absorption (optical) Attenuation of optical signals due to conversion of optical energy into heat energy.

actives Components that handle signals and that require power. Examples are line amplifiers and nodes.

adaptive equalizer A circuit (or software) that compensates for signal degradation in a path by adjusting taps in a delay circuit until the recovered waveform is as good as it can get.

addressability The ability to remotely control parameters of the subscriber’s reception of signals by transmitting signals addressed to that subscriber’s equipment.

AGC Automatic gain control. Circuitry in an amplifier that senses the level of a signal at the output and adjusts the gain such that the signal level is constant regardless of input level.

AGL Above ground level. Used in microwave systems to designate the elevation of various antennas relative to the ground level at the foot of the tower.

aloha protocol A data transmission protocol in which a device needing to transmit information on a common channel first listens on that channel and, if nothing is heard, transmits its information. It then waits for an acknowledgment from the intended receiver and retransmits after a random delay if the acknowledgement is not received.

alpha In data transmission, the excess width of a modulated RF signal compared with the minimum theoretical width needed to transmit data at a particular symbol rate.

AM/FM conversion AM-to-FM conversion. A type of distortion to a modulated signal in which amplitude modulation is translated into frequency modulation. Also known as AM/PM conversion.

AM/PM conversion AM-to-PM conversion. A type of distortion to a modulated signal in which amplitude changes in the signal are translated into phase changes. Also known as AM/FM conversion.

AML Amplitude modulated link. A microwave technology in which the cable television spectrum is up-converted to a microwave band for transmission and then down-converted at the receiver for transmission through a cable distribution system.

AMSL Above mean sea level. The official designation of elevation used in microwave systems.

analog television The system of television transmission that has been practiced since the medium was invented. Picture levels are represented by a continuously varying voltage level.

ANI Automatic number identification. A capability of most telephone systems that allows the number of the calling party to be known to the receiving party. Used in some pay-per-view ordering systems.

ANSI American National Standards Institute. An umbrella standards organization for the United States.

APC Angle polished connector. A fiber-optic connector that exhibits reduced reflections due to an angled fiber end.

application software Software that allows for any prescribed functionality in a set-top terminal.

artifact As used commonly in television technology, any artificial element introduced into a picture or sound signal as a result of the processing the signal undergoes.

ARU Audio response unit. A telephone answering system that guides the caller through audio menus and accepts inputs via Touch-Tone key presses. Used in some pay-per-view ordering systems.

ASC Automatic slope control, also known as dual-pilot AGC. A system in which one low-frequency carrier and one high-frequency carrier are both monitored for AGC purposes. By monitoring two carrier levels in different parts of the spectrum, the system can compensate for changes in gain over the entire spectrum. ASC systems tend not to be used in newer designs because of cost and the reduced need due to the relatively short cascades used with HFC architectures.

ASG Automatic slope and gain. A control system used in many modern pieces of distribution equipment in which an AGC function is combined with compensation for varying cable loss with frequency. As the gain at a pilot frequency is changed, the gain at higher frequencies is changed more and that at lower frequencies is changed less, matching an assumed profile for the coaxial cable.

ASI Asynchronous serial interface. A popular video interface for headend equipment. It uses 75-ohm coaxial cable or fiber-optic cable and operates at a wire rate of 270Mb/s.

aspect ratio The ratio of width to height of a picture. Standard-definition television uses a 4:3 aspect ratio, and most HDTV systems use a 16:9 aspect ratio.

asymmetric key pair See public/private key pair.

ATM Asynchronous transfer mode. A set of standards for transmitting many types of baseband digital signals over a network. Very efficient for sharing channels among bitstreams of varying bit rates.

ATTC Advanced Television Test Center. An organization established to provide impartial testing for proponent digital video systems, which more recently has coordinated much of the testing required to make digital television, and especially HDTV, a reality.

attenuation A measure of the RF or optical signal loss (generally in decibels) of a component, circuit, or cable.

audio A baseband signal conveying at least one channel of sound information.

aural An adjective implying an RF or IF carrier that is modulated with an audio signal.

availability A measure of the fraction of time that a circuit or system is available to carry signals.

AVI Audio-video interface. A consumer interface for transferring digital video to a display.

azimuth The compass heading of an antenna, measured in degrees clockwise from north.

backbone Point-to-point or ring connections between headends or linking headends and major hubs in a cable system. Often signals traveling in the backbone are not in the same format used to deliver services to homes (for example, digital baseband).

balanced transmission A technique of coupling signals between two pieces of equipment using two conductors of equal and opposite signal voltage, neither of which is grounded. Used extensively for audio and infrequently for video and RF.

balun Balanced to unbalanced. A device that converts a transmission between balanced and unbalanced media.

bandstop filter A filter that passes all frequencies except those within some band. The term is specifically used to indicate a filter that goes in a drop, whose purpose is to prevent interference in the house from getting on the cable return plant, with the exception of a band of frequencies in the return spectrum that are allowed through, to support legacy services such as RF impulse pay-per-view.

bandwidth efficiency The ratio of bits per second transmitted through a communications channel to the channel bandwidth in hertz. The units are bits per second per hertz.

barker channel A channel used to promote programming on other channels. It is often automatically tuned when the subscriber attempts to tune a channel for which he or she is not authorized. It is implemented in some set-top converters.

baseband A signal not modulated onto an RF carrier. In video, refers to the visual signal as it is handled before being modulated onto an RF carrier.

basic service The foundation service all subscribers are required to take. Usually consists of at least local off-air channels and public channels and often is a reasonably complete set of signals.

baud In digital transmission, the number of symbols transmitted per second. Except for a few simple modulation formats, the baud rate is less than the bit rate.

Bellcore Bell Communications Research. The research and development arm of the Bell Telephone companies.

BER Bit error rate. A measure of the proportion of the bits in a data stream that are corrupted in transmission.

BERT Bit error rate test set. A test instrument used in data communications to insert a known data pattern at a transmitter and to count the number of errors received per second at a receiver.

binary Representation of a number by a series of elements (usually called “bits”), which can take on only one of two values. Contrast binary representation with our normal base-10 representation of numbers, where each element representing the number can take on any of 10 values.

bit A single binary data element having a value of either 1 or 0, usually represented by two different voltage levels.

bit rate The number of bits of data transmitted per second.

bit stuffing The process of adding extra data bits to a bitstream to get the data rate up to the transmission data rate. Practiced when the incoming data streams have a total bit rate less than that demanded by the channel.

blanking In a television picture tube, the process of temporarily shutting off the electron beam except during the “painting” of a picture, to avoid visible artifacts.

block conversion A technique for putting more signals on a return optical path by converting some incoming signals to alternate frequency bands.

BPSK Biphase shift keying. A digital modulation method in which the phase of a carrier is changed by 180° to represent transmission of a 1 or a 0.

bridger An amplifier (or module within a larger amplifier station) that is fed a sample of the trunk input signal and that is used to create a distribution leg.

broadband As used in the cable industry, refers to the ability to frequency division multiplex many signals in a wide bandwidth of RF frequencies, using an HFC network.

BTSC Broadcast Television System Committee. An entity that developed the analog TV stereo system used for transmission in North America and elsewhere.

byte A collection of eight bits.

CA certificate authority. An organization that can be trusted by both parties to a data exchange, which can sign a digital certificate proving the authenticity of the communicating parties.

CableLabs Cable Television Laboratories. The research consortium of the cable television operating companies.

caching A technique of retrieving information from Web sites and storing it on a local server, for the purpose of sending Web pages to users from that local server. The technique speeds up access to popular sites by eliminating the Internet delays involved in going back to the source for information. (The term also has an analogous meaning in retrieving data from memory.)

carrier Or RF carrier. A signal on which another, lower-frequency signal is modulated in order to transport the lower-frequency signal to another location.

carrier to noise (C/N) ratio In visual transmission, the ratio, usually expressed in decibels, of the RMS power present in the visual carrier during sync tips to the RMS noise power in 4 MHz. In cable television work, the term implies a measurement made at radio frequencies. Contrast with S/N, measured at baseband.

