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GLOSSARY
Access Channels
US term for dedicated 'public service' channels set aside by cable companies for non-discriminatory access to the network by the public, government agencies, or educational institutions.
Access Node (AN)
Part of the Access Network which performs some or all of the following:
- Modulating forward data onto the Access Network.
- Demodulating return-path data.
- Enforcing the MAC protocol for access onto the Access Network.
- Separating or classifying traffic prior to multiplexing onto the Transport Network, such as: differentiating traffic that is subject to QoS guarantees from traffic that receives; best-effort support.
- Enforcing signaling.
- Handling passive operations, such as splitting and filtering.
Accounting Separation
Regulatory requirement for dominant companies (usually telcos) to operate separate accounts for different activities to avoid unfair cross subsidies (EG telephony, Internet access and video offering).
Active
Power circuitry containing transistors, such as amplifiers, power supplies or converters.
Addressable
Able to signal from the headend or hub so that only the particular specified subscriber's receiving the equipment is affected, enabling changes in the subscriber's level of service for premium channels/PPV etc.
ADSL
Asymmetric Digital Subscriber Line. A method of enhancing the bandwidth of twisted pair copper cable to speeds of more than 500 Kbps — often 2Mbps, the minimum to deliver video — and up to 6Mbps. Although two way, as the name suggests the data transfer is uneven, with more bandwidth downstream. Also see xDSL.
Ariel plant
Generally US - cable suspended in the air on telephone or electric utility poles. Not usually allowed in Europe.
Alternative access provider
A telecommunications provider, other than the local telephone company, that provides a connection between a customer's premises to a point of presence of the long distance carrier.
Amplifier
A device the boosts the strength of an electronic signal. In a cable system, amplifiers are spaced at regular intervals throughout the system to keep signals picture-perfect regardless of how far your live from the headend.
Amplitude Modulation
The process of impressing information on a radio-frequency signal by varying its amplitude. Generally amplitude modulation is due for the purpose of relaying messages by voices, television, facsimile or other modes.
Analogueue (data transmission)
Signals in the form of continuously variable physical quantities.
Analogueue Device
A devise that operates with variables represented by continuously measured quantities such as voltages, resistances, rotations and pressures.
Analogueue Signal
A signal that is solely dependent of magnitude to express the information content.
Analogueue-To-Digital
A device that converts a signal whose input is information in analogue form and whose output is the same information in digital form.
Antenna
An structure or devise used to receiving or transmitting electromagnetic waves.
Antenna Array
A group of identical antennas arranged and interconnected for achieving greater directivity (gain) or beam shaping.
Antenna Stack
Antenna tower with multiple antennas and supports.
Asynchronous transfer mode (ATM)
The transfer mode in which the information is organised into cells. It is asynchronous in the sense that the recurrence of cells containing information from an individual user is not necessarily periodic.
ATM cell
A digital information block of fixed length (53 octets) identified by a label at the ATM layer.
Attenuation
The decrease in amplitude of a signal between any two points in a circuit. Usually expressed in decibels. Attenuation is the opposite of amplification.
Audio
Relating to sound or its reproduction; used in the transmission or reception of sound.
Automatic Gain Control (AGC)
Used to protect a device from optical overload while maintaining bandwidth and sensitivity performance.
Automatic Slope Control (ASC)
Circuitry which permits amplifier response compensation for varying slope (tilt) at its input.
Available bit rate (ABR)
An ATM layer service where the limiting ATM-layer transfer characteristics provided by the network may change subsequent to connection established.
Backbone Microwave System
A series of directional microwave paths carrying common information to be relayed between remote points; engineered to allow insertion of signals, dropping off of signals and switching of signals along its length at designated relay points.
Background Noise
In an amplifier or other device that draws current, there is always some noise output in addition to the desired signal.
Bandwidth
A measure of the information-carrying capacity of a communication channel. The bandwidth corresponds to the difference between the lowest and highest frequency signal which can be carried by the channel.
Baud Rate
The measure of the speed of transmission of a digital code.
Basic Cable
The basic program services distributed by a cable system for a basic monthly fee. These include one or more local broadcast stations, distant broadcast stations, non-pay networks and local origination programming.
