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ANSI American National Standards Institute

Analog Signal
An electrical signal that varies continuously without having discrete values (as with a "digital" signal).

AppleTalk
Apple Computer's networking scheme, integrated into most Apple system software, that allows Apple computing systems to participate in peer to peer computer networks and to also access the services of AppleTalk servers. See also LocalTalk.

ARCnet
Attached Resource Computer Network. A relatively low speed form of LAN data link technology (2.5 Mbps) developed by Datapoint, in which all systems are attached to a common coaxial cable. ARCnet uses a token-bus form of medium access control in which a system transmits only when it has the token

Asynchronous
Transmission where sending and receiving devices are not synchronized. Data must carry signals to indicate data division.

Asynchronous Transfer Mode (ATM)
A form of very fast packet switching in which data is carried in fixed length units called "cells". Each cell is 53 bytes in length, with 5 bytes used as a header in each cell. ATM employs mechanisms that can be used to set up virtual circuits between users, in which a pair of users appear to have a dedicated circuit between them. ATM is defined in specifications from the ITU and ATM Forum.

Attachment Unit Interface.
The IEEE 802.3 standard name for the cable connecting an Ethernet transceiver (MAU) to a networked device. An AUI cable is equipped with a 15-pin connector that mates with a 15-pin connector on the networked device.

Attenuation
The decrease in magnitude of a signal as it travels through any transmission medium such as a cable or optical fiber. Measured in dB per unit of length.

Attenuation Crosstalk Ratio (ACR)
The difference between attenuation and crosstalk, measured in dB, at a given frequency. A quality factor for cabling to assure that signal sent down a twisted pair is stronger at the receiving end of the cable than any interference imposed on the same pair by crosstalk from other pairs.

Audio
Used to describe the range of frequencies within range of human hearing; approximately 20 to 20,000 Hz.

AWG
American Wire Gage - A wire diameter specification. The smaller the AWG number, the larger the wire diameter.

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B

Backbone
A cable connection between telecommunication or wiring closets, floor distribution terminals, entrance facilities, and equipment rooms either within or between buildings. In star networks, the backbone cable interconnects hubs and similar devices, as opposed to cables running between hub and station. In a bus network, the bus cable.

Balanced Cable, Balanced Line
A cable having two identical conductors that carry voltages of opposite polarities and equal magnitude with respect to ground. The conductors are twisted to maintain balance over a distance.

Balun
An impedance matching transformer that converts the impedance of one interface to the impedance of another interface. Generally used to connect balanced twisted pair cabling with unbalanced coaxial cabling. The term is derived from "balanced / unbalanced".

Baseband
A transmission method in which the entire bandwidth of the transmission medium is used to transmit a single digital signal. The signal is driven directly onto the transmission medium without modulation of any kind. Baseband is simpler, cheaper and less sophisticated than Broadband.

Bandwidth
The range of frequencies required for proper transmission of a signal. Expressed in Hertz (cycles per second). The higher the bandwidth, the more information that can be carried. A continuous range starting from zero is said to be "baseband", while a range starting substantially above zero is "broadband".

Baud
The number of changes in signal per second. A given baud rate does not necessarily transmit an equal number of bits/sec. For example, a signal with four voltage levels may be used to transfer two bits of information for every baud.

Beacon
A special frame in Token-Ring systems indicating a serious problem with the ring such as a break.

Bend Loss
A form of increased attenuation in an optical fiber caused by an excessively small bend radius. The attenuation may be permanent if microfractures caused by the bend continue to affect transmission of the light signal.

Bend Radius
Radius of curvature that a fiber optic or metallic cable can bend before the risk of breakage or increased attenuation occurs.

BICSI Building Industry Consulting Service International.

Binder
A tape or thread used to hold assembled cable components in place.

BISDN
Broadband ISDN

Bit
One binary digit.

Bit Error Rate
A measure of data integrity, expressed as the ratio of received bits that are in error, relative to the amount of bits received. Often expressed as a negative power of ten.

Bit Stream
A continuous transfer of bits over some medium.

Bit Stuffing
A method of breaking up continuous strings of 1 bits by inserting a 0 bit. The 0 bit is removed at the receiver.

Bit Time
The length of time required to transmit one bit of information.

BNC
A coaxial connector that uses a "bayonet" style turn and lock mating method. Used with RG-58 or smaller coaxial cable. Used with 10Base2 Ethernet thin coaxial cable. BNC is an acronym for Bayonet-Neill-Concelman.

BPS
Bits per second.

Braid
Fine wires interwoven to form a tubular flexible structure that may be applied over one or more wires for the purpose of shielding. May also be formed into a flattened conductor to be used as a grounding strap.

BRI
ISDN Basic Rate Interface

Broadband
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" (empty spaces) to ensure that each channel will not interfere with its neighboring channels. This technique is used to provide many CATV channels on one coaxial cable.

Broadcast
Sending data to more than one receiving device at a time.

Buffer
A protective coating over a strand of optical fiber.

Bus Topology
In general, a physical layout of network devices in which all devices must share a common medium to transfer data, and no two devices may transmit simultaneously. With LANs, a linear network topology in which all computers are connected to a single cable.

Byte
A group of 8 bits.

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C Cable
A group of insulated conductors enclosed within a common jacket.

Cable Sheath
A covering over the conductor assembly that may include one or more metallic members, strength members, or jackets.

Campus
The buildings and grounds of a complex, such as a university, college, industrial park or military establishment.

Capacitance
The ability to store electric charge between two conductors separated by a dielectric material. Capacitance is expressed in Farads.

Carrier Sense
With Ethernet, a method of detecting the presence of signal activity on a common channel.

Carrier Sense Multiple Access with Collision Detect
A network access method used by Ethernet in which a station listens for traffic before transmitting. If two stations transmit simultaneously, a collision is detected and both stations wait a brief time before attempting to transmit again.

Category 1, Cat 1
Unshielded twisted pair used for transmission of audio frequencies. Used as speaker wire, door bell wire, etc. Not suitable for networking applications.

Category 2, Cat 2
Unshielded twisted pair used for transmission at frequencies up to 1.5 Mhz. Used in analog telephone applications. Not suitable for networking applications.

Category 3, Cat 3
Unshielded twisted pair with 100 ohm impedance and electrical characteristics supporting transmission at frequencies up to 16 MHz. Defined by the TIA/EIA 568-A specification.

Category 4, Cat 4
Unshielded twisted pair with 100 ohm impedance and electrical characteristics supporting transmission at frequencies up to 20 MHz. Defined by the TIA/EIA 568-A specification.

Category 5, Cat 5
Unshielded twisted pair with 100 ohm impedance and electrical characteristics supporting transmission at frequencies up to 100 MHz. Defined by the TIA/EIA 568-A specification.

