Technical Information

Here we provide some information for your reference which may be useful for you :


Organization and Standards






A device that enables, any or all of the following: 1) different sizes or types of plugs to mate with one another or to fit into a telecommunications outlet, 2) the rearrangement of leads, 3) large cables with numerous wires to fan out into smaller groups of wires, and 4) interconnection between cables.


An electronic component used to increase the strength of a transmitted analog signal. Performance is measured in deciBels (dB). Similar to a repeater in digital systems.


One of three basic methods (see also FREQUENCY and PHASE MODULATION) of adding information to a sine wave signal in which the magnitude of the signal is varied to impose information on it. ANALOG A mode of transmission in which information is represented by a continuously variable electrical signal.


A nominally continuous electrical signal that varies in amplitude or frequency in response to changes in the physical quantity (such as sound) that it represents.


A reduction in strength or deterioration of an electrical signal as it passes through a transmission medium. Attenuation generally increases with frequency, cable length and the number of connections in a circuit. Attenuation is measured in deciBels (dB). In optical fiber, a diminution of the signal as a function of length traveled.

AWG (American Wire Gauge)

A unit of measure used to describe the cross sectional area of a conductor.


A panel, usually made of plywood, fixed to a wall and used for mounting equipment.


Generally, the more permanent part of a communications network which carries the heaviest traffic. Usually a vertical arrangement that connects floors in a multi-story building. However, the same function may be served by a lateral backbone for horizontal distribution in a low-wide building.


A range of frequencies between two predetermined limits.


In electrical transmission systems, the range between the highest and lowest frequencies of a transmission channel. A measure of the information capacity of the transmission channel. Bandwidth varies with the type and method of transmission. Bandwidth is measured in Hertz (Hz, cycles per second).


A transmission method in which the entire bandwidth of the transmission medium is used to transmit a single digital signal. The signal is ascribed directly onto the transmission medium without modulation of any kind. Simultaneous transmissions can be achieved through time division multiplexing. Baseband is simpler, cheaper and less sophisticated than Broadband.


A measurement of the signaling speed of a data transmission device. The speed in baud is equal to the number of times the line condition (frequency, amplitude, voltage or phase) changes per second. If each signal event represents only one bit, then the baud rate is the same as the bit rate; if each signal event represents more than one bit, the baud rate is less than the bit rate.


The smallest unit of information (data) and the basic unit in data communications. A bit can have a value of zero or one (a mark or a space).


Bits per second. A measure of speed or data rate. Often combined with metric prefixes such as Kbps (kilo or thousands of bits per second) and Mbps (mega or millions of bits per second).


A bayonet-locking connector used to terminate coaxial cables. BNC is an acronym for Bayonet-Neill-Concelman.


1. To connect one circuit or component to another in parallel. When two single line phones share the same line they are said to be bridged.

2. The interconnection or equipment used between two networks using the same communication protocols, transmission methods and addressing structure. Compare with gateway, which connects LANs using different protocols.


A transmission facility having a bandwidth sufficient to carry multiple voice, video or data channels simultaneously. Each channel occupies (is modulated to) a different frequency bandwidth on the transmission medium and is demodulated to its original frequency at the receiving end. Channels are separated by Guardbands to ensure that each channel won't interfere with its neighboring channels. This technique is used to provide 50 CATV channels on one coaxial cable.


1. A data path shared by many devices. 2. A linear network topology in which all workstations are connected to a single cable. On a bus network, such as Ethernet, all workstations receive all transmissions; only the workstation that the information is addressed to will use the information. Contrast with ring and star.


A collection of bits operated upon as a unit, usually 8 bits long. Often used to represent one character. Also used to measure the capacity of storage devices. (1K byte = 1024 bytes)


1. A company which provides transmission services. 2. A continuous electrical signal capable of being modified to carry information. The carrier carries no information until some component of the signal (amplitude, frequency or phase) is changed. These changes convey the information. (See also Amplitude Modulation, Frequency Modulation and Phase Modulation.)

CATV(Community Antenna Television)

A method of delivering high quality television reception by transmitting signals from a central antenna throughout the community, via coaxial cable. CATV is a broadband transmission facility which generally uses a 75 Ohm coaxial cable to carry numerous frequency-divided TV channels simultaneously.

CCTV (Closed Circuit Television)

In general, a video channel which is broadcast to a limited number of locations. Often used in security applications.


Any electrical or electromagnetic communications path, either physical or logical, between two communicating units.


