Note that maroon colored items are fiber optic related, and red items are telecommunications, data communications, LAN/WAN related.

Acceptance Angle: the half-angle of the cone within which incident light is totally internally reflected by the fiber core. It is equal to arcsin (NA).

ADSL:Asymmetrical Digital Subscriber Line, a form of high speed transmission offered by the local telephone company, where downstream (to the user) data rates are typically higher than the upstream (to the service provider) data rate. This model matches the Internet data transfer requirements where more data flows to the user, initiated by a request consisting of a small data packet, see XDSL

AM (Amplitude Modulation): A transmission technique in which the amplitude of the carrier is varied in accordance with the signal.

Analog: A format that uses continuous physical variables such as voltage amplitude or frequency variations to transmit information.

Angular Misalignment: The loss of optical power caused by deviation from optimum alignment of fiber to fiber or fiber to waveguide.

Aramid Yarn: Strength element used in fiber optic cables to provide support and additional protection. Kevlar is an example.

Armoring: Additional protection between jacketing layers of a cable to provide additional protection against severe outdoor elements. Plastic coated steel corrugated tape is usually used.

ATM:Asynchronous Transfer Mode, a protocol for transferring high-speed data in sequential envelopes called cells, each cell consisting of 53 eight-bit characters. Cells can be made to represent a voice conversation, a data transmission, or a compressed video stream.

Attenuation: (or loss) is a measure of how much of the light "launched" into one end of the fiber comes out of the other end, or the decrease in magnitude of light intensity (power) from the transmitting LED to the receiving photodiode. Attenuation is usually measured in decibels per kilometer (db/km) at specific wavelengths. Every component in a fiber optic system introduces some attenuation (connector, coupler, splice), added to the linear loss of the fiber itself. Typically, single mode fibers have attenuations of less than 1 db/km, and multimode fibers less than 5 db/km.

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: A measure of the information-carrying capacity of an optical fiber or an entire system.

Bandwidth Distance Product: The information carrying capacity of a transmission medium is normally referred to as MHz/km. This is called bandwidth-distance product, or more commonly, bandwidth. The amount of information that can be transmitted over any medium changes according to distance. The relationship is not linear, however. A 500 MHz/km fiber does not translate to 250 MHz for a 2 kilometer length or 1000 MHz for a 0.,5 kilometer length. It is important, therefore, when comparing media, to ensure that the same units of distance are being used.

Baseband: A method of communication in which a signal is transmitted at its original frequency without being impressed on a carrier.

Baud: A unit of signaling speed equal to the number of signal symbols per second, which may or may not be equal to the data rate in bits per second.

Beamsplitter: An optical device, such as a partially reflecting mirror, that splits a beam of light into two or more beams and that can be used in fiber optics for directional couplers.

Bend Loss: A form of increased attenuation in a fiber that results from bending a fiber around a restrictive curvature (a macrobend), or from minute distortions in the fiber (microbends).

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

BER (bit error rate): The ratio of incorrectly transmitted bits to correctly transmitted bits.

Broadband: A broad reference to a method of communication where baseband signals are modulated with different carrier frequencies comprising a wider total bandwidth being transmitted over a single fiber, allowing the simultaneous transmission of many channels. Infers the use of many carrier signals rather than direct modulation (i.e., baseband) of one carrier. Baseband signals could be TV, voice, data, video.

Buffer: A protective layer over a fiber, such a coating, inner jacket, or a tube.

Buffer Coating: A protective layer such as acrylic polymer, applied directly over the fiber cladding for added protection.

Buffer Tube: A hard plastic tube, that holds one or more fibers.

Bundle: Many individual fibers contained within a single jacket or buffer tube. Also, a group of buffered fibers sub-bundled within a cable core.

Bus Network: A network topology where all terminals are attached to a transmission medium serving as a bus.

Butt Splice: A joining of two fibers using optical connectors arranged end-to-end with a coupling device.

Cable Modem:A cable TV company service which is integrated with the delivery of TV services to the household or business. This service requires a unique modem, a cable modem, at the user premise, which splits the TV signals from the Internet connection signals. Typically, there is no telephone capability in the cable modem. The user can get connection speeds of up to 10,000,000 bps using this technique. Note that this rate will vary dependent upon the usage of other neighboring subscribers to the service. Some providers guarantee a 128,000 bps connection rate. The user’s PC connection to the cable modem is an Ethernet interface, requiring a plug-in card for the PC or laptop and appropriate software.

