Glossary

1Base5 IEEE 802.3 shorthand term for StarLAN at 1Mbps data transfer rate.
10Base2 IEEE 802.3 shorthand term for 10 Mbps Ethernet based on Manchester signal encoding over thin coaxial cable. Also called "Thinnet" or "Cheapernet".
10Base5 IEEE 802.3 shorthand term for 10 Mbps Ethernet based on Manchester signal encoding over thick coaxial cable. Also called "Thicknet".
10Base-F IEEE 802.3 shorthand term for 10 Mbps Ethernet based on Manchester signal encoding over fiber optic cable.
10Base-T IEEE 802.3 shorthand term for 10 Mbps Ethernet based on Manchester signal encoding over category 3 or better twisted pair cable.
10Broad36 IEEE 802.3 shorthand term for 10 Mbps Ethernet on broadband cable.
100Base-FX IEEE 802.3 shorthand term for 100 Mbps Fast Ethernet based on 4B/5B signal encoding over fiber optic cable.
100Base-T IEEE 802.3 shorthand term for entire 100 Mbps Fast Ethernet system.
100Base-T2 IEEE 802.3 shorthand term for 100 Mbps Fast Ethernet based on PAM5x5 signal encoding and using two pairs of category 3 twisted pair cable.
100Base-T4 IEEE 802.3 shorthand term for 100 Mbps Fast Ethernet based on 8B6T signal encoding and using four pairs of category 3 twisted pair cable.
100Base-TX IEEE 802.3 shorthand term for 100 Mbps Fast Ethernet based on 4B/5B signal encoding and using two pairs of category 5 twisted pair cable.
100Base-X IEEE 802.3 shorthand term for any 100 Mbps Fast Ethernet system based on 4B/5B signal encoding. Includes 100Base-TX and 100Base-FX.
1000Base-CX IEEE 802.3 shorthand term for 1000 Mbps Gigabit Ethernet based on 8B/10B signaling over copper cable.
1000Base-LX IEEE 802.3 shorthand term for 1000 Mbps Gigabit Ethernet based on 8B/10B signaling using long wavelength laser transmitters over fiber optic cable.
1000Base-SX IEEE 802.3 shorthand term for 1000 Mbps Gigabit Ethernet based on 8B/10B signaling using short wavelength laser transmitters over fiber optic cable.
1000Base-T IEEE 802.3 shorthand term for 1000 Mbps Gigabit Ethernet over twisted pair cable.
1000Base-X IEEE 802.3 shorthand term for any 1000 Mbps Gigabit Ethernet based on 8B/10B signaling. Includes 1000Base-CX, 1000Base-LX, and 1000Base-SX.
2B+D Describes basic ISDN service (2B+D = Two bearer channels and one data channel).
4B/5B Signal encoding method used in 100Base-TX/FX Fast Ethernet and and FDDI standards. 4-bit binary values are encoded into 5-bit symbols.
66-type Connecting Block Used by telephone company to terminate twisted pairs. Not recommended for LAN use.
8B6T Signal encoding method used in 100Base-T4 Fast Ethernet standard.
8B/10B Signal encoding method used in the 1000Base-X Gigabit Ethernet standards.
802.1 see IEEE 802.1
802.2 see IEEE 802.2
802.3 see IEEE 802.3
802.5 see IEEE 802.5
Air Blown Fiber (ABF):  Small, flexible plastic microduct tubing installed prior to the installation of individual or multiple optical fibers that are blown in through the microduct using compressed air.
Asynchronous Transfer Mode (ATM):  Technology selected by the International Telecommunications Union (ITU, formerly CCITT) for broadband ISDN. This communications protocol is also specified by the ATM Forum (Foster City, CA) for 155 Mb/s transmission over twisted-pair cable and various bit rate optical fiber cabling applications.
Attenuation:  A reduction in power or amplitude of the transmitted signal. In cables, it is generally expressed in decibels per unit length.
Attenuation to Crosstalk Ratio (ACR):  The difference between attenuation and crosstalk measured in decibels.
Auxiliary Disconnect Outlet (ADO):  A device usually located within the tenant or living unit used to terminate the ADO cable or backbone cable.
Auxiliary Disconnect Outlet (ADO) Cable:  In residential applications, the cable from the auxiliary telecommunications disconnect outlet/connector or the distribution device in a customer's premises to the backbone facility or the point of demarcation.
Ampere - A unit of measure of electrical current.
Acceptance Angle The largest angle that a guided ray of light is accepted by a fiber optic cable.
Access Method The rules by which a network device gains the rights to transmit a communication on the network. Common methods include carrier sense multiple access with collision detection, token passing, and demand priority.
ACR see Attenuation Crosstalk Ratio.
Alternating Current An electric current that cyclically reverses the direction of flow. Frequency is the rate at which a full cycle occurs in one second.
Amplitude The maximum value of a varying signal.
Amplitude Modulation 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.
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.
Audio Used to describe the range of frequencies within range of human hearing; approximately 20 to 20,000 Hz.
AUI see Attachment Unit Interface.
AWG American Wire Gage - A wire diameter specification. The smaller the AWG number, the larger the wire diameter.
Administrator Person with unlimited access to all features of a local network; responsible for the administration and maintenance of the network. Among other tasks, the administrator assigns IP addresses and must ensure that they are unique.
AUI - Attachment Unit Interface Interface for the connection of an external Ethernet transceiver.

The data is made available by the receiver through a 15-pin D-SUB adapter in separate packets of send, receive and collision information. The terminal device is connected by means of an 8-wire TP cable of max. 50m in length.

In the past, the AUI interface was mainly used to connect terminal devices to 10Base5-transceivers (yellow cable), they are today increasingly applied for the connection of FOC transceivers (fiber-optic technology) and similar devices.