Bit
A binary digit. The binary systems of numbers is often called base 2. All binary digits consist of combinations of 0's and 1's.
Bit Error Rate (BER)
The fraction of bits transmitted that are received incorrectly.
Bit Rate
The rate of a binart-coded transmission which is the number of bits per second.
Bridger Amplifier
Trunk amplifiers serve to boost the signal and pass it along, and to provide branching lines, called feeders, for distribution of the signals to subscribers. The bridger amplifier is housed in the same case as the trunk amplifier. It taps the trunk at about +20 dBmV and splits the signal into 2 to 4 feeder lines.
Bridged Tap
Wires that are connected to a network, in which one end of the wire is unconnected to proper termination equipment. (Ex: A consumer or technician removes devices without completely disconnecting to the old device.)
Broadband
Any system able to deliver multiple channels and/or services to its users or subscribers. Broadcast television, cable television, microwave and satellite are examples of broadband technologies.
Broadband Modulation
The transfer of information by a radio signal requires a certain minimum amount of spectrum space. This minimum depends on the rate at which this information is conveyed. Sometimes called wideband modulation.
Broadcasting
The dissemination of any form of radio electric communications by means of Hertzian waves intended to be received by the public. Transmission of over-the-air signals for public use.
Broadcast addresses
A predefined destination address that denotes the set of all service access points.
Brouter
A device that routes specific protocols, such as TCP/IP and IPX, and bridges other protocols, thereby combining the functions of both routers and bridges.
Burst error second
Any errored second containing at least 100 errors.
Bus
A LAN topology in which all the nodes are connected to a single cable. All nodes are considered equal and receive all transmissions on the medium.
Byte
A data unit of eight bits.
Cable Loss
Defines the amount of cable loss that an amplifier is aligned (pre-equalised) through during factory alignment. Aligning an amplifier through cable creates a tilted gain response.
Cable System
Facility that provides cable service in a given geographical area, comprised of one or more headends.
Cable-Powered
Devices obtaining ac power simultaneously with RF on the coaxial cable.
CableSCAN
A software product developed by TapSCAN which tabulates Nielson household and demographic data for cable.
Cable Termination
RF frequency signals travelling in coaxial cable will reflect off any impedance that does not match the 75 Ohm impedance of the cable. This will cause serious signal distortion. For this reason, the ends of all the trunk and distribution cables are terminated with a 75 Ohm load to ground.
CATV
Community Antenna TeleVision. Also called Cable TV. Widely used as a synonym for Cable TV.
Carrier
An alternating-current wave of constant frequency, phase and amplitude. By varying the frequency, phase or amplitude of a carrier wave, information is transmitted.
Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
The Ethernet media access method. All network devices contend equally for access to transmit. If a device detects another device's signal while it is transmitting, it aborts transmission and retries after a brief pause.
Cascade Depth
The number of amplifiers between the headend and the specific subscriber.
Cell
ATM layer protocol data unit.
Central office (CO)
The central location in a traditional public network telecommunication environment where access is available to signals travelling in both the forward and reverse paths.
Channel
A signal path of specified bandwidth for conveying information.
Channel Capacity
The number of channels available for current or future use on a cable system.
Cluster
The group of homes passed by a single fibre node.
Coaxial cable
Actual line of transmission for carrying television signals.Cable with a central copper strand for transmitting electrical signals, surrounded by a concentric air or insulation (nonconducting) core, and enclosed by an outer (electrically shielding) concentric metal fibre, either braided or solid. Even where a cable plant uses fibre optic cable from its headend,, coaxial cable is usually used from the node to the subscriber household (from the kerb).
Co-Channel
A form of interference caused by another signal occupying the same channel frequency. Example - two signals are received in a headend, from different locations, causing interference with each other as received.
Code Division Multiple Access (CDMA)
A digital technology developed by QUALCOMM. With CDMA, unique digital codes, rather than separate RF frequencies or channels, are used to differentiate subscribers.
Collision
The result of two network nodes transmitting on the same channel at the same time. The transmitted data is not usable.
Combiner
A signal combining network which allows several discrete inputs to be added into a common bandwidth and having high isolation between inputs. Also nay refer to a power combining network.