Category 5e, Cat 5e, Enhanced Cat 5, Cat 5+
Category 5e is a new standard that will specify transmission performance that exceeds Cat 5. Cat 5e has improved specifications for NEXT, PSELFEXT, and Attenuation. Like Cat 5, it consists of unshielded twisted pair with 100 ohm impedance and electrical characteristics supporting transmission at frequencies up to 100 MHz. To be defined in the TIA 568-A-5 update.

Category 6, Cat 6
Category 6 is a proposed standard that aims to support transmission at frequencies up to 250 MHz over 100 ohm twisted pair.

Category 7, Cat 7
Category 7 is a proposed standard that aims to support transmission at frequencies up to 600 MHz over 100 ohm twisted pair.

CATV
Community antenna television, or "Cable TV". CATV is a broadband transmission facility which generally uses a 75 Ohm coaxial cable to carry numerous frequency-divided TV channels simultaneously.

CDDI
Copper Distributed Data Interface - A version of FDDI that uses copper wire media instead of fiber optic cable.

Centronics 36
The 36-pin connector is often used for parallel applications, especially for printers. It is also referred to as an IEEE-1284 Type B connector. The Centronics 36-pin connector is arranged in two rows of pins, each with 18 contacts. The connector is held in place by bail locks.

Centronics 50
The Centronics 50 connector has 50 pins arranged in two rows�25 on the top, and 25 on the bottom. This connector is most often used by older SCSI-1 devices (scanners, storage devices, etc.). The Centronics 50 connector is held in place by bail locks. A slight variant of the Centronics 50 connector is used in voice/data applications. Commonly referred to as a Telco connector.

Channel Insertion Loss
For fiber optic links, the static loss of a link between a transmitter and receiver. It includes the loss of the fiber, connectors, and splices.

Cladding
The material surrounding the core of a fiber optic cable. The cladding must have a lower index of refraction than the core in order to contain the light in the core.

Class A
ISO/IEC 11801 designation for twisted pair cabling rated to 100 KHz. Used in voice and low frequency applications. Comparable to Category 1 cabling. Not suitable for networking applications

Class B
ISO/IEC 11801 designation for twisted pair cabling rated to 1 MHz. Used in medium bit rate applications. Comparable to Category 2 cabling. Not suitable for networking applications

Class C
ISO/IEC 11801 designation for twisted pair cabling rated to 16 MHz. Used in high bit rate applications. Corresponds to TIA/EIA Category 3 cabling.

Class D
ISO/IEC 11801 designation for twisted pair cabling rated to 100 MHz. Used in very high bit rate applications. Corresponds to TIA/EIA Category 5 cabling.

Class E
ISO /IEC proposal for twisted pair cabling rated to 250 MHz. Corresponds to the proposed TIA/EIA Category 6 cabling standard.

Closet
An enclosed space for housing telecommunications and networking equipment, cable terminations, and cross-connect cabling. It contains the horizontal cross connect where the backbone cable cross-connects with the horizontal cable.

Coating

Material surrounding the cladding of the fiber for protection.

Coax, Coaxial Cable
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.

Collision
When electrical signals from two or more devices sharing a common data transfer medium crash into one another. This commonly happens on Ethernet type systems.

Conduit
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.

Conductor
A material that offers low resistance to the flow of electrical current.

Continuity
An uninterrupted pathway for electrical signals..

Cord
A very flexible insulated cable.

Core
The central region of an optical fiber through which light is transmitted
.
Cross Connect
A facility enabling the termination of cable elements and their interconnection, and/or cross-connection, primarily by means of a patch cord or jumper.

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

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

Crossover Cable
A twisted pair patch cable wired in such a way as to route the transmit signals from one piece of equipment to the receive signals of another piece of equipment, and vice versa.

Crosstalk
The coupling of unwanted signals from one pair within a cable to another pair. Crosstalk can be measured at the same (near) end or far end with respect to the signal source.

CSA
Canadian   Standards   Association

Customer  Premises
Buildings , offices, and other structures under the control of a telecommunications customer.  

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D 

D Connector 
see Subminiature D Connector

Data Connector
A four position connector for 150-ohm STP used primarily with Token-Ring networks.

Data Grade
A term used for twisted-pair cable used in networks to carry data signals. Data grade media has a higher frequency rating than voice grade media used in telephone wiring.

DAS
Dual Attachment Station. Term used with FDDI networks to denote a station that attaches to both the primary and secondary rings.

dB
Decibel. 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 decibel is one tenth of a "bel".

DB-9
Nine pin D connector.

DB-15
Fifteen pin D connector.

DB-25
Twenty-five pin D connector.

DCE
Data Communications Equipment. Any equipment that connects to Data Terminal Equipment (DTE) to allow transmission between DTEs.

Demand Priority
A network access method used by 100VG-AnyLAN. The hub arbitrates requests for network access received from stations, assigning access based on priority and traffic loads.

Demarcation Point
A point where the operational control or ownership changes, such as the point of interconnection between telephone company facilities and a user's building or residence.

Dielectric
An insulating (non-conducting) material.

Dielectric Constant
The property of a dielectric which determines the amount of electrostatic energy that can be stored by the material when a given voltage is applied to it. Also called permattivity.

Digital Signal
An electric signal which possesses two distinct states (on/off, positive/negative, one/zero).

Din
DIN connectors are round, with pins arranged in a circular pattern. This type of connector was used widely for PC keyboards. Another type of DIN connector is the mini-DIN. As the name suggests, mini-DIN connectors are smaller in size than a regular DIN.

5 Pin Din
Used for older AT-style computer keyboards.

4 Pin Mini Din
The 4 pin mini-DIN connector is most often used for S-video applications.

6 Pin Mini Din
6 pin mini-DIN connectors are often called PS/2 connectors. Most Commonly used on PS/2 Keyboards and Mice.

8 Pin Mini Din
8 pin mini-Din connectors where commonly used with the serial interface on older Apple computers.

Dispersion
The phenomenon in an optical fiber whereby light photons arrive at a distant point in different phase than they entered the fiber. Dispersion causes receive signal distortion that ultimately limits the bandwidth and usable length of the fiber cable. The two major types of dispersion are 1) mode (or modal) dispersion caused by differential optical path lengths in a multimode fiber, and 2) material dispersion caused by differing transmission times of different wavelengths of light in the fiber optic material.

Distribution Frame
A structure with terminations for connecting the permanent cabling of a facility in a manner that interconnections or cross connects may be readily made.

DIW
Direct Inside Wire. Twisted pair wire used inside a building, usually two or four pair AWG 26.

Drain Wire
An uninsulated wire in contact with a shield throughout its length. Used to terminate the shield.

Drop Cable
The cable which allows connection and access to and from the trunk cables of a network such as the cables that connect individual PCs to the bus on a bus LAN. In a CATV system, the transmission cable from the distribution cable to a dwelling.

DS1/DS3
see T1 and T3

DTE
Data Terminal Equipment. Any piece of equipment at which a communications path begins or ends.

Duct 
A single enclosed raceway for wires or cable. An enclosure in which air is moved.

Duplex
A circuit used to transmit signals simultaneously in both directions. Two receptacles or jacks in a common housing which accepts two plugs.

