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Glossary

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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z #




A
ACR:
attenuation to crosstalk ratio, a measure of how much more signal than noise exists in the link, by comparing the attenuated signal from one pair at the receiver to the crosstalk induced in the same pair.

ANSI:
American National Standards Institute, oversees voluntary standards in the USA.

Access Panel
An opening in the wall or ceiling near the fixture that allows access for servicing the plumbing/electrical system.

Active:
Any circuit containing amplifying devices, such as tubes or transistors.

Adapters:
a type of balun that physically allows one connector to mate to another.

Adaptor:
A fitting that unites different types of pipe together, e.g. ABS to cast iron pipe.

Advanced Research Projects Agency Network (ARPANetTM):
A predecessor of the Internet, developed in the 1960s by the US Department of Defense. Designed to link widely dispersed research sites, ARPANet established high-level standards for the addressing and routing of data, allowing different types of computer to communicate. It also foreshadowed the Internet in its ability to withstand local disruption.

Agent:
A small program which can search for, and retrieve, information on networks such as the Internet. An agent is capable of independent decision-making - for instance, it can use the results of previous searches to determine where to look in the future. Semi-intelligent and wide-ranging in the searches it performs, an agent is distinguished from a search engine, which looks for items that match specific terms, as defined by a user, and generally looks for them in a database rather than across a network.

Allocations:
The assignments of frequencies by the FCC for various communications uses (e.G., Television, radio, land-mobile, defence, microwave, etc.) To achieve a fair division of the available spectrum and minimize interference among users.

American Standard Code for Information Interchange. (ASCII):
Pronounced 'ask-ee', a code used by computers to represent alphanumeric characters and some punctuation marks. Each character is represented by a 7-digit binary number, 0000000 to 1111111, giving a total character set of 128. E-mail messages sent over the Internet take ASCII form, meaning that some kind of conversion is often required.

American wire gage (AWG):
an American system of defining the size of copper wire.

Analog:
an electrical signal that carries information in a continuously varying format.

Analogue:
A term used to describe a signal, such as the human voice, whose value varies continuously with time; or a transmission method, such as the traditional telephone network, which carries source signals as electrical waves. Compared with digital systems, an analogue telephone line carries data at low speed; it also requires a modem to convert the computer's digital output into a form (sound) which it can handle.

Applet:
Applications written in Java run on any computer and under any operating system, contributing to its widescale adoption on the Internet. Applets - JavaTM mini-programs - can be embedded in World-Wide Web pages to add special functions such as animation and calculation.

Application Connectivity Services:
Application Connectivity Service is that domain occupied by the desktop device, its operating systems, application software, and the business enterprise. Application Connectivity Service is dependent on, Customer Connectivity Services, Virtual Connectivity Services and Bandwidth Connectivity Services to transport information across networks. An example of Application Connectivity Service would be a range of value added Consultancy services initially focused on Messaging, Video conferencing and Local Area Networking.

Archie:
A software tool for finding files on the Internet.

Asymmetric Digital Subscriber Line (ADSL):
Technology under which video pictures can be transmitted in a digitally compressed form over copper wire (i.E. Existing telephone wires), including the capability for an upstream path from consumers to the network operator. BT are currently trialling this technology as a means of providing a VOD service over their existing network.

Asynchronous Transfer Mode (ATM):
A broadband switch technology that will allow varying bandwidth to be switched at very high speeds, allowing the development of true VOD services. Asynchronous Transfer Mode. A method of transmission whereby information - voice, data video, etc. - Is transported as a series of fixed-length (53-byte) units (cells). It is used for high-speed data transmission on broadband networks.

Asynchronous transmission:
A basic form of data transmission, in which characters are sent separately. Each character is bracketed by markers, indicating where it starts and finishes. Originating and receiving machines therefore do not need to agree in advance how and when they will communicate (i.E. They do not need to be synchronised) and transmission can occur at random intervals.

Attenuation Unbalance:
A measure of the inequality of attenuation between two pairs in a multi-pair cable.

Attenuation coefficient:
The factor relating transmission line attenuation to unit distance.

Attenuation:
The reduction in amplitude of an electrical signal due to a transmission line or other network.


B
Backbone:
A high-capacity network linking together networks of lower capacity.

Balanced pair:
A transmission line in which the two conductors are electrically identical and symmetrical with respect to a common reference point, usually earth.

Balanced transmission:
sending signals of opposite polarity on each wire in a pair to maximize bandwidth and minimize interference. Used with all UTP cable.

Balun:
a device that adapts one cabling type to another, including physical layout, impedance and connecting balanced to unbalanced cables.

Bandwidth:
The maximum amount of data that a connection can transmit in a given period of time, generally measured as bits per second (bit/s). A digital telephone line has a bandwidth of 64,000 bits per second (64 kbit/s). An analogue telephone line has a bandwidth equivalent to 9600 bits per second. However, the effective bandwidth of an analogue line can be increased by the attachment of a modem employing data compression.

Baseband:
A network that supports high-speed data transmission. Unlike broadband systems, a baseband network uses the whole of its bandwidth to transmit a single digital signal:
multiple simultaneous transmissions are therefore not possible.

Baud:
A measurement of digital signalling speed, often (and wrongly) used interchangeably with bits per second (bit/s) to specify the data-throughput rate of a modem. Strictly speaking, the two are equivalent only when one discrete signalling condition (baud) is used to represent one bit of data: this is true at low speeds only (under 300 bit/s); at higher speeds, several bits of data are encoded in a single baud. The distinction will be visible to most people as a difference in the computer's setting for 'baud rate' and 'bit rate'.

Bending radius:
minimum radius a cable can be bent without permanent damage.

Binary:
A number system which uses two digits only, typically 0 and 1, in comparison with the decimal system which has ten digits, 0 to 9. All digital computers use various binary codes to represent numbers, characters, etc.

Bit Error Rate (BER):
On a digital link, the percentage of received bits that are in error relative to the total number of bits received; a measure of network performance.

