Data Communications



AC - Alternating current. A signal that alternates its polarity between positive and negative with respect to an earth ground. Dynamic signals such as audio, radio waves and utility power are typically AC.

ACK - Abbreviation for the Acknowledge response in data communications.

ADC - Analog to Digital Converter.

ADMINISTRATION - The method of labeling, identification, documentation and usage needed to implement moves, additions and changes of the telecommunications infrastructure.

ACR - Attenuation to Crosstalk Ratio. ACR is a comparison of signal strength to noise interference and is used as a bandwidth indicator.

ATTENUATION - Attenuation is the degradation of signal level along the cable due to losses in the cable. It measured in dB and calculated as follows: Attenuation = 10 log Received Voltage/Transmitted Signal Voltage. See also OPTICAL LOSS.

AUTOTEST - A series of tests performed by a LAN Cable Tester activated by the AUTOTEST key. The content of a test series and the test limits are predefined by the selection of a Standard (e.g. Category 6), or a cable manufacturer's test suite, or may be constructed by the test unit's user.

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BACK REFLECTION - Light reflected from the cleaved or polished end of a fiber caused by the difference of the refractive indices of air and glass. Back Reflectance is typically 4% of the incident light. It is expressed in dB relative to incident power.

BACKBONE - A facility (e.g. pathway, cable or conductors) between telecommunications rooms, or floor distribution terminals, the entrance facilities, and the equipment rooms within or between buildings.

BACKSCATTERING - The scattering of light in a fiber back toward the source. This backscattered light is used to make Optical Time Domain Reflectometer (OTDR) measurements.

BALANCE - Balance is the ratio of the differential signal output at either end of any pair to a common mode

BALUN - A passive line matching transformer designed to match the impedance of a transmission medium referenced to ground such as coaxial cable to transmission media whose signals are differential, or referenced to each other, such as TV antenna twin lead. Frequently used to connect twisted pair media to coaxial cable.

BANDWIDTH - The range of electrical frequencies that an electronic device or transmission system can effectively handle. For LAN's, it describes the maximum data rate for a given topology. The best bandwidth indicator of a cabling system is Attenuation Crosstalk Ratio (ACR), and one should strive for 7-10 dB ACR at the highest frequency level of transmission. The higher the ACR, the stronger the signal. (See Attenuation Crosstalk Ratio (ACR)).

BASEBAND - The use of the entire bandwidth of the network cable to transmit a single digital signal. The frames are applied directly to the cable in digital form without modulation or multiplexing. Ethernet and Token Ring are Baseband transmissions because they use only one protocol.

BASEBAND VIDEO - An application that defines transmission characteristics up to 862 MHz.

BASIC LINK - A testing configuration that appeared in older editions of the ANSI/TIA/EIA-568-A Standard. It has been replaced by Permanent Link test configuration in the 568-B Standard that replaced 568-A. See PERMANENT LINK.

BAUD - The most basic unit of data transmission speed, one baud represents one signal state change per second. It is often confused with bits per second (bps) because they were at one time very similar. By using current data compression and modulation techniques, many times the baud rate in bits per second can be achieved.

BENDING RADIUS - The minimum allowed curvature of any piece of cable (fiber or metallic). It is absolutely critical that the bending radius be maintained so that neither the cable's impedance (metallic) nor refractive index (fiber optic) is affected.

BER - Bit Error Rate. The ratio of received error bits of data to the total number of bits transmitted.

BINARY - Information contained in one of two states, either 0 (zero) or 1 (one). Digital computers are designed to respond to streams or groups of binary information. By combining and manipulating this information, these machines can be instructed to perform useful tasks. All information, whether alpha or numeric, must be converted into a binary equivalent to be processed by these systems. It forms the basis of the Binary digIT or BIT. Eight bits together form a BYTE. (Four bits form a NIBBLE).

BINARY SYNCHRONOUS COMMUNICATIONS - BCS or BISYNC. Developed by IBM as a form of communications between their mainframes and other devices. This protocol depends on synchronization between transmitter and receiver via timing signals.

BIT - Binary Digit. The smallest unit of data (and most basic) for data communications. It can have a value of a one (mark) or a zero (space).

