from 132 Mb/s to 1062.5 Mb/s at distances of up to 10 kilometers.

Fiber Distributed Data Interface (FDDI)

1) A dual counter-rotating ring local area network. 2) A connector used in a dual counter-rotating ring local area network (illustrated).

Fiber Optic Attenuator

A component installed in a fiber optic transmission system that reduces the power in the optical signal. It is often used to limit the optical power received by the photodetector to within the limits of the optical receiver.

Fiber Optic Cable

A cable containing one or more optical fibers.

Fiber Optic Communication System

The transfer of modulated or unmodulated optical energy through optical fiber media which terminates in the same or different media.

Fiber Optic Link

A transmitter, receiver, and cable assembly that can transmit information between two points.

Fiber Optic Span

An optical fiber/cable terminated at both ends which may include devices that add, subtract, or attenuate optical signals.

Fiber Optic Subsystem

A functional entity with defined bounds and interfaces which is part of a system. It contains solid state and/or other components and is specified as a subsystem for the purpose of trade and commerce.

Fiber-In-the-Loop (FITL)

Fiber optic service to a node that is located in a neighborhood.

Fiber-to-the-Curb (FTTC)

Fiber optic service to a node connected by wires to several nearby homes, typically on a block.

Fiber-to-the-Home (FTTH)

Fiber optic service to a node located inside an individual home.

Filter

A device which transmits only part of the incident energy and may thereby change the spectral distribution of energy.

Free-Space Optics

Also called free-space photonics. The transmission of modulated visible or infrared (IR) beams through the atmosphere via lasers, LEDs, or IR-emitting diodes (IREDs) to obtain broadband communications.

Frequency-Division Multiplexing (FDM)

A method of deriving two or more simultaneous, continuous channels from a transmission medium by assigning separate portions of the available frequency spectrum to each of the individual channels.

Fusion Splicer

An instrument that permanently bonds two fibers together by heating and fusing them.

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Germanium (Ge)

Generally used in detectors. Good for most fiber optic wavelengths (e.g., 800-1600 nm). Performance is inferior to InGaAs

Gigahertz (GHz)

One billion Hertz (cycles per second) or 109 Hertz.

Graded-Index Fiber

Optical fiber in which the refractive index of the core is in the form of a parabolic curve, decreasing toward the cladding.

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Half-Duplex Transmission

A bi-directional link that is limited to one-way transfer of data, i.e., data cannot be sent both ways at the same time. Also referred to as simplex transmission.

Hard Clad Silica Fiber

An optical fiber having a silica core and a hard polymeric plastic cladding intimately bounded to the core.

Headend

1) A central control device required within some LAN and MAN systems to provide such centralized functions as remodulation, retiming, message accountability, contention control, diagnostic control, and access to a gateway. 2) A central control device within CATV systems to provide such centralized functions as remodulation (illustrated). See also local area network (LAN).

Hertz (Hz)

One cycle per second.

High Data-Rate Digital Subscriber Line (HDSL)

A DSL operating at a high data rate compared to the data rates specified for ISDN.

High Definition Television (HDTV)

Television that has approximately twice the horizontal and twice the vertical emitted resolution specified by the NTSC standard.

Homes Passed (HP)

Homes that could easily and inexpensively be connected to a cable network because the feeder cable is nearby.

Hot Swap

In an electronic device subassembly or component, the act or process of removing and replacing the subassembly or component without first powering down the device.

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In-Line Amplifier

An EDFA or other type of amplifier placed in a transmission line to strengthen the attenuated signal for transmission onto the next, distant site. In-line amplifiers are all-optical devices.

Index of Refraction

The ratio of the velocity of light in free space to the velocity of light in a fiber material. Always greater than or equal to one. Also called refractive index. Where n = C/V, c = The speed of light in a vacuum,C107 v = The speed of the same wavelength in the fiber material

Index-Matching Fluid

A fluid whose index of refraction nearly equals that of the fibers core. Used to reduce Fresnel reflection loss at fiber ends. Also known as index-matching gel.

Indium Gallium Arsenide (InGaAs)

Generally used to make high-performance long-wavelength detectors.

Infrared (IR)

The region of the electromagnetic spectrum bounded by the long-wavelength extreme of the visible spectrum (about 0.7

Insertion Loss

The loss of power that results from inserting a component, such as a connector, coupler (illustrated), or splice, into a previously continuous path.

Institute of Electrical and Electronic Engineers (IEEE)

A technical professional association that contributes to voluntary standards in technical areas ranging from computer engineering, biomedical technology and telecommunications, to electric power, aerospace and consumer electronics, among others.

Integrated Circuit (IC)

An electronic circuit that consists of many individual circuit elements, such as transistors, diodes, resistors, capacitors, inductors, and other passive and active semiconductor devices, formed on a single chip of semiconducting material and mounted on a single piece of substrate material.