Bit/s:
A single-digit binary number, taking the value 0 or 1. The smallest unit of computerised data. The word is a contraction of 'binary digit'. Bit/s is a unit of measurement in digital transmission, indicating the number of bits transmitted per second.

Bit:
A single-digit binary number, taking the value 0 or 1. The smallest unit of computerised data. The word is a contraction of 'binary digit'. Bit/s is a unit of measurement in digital transmission, indicating the number of bits transmitted per second.

Block:
devices used for interconnection of cables.

Bonding:
a permanent electrical connection.

Bridge:
A device that connects two separate networks - usually LANs - allowing them to exchange traffic as if they were a single network.

Bridging Amplifier or Bridger:
An amplifier which is connected directly into the main trunk of a CATV system but isolated from it. It provides service into the distribution or feeder systems.

Broadband Integrated Services Digital Network. (B-ISDN):
Broadband Integrated Services Digital Network. The proposed high-speed version of ISDN. Based on ATM technology, B-ISDN will transmit traffic - including data, voice and video - at speeds of 155 Mbit/s and

Broadband:
A general term used to describe wide bandwidth equipment or systems which can carry a large proportion of the electromagnetic spectrum. A Broadband communications system can accommodate all broadcast and many other services.

Broadcasting Standards Council (BSC):
Statutory body concerned with broadcast portrayal of violence, sexual conduct and matters of taste and decency. Also conducts research and considers consumer complaints.

Broadcasting:
Transmitting electromagnetic signals in a multidirectional pattern over the air.

Browser:
Software that allows users to communicate with World-Wide Web sites; hence, a particular type of client.

Bulletin board:
A place on a network where electronic messages can be posted and read. Especially popular on Usenet, enabling worldwide 'newsgroups' to exchange information on topics of interest.

Bus:
a network where all computers are connected by a single (usually coax) cable. Bus architecture can also be implemented with a hub and star configuration.

Byte:
A group of bits representing a single character. Usually, there are 8 bits to 1 byte.


C
CATV Penetration:
The ratio of the number of subscribers to the total number of households passed by the cable system. Penetration is the basis of a system's profitability.

CATV:
The term CATV originally indicated Community Antenna TV - a cable system covering a whole community. The term is now used to define all Cable television systems in the country.

CCTV:
closed circuit television, commonly used for security.

Cable Communications Association (CCA):
The cable industry trade body representing the interests of companies providing cable communications in the UK.

Cable TV:
Previously called Community Antenna Television (CATV). A communications system which distributes broadcast programs and original programs and services by means of coaxial cable.

Cable tray:
a channel system used to hold and support communications cables.

Call Line Identification (CLI):
An electronic identifier transmitted in the call signal that identifies the number of the telephone making the call.

Capacitance:
A measure of the ability of two conductors to store electric charge.

Carriage:
A cable system's procedure of carrying the signals of television stations on its various channels. CRTC rules determine which signals cable systems must or may carry.

Category 3:
the UTP cable specified for signals up to 16 MHz. But commonly used for telephones.

Category 4:
the UTP cable specified for signals up to 20 MHz, but not commonly used for structured wiring systems.

Category 5:
the UTP cable specified for signals up to 100 MHz, commonly used for all LANs.

Cell relay:
A generic term for technologies such as ATM, in which the data to be transmitted is organised into fixed-length units (cells). Uniform cell size enables high-speed transmission and switching of voice, video and data traffic.

Characteristic impedance:
The terminal impedance that a transmission line tends towards as its length tends to infinity.

Client-server computing:
On a network, an efficiency-enhancing division of labour between computers. The 'back-end' server stores and manages data; the 'front-end' client - usually a PC or workstation - accesses and processes it. The arrangement maximises the availability of a shared resource, such as a database: many clients can be connected simultaneously; server response times are optimised because all processing occurs at the desktop.

Client:
Software that requests actions from a server program running on another computer; a computer on which such software has been installed. Each type of server requires a specific kind of client. The client required for accessing the World-Wide Web is called a browser.

Closed Circuit:
A system of transmitting TV signals in which the receiving and originating equipment are directly linked by cable, microwave or telephone lines, without broadcasting through the air.

Coax:
a type of cable that uses a central conductor, insulation, outer conductor/shield and jacket, used for high frequency communications like CCTV or CATV.

Coaxial Cable:
Copper or copper-sheathed aluminum wire surrounded by an insulating layer of polyethylene foam, used by CATV systems. The insulating layer is covered with tubular shielding composed of tiny strands of braided copper wire, or a seamless aluminum sheath, and protective outer skin. The wire and the shielding react with each other to set up an electromagnetic field between them. This system reduces frequency loss and gives cable its great signal-carrying capacity.

Coaxial line:
A transmission line in which one conductor is located at the centre of a metal tube which acts as the second conductor.

Common mode conversion ratio:
A measure of the balance of the two conductors of a pair with respect to earth.

Compression:
An undesired decrease in amplitude of a portion of the composite video signal relative to that of another portion. Also, a less than proportional change in output of a circuit for a change in input level. For example, compression of the sync pulse means a decrease in the percentage of sync during transmission.

Conductance:
The real (non-reactive) part of the admittance of a circuit, where admittance is the reciprocal of impedance.

Conducted interference:
Interference that occurs because of inductive or capacitive coupling.

Conductor losses:
Power losses due to the resistance of conductors.

Connector:
the attachment on the end of a cable that allows interconnection to other cables.

Copper losses:
Power losses due to the resistance of copper conductors.

Crimper:
a tool used to install plugs on cable.

Critical Distance or Cable Length:
The length of a particular cable which causes a worst-case reflection if mismatched; depends on velocity of propagation, attenuation of cable, and frequency.

Cross-Modulation:
A form of signal distortion in which modulation from one or more r-f carrier(s) is imposed on another carrier.

Crossed pair:
a pair of wires in a UTP cable that have two pairs cross-connected in error.

Crosstalk attenuation:
See Crosstalk Ratio.

Crosstalk distance:
The decibel difference between the level of a wanted signal on a transmission line and an unwanted signal caused by crosstalk.