Common Path Distortion (CPD)
The interference of return path signaling caused by the forward path. Often referred to as ingress - of particular significance in interactive applications where the return path is being used to contact the cable headend.
Communications Satellite
An electronic retransmission vehicle located in space in a fixed earth orbit. Signals are transmitted to the satellite from earth station antenna, amplified and sent back to earth for reception by other earth station antennas.
Communication Server
A dedicated, stand-alone system that manages communications activities for other computers.
Composite Triple Beat (CTB)
In multichannel systems using push-pull, PHD, and feed-forward amplifiers, the limiting performance factor is usually composite third order beats. The total number of beats that 'pile up' at a single frequency can be calculated. The composite triple figures are with CW carriers at the output level and tilt listed on the specification sheets. Any deviation creates on a 2:1 basis. Worst-case CTB occurs at the high end of the amplifier's passband. With TV modulated carriers, the average signal power is reduced. measured composite triple beat levels are at least 6dB lower than with CW carriers, and possibly as much as 10 dB lower when frequency offsets are considered. the composite triple beat is measured with a spectrum analyzer of 30 kHz resolution.
Compression
A method for compacting the digital representation of a signal for more efficient transmission or storage.
Constant bit rate (CBR)
A service class intended for real-time applications, or those requiring tightly constrained delay and delay variation, as would be appropriate for voice and video applications. The consistent availability of a fixed quantity of bandwidth is considered appropriate for CBR service.
Contour
Grade A: The geographical boundary of an area receiving a given TV signal that is satisfactory for 70% of the viewers 90% of the time.
Grade B: Borders of an area where the TV signal is satisfactory to at least 50% of the viewer locations 90% of the time.
Converter
A device (in CATV) for permitting a standard TV set with a 12 channel VHF tuner to receive over 12 cable channels. Older types use a multichannel TV tuner.
Critical Length
Distance along a specific cable to cause worst-case mismatch reflection. A function of frequency-attenuation-velocity of propagation parameters of specific cable types.
Cross Modulation
'Cross-mod' - A form of synchronous triple beat between any two channels where the modulation sideband (+/-)constitutes the third beating frequency. More than one channel source may be additive and appear to be baseband (modulation) interference on the affected channel.
Crosstalk
Noise passed between communications cables or device elements.
DAVIC
Digital Audio Visual Council - A technical standards setting body, particularly referred to in relation to cable modems.
Data Communication
The movement of encoded information by means of electrical transmission systems. The transmission of data from one point to another over communication channels.
Data Compression
A technique that saves storage space by eliminating gaps, empty fields, redundancies, or unnecessary data to shorten the length of records or blocks.
Decibel (dB)
A unit of measuring relative levels of current, voltage, power or noise volume.
Delay
The elapsed time between the instant when user information is submitted to the network and when it is received by the user at the other end.
Demographics
Breakdown of television viewers by such factors as age, sex, income levels, education and race.
Demodulation
The extraction of the modulation or information from a radio-frequency current.
Dense Wave Division Multiplexing (DWDM)
A technology that provides in fibre the equivalent of frequency division multiplexing, in metallic wire. Separate parallel channels are transmitted on a single fibre, with one wavelength for each channel. Current products enable 16 channels of 2.5 Gb each for a total of 40 Gb per fibre. DWDM can operate over existing single-mode fibre, and therefore reduce upgrade costs.
Descrambler
An electronic circuit that restores a scrambled video signal to its standard form.
Detector
The photodiode in optical receivers.
Digital
The use of a binary computer code to represent information. In cable, digital transmission is much clearer than analogue. Digital technology also allows for more information to be processed.
Digital Set Top Box
A device which accepts digital encoded television broadcasts and converts them to display on an analogueue television set. New boxes with added functionality provide local storage of programming on hard discs, and Internet access.
Direct Broadcast Satellite (DBS)
A high-powered ku-band satellite capable of offering TV signals from a satellite to the home, for multichannel reception, with a small (0.5m) antenna.
Digital compression
An engineering technique for converting an analogueue television signal into a digital format. A rule of thumb is that ten digital channels fit into the spectrum of a single analogueue channel.
Dish Antenna
A high-grain antenna, shaped like a dish, that is used for the transmission and reception of ultra-high-frequency and microwave signals.