DVI-D Dual-link
This connector contains 24 pins arranged in three horizontal rows of eight pins. To the side of this grouping of 24 pins is a wide, flat pin called a ground bar. A dual-link interface provides two TMDS links, or groups of data �channels� that can carry more than 10 Gbps of digital video information. A dual-link cable is backwards-compatible with single-link applications. DVI interfaces in the A/V world are found on HDTVs and on HD sources such as DVRs or satellite receivers. 

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E

 
E1/E3 
The European versions of T1 and T3. E1 runs at 2.048 Mbps and E3 runs at 34 Mbps.

EC
European Community

ECMA
European Computer Manufacturer's Association. A European trade organization that issues its own standards and is a member of the ISO.

EIA
Electronic Industry Association (formerly RMA or RETMA). An association of manufacturers and users that establishes standards and publishes test methodologies.

Electromagnetic Interference
An interfering electromagnetic signal. Network wiring and equipment may be susceptible to EMI as well as emit EMI.

ELFEXT
Equal Level Far End Crosstalk

EMI
see Electromagnetic Interference.

Entrance Facility
An entrance to a building for both public and private network service cables (including antennae) including the entrance at the building wall and continuing to the entrance room or space.

Entrance Point
The point of emergence of telecommunications conductors through an exterior wall, a concrete floor slab, or from a rigid metal conduit or intermediate metal conduit.

Entrance Room
A space in which the joining of inter- or intra-building telecommunications or networking backbone facilities takes place. An entrance room may also serve as an equipment room.

Equipment Room
An enclosed area housing telecommunications and network equipment, distinguished from the telecommunications or wiring closet by its increased complexity and presence of active equipment.

Ethernet
A local area network (LAN) protocol defined in the IEEE 802.3 standard in which computers access the network through a Carrier Sense Multiple Access / Collision Detect (CSMA/CD) protocol.

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F

F
Frequency

F-type
The F-type connector is used on coaxial cable, and is widely used for cable TV, satellite TV, and off-air TV antenna applications. The connector is round with the conductor of the cable itself poking through the center of the connector body. Most F-type connectors are threaded, so that they can be screwed into place.

Farad
A unit of capacitance that stores one coulomb of electrical charge when one volt of electrical pressure is applied.

Far End Cross Talk (FEXT)
Crosstalk that is measured on the quiet line at the opposite end as the source of energy on the active line. FEXT is not typically measured in cabling, with Near End Cross Talk (NEXT) being the preferred crosstalk measurement.

Fast Ethernet
Ethernet standard supporting 100 Mbps operation.

FCC
Federal Communications Commission.

FDDI
Fiber Distributed Data Interface. An ANSI Standard (ANSI X3T12) for a 100 Mbps token passing network based on fiber-optic (FDDI) and twisted-pair (CDDI) cabling.

Feeder Cable
In a CATV system, the transmission cable from the head end (signal pickup) to the trunk amplifier. Also called a trunk cable.

FEXT
see Far End Cross Talk

Fiber Optics
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.

Fifty-pin Connector
Commonly referred to as a Telco, CHAMP, or blue ribbon connector, this connector is used on Ethernet 10Base-T hubs as an alternate twisted-pair segment connection method. The 50-pin connector connects to 25-pair cables, which are frequently used in telephone wiring systems and which typically meet Category 3 specifications.

FOIRL
Fiber Optic Inter-Repeater Link. An Ethernet fiber optic connection method intended for connection of repeaters.

Frequency
The number of times a periodic action occurs in a unit of time. Expressed in hertz (abbreviated Hz). One hertz equals one cycle per second.

Frequency Division Multiplexing (FDM)
A technique for combining many signals on a single circuit by dividing the available transmission bandwidth by frequency into narrower bands, each used for a separate communication channel.

Frequency Modulation (FM)
One of three basic methods (see also Amplitude and Phase Modulation) of adding information to a sine wave signal in which its frequency is varied to impose information on it.

Frequency Response
The range of frequencies over which a device operates as expected.

FTP
see Screened Twisted Pair (ScTP) cable

Full Duplex Transmission
Data transmission over a circuit capable of transmitting in both directions simultaneously.  

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G

Gbps
Gigabits per second.

Giga
A prefix meaning one billion

Gigahertz (GHz)
One billion hertz.

GIPOF
Graded Index Plastic Optical Fiber

Graded Index Fiber
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 modal dispersion of the signal.

Ground
A common point of zero potential such as a metal chassis or ground rod.

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H

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

HC
see Horizontal Cross Connect.

HDMI
The current version of HDMI carries one TMDS link of digital video. Found on many home-theater/consumer electronics devices, HDMI uses a 19-pin connector that is held in place by friction. This connector is technically described as a Type A HDMI connector. The Type B connector is larger (28 pins), but it is not currently used by any devices in the marketplace. HDMI is the interface of choice for most newer HD A/V devices. Not only does it provide outstanding audio and video performance, but it also supports High-bandwidth Digital Content Protection (HDCP), a technology built into consumer electronic equipment that prevents illicit duplication of copyrighted material.

HD15
A very common connector used mostly as a video interface for computers and monitors. It can also be found on HD displays, and on older HD source devices such as satellite receivers and cable boxes. The HD15 is a High Density DB-style connector, so it can also be called an HD DB15. Another popular name is �VGA connector�, although it is used in video applications that support much higher resolutions (SVGA, XGA, UXGA, etc.). An HD15 connector is the same size as a DB9 connector, but it has three rows of 5 pins. On most HD15 male connectors, there is one pin (pin 9) missing in the middle row.

Headend
The equipment in a cable system which receives the various program source signals, processes them, and retransmits them to subscribers.

Headroom
The amount by which a cable ACR exceeds 10dB.

Hertz
The unit of frequency, one cycle per second (abbreviated Hz).

HF
High Frequency

Home Run
A cable run that connects a user outlet directly with the telecommunications or wiring closet, with no intermediate splices, bridges, taps, or other connections.

Horizontal Cabling, Horizontal Wiring
The portion of the cabling system that extends from the work area outlet to the horizontal cross connect in the telecommunications or wiring closet.

Horizontal Cross Connect
A cross connect of horizontal cabling to other cabling, e.g. horizontal, backbone, or equipment.

Host
Computer that offers services on a network.

Hub
A hardware device that contains multiple independent but connected modules of network and internetworking equipment. Hubs can be active (where they repeat signals set to them) or passive (where they do not repeat but merely split signals sent through them). Hub may also refer to a repeater, bridge, switch, router, or any combination of these.

Hybrid Cable
An assembly of two or more cables (of the same or different types or categories) covered by one overall sheath.

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I

IC
see Intermediate Cross Connect.

ICEA
Insulated Cable Engineers Association

ICS
IBM Cabling System

IDC
Insulation Displacement Contact/Connector

IDF
Intermediate Distribution Frame. This is usually located on each floor within a building. It is tied directly to the Main Distribution Frame via cables.