International Standards Organization (ISO)

Established in 1947, ISO is a worldwide federation of national standards committees from 140 countries. The organization promotes the development of standardization throughout the world with a focus on facilitating the international exchange of goods and services, and developing the cooperation of intellectual, scientific, technological, and economical activities.

Internet

A worldwide collection of millions of computers that consists mainly of the world wide web and e-mail.

Internet Protocol (IP)

A standard protocol, developed by the DOD, for use in interconnected systems of packet-switched computer communications networks.

Internet Services Provider (ISP)

A company or organization that provides Internet connections to individuals or companies via dial-up, ISDN, T1, or some other connection.

ISDN

See integrated services digital network.

ITU

International Telecommunications Union.

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Jacket

The outer, protective covering of the cable. Also called the cable sheath.

Jumper

A short fiber optic cable with connectors on both ends.

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Kevlar

A very strong, very light, synthetic compound developed by DuPont which is used to strengthen optical cables.

kHz

One thousand cycles per second.

km

Abbreviation for kilometer. 1 km = 3,280 feet or 0.62 miles.

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L-Band

The wavelength range between 1570 nm and 1610 nm used in some CWDM and DWDM applications. LEAF

Large Core Fiber

Usually, a fiber with a core of 200

Large Effective Area Fiber (LEAF)

An optical fiber, developed by Corning, designed to have a large area in the core, which carries the light.

Laser

Acronym for Light Amplification by Stimulated Emission of Radiation. A light source that produces, through stimulated emission, coherent, near monochromatic light.

Laser Diode (LD)

A semiconductor that emits coherent light when forward biased.

Least Significant Bit

In a binary code, the bit or bit position assigned to the smallest quantity or increment that can be represented by the code.

Light

In a strict sense, the region of the electromagnetic spectrum that can be perceived by human vision, designated the visible spectrum, and nominally covering the wavelength range of 0.4

Light Piping

Use of optical fibers to illuminate.

Light-Emitting Diode (LED)

A semiconductor that emits incoherent light when forward biased. Two types of LED's include edge-emitting LED's and surface-emitting LED's (illustrated).

Lightguide

Synonym for optical fiber.

Lightwave

The path of a point on a wavefront. The direction of the lightwave is generally normal (perpendicular) to the wavefront.

Linear Device

A device for which the output is, within a given dynamic range, linearly proportional to the input.

Linearity

The basic measurement of how well analog-to-digital and digital-to-analog conversions are performed. To test for linearity, a mathematically perfect diagonal line is converted and then compared to a copy of itself. The difference between the two lines is calculated to show linearity of the system and is given as a percentage or range of least significant bits.

Local Area Network (LAN)

A communication link between two or more points within a small geographic area, such as between buildings. Smaller than a metropolitan area network (MAN) or a wide area network(WAN).

Local Exchange (LEX)

Synonym for central office.

Local Exchange Carrier (LEC)

A local telephone company, i.e., a communications common carrier that provides ordinary local voice-grade telecommunications service under regulation within a specified service area.

Long Haul (LH)

A classification of video performance under RS-250C. Lower performance than medium-haul or short-haul.

Long-Haul Telecommunications

1. In public switched networks, regarding circuits that span long distances, such as the circuits in inter-LANA, interstate, and international communications. 2. In military use, communications among users on a national or worldwide basis. Long-haul communications are characterized by a higher level of users, more rigorous performance requirements, longer distances between users, including world wide distances, higher traffic volumes and densities, larger switches and trunk cross sections, and fixed and recoverable assets. Usually pertains to the U.S. Defense Communications System.

Longitudinal Mode

An optical waveguide mode with boundary condition determined along the length of the optical cavity.

Loose-tube

A type of fiber optic cable construction where the fiber is contained within a loose tube in the cable jacket.

Loss

The amount of a signal

Loss Budget

An accounting of overall attenuation in a system. See optical link loss budget.

Lossless Compression

1) Reduction of the storage size of digital data by employing one or more appropriate algorithms in such a way that the data can be recover without loosing integrity. 2) Reduction of the amount of data that needs to be transmitted per unit time though an analogous real-time process that does not compromise the ability to completely restore the data.

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Margin

Allowance for attenuation in addition to that explicitly accounted for in system design.

Mean Time Between Failure (MTBF)

Time after which 50% of the units of interest will have failed. Also called MTTF (mean time to failure).

Medium Access Control (MAC)

1) A service feature or technique used to permit or deny use of the components of a communication system. 2) A technique used to define or restrict the rights of individuals or application programs to obtain data from, or place data onto, a storage device, or the definition derived from that technique.

Metropolitan Area Network (MAN)

A network covering an area larger than a local area network. A series of local area networks, usually two or more, that cover a metropolitan area.

MH

Abbreviation for medium-haul. A classification of video performance under RS-250C. Higher performance than long-haul and lower performance than short-haul. MHz

Microbending

Mechanical stress on a fiber that introduces local discontinuities, which results in light leaking from the core to the cladding by a process called mode coupling.