Crosstalk ratio:
The ratio of crosstalk signal level to the level of the originating source of the crosstalk.

Current loop:
transmission using variable current to carry information, like a simple analog telephone.

Customer Connectivity Services:
Customer Connectivity Services are a range of managed services that comprise a combination of Bandwidth Connectivity Services, Virtual Connectivity Services, LAN based technologies and network management. They support both National and Global customer applications.

Cutoff Frequency:
That frequency beyond which no appreciable energy is transmitted. It may refer to either an upper or lower limit of a frequency band.


D
DWV:
Abbreviation for drain, waste and vent.

Data compression:
Various techniques for reducing the number of bits needed to represent information.

Data mirroring:
A technique whereby files saved on one computer are simultaneously copied to a remote - or 'mirror' - site; if anything happens to the original, the duplicate remains available. It is used as a security measure to protect data in the event of corruption, inadvertent deletion or disaster. Where the data is accessed by a large user base - as on the Internet - it is also a form of demand management, reducing pressures on the main site.

Data:
As normally used in the communications industry, anything transmittable other than audio voice signals or TV video signals. The term includes: characters - the individual letters and figures in a text message - graphics. It does not include: a telephone conversation, broadcast television or facsimile (the characters in a fax message are not separately encoded; fax, confusingly, is classified as a voice service).

Decibel:
A logarithmic unit used for expressing the ratio of two powers.

Delay Distortion:
Distortion resulting from nonuniform speed of transmission of the various frequency components of a signal; i.E., The various frequency components of the signal have different times of travel (delay) between the input and the output of a circuit.

Dial tone:
the tone heard in a phone when the receiver is picked up, indicating the line is available for dialing.

Dial-up:
Connection to a data network over the telephone line.

Dielectric losses:
Power losses due to the conductance of dielectric materials.

Dielectric:
A material which acts as an electrical insulator.

Digital Compression:
A technique that enables a given message, such as a television picture, to be converted from an analogue signal to a digitised code of data that occupies a smaller amount of transmission capacity than the original analogue signal. This technique can effectively increase the amount of usable spectrum currently allocated and expand the number of available channels on cable TV systems.

Digital:
A term used to describe a signal represented by two digits - usually 0 or 1 - during transmission; commonly contrasted with an analogue signal, whose value varies continuously. Digital transmission methods transport a computer's two-value (binary) language, dispensing with the need for a modem to translate between them. Conversely, human speech and other analogue signals do require conversion. The benefits of digital transmission include high bandwidth and virtually error-free communications.

Directional Coupler:
A high-quality tapping device providing isolation between tap and output terminals.

Distortion:
The departure, during transmission and amplification, of the received signal wave form from that of the original transmitted wave form.

Distribution Plant:
The hardware of a cable system -- amplifiers, trunk cable and feeder lines, attached to utility poles or fed through underground conduits like telephone and electric wires.

Distribution media:
types of wire used to link Network equipment (telephone, PC, terminal) to the main Intellipath system or local area network (LAN). Various types of media may be used in one Distribution System.

Domain name:
A logical grouping, used to organise networked computers. On the Internet, the highest-level domain is the country; sub-domains, listed to the left and separated by dots, work through an increasingly specific hierarchy in order to identify a unique location, known as the 'domain name'. Reading from right to left is analogous to reading from the bottom to the top line of a postal address.

Domain:
A logical grouping, used to organise networked computers. On the Internet, the highest-level domain is the country; sub-domains, listed to the left and separated by dots, work through an increasingly specific hierarchy in order to identify a unique location, known as the 'domain name'. Reading from right to left is analogous to reading from the bottom to the top line of a postal address.

Downstream:
Signals travelling from the headend to subscriber's homes.

Duplex:
A transmission system that allows data to flow in two directions simultaneously.


E
E1:
The European standard for digital transmission at 2.048 Mbit/s, over thirty-two 64 kbit/s channels.

EIA/TIA 568 standard:
a voluntary standard developed by vendors to insure interoperability of equipment used on network cabling.

EIA/TIA:
Electronics Industry Association/Telecommunications Industry Association, a vendor-based group that writes interoperability standards for communications and electronics.

ETV (Educational Television Station):
A noncommercial television station primarily devoted to educational broadcasting.

Echo (or Reflection):
A wave which has been reflected at one or more points in the transmission medium, with sufficient magnitude and time difference to be perceived in some manner as a wave distinct from that of the main or primary transmission. Echoes may be either leading or lagging the primary wave and appear on the picture monitor as reflections or "ghosts.&Quot

Electrical screen:
A metal shield which isolates a device from external fields.

Electromagnetic Spectrum:
A continuous range of frequencies of electromagnetic radiation (i.E., Oscillating electrical and magnetic energy which can travel through space). Within the spectrum, waves have some specified common characteristics; the TV broadcast spectrum, for instance, ranges from 45 to 890 MHz. (See Frequency)

Electromagnetic compatibility:
The capability of different electrical systems to coexist in the electromagnetic environment without causing or being subjected to interference.

Electronic Data Interchange (EDI):
The transmission of data between computers belonging to different organisations, in a mutually agreed format. EDI is commonly used as an adjunct to Just-in-Time management techniques: when inventory levels recorded in a database fall below a certain threshold, an electronic request for new parts is automatically sent to the supplier's order-entry system. Speed and the minimisation of administrative overheads are key EDI advantages.

Electronic mail (E-mail):
Messages, usually text, sent from one person to another, or from one person to many, via computer. The recipient does not need to be physically present or connected to the network at the time of transmission.

Encoding:
The conversion of data into a particular form for a particular purpose. In relation the Internet, a way of converting files into a form that can be sent as e-mail. Internet e-mail follows the ASCII standard. ASCII characters are represented by seven bits; computer programs - including spreadsheet and word-processing packages - use eight-bit codes. Such programs thus extend the number of characters and formatting options beyond what ASCII can handle. Encoding techniques get around the problem. They involve separating and regrouping the number of bits so that the binary output from a computer program can be coded as basic ASCII for transmission purposes, and restored to its original form at its destination.