IEC
International Electrotechnical Commission

IEEE
Institute of Electrical and Electronics Engineers. A professional organization and standards body. The IEEE Project 802 is the group within IEEE responsible for LAN technology standards.

IEEE 802.1
The IEEE standards committee defining High Level Interfaces, Network Management, Internetworking, and other issues common across LAN technologies.

IEEE 802.2
The IEEE standards committee defining Logical Link Control (LLC).

IEEE 802.3
The IEEE standards committee defining Ethernet networks.

IEEE 802.5
The IEEE standards committee defining Token-Ring standards.

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

Impedance Match
A condition where the impedance of a particular circuit cable or component is the same as the impedance of the circuit, cable, or device to which it is connected.

Interconnection
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.

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

Insertion Loss
A measure of the attenuation of a device by determining the output of a system before and after the device is inserted into the system. For example, a connector causes insertion loss across the interconnection (in comparison to a continuous cable with no interconnection).

ISDN
Integrated Services Digital Network

ISO
International Standards Organization

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

Isochronous
Signals which are dependent on some uniform timing or carry their own timing information imbedded as part of the signal. Voice and video signals are isochronous signals, but data transfer is generally not.

ITU
International Telecommunications
Union . An international organization that develops communications standards.

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J

Jabber
Term used with Ethernet to describe the act of continuously sending data. A jabbering station is one whose circuitry or logic has failed, and which has locked up a network channel with its incessant transmission.

Jack
A female connector.

Jacket
The outer protective covering of a cable.

Jitter
The slight movement of a transmission signal in time or phase that can introduce errors and loss of synchronization. More jitter will be encountered with longer cables, cables with higher attenuation, and signals at higher data rates. Also, called phase jitter, timing distortion, or intersymbol interference.

Jumper
An assembly of twisted pairs without connectors used to used to join telecommunications circuits at the cross connect. Similar to a patch cable (which has connectors).

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K Keying
The mechanical feature of a connector system that guarantees correct orientation of a connection, or prevents the connection to a jack, or to an optical fiber adapter, of the same type intended for another purpose. 

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L
 
LAN
Local Area Network

LAN Adapter
see Network Interface Card

LATA
Local Access and Transport Area.

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

Link
A transmission path between two points not including terminal equipment, work area cables, or equipment cables.

Listed
Equipment included on a list published by an organization, acceptable to the authority having jurisdiction, that maintains periodic inspection of production of listed equipment, and whose listing states either that the equipment or material meets appropriate standards or has been tested and found suitable for use in a specified manner.

Lobe
An arm of a Token-Ring which extends from a Multistation Access Unit (MSAU) to a workstation adapter.

LocalTalk
A low-speed form of LAN data link technology, part of Apple Computer's AppleTalk networking scheme, that uses a carrier sense multiple access with collision avoidance (CSMA/CA) form of medium access control. Supports transmission at 230 Kbps.

Loopback
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.

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M  mA
Milliampere (one thousandth of an ampere)

MAC
see Medium Access Control

Main Cross Connect
A cross connect for first level backbone cables, entrance cables, and equipment cables. The main cross connect is at the top level of the premises cabling tree.

ManchesterCodingMD50  A method of LAN signal encoding in which each bit time that represents a data bit has a transition in the middle of the bit time. Used with 10 Mbps Ethernet (10Base2, 10Base5, 10Base-F, & 10Base-T), and Token-Ring LANs.

MAU
Media Attachment Unit. The transceiver in Ethernet networks. Also a common name for the MSAU (Multi-station Access Unit) in Token-Ring networks.

Mbaud
Megabaud. One million baud.

Mbps
Megabits per second.

MC
see Main Cross Connect

MDF0
The MD50 connector is used primarily with SCSI devices. Some alternate terms for this connector include HD50, HD DB50, and SCSI-2 50-pin. The MD50 has two rows of 25 pins. The pins are very small, and placed closely together. Most MD50 connectors use squeeze-latches to hold the connection in place.

MD68
The MD68 connector is similar in shape to an MD50, but has more pins. Its pins are also arranged in two rows, each row with 34 pins. MD68 connectors are very common on SCSI devices, and they are sometimes referenced as HD68, HD DB68, SCSI-3, or Wide SCSI connectors. Some MD68 connectors have latchclips, but most use thumbscrews.  Its pins are also arranged in two rows, each row with 34 pins. MD68 connectors are very common on SCSI devices, and they are sometimes referenced as HD68, HD DB68, SCSI-3, or Wide SCSI connectors. Some MD68 connectors have latchclips, but most use thumbscrews.

DF 
Main Distribution Frame

MDI
see Media Dependent Interface

Media
Wire, cable, or conductors used for transmission of signals.

Media Filter
An impedance matching component used in Token-Ring networks to transform the 100 ohm impedance of UTP cabling to the 150 ohm impedance of media interface connections.

Medium Access Control (MAC)
A mechanism operating at the data link layer of local area networks which manages access to the communications channel (medium).

Medium Dependent Interface (MDI)
In Ethernet, the connector used to make the mechanical and electrical interface between a transceiver and a media segment. An 8-pin RJ-45 connector is the MDI for the 10Base-T, 100Base-TX, 100Base-T2, 100Base-T4, and 1000Base-T media systems.

Medium Independent Interface (MII)
Used with 100 Mbps Ethernet systems to attach MAC level hardware to a variety of physical media systems. Similar to the AUI interface used with 10 Mbps Ethernet systems. An MII provides a 40-pin connection to outboard transceivers (also called PHY devices).

Mega
Prefix meaning one million.

Megahertz (MHz)
One million hertz.

MIC
Medium Interface Connector. Duplex fiber optic connector used with Fiber Distributed Data Interface (FDDI) networks.

Micro
Prefix meaning one millionth.

Micro Centronics 36
This connector can described more accurately as a mini-D ribbon (MDR) connector. It looks very similar to the Centronics 36-pin, but is about half the size. This interface is also called an IEEE-1284 Type C connector, and is commonly found on parallel multifunction (printer/scanner/copier/fax) devices. This connector is held in place by squeeze latches.

Microfarad
One millionth of a farad. Abbreviated µF (less commonly µfd, mf, and mfd).

Micron
One millionth of a meter. Abbreviated µm.

Midsplit Broadband
A broadcast network configuration in which the cable is divided into two channels, each using a different range of frequencies. One channel is used to transmit signals and the other is used to receive.

Mil
Unit of length equal to one thousandth of an inch (0.001 inch).

Milli
Prefix meaning one thousandth.

Mixing Segment
Ethernet term used in IEEE 802.3 standards to describe a segment that may have more than two MDI connections.

MMF
see Multimode Fiber

Modal Dispersion
Dispersion that results from the different transit lengths of different propagating modes in a multimode optical fiber.

Mode
A single electromagnetic wave traveling in an optical fiber.

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

Modem
A device that implements "modulator-demodulator" functions to convert between digital data and analog signals.