Micrometer

One millionth of a meter or 10-6 meters. Abbreviated

Microsecond

One millionth of a second or 10-6 seconds. Abbreviated

Microwatt

One millionth of a Watt or 10-6 Watts. Abbreviated

Microwave Transmission

Communication systems using very high-frequency RF to carry the signal information.

Military Specifications (MIL-SPEC)

Performance specifications issued by the Department of Defense that must be met in order to pass a MIL-STD.

Military Standard (MIL-STD)

Standards issued by the Department of Defense.

Minimum Bend Radius

The smallest radius an optical fiber or fiber cable can bend before increased attenuation or breakage occurs.

Misalignment Loss

The loss of power resulting from angular misalignment, lateral displacement, and fiber end separation. MLM

Modal Dispersion

See multimode dispersion.

Modal Noise

Noise that occurs whenever the optical power propagates through mode-selective devices. It is usually only a factor with laser light sources.

Mode

A single electromagnetic wave traveling in a fiber.

Mode Coupling

The transfer of energy between modes. In a fiber, mode coupling occurs until equilibrium mode distribution (EMD) is reached.

Modulation

The process by which the characteristic of one wave (the carrier) modifies another wave (the signal). Examples include amplitude modulation (AM), frequency modulation (FM), and pulse-coded modulation (PCM). Modulation Index

Modulator

A device that imposes a signal on a carrier.

Monitor

1) a CRT that receives its signal directly from a VCR, camera, or separate TV tuner for high-quality picture reproduction. 2) A device used for the real-time temporary display of computer output data. 3) Software or hardware that is used to scrutinize and to display, record, supervise, control, or verify the operations of a system.

Multilongitudinal Mode (MLM) Laser

An injection laser diode which has a number of longitudinal modes.

Multimode (MM) Fiber

An optical fiber that has a core large enough to propagate more than one mode of light The typical diameter is 62.5 micrometers.

Multimode Dispersion

Dispersion resulting from the different transit lengths of different propagating modes in a multimode optical fiber. Also called modal dispersion.

Multimode Laser Diode (MMLD)

Synonym for multilongitudinal mode laser.

Multiple Reflection Noise (MRN)

The fiber optic receiver noise resulting from the interference of delayed signals from two or more reflection points in a fiber optic span. Also known as multipath interference.

Multiple Service Operator (MSO)

A telecommunications company that offers more than one service, e.g. telephone service, Internet access, satellite service, etc.

Multiplexer

A device that combines two or more signals into one output.

Multiplexing

The process by which two or more signals are transmitted over a single communications channel. Examples include time-division multiplexing and wavelength-division multiplexing (WDM).

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National Cable Television Association (NCTA)

The major trade association for the cable television industry.

National Electric Code

A standard governing the use of electrical wire, cable and fixtures installed in buildings; developed by the American National Standards Institute (ANSI), sponsored by the National Fire Protection Association (NFPA), identified by the description ANSI/NFPA 70-1990.

National Electrical Manufacturers Assocation (NEMA)

Organization responsible for the standardization of electrical equipment, enabling consumers to select from a range of safe, effective, and compatible electrical products.

National Fiber Protection Association (NFPA)

Abbreviation for National Fire Protection Association. Publisher of the National Electrical Code

National Television Systems Committee (NTSC)

1) Abbreviation for National Television Systems Committee. The organization which formulated the NTSC system. 2) Standard used in the U.S. that delivers 525 lines at 60 frames per second.

Near Infrared

The part of the infrared near the visible spectrum, typically 700 nm to 1500 nm or 2000 nm; it is not rigidly defined.

Near-End Crosstalk (NEXT RN)

The optical power reflected from one or more input ports, back to another input port. Also known as isolation directivity.

Network

1) An interconnection of three or more communicating entities and (usually) one or more nodes (illustrated). 2) A combination of passive or active electronic components that serves a given purpose.

Network Topology

The specific physical, i.e., real, logical, or virtual, arrangement of the elements of a network. Common network topologies include a bus (or linear) topology, a ring topology, and a hybrid topology, which can be a combination of any two or more network topologies. Illustrated to the right is a bus topology utilizing tee couplers to connect a series of stations that listen to a single backbone of cable.

Node

1) A terminal of any branch in network topology or an interconnection common to two or more branches in a network. 2) One of the switches forming the network backbone in a switch network. 3) A point in a standing or stationary wave at which the amplitude is a minimum.

Noise

1) An undesired disturbance within the frequency band of interest; the summation of unwanted or disturbing energy introduced into a communications system from man-made and natural sources. 2) A disturbance that affects a signal and that may distort the information carried by the signal. 3) Random variations of one or more characteristics of any entity such as voltage, current, or data.

Noise Equivalent Power (NEP)

The noise of optical receivers, or of an entire transmission system, is often expressed in terms of noise equivalent optical power.