CATV: Cable Television, as opposed to CCTV or Closed Circuit Television

CD: Compact Disk, a form of data storage used with PC’s

Chromatic Dispersion: Spreading of a light pulse caused by the difference in refractive indices at different wavelengths.

Cladding: The outer glass layer that keeps the light trapped inside the fiber core and as a lower index of refraction.

CLEC: Competitive Local Exchange Company, see LEC

Co-location: Recent FCC and PUC rulings requiring a LEC to provide floor space and access to telephony services within the LEC central offices, with the intent of providing competitive telephony services.

Conduit: Pipe or tubing through which cables can be pulled or housed.

Connector: Devices to connect/disconnect fiber to another fiber, source, detector, or other devices.

Core: The central, light-carrying part of a fiber. The diameter of a single mode fiber core is generally less than 10 microns; multimode fiber core is typically 50, 62.5, or 100 microns.

Core Essentricity: A measure of the displacement of the center of the core, relative to the cladding center of a fiber.

Core Ellipticity: Non-Circularity. A measure of the non-circularity of the core.

Coupler: A multiport device used to distribute optical power.

CSU: Channel Service Unit, a device that provides the interface between a customer and the telephone company, typically for 4 wire T1’s or FT1’s.

dB: Decibel. A standard logarithmic unit for the ratio of two powers, voltages, or currents.

dBm: Decibel referenced to a milliwatt.

dBu: Decibel referenced to a microwatt.

Dense Wavelength-Division Multiplexer (DWDM): A transmission technique using a special coupling device whereby separate optical channels, distinguished by wavelengths, are multiplexed onto an optical fiber for transmission. Typical DWDM systems can multiplex 2,4,8,16,32, 64 and higher numbers of wavelengths.

Detector: A device at the receiving end of a fiber optic system that converts incoming optical pulses into electrical signals, usually a photodiode.

dial tone: A local telephone company offering, see POTS

dial up modem: This is the most common telephone company technique for data transmission, where the customer has a dial up modem, either integrated into his PC or Laptop or as a stand-alone modem, and can get connection rates from 2,400 bps up to 56,000 bps. This connection requires a standard telephone line to which the modem is connected. Typical users have more than one device switched or bridged together, however, only one device can be active at any point in time. The user PC interface connection is the serial interface or for laptops the PC’s PCMCIA bus. The modem uses analog frequencies to represent digital 1’s and 0’s that comprise a data byte.

Dielectric: Nonmetallic and therefore, non-conductive. Glass fibers are considered dielectric. A dielectric cable contains no metallic components.

Dispersion: The cause of bandwidth limitation in a fiber. Dispersion causes a broadening or spreading of light as it propagates along the length of the fiber. Three types are: a) mode (modal) dispersion caused by differential optical path lengths in a multimode fiber; b) material dispersion caused by a differential delay of various wavelengths of light in a fiber; and c) waveguide dispersion caused by light traveling in both the core and cladding materials in single mode fibers.

DSL: Digital Subscriber Line, a telephone company offering for high speed digital data service, see ADSL, HSDL, RADSL, VDSL, XDSL

DSU: Digital Service Unit, a modem like device that provides the interface between a customer and the telephone data service provider, unlike a modem this device is digital in its operation, that is transmitting 1’s and 0’s directly, typically at rates lower than T1

Duplex Cable: A two-fiber cable, typically for indoor use, suitable for duplex transmission using one fiber for transmit and the second for receive functions.

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

E-Commerce, e-commerce: electronic commerce, where items for sale, offers for such, exchange of funds, verification of such, etc. are done via the Internet or an electronic network

e-fax: electronic fax, where conversion from facsimile formats are converted to e-mail text formats and vice versa, also providing users with virtual fax machines

e-mail, email: electronic mail, a form of communications using a network capable of addressing unique locations and with storage capability to allow end user viewing on a discretionary basis.

EMD (Equilibrium Mode Distribution): The steady modal state of a multimode fiber in which the relative power distribution among modes is independent of fiber length.

EMI (Electromagnetic Interference): An electrical or electromagnetic interference that causes undesirable response, degradation, or failure in electronic equipment. Optical fiber does not emit or receive EMI.