Distant Signal
A broadcast signal originating outside the cable system's local market.
Distribution system
Part of a cable system consisting of trunk and feeder cables.
DOCSIS
Data Over Cable Service Interface Specifications
Specification for transmission of data over a cable network that has been approved by the ITU as an international standard. DOCSIS was developed by MCNS, a consortium consisting of CableLabs and a consortium of North American multi-system operators. Competes with the DVB standard in Europe.
Downlink
Transmission of signals from a satellite to a dish or earth station.
Downstream (or Forward Traffic)
Signals transmitted to a subscriber.
Drop
The cable and hardware from tap to subscriber is called the drop.
Drop Cable
Generally 100m or less, of coaxial cable, starting at a tap and contiing on to the subscriber's connection.
Dual Cable
Two independent distribution systems operating side by side, providing double the channel capacity of a single cable.
Duplex
In a communications channel, the ability to transmit in both directions.
Earth Station
The antennas and other equipment needed on the ground to transmit or receive satellite communication signals.
Educational Access Channel
A cable television channel specifically designated for use by local education authorities in the US.
End user
A person, organisation, or telecommunications system that accesses the network to communicate via the services provided by the network.
Errored second
Any one-second interval containing at least one bit error.
Ethernet
The most popular LAN technology in use today. The IEEE standard 802.3 defines the rules for configuring an Ethernet network. It is a 10 Mbps, CSMA/CD baseband network that runs over thin coax, thick coax, twisted pair or fibre optic cable.
Extended subplot
A frequency division scheme that allows bi-directional traffic on a single cable. Reverse path signals come to the headend from a 5 to 45 MHz. Forward path signals go to the headend from 54 to the upper frequency limit.
F-Connector
The final piece of hardware to subscribers on a drop cable. It is cylindrical with a centre pin sticking out, that plugs into the set-top box, cable ready TV or VCR.
Factory Alignment
Refers to the bench test alignment conditions with the slope and gain controls (where applicable) turned to maximum and no pad or equaliser installed. These specs can be used to verify operation during a bench test.
Fibre Distributed Digital Interface (FDDI)
A network based on the use of optical fibre to transmit data at a rate of 100 Mb/s.
Feeder Cables
The cables that take signals from the trunk line to the subscriber area and to which the subscriber taps are attached.
Feeder Line
Cable distribution lines that connect the main trunk line or cable to the smaller drop.
Fibre optics
Very thin and pliable tubes of glass or plastic used to carry wide bands of frequencies transmitting signals over light waves.
Field Effect Transistor (FET)
A low amplifying device available in many different forms including gallium arsenide. Ideal for use in high-gain, low-noise amplifier circuits, especially at ultra-high and microwave frequencies.
Filter
A passive or active frequency selective circuit designed to modify a signal or source of power.
FM Broadcast Band
The band of frequencies extending from 88 to 109 MHz.
FM Cable system
FM radio signals offered by the cable system (the cable must be connected to the subscriber's FM stereo receiver.)
Forward Error Correction (FEC)
FEC enables the receiver to detect and fix errors to packets without the need for the transmitter to retransmit packets.
Forward Traffic (also Downstream or forward channel)
Signals transmitted to a subscriber from the headend.
Fragmentation
When broad television audiences break into smaller segments due to multiple viewing choices and niche programming that targets particular demographics.
Franchise
A contract between a cable television company and a municipal government authorising the company to install cable and offer cable television service within the specified area.
Frequency
The number of times a complete electromagnetic wave cycle occurs in a fixed unit of time, usually one second. The rate at which a current alternates, measured in Hertz on a telecommunications medium.
Frequency Modulation (FM)
A common method of transmitting information over a carrier wave by changing its frequency.
Front End
The first radio-frequency amplifier stage in a receiver. This is one of the most critical components of the receiver because because the sensitivity of the front end dictates the sensitivity of the entire receiver.
Full-Duplex
Independent, simultaneous two-way transmission in both directions, as opposed to half-duplex transmission.
Full-Motion Video
Not compressed; a standard video signal of 30 frames per second, 525 horizontal lines per frame, capable of complete action.
Full Service Network (FSN)
Cable networks that are intended to provide everything; that is broadcast TV, Internet access, VOD, and voice telephony.