BIT RATE - The number of bits passing a given point in a measured period of time. Usually expressed as bits per second (bps), thousands of bits per second (Kbps), or millions of bits per second (Mbps).

BLOCK - A group of transmitted data, typically framed with control characters and having a fixed size, such as 256, 512, 4096, etc.

BNC - The Bayonet-Neill-Concelman connector. Widely used in 10BASE2 and other thin coaxial applications.

BPS - Bits Per Second. (See also BIT RATE)

BRAID - The stranded shield found on most types of axial metallic media and some types of twisted pair, such as IBM Type 1.

BRIDGE - In the LAN arena, it is a device used to connect two physically separate networks.

BROADCAST - To send a message to two or more receiving devices at the same time.

BROADCAST STORM - In a NETBIOS based network, devices broadcast their addresses when queried. When several or all devices broadcast their addresses, the network slows down with the excess traffic.

BROUTER - A combination bridge and router, performing the functions of both in a single device. See also BRIDGE and ROUTER.

BUNDLED CABLE - An assembly or two or more cables continuously bound together to form a single unit.

BUS - An electrical connection tying two or more points together. A bus can be serial or parallel and can carry both dynamic signals or DC voltage.

BUS NETWORK - A topology based on all communicating devices being attached to a common medium. Various access methods are used including CSMA/CD and Token Passing. Typically bus networks carry data in the millions of bits per second data rate.

BYTE - Eight data bits or two nibbles.

BYTE COUNT - The number of bytes in a given message or block of data.

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CABLE - An assembly of one or more conductors within an enveloping sheath, constructed so as to permit use of the conductors singly or in groups.

CABLE RISER - Vertically installed cable connecting floors of a building. Cable tested to UL 1666 is "riser" rated. Typically multi-pair copper and fiber.

CABLE RUN - A length of installed media who may include other components along its path.

CABLE SHEATH - A covering over the optical fiber or conductor assembly that may include one or more metallic members, strength members or jackets.

CABLE SHIELD - A conductive layer of material located just under the cable's outer sheath which is designed to increase the cable's immunity to outside electrical noise interference. It may be constructed of metal foil or braided strands.

CABLING - A combination of all cables, jumpers, cords and connecting hardware.

CAMPUS - The buildings and grounds having legal contiguous interconnection.

CAPACITANCE - The measured ability of an electronic component to store an electrical charge. Capacitance is rated in units called FARADS. Common divisions of farads include microfarads (mF = X 10 6 ), nanofarads (nF = X 10 9 ) and picofarads (pF = X 10 12 ).

CARRIER SENSE MULTIPLE ACCESS/COLLISION DETECTION (CSMA/CD) - The most common form of access control found in an Ethernet environment. It is used to avoid data collisions in a logical bus topology, such Ethernet.

CARRIER SIGNAL - A continuous signal, upon which is modulated the data or other signal that is to be transmitted.

CATEGORY 3 (CAT 3) - 4-pair UTP cable and associated connecting hardware whose transmission characteristics are specified up to 16 MHz. (SEE ISO 11801 CLASSES A, B, C)

CATEGORY 4 (Cat 4) - 4-pair UTP cable and associated connecting hardware whose transmission characteristics are specified up to 20 MHz. (SEE ISO 11801 CLASSES A, B, C)

CATEGORY 5 (CAT 5) - 4-pair UTP cable and associated connecting hardware whose transmission characteristics are specified up to 100 MHz.

CATEGORY 5e (CAT 5e) - 4-pair UTP cable and associated connecting hardware whose transmission characteristics are specified up to 100 MHz. It has approximately 3 dB stronger signal strength than standard CAT 5. Category 5e includes additional tests (Headroom, PSACR, PSELFEXT, PSNEXT, and ACR) to ensure that Gigabit Ethernet can run over unshielded Twisted Pair (UTP) cabling. (SEE ISO 11801 CLASS D)

CATEGORY 6 (CAT 6) - a proposed addition, in draft form, to the ANSI/EIA/TIA-568-B.2 and ISO 11801 Standards specifying testing transmission characteristics for 4-pair STP and UTP cabling and connectors up to 250 MHz (See ISO 11801 CLASS E). Additionally, tests for Capacitance, Resistance and Impedance are required in addition to all tests required for Category 5e. Approval is expected in early 2002.