Encryption:
For security purposes, a way of encoding data to prevent unauthorised use.

Enterprise network:
A term coined by IBM to describe a private network linking sites within a company. An enterprise network is distinguished from a wide area network (WAN) in that it is completely private and confined to a single organisation.

Error detection:
Various techniques for detecting, but not correcting, errors in transmitted data. They usually involve sending 'check' information along with the content-bearing data - for instance, the addition of a 'parity' bit indicates whether a byte should sum to an odd or an even number.

Ethernet:
A baseband system supporting data transmission at speeds typically up to 10 Mbit/s; widely used to connect computers on a LAN.

European Telecommunications Standards Institute (ETSI):
An autonomous organisation responsible for standards writing activities within Europe.


F
FDDI:
Fiber Distributed Data Interface. An American National Standards Institute (ANSI) standard for fiber-based token ring physical and data link protocol that operates at 100Mbps data transfer rate.

Far end crosstalk ratio:
Crosstalk measured at the far end of a transmission line.

Far field:
The electromagnetic field which exists at a distance of several wavelengths from the source of radiation.

Feeder Line:
Intermediate cable distribution lines that connect the main trunk line to the smaller house drops that lead into residences.

Fiber optic cable:
thin glass filaments that transmit signals as very high-frequency light pulses.

Fibre Distributed Data Interface (FDDI):
A standard for transmitting data over optical fibres at 100 Mbit/s; typically used for high-speed backbone connections between LANs and MANs.

File Transfer Protocol (FTP):
A method for transferring files between computers. Often used on the Internet for downloading software or data files.

Filter:
A circuit that selects the frequency of desired channels. Used in trunk and feeder lines for special cable services such as two-way operation.

Firestop:
restore a fire rated partition to it's fire rating after penetration with cabling,

Firewall:
A combination of hardware and software used to separate a LAN into two or more parts for security purposes. Firewalls are like sentry-posts: they check a user's credentials before granting access to the 'defended' part of the network, allowing only authorised users to enter. They are increasingly used by companies wishing to give secure remote access to corporate resources - for example, by off-site employees, suppliers, and, in some cases, customers. The firewall is also the bastion that hackers attempt to breach.

Frame:
One complete picture consisting of two fields of interlaced scanning lines.

Frequency Response:
The change of gain with frequency.

Frequency:
The number of times an electromagnetic signal repeats an identical cycle in a unit of time, usually one second. One Hertz (Hz) is one cycle per second. A KHz (Kilohertz) is one thousand cycles per second; a MHz (Megahertz) is one million cycles per second; a GHz (Gigahertz) is one billion cycles per second.


G
GSM:
Data services which are accessible over cellular telephone networks. Primary users include on-the-road staff such as sales reps and service engineers. Access normally involves attaching a modem and computer (palmtop or laptop) to the mobile handset, although integrated equipment is becoming increasingly available. Digital transmission is regarded as inherently more reliable than analogue. The two dominant digital systems in Europe are: GSM networks, which operate to the Global System for Mobile communications standard; and the GSM-compliant services offered by Personal Communications Network (PCN) operators.

Gain:
A measure of amplification expressed in dB. For matched CATV components. Gain of an amplifier is usually specified at the highest frequency of operation, for example, at Channel 13 of all-band equipment.

Gateway:
An interface between two dissimilar networks or systems, providing inter-system communication which is transparent to the user. A gateway differs from a bridge or router in the greater complexity of the operations it performs.

Gigabit/s:
1 Gigabit/s = 1,000 Mbit/s/s

Gigahertz (GHz):
Frequency of one billion cycles per second. 1 GHz = 1,000 MHz.

Global Digital System for Mobile Communications (GSM):
International system for digital cellular communications. Operates at 900 MHz i.E. The new Cellnet and Vodafone networks.

Ground loop:
the flow of current caused by unequal ground potentials.

Ground:
a connection between a circuit or equipment and the earth.

Group Delay:
Delay of colour components to picture components of signal caused by movement through device which has non-linear frequency response components; i.E., Inductors and capacitors.


H
Half duplex:
A transmission system that allows data to flow in two directions, but not at the same time.

Hardware:
The equipment involved in production, storage, distribution or reception of electronic signals. In CATV it means the headend, the coaxial cable network, amplifiers, the television receiver and production equipment like cameras and videotape recorders.

Harmonic Distortion:
Form of interference involving the generation of harmonics according to the frequency relationship f = nf1 for each frequency present, where n is a whole number equal to 2 or more.

Headend:
Electronic control center -- generally located at the antenna site of a CATV system -- usually including antennas, preamplifiers, frequency converters, demodulators, modulators and other related equipment which amplify, filter and convert incoming broadcast TV signals to cable system channels.

High Definition Television (HDTV):
The transmission of a TV signal using a greater density of pixels (picture dots) than normal TV (1125 lines of signal against the regular 800), allowing the transmission of a much sharper picture.

High VHF Band:
Part of the frequency band which the CRTC allocates to VHF broadcasting, including channels 7 through 13, or 174 through 216 MHz.

Horizontal crossconnect:
connection of horizontal wiring to other equipment or cabling.

Horizontal distribution (also called station wiring):
wires connecting the station outlet (jack) to the IDF.

Horizontal:
cable that runs from a device to the communications closet.

House Drop:
The coaxial cable that connects each building or home to the nearest feeder line of the cable network.

HyperText Markup Language. (HTML):
A coding language that determines the look of documents on the World-Wide Web.

HyperText Transport Protocol. (HTTP):
The protocol for moving hypertext files across the World-Wide Web.

Hypertext:
Any electronically stored text that contains links to other documents. When selected, the link - or hotspot - retrieves and displays related information, enabling readers to structure an enquiry according to their own interests and knowledge level. Information on the World-Wide Web is in hypertext format.


I
I.D.:
Abbreviation for inside diameter. All pipes are sized according to their inside diameter.

IEC:
International Electrotechnical Committee, oversees international communications standards.