Backbone Cabling:  Cable and connecting hardware that comprise the main and intermediate cross-connects, as well as cable runs that extend between telecommunications rooms, equipment rooms and entrance facilities.
Balance:  An indication of signal voltage equality and phase polarity on a conductor pair. Perfect balance occurs when the signals across a twisted-pair are equal in magnitude and opposite in phase with respect to ground.
Balanced Signal Transmission:  Two voltages, equal and opposite in phase with respect to each other, across the conductors of a twisted-pair (commonly referred to as tip and ring).
Balun:  An impedance matching transformer used to convert unbalanced coaxial signals to balanced signals.
Bandwidth:  A range of frequencies, usually the difference between the upper and lower limits of the range, typically expressed in megahertz (MHz). It is used to describe the information-carrying capacity of a medium. In copper and optical fibers, the bandwidth decreases with increasing length. Optical fiber bandwidth is specified in megahertz kilometers (MHz-km).
Bonding :  The permanent joining of metallic parts to form an electrically conductive path that will assure electrical continuity and the capacity to conduct safely any current likely to be imposed on it.
Break Test Access:  Method of disconnecting a circuit that has been electrically bridged to allow testing on either side of the circuit without disturbing cable terminations. Devices that provide break test access include: disconnect blocks, bridge clips, plug-on protection modules, and plug-on patching devices.
Bridged Tap:  The multiple appearances of the same cable pair or fiber at several distribution points. Also known as parallel connections.
Bridging:  A means of providing through connections between conductors or pairs that are terminated on connecting blocks. These through connections are commonly provided by means of individual metallic bridging clips or multiple bridging clips that are Upgrading_Current_Officed in a plastic insulator.
Building Distributor (BD):  The international term for intermediate cross-connect. A distributor in which the building backbone cable(s) terminates and at which connections to the campus backbone cable(s) may be made.
Bundled Cable:  An assembly of two or more cables continuously bound together to form a single unit prior to installation (sometimes referred to as loomed, speed-wrap or whip cable constructions).
Bus Topology:  A linear configuration where all network devices are placed on a single length of cable. It requires one backbone cable to which all network devices are connected.
10Base2 - 10Mbit/s BASEband 200(185)m/segment Ethernet topology based on coaxial wiring with a transfer rate of 10Mbit/s.

10Base2 is more commonly known as Cheapernet or thin Ethernet. Its wiring consists of coaxial cables with impedance of 50 Ohm in a thin a flexible design, whereby the individual stations are connection in a bus-type system. The beginning and the end of each section must be equipped with terminal resistors of 50 Ohm.

The transceivers are integrated in network cards, so that the bus must be routed directly to each workstation, where it is terminated by means of BNC T adapters. The attenuation of the cable and the often numerous plug-type connections limit the range of a 10Base2 segment to max. 185 m and 30 connections. Between two stations, not more than four repeaters might be installed.

The disadvantage of the physical bus topologies of Ethernets is due to the fact that a disruption in the cabling, e.g. a disconnected adapter, results in the shutdown of the entire network segment.

10Base5 - 10Mbit/s BASEband 500m/segment 10Base5 is the original Ethernet specification. In this case, the wiring consists of coaxial bus cables with an impedance of 50 Ohm and a max. permitted length of 500m (yellow cable). Due to the coaxial technology with two conductors (core and shield), both 10Base5 and 10Base2 allow only for half-duplex operation. The network stations are connected by means of external transceivers that receive the signal through vampire connectors directly from the bus cable without interrupting the cable by plug adapters or similar devices. The data is made available by the receiver through a 15-pin D-SUB adapter in a separate packets of send, receive and collision information. The terminal device is connected by means of an 8-wire TP cable of max. 50m in length. Maximum four repeaters are permitted between any two stations. This rule however only applies to repeaters in series. In the case of tree-type networks, an unlimited number of repeaters can thus be integrated.

Due to the use of a relatively high-quality cable without interruptions from connectors, these networks have the advantage that they allow for long segments and a large number of possible tie-ins per segment (max. 100).

The rather thick and hard to bend yellow cable and the additional costs for external transceivers are however considerable disadvantages of 10Base5 and have contributed to the popularity of 10Base2 systems.

10BaseT - 10Mbit/s BASEband twisted pair With the definition of 10BaseT, the physical and the logical topology were separated. The cabling originates from a hub that provides the central active component. A category 3 cable of 100 Ohm with at least two pairs of wires is required, in which data is sent on separated send and receive wires. The connectors are 8-pin RJ45-type adapters in which the pairs are assigned to pins 1/2 and 3/6. The maximum length of a segment (= connection from the hub to the terminal device) is limited to 100m. 10BaseT technology was first introduced in the US, as it permitted the use of standard telephone wires for networking purposes. For Germany, this advantage was irrelevant, as the national telephone system was based on star-shape 4-conductor cables that did not conform to the requirements of category 3.

With 10BaseT, interruptions in cables or disconnected adapters, which, in all other physical bus structures result in the complete shutdown of the affected segment, only affect the respective workstation

100BaseT4 - 100Mbit/s BASEband twisted 4 pairs 100BaseT4 is specified as an Ethernet transmission with 100Mbit/s. Similar to 10BaseT, the system is based on a star structure with a central hub. Also here, category 3 cables with impedance of 100 Ohm and RJ45 adapters are used in a system of max. 100m length. The ten times greater data transfer rate of 100mbit/s combined with the category 3 bandwidth of 25 MHz is mainly achieved by the use of all four available conductors. With 100BaseT4, three pairs are always used simultaneously in each data direction.
100BaseTX - 100Mbit/s BASEband twisted 2 pairs 100BaseTX describes a 100Mbit/s data transfer with 2 wire pairs over a network with category 5 components. Cable, RJ45 wall sockets, patch panels, etc. must be dimensioned for a transmission frequency of at least 100MHz.
BNC - Bayonet Neill Concelmann The BNC adapter is a bayonet locking connector for the linking of two coaxial cables. BNC adapters are used in 10Base2 networks for the physical linking of RG-58 cables (Cheapernet).
Bridge Bridges connect subnetworks and determine, based on the Ethernet address, which packets are to pass the bridge and which are to be refused. The respective information is retrieved from the bridge tables. Depending on the bridge type, this data must be manually entered by the administrator or is generated dynamically by the bridge.

