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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. |
| A | |
| Absorption | Optical fiber attenuation resulting from the conversion of optical power to heat. Caused by impurities in the fiber such as hydroxyl ions. |
| AC (Alternating Current) | An electric current that reverses its direction at perodic 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 that allows signals to be added or dropped from a high-speed optical carrier. |
| ADM (Add-Drop Multiplexer) | A device which adds or drops signals from a communications network. |
| ADSL (Asynchronous 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 | Misalignent of fiber end face angles being. Angular Misalignment causes signal loss. |
| APC (Angled Physical Contact) | A style of fiber optic connector where the fiber is polished at an angle, typically 8°, to minimize backreflection. |
| APD (Avalanche Photodiode) | A special type of diode that exhibits internal amplification of current when photons are absorbed. Amplification is done by avalanche multiplication of charge 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 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 or dB/km. |
| Attenuator | A passive device for reducing the amplitude of a signal without appreciably distorting the waveform. See also fiber optic attenuator. |
| Average Power | The average level of power in a signal that varies with time. |
| Axis | The center of an optical fiber. |
| B | |
| 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. |
| Baud | Another name for symbol rate. Also known as baud rate, or used as a unit meaning symbols per second. |
| 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 number of incorrect bits received divided by the total number of bits received. |
| BIDI (Bi-Directional Transceiver) | A device that sends information in one direction and receives information from the opposite direction. |
| 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. |
| Bit | The smallest unit of information upon which digital communications are based. |
| Bit Rate | The rate at which a binary bit is transmitted, measured in bits per second (bits/s, bps, or b/s). |
| 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 in the form of Fresnel reflection where a glass-air interface causes a reflection. |
| Brillouin Scattering | When a powerful light wave travels through a fiber, it interacts inelastically with large-scale vibration modes in the glass, such as acoustical vibration, vibration from charge displacements, or magnetic spin oscillation. This causes a scattering mechanism to be formed that reflects the light back to the source. |
| 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. 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 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. |
| C | |
| 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 | A cable plant consists of all the optical elements including fiber, connectors splices, etc. between a transmitter and receiver |
| CATV (Community Antenna Television) | The term now typically refers to cable television. |
| C-Band | The wavelength range between 1530 nm and 1565 nm used in some CWDM and DWDM applications. |
| 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 a unique modulation scheme for each channel. |
| Center Wavelength | The nominal central operating wavelength of a laser. |
| Channel | 1) A transmission medium of a communication signal. 2) A signal sent over a communications path. |
| Chromatic Dispersion | An optical phenomenon where light of different wavelengths propogate at different speeds in a medium, such as a fiber. |
| 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 | A cable consisting of a center conductor surrounded by an insulating material and a concentric outer conductor and optional protective covering. |
| Concatenation | The process of connecting pieces of fiber together. See also splice. |
| Connector | A device that provides a demountable connection between two fibers or a fiber and a source or detector. |
| Connector Plug | A mechanical or optical device used to terminate an electrical or 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. |
| Crosstalk (XT) | 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 an undesired effect in another circuit or channel. |
| CWDM (Coarse Wavelength-Division Multiplexing) | A type of multiplexing where up to 18 C-band signals can be stacked onto a single fiber. |
| D | |
| Data Rate | The number of bits of information in a transmission system, expressed in bits per second (b/s or bps). |
| dB (Decibel) | A unit of measurement indicating relative power on a logarithmic scale. |
| dBc | Decibel relative to the power of a carrier signal. |
| dBm | Decibel relative to 1 milliwatt (mW). |
| dBμ | Decibel relative to 1 microwatt (1μW). |
| 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 only of discrete states. Opposite of analog. A binary signal has only two states, and a 4-level signal (such as PAM-4) has only four states. |
| 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 commonly include laser diodes and photodiodes. |
| Diode Laser | A semiconductor device that converts electricity into coherent, near-monochromatic light. Sometimes referred to as Injection Laser Diode or simply laser. Depending on the specific type of diode laser, different longitudinal modes can produce different wavelengths from the same laser. |