IEEE:
Institute of Electrical and Electronics Engineers, professional society that oversees most network standards.

IP number:
The unique number that identifies any machine on the Internet. It is the form of the domain name used by the Internet itself for handling traffic.

ISO:
International Standards Organization, oversees international standards.

Impedance matching devices:
a type of balun that matches impedance between tow cables.

Impedance:
The complex ratio of voltage to current.

Impulse Pay-Per-View (IPPV):
Impulse Pay-Per-View

Inductance:
The property of a conductor whereby a voltage is induced into it as a result of a changing current.

Insertion Loss:
Additional loss in a system when a device such as a directional coupler is inserted; equal to the difference in signal level between input and output of such a device.

Integrated Services Digital Network Integrated Services Digital Network (ISDN):
A public, digital network which allows multimedia traffic - voice, data, video, graphics, music, etc. - To be carried over a single transmission path. There are two forms of access. Basic Rate Access, which provides two 64 kbit/s traffic-bearing lines, plus one 16 kbit/s line (known as the D channel) for call-management and signalling information; and Primary Rate Access, which provides thirty 64 kbit/s traffic-bearing lines, plus 64 kbit/s lines for call-management and signalling information. Basic Rate Access is possible over copper-wire telephone lines. ISDN lines can be combined - or multiplexed - in order to support transmission above the 64 kbit/s base rate: 128 kbit/s on Basic Rate Access; up to 1.92 Mbit/s on Primary Rate Access. As a digital service, ISDN does away with the need for a modem.

Interface:
In relation to human communication with a computer, the appearance of the screen via which the interaction occurs. Also:
the boundary between two devices or programs in a transmission path. At an interface, the circuitry and/or software routine is standardised so as to allow information to pass from one device to the other. The interfaces themselves must be compatible for standardisation to occur.

Interference:
Energy which tends to interfere with the reception of the desired signals, such as fading from airline flights, r-f interference from adjacent channels, or "ghosting" from reflecting objects such as mountains and buildings.

Intermodulation Distortion:
Form of interference involving the generation of interfering beats between two or more carriers according to the frequency relationship f = nf1 ± mf2, where n and m are whole numbers (but not zero), with appropriate expansion for additional carriers.

Internet:
a worldwide network of computers that allows communications from computers.

Intranet:
Offering similar facilities to the Internet, an intranet is distinguished by its restriction to a closed group of users - for example, within the same company. Intranets generally use software designed for the World-Wide Web. Current interest focuses on facilitating authorised access to the intranet - for off-site staff, etc. - But security remains an issue (see also The Internet).


J
Jacket:
the outer protective covering of a cable.

Java™:
A programming language developed by Sun Microsystems. Applications written in Java run on any computer and under any operating system, contributing to its widescale adoption on the Internet. Applets - JavaTM mini-programs - can be embedded in World-Wide Web pages to add special functions such as animation and calculation.

Jumper Cable:
Short length of flexible coaxial cable used in older CATV systems to connect system coaxial cable to amplifiers or other CATV components; they have no place in a modern, high quality system. The automotive equivalent will be required to restart the hearts of telco Internet project managers when we launch Internet over cable.


K
KBit/s:
1,000 Bits per second i.E. 64 KBit/s for digital voice.

Kilobit (kbit):
A kilobit is roughly one thousand (precisely 1,024) bits; kbit/s is a unit of measurement in digital transmission, indicating the number of kilobits transmitted per second.

Kilohertz (KHz):
1 kHz is equal to a thousand Hertz (frequency cycles) per second.


L
LAN:
local area network, a group of computers and peripherals set up to communicate with each other.

Leased line:
Also known as a private circuit, is a communications link between two points. It is separate from the public telephone network, reserved exclusively for the use of the owner, and rented at a fixed tariff regardless of usage levels. Private circuits are commonly used where inter-site traffic volumes indicate a cost-benefit advantage over switched alternatives; where there is a requirement for high bandwidth; or where reliability and availability are critical considerations, as in financial trading.

Local Area Network. (LAN):
A network linking together computers, printers and related devices, usually over a short distance (less than 1 km) and normally within a single building or site. A LAN allows all users on the network to share resources, optimising efficiency and avoiding unnecessary duplication of assets or effort. Separate from the public network, a LAN can support high transmission speeds - typically between 1 Mbit/s and 16 Mbit/s.

Local loop:
the interconnection of telephone central offices in a small region.

Longitudinal mode:
A propagation mode in which the two conductor of a pair act as a single conductor.

Loop resistance:
measurement of the resistance of both wires in a pair measured from one end with the other end shorted.

Low VHF Band:
The part of the frequency band allocated by the FCC for VHF broadcast television, including television channels 2 through 6, or 54 through 108 MHz.


M
Main Trunk:
The major link from the headend to feeder lines.

Mayer method:
A method of evaluating the propagation delay of a transmission line.

Megabit (Mbit):
A megabit is roughly one million (precisely 1,048,576) bits; Mbit/s is a unit of measurement in digital transmission, indicating the number of megabits transmitted per second.

Megabyte:
A megabyte is roughly one million (precisely 1,048,576) bytes; it will be most widely familiar as the unit of measurement of a computer's memory or storage capacity.

Megahertz (MHz):
Frequency of one million cycles per second. 1MHz = 1,000 kHZ.

Messenger cable:
the aerial cable used to attach communications cable that has no strength member of its own.

Metropolitan Area Network. (MAN):
A group of LANs with high-speed, seamless interconnection within a 'metropolitan' area. The latter is not necessarily a city; it normally means any area which is spread out but in some sense a single entity: for instance, two company buildings on opposite sides of the road or on a large site.

Microcom Networking Protocol. (MNP):
A series of protocols supporting error control and data compression for asynchronous modem transmission.

Microsecond:
One millionth of a second.

Microwave:
Line-of-sight, point-to-point transmission of signals at high frequency. Many CATV systems receive some television signals from a distant antenna location with the antenna and the system connected by microwave relay.