See also Router

Bus system In a bus system, several terminal devices share a common data line (bus line). Since only one terminal device may use the line at any one time, bus systems require a protocol that controls the access rights to the line. Traditional bus systems are the Ethernet topologies 10Base2 and 10Base5.
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.
Backreflection The light reflected back towards the source from the fiber optic ends and deformations.
Backscattering Refers to light diffraction at microscopic non-uniformities in the index of refraction of the optical fiber causing backreflection of optical power towards the source.
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.
Bandpass A range of frequencies or wavelengths within which a component operates.
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.
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.
Bel A unit that represents the logarithm of the ratio of two levels.
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.
BL Blue.
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.
Bonding A method used to produce good electrical contact between metallic parts. Also refers to the grounding bars and straps used in buildings to bond equipment to an approved ground.
BPS Bits per second.
BR Brown.
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 New_Officetened conductor to be used as a grounding strap.
BRI ISDN Basic Rate Interface
Bridged Tap Multiple appearances of the same cable pair at several distribution points.
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 1. 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. 2. With LANs, a linear network topology in which all computers are connected to a single cable.
Butyl Rubber A synthetic rubber with good electrical insulating properties.
Byte A group of 8 bits.
Cabling:  A combination of cables, wire, cords and connecting hardware used in the telecommunications infrastructure.
Campus Backbone:  Cabling between buildings that share telecommunications facilities.
Campus Distributor (CD):  The international term for main cross-connect. The distributor from which the campus backbone cable emanates.
Category (1):  ANSI/TIA/EIA-568-B series of documents, the North American standards for cabling describes mechanical properties and transmission characteristics of unshielded twisted-pair (UTP) cables and screened twisted-pair (ScTP) cables and assigns a unique number classification (category 3, category 5e, and category 6).
Category (2):  ISO/IEC IS 11801 2nd edition, the international standard for cabling and local standardization documents define cabling component categories based on transmission performance parameters such as attenuation and NEXT loss, over a specified frequency range. Component categories category 5, category 6 and category 7.
Channel:  The end-to-end transmission path connecting any two points at which application specific equipment is connected. Equipment and work area cables are included in the channel.
Classification:  Application classes for cabling have been identified for the purpose of the ISO/IEC 11801 standard;
  • Class A: cabling is characterized up to 100 kHz
  • Class B: cabling is characterized up to 1 MHz
  • Class C: cabling is characterized up to 16 MHz
  • Class D: cabling is characterized up to 100 MHz
  • Class E: cabling is characterized up to 250 MHz
  • Class F: cabling is characterized up to 600 MHz
  • Optical Class: optical fiber links are characterized from 10 MHz and above.
Collapsed Backbone:  A centralized network contained in one device. The network is said to be collapsed and made to fit into a box. Individual networks are connected to this central device and can then communicate with one another.
Common Mode Transmission:  A transmission scheme where voltages appear equal in magnitude and phase across a conductor pair with respect to ground. May also be referred to as longitudinal mode.
Consolidation Point (CP):  A location for interconnection between horizontal cables that extend from building pathways and horizontal cables that extend into work area pathways.
Cross-connect:  A facility enabling the termination of cables as well as their interconnection or cross-connection with other cabling or equipment. Also known as a distributor.
Cross-connection:  A connection scheme between cabling runs, subsystems and equipment using patch cords or jumpers that attach to connecting hardware on each end.
Crosstalk:  Noise or interference caused by electromagnetic coupling from one signal path to another. Crosstalk performance is generally expressed in decibels.
Cheapernet Alternative name for an Ethernet based on 10Base2..
Com-Server Small terminal devices in TCP/IP-Ethernet networks, providing interfaces for serial devices and digital I/O ports via the network. Com-Servers can be used as servers or clients respectively.
c A small "c" is the symbol for the speed of light in a vacuum.
C A capital "C" is the designation for celsius.
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 An electrical signal of a set frequency that can be modulated in order to carry data.
Carrier Detect A circuit that detects the presence of a carrier.
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 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.
CBX Computerized Branch Exchange.
Cellular Polyethylene Expanded or "foam" polyethylene, a material with a reduced dielectric constant consisting of individual closed cells of inert gas suspended in a polyethylene medium.
CDDI Copper Distributed Data Interface - A version of FDDI that uses copper wire media instead of fiber optic cable.
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.
Characteristic Impedance 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.
Cheapernet Another name for thin Ethernet or 10Base2 systems.
Chirping Refers to the change of optical frequency of laser diodes when the laser diode is pulsed between two different optical power levels. Chirp broadens the laser's spectral width causing chromatic dispersion.
Chromatic Dispersion Synonym for "material dispersion".
Circuit 1. A system of conducting media designed to pass a signal or voltage between two points. 2. A bi-directional communications path between two pieces of associated equipment.
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.
Coherence Refers to the phase stability of two wavetrains, from the same optical wave, separated in time
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 Upgrading_Current_Officed for protection and to prevent burning cable from spreading flames or smoke in the event of a fire.
Conductivity The ability of a material to allow the flow of electrical current. It is the reciprocal of resistivity. Measured in "mhos" (ohms backwards).
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.
Coupling ratio The percentage of optical power transfered to the secondary output port of a coupler relative to the total power of the primary and the secondary output ports.
CRC see Cyclic Redundancy Check
Critical angle The angle at the interface between core and cladding where a guided ray in the core undergoes total internal reflection.
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.
CSA Canadian Standards Association
CSMA/CD see Carrier Sense Multiple Access with Collision Detect.
Current The flow of charge in a conductor. See "alternating current" and "direct current".
Current Loop A two wire transmit/receive interface.
Customer Premises Buildings, offices, and other structures under the control of a telecommunications customer.
Cutoff Wavelength A distinct boundary, in the wavelength spectrum, which characterizes the mode of operation of a fiber. A fiber operating at wavelengths lower than the cutoff wavelength is multimode while the same fiber operating at wavelengths higher than cutoff wavelength is single mode.
Cut-through Resistance The ability of a material to withstand mechanical pressure without damage.
Cyclic Redundancy Check (CRC) An error checking technique used to ensure the accuracy of transmitting digital code over a communications channel. The transmitted messages are divided into predetermined lengths which, used as dividends, are divided by a fixed divisor. The remainder of the calculation is appended onto and sent with the message. At the receiving end, the computer recalculates the remainder. If it does not match the transmitted remainder, and error is detected.
Decibel (dB):  A standard unit for expressing transmission gain or loss as derived from a ratio of signal voltages or power.
Delay Skew :  The difference in propagation delay between the fastest and slowest pair in a cable or cabling system.
Demarcation Point (DP):  A point at which two services may interface and identify the division of responsibility.
Differential Mode Transmission:  A transmission scheme where voltages appear equal in magnitude and opposite in phase across a twisted-pair with respect to ground. May also be referred to as balanced mode.
Distributor:  The term used for the functions of a collection of components (e.g. patch panels, patch-cords) used to interconnect cables.
Ducting:  See Pathway.
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.
DC see Direct Current.
DCE Data Communications Equipment. Any equipment that connects to Data Terminal Equipment (DTE) to allow transmission between DTEs.
DC Loop Resistance The total DC resistance of a cable. For twisted pair cable, it includes the round trip resistance, down one wire of the pair and back up the other wire.
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.
DGM Data Grade Media (see Data Grade)
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).
Direct Current An electric current that flows in one direction and does not reverse direction as with "alternating current".
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.
Distortion Any undesired change in a wave for or signal.
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 1. A single enclosed raceway for wires or cable. 2. An enclosure in which air is moved.
Duplex 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 two plugs.
Electromagnetic Compatibility (EMC):  The ability of a system to minimize radiated emissions and maximize immunity from external noise sources.
Electromagnetic Interference (EMI):  The interference in signal transmission or reception caused by the radiation of electrical and magnetic fields.
Electronic Industries Alliance (EIA):  An organization that sets standards for interfaces to ensure compatibility between data communications equipment and data terminal equipment.
Electronic Industries Association:  A standards organization that specializes in the electrical and functional characteristics of interface equipment. The organization sets standards for interfaces to ensure compatibility between data communications equipment and data terminal equipment.
Entrance Facility (EF):  An entrance to a building for both public and private network service cables (including antennae), including the entrance point at the building wall and continuing to the entrance room or space. Entrance facilities are often used to Upgrading_Current_Office electrical protection equipment and connecting hardware for the transition between outdoor and indoor cable.
Entrance Facility, Telecommunications:  An entrance to a building for both public and private network service cables (including antennae) beginning with the entrance point at the building wall and continuing to the entrance room or space.
Entrance Point, Telecommunications:  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
Equal Level Far-end Crosstalk (ELFEXT):  Crosstalk measured at the opposite end from which the disturbing signal is transmitted, normalized by the attenuation contribution of the cable or cabling.
Equipment Cable:  A cable or cable assembly used to connect telecommunications equipment to horizontal or backbone cabling.
Equipment Room (ER):  A centralized space for telecommunications equipment that serves the occupants of the building or multiple buildings in a campus environment. An equipment room is considered distinct from a telecommunications room because it is considered to be a building or campus serving (as opposed to floor serving) facility and because of the nature or complexity of the equipment that it contains.
Equipment Room, Telecommunications:  A centralized space for telecommunications equipment that serves the occupants of the building. An equipment room is considered distinct from the telecommunications room because of the nature and complexity of the equipment it Upgrading_Current_Offices.
Ethernet Ethernet is the currently most commonly used technology for local networks. There are three different Ethernet topologies: 10Base2, 10Base5 and 10BaseT ; the transfer rate of Ethernets is 10 Mbit/s.
E1/E3 The European versions of T1 and T3. E1 runs at 2.048 Mbps and E3 runs at 34 Mbps.
Earth A term for zero reference ground.
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 Coupling The transfer of energy by means of a varying magnetic field. Inductive coupling.
Electromagnetic Field The combined electric and magnetic field caused by electron motion in conductors.
Electromagnetic Interference An interfering electromagnetic signal. Network wiring and equipment may be susceptible to EMI as well as emit EMI.
Electrostatic Electrical charge that exists when the charge is at rest.
Electrostatic Coupling The transfer of energy by means of a varying electrostatic field. Capacitive coupling.
ELFEXT Equal Level Far End Crosstalk
EMI see Electromagnetic Interference.
Encoding A means of combining clock and data information into a self-synchronized stream of signals.
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.
EPDM Ethylene-propylene-diene monomer rubber. A material with good insulating properties.
EPR Ethylene-propylene copolymer rubber. A material with good insulating properties.
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.
FC Connector:  A type of optical fiber connector identifiable by its round, screw-operated locking nut. It is usually metal. Its ruggedness leads it to be widely used in test equipment
Far-end Crosstalk (FEXT):  Crosstalk measured at the opposite end from which the disturbing signal is transmitted.
Fiber Distributed Data Interface (FDDI):  Operates at 100 megabits per second (Mb/s). Developed by the ANSI X3T9.5 committee. This is a token-passing, dual-ring architecture that provides redundancy using fiber optic cable with transmission up to 2 kilometers.
Fiber Optic Transmission:  A communications scheme whereby electrical data is converted to light energy and transmitted through optical fibers.
Firestop:  A material, device, or assembly of parts installed in a cable pathway at a fire-rated wall or floor to prevent passage of flame, smoke or gases through the rated barrier (e.g., between cubicles or separated rooms or spaces).
Floor Distributor (FD):  The international term for horizontal cross-connect. The distributor used to connect between the horizontal cable and other cabling subsystems or equipment.
Fast Ethernet A fast Ethernet is basically an upgrade of a 10BaseT topology from 10Mbit/s to 100Mbit/s.