CARS Cable antenna relay service. The official FCC designation for a set of microwave frequencies reserved for the use of cable television companies.

cascade A configuration in which a signal passes through more than one stage or system. In cable usage, it usually refers to the system of line amplifiers through which the RF signals pass between the optical node and the subscriber. It can also refer to multiple stages of amplification or filtering through which a signal passes.

Cassegrain feed An antenna for microwave (including satellite) reception consisting of a parabolic main reflector that focuses power on a hyperbolic subreflector, which in turn focuses the power to the feed.

Cat 5 Category 5 cable. A data and voice transmission cable consisting of four pairs of twisted cables having a characteristic impedance of 100 ohms.

CBR Constant bit rate. An adjective describing a service or communications channel that carries a constant number of bits per second.

CCS 1. Custom calling services. A particular collection of enhanced telephone services, distinct from CLASS services. 2. Centum call seconds. Usage of a telephone resource (such as a phone line) for 100 seconds per hour.

CDMA Code division multiple access. A data transmission method in which a number of individual transmitters occupy the same spectrum at the same time, each using a different spreading sequence.

CEA Consumer Electronics Alliance. A branch of the Electronic Industries Alliance that represents manufacturers of consumer electronics equipment.

CEMA Consumer Electronics Manufacturers Association. A division of the Electronic Industries Alliance that represents manufacturers of consumer electronics. Name has been changed to CEA.

centum call second (CCS) In telephony, use of one telephone line for 100 seconds. There are 36 CCS in one hour per line.

channel A range of frequencies assigned to a signal in an FDM transmission system. In North America, analog video and most other downstream channels are 6 MHz wide and correspond to one of the allocation forms defined in the ANSI/EIA-542 standard.

channel mapping A feature of some set-top converters, TVs, and VCRs that allows programmable correspondence between channel number and received frequency. Useful where an off-air station must be channel shifted due to direct pickup problems. The station loses its channel identity to cable subscribers, but if channel mapping is available, it is possible to make the station appear on its off-air channel even though it is carried on another.

characteristic impedance The impedance of a transmission line such that, if terminated in a pure resistance of the same value, the return loss would be infinite. That is, the cable would “look” to a driving circuit like a resistor of the characteristic impedance.

chroma Or chrominance. Referring to the color information in a television signal, as opposed to the luminance (black and white) and aural (sound) portions.

chromatic dispersion The degree to which the transmission speed of an optical signal through a fiber or device varies as a function of wavelength.

chroma/luma delay A form of distortion of analog video signals in which the times of arrival of the luma (black-and-white) and chroma (color) signals are offset, resulting in the shift of color information with respect to the black-and-white outline. Also called chrominance delay.

CIN Composite intermodulation noise. Noiselike distortion products resulting from even- or odd-order mixing among RF signals, at least one of which is digitally modulated.

clamping See dc restoration.

cladding In optical fiber, the signals are transmitted primarily through the central, or core, glass, whereas the outer layers, or cladding, serve to add strength and, in combination with the core, to constrain the signals within the fiber.

CLASS Custom local area signaling services. A particular collection of enhanced telephone services.

CLEC Competitive local exchange carrier. A provider of telephone services who is not the original “incumbent” provider in a given market. Where cable television or OVS companies provide local phone service, it is almost always as a CLEC.

client A recipient of services provided by a central machine or process often called a server.

clipping A phenomenon where the voltage or current peaks of a signal are sharply limited at some value (for example, in directly modulated DFB laser diode transmitters).

closed captioning A system used to transmit captioning information to hard-of-hearing viewers, allowing text to overlay the picture. The system has been expanded to permit transmission of other types of data, most notably V-chip rating data.

CMI Cable microcell integrator. See RAD.

coax Short name for coaxial cable, which is used extensively for transmission of RF and baseband signals. The cable consists of an inner conductor on which signal voltage is impressed with respect to the shield. The center conductor is surrounded by a dielectric and then a shield. Frequently an insulation layer will surround the shield.

coaxial distribution The portion of the broadband cable television distribution network that starts at the node and terminates at the tap. Sometimes the drop system is included in the definition.

coding gain A measure of the efficiency with which a data stream is prepared for transmission. The ratio of the input to output bit rate of the encoder.

color difference signals The two signals in a TV picture that add color information. Derived from the original red, green, and blue primary signals, they are called color difference signals due to the way in which they are defined.

color subcarrier A signal in an analog TV signal that carries color information.

combiner A device with three or more ports used to combine two signals without regard for the frequency of the signals. Identical with a splitter, except for the direction of use.

community access Programming produced locally over which the cable operator has no editorial control. It may be produced by community groups, schools, etc.

composite video A baseband signal that contains multiple components of the signal required to reproduce a picture. The term has multiple meanings depending on context. It may mean a video signal including synchronizing (sync) information. It is also used to mean the signal including chroma (color) information.

compression A number of techniques for reducing the bandwidth needed to transmit a signal by removing unnecessary or redundant information from the signal.

concentration In telephony, the sharing of a resource among many users, based on the presumption that not all users will demand the resource at the same time.

conditional access A generic term used to indicate that access to a program or channel is limited to subscribers who have paid additional money for it.

cone of acceptance A theoretical cone whose point touches the end of a fiber whose axis is collinear with the fiber and that represents the maximum angles at which light may be introduced into the fiber and still have the transmitted portion of the light not “leak” out the sides due to refractive loss.

constellation diagram In data transmission, a diagram that plots the amplitude and phase of each state in a symbol.

CSO Composite second order. A form of distortion generated by amplifiers and other devices handling multiple RF signals. It is second-order distortion that combines signals at frequencies A and B, as A ± B. The A + B products fall 1.25 MHz above picture carriers, and the A — B products fall 1.25 MHz below picture carriers in the standard channel allocation. The ratio of carrier to distortion product is often called C/CSO, carrier to composite second order.

CSR Customer service representative. An employee of a cable system who handles incoming telephone calls from customers.

CTB Composite triple beat. A form of distortion generated by amplifiers and other devices handling multiple RF signals. It is a third-order distortion product that combines signals A, B, and C as A + B — C. CTB products fall on the nominal frequency of carriers in the standard channel allocation. Also known as C/CTB.

cutoff frequency In filter terminology, a frequency at which the response of a filter is reduced by some specified amount, usually 3 dB.

CWDM Coarse wavelength division multiplexing. Wavelength multiplexing in which the combined wavelengths differ by 8-50 nm, but typically 20 nm.

data slicer In the recovery of a transmitted data signal, a circuit that compares the input signal voltage with a predetermined level. If the input signal is above the threshold, it is assigned one of the two logic levels. If it is below the threshold, it is assigned the other logic level.

dB Decibel. A measure of the relative strength of two signals. Defined as 10 times the logarithm (to the base 10) of the ratio of the two power levels, in any consistent units, such as watts, or 20 times the logarithm of the ratio of the voltage or current levels.

dBm Decibels with respect to one milliwatt. A unit of RF signal strength used in satellite work and other communications applications.

dBmV Decibels with respect to one millivolt in a 75-ohm system. The unit of RF power used in cable television work in North America. In a 75-ohm system, 0 dBmV = −48.75 dBm.

DBS Direct broadcast satellite. A (primarily television) service in which signals are sent from a multichannel program supplier (for example, DirecTV or Dish Network) through a high-powered geostationary satellite to small-aperture receiving antennas and receivers typically mounted on each subscriber’s house.

dc restoration In analog television transmission, the process of recovering a true black level in the picture by forcing the sync tip or back porch to be at a desired voltage. Also called clamping.

decibel See dB.

deemphasis In FM transmission, the process complementary to preemphasis. A frequency-selective reduction of the amplitude of higher modulating -frequencies after reception, to restore flat response. Used to improve the signal-to-noise ratio.

demodulation The process complementary to modulation. Recovery of information modulated onto a carrier.

demodulator A device used by cable television systems to convert an RF modulated video and/or audio signal to baseband.