Fan-Out Cables: Multi-fiber cable constructed in the tight buffered design. Designed for ease of connectorization and rugged applications for intra or interbuilding requirements.

Ferrule: A mechanical fixture, generally a rigid tube used to confine and align the stripped end of a fiber in a connector.

Fiber: Thin filament of glass. An optical waveguide consisting of a core and a cladding which is capable of carrying information in the form of light.

FM (Frequency Modulation): A method of transmission in which the carrier frequency varies in accordance with the signal.

FOTP: Fiber Optic Test Procedures.

Frame Relay: This is a telephone company service offering, although competitive local exchange carriers are also capable of providing and delivering the service. This is a 4-wire service typically at FT1 or T1 rates, that is 64,000 bps, 128,000 bps, 256,000 bps, 384,000 bps up to 1,544,000 bps. It requires a specific formatting of the data to be carried over it. This Frame Relay format requires the use of a frame relay access device (FRAD) or a specific type of network component called a router with a Frame Relay interface built into it. It also requires a DSU/CSU as was the case of the FT1 or T1 circuit described below.

Fresnel Reflection: The reflection of a portion of the light incident on a planar surface between two materials having different reflective indices. Fresnel reflection occurs at the air/glass interfaces at entrance and exit ends of an optical fiber.

FT1: Fractional T1, a telephone company service offering which has various data rates that can be subscribed to. It requires a customer premise DSU/CSU or channel service unit that converts the customer equipment signals to telephone company standard digital signals. Rates vary from 64,000 bps to any multiple of 64,000 bps up to a maximum of 1,544,000 bps where it is then classified as a T1.

Gap Loss: Loss resulting from the end separation of two axially aligned fibers.

Gateway: A network element performing specific functions for specific services, such as a voice over IP gateway performs the function of assembling voice phone calls from an IP network and translates it to the public switched telephone network

GIS: Geographic Information System, a software system of geographic mapping data

Graded-Index Fiber: Optical fiber design where the core has a lower index of refraction towards the outside of the core and increases towards the center of the core, bending the rays inward, and allowing them to travel faster in the lower index of refraction region, producing a higher bandwidth fiber.

Hardened facility: A 24 hour a day monitored, controlled environment facility in which mission critical network and network elements are housed.

Hertz (Hz): The frequency or bandwidth of a communication signal or channel, measured in oscillations per second. Oscillations refers to how fast the binary (on/off) code switches per second to keep up with the incoming signal.

HDSL: High speed DSL specifically a technique for extending T1 transmission distances beyond the present limitation of 6,000 feet.

ILEC: Incumbent Local Exchange Company, see LEC, for Hawaii GTE Hawaiian Tel

Index Matching Material: A liquid, gel or cement type material, used at optical interconnections, having refractive index close to that of the fiber core and used to reduce fresnel reflections from a fiber end face.

Index of Refraction: The ratio of light velocity in a free space, to its velocity in a given transmitting media.

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

Insertion Loss: The attenuation caused by the insertion of an optical component, such as a connector or a splice, into a previously continuous path.

IP: Internet Protocol, see TCP/IP

ISDN: Integrated Services Digital Network, this is a telephone company offering using the standard 2 wire telephone line, and where the customer has an ISDN modem connected at the end of the line. This allows him to connect a variety of devices in his home or office to the modem, such as a standard telephone, a fax machine, his personal computer. The user has several channels that can transmit and receive simultaneously at 64,000 bps, and other channels that are used for signaling (between the telephone company and the user equipment) and for additional data transmission. The separate 64,000 bps channels can also be used in parallel giving the user a total of 128,000 bps if so desired. In a typical situation a user could be having a telephone connection while receiving a fax on the second connection, or have his PC connected to the Internet. The user PC connection is either the serial or the parallel interface on the PC.

ISP: Internet Service Provider, typically, a company providing customers with the ability to access the Internet and to obtain a variety of services that are made available through the Internet, such as, access to home pages, email, interactive chat rooms, etc.

IXC: Inter-Exchange Carrier, Long Distance carrier, as opposed to Local Exchange Carrier

Jumper: Fiber optic cable assembly that has connectors installed on both ends.

Kevlar: Aramid yarn. Used as strength members in some fiber optic cables.

Kpsi: A unit of tensile strength expressed in thousands of pounds per square inch (e.g. 50 Kpsi; 100 Kpsi).