The impedance that an infinitely long transmission line would have at its input terminal. If a transmission line is terminated in its characteristic impedance, it will appear (electrically) to be infinitely long, thus minimizing signal reflections from the end of the line.


1. (Communications) A bi-directional communications path between two pieces of associated equipment. 2. (Power) An arrangement of conductors, devices and utilization equipment (loads) such that current will pass through them.


A type of communication transmission cable in which a solid center conductor is surrounded by an insulating spacer which in turn is surrounded by a tubular outer conductor (usually a braid, foil or both). The entire assembly is then covered with an insulating and protective outer layer. Coaxial cables have a wide bandwidth and can carry many data, voice and video conversations simultaneously.

CODEC (Coder/Decoder)

Equipment used to transform analog voice signals to digital signals (coder) and digital signals to analog signals (decoder). May be in the digital PBX or in the phone itself.


A rigid or flexible metallic or nonmetallic raceway of circular cross section in which cables are housed for protection and to prevent burning cable from spreading flames or smoke in the event of a fire.


A device used to control the input/output operations between the host computer and a group of terminals.


A facility enabling the termination of cable elements and their interconnection, and/or cross-connection, primarily by means of a patch cord or jumper.


A connection scheme between cabling runs, subsystems, and equipment using patch cords or jumpers that attach to connecting hardware on each end.


A wiring configuration that permits two DTE devices or two DCE devices to communicate.


A conductor which connects to a different pin number at each end.


The phenomenon in which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel, generally related to wire placement, shielding, and transmission techniques.


The interface equipment sometimes needed to connect the data terminal equipment (DTE) to a transmission circuit or channel. Synonymous with modem.


A private, leased line digital service offered by DATAPHONE AT&T DIGITAL SERVICE which eliminates the need for modems.


A unit for measuring the relative strength of a signal. Usually expressed as the logarithmic ratio of the strength of a transmitted signal to the strength of the original signal.


A material that is nonmetallic and non-conductive. Generally used to describe the insulating material surrounding the center conductor of a coaxial cable.


A discontinuous signal. One whose state consists of discrete elements, representing very specific information, usually on or off, one or zero.


A LAN that uses a shared communications medium (such as bus or ring LAN) and uses shared access methods.


Any form of computer equipment, peripheral or terminal capable of originating or receiving data over a communications channel.


1. (data communications) A circuit used to transmit signals simultaneously in both directions. 2. (general) Two receptacles or jacks in a common housing which accepts 2 plugs.


(Electromagnetic Interference/Radio Frequency Interference)
The interference in signal transmission or reception resulting from the radiation of Frequency Interference undesirable electrical or magnetic and electrical fields.


A baseband local area network used for connecting computers and terminals, etc., within the same building. Ethernet was marketed (and trademarked) by Xerox and developed jointly by Digital Equipment Corporation, Intel and Xerox. It is the basis for the IEEE Standard 802.3.


The technology in which communication signals in the form of modulated light beams are transmitted over a glass fiber transmission medium. Fiber optic technology offers high bandwidth, small space needs and protection from electromagnetic interference, eavesdropping and radioactivity.


The interconnection between two networks with different communications protocols.

GHz (GigaHertz)

A unit of frequency equal to one billion Hertz (1,000,000,000 Hertz).


A multimode fiber optic cable design in which the index of refraction of the core is lower toward the outside of the core and progressively increases toward the center of the core, thereby reducing dispersion of the signal.


The conductor used to connect the grounding electrode to the building's main grounding busbar.


A conductor or group of conductors (usually a rod, pipe, or plate) in direct contact with the earth, providing a low impedance connection to the earth.


Data transmission over a circuit capable of transmitting in either direction, but not simultaneously.


A preliminary procedure, usually part of a communications protocol, to establish a connection between devices.

Hz (Hertz)

A unit of frequency equal to one cycle per second.


A pathway or cable between two locations without a point of access in between.


The cabling between and including the telecommunications outlet/connector and the horizontal cross-connect.


A cross-connect of horizontal cabling to other cabling, eg. horizontal, backbone, equipment.


The central computer in a data communications system which provides the primary data processing functions such as computation, data base access, special programs or programming languages.


An assembly of 2 or more cables, of the same or different types or categories, covered by one overall sheath.


A unit of measure, expressed in Ohms, of the total opposition (resistance, capacitance and inductance) offered to the flow of an alternating current.


A connection scheme that provides for the direct connection of a cable to another cable or to an equipment cable without a patch cord or jumper.