DES Data encryption standard. A recognized data encryption system based on performing a prescribed set of operations on a block of plaintext data.

DFB laser Distributed feedback laser. A laser technology in which the wavelength of the laser is set by the distance between reflecting surfaces at each end of the laser cavity, augmented by a grating running the length of the cavity.

differential gain A measure of the variance in gain at the chrominance frequency as a function of luminance level.

differential phase A measure of the variance in phase at the chrominance frequency as a function of luminance level.

digital repeating ring An architectural structure in which a baseband digital signal is received and retransmitted at each terminal point around a closed ring.

digital return A return path from a node to a headend whereby the return signals are digitized and the digital signal is transmitted to the headend, where it is converted back to analog/RF form.

digital signature An electronic file that has been generated by a certificate authority (CA), which may be supplied from one member of a proposed data exchange session to the other member. The member receiving the signature is able to verify that it did, indeed, come from someone trustworthy.

digital television Television signals transmitted using digital techniques in which video levels are converted to digital states that approximate the analog level of the original signal. As used in the consumer world, it also implies compressing the signal to minimize the transmission bandwidth required.

digital video Representation of video signals in digital format. It does not necessarily imply a compressed video signal.

diplex filter A filter used to separate RF signals into one of two paths, based on the frequency of the signals. Can also be used to combine signals that exist in different frequency bands.

dipole A basic antenna consisting of a straight conductor usually broken in the middle to connect to a feed line.

direct pickup Or DPU. The characteristic of a TV or VCR by which a signal is picked up off the air in the device, creating interference with the signal being received via cable.

directional coupler A three port device for unequally dividing signal between two paths. Can also be used to combine signals with more loss in one input than in the other, with the signal from the high loss port being routed to only one of the other two ports.

directivity In a tap or directional coupler, the difference in sensitivity to upstream and downstream signals, as measured at the side port.

discrete cosine transform (DCT) A fundamental process used in video compression in which two-dimensional blocks of pixels are converted to a frequency domain representation, with the option of dropping higher-frequency components if they are small.

dispersion The variation of transmission time due to some controlling parameter.

dispersion-shifted fiber Most optical fiber exhibits a dispersion “zero” near the 1,310-nm wavelength. Dispersion-shifted fiber is modified so that the point of zero dispersion is moved to another wavelength, often near 1,550 nm.

distribution The broadband portion of a cable television network extending from the point where the broadband spectrum is created in the same format in which it will be received by subscribers (for example, in a simple star HFC network, the distribution system starts at the input to the linear optical transmitter).

DLC Digital loop carrier. A telephony system in which the analog interfaces of a switch are extended closer to the using telephones through use of a data stream to a remotely located interface.

DOCSIS Data-over-cable service interface specification. The formal name of the cable modem standard produced by a consortium led by CableLabs.

double sideband modulation Amplitude modulation in which both the upper and lower sidebands are retained. Also called DSB.

downstream Signal flow from a headend toward subscribers.

DPU Direct pickup. Signals picked up in the drop system and the customer’s equipment due to inadequate shielding that may interfere with reception.

drop The portion of the distribution plant between the tap and the individual subscriber’s home.

DSL Digital subscriber line. A method of sending digital information over existing twisted-pair telephone lines between a central office or remote terminal and an individual subscriber. Uses frequencies above the voice audio range and thus can operate simultaneously with normal analog baseband voice service.

DSM Demand side management. A method used by utility companies to limit peak usage of electrical power by controlling customer equipment.

DTCP Digital transmission content protection. The encryption system used with video transmission on IEEE 1394 networks.

DWDM Dense wavelength division multiplexing. Wavelength division multiplexing in which the optical channels are spaced 200 GHz or closer together.

EDFA Erbium-doped fiber amplifier. A common construction of optical amplifier, consisting of an erbium-doped fiber in which the signal to be amplified and a “pump” signal are inserted, with energy from the pump signal being converted into gain at the signal wavelength.

egress A measure of the degree to which signals from the nominally closed coaxial cable system are transmitted through the air. Also known as signal leakage.

EIA Electronic Industries Alliance. A trade organization in Washington, D.C., that represents companies that manufacture electronic equipment.

8B/10B encoding An encoding method used in gigabit Ethernet, ASI video interconnections, and other applications in which each 8-bit binary word is replaced by 10 bits such that a minimum number of data transitions per symbol is enforced.

EIRP Effective isotropic radiated power. The total power supplied to an antenna, multiplied by the directive gain of the antenna in a certain direction.

electronic program guide (EPG) A display on the TV of a selection of programs available to the subscriber. Generally, all the subscriber need do to see the program is to highlight it using cursor keys on a remote control transmitter and press a “select” button. A database cross-references the program identification to the channel and automatically tunes to it. The EPG may include other features, such as information on programs and the ability to program a VCR.

elevation 1. The number of feet that a location is above mean sea level (AMSL). 2. The number of degrees by which an antenna is tilted upwards from the horizontal.

emergency override A technique whereby, in an emergency, normal audio and/or video programming on all or most channels can be replaced with emergency announcements generated by an authorized entity.

encryption The process of rendering a digital signal unintelligible to any receiver that doesn’t have some unique piece of information needed to recover that signal.

envelope In amplitude modulation, the shape that contains the amplitude modulated carrier. That is, the envelope is the outline of the carrier amplitude versus time.

envelope detection The process of recovering modulation from an amplitude modulated signal by recovering the envelope shape of the modulated signal. The most common envelope detector is a diode.

erlang In telephony, the maximum physical capacity of a line or trunk. One telephone line has a capacity of 1 erlang, or 36 CCS.

error correction In data transmission, the technique of adding extra bits to a transmitted signal, with the extra bits being used to detect and correct errors in the transmission.

Ethernet A popular layer 2 protocol used for interconnecting data equipment.

expanded basic service A subscription service offered by a cable company, which consists of basic service plus more advertiser-supported channels (as opposed to pay services).

express feeder An untapped coaxial line between two amplifiers in the coaxial portion of an HFC distribution system.

extinction ratio In a binary laser transmitter, the ratio of the maximum light output in one binary state to the minimum light output on the other binary state.

eye diagram In data transmission, a plot of the trajectory of either an in-phase or quadrature signal.

Fabry-Perot laser A laser technology in which the wavelength of the laser is set by the distance between reflecting surfaces at each end of the laser cavity.

failure rate The per-unit average rate at which a group of similar devices will randomly fail during their normal service life. Usually expressed in fraction or percentage per year.

FAT channel Forward application transport channel. The channel used to convey video and/or audio programming.

F connector The RF connector commonly used to attach drop cables to taps and other devices.

FCC Federal Communications Commission. The governmental body in the United States that oversees telecommunications entities. In other countries, the corresponding body may be called the Department of Communications or may be part of a Ministry of Posts, Telegraph, and Telecommunications.

FDM Frequency division multiplexing. The process whereby modulated signals occupying nonoverlapping spectra are combined for transmission through shared equipment. Used for transmitting multiple video and nonvideo signals to homes in conventional cable television networks.

feeder The portion of the coaxial subnetworks that starts at an amplifier fed by an express feeder or trunk and supplies signals directly to subscriber taps.

field One-half of a TV picture, consisting of alternate lines. Two fields make up a complete frame.

filtering In communications, usually refers to the transmission of power in some frequency range(s), combined with the nontransmission of power in other frequency range(s). In computer use, may also refer to the elimination of certain types of information, with passage of other types.

FireWire See IEEE 1394.