Modular Jack
The equipment mounted half of a modular interconnection. Typically a female connector. A modular jack may be keyed or unkeyed and may have six or eight contact positions, but not all the positions need to be equipped with jack contacts.

Modular Plug
The cable mounted half of a modular interconnection. Typically a male connector. A modular plug may be keyed or unkeyed and may have six or eight contact positions, but not all the positions need to be equipped with contacts.

Modulation
Altering the characteristics of a carrier wave to convey information. Modulation techniques include amplitude, frequency, phase, plus many other forms of digital encoding.

MSAU
Multi-station Access Unit. Device used to interconnect lobe cables from stations on a Token-Ring network.

MT-RJ
Proposal for a new duplex fiber optic connector standard from AMP/Siecor.

Multimode Fiber
A fiber optic cable which supports the propagation of multiple modes. Multimode fiber may have a typical core diameter of 50 to 100 µm with a refractive index that is graded or stepped. It allows the use of inexpensive LED light sources and connector alignment and coupling is less critical than single mode fiber. Distances of transmission and transmission bandwidth are less than with single mode fiber due to dispersion.

Mutual Capacitance
Capacitance between two conductors when all other conductors are connected together.

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N
N connector
A coaxial connector used for Ethernet 10Base5 thick coax segments.

Nanometer (nm)
One billionth of a meter.

Nanosecond (ns)
One billionth of a second.

Near-End Crosstalk
Crosstalk between two twisted pairs measured at the same end of the cable as the disturbing signal source. NEXT is the measurement of interest for crosstalk specifications.

NEC
National Electrical Code.

NEMA
National Electrical Manufacturers Association.

Network
An interconnection of computer systems, terminals or data communications facilities.

Network Interface Card
A circuit board installed in a computing device used to attach the device to a network. A NIC performs the hardware functions that are required to provide a computing device with physical communications capabilities. Also Network Interface Unit (NIU).

NEXT
see Near-End Crosstalk.

NFPA
National Fire Protection Association

Nibble
One half byte.

NIC
see Network Interface Card.

NIR
Near-end Crosstalk-to-Insertion Loss Ratio

Node
End point of a network connection. Nodes include any device connected to a network such as file servers, printers, or workstations.

Noise
In a cable or circuit, any extraneous signal which interferes with the desired signal.
Numerical Aperture (NA)
The "light gathering ability" of an optical fiber, defining the maximum angle to the fiber axis at which light will be accepted and propagated.

NVP
Nominal Velocity of Propagation. The speed a signal propagates through a cable expressed as a decimal fraction of the speed of light in a vacuum.

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O
Octet
8 bits (also called a byte).

OFSTP
Optical Fiber Standard Test Procedure.

Ohm
The electrical unit of resistance. The value of resistance through which a potential of one volt will maintain a current of one ampere.

Ohm's Law
Stated E=IR, I=E/R, or R=E/I, the current "I" in a circuit is directly proportional to the voltage "E", and inversely proportional to the resistance "R".

Optical Carrier n
Optical signal standards. The "n" indicates the level where the respective data rate is exactly "n" times the first level OC-1. OC-1 has a data rate of 51.84 Mbps. OC-3 is 3 times that rate or 155.52 Mbps, etc. Associated with SONET.

OLTS
Optical Loss Test Set

Open
A break in the continuity of a circuit.

Optical Fiber
A thin glass or plastic filament used for the transmission of information via light signals. The signal carrying part of a fiber optic cable.

Optical Fiber Cable
An assembly consisting of one or more optical fibers.

Optical Fiber Duplex Adapter
A mechanical media termination device designed to align and join two duplex connectors.

Optical Fiber Duplex Connection
A mated assembly of two duplex connectors and a duplex adapter.

Optical Fiber Duplex Connector
A mechanical media termination device designed to transfer optical power between two pairs of optical fibers.

Optical Time Domain Reflectometry.
A method for evaluating optical fiber based on detecting and measuring backscattered (reflected) light. Used to measure fiber length and attenuation, evaluate splice and connector joints, locate faults, and certify cabling systems.

OSI
Open Systems Interconnection

Outside Plant
Cabling, equipment, or structures that are out of doors.

OTDR
Optical Time Domain Reflectometry.

Outlet
A connecting device in the work area on which a horizontal cable terminates.

Outlet Box
A metallic or non-metallic box mounted within a wall, floor, or ceiling used to hold outlet, connector, or transition devices.

Output
The useful signal or power delivered by a circuit or device.

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P
  

ABX 
Private Automatic Branch Exchange

Packet
Bits grouped serially in a defined format, containing a command or data message sent over a network.

PAM5x5
Signal encoding scheme used in the Ethernet 100Base-T2 and 1000Base-T media systems.

Patch Cable, Patch Cord
A flexible piece of cable terminated at both ends with connectors. Used for interconnecting circuits on a patch panel or cross connect.

Patch Panel
A passive device, typically flat plate holding feed through connectors, to allow circuit arrangements and rearrangements by simply plugging and unplugging patch cables.

Pathway
A facility for the placement of telecommunication or networking cables.

PBX
Private Branch Exchange

PC
Personal Computer

PCC
Premises Com

PDN
Public Data Network

Pedestal
A device, usually mounted on the floor, which is used to house voice/data jacks or power outlets at the point of use. Also referred to as a monument, tombstone, above floor fitting or doghouse.

PHY
Physical Layer device.

Physical Layer
Layer one of the seven layer ISO Reference Model for Open Systems Interconnection. The physical layer is responsible for the transmission of signals, such as electrical signals, optical signals, or radio signals, between computing machines.

Pico
Prefix meaning one millionth of one millionth.

Picofarad
One millionth of one millionth of a farad. Abbreviated "pf".

Pin-diode
A photodetector used to convert optical signals to electrical signals in a receiver.

Plastic Fiber
An optical fiber made of plastic rather than glass.

Plenum
The air handling space between the walls, under structural floors, and above drop ceilings used to circulate and otherwise handle air in a building. Such spaces are considered plenums only if they are used for air handling. Work spaces are generally not considered plenums.

Plenum Cable
A cable that is rated as having adequate fire resistance and low smoke producing characteristics for use in air handling spaces (plenum).

Plug
A male connector.

PMD
Physical Media Dependent

POF
Plastic Optical Fiber.

Polyvinyl Chloride (PVC)
A general purpose thermoplastic used for wire and cable insulation and plastics. PVC is know for high flexibility. Often used in nonplenum wire insulation and cable jackets. A modified version of the material may be found in jacketing of some plenum rated cables.

POTS
Plain Old Telephone System

Power Ratio
The ratio of power appearing at the load to the input power. Expressed in dB.

Premise Cabling

The entire cabling system on the user's premises used for transmission of voice, data, video and power.

Prewiring
Wiring installed before walls and ceilings are enclosed.

Private Branch Exchange (PBX)
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).

Propagation Delay
Time required for a signal to pass from the input to the output of a device.