Mismatch loss:
The loss of power delivered into a load as a result of the interconnection of devices having unequal impedances

Mobile data:
Data services which are accessible over cellular telephone networks. Primary users include on-the-road staff such as sales reps and service engineers. Access normally involves attaching a modem and computer (palmtop or laptop) to the mobile handset, although integrated equipment is becoming increasingly available. Digital transmission is regarded as inherently more reliable than analogue. The two dominant digital systems in Europe are: GSM networks, which operate to the Global System for Mobile communications standard; and the GSM-compliant services offered by Personal Communications Network (PCN) operators.

Modem:
A device connected to a computer and a telephone line so that computers can communicate over the telephone network. The modem converts the computer's digital signal into sound, enabling transmission over an analogue path; the process is reversed when receiving data. The faster the modem, the quicker the rate of data throughput, the shorter the phone call and the lower the bill.

Modulator:
The electronic equipment required to combine video and audio signals from a studio and convert them to radio frequencies (r-f) for distribution on a cable system. Also, a very low-powered television signal generator used to provide signals for distribution on a CATV system.

Motion Pictures Expert Group (MPEG 1):
The original standard used mainly in the USA with 1.554 Mbits/s over copper.

Motion Pictures Expert Group (MPEG 2):
Following from MPEG 1, further research resulted in the MPEG 2 standard giving high quality pictures with capacity for variable bandwidth in the future.

Motion Pictures Expert Group (MPEG):
A standards body to develop international standards for compressed video transmission.

Multiplexer:
A device that can combine several communications channels over a single line. The channels are then separated by a similar device (a demultiplexer) at the other end of the link. Multiplexing optimises the use of available bandwidth.


N
NEC:
National Electrical Code, written by NFPA, sets standards for fire protection for construction.

NEXT:
near end crosstalk, measure of interference between pairs in UTP cable.

Near end crosstalk ratio:
Crosstalk measured at the transmit end of a transmission line.

Near field:
The electromagnetic field that exists within one wavelength of a source of radiation.

Neper:
A logarithmic unit used for expressing the ratio of two voltages.

Netiquette:
What's cool behaviour and what's not on the Internet.

Network analyser:
A measuring instrument for evaluating the complex characteristics of linear electrical circuits.

Nodes:
Positions on a network where transmission paths are interconnected. The term is sometimes used to refer simply to a networked workstation, terminal or digital switchboard (PBX).

Noise Figure:
A measure of the noise in dB generated at the input of an amplifier as compared with the noise generated by a 75-ohm resistor.

Noise:
The word "noise" is a carryover from audio practice. Refers to random spurts of electrical energy or interference. May produce a "salt-and-pepper" pattern over the picture. Heavy noise sometimes is called "snow.&Quot

Nominal velocity of propagation (NVP):
that speed of signal travel in the cable, expressed relative to the speed of light.


O
O.D.:
Abbreviation for outside diameter.

Optical fibre:
A thin, flexible glass fibre over which digitally encoded data is transmitted as pulses of light, giving high rates of data throughput, enhanced security and virtually error-free transmission.

Outsourcing:
The transfer of a business function and its resources to a third-party supplier who then sells back the function as a service.


P
POTS:
plain old telephone service.

PVC (Poly-vinyl chloride):
type of cable used in areas with non-plenum ceilings. The minimum type of PVC required is: UL-listed CMR/CMP semi-rigid PVC.

Packet:
Data which has been grouped into short, fixed-length 'chunks' for transmission. Each packet carries a header - defining its destination - control information and, during transmission, content-bearing data.

Page:
That part of the Internet whose servers operate to the HyperText Transport Protocol (HTTP). The World-Wide Web supports the presentation and distribution of information in multimedia form - as integrated text, graphics, video and audio - and allows users to identify and display associated information by means of embedded hypertext links. A World-Wide Web site is a place where information belonging to an individual or organisation is located. It is generally entered through the home page. A site may be divided into a number of pages, each with a separate URL, and each covering a different aspect of the information held on the site as a whole. In the terms of conventional publishing: a site can be thought of as a book; the home page is its table of contents; and the pages are equivalent to chapters. The World-Wide Web is the fastest growing part of the Internet: 3 million new pages were created in the 18 months to September 1995. Commercial uses include advertising, marketing, market research, retailing, distribution. Current initiatives are focused on developing encryption techniques to support secure monetary transactions.

Passive Device:
A circuit or network not using active devices such as tubes to transistors.

Pay-Per-View (PPV):
Payment made for specific cable programmes as opposed to a subscription for a whole channel or group of channels. An event or movie is transmitted on a specified channel for which access has to be specifically authorised by the cable operator in return for a fee. Requires system links between set-top, head-end operations and billing computers which are not always available in older systems.

Plain Old Telephone Service (POTS):
Colloquial term for basic voice services.

Plenum:
the air carrying portion of a heating or air conditioning system that can be used for running communications cables. Also a type of cable used in plenums, specially rated by the NEC.

Point of Presence (POP):
A location from which a network can be accessed, mostly for dial-up usage. POP location is an important consideration for Internet users: where an Internet Access Provider or Internet Service Provider has a local POP, calls are charged at the same rate as a local telephone call; where the nearest POP is in another city, long-distance telephony charges will normally apply.

Point-to-Point Protocol (PPP):
An addition to the TCP/IP Internet protocol suite that enables devices - such as modems - to communicate despite dissimilarities.

Power Sum NEXT:
Near end crosstalk tested with all pairs but one energized to find the total amount of crosstalk caused by simultaneous use of all pairs for communication.

Private circuit:
Also known as a leased line, a private circuit is a communications link between two points. It is separate from the public telephone network, reserved exclusively for the use of the owner, and rented at a fixed tariff regardless of usage levels. Private circuits are commonly used where inter-site traffic volumes indicate a cost-benefit advantage over switched alternatives; where there is a requirement for high bandwidth; or where reliability and availability are critical considerations, as in financial trading.

Propagation coefficient:
The complex factor which resolves into the attenuation and phase coefficients of a transmission line.