Gain Control
An adjustable control that changes the gain of an amplifier.
Gain Slope
A linear variation in gain from the lowest frequency to the highest frequency.
Gateway
A computing machine which is both connected to one or more networks, and is capable of passing network information from one network to another.
GigaHertz (GHz)
One billion cycles of electrical frequency per second.
Ground Communication Equipment
Satellite earth station electronic equipment.
Half-Duplex
Two-way transmission, one way at a time.
Head-End
The control centre of a cable television system, where incoming signals are amplified, converted, processed and combined into a common cable along with any original cablecasting, for transmission to subscribers. The system usually includes antennas, preamplifiers, frequency converters, demodulators, modulators, processors and other related equipment.
Head-End Router
The computer, at the cable headend, responsible for gateway operations between the headend and the Internet.
Header
Protocol control information located at the beginning of a protocol data unit.
Hertz (Hz)
A unit of frequency equivalent to one cycle per second.
Heterodyne
A process of the shifting of a signal of interest down to a frequency at which it may be processed more easily to extract information.
High Definition Television (HDTV)
A very high quality television signal with picture resolution nearly equal to that of film.
High Electron Mobility (HEMT)
A transistor that yields the lowest noise figures in single FET devices.
High Q
A fibre circuit with a great deal of selectivity.
High Split
When the upstream frequencies are 5-150/174-750 MHz; this split provides the greatest amount of return path.
Homes Passed
The number of homes in which a cable television service id or can be made available by adding a drop to an already existing feeder line.
Hub
A signal distribution point for part of an overall system. Larger cable systems are often served by multiple hub sites, with each hub in turn linked to the main headend with a transportation link such as fibre optics, coaxial supertrunk, or microwave.
Hybrid fibre Coax (HFC)
A network consisting of fibre optical cables and coaxial cables.
IEEE
Institute of Electrical and Electronics Engineers.
Impedance
Resistance to alternating-current flow.
Independent Operator
Individually owned and operated cable television system, not affiliated with an MSP.
Inductance
The ability of a device to store energy in the form of a magnetic field.
Inductor
An electronic component designed to provide a controlled amount of inductance.
Infomercial
A commercial, usually 90 seconds or more in length, designed to supply information about a product or service rather than to present a specific sales message.
Interactive Cable
Cable systems that have the technical ability to let subscribers communicate directly with a computer at the system headend from their television sets, using special converters and the regular cable lines. Viewers are able to order movies and video games, access library information and request sales brochures from home.
Interconnect
Two or more cable systems distributing a programming or commercial signal simultaneously.
Interdiction
A method of receiving TV signals by jamming unauthorised signal having all other signals received in the clear. Becuse jamming is accomplished outside the home it does not require a set-top terminal in the home.
Interlacing
The television display format, where horizontal lines of pixels are illuminated in an alternating pattern rather than sequentially.
Intermodulation
In a receiver, an unwanted signal sometimes interacts with the desired signal. The desired signal appears to be modulated by the undesired signal.
Internet, The
A series of interconnected local, regonal, national and international networks, linked using TCP/IP. The Internet is accessible vie telephony wires, HFC networks and by satellite.
International Television Fixed Services (ITFS)
The ITFS television transmission system was first authorised by the FFF for educational television in the 2.5 to 2.686 GHz band. The ITFS band has been re-allocated for shared operation among multipoint distribution services, multichannel multipoint distribution services, operational fixed services, and ITFS users.
Internet Protocol (IP)
The computer network protocol (analogueous to written and verbal languages) that all machines on the Internet must know so that they can communicate with one another.
Ku-band
The group of microwave frequencies from 12 to 18 GHz; the band of satellite downlink frequencies from 11.7 to 12.2 GHz.
Laser
A device that generates coherent electromagnetic radiation in, or near, the visible part of the spectrum.
Last Mile Framing
The data encapsulation and transmission protocols used between the consumer premises and the head end. Framing techniques include ATM, MPEG and IP.
Layer
In networks, layers refer to software protocol levels comprising the architecture, with each layer performing functions for the layers above it.
Leased Access (or Leased Channel)
On some systems, a public access channel for which programmers pay a fee for use and are permitted to sell commercial time in their programming.