See also 100BaseT4 and 100BaseTX

f Frequency
Farad A unit of capacitance that stores one coulomb of electrical charge when one volt of electrical pressure is applied.
Fast Ethernet Ethernet standard supporting 100 Mbps operation.
FCC Federal Communications Commission.
FCS Frame Check Sequence. Error detection field.
Feeder Cable In a CATV system, the transmission cable from the head end (signal pickup) to the trunk amplifier. Also called a trunk cable.
FEP Fluorinated ethylene propylene. A thermoplastic with excellent dielectric properties which is often used as insulation in fire rated cables.
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.
Fillers Nonconducting components cabled with the insulated conductors or optical fibers to impart roundness, flexibility, tensile strength, or a combination of all three.
Floating Refers to a circuit that has no connection to ground.
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.
Full Duplex Transmission Data transmission over a circuit capable of transmitting in both directions simultaneously.
Ground:  A conducting connection, whether intentional or accidental, between an electrical circuit (telecommunications) or equipment and earth, or to some conducting body that serves in place of the earth.
G Green
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 Loop A condition where an unintended connection to ground is made through an interfering electrical conductor.
Hertz (Hz):  A measure of frequency as defined in units of cycles per second.
Home-run Cabling:  A distribution method in which individual cables are run directly from the horizontal cross-connect to each telecommunications outlet. This configuration is also known as star topology.
Horizontal Cabling:  The cabling between and including the telecommunications outlet and the horizontal cross-connect.
Horizontal Cross-connect (HC):  A cross-connect of horizontal cabling to other cabling, e.g., horizontal, backbone, or equipment.
Hub:  Equipment that serves as the centralized connection point for a network or portion thereof. Hubs are used for multiplexing, multi-port bridging functions, switching and test access. They can be either passive or active and are not considered to be part of the cabling infrastructure.
Hybrid cable:  An assembly of two or more cables, of the same or different types or categories, covered by one overall sheath.
Hub A hub, also referred to as a star coupler, allows for the connection of multiple network stations in a star configuration. Data packets received at a port are forwarded to all other ports.