Propagation delay:
The time required for a signal to pass along a transmission line

Propagation velocity:
The velocity of wave propagation along a transmission line.

Proximity effect:
The redistribution of current in a conductor brought about by the proximity of another conductor.

Public Telecommunications Operator (PTO):
General term to cover any licensed national telecoms operators.


Q
Quad:
A series of four separately insulated conductors, generally twisted together.

R
RJ-45:
a modular 8 pin connector, actually referring to a specific telephone application, but usually referring to the connector used in EIA/TIA568 standard.

Reflections or Echoes:
In video transmission this may refer either to a signal or to the picture produced. 1. Signal: a) Waves reflected from structures or other objects. B) Waves which are the result of impedance or other irregularities in the transmission medium. 2. Picture: "Echoes" observed in the picture produced by the reflected waves.

Resistance unbalance:
A measure of the inequality of the resistance of the two conductors of a transmission line.

Resistance:
The real (non-reactive) part of the impedance of a circuit.

Return loss:
The difference between the power incident upon a discontinuity in a transmission system and the power reflected from the discontinuity.

Reversed pair:
a pair of wires in a UTP cable that have the two wires cross-connected in error.

Ring:
a network where computers are connected in series to form a ring. Each computer in turn has an opportunity to use the network.


S
STP:
shielded twisted pair cable, where each pair has a metallic shield to prevent interference.

ScTP:
screened twisted pair cable, UTP cable with a outer shield under the jacket to prevent interference.

Screening attenuation:
The decibel difference between the signal level present at the input of a device, and the radiated power originating from the device.

Screening:
See Electrical Screen.

Second Harmonic:
A second order beat whose two beating carriers have the same frequency.

Second Order Beat:
An unwanted carrier created by two separate carriers beating against each other. These beating carriers may have the same or different frequencies.

Secondary coefficients:
Attenuation and phase coefficients and characteristic impedance of a transmission line.

Shorted pair:
a pair of wires in a UTP cable that are electrically connected in error.

Signal Level:
The rms voltage measured during the r-f signal peak. It is usually expressed in microvolts referred to an impedance of 75 ohms, or in dBmV, the value in decibels with respect to a reference level of 0 dBmV, which is 1 millivolt across 75 ohms.

Signal-to-noise Ratio:
The ratio of the signal to noise level with both measured either at the input or output of electronic equipment, usually expressed in dB.

Simplex:
A transmission system that allows data to flow in one direction only.

Skin effect:
The tendency of alternating currents to increasingly flow nearer the surface of a conductor as frequency increases.

Slope-compensation:
The action of a slope-compensated gain control, whereby slope of amplifier equalization is simultaneously changed with the gain so as to provide the correct cable equalization for different lengths of cable; normally specified by range and tolerance.

Slope:
Difference in amplifier gain, or change in cable attenuation, between lowest and highest frequency present.

Snail Mail:
Letters sent through the postal service; the opposite of e-mail.

Spacing:
Length of cable between amplifiers expressed as dB loss at the highest TV channel provided for in a system, equal to amplifier gain in main trunks.

Span:
Distance between line extenders or distribution amplifiers; also, distance between taps.

Split pair:
a pair of wires in a UTP cable that have the two wires of two different pairs cross-connected in error.

Splitter:
A passive device (one with no active electronic components) which distributes a television signal carried on a cable in two or more paths and sends it to a number of receivers simultaneously.

Structural return loss:
A measure of the uniformity of a transmission line's impedance.

Structured cabling:
a method of installing cable per industry standards to allow interoperability among vendors and upgrades.

Subscriber loop:
connection of the end-user to the local central office telephone switch.

Subscriber:
A person who pays a fee for cable services.

Super Band:
The frequency band from 216 to 600 MHz, used for fixed and mobile radios and additional television channels on a cable system.

Switched, switching:
A service, or a technique, used to relay traffic over a network. Often described as 'point to multipoint', a switched service allows a call originating at any point on the network to be connected to any other point; intermediate points on the networks - 'exchanges' in traditional voice telephony - set up and maintain the link, which remains open only for the duration of the call. By contrast, a private or leased connection remains available all the time - whether or not it is being used - connects two sites only, and is reserved from public use.

Synchronous Digital Hierarchy (SDH):
New international standard for high speed wideband transmission systems. SDH allows varying capacity to be flexibly allocated according to customer requirements. The fibre-optic ring around NYNEX northern franchises is operated on an SDH platform.

Synchronous transmission:
A method of transmitting data. The transmitter and receiver are synchronised: that is, they pre-arrange when to start and end their communication; transmission must occur at a fixed rate within that time-slot.

System Noise:
Refers to the random energy generated by thermal and shot effects in the system. It is specified in terms of it rms level as measures in a 4 MHz bandwidth centred within a 6 MHz cable television channel.


T
T1:
A US and Japanese standard for digital transmission at 1.544 Mbit/s, over twenty-four 64 kbit/s channels; a separate 8 kbit/s channel handles control information used by the network.

Tee:
A T-shaped fitting with three openings used to create branch lines.

Teflon:
material required as a casing for cables in areas with plenum ceilings.

Telecommunication Industry Association (TIA):
National trade body representing the telecommunications industry involving the manufacturers, suppliers, service providers and operators.

Telegraph:
earliest form of long-distance communications, using coded letters.

Telephone:
a voice instrument for communications.

Terminal adapter:
A device which converts signals from a piece of communications equipment into a format suitable for transmission on a given network. For example, an ISDN terminal adapter does for analogue hardware (non-ISDN handsets, answering machines, fax machines, etc.) Much the same as what a modem does for the computer: translates - in this instance, from analogue to digital.

Terminal equipment:
telephones, data communication equipment, and peripherals used at station locations.

Terminal wiring:
wires connecting network equipment (PC, telephone, or terminal) to the jack on the wall.

Terminal:
A device for sending and receiving data on a communications channel; intelligent processing functions are performed on the host computer, while the terminal itself simply allows the user to connect, key in command sequences, see results screens, etc. Terminal-emulation software enables a PC to masquerade as a terminal belonging to a particular host.