| 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) | A module that has the opposite dispersion of the fiber being used in a transmission system. It is used to nullify the dispersion caused by the fiber. |
| 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 | Any changes to the shape of a communication signal. Typically undesirable. |
| Distributed Feedback Laser (DFB) | A special type of laser diode that has a Bragg reflection grating in the active region to suppress multiple longitudinal modes and enhance a single longitudinal mode to generate a single wavelength. Commonly used in DWDM systems where a single, stable wavelength is required. |
| 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 T-carrier digital telephone hierarchy. |
| Dual In-Line Package (DIP) | A specific type of electronic package with a rectangular housing and a row of pins along each of the two opposite sides. |
| Dual Ring (FDDI Dual Ring) | A pair of counter-rotating logical rings in a Fiber Distributed Data Interface (FDDI). |
| Duplex | 1) Dual-element (e.g., a duplex connector is a connector for two fibers). 2) Transmission in both directions, either one direction at a time (half-duplex) or both directions simultaneously (full-duplex). |
| Duplex Cable | A two-fiber cable suitable for duplex transmission. |
| DWDM (Dense Wavelength-Division Multiplexing) | The transmission of many 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. |
| E | |
| EDFA (Erbium-Doped Fiber Amplifier) | 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. |
| EEPROM | Acronym for Electrically Erasable Programmable Read-Only Memory. A form of non-volatile memory for storing data. Fiber optic transcievers with EEPROMs store data in a standardized format and include information such as laser wavelength, vendor identification, or special hardware compatibility data. |
| 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 propogating at the speed of light. Includes gamma radiation, X-rays, ultraviolet, visible, infrared, microwaves, and radio waves. |
| Enterprise Systems Connection (ESCON) | A duplex optical connector used for computer-to-computer data exchange. |
| EO (Electrical-to-Optical Convertor) | A device that converts electrical signals to optical signals, such as a laser diode. |
| 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. If the receiver detects an error, it may be corrected, or it can simply be reported. |
| Ethernet | A standard protocol (IEEE 802.3) for networks. Ethernet has set standards 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 of overlapping bits that display many performance characteristics of a communication system. |
| F | |
| FC (Ferrule Connector) | A threaded optical connector that uses a special curved polish on the connector for very low backreflection. Good for single-mode or multimode fiber. |
| FCC | Abbreviation for Federal Communications Commission. A United States government agency that regulates communications by radio, television, wire, satellite, and cable. |
| FDM | See Frequency Division Multiplexing. |
| Ferrule | A rigid tube that confines or holds a fiber as part of a connector assembly. |
| 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. |
| 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 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. |
| Fibre Channel | An industry-standard specification which details high-speed communication. Typically used in data centers or for transferring data storage. |
| Filter | A device which transmits only a part of a signal’s energy by amplifiying or attenuating select wavelengths. |
| Free-Space Optics | Also called free-space photonics. Transmission of modulated light through the atmosphere via lasers, LEDs, or infrared-emitting diodes for 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. |
| Fresnel Reflection | Reflection of light caused by differing indexes of refraction at an interface, such as an air-glass interface. |
| Fusion Splicer | An instrument that permanently bonds two fibers together by heating and fusing them. |
| G | |
| Germanium (Ge) | Element generally used in detectors. Good for most fiber optic wavelengths (800-1600 nm). Performance is inferior to InGaAs. |
| Gigahertz (GHz) | One billion Hertz (cycles per second). |
| 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. |
| H | |
| Half-Duplex Transmission | A bi-directional link that is limited to one-way transfer of data, meaning 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 | 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. |
| Hertz (Hz) | Unit defined as one cycle per second in the International System of Units. |
| 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 Pluggable | An electronic device subassembly or component able to be removed or replaced without first powering down the device. |
| Hot Swapable | See hot pluggable. |
| I | |
| Index of Refraction | The ratio of the velocity of light in free space to the velocity of light in a material. Also called Refractive Index. |
| Index-Matching Fluid | A fluid whose index of refraction nearly equals that of the fiber core. Used to reduce backreflection loss at fiber ends. Also known as index-matching gel. |
| Indium Gallium Arsenide (InGaAs) | Compound used to make high-performance long-wavelength detectors, around 900-1700 nm. |
| Infrared (IR) | A region of the electromagnetic spectrum bounded by the long-wavelength extreme of the visible spectrum (700 nm) and the shortest microwaves (1 mm). |