1. A shared boundary. A physical point of demarcation between two devices where the electrical signals, connectors, timing and handshaking are defined. 2. The procedures, codes and protocols that enable two entities to interact for a meaningful exchange of information.


A cross-connect between 1st level and 2nd level backbone cabling.


A CCITT Standard, currently under development, that will cover a wide range of data communications issues, but primarily the total integration of voice and data. Already having major effects on exchange and multiplexer design.

A separate ground conductor which is insulated from the equipment or building ground.


The SI unit of energy, work, or quantity of heat. One Joule is the energy expended when a force of one newton is applied over a displacement of one meter in the direction of the force.

An assembly of twisted pairs without connectors, used to join telecommunications circuits/links at the cross-connect.


A non-public data communications network confined to a limited geographic area (usually within a few miles), used to provide communication between computers and peripherals. The area served may consist of a single building, a cluster of buildings, or a campus-type arrangement. It is owned by its user, includes some type of switching technology and does not use common carrier circuits - although it may have gateways or bridges to other public or private networks.

LASER (Light Amplification by Stimulated Emission of Radiation)

A device which produces light with a narrow spectral width. Used in fiber optic communication systems, usually single mode, where high capacity and low attenuation are required.


A private telephone line rented for the exclusive use of a leasing customer, without interchange switching arrangements.

LED (Light Emitting Diode)

A semiconductor diode which emits light when a current is passed through it. In lightwave transmission systems, LEDs or lasers are used as light sources.


A signal converter that conditions the digital signal transmitted by an RS232 interface to ensure reliable transmission beyond the 50 foot RS232 limit and often up to several miles; it is a baseband transmission device. Also called a baseband modem, limited distance modem or short haul modem.


The communications circuit or transmission path connecting two points, not including terminal equipment, work area cables, and equipment cables.


A type of diagnostic test in which a transmitted signal is returned to the sending device after passing through a data communications link or network. This test allows the comparison of a returned signal with the transmitted signal.

MHz (Mega Hertz)

A unit of frequency equal to one million Hertz (1,000,000 Hertz).


An extended LAN operating within a metropolitan area and provides an integrated set of services for real-time data, voice and image transmission.


A desktop personal computer that serves a single user.


A unit of length equal to one millionth of a meter. (.000001 meter). Short for micrometer.

MODEM (MOdulator DEModulator)

A device which converts digital signals to analog signals (and vice-versa) for transmission over the telephone network, which usually is analog.


A device used in place of the pair of modems normally needed to connect a local terminal and computer. It allows DTE to DTE data and control signal connections not easily achieved by standard cables and connectors.


The process of varying some characteristic (See Amplitude Modulation, Frequency Modulation or Phase Modulation) of the electrical carrier wave to impose information on it.


An optical fiber cable containing two or more fibers, each providing a separate information channel.


An electronic device which is used to combine several signals for transmission over one communications channel by varying the physical characteristics (frequency, amplitude or phase) or timing of the signals to prevent them from interfering with each other.


A unit of length equal to one billionth of a meter (.000000001 meter).


An interconnection of computer systems, terminals or data communIcations facilities.


A formalized definition of the structure and protocols of a computer network.


The point of interconnection between telephone company communications facilities and terminal equipment, protective apparatus or wiring at a subscriber's premises.


In general, any point of interconnection to a network where service is provided, used or communication channels are interconnected.


A device which allows the connection of two DTE devices by emulating the physical connections of a DCE device.


A group of bits, including address, data and control elements, that are switched and transmitted together.


A data transmission method whereby data is transmitted in packets through a network to a remote location. The packet switch sends packets from different data conversations along the best route available in any order. At the other end the packets are reassembled to form the original message which is then sent to the receiving computer. Because packets need not be sent in a particular order, and go any route as long as they reach their destination, packet switching networks can choose the most efficient route and send the most efficient number of packets down that route before switching to another route.


A method of transmission in which all bits of a character are sent simultaneously over separate lines to a high speed printer or other locally attached peripheral. Contrast with Serial Transmission.


A cross-connect system of mateable connectors that facilitates administration.


Computer for personal, single-user use, as opposed to main frames or mini-computers, which are shared by many users.


An uninterrupted connection between two pieces of equipment.


A functional unit of a node through which data can enter or leave a data network.


A copper foil circuit formed on one or both faces of an insulating board to which circuit components are soldered. The copper foil pattern serves to connect components and is produced either by etching or plating.


A private telephone switching system, usually located on a customer's premises connecting a common group of lines from one or more central offices to provide service to a number of individual phones. Now used interchangeably with PABX (Private Automatic Branch Exchange).