Protocol
A set of agree-upon rules and message formats for exchanging information among devices on a network.

PSELFEXT
Power Sum Equal Level Far End Crosstalk

PSNEXT
Power Sum Near End Crosstalk

Public Data Network
A network established and operated for the specific purpose of Providing data transmission services to the public.

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

Pull Strength, Pull Tension
The pulling force that can be applied to a cable without affecting the specified characteristics of the cable.

PVC
Polyvinyl Chloride
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Q

Quartet Signaling
The signaling method used by 100VG-AnyLAN, in which the 100 Mbps signal is divided into four 25 Mbps channels and then transmitted over different pairs of a cable. Category 3 cables transmit one channel on each of four pairs. 

Raceway
Any channel designated for holding wires or cables. Raceways may be metallic or nonmetallic and may totally or partially enclose the wiring. (e.g. conduit, cable trough, cellular floor, electrical metallic tubing, sleeves, slots, underfloor raceways, surface raceways, lighting fixture raceways, wireways, busways, auxiliary gutters, and ventilated flexible cableways)

Radio Frequency
The frequencies in the electromagnetic spectrum that are used for radio communications.

RBOC
Regional Bell Operating Company. One of the seven Bell operating companies that were formed during the divestiture of AT&T.

RCA
The venerable RCA plug gets its name from the RCA Corporation, which popularized its use on radios and phonograph players as far back as the 1940s. The RCA connector is a round plug with a central tip and a metal ring, separated by insulating material. The tip has a smooth, domed shape. The shape and design makes the connector extremely easy to plug and unplug into equipment. RCA connectors are often used with coaxial cables, where the center conductor terminates to the tip, and the coaxial shield is in contact with the metal ring of the plug. Even though they are used for video applications, most RCA connectors do a poor job of maintaining a precise impedance. As such, they are rarely used for broadcast or professional applications. The RCA plug is sometimes referred to as a Cinch or phono connector.

RCDD
Registered Communication Distribution Designer. A certification of BICSI, an industry organization, for individuals qualified to consult and design telecommunications distribution systems.

Receiver
A device whose purpose is to capture transmitted signal energy and convert that energy for useful functions. In fiber optic systems, an electronic component that converts light energy to electrical energy.

Reflection
A return of electromagnetic energy that occurs at an impedance mismatch in a transmission line, such as a LAN cable.

Refractive Index
The ratio of the speed of light in a vacuum to its velocity in a transmitting medium, such as an optical fiber core.

Repeater
A device that receives, amplifies (and sometimes reshapes), and retransmits a signal. It is used to boost signal levels and extend the distance a signal can be transmitted. It can physically extend the distance of a LAN or connect two LAN segments.

Retractile Cord
A cord having specially treated insulation or jacket so that it will retract like a spring. Retractibility may be added to all or part of a cord's length.

Reversed Pair
A wiring error in twisted pair cabling where the conductors of a pair are reversed between connector pins at each end of a cable.

RF
see Radio Frequency

RFI
Radio Frequency Interference. Electromagnetic interference at radio frequencies.

RFP
Request for Proposal

RFQ
Request for Quote (or Quotation)

RG/U
Radio Grade/Universal. RG is the common military designation for coaxial cable.

Ring
A polarity designation of one wire of a pair indicating that the wire is that of the secondary color of a 5-pair group (e.g. the blue white wire of the blue pair). A wiring contact to which the ring wire is attached. The negative wiring polarity.

Ring Network
A network topology in which terminals are connected in a point-to-point serial fashion in an unbroken circular configuration. Many logical rings are wired as a star for greater reliability.

Ripcord
A cord placed directly under the jacket of a cable in order to facilitate stripping (removal) of the jacket.

Riser
The conduit or path between floors of a building into which telephone, networking, and other utility cables are placed to bring service from one floor to another.

Riser Cable
A type of cable used in vertical building shafts, such as telecommunications and utility shafts. Riser cable typically has more mechanical strength than general use cable and has an intermediate fire protection rating.

RJ
A term from the telephone industry, used for jacks (connectors) that were registered for use with particular types of telephone services. RJ stands for "registered jack".

RJ-45
A USOC code identifying an 8-pin modular plug or jack used with unshielded twisted pair cable. Officially, an RJ-45 connector is a telephone connector designed for voice grade circuits only. RJ-45 type connectors with better signal handling characteristics are called 8-pin connectors in most standards documents, though most people continue to use the RJ-45 name for all 8-pin connectors.

Rope Strand
A conductor composed of groups of twisted strands.

Rx
Receive
RZ
Return to Zero

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S

SAS
Single Attachment Station. Term used with FDDI networks to denote a station that attaches to only one of two rings in a dual ring environment.

SC Connector
A fiber optic connector having a 2.5mm ferrule, push-pull latching mechanism, and the ability to be snapped together to form duplex and multifiber connectors. SC connectors are the preferred fiber optic cable for premises cabling, and are recommended by the TIA/EIA-568-A Standard for structured cabling. Used with Ethernet 100Base-FX and 1000Base-LX/SX fiber optic media systems.

Scanner
A cable testing device which uses TDR methods to detect cable transmission anomalies and error conditions.

Screened Twisted Pair (ScTP) cable
Four pair UTP, with a single foil or braided screen surrounding all four pairs in order to minimize EMI radiation or susceptibility. Screened twisted pair is sometimes called Foil Twisted Pair (FTP). ScTP can be thought of as a shielded version of the Category 3, 4, & 5 UTP cables.

Screened/Shielded Twisted Pair (SSTP)
Four pair cabling, with each pair having its own individual Shield, in addition to an overall shield surrounding all four pairs. SSTP offers similar performance to Type 1 STP except with 4 pairs (rather than 2) and in a 100 ohm impedance (rather than 150).

ScTP
see Screened Twisted Pair cable

Segment
On Ethernet a media segment may be made up of one or more cable sections joined together to produce a continuous cable for carrying Ethernet signals.

Semiconductor
In wire industry terminology, a material possessing electrical conductivity that falls somewhere between that of conductors and insulators. Usually made by adding carbon particles to an insulator. Not the same as semiconductor materials such as silicon, germanium, etc.

Shield
A metallic foil or multiwire screen mesh that is used to prevent electromagnetic fields from penetrating or exiting a transmission cable. Also referred to as a "screen".
Shield Coverage
The physical area of a cable that is actually covered by shielding material, often expressed as a percentage.

Shield Effectiveness
The relative ability of a shield to screen out undesirable interference. Frequently confused with the term shield coverage.

Shielded Twisted Pair (STP)
A type of twisted pair cable in which the pairs are enclosed in an outer braided shield, although individual pairs may also be shielded. STP most often refers to the 150 ohm IBM Type 1, 2, 6, 8, & 9 cables used with Token Ring networks.

Signal
The information conveyed through a communication system.

Signal to noise ratio
The ratio of received signal level to received noise level, expressed in dB. Abbreviated S/N. A higher S/N ratio indicates better channel performance.