| In-Line Amplifier | An 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. |
| Insertion Loss | The loss of power that results from inserting a component, such as a connector, coupler, or splice, into a previously continuous path. |
| Institute of Electrical and Electronic Engineers (IEEE) | A technical professional organization 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 interconnected computer networks. |
| 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. |
| ISDN | See integrated services digital network. |
| ITU | Acronym for the International Telecommunications Union, an agency of the United Nations to set and administer international standards. |
| J | |
| Jacket | The outer, protective covering of the cable. Also called the cable sheath. |
| Jumper | A short fiber optic cable with connectors on both ends. |
| K | |
| Kevlar | A very strong, very light, synthetic compound developed by DuPont which is used to strengthen optical cables. |
| kHz | One thousand Hertz (cycles per second). |
| km | One thousand meters. 1km = 3,280 feet or 0.62 miles. |
| L | |
| Large Core Fiber | A fiber with a core 100μm or larger. |
| 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 coherent, near-monochromatic light through stimulated emission. |
| Laser Chirp | A slight change in wavelength due to a change in voltage or current to the laser. |
| Laser Diode (LD) | See Diode Laser. |
| L-Band | The wavelength range between 1570 nm and 1610 nm used in some CWDM and DWDM applications. |
| LC (Lucent Connector) | A small form-factor optical connector originally developed by Lucent. Available in many different physical contact polishes, such as Angled Physical Contact (APC) or Ultra Physical Contact (UPC). Good for single-mode or multimode fiber. |
| Least Significant Bit (LSB) | In a binary code, the bit assigned to the lowest order position that can be represented by the code. |
| Light | Usually refers to the region of the electromagnetic spectrum that can be perceived by human vision, designated the visible spectrum, between 400 nm and 700 nm. Also used as a general term for any part of the electromagnetic spectrum. |
| Light Piping | Use of optical fibers to illuminate. |
| Light-Emitting Diode (LED) | A semiconductor device that converts electricity into incoherent, non-monochromatic light when forward biased. |
| 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. |
| Line Code | A physical waveform representation of bits. |
| 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-LATA, 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. |
| 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 | A decrease of the desired signal power. In optical communication systems, this is primarily due to attenuation. |
| Loss Budget | An accounting of overall loss in a system. |
| 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 recoverd 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. |
| M | |
| Macrobending | Large-scale bending on a fiber that contributes to attenuation. |
| Margin | Allowance for attenuation in addition to that explicitly accounted for in system design. |
| Mean Time Between Failure (MTBF) | Average time between unit failures. 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. |
| Microbending | Small local imperfections in the fiber created during manufacturing or by external forces applied to the fiber that contribute to attenuation. |
| Micrometer | One millionth of a meter. Abbreviated as μm. |
| Microsecond | One millionth of a second. Abbreviated as μs. |
| Microwatt | One millionth of a watt. Abbreviated as μW. |
| Microwave Transmission | Communication systems using very high-frequency radio waves 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 excessive macrobending attenuation or breakage occurs. |
| Misalignment Loss | The loss of optical power resulting from angular misalignment, lateral displacement, and fiber end seperation. |
| 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. |
| Modulation | The process by which an information signal is encoded in a carrier signal. For example, in the case of fiber optic communication using binary signals, a laser acting as a carrier signal may be switched between a high power level and a low power level to represent a 1 and a 0. |
| Modulator | A device that incodes an information signal on a carrier signal. |
| 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 | A diode laser that has a number of longitudinal modes. |
| Multimode Dispersion | Dispersion resulting from the different transit lengths of different propagating modes in a multimode optical fiber. Also called modal dispersion. |
| Multimode Fiber (MMF) | An optical fiber that has a core large enough to propagate more than one mode of light. Sometimes abbreviated as MM fiber. |
| 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). |
| N | |
| 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 |
| 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 Fire 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 End Cross-Talk (NEXT) | The optical power reflected from one or more input ports, back to another input port. Also known as isolation directivity. |
| 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. |
| Network | 1) An interconnection of three or more communicating entities and (usually) one or more nodes. 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. |