Noise Figure (NF)

The ratio of the output signal-to-noise ratio to the input signal-to-noise ratio for a given element in a transmission system. Used for optical and electrical components.

Non Dispersion-Shifted Fiber (NDSF)

The most popular type of single-mode fiber deployed. It is designed to have a zero-dispersion wavelength near 1310 nm.Nonlinearity

Non Zero-Dispersion-Shifted Fiber (NZ-DSF)

A dispersion-shifted single-mode fiber that has the zero-dispersion wavelength near the 1550 nm window, but outside the window actually used to transmit signals. This strategy maximizes bandwidth while minimizing fiber nonlinearities.

Numerical Aperture (NA)

The light-gathering ability of a fiber; the maximum angle to the fiber axis at which light will be accepted and propagated through the fiber. NA also describes the angular spread of light from a central axis, as in exiting a fiber, emitting from a source, or entering a detector.

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Open Systems Interconnection (OSI)

Pertaining to the logical structure for communications networks standardized by the International Organization for Standardization (ISO).

Operation Administration and Maintenance (OAM)

Refers to telecommunications networks.

Optical Access Network (OAN)

A network technology, based on passive optical networks (PONs), that includes an optical switch at the central office, an intelligent optical terminal at the customer

Optical Add-Drop Multiplexer (OADM)

A device which adds or drops individual wavelengths from a WDM system.

Optical Amplifier

A device that amplifies an input optical signal without converting it into electrical form. The best developed are optical fibers doped with the rare earth element, erbium. See also EDFA.

Optical Bandpass

The range of optical wavelengths which can be transmitted through a component.

Optical Carrier (OC-x)

Abbreviation for optical carrier. A carrier rate specified in the SONET/SDH standard.

Optical Channel

An optical wavelength band for WDM optical communications.Optical Channel Spacing

Optical Cross-Connect (OXC)

See cross-connect.

Optical Distribution Network (ODN)

Term for optical networks being developed for interactive video, audio, and data distribution.

Optical Fiber

A glass or plastic fiber that has the ability to guide light along its axis. The three parts of an optical fiber are the core, the cladding, and the coating or buffer.

Optical Interface (OOI)

A point at which an optical signal is passed from one equipment medium to another without conversion to an electrical signal

Optical Isolator

A component used to block out reflected and unwanted light. Also called an isolator.

Optical Line Termination (OLT)

Optical network elements that terminate a line signal.

Optical Link Loss Budget

The range of optical loss over which a fiber optic link will operate and meet all specifications. The loss is relative to the transmitter output power and affects the required receiver input power.

Optical Loss Test Set (OLTS)

A source and optical power meter combined used to measure optical loss.

Optical Multiplex Section (OMS)

A section of a DWDM system that incorporates an optical add/drop multiplexer.

Optical Network Interface (ONI)

A device used in an optical distribution network to connect two parts of that network.

Optical Network Termination (ONT)

Optical network element that terminates a line signal in installations where the fiber extends into the customer premises.

Optical Network Unit (ONU)

Abbreviation for optical network unit. A network element that is part of a fiber-in-the-loop system.

Optical Path Power Penalty

The additional loss budget required to account for degradations due to reflections, and the combined effects of dispersion resulting from intersymbol interference, mode-partition noise, and laser chirp.

Optical Power Meter

An instrument that measures the amount of optical power present at the end of a fiber or cable.

Optical Pump Laser

A shorter wavelength laser used to pump a length of fiber with energy to provide amplification at one or more longer wavelengths. See also EDFA.

Optical Return Loss (ORL)

The ratio (expressed in dB) of optical power reflected by a component or an assembly to the optical power incident on a component port when that component or assembly is introduced into a link or system.

Optical Rise Time

The time interval for the rising edge of an optical pulse to transition from 10% to 90% of the pulse amplitude. Alternatively, values of 20% and 80% may be used.

Optical Spectrum Analyzer (OSA)

A device that allows the details of a region of an optical spectrum to be resolved. Commonly used to diagnose DWDM systems.

Optical Time Domain Reflectometer (OTDR)

An instrument that locates faults in optical fibers or infers attenuation by backscattered light measurements.

Optical Waveguide

Another name for optical fiber.

Optical-to-Electrical Converter (OE)

A device used to convert optical signals to electrical signals. Also known as OEC.

Opto-Electronic Integrated Circuit (OEIC)

An integrated circuit that includes both optical and electrical elements.

Original Equipment Manufacturer (OEM)

The manufacturer of any device that is designed and built to be distributed under the label of another company.

Outside Plant (OSP)

In telephony, all cables, conduits, ducts, poles, towers, repeaters, repeater huts, and other equipment located between a demarcation point in a switching facility and a demarcation point in another switching facility or customer premises.