FITL Fiber in the loop. Used by the telephone industry to describe the deployment of fiber on the subscriber side of class 5 telephone switches. See loop.

flat loss The loss in a cable plant that is not a function of frequency. Typically, taps and attenuators have flat loss, as contrasted to coaxial cable, whose loss varies approximately as the square root of frequency.

FM/AM conversion FM-to-AM conversion. A type of distortion to a modulated signal in which frequency modulation is translated into amplitude modulation.

forward Downstream transmission of cable signals.

forward error correction (FEC) In data transmission, a process by which additional data is added that is derived from the payload by an assigned algorithm. It allows the receiver to determine if certain classes of errors have occurred in transmission and in some cases allows other classes of errors to be corrected.

Fourier series A mathematical expression relating the time domain representation of a periodic waveform with the frequency domain representation. It shows that any periodic waveform may be expressed as a series of harmonically related sine and cosine waves. (Sine and cosine waves have the same shape but are shifted in phase by 90°.)

frame One complete TV picture, consisting of two fields.

franchise An agreement with a local governing body that permits a cable operator to construct a cable system and that spells out the conditions that must be met by that system.

frequency agile The ability to operate on more than one frequency (but not simultaneously).

frequency response The gain as a function of frequency through a system or device, relative to the defined ideal. In the case of a cable distribution system, this is also known as peak-to-valley response, or P/V.

Fresnel zone In a microwave path, this describes a hypothetical ring centered on the path such that the distance from transmitter to ring to receiver is one-half wavelength longer than the distance from transmitter to receiver.

FSAN Full-service access network. A standard for passive optical networks based on ATM.

FSK Frequency shift keying. A low-cost, spectrum-inefficient, very robust form of digital modulation in which the frequency of a carrier is changed to represent data.

FTF Fiber-to-the-feeder. A distribution architecture in which fiber nodes feed coaxial feeder lines without any intervening coaxial trunk links.

FTTC Fiber-to-the-curb. A delivery technology in which signals are delivered from the headend to a small cluster of homes, completely in the optical domain. Most commonly the electronic signals at the end of the network are delivered over a short, completely passive network.

FTTH Fiber-to-the-home. A delivery technology in which signals are delivered from the headend to the home, completely in the optical domain.

ground block A passive device located on the subscriber’s premises that allows a safety ground to be connected to the drop.

group delay Generally, the deviation from linear phase shift versus frequency through a circuit or network. This can occur due to reflections in a network. Also, it is a property of many practical filters. Signal power near the edge of the passband are delayed in traversing the filter with respect to signals away from the edge. This gives rise to waveform distortion, which can damage both analog and digital signals.

G/T “G over T.” A figure of merit for a satellite earth station, expressing the ratio of the gain of the station to its effective noise temperature. Allows computation of the signal strength needed to receive a signal satisfactorily. The higher the station G/T, the lower the signal level required.

hard cable Sometimes called hard line. An informal term applied to the solid-jacketed coaxial cable used in the coaxial distribution portion of a cable system ahead of the subscriber tap. Also applied as an adjective to that portion of the distribution system.

harmony agreement An agreement among manufacturers of digital video scrambling systems whereby multiple addressable control systems can share a common scrambled video stream.

HDCP High-bandwidth digital copy protection. The encryption system used with video transmission on AVI video display interfaces.

HDT Host digital terminal. Digital headend equipment used to interface with a distribution plant.

HDTV High-definition television. Television with significantly more picture information (resolution) than that provided by a good NTSC or PAL television signal. Although the definition of HDTV is nonspecific, it usually implies about twice the resolution in both the horizontal and vertical directions and a wide aspect ratio.

headend The point at which all programming is collected and formatted for placement on the cable system.

header A set of bits added at the beginning of a transmitted data group that identifies the transmission and its source and destination.

HFC Hybrid fiber-coax. A network for transmitting signals modulated onto RF carriers that consists of RF carriers modulated onto optical carriers and transmitted on fiber-optic cable, followed by transmission of the RF carriers on coaxial cable medium. The majority of cable plant built since the early 1990s is in such an architecture.

high-pass filter A filter that passes all frequencies above its cutoff frequency but not below. The term is specifically used to indicate a filter that goes in a drop and whose purpose is to prevent interference in the house from getting on the cable return path.

horizontal blanking interval (HBI) That time in a television signal during which the electron beam in the receiver is moving from the right side of the screen back to the left to start a new line. Normally consists of a sync pulse and color burst.

host A generic term used in OpenCable work to define a device that is involved with receiving and decoding a digital video signal. Hosts are assumed to include either an interface for a POD module or the same functionality.

HRC Harmonically related coherent. A method of establishing picture carriers on a cable plant such that all carriers are harmonics of a single fundamental frequency close to 6 MHz.

hub A point in a distribution system where signals are converted to the form used to transmit them to subscribers. If a hub system is used, each hub typically will supply signals to a number of nodes.

Huffman coding A digital compression technique in which longer symbols (sequences of bits) that occur more commonly are replaced by shorter symbols and shorter less common sequences are replaced by longer symbols.

IEEE Institute of Electrical and Electronics Engineers. A professional organization of technologists interested in all aspects of electrical engineering.

IEEE 1394 A digital bus used to interconnect consumer audio and video equipment, among other things. Known as FireWire.

IIN Interferometric intensity noise. Noise in an optical link caused by mixing of direct and doubly reflected signals in the optical detector diode.

image response The response of a tuner to signals in a portion of the spectrum separated from the IF by the local oscillator frequency but on the wrong side of the IF.

incidental wavelength modulation A property of optical transmitters whereby the wavelength varies, along with the amplitude, as a function of the modulating signals, also known as chirp.

index of refraction The ratio of the speed at which light is transmitted in a vacuum to its speed in a material. It is a property of any material that can transmit light.

ingress Over-air signals that are inadvertently coupled into the nominally closed coaxial cable distribution system.

intercarrier Refers to a process in television reception in which the picture and sound carriers are mixed together to form a sound IF at the difference frequency (called the intercarrier frequency).

interdiction A program denial technique in which a jamming signal is inserted very near the picture carrier of programs for which the subscriber has not paid. The interdiction equipment is usually integrated with the tap. Signals are sent in the clear from the headend.

interlaced scanning The process of scanning every other horizontal line in a picture during one-half of the picture transmission, followed by scanning the intervening lines. The purpose is to reduce the flicker that is perceived by the viewer.

interleaving In data transmission, a technique by which the order of bits transmitted is changed. The bits are returned to the original order before error correction. If a burst of errors occurs, then the errored bits will be “spread out” before error correction is applied. This makes error correction more effective.

IP Internet Protocol. A particular layer 3 protocol that assigns addresses to different endpoints in a network and handles transport of data to and from those endpoints.

IPPV Impulse pay-per-view. Enhanced pay-per-view technology in which a subscriber can make a last-minute impulsive purchase of a program rather than having to order it in advance.

IPTV Internet Protocol television. A technology for sending video information over an IP network.

IR blaster A technique in which one device controls another through the controlled device’s infrared (IR) input. For example, a set-top converter with electronic program guide may program a VCR using the VCR’s IR input. Typically, the blaster will consist of an IR transmitter on the end of a cable, with the transmitter possibly taped to the device it is controlling, such that its transmissions can be picked up by the controlled device.

IRC Incrementally related coherent. A method of establishing picture carriers on a cable plant such that all carriers are spaced 6 MHz apart based on a master oscillator, but the carrier frequencies are offset 1.25 MHz from harmonics of 6 MHz.

IRD Integrated receiver-decoder. A device used in a cable television headend to receive a scrambled signal from a satellite and to convert it to baseband. Consists of a satellite signal receiver and a descrambler.

isolation In a tap or directional coupler, the difference between the amount of signal coupled to the side port and the directivity.

ISP Internet service provider. An organization whose business it is to connect users to the Internet.

IXC Interexchange carrier. An acronym for a long-distance telephone carrier.