| 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 | Any unwanted energy that corrupt or distort a data signal. |
| Noise Equivalent Power (NEP) | The noise of an optical receiver, often expressed in terms of noise equivalent optical power |
| Noise Figure (NF) | The ratio of the input signal-to-noise ratio to the output signal-to-noise ratio for a given element in a transmission system. Used for optical and electrical components. |
| Non Dispersion-Shifted Fiber (NDSF) | A popular type of single-mode fiber deployed; designed to have a zero-dispersion wavelength near 1310 nm. |
| 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. |
| Normal | In physics and mathematics, normal means perpendicular or at a right angle. The term ‘the normal’ refers to a perpendicular perspective of an object. |
| NRZ (Non-Return-to-Zero) | A line code format that encodes a digital signal into two discrete levels, where the signal does not return zero after each bit period. |
| 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. |
| O | |
| 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 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 Cross-Connect (OXC) | See cross-connect. |
| Optical Distribution Network (ODN) | Term for optical networks being developed for data distribution using optical equipment. |
| 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 meet all operational 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 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. |
| 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 Waveguide | Another name for optical fiber. |
| Optical-to-Electrical Converter (OE) | A device used to convert optical signals to electrical signals, such as a photodiode. 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. |
| OTDR (Optical Time Domain Reflectometer) | An instrument that locates faults in optical fibers or infers attenuation by backscattered and backreflected light measurements. |
| Outside Plant (OSP) | 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. |
| P | |
| Packet | In data communications, a sequence of digital symbols, 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. |
| PAM-4 (Pulse-Amplitude Modulation 4-level) | A line code format that encodes a signal into four discrete levels. Each level represents the information of two bits, meaning PAM-4 signaling encodes twice as much information per symbol as binary signaling. |
| Parity | Parity bits, also called a check bits, are redundant bit sequences appended to a binary sequence for error detection or error correction. |
| 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. Electrical examples include resistors, capacitors, or diodes; optical examples include optical fiber, cable, wires, glass, lenses, or filters. |
| Passive Optical Network (PON) | Abbreviation for passive optical network. A broadband fiber optic access network that uses a means of sharing fiber to multiple points without running individual fiber optic lines between the points. |
| 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 or avalanche photodiode. |
| 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 term ‘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) | 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) | Sometimes referred to as Printed Wiring Board (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, pulse width, and 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. |
| 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. |
| Q | |
| 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. |
| R | |
| Raman Scattering | Light in a fiber interacting inelastically with the small-scale vibrations between neighboring atoms. This mechanism can cause power to be robbed from shorter wavelength signals and provide gain to longer wavelength signals. |
| Random Jitter (RJ) | Random timing jitter due to thermal noise and 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. |
| Rayleigh Scattering | Random scattering caused by light interaction with small particles. |
| Rays | Lines that represent the path taken by light. |
| 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 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 | See Index of Refraction. |
| Refractive Index Gradient | 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. Used to extend operating range. |
| Regenerator | Synonym for regenerative repeater. |
| Repeater | A receiver and transmitter set designed to amplify attenuated signals without reshaping or retiming the signal. Used to extend operating range. |
| Request to Send (RTS) | 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 optical sensitivity of a photodetector. |
| Return Loss | See optical return loss. |
| Return Path | A communications connection that carries signals from the subscriber back to the operator. |
| 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. |
| Root Mean Square (RMS) | A technique used to measure AC voltages and currents. |
| 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). |
| RZ (Return-to-Zero) | A line code format that encodes a digital signal where the signal returns to zero during a portion of the bit period. |
| S | |
| Sampling Rate | The number of discrete sample measurements made in a given period of time. The sampling rate must be at least twice the highest frequency in the signal in order to satisfy a mathematical constraint. |