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Packet

In data communications, a sequence of binary digits, including data and control signals, that is transmitted and switched as a composite whole. The packet contains data, control signals, and possibly error control information, arranged in a specific format.

Packet Switching

The process of routing and transferring data by means of addressed packets so that a channel is occupied during the transmission of the packet only, and upon completion of the transmission the channel is made available for the transfer of other traffic.

Parity

A term used in binary communication systems to indicate whether a number of 1

Passband

The region of usable frequency in electronics or wavelength in optics.

Passive Branching Device

A device which divides an optical input into two or more optical outputs.

Passive Device

Any device that does not require a source of energy for its operation. Examples include electrical resistors or capacitors, diodes, optical fiber (photo), cable, wires, glass, lenses, and filters.

Passive Optical Network (PON)

Abbreviation for passive optical network. A broadband fiber optic access network that uses a means of sharing fiber to the home without running individual fiber optic lines from an exchange point, telco CO, or a CATV headend and the subscriber's home.

Pathological Test Code

A special test pattern used with DTV and HDTV signals to create the longest strings of zeros and ones over the serial link. This requires the serial transport link to handle much lower frequency components than is typical in a normal data link.

Pay-Per-View (PPV)

An event that has an associated viewing cost, and which may be purchased separately from any package or subscription. The ordered events could include movies, special events, such as sporting, or adult programming. The event could be purchased by either impulse PPV by using a television remote (this application requires a continuous land line phone based connection), or over the phone PPV (this application may have additional costs for processing).

Phase Alternation by LIne (PAL)

Abbreviation for phase alternation by line. A composite color standard used in many parts of the world for TV broadcast. The phase alternation makes the signal relatively immune to certain distortions (compared to NTSC). Delivers 625 lines at 50 frames per second. PAL-plus is an enhanced-definition version.

Photoconductive

Losing an electrical charge on exposure to light.

Photodetector

An optoelectronic transducer such as a PIN photodiode (illustrated) or avalanche photodiode. In the case of the PIN diode, it is so named because it is constructed from materials layered by their positive, intrinsic, and negative electron regions.

Photodiode (PD)

A semiconductor device that converts light to electrical current.

Photon

A quantum of electromagnetic energy. A particle of light.

Photonic

A term coined for devices that work using photons, analogous to the electronic for devices working with electrons.

Photovoltaic

Providing an electric current under the influence of light or similar radiation.

Physical Contact (PC)

Refers to an optical connector that allows the fiber ends to physically touch. Used to minimize backreflection and insertion loss.

Pigtail

A short optical fiber permanently attached to a source, detector, or other fiber optic device at one end and an optical connector at the other.

Plain Old Telephone System (POTS)

A call that requires nothing more than basic call handling without additional features.

Planar Lightwave Circuit (PLC)

Abbreviation for planar lightwave circuit. A device which incorporates a planar waveguide.

Planar Waveguide

A waveguide fabricated in a flat material such as thin film.

Plastic Fiber

An optical fiber having a plastic core and plastic cladding.

Plenum

The air handling space between walls, under structural floors, and above drop ceilings, which can be used to route intrabuilding cabling.

Plenum Cable

A cable whose flammability and smoke characteristics allow it to be routed in a plenum area without being enclosed in a conduit.

Point-to-Point Transmission

Transmission between two designated stations.

Polarization

The direction of the electric field in the lightwave. If the electric field of the lightwave is in the Y Axis, the light is said to be vertically polarized. If the electric field of the lightwave is in the X axis, the light is said to be horizontally polarized.

Polarization Maintaining Fiber

Fiber designed to propagate only one polarization of light that enters it.

Polarization Mode Dispersion (PMD)

Polarization mode dispersion is an inherent property of all optical media. It is caused by the difference in the propagation velocities of light in the orthogonal principal polarization states of the transmission medium. The net effect is that if an optical pulse contains both polarization components, then the different polarization components will travel at different speeds and arrive at different times, smearing the received optical signal.

Port

Hardware entity at each end of the link.

Printed Circuit Board (PCB)

Also referred to as PWB

Private Branch Exchange (PBX)

Abbreviation for private branch exchange. A subscriber-owned telecommunications exchange that usually includes access to public switched networks.

Public Switched Networks (PSN)

1. Any common carrier network that provides circuit switching among public users. 2. A switched network accessible to the public for originating and terminating telecommunications messages. 3. Any common carrier switched network, whether by wire or radio, including local exchange carriers, interexchange carriers, and mobile service providers, that use the North American Numbering Plan in common with provision of switched services.

Public Switched Telephone Network (PSTN)

A domestic telecommunications network usually accessed by telephones, key telephone systems, private branch exchange trunks, and data arrangements.

Pulse

A current or voltage which changes abruptly from one value to another and back to the original value in a finite length of time. Used to describe one particular variation in a series of wave motions. The parts of the pulse include the rise time, fall time, and pulse width, pulse amplitude. The period of a pulse refers to the amount of time between pulses.