JEC Joint Engineering Committee. A joint committee of the EIA-CEMA and the NCTA that met periodically to discuss technical issues of interest to both the cable television and the consumer electronics industries. It has been responsible for developing several standards in use by the two industries, such as the ANSI/EIA-542 band plan. The committee is inactive as this is written.

Kell factor The vertical resolution of an interlace scanned picture is less than the number of active lines in the picture, due to interlace. The Kell factor estimates the practical reduction and is commonly taken as 0.7.

key A piece of information used to encrypt or decrypt data by operating on the data with the key.

key exchange The process by which a data transmitter and receiver agree on the encryption key(s) to use in encrypting and decrypting data.

LAN Local area network. A group of devices in the same general location that share data.

laser In the context of cable systems, the device used to convert electrical signals to optical signals.

lashing The wire used to attach cable to a strand.

latency A net delay in the time information is delivered, from when it is transmitted. A satellite circuit introduces latency due to the propagation time to the satellite and back. A more common use of the term is with respect to video compression, where practical delays in the compression system delay the reception of the signal with respect to the origination.

LE Line extender. A single-input, single-output amplifier used to boost signals in a coaxial distribution plant.

LEC Local exchange carrier. An acronym used to identify a local telephone company.

local origination Programming over which the cable operator has editorial control. It is usually produced in the system.

local oscillator A circuit that generates a frequency that is mixed with a signal to produce a signal at a desired third frequency.

log periodic An antenna type consisting of multiple driven elements having a specified ratio of length and spacing and used to direct energy along a single axis. Performance is similar to that of a Yagi, except the bandwidth can be much larger.

loop Local office outside plant. Used to describe that portion of a telephone network extending from the local (class 5) switch to the network termination points at individual subscribers.

low-pass filter A filter that passes all frequencies below its cutoff frequency but none above.

luminance Or luma. Referring to the black-and-white portion of the television signal, as opposed to the chrominance (color) and aural (sound) portions.

Mach-Zehnder device A device used to modulate a light signal external to the source, resulting in less incidental waveguide modulation than with directly modulated sources.

Manchester encoding In data transmission, a method of embedding clock into data such that recovery is simple.

material dispersion A property of material that causes the speed of transmission of light waves to vary as a function of wavelength.

MCNS Multimedia Cable Network System. An industry consortium that produced the DOCSIS procurement standard for modems to be used on cable television networks.

media gateway A device that translates voice signals and sometimes signaling protocols between VoIP and switched voice systems.

MER Modulation error ratio. A measurement of the quality of a digital modulated signal that defines the average error between the proper location of all points in the constellation and their actual location.

mesh An architecture in which terminal points are connected to several other terminal points directly rather than just to a central point (a star) or the adjacent terminals in a ring.

messenger A support member in an electronic or fiber cable.

MGCP Multimedia Gateway Control Protocol. A popular thin client protocol for use with VoIP systems.

microreflections Small reflections occurring within both the coaxial distribution and drop portions of a cable plant. They can lead to impaired analog reception, group delay, and errors in digital signals.

middleware The layer of software that provides for standardized application software to run on any set-top terminal.

mixer A circuit that accepts two signals at different frequencies and produces a third frequency equal to the sum or the difference of the two input frequencies.

modal dispersion In a multimode fiber, the variation of transmission time among the various possible paths for the light.

modulation The process of imposing information on an RF carrier by varying some parameter of the carrier. The parameters that can be varied are the amplitude, the frequency, and the phase.

modulator A device used by cable television systems to convert a baseband video and/or audio signal from baseband to the RF channel on which it is to be transmitted.

MPEG Motion Picture Experts Group. A group that developed standards for digital compression of television pictures. The second generation of this standard, MPEG-2 is used, in one form or another, for transmission of digital television in all parts of the world that have introduced such transmission.

MPEG-2 The set of digital video decoding rules that form the basis of off-air and cable TV digital video transmission.

MPEG-4 An advanced set of digital video decoding rules. The basic MPEG-4 is intended to provide for very low data rate transmission of less than entertainment-grade video. MPEG-4 level 10 (also known as AVC, advanced video coding) is intended for entertainment-grade video. Compare with MPEG-2.

MSO Multiple system operator. A company that owns more than one separate cable system.

MTBF Mean time between failure. A measure of the average time interval between circuit restoration from a previous failure and the onset of the next failure in a network.

MTTR Mean time to restore. A measure of the average time required to restore proper network/circuit operation after a failure.

multimode An optical fiber that supports more than one transmission path and thus has a transmission delay whose uncertainty increases with length, thereby limiting bandwidth.

multipath A condition where an over-the-air signal may reach a receiver via more than one path from a transmitter, leading to degraded reception. Applies to all transmission systems and frequencies.

multiplex Use of a single data path for more than one set of data.

multiplexing The combining of many independent signals into one signal path for transmission. Cable systems operate in a frequency division multiplexing mode, in which many signals at different frequencies are combined in one signal path. Another common example is time division multiplexing, where many signals share the same path but are segregated in terms of time.

mux See multiplex.

NCS Network-based call signaling. A signaling profile of the MGCP specified for use with cable-based VoIP systems. Similar to TGCP.

NCTA National Cable Telecommunications Association. A trade organization that represents companies in the cable television industry.

negative trap A technology for denying analog television programs to subscribers who have not purchased them. Negative trap systems work by transmitting normal signals on the cable plant. At the tap of subscribers who have not bought the program, a trap is inserted to remove the picture carrier.

network-based PVR Broadcasts are saved on hard drive at the headend and played out to subscribers as a VOD program.

NICAM Near instantaneous amplitude companding and modulation. A system of transmitting stereo audio digitally in a TV signal, developed in the United Kingdom and used there and in a number of other countries.

NID Network interface device. One of many names for a box on the side of the house that contains any required interfaces between a telephone line or cable plant and inside wiring.

node 1. The portion of a coaxial cable plant served from one optical receiver. 2. The equipment that receives the linearly modulated FDM spectrum, converts it back to RF form, and transmits into one or more coaxial distribution legs.

noise Generally defined as undesired signals in a transmission channel. In television, the term is commonly applied to broadband thermal noise excluding discrete carriers and distortion products.

noise figure The ratio, expressed in decibels, of the noise produced by a device, over and above the thermal noise produced in a matched resistor at the input to that device. Higher-noise-figure devices require a higher signal level to deliver a given signal-to-noise ratio.

NPR Noise power ratio. A method of specifying the quality of a transmission path by loading it with noise, eliminating the noise in a narrow band, and measuring the amount of noise filled in by the transmission path.

NRZ Nonreturn to zero. A method of transmitting digital data bit by bit, with each bit immediately following the preceding one, with no time between.

NTSC National Television System Committee. An entity that developed the analog TV system used in North America and elsewhere. There were actually two NTSCs: the first developed the monochrome transmission system and the second added color.

NVOD Near-video-on-demand. A PPV service that offers sufficiently frequent start times for popular events (movies) such that it approaches on-demand availability. Half- to quarter-hour incremented start times are common.

Nyquist frequency In a sampled data system, the highest frequency that can be sampled and then recovered without distortion.

Nyquist slope filter A filter applied to a VSB modulated signal just prior to detection to restore flat frequency response.

OAM&P Operations, administration, maintenance, and provisioning. A generic term for software suites that allow centralized administering of a telephone network. A superset of what the cable industry knows as status monitoring.

OCAP OpenCable application platform. Standardized middleware that provides certain applications for a set-top terminal.

offset feed An antenna for microwave reception consisting of a parabolic reflector and feed, shaped such that the axis of the focus meets the reflector at or about at the edge of the reflector. Offset feeds are popular with very-small-aperture antennas because of reduced blockage.

OOB channel Out-of-band channel. A channel used to convey data to and from a set-top terminal other than the channel used to convey video and/or audio programming.