Apart from hubs for 10BaseT (10Mbit/s) and 100BaseTX (100Mbit/s), there are also autosensing hubs that automatically detect whether a connected terminal device operates at 10Mbit/s or 100Mbit/s. By means of autosensing hubs, it is thus possible to integrate older 10BaseT devices into new 100BaseT networks.

Half Duplex Transmission Data transmission over a circuit capable of transmitting in either direction, but not simultaneously.
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.
HF High Frequency
Host Computer that offers services on a network.
HVAC Heating, ventilation, and air conditioning system.
Hypalon A DuPont trade name for a synthetic rubber (chlorosulfonated polyethylene) used as insulating and jacketing material for cabling.
Insertion loss (1):  The loss resulting from the insertion of a device in a transmission line, expressed as the reciprocal of the ratio of the signal power delivered to that part of the line following the device to the signal power delivered to that same part before insertion.
Insertion loss (2):  In an optical fiber system, the loss of optical power caused by inserting a component, such as a connector, coupler or splice, into a previously continuous optical path.
Insulation Displacement Connection (IDC):  A wire connection device that penetrates the insulation of a copper wire when it is being inserted (punched-down) into a metal contact, allowing the electrical connection to be made.
Intelligent Hub:  A hub that performs bridging and routing functions in a collapsed backbone environment.
Interbuilding Backbone :  Telecommunications cable(s) that are part of the campus subsystem that connect one building to another.
Interconnection:  A connection scheme that provides direct access to the cabling infrastructure and the ability to make cabling system changes using equipment cords.
Intermediate Cross-Connect (IC):  The connection point between a backbone cable that extends from the main cross-connect (first-level backbone) and the backbone cable from the horizontal cross-connect (second-level backbone).
Intermediate Distribution Frame (IDF):  In a central office or customer premises, a frame that (a) cross connects the user cable media to individual user line circuits and (b) may serve as a distribution point for multipair cables from the main distribution frame (MDF) to individual cables connected to equipment in areas remote from these frames.
Intrabuilding Backbone:  Telecommunications cable(s) that are part of the building subsystem that connect one equipment room to another.
ISDN - Integrated Services Digital Network ISDN is the new standard of the telecommunications technology and has replaced the analog telephone network in Germany and other countries. ISDN integrates a number of services such as telephone, fax but also video conferencing and data transfer into one system. Therefore, ISDN is suitable for the transfer of voice, text, graphics and other digital data from one terminal device to an other.

Through the S0 interface of a basic connection, ISDN provides two basic channels (B channels) at 64kbit/s each and a control channel (D channel) at 16kbit/s. The digital connection to the end user has thus a combined transfer rate of 144kbit/s (2B+D). The two B channels can be used simultaneously for two different services at a bit rate of 64kbit/s.