Pulse Dispersion

The dispersion of an optical signal as it propagates through an optical fiber. Also called pulse spreading.

Pulse-code Modulation (PCM)

A technique in which an analog signal, such as a voice, is converted into a digital signal by sampling the signal's amplitude and expressing the different amplitudes as a binary number. The sampling rate must be at least twice the highest frequency in the signal.

Pump Laser

A power source for signal amplification, typically a 980 nm or 1480 nm laser, used in EDFA applications.

Push

1) In electronic marketing, to send data to another computer without a direct request from that computer. 2) In networking, to send data from a server to a client in compliance with a previous request from the client, as soon as the data becomes available.

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Quality of Service (QoS)

1. The performance specification of a communications channel or system which may be quantitatively indicated by channel or system performance parameters such as signal-to-noise ratio, bit error rate, message throughput rate, and call blocking probability. 2. A subjective rating of telephone communications quality in which listeners judge transmissions by qualifiers such as excellent, good, fair, poor, or unsatisfactory.

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Random Jitter (RJ)

Random jitter is due to thermal noise and may be modeled as a Gaussian process. The peak-to-peak value of RJ is of a probabilistic nature, and thus any specific value requires an associated probability.

Rays

Lines that represent the path taken by light. Receiver

Recombination

Combination of an electron and a hole in a semiconductor that releases energy, leading to light emission.

Refraction

The changing of direction of a lightwave in passing through a boundary between two dissimilar media, or in a graded-index medium where refractive index is a continuous function of position.

Refractive Index

A property of optical materials that relates to the speed of light in the material versus the speed of light in a vacuum.

Refractive Index Gradient

The description of the value of the refractive index as a function of distance from the optical axis along an optical fiber diameter. Also called refractive index profile.

Regenerative Repeater

A repeater, designed for digital transmission, in which digital signals are amplified, reshaped, retimed, and retransmitted.

Regenerator

Synonym for regenerative repeater.

Repeater

A receiver and transmitter set designed to regenerate attenuated signals. Used to extend operating range.

Request to Send (RTS)

Abbreviation for request to send. In a communications network, a signal from a remote receiver to a transmitter for data to be sent to that receiver.

Residual Loss

The loss of the attenuator at the minimum setting of the attenuator.

Responsivity

The ratio of a photodetector

Return Loss

See optical return loss.RF

Return Path

A communications connection that carries signals from the subscriber back to the operator. The return path allows for interactive television and on-demand services, such as pay-per-view, video on demand, and interactive games.

Return to Zero (RZ)

A common means of encoding data that has two information states called zero and one in which the signal returns to a rest state during a portion of the bit period.

Ribbon Cables

Cables in which many fibers and/or copper wires are embedded in a plastic material in parallel, forming a flat ribbon-like structure.

Ring Network

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

Rise Time

The time taken to make a transition from one state to another, usually measured between the 10% and 90% completion points of the transition. Alternatively the rise time may be specified at the 20% and 80% amplitudes. Shorter or faster rise times require more bandwidth in a transmission channel.

Root Mean Square (RMS)

Technique used to measure AC voltages.

RS-250C

An ANSI recommended standard for video transmission used to evaluate the quality of a received picture quality. Different requirements exist for short-haul, medium-haul, and long-haul RS-250C. Each of these three levels is defined by the number of intermediate processing devices and the type of path (optical or electrical).

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S-Band

The wavelength region between 1485 nm and 1520 nm used in some CWDM and DWDM applications.

Sampling Rate

The number of discrete sample measurements made in a given period of time. Often expressed in megahertz (MHz) for video.

Saturation

1) In a communications system, the condition in which a component of the system has reached its maximum traffic handling capacity. 2) The point at which the output of a linear device, such as a linear amplifier, deviates significantly from being a linear function of the input when the input signal is increased. 3) The degree of the chroma or purity of a color.

Self Phase Modulation (SPM)

Self-phase modulation.

Sensitivity

See receiver sensitivity.

Serial

One bit at a time, along a single transmission path.

Set-Top Box (STB)

An auxiliary device that usually sits on top of or adjacent to a television receiver used in direct analog or digital satellite transmission and digital television to view the signals on an analog TV. Converter boxes are becoming obsolete as old model televisions requiring a converter are replaced by modern televisions, which incorporate a converter into the television. Also called a set-top converter.

Simple Network Management Protocol (SNMP)

The Internet standard protocol for network management software. It monitors devices on the network, and gathers device performance data for management information data bases (MIB).

Simplex

Single element (e.g., a simplex connector is a single-fiber connector).

Simplex Cable

A term sometimes used for a single-fiber cable. Simplex

Single Attachment Concentrator

A concentrator that offers one attachment to the FDDI network.

Single-line Laser

See single-longitudinal mode laser.