OpenCable A set of industry standards intended to define the next-generation digital consumer devices used by the cable TV industry, to encourage supplier competition, and to create a retail hardware platform.

optical modulation index (OMI) A measure of how much optical modulation is applied to a laser. Usually stated in terms of how much of the range from the laser’s quiescent bias point to cutoff is taken up by the signal. The OMI may be expressed in terms of per-channel or composite signal.

orthogonal Literally, at right angles. Often used by the engineering community to describe two functions that are independent of each other.

oscilloscope A piece of test equipment that allows one to display the time value of a waveform.

overhead In data transmission, the portion of the data that is included to enable transmission. The remaining data transmitted is the payload.

overload In a receiver, the condition of supplying too much signal to that receiver, resulting in the generation of distortion in the receiver.

OVS Open video system. A regulatory alternate to conventional cable television franchising for the operator of a broadband video distribution network. OVS operators are regulated at both the federal and state or local levels. A greater portion of the bandwidth of an OVS system is available for lease to unaffiliated third parties than is the case for cable television franchisees.

PacketCable A set of interoperable interface specifications for delivering advanced, real-time multimedia services over two-way cable plant. PacketCable is built on top of DOCSIS.

packetized elementary stream (PES) In MPEG-2 transmission, a collection of bits containing data from one source only. May contain video, audio, or data.

PAL Phase alternate line. The television system used in most of Europe and many other places, in which the color carrier phase definition changes in alternate scan lines.

parity An extra bit added to a word to make the total number of logical 1s either odd (odd parity) or even (even parity). Used to check for errors that may have been introduced during data transmission or storage.

passband The frequency or wavelength region passed by a filter.

passive A component that handles signals but that requires no power of its own. Examples are taps and power inserters.

pay services Non-advertiser-supported channels for which a subscriber pays on a subscription basis. Also called premium services.

payload In data transmission, the portion of the data that is desired to be transmitted. Other transmitted data, such as error correction and headers, is considered overhead.

PCS Personal communications services. An alternative to cellular telephone service that uses a different frequency range and generally smaller cell sizes.

PDL Polarization-dependent loss. A property of a device or fiber that causes the loss to vary as a function of the polarization of the signal, where the polarization is measured normal to the transmission axis.

peak-to-average ratio In data transmission, the ratio, usually expressed in decibels, between the peak power of a signal and the average power.

PEG Public, educational, and government. A set of locally generated channels many systems are required to carry as a public service.

PES See packetized elementary stream.

phase noise A distortion in which a carrier signal is subjected to random variations in phase.

picture-in-picture A feature of some television sets and set-top converters that allows display of a small second picture within the main picture.

picture-to-sound ratio The ratio between the amplitude of the picture carrier and the associated sound carrier. Usually set to 15 dB in cable television work.

PID Packet Identifier. A header preceding a PES in an MPEG-2 transport stream that identifies the purpose of the PES. In a multiplex of several different TV programs, for example, each audio and video will contain its unique PID, which allows for the selection of the desired program out of the multiplex.

pilot A signal on the distribution plant that is used for AGC or ASG purposes. In most cases, the pilot is one of the normal analog picture carriers that has been so designated.

pixel Picture element. The smallest unit of a picture that can be represented as combinations of the three primary colors only, with no unique shape. Frequently it is assumed that a pixel has either a square or rectangular shape.

plaintext An unencrypted digital data stream that can be read by anyone who understands the data transmission format.

PMD Polarization mode dispersion. The property of a device or fiber that causes signals at one polarization to travel at a different rate than signals at another polarization, where the polarizations are measured normal to the transmission axis.

POD module Point of deployment module. A module intended to be plugged into a host, which includes the intelligence for descrambling a digital video signal and communicating with a headend for the purpose of controlling the delivery of scrambled digital video signals. The module is also called a cablecard.

POE Point of entry. Equipment that is placed between the drop and inside wiring of a dwelling and that processes some or all of the signals for specific services. One application is cable telephony, where the POE device interfaces standard analog in-home wiring to the RF distribution system. See NID.

polarization An expression of the orientation of the electric field in a radiated RF signal.

polarization diversity The use of the same frequency band to radiate two sets of signals by using orthogonal polarizations, usually either vertical and horizontal or left- and right-hand circular.

PON Passive optical network. An all-optical network that consists of nothing more than fiber-optic cable and splitters.

port A logical construct through which data is transferred from one process to another.

positive trap A technology for denying analog television programs to subscribers who have not purchased them. Positive trap systems work by adding a high-level interfering carrier between the picture and sound carriers. Subscribers who have paid for the program are supplied with a filter (trap) to remove the interfering signal.

POTS Plain old telephone service.

power inserter A passive device used to add ac power to the center conductor of a coaxial cable for the purpose of powering active devices.

power pack In a cable system, the module within an amplifier station (or other active equipment) that receives the power multiplexed with the RF signals on the distribution system and creates the voltages required by the station’s internal circuits.

power supply In a cable system, the device that receives power from the utility, processes it for use in the cable system, and inserts it into the coaxial plant through a power inserter.

PPV Pay-per-view. A video service in which the operator transmits movies or events on a fixed schedule and customers have the option of purchasing an individual event or movie showing.

Predistortion A technique for reducing distortion in a linear transmission system by intentionally generating distortion at the transmit end, which distortion will be cancelled by the real distortion of the network.

preemphasis In FM transmission, a technique for reducing noise by selectively increasing the deviation of higher frequencies before transmission. Deemphasis is used to restore flat response at the receiver.

primary colors The three colors that can be combined in differing amounts to yield any color that can be perceived by the human visual system. For the emission spectrum used in television, the primary colors are red, green, and blue.

prime focus feed An antenna for microwave reception consisting of a parabolic reflector and a feed assembly (antenna and, usually, preamplifier and converter) located at the focus of the parabola.

processor Or signal processor. In cable television terminology, an equipment used in the headend to receive a television signal and reformat it for transmission on cable. Reformatting consists of amplification, bandpass filtering, shifting the relative levels of the picture and sound carriers, and, frequently, changing the carrier frequency (channel).

protocol In data transmission, a set of rules defining how various pieces of equipment or software will interact cooperatively.

PSIP Program and System Information Protocol. A series of tables transmitted as part of a digital television transport stream that gives the receiver information needed to recover a program.

PSK Phase shift keying. In data transmission, a modulation format that depends solely on differences in the phase of a modulated signal to convey information.

public/private key pair A set of keys used to encrypt and decrypt messages. One of the keys of the pair is used for encryption and the other for decryption. The key used for encryption cannot be used for decryption. Also known as asymmetric keys.

P/V Peak to valley. The peak-to-peak variation in the frequency response of a cable distribution network relative to the ideal response curve.

PVR Personal video recorder. A device that records and plays back a compressed digital video signal on a hard drive.

QAM Quadrature amplitude modulation. A digital modulation method in which the value of a symbol consisting of multiple bits is represented by amplitude and phase states of a carrier. Typical types of QAM include 16QAM (four bits per symbol), 32QAM (five bits), 64QAM (six bits), and 256QAM (eight bits).

QoS Quality of service. Techniques for ensuring the delivery of data in a reliable and timely manner.

QPSK Quadrature phase shift keying. A digital modulation method in which the state of a two-bit symbol is represented by one of four possible phase states.

quadrature At right angles. In transmission, often used to express independence between two signals.

quantization noise The noiselike uncertainty imparted to an analog signal when it is digitized. An alternate term is quantization error. The more bits used in an analog-to-digital conversion process, the smaller the quantization noise.

RAD Remote antenna driver. A technique by which signals from PCS antennas are frequency converted and transmitted through cable systems to remotely located base stations.