I Symbol used to designate current.
IC see Intermediate Cross Connect.
ICEA Insulated Cable Engineers Association
ICS IBM Cabling System
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.
Impedance Matching Transformer A transformer designed to match the impedance of one circuit to another.
Index of Refraction The ratio of light velocity in a vacuum to its velocity in a given transmission medium.
Infrastructure, Telecommunications A collection of those telecommunications components, excluding equipment, that together provide the basic support for the distribution of all information within a building or campus.
Injection Laser Diode A semiconductor laser in which the lasing occurs at the junction of n-type and p-type semiconductor materials.
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.
Isolation The ability of a circuit or component to reject interference.
Insulation A material which is nonconductive to the flow of electrical current.
Interference Undesirable signals which interfere with the normal operation of electronic equipment or electronic transmission.
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.
Jumper Wire:  An assembly of twisted-pairs without connectors on either end used to join telecommunications links at a cross-connect.
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.
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.
Link:  An end-to-end transmission path provided by the cabling infrastructure. Cabling links include all cables and connecting hardware that comprise the horizontal or backbone subsystems. Equipment and work area cables are not included as part of a link.
Local Area Network (LAN):  A geographically limited data communications system for a specific user group consisting of a group of interconnected computers, sharing applications, data and peripheral devices such as printers and CD-ROM drives intended for the local transport of data, video, and voice.
Local Exchange Carrier (LEC):  The local regulated provider of public switched telecommunications services.
Longitudinal Conversion Loss (LCL):  A measure (in dB) of the differential voltage induced on a conductor pair as a result of subjecting that pair to longitudinal voltage. LCL is considered to be a measure of circuit balance.
LAN - Local Area Network Local network within a defined area, using a fast transmission medium such as Ethernet.
L Symbol used to designate inductance.
LAN Adapter see Network Interface Card
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.
LATA Local Access and Transport Area.
Lay The axial distance required for one cabled conductor or conductor strand to complete one revolution about the axis around which it is cabled.
Lay Direction The direction of the progressing spiral twist in while looking along the axis of the cable away from the observer. The lay direction can be either "left" or "right".
LCTL see Longitudinal Conversion Transfer Loss
Leakage An undesirable passage of current over the surface of or through a connector.
Leased Line A private telephone line rented for the exclusive use of a leasing customer, without interchange switching arrangements.
LED see Light Emitting Diode.
LF Low frequency.
Light Emitting Diode A semiconductor diode which emits incoherent light when a current is passed through it. Used as a light source in fiber optic transmission.
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.
Longitudinal Coversion Transfer Loss (LCTL) Also called far-end unbalance attenuation, measures cable balance by the comparison of the signal appearing across the pair to the signal between ground and the pair, where the applied signal is at the opposite end of the cable from where the across pair signal is measured.
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.
Loss The portion of energy applied to a system that is dissipated and performs no useful work.
Lossy Having poor efficiency.
MAU (1):  Multi-station Access Unit in reference to Token Ring.
MAU (2):  Medium Attachment Unit in reference to Ethernet A wiring concentrator used in Local Area Networks. A device that allows terminals, PCs, printers, and other devices to be connected in a star-based configuration to Token Ring or Ethernet LANs. MAU hardware can be either active or passive and is not considered to be part of the cabling infrastructure.
Main Cross-connect (MC):  A cross-connect for first level backbone cables, entrance cables, and equipment cables.
Modular Jack:  A telecommunications outlet/connector for wire or cords as defined in the FCC Part 68 Subpart F. Modular jacks can have 4, 6 or 8 contact positions, but not all the positions need be equipped with contacts.
Modular Plug:  A telecommunications connector for wire or cords as defined in the FCC Part 68 Subpart F. Modular plugs can have 4, 6 or 8 contact positions, but not all the positions need be equipped with contacts.
Multi-user Telecommunications Outlet Assembly (MuTOA):  A grouping in one location of several telecommunications/outlet connectors.
Multimedia (1):  An application that communicates to more than one of the human sensory receptors.
Multimedia (2):  Applications that communicate information by more than one means or cabling media.
Multimode Optical Fiber:  An optical fiber that will allow many bound modes to propagate. The fiber may be either a graded-index or step-index fiber. Multimode optical fibers have a much larger core than singlemode fibers. See also Optical Fiber Cable.
M Mutual Inductance
mA Milliampere (one thousandth of an ampere)
MAC see Medium Access Control
Manchester Coding 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.
Material Dispersion Dispersion that results from each wavelength traveling at a different speed than other wavelengths through an optical fiber. Also called "chromatic dispersion".
Mbaud Megabaud. One million baud.
Mbps Megabits per second.
MC see Main Cross Connect
MDF 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.
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.
MII see Medium Independent Interface.
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 set 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.
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.
Mutual Capacitance Capacitance between two conductors when all other conductors are connected together.
MV Millivolt (one thousandth of a volt)
MW Milliwatt (one thousandth of a watt)
Mylar DuPont trademark for polyethylene terephtalete (polyester) film.
Nanosecond (ns):  One billionth of a second (10-9 seconds).
Near-end Crosstalk (NEXT Loss) :  The undesired coupling of a signal from one pair of wires to another. Signal distortion as a result of signal coupling from one pair to another at various frequencies.
Network Demarcation Point :  The point of interconnection between the local exchange carrier’s telecommunication facilities and the telecommunications systems wiring and equipment as the end user’s facility. This point shall be located on the subscriber side of the telephone company’s protector or the equivalent thereof in cases where a protector is not required.
N connector A coaxial connector used for Ethernet 10Base5 thick coax segments.
Nanometer (nm) One billionth of a meter.
NBR Butadiene-acrylonitrile copolymer rubber, a material with good oil and chemical resistance.
NEC National Electrical Code.
NEMA National Electrical Manufacturers Association.
Neoprene A synthetic rubber with good resistance to oil, chemical, and flame. Also called polychloroprene.
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).
NFPA National Fire Protection Association
Nibble One half byte.
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.
Nomex Dupont trademark for a temperature-resistant, flame retardant nylon.
NRZ Non Return to Zero.
NRZI Non Return to Zero Inverted.
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.
Nylon An abrasion resistant thermoplastic with good chemical resistance.
Open Office Cabling:  The cabling that distributes from the telecommunications closet to the open office area utilizing a consolidation point or multi-user telecommunications outlet assembly.
Outlet, Telecommunications :  A fixed connecting device where the horizontal cable terminates. The telecommunications outlet provides the interface to the work area cabling. Sometimes referred to as a telecommunications outlet/connector.
Outlet/Connector, Telecommunications:  A connecting device in the work area on which horizontal cable terminates.
O Orange
OC-n See Optical Carrier n
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.
Patch Cord:  A length of cable with connectors on one or both ends used to join telecommunications links at a cross-connect.
Patch Panel:  Connecting hardware that typically provides means to connect horizontal or backbone cables to an arrangement of fixed connectors that may be accessed using patch cords or equipment cords to form cross-connections or interconnections.
Pathway:  A facility (i.e., conduit) for the placement and protection of telecommunications cables. Same as raceway or ducting.
Plenum:  A compartment or chamber to which one or more air ducts are connected and that forms part of the air distribution system.
Private Branch Exchange (PBX):  A private switching system usually serving an organization, such as a business, located on the customer’s premises. It switches calls both inside a building or premises and outside to the telephone network, and can sometimes provide access to a computer from a data terminal.
Propagation Delay:  The amount of time that passes between when a signal is transmitted and when it is received at the opposite end of a cable or cabling.
Punch Down:  A method for securing wire to a quick clip in which the insulated wire is placed in the terminal groove and pushed down with a special tool. As the wire is seated, the terminal displaces the wire insulation to make an electrical connection. The punch down operation may also trim the wire as it terminates. Also called cut down.
PABX 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.
PBX Private Branch Exchange
PC Personal Computer
PCC Premises Communication Cable, CSA Cable Designation.
PDN Public Data Network
Peak The maximum instantaneous value of a varying current or voltage.
Pedestal A device, usually mounted on the floor, which is used to Upgrading_Current_Office voice/data jacks or power outlets at the point of use. Also referred to as a monument, tombstone, above floor fitting or dogUpgrading_Current_Office.
Periodicity Uniformly spaced variations in the insulation diameter of a transmission cable that result in reflections of a signal.
Phase An angular relationship between waves.
Phase Modulation (PM) One of three basic methods (see also Amplitude and Frequency Modulation) of adding information to a sine wave signal in which its phase is varied to impose information on it.
Phase Shift A change in the phase relationship between two alternating quantities.
Photodetector Used on the receiving end of a fiber optic cable to convert light energy into electrical energy.
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 High polymeric substances, including both natural and synthetic products, but excluding the rubbers that are capable of flowing under heat and pressure.
Plastic Fiber An optical fiber made of plastic rather than glass.
Plasticizer A chemical added to plastics to make them softer and more flexible.
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.
Polybutadiene A type of synthetic rubber often blended with other synthetic rubbers to improve their properties.
Polyethylene A thermoplastic material having excellent electrical properties.
Polymer A substance made of repeating chemical units or molecules. The term is often used in place of plastic, rubber, or elastomer.
Polypropylene A thermoplastic material similar to polyethylene but somewhat stiffer and with a higher softening point (temperature).
Polyurethane Broad class of thermoplastic polymers with good abrasion and solvent resistance. Can be solid or cellular (foam).
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
Potting Sealing by filling with a substance to exclude moisture.
Power Level The difference between the total power delivered to a circuit, cable, or device and the power delivered by that device to a load.
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).
Protector A device that limits damaging voltages on metallic conductors.
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.
Pulse A current or voltage which changes abruptly from one value to another and back to the original value in a finite length of time.
Pulse Code Modulation (PCM) The most common method of representing an analog signal, such as speech, by sampling at a regular rate and converting each sample to an equivalent digital code.
PVC Polyvinyl Chloride
PVDF Polyvinylidene Fluoride
Quick Clip:  An electrical contact used to provide an insulation displacement connection to telecommunications cables.
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:  See Pathway.
Return Loss:  Noise or interference caused by impedance discontinuities along the transmission line at various frequencies. Return loss is expressed in decibels.
Ring Conductor:  A telephony term used to describe one of the two conductors in a cable pair used to provide telephone service. This term was originally coined from its position as the second (ring) conductor of a tip-ring-sleeve switchboard plug.
Repeater In local networks, repeaters are used to connect two Ethernet segments in order to expand the network across several sections. Repeaters forward data packets from one network segment to the next, by "boosting" the electrical signals according to the standards, whereby the content of the packets remains unchanged. When a repeater detects a physical error in one of the segments, the respective segment is disconnected ("partitioned"). The partitioning is automatically removed as soon as the error has been eliminated.