Single-longitudinal Mode Laser (SLM)

An injection laser diode which has a single dominant longitudinal mode. A single-mode laser with a side mode suppression ratio (SMSR)< 25 dB.

Single-mode (SM) Fiber

A small-core optical fiber through which only one mode will propagate. The typical diameter is 8-9 microns.

Single-mode Laser Diode (SMLD)

See single-longitudinal mode laser.

Single-mode Optical Loss Test Set (SMOLTS)

An optical loss test set for use with single-mode fiber.

SMA

A threaded type of optical connector. One of the earliest optical connectors to be widely used. Offers poor repeatability and performance.

Small Computer Sytems Interface (SCSI)

An intelligent interface device that expands a microprocessor (CPU) bus to facilitate connections to multiple peripherals (e.g., CD-ROM drives, hard drives, or scanners) and exchange data with those peripherals via a separate communications bus.

Smart Structures

Also smart skins. Materials containing sensors (fiber optic or other types) to measure their properties during fabrication and use.

Society of Motion Picture and Television Engineers (SMPTE)

Organization that publishes ANSI-approved standards, recommended practices, and engineering guidelines for the motion picture and television industry.

Soliton Pulse

An optical pulse having a shape, spectral content, and power level designed to take advantage of nonlinear effects in an optical fiber waveguide, for the purpose of essentially negating dispersion over long distances.

Source

In fiber optics, a transmitting LED or laser diode, or an instrument that injects test signals into fibers.

Span Engineering

The process of designing a DWDM transmission span to achieve the required performance based on fiber type, the transmission distance, amplifier spacing, noise, power, and channel count.

Spectral Efficiency

The number of data bits per second that can be transmitted in a one Hertz bandwidth range.

Spectral Width

A measure of the extent of a spectrum. For a source, the width of wavelengths contained in the output at one half of the wavelength of peak power. Typical spectral widths are 50 to 160 nm for an LED and less than 5 nm for a laser diode.

Spectral Width Full Width Half Maximum (FWHM)

The absolute difference between the wavelengths at which the spectral radiant intensity is 50 percent of the maximum power.

Splice

A permanent connection of two optical fibers through fusion or mechanical means.

Splitter

see Coupler.Splitting Ratio

Stabilized Light Source

An LED or laser diode that emits light with a controlled and constant spectral width, center wavelength, and peak power with respect to time and temperature.

Star Coupler

A coupler in which power at any input port is distributed to all output ports.

Star Network

A network in which all terminals are connected through a single point, such as a star coupler or concentrator.

Step-index Fiber

Fiber that has a uniform index of refraction throughout the core that is a step below the index of refraction in the cladding.

Stimulated Brillouin Scattering (SBS)

The easiest fiber nonlinearity to trigger. When a powerful light wave travels through a fiber it interacts with acoustical vibration modes in the glass. This causes a scattering mechanism to be formed that reflects much of the light back to the source.

Stimulated Raman Scattering (SRS)

A fiber nonlinearity similar to SBS but having a much higher threshold. This mechanism can also cause power to be robbed from shorter wavelength signals and provide gain to longer wavelength signals.

Storage Area Network (SAN)

Connects a group of computers to high-capacity storage devices. May be incorporated into local area networks (LAN), metropolitan area networks (MAN), and wide area networks (WAN).

Straight Tip Connector (ST)

Popular fiber optic connector originally developed by AT&T.

Strength Member

The part of a fiber optic cable composed of aramid yarn, steel strands, or fiberglass filaments that increase the tensile strength of the cable.

Subcarrier Multiplexing (SCM)

The process by which multiple subcarrier signals are combined onto one signal.

Submarine Cable

A cable designed to be laid underwater.

Subscriber Loop

Also called local loop. The link from the telephone company central office (CO) to the home or business (customer premises).

Subscription Channel (SC)

A push-pull type of optical connector that features high packing density, low loss, low backreflection, and low cost.

Supertrunk

A cable that carries several video channels between facilities of a cable television company. Surface-emitting Diode

Surface Mount Technology (SMT)

An electronics manufacturing technique.

Switch

1) In communications systems, a mechanical, electro-mechanical, or electronic device for making, breaking, or changing the connections in or among circuits. 2) Synonym for central office, switching center. 3) In communications systems, to transfer a connection from one circuit to another.

Synchronization Pulse

1) A signal derived from the composite or combination of the horizontal and vertical drives. 2) A pulse used to achieve or maintain synchronism, usually applied to analog signals. (The term synchronization bit is usually applied to digital data streams.) Commonly called the sync pulse. See also composite sync.

Synchronous

A data signal that is sent along with a clock signal. A system in which events, such as signals, occur at evenly spaced time durations. Opposite of asynchronous.

Synchronous Code Division Multiple Access (S-CDMA)

A synchronized version of CDMA.

Synchronous Optical Network Transport System (SONET)

An interface standard widely used by the telecom industry where OC-3 is the lowest current rate (155.5 Mb/s), and OC-768 is the highest rate being contemplated (39.808 Gb/s). Valid rates increase by a factor of four from the OC-3 rate up to OC-768.