Line Speed
Expressed in bps, the maximum rate at which data can reliably be transmitted over a line using given hardware.
Local Area Network (LAN)
Private transmission network interconnecting offices within a building or group of buildings, and usually designed to convey traffic (voice, video, data, and facsimile.) A LAN usually includes a computer network made up of computer, printers and mass storage units.
Local Exchange
An exchange where telephone subscriber lines connect.
Local Exchange Carrier (LED)
A local telephone company within a serving area or LATA.
Local Loop
The set of facilities used by a telephone company to transport signals between a central office, roughly similar to a cable TV headend, and a customer location. Also called the last mile.
Local Origination
Programming produced by a local cable system for presentation on the system. It may also include syndicated programming acquired by the system.
Low Noise Amplifier (LNA)
A low noise signal booster used to amplify the weak signals received on a satellite antenna. Usually found in the receiver front ends.
Low Pass Filter (LPF)
Replaces the regular filter (used for one way transmission) on a drop, and enables a subscriber to have 2-way service. The LPF allows low frequencies to pass, but blocks out higher frequencies.
Low Power Television
Broadcast medium that is similar to commercial TV but limited in broadcast coverage area by its low power signal.
Low Split
When upstream frequencies are assigned below 54 MHz.
MAC Address
An address identifies a particular medium access control (MAC) sublayer service access point.
Master Antenna Television (MATS)
Antenna and distribution system which serves multiple dwelling complexes such as hotels and blocks of flats.
MCNS
Multimedia Cable Network System - A consortium of CableLabs and North American multi-system operators that developed DOCSIS, a specification for the transmission of data over a cable network that has been approved by the ITU as an international standard.
Medium Access Control (MAC) Protocol
In a subnetwork, that part of the protocol that governs access to the transmission medium, independent of the physical characteristics of the medium , but taking into account the topological aspects of the subnetworks in order to enable the exchange of data between nodes.
MegaHertz (MHz)
One million cycles per second.
Microwaves
High frequency radio waves used for telecommunications transmission, usually above 890 MHz. Microwave frequencies require direct line-of-sight to operate. Trees and buildings distort or block the signal.
Microwave Oscillator
A device used to generate a microwave signal. it consists of two parts:
- a resonator to control the frequency of the microwave signal.
- an active device to generate the power.
Mid Split
When upstream frequencies are assigned above 100 MHz.
Miles of Plant
The number of cable plant miles laid or strung by a cable system.
Mixer
A nonlinear circuit that produces an output at the sum and difference frequencies of an applied fixed or variable oscillator called the LO, and the RF input signal of interest.
Modem
Also Modulator/Demodulator - A device that converts digital signals to analogue or converts analogue to digital, allowing computer data to be carried over normal telephone and cable lines.
Modulation
When some characteristics of an electromagnetic wave are deliberately changed or manipulated for the purpose of transmitting information.
Modulator
A device that takes the video signal and audio signal that are separated by the receiver and combines them into a signal that can be received by an ordinary TV set.
Mode
The path a photon takes in going from one end of an optical fibre to another.
Monomode (also Single-mode fibre)
All photons take the same path down the centre of the core of an optical fibre.
MPEG-2 (also MPEG-4)
Motion Picture Expert Group - a set of protocols designed for encoding, compressing, storing and transmitting audio, video and data in digital form.
Multiple System Operator (MSO)
A company that owns and operates more than one cable system.
Multicast
A multicast is a message that is sent out to multiple devices on the network by a host.
Multiple Subnyquist Sampling Encoding (MSSE)
The Japanese analogue system using more than 6 MHz per channel.
Multiplexer
A device that allows several users to share a single circuit. It funnels different data streams into a single stream. At the other end of the communications link, another multiplexer reverses the process by splitting the data stream back into the original streams.
Multiplexing
Transmitting multiple signals simultaneously on a single chain.
Multinode
When a photon careens off the optical fibre wall as it goes from one end to the other. Other photons take different paths. There are approximately 200 different paths in a single fibre.
Must-Carry
Channels which local or national authorities stipulate must be carried by a particular operator. Usually government or local channels that must be carried by pay-TV providers.