The time it takes for a signal to travel from one point on a circuit to another.


A specific set of rules, procedures or conventions that two data devices must accept and use to be able to communicate. Protocols for data transmission cover such things as framing, error handling, transparency and line control.


A network established and operated for the specific purpose of providing data transmission services to the public.


Any common carrier network that provides circuit switching between public users, such as the public telephone network, telex or MCI's Execunet.


A device inserted at intervals along a circuit to boost and amplify an analog signal being transmitted. Repeaters may also regenerate a digital signal - squaring it and cleaning it up - but not changing it. Regenerating the signal removes noise and thus reduces the likelihood of error.


The time it takes a system to react to a given input. The response time includes the transmission time, the processing time, the time for searching records and the transmission time back to the originator.


A set of standards specifying various electrical and mechanical characteristics for interfaces between computers, terminals and modems. The RS232-C standard was developed by the Electronics Industries Association (EIA), and defines the mechanical and electrical characteristics for connecting DTE and DCE data communication devices. It defines what the interface does, circuit functions and their corresponding connector pin assignments. The standard applies to both synchronous and asynchronous binary data transmission. The "Traditional" RS232-C plug has 25 pins. Functionally equivalent to CCITT V.24/V.28.


An EIA recommended standard for cable lengths that extend the RS232-C 50 foot limit and describes the electrical characteristics of balanced-voltage digital interface circuits.


An EIA recommended standard for cable lengths that extend the RS232-C 50 foot limit and describes the electrical characteristics of unbalanced-voltage digital interface circuits.


An EIA recommended standard for the mechanical characteristics of two connectors (a 37 pin connector and a 9 pin connector). Designed for higher speeds. Not widely used.

A metallic layer, usually in the form of a braid or foil, surrounding one or more electrical conductors to insulate them from electromagnetic interference.


Data transmission over a circuit capable of transmitting in one preassigned direction only.


A family of multipin data connectors used in RS232-C communications. The connectors are available in 9, 15, 25 and 37 pin configurations. Sometimes referred to as DB9, DB15, DB25 and DB37 connectors respectively.


Transmission in which the data character and bits are transmitted at a fixed rate with the transmitter and receiver being synchronized. Compare with Asynchronous Transmission.


A digital transmission link with 1.544 Mbps bandwidth. T1 operates on two twisted pairs and can handle 24 voice conversations, each digitized at 64 Kbps. More voice channels are available with advanced digital voice encoding techniques.


The AT&T digital transmission system which transmits data at 1.544 Mbps.

1. (Communications) An electrical connection permitting signals to be transmitted onto or off a bus. The link between the bus and the drop cable that connects the workstation to the bus. 2. (Power) An intermediate point in an electric circuit where a connection may be made.


A collective term referring to any DTE that can be connected to a network node that is capable of sending and receiving data over a data communication channel.


An Ethernet LAN or IEEE 802.3 LAN which uses smaller diameter coaxial cable than standard Ethernet.


A technique for combining many signals on a single circuit by interleaving bits or bytes of data from successive channels.


A method of computer operation that allows many users to use one computer. Due to the power and speed of the computer, it appears as though the users are served simultaneously, when in fact they are being served in sequence.


A threaded connector used to terminate coaxial cables. TNC is an acronym for threaded Neill-Concelman.


A unique combination of bits used in LANs to grant permission to a station to transmit. In a ring network, the token circulates continuously; in a bus it must be addressed.


The geometric description of the physical or logical connections of a telecommunications system. Typically described as bus, ring or star.


A single device capable of both sending and receiving information.


An abrupt change in voltage, of short duration, which may cause signal impairments, loss of memory or physical damage to equipment.


Anything such as wire, coaxial cable, fiber optics, air or vacuum, that is used to carry an electrical signal.


A specialized communications path between two points, one of them usually being a telephone company central office or switching center.


A type of communication transmission cable consisting of two center conductors surrounded by an insulating spacer which in turn is surrounded by a tubular outer conductor (usually a braid, foil or both). The entire assembly is then covered with an insulating and protective outer layer.


A type of communication transmission cable in which two individually insulated wires are twisted around each other to reduce induction (thus interference) from one wire to the other. The pair may be surrounded by a shield, insulating jacket or additional pairs of wires.


A cable distribution method which uses flat cables placed beneath carpeting to provide voice, data, video and power services to open office workstations.


A data communications network leased from a common carrier with extra equipment, such as an interface computer with a database or storage designed to provide additional services.