Silver Satin
The name for the silver-gray voice-grade patch cable used to connect a telephone to a wall jacket. Typical silver satin patch cables do not have twisted pair wires, which makes them unsuitable for use in LAN applications. The lack of twisted pairs will result in high levels of crosstalk.

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

Single Mode Fiber
An optical fiber that will allow only one mode to propagate. The fiber has a very small core diameter of approximately 8 µm. It permits signal transmission at extremely high bandwidth and allows very long transmission distances.

SMA Connector
A threaded type fiber optic connector. The 905 version is a straight ferrule design, whereas the 906 is a stepped ferrule design.

SMF
see Single Mode Fiber

Source
In fiber optics, the device which converts the electrical information carrying signal to an optical signal for transmission over an optical fiber. A fiber-optic source may be a light emitting diode or laser diode.

Spectral Bandwidth
The difference between wavelengths at which the radiant intensity of illumination is half its peak intensity.

Spectrum
Frequencies that exist in a continuous range and have a common characteristic. A spectrum may be inclusive of many spectrums (e.g. the electromagnetic radiation spectrum includes the light spectrum, radio spectrum, infrared spectrum, etc.)

Speed of Light (c)
In a vacuum, 299,800,000 meters per second.

Splice
A joining of conductors generally from separate sheaths.

Splice Closure
A device used to protect a cable or wire splice.

SplitPair 
A wiring error in twisted pair cabling where one of a pair's wires is interchanged with one of another pair's wires. Split pair conditions may be determined with a transmission test. Simple DC continuity testing will not reveal the error, because the correct pin-to-pin continuity exists between ends. However, the error may result in impedance mismatch, excessive crosstalk, susceptibility to interference, and signal radiation.

SSTP, S/STP
see Screened/Shielded Twisted Pair

ST Connector
Designation for the "straight tip" connector developed by AT&T. This fiber optic connector features a physically contacting non-rotating 2.5mm ferrule design and bayonet connector-to-adapter mating. Used with Ethernet 10Base-FL and FIORL links.

Standing Wave
The stationary pattern of waves produced by two waves of the same frequency traveling in opposite directions on the same transmission line. The existence of voltage and current maxima and minima along a transmission line is a result of reflected energy from an impedance mismatch.

Star Network
A network in which all stations are connected through a single point.

Star Topology
A topology in which each outlet/connector is wired directly to the distribution device.

Station
A unique, addressable device on a network.

STP
see Shielded Twisted Pair

STP-A
Refers to the enhanced IBM Cabling System specifications with the Type "A" suffix. The original IBM Type 1, 2, 6, & 9 specifications were designed to support operation of 4 and 16 Mbps Token-Ring. The enhanced Type 1A, 2A, 6A, & 9A cable specifications were designed to support operation of 100 Mbps FDDI signals over copper.

Strength Member
That part of a fiber optic cable that increases the cable's tensile strength and serves as a load bearing component. Usually made of Kevlar aramid yarn, fiberglass filaments, or steel strands.

Structural Return Loss (SRL)
A measure of the impedance uniformity of a cable. It measures energy reflected due to structural variations in the cable. A higher SRL number indicates better performance (more uniformity and lower reflections).

Structured Wiring
Telecommunications cabling that is organized into a hierarchy of wiring termination and interconnection structures. The concept of structured wiring is used in the common standards from the TIA and EIA.

Subminiature D Connector
A family of multipin data connectors available in 9, 15, 25 and 37 pin configurations. Sometimes referred to as DB9, DB15, DB25 and DB37 connectors respectively.

Surge
A temporary and relatively large increase in the voltage or current in an electric circuit or cable. Also called transient.

Surge Suppression
The process by which transient voltage surges are prevented from reaching sensitive electronic equipment.

S-VIDEO
The 4-pin mini-DIN connector is most often used for S-video applications. It has 4 pins arranged in 2 rows, and a keying block to make certain the plug cannot be inserted improperly.

Sweep Test
Pertaining to cable, the frequency response is verified by generating an rf voltage whose frequency is swept repeatedly through a given frequency range at a rapid constant range. The cable response is observed on an oscilloscope. The structural return loss sweep test measures the magnitude of internal cable reflections. A high structural return loss is desirable.

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

Synchronous Digital Hierarchy (SDH)
International standard for optical digital transmission at hierarchical rates from 155 Mbps to 2.5 Gbps and beyond.

Synchronous Optical Network (SONET)
A USA standard for optical digital transmission at hierarchical rates from 155 Mbps to 2.5 Gbps and beyond.

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T

T1
T1 is a 1.544 Mbps multichannel digital transmission system for voice or data provided by long distance carriers. Also referred to as DS1 (Data Services).

T3
T3 is a 44.736 Mbps multichannel digital transmission system for voice or data provided by long distance carriers. Also referred to as DS3 (Data Services).

Tap
On Ethernet 10Base5 thick coaxial cable, a tap is a method of connecting a transceiver to the cable by drilling a hole in the cable, inserting a contact to the center conductor, and clamping the transceiver onto the cable at the tap.

TC
Telecommunications Cross Connect.

TDR
See Time Domain Reflectometry

Teflon
Dupont Company trademark for flourocarbon resins (see FEP and TFE).

Telecommunications Closet
see Closet

Telecommunications Equipment Room
see Equipment Room

Terminal
1. A point at which information may enter or leave a communications network. 2. A device by means of which wires may be connected to each other.

Terminator
A device that provides electrical resistance at the end of a transmission line. Its function is to absorb signals on the line, thereby keeping them from bouncing back and being received again by the network.

Thicknet
Ethernet 10Base5 coaxial cable.

Thinnet
Ethernet 10Base2 coaxial cable. Also called "cheapernet".

TIA
Telecommunications Industry Association. Body which authored the TIA/EIA 568-A "Commercial Building Telecommunications Wiring Standard" in conjunction with EIA.

Time Division Multiplexing (TDM)
A technique for combining many signals on a single circuit by interleaving bits or bytes of data from successive channels.

Time Domain Reflectometry
A technique for measuring cable lengths by timing the period between a test pulse and the reflection of the pulse from an impedance discontinuity on the cable. The returned waveform reveals many undesired cable conditions, including shorts, opens, and transmission anomalies due to excessive bends or crushing. The length to any anomaly, including the unterminated cable end, may be computed from the relative time of the wave return and nominal velocity of propagation of the pulse through the cable. See also Optical Time Domain Reflectometry.

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

Token Passing
A network access method in which a station must wait to receive a special token frame before transmitting.

Token-Ring
A local area network (LAN) protocol defined in the IEEE 802.5 standard in which computers access the network through a token passing scheme. Uses a star-wired ring topology.

Topology
The physical or logical interconnection pattern of a network.

Transceiver
A combination of the words TRANSmitter and reCEIVER. A transceiver is the set of electronics that send and receive signals on the Ethernet media system. Transceivers may be small outboard devices, or may be built into an Ethernet port. Also called Media Attachment Unit, or MAU.