LAN: Local Area Network, a collection of elements such as PC’s or workstations, printers, servers, hubs, and switches that allow data communication between the all elements, all located within a single physical location, typically a building. A geographically limited communications network intended for the local transport of data, video and voice.

Laser: Light source producing, through stimulated emission, coherent, near monochromatic light. Lasers in fiber optics are usually solid state semiconductor types.

Lateral Displacement Loss: The loss of power that results from lateral displacement from optimum alignment between two fibers or between a fiber and an active device.

LEC: Local Exchange Company, normally referring to the local telephone company and differentiating it from the long distance telephone carrier

LED (Light Emitting Diode): A light source mostly used in multimode systems. Distance limited by optical power.

Link: A fiber optic cable with connectors attached to a transmitter (source) and receiver (detector).

Loss Budget: The total loss introduced by the components (cable, connectors, splices, couplers) in your fiber optic system subtracted from the attenuation (loss) allowed by your system equipment.

Macrobending: Macroscopic axial deviations of a fiber from a straight line, in contrast to microbending.

Material Dispersion: Dispersion resulting from the different velocities of each wavelength in an optical fiber.

Mechanical Splicing: Joining two fibers together by mechanical means to enable a continuous signal.

Megahertz (MHz): A unit of frequency that is equal to one million hertz.

Microbending: Curvatures of the fiber which involve axial displacements of a few micrometers and spatial wavelengths of a few millimeters. Microbends cause loss of light and consequently increase the attenuation of the fiber.

Micron (um): Another term for micrometer. One millionth of a meter.

Misalignment Loss: The loss of power resulting from angular misalignment, lateral displacement, and end separation.

Modal Dispersion: Pulse spreading due to multiple light rays traveling different distances and speeds through a fiber.

Mode: A term used to describe different ways light can get from one end of the fiber to the other. Single mode has only one route (monomode) so dispersion is lower and bandwidth is higher, whereas multimode has many routes with higher dispersion and lower bandwidth.

Mode Field Diameter: The diameter of optical energy in a single mode fiber. Because the mode field diameter is greater than the core diameter, MFD replaces core diameter as a practical parameter.

Modulation: Coding of information onto the carrier frequency. This includes amplitude, frequency, or phase modulation techniques.

Multimode Fiber: Usually 50, 62.5, 100 mm core, with 125 mm cladding. Used with LED systems and operates at 850 or 1300 nanometers.

Multiplexing: The process where two or more signals are transmitted over a single communications channel. Examples are time-division multiplexing and wave division multiplexing.

NA (Numerical Aperture): The light gathering power of a fiber. Also used to describe the angular spread of light from a central axis, as in exiting a fiber, emitting from a course, or entering a detector.

NA Mismatch Loss: The loss of power at a joint that occurs when the transmitting half has a NA greater than the NA of the receiving half. The loss occurs when coupling light from a source to fiber, from fiber to fiber, or from fiber to detector.

Nanometer: A unit of measurement equal to one billionth of a meter.

OC-3: Optical Carrier level 3, the designation for a SONET transmission at rate of 155 Mbps, using fiber optics as the transmission medium. Also OC-12, OC-48, OC-192, see Exsell Fiber Facts for a table describing the rates.

Optical Return Loss (ORL): A measurement of optical energy returned to the source or transmitter end of a fiber optic link. Major sources of reflected energy are Fresnel reflections and Rayleigh backscatter. Associated with increased bit error rate when ORL readings are to high, typically higher than -27 dB.

Optical Time Domain Reflectometer (OTDR): A method of evaluating optical fibers based on detecting backscattered (reflected) light. An OTDR trace shows fiber attenuation for the system and location and magnitude of any losses from splices, connectors, and fiber anomalies or fiber discontinuities.

Opto-electronic: Pertaining to a device that responds to optical power, emits, or modifies optical radiation, or utilizes optical radiation for its internal operation. Any device that functions as an electrical-to-optical or optical-to-electrical transducer.

PBX: Private Branch Exchange, a telephone switch located on the premise of a private owner, as opposed to the LEC, a public switch.

PC: Personal Computer, could be a stand alone or a portable

PCS: Personal communications service, typified by cellular telephones and expanding to Internet related services

PCM (Pulse Coded Modulation): A technique where analog signals, such as 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 twice the highest frequency in the signal.