A transmission channel usually limited to the bandwidth of the human voice (300 - 3000 Hz).


A communications channel which can transmit and receive voice frequencies(300 - 3000 Hz).


The length of an electromagnetic waveform as measured from any point on one wave to the corresponding point on an adjacent wave, such as from crest to crest. Wavelength is inversely proportional to frequency.


A communications network designed to serve hundreds or thousands of miles using common carrier-provided lines, such as the nationwide telephone network.


A communications channel or medium having a bandwidth sufficient to carry multiple voice/video or data signals simultaneously.


A CCITT Standard defining the interface specifications between DTE and DCE for synchronous operation on public data networks, using a 15 pin connector.


A CCITT Standard defining the protocol between DTE and DCE for access to public packet switched networks.

Organization and Standards


ANSI -- American National Standards Institute

Non-profit organization supported by U.S. industry to establish uniformity of standards. Members include manufacturers, common carriers and other standards organizations such as the IEEE. ANSI represents the USA in the ISO. Compliance with ANSI standards is purely voluntary and, in some respects, almost identical to existing trade association standards such as NEMA, SAE, EEI, IEEE, etc. ANSI standards usually form the basis for the general direction of a UL standard.

BICSI-- Building Industry Consulting Service International

A non-profit, professional organization that promotes the economical and efficient design and implementation of communications distribution systems in commercial and multi-family buildings.

CCITT-- Comite Consultatif Internationale de Telegraphique et Telephonique

An international consultative committee that sets international communications recommendations, which are frequently adopted as standards. Develops interface, modem and data network recommendations. Private companies, scientific and trade associations, as well as member nations can participate. CCITT is part of the International Telecommunications Union (a United Nations Treaty organization in Geneva).

CSA-- Canadian Standards Association

A testing and certification agency comparable in function to UL and is primarily concerned with the safety of devices, materials and components in the electrical industry.

CSA develops standards of its own for electrical products which parallel UL standards in many aspects but are not always identical. CSA tests products and grants paying clients "certification" that their products meet CSA standards.

EIA-- Electronic Industries Association

An USA trade organization that specializes in the development of standards for the electrical and functional characteristics of interface equipment.

FCC-- Federal Communications Commission

A board of seven commissioners, appointed by the President under the Communications Act of 1934, having the power to regulate all electrical communications systems originating in the United States, including radio, television, facsimile, telegraph, telephone and cable systems.

IEEE-- Institute of Electrical and Electronic Engineers

An international professional engineering society that issues its own standards and Engineers is a member of ANSI and ISO.

ISO-- International Standards Organization

An international, non-profit standards organization whose membership includes standards organizations from participating nations. (ANSI is the USA representative)

NEMA-- National Electrical Manufacturers Association

An US industry association which standardizes specifications for electrical components and power wires and cables.

NEMA is the "voice" of the electrical industry, and through it, standards for electrical products are formulated. Generally these standards promote interchangeability between products of one manufacturer with like products made by another manufacturer.

In some cases, standards relating to product "performance" are also formulated by NEMA but these are the exception rather than the rule. NEMA standards are certainly not compulsory, but generally they are accepted by those manufacturers that help to write them as a way of making their products more saleable and acceptable.

NEMA standards are referenced by many consumers in writing specifications for the materials they purchase. NEMA standards generally form the basis for ANSI standards.

TIA-- Telecommunications Industry Association

An USA trade organization that specializes in the development of standards for telecommunications cabling and its support structures.

UL-- Underwriters Laboratories

A non-profit corporation, operating as a testing facility and developer of safety standards. UL also has the capability for testing to various industry performance specifications such as TIA/EIA, IBM and Bellcore.

By its own definition, Underwriters Laboratories defines itself as follows: "Underwriters Laboratories Inc., founded in 1894, is chartered as a not-for-profit organization without capital stock, under the laws of the state of Delaware, to establish, maintain and operate laboratories for the examination and testing of devices, systems and materials to determine their relation to hazards to life and property."

UL tests products for paying "clients" and if the product submitted passes the requirements of the UL standard for which it is submitted, a UL "listing" or "verification" is granted which allows the manufacturer to use the UL manifest or "label" on its product.

It is important to remember that UL is not an approval agency. It approves nothing, but merely lists a product as meeting its minimum standard for safety or verifies/classifies a product as meeting an industry standard for performance.

Underwriters "Listing" mark on a product is generally accepted by the public and government agencies as evidence of a "safe" product, not necessarily a "quality" product. 


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Last Updated at 22-3-1999