Maximum four repeaters are permitted between any two stations. This rule however only applies to repeaters in series. In the case of tree-type networks, an unlimited number of repeaters can thus be integrated.

R Symbol for Resistance
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.
RCDD Registered Communication Distribution Designer. A certification of BICSI, an industry organization, for individuals qualified to consult and design telecommunications distribution systems.
Reactance A measure of the combined effects of capacitance and inductance on an alternating current. The amount of such opposition varies with the frequency of the current. The reactance of a capacitor decreases with an increase in frequency. The opposite occurs with an inductance.
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.
Resistance In dc circuits, the opposition a material offers to current flow, measured in ohms. In ac circuits, resistance is the real component of impedance and may be higher than the value measured at dc.
Resonance An ac circuit condition in which inductive and capacitive interact to cause a minimum or maximum circuit impedance.
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 1. 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). 2. A wiring contact to which the ring wire is attached. 3. The negative wiring polarity (see Tip).
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.
RMS Root Mean Square.
Rope Strand A conductor composed of groups of twisted strands.
Rubber A general term used to describe wire insulations made of thermosetting elastomers, such as natural or synthetic rubbers, neoprene, Hypalon, butyl rubber, and others.
Rx Receive
RZ Return to Zero
Screened twisted-pair (ScTP):  A balanced twisted-pair cable surrounded by metallic braid, foil (screen) or both and bound in a single cable sheath.
Shielded twisted-pair (SSTP):  A cable surrounded by a metallic braid, foil or both and bound in a single plastic sheath containing balanced twisted-pair conductors that are individually shielded.
Singlemode Optical Fiber:  An optical fiber that will allow only one mode to propagate; this fiber is typically a step-index fiber.
Small Form Factor:  An optical fiber connector and adapter that provide for two strands of fiber in a surface area similar to an unshielded twisted-pair (RJ-style) plug and socket.
Sneak Current:  A low-level current that is of insufficient strength to trigger electrical surge protectors and, therefore, is able to pass through them undetected. These currents may result from contact between communications lines and AC power circuits or from power induction, and may cause equipment damage unless secondary protection is used.
Star Topology (1):  A method of cabling each telecommunications outlet/connector directly to a cross-connect in a horizontal cabling subsystem
Star Topology (2):  A method of cabling each cross-connect (HC and IC) to the main cross-connect (MC) in a backbone cabling subsystem.
Surge:  A rapid rise in current or voltage, usually followed by a fall back to a normal level. Also referred to as transient.
STP - Shielded Twisted Pair Shielded data cable containing twisted pair wires.

See also Twisted pair

Switch Similar to a hub, a switch allows for the connection of several workstations in a star configuration. Switches combine the functions of a Hub with those of a Bridge.: A switch is able to "memorize" the Ethernet address of a network station connected to a port and thus only forwards data packets destined for this address to the respective station. This does not apply to broadcast messages that are forwarded to all ports. (Switches and bridges differ in this regard, as bridges generally don’t forward broadcast messages).

In addition to switches for 100BaseTX (100Mbit/s) networks, there are also autosensing switches that automatically detect whether a connected terminal device operates at 10Mbit/s or 100Mbit/s. Autosensing switches thus allow for the integration of older 10BaseT devices into new 100BaseT networks.