RAID drive Redundant array of independent (or inexpensive) disks. A category of disk drives that employ two or more drives in combination for fault tolerance and performance.

rain fade In a terrestrial or satellite microwave link, signal loss due to absorption and reflections caused by raindrops within the signal path.

reflectometer A device used to determine the location of a fault in a cable by propagating a signal down the cable and reading any signal reflected. May be used for RF or optical transmission.

refraction The process by which optical signals are transmitted through the interface between two dissimilar materials. See index of refraction.

remultiplex Or remux. The process of taking some signals from each of two or more channels and recombining them into one new channel.

renewability In video scrambling, the ability to change a scrambling system if it is broken, or the ability to refuse to communicate with a device that is found to be treating programming in ways not intended by the program owner.

resolution A measure of the “sharpness” of a picture. Usually measured in pixels in the horizontal direction and lines or pixels in the vertical. It is frequently the case that horizontal and vertical resolution are different.

retrace In a scanned television picture, the retrace is the process of moving the electron scanning beam back to the start of each line (horizontal retrace) or the top of the screen (vertical retrace). The beam is shut off (“blanked”) during retrace to avoid picture artifacts.

return loss A measure of the amount of incident power that is reflected back toward the opposite end of a cable from a termination or other discontinuity in the characteristic impedance of the cable.

reverse See upstream.

RIN Relative intensity noise. A measure of the residual internal noise modulation of an optical transmitter. Often limits the attainable C/N of RF signals transmitted through an optical link.

ring network An architecture in which terminal points are connected in a continuous ring and each terminal is connected to both of its neighbors.

router In data communications, a device used to switch packets from any number of input ports to any one of a number of output ports.

RSA An encryption algorithm named for its developers: Rivest, Shamir, and Adleman.

RTP/RTCP Real-time protocol/real-time control protocol. Two layer-4 protocols used to transmit real-time information, and to control playout of packets at the proper time.

run-in A signal preceding some asynchronous data transmissions that permits the receiver to synchronize itself with the transmission.

SBS Stimulated Brillouin scattering. A mechanism that limits the amount of optical power at a single wavelength that can be transmitted through an optical fiber.

scanning The process of sequentially picking up, or “painting,” a picture, wherein each picture element is delivered one at a time in a set sequence over the entire picture. Commonly, the scanning sequence is top to bottom and left to right, as viewed from in front of the picture tube.

scattering In an optical network, any process by which light is briefly delayed and then retransmitted. Forward scattering causes an overall slowing of the signal (see index of refraction), whereas scattering in other directions leads to signal loss and, sometimes, distortion).

scrambling In cable television, the process of rendering a video signal unintelligible without the knowledge of some secret information. In data transmission, scrambling refers to the process of randomizing the bit pattern of a transmitted signal to prevent peaks in the spectrum of the modulated signal. Note that the cable television and data transmission definitions are not equivalent.

SCTE Society of Cable Telecommunications Engineers. A professional organization of technologists interested in cable telecommunications technology.

SDM Space division multiplexing. The simultaneous use of different physical portions of a network (for example, nodes) to carry different signals at the same frequencies.

SECAM A television system used in France and some former Soviet bloc countries.

second audio program In BTSC stereo signals, a second, monaural, audio channel that is available to carry a second audio channel, such as a foreign-language soundtrack.

server A computer that sends information to client machines.

set-top converter Also known as a set-top terminal. A device used with a subscriber’s TV to allow reception of television programs. It may tune channels the TV does not tune and may include descrambling circuitry. It also may include a digital decoder and auxiliary functions such as an electronic program guide.

sheath ring network A ring architecture in which separate fibers are used in each direction from a common terminal to each subterminal. Sheath rings require more fiber than repeating rings but are more secure and offer higher potential bandwidth to a common location.

shielding An expression of the ability of a device either to prevent radiation of signals contained within that device or to prevent undesired pickup of signals outside of the device.

shot noise In an optical link, noise at the optical receiver that is caused by the statistical variation in the arrival of photons.

signal level In analog television work, the RMS level of the picture carrier measured over the occupied bandwidth of the signal during sync tips. In digital communications, as practiced by the cable industry, it is the average level of the modulated signal or the level that would be read on a thermocouple-type RF power meter.

signal level meter A frequency selective RF voltmeter used to measure the level of individual RF carriers.

signal-to-noise (S/N) ratio In video work, the ratio between the video signal amplitude and the noise power measured in a reference bandwidth. Many variations in the definition of “signal” and “noise” exist, and the reader must be sure that the definitions in use are accurately conveyed.

single mode fiber Optical fibers that support only a single transmission path and thus that offer a better-defined transmission delay.

single sideband modulation Amplitude modulation in which one or the other of the modulation sidebands is removed.

skin effect The tendency of RF signals to travel near the surface of conductors.

SLM Signal level meter. A tunable power meter commonly used to measure signal levels in an FDM network.

softswitch A server in some VoIP systems that sets up and tears down calls by sending commands to the endpoints of the call in response to stimulus from the calling endpoint.

SONET Synchronous optical network. A set of standards describing an optical baseband network designed for carrying many types of data.

S/PDIF Sony/Philips Digital Interface. A standard digital audio interface.

spectrum analyzer A piece of test equipment used to plot amplitude vs. frequency.

splitter A device having three or more ports, used to divide RF signal equally between two paths, without regard for the frequency of the signal. Can also be used to combine two signals.

SPM Self-phase modulation. A distortion mechanism in optical fibers whereby, at high transmitted power levels, the optical signal instantaneously modulates the index of refraction of the glass and thus modulates the speed of transmission of the signal, ultimately leading to CSO distortion in the demodulated RF modulating signals.

spread spectrum Any of several techniques used to increase the transmitted spectrum of a signal with respect to the minimum spectrum that can be used for the transmission. The purposes are usually to reduce noise and interference pickup, to allow more than one signal to occupy the same spectrum, to mitigate transmission problems in one portion of the spectrum, or for security.

SRL Structural return loss. A measure of the degree to which signals are reflected from a length of cable as a function of frequency.

SRS Stimulated Raman scattering. A phenomenon in fiber whereby energy from one signal is transferred to one or more other signals sharing the fiber, leading to crosstalk among the RF signals after detection.

standard definition Refers to today’s NTSC, PAL, and SECAM transmissions, with their normal resolution.

star network An architecture in which each terminal is directly connected through separate fibers to a common master terminal. In a simple HFC cable system, the master terminal is the headend and the other terminals are nodes.

start bit(s) One or more bits that precede a digital word in asynchronous transmission, used to identify the beginning of the transmission.

statistical multiplexing In multiplexed video compression systems, the process of assigning more or less of the available channel bandwidth to each of the several signals being multiplexed, according to the instantaneous needs of each.

stopband The frequency or wavelength region rejected by a filter.

strand A heavy wire attached to utility poles to which coaxial and fiber-optic cables are attached.

supertrunk In a cable system, the signal transportation link used to connect the point where the FDM signal complex is created to local coaxial distribution networks. In an HFC network, linearly modulated optical links are used, but other systems use AML microwave or coaxial supertrunks.

S-VHS Super-VHS. An analog video interface that carries the luminance and modulated chrominance signals on separate conductors. Also known as S-video.