PE (Polyethylene): A type of plastic material used to make cable jacketing.

Photodetector: An opto-electronic transducer, such as a pin photodiode or avalanche photodiode.

Photodiode: A semiconductor diode that is designed to produce photocurrent by absorbing light. Photodiodes are used to detect optical power and for the conversion of optical power into electrical power.

Photon: A quantum of electromagnetic energy. A particle of light.

Pigtail: A short length of fiber optic cable that has a connector installed on one end.

PIN Diode: A photodiode having a large intrinsic layer sandwiched between p-type and n-type layers. Photons in this region create electron hole pairs that are separated by an electric field, thus generating an electric current in the load circuit.

Plastic Fiber: An optical fiber having a plastic core and cladding.

Plastic Clad Silica Fiber: An optical fiber having a glass core and plastic cladding.

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

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

Power Meter: Instrument used to measure optical power or optical power loss over a fiber optic path. Can assess the performance of the optical terminal equipment by measuring the absolute power being injected into or emerging from the fiber network. When used with a light source, the combination can measure link loss to verify continuity and help assess the quality of the transmission path through the optical fiber.

Polarization Mode Distortion (PMD): The property of the two polarization modes of light to travel with independent but related effects; intrinsic to the fiber but affected by environmental conditions that the fiber is in; it will affect BER in high speed digital systems and will affect distortion in analog CATV systems

POTS: plain old telephone service, typified by a telephone hand set and dial ring or pad, a 2 wire service for two way communications, see dial tone

Preform: The glass rods from which an optical fiber waveguide is drawn.

Prefusing: Fusing with a low current to clean the fiber end. Precedes fusion splicing.

PSTN: Public Switched Telephone Network, another way of referencing the voice telephone network put together by the Local Exchange Companies (LEC’s)

Pulse Spreading: The dispersion of an optical signal over time as it propagates through an optical fiber.

PUR (Polyurethane): Material used in manufacture of cable jackets.

PVC (Polyvinyl Chloride): Material used in manufacture of cable jackets.

QoS: Quality of Service, a measurable set of parameters that define the level of service that a service provider can be held accountable for

RADSL: Rate adaptive digital subscriber line, another form of DSL service where the transmission rate adapts to the user demands via programmable techniques

Rayleigh Scattering: The scattering of light that results from small inhomogeneities in material density or composition.

Receiver Sensitivity: The optical power required by a receiver for low error signal transmission. In the case of digital signal transmission, the mean optical power is usually quoted in Watts or dBm.

Reflectance: A measure of the amount of reflected energy from a single event (e.g. a mechanical splice, a connector mating, etc.)on a fiber cable. Measured in -dB and pertains only to the specific event. A contributing factor to ORL.

Reflection: The abrupt change in direction of a light beam at an interface between two dissimilar media so that the light beam returns into the media from which it originated.

Refraction: The bending of a beam of light at an interface between two dissimilar media or a medium whose refractive index is a continuous function of position (graded index medium).

Refractive Index: See index of refraction.

Regenerative Repeater: A repeater designed for digital transmission that both amplifies and reshapes the signal.

Repeater: A device that receives, amplifies, and retransmits a signal. Consists of a transceiver (transmitter and receiver). It is used to boost signal levels to extend the system distance.

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

Riser: Application for indoor cables that passes between floors. It is normally a vertical shaft or space.

Rise Time: The time required for the leading edge of a pulse to rise from 10% to 90% of its amplitude; the time required for a component to produce such a result. "Turn-on time."

Scattering: A property of glass which causes light to deflect from the fiber and contributes to losses.

Sensitivity: The minimum optical power required to achieve a specified level of performance, such as BER.

Server Farm: Reference to a physical place in a network where mission critical computers performing server functions are housed

Signal-to-Noise-Ratio (SNR): The ratio of signal power to noise power.

Simplex Cable: A term sometimes used for a signal-fiber cable.

Single Mode Fiber: An optical fiber where a signal travels in one "mode," Fiber core is normally less than 10 microns.

SOHO: Small Office, Home Office, a term coined to define a market segment for home offices and small businesses

SONET: Synchronous Optical Network, a worldwide transmission standard allowing digital data transmission between local exchange companies, competitive local exchange companies, long distance carriers, competitive long distance carriers, and any foreign country

Source: The light emitter, either a LED or laser diode in a fiber optic link.