| 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. |
| S-Band | The wavelength region between 1460 nm and 1530 nm used in some CWDM and DWDM applications. |
| Self Phase Modulation (SPM) | A self-induced optical phase delay. As the pulse’s amplitude changes, the signal is phase modulated. |
| Sensitivity | The mininum acceptable power needed to achieve an acceptable BER or performance. |
| Serial | Transmission of one symbol 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) | An 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 | 1) Single element (e.g., a simplex connector is a single-fiber connector). 2) A one-way transmission link. |
| Simplex Cable | A term sometimes used for a single-fiber cable. |
| Single Attachment Concentrator | A concentrator that offers one attachment to the FDDI network. |
| Single Mode Suppression Ratio | A measure of a laser’s power at the peak center wavelength compared to the power of the nearest mode. Used to describe how wavelength selective a laser is. |
| 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 Fiber (SMF) | A small-core optical fiber through which only one mode will propagate. The typical diameter is 8-9 microns. Sometimes abbreviated as SM fiber. |
| 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 | 1) A threaded type of RF connector for frequencies between 0 and 18 GHz, and occassionally higher. 2) An optical variation of the RF connector used as one of the first fiber connectors. |
| 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 | 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 source such as 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 for each Hertz of available bandwidth. |
| 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 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. |
| Stabilized Light Source | A light source, such as a 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) | Brillouin scattering in an optical amplifier. See Brillouin scattering. |
| Stimulated Raman Scattering (SRS) | Raman scattering in an optical amplifier. See Raman scattering. |
| Storage Area Network (SAN) | Connects a group of computers to high-capacity storage devices. May are incorporated into local area networks (LAN), metropolitan area networks (MAN), and wide area networks (WAN). |
| Straight Tip Connector (ST) | Fiber optic ‘Straight Tip’ connector originally developed by AT&T. Also known as Bayonet Fiber Optic Connector (BFOC). |
| 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 Connector (SC) | A push-pull type of optical connector that features high packing density, low loss, and low backreflection. |
| Subscriber Loop | Also called local loop. The link from the telephone company central office (CO) to the home or business (customer premises). |
| Surface Mount Technology (SMT) | An electronics manufacturing technique for smaller, more compact circuits. |
| 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. |
| Symbol | A grouping of bits represented in a single waveform. In binary systems, each symbol is conventionally represented by one bit in the form of a high or low pulse. In PAM-4 systems, each symbol represents two binary bits in the form of four different pulse levels. |
| Symbol Rate | The rate at which each symbol is transmitted, measured in symbols per second. Also known as baud. |
| 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) | A digital communication standard designed for data transmission with accurate synchronization from atomic clocks. |
| Système International | In English, ‘International System of Units’, commonly known as the metric system. |
| T | |
| 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. |
| T-Carrier | Generic designator for any of the several digitally multiplexed telecommunications carrier systems. |
| 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). |
| Throughput | See symbol rate. |
| 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 for communications among multiple users by allocating unique time slots to each user. |
| 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 (TCP/IP) | 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. In fiber optics, it functions as an electrical-to-optical converter. |
| 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 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. |
| U | |
| Ultraviolet (UV) | A region of the electromagnetic spectrum bounded by the short-wavelength extreme of the visible spectrum (400 nm) and the longest X-rays (10 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 input. |
| V | |
| 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 other types of 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) | A service where users can choose video programming on demand, instead of viewing programing according to a set broadcasting schedule. |
| 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 | A region of the electromagnetic spectrum bounded by the long-wavelength extreme of the infrared spectrum (700 nm) and the shortest wavelengths of the ultraviolet spectrum (400 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. |
| W | |
| Wave Division Multiplexing (WDM) | Sending several signals through a single 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, laser, visible light, and acoustic energy, not wires, for telecommunications. |
| Z | |
| 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. |
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