S-VOD Subscription video on demand. A variation of VOD in which a subscriber pays a monthly fee to gain access to a set of VOD content.

switch In telephony, the device used to connect one telephone line to another for the duration of a call.

switched broadcast A technique whereby signals are delivered to the portions of a network serving groups of customers only when one or more customers request them. Unlike on-demand service, however, the signals are not spooled from a server, but only connected from real-time sources and thus are not under interactive control of customers.

switched circuit A data or voice transmission method in which resources are set up at the beginning of the transmission and removed at the end, with certain system resources being available continuously to the parties in communication during the call. Conventional telephony is switched circuit. Contrast with VoIP.

symbol A collection of some number of bits of data that are transmitted together.

symmetric key A key that may be used for encrypting and decrypting data, as opposed to an asymmetric key.

sync Or sync tip. The portion of the analog television signal used to synchronize scanning in the receiver to scanning in the camera. Corresponds to the most negative portion of the baseband waveform (“blacker than black”). In digital transmission, a set of bits of known value, used to locate a position in a data stream.

synchronization In data transmission, the process of ensuring that data recovery at the receiver is timed properly with the data being transmitted. In video, the process of ensuring that the camera pickup and the receiver display are scanning the same part of the image at the same time.

synchronous detection The process of recovering modulation from an amplitude modulated signal by mixing the signal with a replica of the original unmodulated carrier. In modulation methods with asymmetrical sidebands (such as analog television transmission), synchronous detection can be shown to provide more accurate detection than can the simpler envelope detection.

sync suppression scrambling A scrambling technique in which the synchronization portion of the picture is hidden, usually by moving it to a level normally occupied by picture information.

taboo channels In FCC assignment of off-air UHF channels, certain channels that cannot be used in a particular location due to the use of other channels. The taboo channels exist due to certain limitations in UHF converter performance that are brought about by the need to keep cost low.

tap The component installed in the distribution cable that diverts a portion of the downstream distribution signal and splits it to feed two to eight individual subscribers. In the reverse direction, it combines the signals from subscribers and inserts them into the upstream direction of the distribution cable.

TASO Television Allocations Study Organization. A group that in the late 1950s studied the subjective effects of noise and distortion on the television viewing experience. Used a six-point rating scale that is still referred to today.

TCP Transmission control protocol. A connection-oriented layer 4 protocol often used with IP to transmit data. Includes various mechanisms to enhance the probability that a packet will arrive.

TDM Time division multiplex. A data transmission method in which a number of individual digital data streams share a transmission channel, each occupying the channel for a portion of the total time.

TDMA Time division multiple access. A data transmission method in which a number of individual transmitters in different locations share a transmission channel, each occupying the channel for a portion of the total time.

TDR Time domain reflectometer. A device that measures the quality of a transmission line by transmitting a pulse and then measuring signals reflected as a function of time. The reflections indicate the distance to the point of reflection.

TEM Transverse electric and magnetic. A description of the normal field configuration for signals transmitted through coaxial cables.

10/100BaseT Two common forms of Ethernet transmission that transmit data at, respectively, 10 or 100 Mb/s.

termination The impedance at the end of a coaxial or fiber-optic cable that accepts power being transmitted on the cable.

TGCP Trunking Gateway Control Protocol. The call management interface protocol specified for use with cable-based VoIP systems. It is a profile of MGCP, similar to NCS.

thick client A term applied to a data communications user endpoint, such as a set-top terminal, that implies relatively high levels of embedded functionality, with the device depending more on itself and less on network resources for its functionality. Contrast with thin client.

thin client A term applied to a data communications user endpoint, such as a set-top terminal, that implies relatively low levels of embedded functionality, with the device depending more on network resources for its functionality. Contrast with thick client.

transition region The frequency or wavelength region(s) of a filter that are between the passband and the stopband(s).

transport stream In MPEG-2 systems, the data formatted for transport. Such data is composed of one or (usually) more PESs, plus overhead.

trap A passive coaxial component inserted in series with a drop line that blocks transmission of a specific frequency or range of frequencies. Used to block or enable specific channels or to tailor the services available in homes.

trunk 1. The untapped portion of a coaxial distribution network. Trunk links are typically operated at lower levels than distribution links, to minimize distortions. 2. An amplifier module used in the trunk portion of a coaxial distribution system. 3. An amplifier station that contains a trunk module. It may also contain a bridger module if it is desired to create a distribution leg at that location.

twisted pair A type of cable used extensively for transmission of balanced audio signals. The cable consists of two insulated conductors twisted on each other. It may or may not have a shield over the twisted pair.

UDP Universal Datagram Protocol. A connectionless layer 4 protocol often used with IP to transmit data. A simple protocol suitable for transmission of real-time audio and video information, for which retransmission of a lost packet is not feasible.

unavailability The fraction of time that a network or channel is unavailable for use. See availability.

universal remote control A remote control transmitter that can control more than one brand of TV, VCR, set-top converter, etc. Often used to control all of a consumer’s entertainment equipment.

UPC Ultra-polished connector. An optical connector that minimizes loss and reflections by careful preparation and polishing of the fiber end and alignment with the mating fiber.

upstream Signal flow from subscribers toward a headend.

UTP Unshielded twisted pair. A data cable consisting of one or more twisted pair without shielding. See Cat 5.

VBI Vertical blanking interval. That time in a television signal during which the electron beam in the receiver is moving from the bottom of the screen back to the top in order to start a new field. The VBI is 11 horizontal lines long, and these lines are frequently used to insert test signals and data.

VBR Variable bit rate. A signal or communications channel that generates or accommodates a digital signal whose bit rate varies with time.

video In television work, this word is reserved to mean a baseband electrical signal that conveys information regarding picture content.

video compression The reduction of bandwidth needed to transmit or store a video signal by removing information in the signal that is not necessary for satisfactory perception of the signal or that can be inferred from other elements of the transmitted signal.

video inversion A scrambling technique in which analog video is inverted so that black corresponds to the minimum carrier amplitude, as opposed to the maximum amplitude (in NTSC and PAL transmission). Sync may or may not be inverted.

visual An adjective implying an RF or IF carrier that is modulated with a video signal.

VITS Vertical interval test signals. Signals that are inserted into the VBI to allow testing of the quality of the transmission link independent of the video programming.

VOD Video on demand. A video service that allows users to select the program and exact start time interactively. In some embodiments, it allows VCR-like control of the playback (for example, pause, rewind, fast-forward).

VoIP Voice over Internet Protocol. A methodology for transmitting digitized voice telephone signals by converting them into packets that can be transmitted through a standard Internet Protocol network that may be shared with other services.

VSB Vestigial sideband. The elimination of a large portion, but not all, of one sideband of an amplitude modulated signal. This may be practiced with either analog or digital modulation.

water peak The property of fiber that causes it to exhibit a loss peak near 1,383 nm due to the presence of trace amounts of hydroxyl ions. Some modern fibers no longer exhibit this phenomenon.

waveguide dispersion The property of fiber that causes the velocity of propagation of an optical signal to vary as a function of wavelength due to the changing mode field diameter and, thus, the relative influence of the differing indices of refraction of the core and cladding glass.

wavelength The distance traveled through a transmission medium by an RF or optical signal in a time equal to the inverse of the frequency (for example, for a 1-GHz signal, the distance traveled in 1 ns). It is equal to the speed of propagation in the medium, divided by the frequency.

wavelength dispersion In an optical fiber, the variation in transmission time as a function of the wavelength of the light.

wavelength multiplexer A device for combining or separating signals of differing wavelengths.

W curve A description of the variation of subscriber perceptibility of interfering signals in an analog television channel as a function of frequency within the channel boundaries. So called because of the shape of the curve, caused by the extreme sensitivity to interfering signals occurring near the visual and chrominance carriers.

WDM Wavelength division multiplexing. The use of an optical fiber to simultaneously carry signals at different wavelengths.

wire rate The actual data rate at which a signal is transferred on an interface, including all overhead.

WWDM Wide wavelength division multiplexing. Wavelength division multiplexing in which the optical signals are greater than 50 nm apart. The combination of a 1,310-nm and a 1,550-nm signals, for instance, would be considered WWDM.

XMOD Cross modulation. A type of distortion in which the amplitude modulation of one signal causes incidental amplitude modulation to another signal. XMOD is an odd order distortion.

XPM Cross-phase modulation. An interference phenomenon in optical fiber whereby a high-level signal at one wavelength modulates the index of refraction of the fiber and, thus, the speed of transmission of one or more other signals. When combined with wavelength dispersion, this leads to crosstalk in the detected RF signals.

Yagi Or Yagi-Uda. A gain antenna consisting of a single driven element and one or more parasitic elements used to direct energy along a single axis.