The Internet:
The Internet is a near-global collection of computer networks and gateways which are able to function as a single network, using the TCP/IP protocol. Services include e-mail, file transfer and bulletin boards; multimedia information - text, graphics, video and sound - can be distributed over the World-Wide Web. The number of Internet hosts has doubled every year since 1989. An internet is a group of networks interconnected in such a way as to support seamless communications between them.

Third Harmonic:
A third order beat whose three beating carriers all have the same frequency.

Third Order Beat:
An unwanted carrier created by three separate carriers beating against each other. These beating carriers may have the same or different frequencies.

Time domain reflectometer (TDR):
a testing device used for cable that operates like radar to find length, shorts or opens, and impedance mismatches.

Topology:
the architecture or layout of a network, eg. Bus, ring, star.

Transmission Control Protocol/Internet Protocol. (TCP/IP):
The suite of protocols originally developed for the ARPANetTM and now used to define membership of its successor, the Internet. TCP/IP specifies how data is sent and received over a network - how it should be routed and addressed. In general usage, though, the term is convenient shorthand for all key Internet standards, and not simply those that are transmission-related.

Transmission line:
A pair of conductors separated by a dielectric.

Transverse Mode:
A propagation mode in which the two conductor of a pair carry equal and opposite currents.

Triple Beat:
A third order beat whose three beating carriers all have different frequencies, but are spaced at equal frequency separations.

Trunk Line:
The major distribution cable used in CATV. It divides into feeder lines which are tapped for service to subscribers.

Twisted pair:
A transmission line in which two insulated conductors are twisted together.


U
UHF:
Ultra High Frequencies, the range of frequencies extending from 300 to 3,000 MHz; also, television channels 14 through 83.

UTP:
unshielded twisted pair cable, comprised of four pairs of conductors carefully manufacturer to preserve frequency characteristics.

Unbalanced pair:
A transmission line in which the voltages on the two conductors are unequal with respect to earth.

Uniform Resource Locator (URL):
The form of the Internet address used on the World-Wide Web.

Upstream:
Signals travelling from subscribers to the headend.

Usenet™:
A near-global system of 'newsgroups' - around 14,000 of them - whose members discuss topics via bulletin boards. Usenet can be accessed through the Internet, although the two are distinct.


V
V Series:
A group of recommendations governing data transmission over telephone lines. The 'V' part of a modem's specification indicates what kind of transmission it supports. For example, V.32Bis means that the modem supports full duplex transmission at rates up to 14.4 Kbit/s.

VHF:
Very High Frequencies, the range of frequencies extending from 30 to 300 MHz; also, television channels 2 through 13.

VSWR:
Abbreviation for Voltage Standing Wave Ratio. Reflections present in a cable due to mismatch (faulty termination) combinewith the original signal to produce voltage peaks and dips by addition and subtraction. The ratio of the peak-to-dip voltage is termed VSWR. A perfect match with zero reflections produces a VSWR of 1.

Velocity of Propagation:
Velocity of signal transmission. In free space, electromagnetic waves travel with the speed of light. In coaxial cables, this speed is reduced. Commonly expressed as percentage of the speed in free space.

Velocity ratio:
The ratio of propagation velocity to the speed of light.

Video Band:
The frequency band utilized to transmit a composite video signal.

Video On Demand (VOD):
True VOD requires specific programmes being made available to individual customers on request. The signal is distributed digitally and is likely to require ATM switching (see below). Customer features are likely to include ëVCRí functionality (e.G. Fast forward, Rewind, Pause etc.) In real time, as well as a level of interactivity to allow educational, banking and shopping services to be developed.

Video Transmission:
The original video signal before it is modulated and converted to radio-frequency and broadcast or cablecast. A home television set reconverts radio-frequencies to a video signal.

Video:
The visual components of a television signal.

Virtual Private Network (VPN):
Virtual Private Network. A service which combines key elements of private-circuit and switched communications. Software on the public switched network defines a closed group of users, who are able to access the service on demand and pay for actual usage. A VPN supports the transmission of voice, data and image traffic.


W
Wide Area Network. (WAN):
A network allowing the interconnection and intercommunication of a group of computers. A WAN covers a larger geographical area than a LAN, and can be comprised of private circuits rented from a Public Telecommunications Operator.

Wideband:
A network that supports a number of simultaneous transmissions over a single physical link.

Wire mapping:
confirming the proper connections of all four pairs.

Wireless:
sending communications over radio waves.

World-Wide Web (WWW or Web):
That part of the Internet whose servers operate to the HyperText Transport Protocol (HTTP). The World-Wide Web supports the presentation and distribution of information in multimedia form - as integrated text, graphics, video and audio - and allows users to identify and display associated information by means of embedded hypertext links. A World-Wide Web site is a place where information belonging to an individual or organisation is located. It is generally entered through the home page. A site may be divided into a number of pages, each with a separate URL, and each covering a different aspect of the information held on the site as a whole. In the terms of conventional publishing: a site can be thought of as a book; the home page is its table of contents; and the pages are equivalent to chapters. The World-Wide Web is the fastest growing part of the Internet: 3 million new pages were created in the 18 months to September 1995. Commercial uses include advertising, marketing, market research, retailing, distribution. Current initiatives are focused on developing encryption techniques to support secure monetary transactions.


X
X.25:
A method of transmitting data whereby packets from different originators and to different addresses are all carried over the same channel, making the most of the bandwidth available at the time. Packets making up a single message may be sent in any sequence and along different routes. They get to the right place because of the addressing information included with each packet; once there, they can be re-assembled into the right order because of the control information sent at the start of, and during, transmission.

X.400:
A series of standards designed to ensure compatibility between different e-mail and other electronic-messaging systems worldwide.


Y


Z


0-9
2Mbit/s/s:
Capacity for 30 voice channels or one VCR channel

8 Mbit/s/s:
Capacity for 120 voice channels or the transmission of one sports event i.E. Football match



 
 
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