Syst

In English, International System of Units, commonly known as the metric system.

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T-Carrier

Generic designator for any of several digitally multiplexed telecommunications carrier systems.

T1

In telecommunications, the cable used to transport DS1 service.

Tap Loss

In a fiber optic coupler, the ratio of power at the tap port to the power at the input port.

Tap Port

In a coupler where the splitting ratio between output ports is not equal, the output port containing the lesser power.

Telecommunications Management Network (TMN)

A network that interfaces with a telecommunications network at several points in order to receive information from, and to control the operation of, the telecommunications network.

Ternary

A semiconductor compound made of three elements (e.g., GaAlAs). Thermal Noise

Throughput Loss

In a fiber optic coupler, the ratio of power at the throughput port to the power at the input port.

Throughput Port

In a coupler where the splitting ratio between output ports is not equal, the output port containing the greater power.

Tight-Buffer

A material tightly surrounding a fiber in a cable, holding it rigidly in place.

Time-Division Multiple Access (TDMA)

A communications technique that uses a common channel (multipoint or broadcast) for communications among multiple users by allocating unique time slots to each user. Used extensively in satellite systems, local area networks, physical security systems, and combat-net radiosystems.

Time-Division Multiplexing

A transmission technique whereby several low-speed channels are multiplexed into a high-speed channel for transmission. Each low-speed channel is allocated a specific position based on time.

Token Ring

A ring-based network scheme in which a token is used to control access to a network. Used by IEEE 802.5 and FDDI.

Total Internal Reflection

The reflection that occurs when light strikes an interface at an angle of incidence (with respect to the normal) greater than the critical angle.

Transceiver

A device that performs, within one chassis, both telecommunication transmitting and receiving functions.

Transducer

A device that converts energy from one form to another, such as optical energy to electrical energy.

Transmission Control Protocol Internet Protocol (TCPIP)

Two interrelated protocols that are part of the Internet protocol suite. TCP operates on the OSI transport layer and breaks data into packets. IP operates on the OSI network layer and routes packets. Originally developed by the U.S. Department of Defense.

Transmitter

A device that includes a source and driving electronics. It functions as an electrical-to-optical converter. Transponder

Tree

In communications networks, a physical topology consisting of a hierarchy of master-slave connections between a concentrator and other FDDI nodes (including subordinate concentrators).

Trunk

1) In a communications network, a single transmission channel between two switching centers or nodes, or both. 2) A circuit between switchboards or other switching equipment, as distinguished from circuits which extend between central office switching equipment and information origination/termination equipment. Trunks may be used to interconnect switches, such as major, minor, public and private switches, to form networks.

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Ultaraviolet (UV)

That portion of the electromagnetic spectrum in which the longest wavelength is just below the visible spectrum, extending from approximately 4 nm to 400 nm.

Unidirectional

Operating in one direction only.

Unity Gain

A concept in which all the amplifiers in a cascade are in balance with their power inputs and outputs. Unity gain can be achieved by adjusting the receiver output, either by padding or attenuation in the node, to the proper level determined by the RF input.

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Vertical Cavity Surface-emitting Laser

Lasers that emit light perpendicular to the plane of the wafer they are grown on. They have very small dimensions compared to conventional lasers and are very efficient.

Very High Data Rate Digital Subscriber Line (VDSL)

A DSL operating at a data rate higher than that of HDSL. See also DSL.

Video on Demand (VOD)

See video on demand.

Virtual Private Network (VPN)

A protected information-system link utilizing tunneling, security controls, and end-point address translation giving the end user the impression that a dedicated line exists between nodes.

Visible Light

Electromagnetic radiation visible to the human eye; wavelengths of 400-700 nm.

Voice Circuit

A circuit capable of carrying one telephone conversation or its equivalent; the standard sub-unit in which telecommunication capacity is counted. The U.S. analog equivalent is 4 kHz. The digital equivalent is 64 kbit/s in North America and in Europe.

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Wave Division Multiplexing (WDM)

Sending several signals through one fiber with different wavelengths of light.

Wide Area Network (WAN)

A physical or logical network that provides capabilities for a number of independent devices to communicate with each other over a common transmission-interconnected topology in geographic areas larger than those served by local area networks or metropolitan area networks.

Wideband

Possessing large bandwidth.

Wireless

A network or terminal that uses electromagnetic waves, such as RF, infrared, laser, visible light, and acoustic energy, not wires, for telecommunications.

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XT (Crosstalk)

1) Undesired coupling from one circuit, part of a circuit, or channel to another. 2) Any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates and undesired effect in another circuit or channel.

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Zipcord

A two-fiber cable consisting of two single fiber cables having conjoined jackets. A zipcord cable can be easily divided by slitting and pulling the conjoined jackets apart.