Spectral Width: A measurement 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 20 to 60 nanometers for an LED, and 2 to 5 nanometers for a laser diode.

Splice: A permanent or semipermanent joint between two optical waveguides or fibers.

Splice Closure: A container used to organize and protect splice trays.

Splice Tray: A container used to organize and protect spliced fibers.

Star Coupler: A fiber optic 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.

Star-Index Fiber: An optical fiber, either multimode or single mode, in which the ocre refractive index is uniform throughout so that a sharp step in refractive index occurs at the core-to-cladding interface. It usually refers to a single mode fiber.

Strength Member: That part of a fiber optic cable composed of Kevlar aramid yarn, steel strands, or fiberglass filaments that increase the tensile strength of the cable.

T1: A telephone company offering at a dedicated rate of 1,544,000 bps and requires a DSU/CSU at the customer premise to terminate the 4 wire telephone company lines.

Tap Loss: In an optical coupler, the ratio of power at the tap port to the power at the input port.

Tap Port: In a coupler, the output port of lesser power where the splitting ratio between the output ports are not equal.

Tee Coupler: A three port optical coupler.

TCP/IP: Transmission Control Protocol/Internet Protocol, part of a standardized data transmission protocol required to transmit data error free between remote locations that comprise a wide area network

Throughput Loss: In a coupler, the ratio of power at the throughput port to the power at the input port.

Throughput Port: In a coupler, the output port with the greater power where the splitting ratio between the output ports are not equal.

Tight Buffer: Type of cable construction where each glass fiber is tightly buffered by a protective thermoplastic coating to a diameter of 900 microns. High tensile strength rating achieved, providing durability, ease of handling, and ease of connectorization.

Time Division Multiplexing (TDM): A transmission technique where 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.

Transducer: A device for converting energy from one form to another, such as optical energy to electrical energy.

Transmitter: An electronic package which converts an electrical signal to an optical signal.

VDSL: Very High Speed Digital Subscriber Line, see XDSL

Virtual ISP: An ISP that serves its customers through a network of physical connections provided by another service provider

VoIP: Voice over IP, voice over the IP network, a technique for using low cost Internet connections to transport voice communications

VPN: Virtual Private Network, a technique for using low cost Internet connections to connect a companies wide spread facilities, contrasted with a private network comprised of dedicated connections at a higher cost

WAN: Wide Area Network, connectivity of disperse local area networks through point to point communications circuits, typically between buildings, cities, countries

Wavelength: The parameter of light used in a fiber optic system. For visible light, wavelength determines the color of light. Because the attenuation of a fiber is highly dependent on the wavelength of the light traveling through it, optimum performance can be achieved only by operating at one or two specific wavelengths (the specific wavelengths at which the light is most transparent is called "window"). Dual window fibers are most commonly produced today in both multimode and single mode fibers. Multimode fibers at 850 and 1300 nanometers, single mode fibers at 1310 and 1550 nanometers.

Wavelength-Division Multiplexer (WDM): A transmission technique by which separate optical channels, distinguished by wavelength are multiplexed onto an optical fiber for transmission.

web tone: phrase coined by Nortel, defining the future of telephony as not just dial tone where voice traffic is the predominant use, but rather, where multimedia traffic is the predominant use

Window: See Wavelength.

WS: Workstation, a form of personal computer, typically refers to an industrial strength computer with higher speed processors and more memory

WWW: World Wide Web, the Internet

XDSL: X standing for a variety of digital subscriber loop techniques. This is a telephone company offering where ADSL is the most current and most hyped service offering. There are other forms such as IDSL, HDSL, SDSL, VDSL, etc. Basically, they all represent different signal coding techniques created to transmit in a digital fashion at higher rates that previously allowed on the public telephone network. These XSDL services use the same telephone lines as the modem or ISDN connections, however, ADSL connection rates can be 1,544,000 bps or higher. Most home users would settle for 128,000, 256,000 or 384,000 bps because of cost. This technique also supports simultaneous connections, that is talking on one connection to the ADSL modem, while being connected to the Internet on another connection from your PC to the ADSL modem. The user PC connection is typically an Ethernet interface, requiring a plug-in card for the PC or laptop.

Zero-Dispersion Wavelength: Wavelength at which net chromatic dispersion of an optical fiber is zero. Arises when waveguide dispersion cancels out material dispersion.