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.
SBR A copolymer of styrene and butadiene. Also GR-S or Buna-S. Most commonly used type of synthetic rubber.
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.
Screen see Shield
ScTP see Screened Twisted Pair cable
SDH see Synchronous Digital Hierarchy.
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.
Separator Pertaining to wire and cable, a layer of insulating material such as textile, paper, Mylar, etc. which is placed between a conductor and its dielectric, between a cable jacket and the components it covers, or between various components of a multiple conductor cable. It can be utilized to improve stripping qualities, flexibility, or can offer additional mechanical or electrical protection to the components it separates.
Sheath see Jacket
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.
Silicone General Electric trademark for a material made from silicone and oxygen. Can be in thermosetting elastomer or liquid form. The thermosetting elastomer form is noted for high heat resistance.
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-ended An unbalanced circuit or transmission line, such as a coaxial cable transmission line (see also Balanced Line).
Sinusoidal A signal which varies over time in proportion to the sine of an angle. Ordinary alternating current is sinusoidal.
Skew Rays A ray that does not intersect the fiber axis. Generally, a light ray that enters the fiber at a very high angle.
Skin Effect The tendency of alternating current to travel on the surface of a conductor as the frequency increases.
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
S/N see Signal to noise ratio
SNR see Signal to noise ratio
SONET see Synchronous Optical Network.
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.
Split Pair 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.
SRL see Structural Return Loss
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.
Standing Wave Ratio (swr) A ratio of the maximum amplitude to the minimum amplitude of a standing wave stated in current or voltage amplitudes.
Star Network A network in which all stations are connected through a single point.
Static Charge An electrical charge that is bound to an object. An unmoving electrical charge.
Station A unique, addressable device on a network.
Stay Cord A component of a cable, usually of high tensile strength, used to anchor the cable ends at their points of termination and keep any pull on the cable from being transferred to the electrical conductors.
Step Index Fiber An optical fiber in which the core is of uniform refractive index with a sharp decrease in the index of refraction at the core-cladding interface. Step index multimode fibers generally have lower bandwidths than graded index multimode fibers.
Step Insulated Process of applying insulation in two layers. Typically used in shielded networking cables such that the outer layer of insulation can be removed and remaining conductor and insulation can be terminated in a RJ-45 type connector.
Stitching The activity of terminating multiconductor cables on a punchdown block.
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.
Strain Gauge A device for determining the amount of strain (change in dimensions) when a stress is applied.
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.
STS-n Synchronous Transport Signal-n (see Optical Carrier-n).
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 Suppression The process by which transient voltage surges are prevented from reaching sensitive electronic equipment.
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.
Telecommunications:  Any transmission, emission or reception of signs, signals, writings, images, sounds or information of any nature by cable, radio, visual, optical or other electromagnetic systems.
Telecommunications Industry Association (TIA):  An organization that sets standards for cabling, pathways, spaces, grounding, bonding, administration, field testing and other aspects of the telecommunications industry.
Telecommunications Room (TR):  An enclosed space for housing telecommunications equipment, cable terminations and cross-connect cabling used to serve work areas located on the same floor. The telecommunications closet is the typical location of the horizontal cross-connect and is considered distinct from an equipment room because it is considered to be a floor serving (as opposed to building or campus serving) facility.
Tip Conductor:  A telephony term used to describe the conductor of a pair that is grounded at the central office when the line is idle. This term was originally coined from its position as the first (tip) conductor of a tip-ring-sleeve switchboard plug.
Topology:  The physical or logical layout of links and nodes in a network. These include star, ring and bus configurations.
Transfer Impedance:  A measure (in W) of shield effectiveness.
Transition Point (TP):  A location in the horizontal cabling subsystem where New_Office under carpet cabling connects to round cabling.
Trunk:  A communication line between two switching systems. The term switching systems typically includes equipment in a central office (the telephone company) and PBXs. A tie trunk connects PBXs. Central office trunks connect a PBX to the switching system at the central office.
Twisted-Pair Distributed Data Interface (TP-DDI):  Trademark of 3COM Corporation. (See Twisted-pair Physical Media Dependent.)
Twisted-Pair Physical Media Dependent (TP-PMD):  Technology under review by the ANSI X3T9.5 working group that allows 100 Mb/s transmission over twisted-pair cable. Also referred to as CDDI or TPDDI.
Terminal resistor For coaxial network topologies such as 10Base5 or 10Base2, each network segment must be equipped with terminal resistors (terminators) at both ends. The resistance of the terminator must corresponds to the cable impedance. For 10Base5 and 10Base2, the resistance must thus be 50 Ohm.
Transceiver The term transceiver is a combination of transmitter and receiver. A transceiver implements the physical network access of a station to the Ethernet. In the modern 10Base2 and 10BaseT Ethernet topologies, it is integrated in the network card. Only in 10Base5 ((see also AUI connection) Ethernets is the transceiver connected directly to the network cable as an external component.
Twisted pair Data cable containing twisted pair wires. The twisting of pairs of wires greatly reduces crosstalk between the wire pairs in the cable. Twisted pair cables are available as unshielded UTP cables (unshielded twisted pair) and shielded STP cables (shielded twisted pair).

Twisted pair cables are mainly used in network technology and are classified according to their maximum transmission frequencies. Today, there are basically only two types used:

Category 3 cables cater for a maximum transmission frequency of 25MHz, which is sufficient for use in 10BaseT and 100BaseT4 networks.

Category 5 cables have a maximum transmission frequency of 100MHz and are therefore suitable for all modern network topologies.

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
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.
TFE Tetraflouroethylene. A thermoplastic material with good electrical insulating properties and chemical and heat resistance.
Thermal Rating The temperature range in which a material will perform its function without undue degradation.
Thermoplastic A material which will soften, flow, or distort appreciably when subjected to sufficient heat and pressure. Examples are polyvinyl chloride and polyethylene.
Thermosetting A material which will not soften, flow, or distort appreciably when subjected to sufficient head and pressure. Examples are rubber and neoprene.
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.
Tinsel A type of electrical conductor comprised of a number of tiny threads, each having a fine, New_Office ribbon of copper or other metal closely spiraled about it. Used for small size cables requiring limpness and extra-long flex life.
Tip 1. A polarity designation of one wire of a pair indicating that the wire is that of the primary (common) color of a 5-pair group (e.g. the white-blue wire of the blue pair). 2. A wiring contact to which the tip wire is connected. 3. The positive wiring polarity (also see "ring").
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.
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.
Transducer A device for converting mechanical energy into electrical energy.
Transmission Line An arrangement of two or more conductors or a wave guide used to transfer a signal from one location to another.
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.
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.
Triboelectric Noise Noise generated in a shielded cable due to variations in capacitance between the shield and conductor as the cable is flexed.
TSB Telecommunications Systems Bulletin
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.
Twin-lead A transmission line having two parallel conductors separated by insulating material. Line impedance is determined by the diameter and spacing of the conductors and the insulating material and is usually 300 ohms for television receiving antennas.
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.
Unshielded Twisted-Pair (UTP):  A cable with multiple pairs of twisted insulated copper conductors bound in a single sheath.
UTP - Unshielded Twisted Pair Not shielded cable containing twisted pair wires.

See also Twisted pair

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.
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.
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.
Webbed Conductors :  The manufacturing process that physically binds the conductor insulation of the wire pairs of an unshielded twisted-pair cable.
Work Area:  The area where horizontal cabling is connected to the work area equipment by means of a telecommunication outlet. A station/desk which is served by a telecommunications outlet. Sometimes referred to as a work station.
Work Area Cable:  A cable assembly used to connect equipment to the telecommunications outlet in the work area. Work area cables are considered to be outside the scope of cabling standards.
W Symbol for Watt or Wattage
W White
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.
Wave Form A graphical representation of the amplitude of a signal over time.
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.
wire fault An error condition caused by a break in the wires or a short between the wires (or shield) in a segment of cable.
Wiring Closet see Closet
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.
X 1. Symbol for reactance. 2. Symbol for cross-connect.
Z Symbol for impedance.