Tracer
The contrasting color coding stripe along an insulated conductor of a wire pair.

Transmission Media
Anything such as wire, coaxial cable, fiber optics, air or vacuum, that is used to carry a signal.

Transmitter
A device that converts electrical signals for transmission to a distant point. In fiber optic systems, the electronic component that converts electrical energy to light energy.

Transition  Point
A location in the horizontal cabling where flat undercarpet cable connects to round cable.

Tree Topology
LAN topology similar to linear bus topology, except that tree networks can contain branches with multiple nodes.

Triaxial Cable, Triax
Triax cable is coax cable with an additional outer copper braid insulated from signal carrying conductors. It has a core conductor and two concentric conductive shields.

Trunk Cable
see Feeder Cable.

Turn-key
A contractual arrangement in which one party designs and installs a system and "turns over the keys" to another party who will operate the system.

Twinaxial Cable, Twinax
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. It is similar to coaxial cable except that there are two conductors at the center.

Twisted Pair
A multiple conductor cable whose component wires are paired together, twisted, and enclosed in a single jacket. Each pair consists of two insulated copper wires twisted together. When driven as a balanced line, the twisting reduces the susceptibility to external interference and the radiation of signal energy. Most twisted-pair cabling contains either 2, 4, or 25 pairs of wires.

Tx
Transmit

Type N Connector
A threaded barrel constant impedance coaxial connector for large diameter cable such as Ethernet 10Base5 thicknet cable.

Type 1
150 ohm shielded twisted pair (STP) cabling conforming to the IBM Cabling System Specifications. Two twisted pairs of 22 AWG solid conductors for data communications are enclosed in a braided shield covered with a sheath. Tested for operation up to 16 MHz. Available in plenum, non-plenum, riser, and outdoor versions.

Type 1A
Enhanced version of IBM Type 1 cable rated for operation up to 300 Mhz. Meets electrical specifications for 150 ohm STP-A Cable as documented in the TIA/EIA 568-A standard.

Type 2
150 ohm shielded twisted pair (STP) cabling conforming to the IBM Cabling System specifications. Two twisted pairs of 22 AWG solid conductors for data communications are enclosed in a braided shield. Four additional pairs of 22 AWG solid conductors for telephones are also included in the cable jacket but outside the braided shield. Tested for operation up to 16 MHz. Available in plenum and non-plenum versions.

Type 2A
Enhanced version of IBM Type 2 cable rated for operation up to 300 Mhz. Meets electrical specifications for 150 ohm STP-A Cable as documented in the TIA/EIA 568-A standard.

Type 3
IBM Cabling System designation for 100 ohm unshielded twisted pair (UTP) cabling similar to TIA/EIA Category 3 cabling. 22 AWG or 24 AWG conductors with a minimum of two twists per linear foot. Typically four twisted pairs enclosed within cable jacket.

Type 5
100/140 micron optical fiber cable conforming to the IBM Cabling System specifications. Two optical fibers are surrounded by strength members and a polyurethane jacket. Type 5J is a 50/125 micron version defined for use in Japan .

Type 6
150 ohm shielded twisted pair (STP) cabling conforming to the IBM Cabling System specifications. Two twisted pairs of 26 AWG stranded conductors for data communications. Flexible for use in making patch cables. Tested for operation up to 16 MHz. Available in non-plenum version only.

Type 6A
Enhanced version of IBM Type 6 cable rated for operation up to 300 Mhz. Meets electrical specifications for 150 ohm STP-A Cable as documented in the TIA/EIA 568-A standard.

Type 8
150 ohm under-carpet cable conforming to the IBM Cabling System Specifications. Two individually shielded parallel pairs of 26 AWG solid conductors for data communications. The cable includes "ramped wings" to minimize visibility when installed under carpeting. Tested for operation up to 16 MHz.

Type 9
150 ohm shielded twisted pair (STP) cabling conforming to the IBM Cabling System Specifications. A plenum rated cable with two twisted pairs of 26 AWG solid or stranded conductors for data communications enclosed in a braided shield covered with a sheath. Tested for operation up to 16 MHz.

Type 9A
Enhanced version of IBM Type 9 cable rated for operation up to 300 Mhz. Meets electrical specifications for 150 ohm STP-A Cable as documented in the TIA/EIA 568-A standard.

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U

UL
Underwriters Laboratories, Inc.

Unbalanced Line
A transmission line in which voltages on the two conductors are unequal with respect to ground. Generally one of the conductors is connected to a ground point. An example of an unbalanced line is a coaxial cable.

Underground Cable
Cable that is intended to be placed beneath the surface of the ground in ducts or conduit. Not necessarily intended for direct burial in the ground.

Unilay
A conductor with more than one layer of helically laid wires with the direction of lay and length of lay the same for all layers.

Unshielded Twisted Pair (UTP)
Twisted pair cabling that includes no shielding. UTP most often refers to the 100 ohm Category 3, 4, & 5 cables specified in the TIA/EIA 568-A standard.

USOC
Universal Service Order Code. Pronounced "U-Sock". An old Bell System term used to identify a particular service or device offered under tariff. Often used to refer to an old cable color code scheme that was current when USOC codes were in use.

UTP
see Unshielded Twisted Pair.  

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V

V
Symbol for Volt.

VA
Volt-ampere. A designation of power in terms of voltage and current.

Vampire Tap
see Tap
Velocity of Propagation
The transmission speed of electrical energy in a length of cable compared to speed in free space. Usually expressed as a percentage. Test devices use velocity of propagation to measure a signal's transit time and thereby calculate the cable's length.

VGM
Voice Grade Media (see Voice Grade)

VHF
Very high frequency. The portion of the electromagnetic spectrum extending from 30 to 300 MHz.

Video
A signal which contains visual information, such as a picture in a television system.

Voice Grade
A term used for twisted-pair cable used in telephone systems to carry voice signals.

Volt
The unit of electrical potential. One volt is the electrical potential that will cause one ampere of current to flow through one ohm of resistance.

Voltage
Electrical potential expressed in Volts.

Voltage Drop
The voltage developed across a component by the current flow through the resistance of the component.

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W

Watt
A unit of electrical power. One watt is equivalent to the power represented by one ampere of current flowing through a load with a voltage drop of one volt in a dc circuit.

Wavelength
The distance between successive peaks or nodes of a wave.

Wavelength Division Multiplexing (WDM)
The process of combining and splitting signals on the basis of difference in their wavelengths.

WAN
Wide Area Network. A network connecting computers within very large areas, such as states, countries, and the world.

Wiring Closet
see Closet

Work Area
That area of the premises cabling where users are located. The area from the communications outlet to the equipment connected to the premises cabling. Loosely, an office, cubicle, and so forth.

Workgroup
A collection of workstations and servers on a LAN that are designated to communicate and exchange data with one another.

Workstation
A computer connected to a network at which users interact with software stored on the network.

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X

X
Symbol for cross-connect.

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Y
 
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Z