CATEGORY 7 (CAT 7) - an anticipated addition to the ANSI/EIA/TIA-568-B.2 Standard specifying testing transmission characteristics for 4-pair STP cabling and connectors up to 600 MHz (See ISO 11801 CLASS F). Approval of the ISO 11801 Standard is possible in late early 2002 with an ANSI/EIA/TIA Standard following at some future date.

CATV - Community Antenna TeleVision or Cable TeleVision. CATV is Broadband transmission effected by multiplexing multiple channels on one medium.

CAU - Controlled Access Unit. A type of semi-intelligent central wiring concentrator for the Token Ring environment. Used in conjunction with LAM's.

CCITT - International Telephone and Telegraph Consultative Committee. An international standards setting body for the telecommunications industry. In 1985, the CCITT chartered the TIA/EIA with drafting the 568 Standards we use today.

CDDI - Copper Distributed Data Interface. A standard describing 100 Mbps data transmission on metallic cable.

CENTRALIZED CABLING - A cabling configuration from the work area to a centralized cross-connect using pull-through cables, an interconnect or splice in the telecommunications room.

CHANNEL LINK - The Channel Link includes up to 90 m (295 ft) of horizontal cable, a work area patchcord, a telecommunications outlet/connector, an optional transition point or consolidation connector, and two connections in the telecommunications room. When a maximum horizontal length of 90 m is used, then the total length of the patchcords shall not exceed 10 m (33 ft). For other lengths of horizontal cabling, refer to ANSI/EIA/EIA-568-B.2.

CONNECTING HARDWARE - A device providing mechanical cable terminations between two cable ends.

CPU - Central Processing Unit. The portion of a computer which performs all arithmetic and logic manipulation in addition to instruction interpretation and processing.

CGA - Color Graphics Adapter.

CHANNEL SERVICE UNIT - A device that interfaces a digital telephone line to a multiplexer or other digital device for high-speed communications.

CHARACTER - A combination of binary digits representing an alphanumeric value.

CHARACTERISTIC IMPEDANCE - Characteristic Impedance is the measure of a transmission medium's impedance throughout its length and over a swept frequency spectrum. When terminating transmission media, it is important to match its Characteristic Impedance so as to minimize reflections.

CHARACTER ORIENTED PROTOCOL - A communications protocol that responds to special control characters as opposed to individual bit values for function control.

CHEAPERNET - Slang for 10BASE-2, also Thinnet, Thinwire Ethernet using a 50 ohm coax cable. (also see THIN ETHERNET)

CICS - Customer Interface Control System. An IBM user interface designed for mainframe interaction and job processing.

CLADDING - The low refractive index optical coating surrounding the core of a fiberoptic cable that prevents light from escaping the core. The cladding guides light along the core.

CLASS D - An approved ISO 11801 Standard specifying testing transmission characteristics for 4-pair STP and UTP cabling and connectors up to 150 MHz (also see Category 6). Approval is expected in late 2001.

CLASS E - A proposed addition, in draft form, to the ISO 11801 Standard specifying testing transmission characteristics for 4-pair STP and UTP cabling and connectors up to 250 MHz (also see Category 6). Approval is expected in early 2002.

CLASS F - An anticipated addition to the ISO 11801 Standard specifying testing transmission characteristics for 4-pair STP cabling and connectors up to 600 MHz (Category 7). Approval of the ISO 11801 Standard is expected in early 2002 with an ANSI/TIA/EIA Category 7 Standard following at some future date.

CMIP - Common Management Information Protocol. One of many network management information exchange protocols. The current favorite is SNMP.

COAXIAL CABLE - A cable constructed of an insulated center conductor surrounded by a shield. 10 BASE-5 and 10 BASE-2 require different types of 50-ohm coax cables.

COLLISION - The event that occurs when data from two devices attached to a common bus are placed on the bus at the same time. In Ethernet this typically generates a re-transmission.

COMMUNICATIONS PROTOCOL - The rules that govern the behavior and attributes of both hardware and software as they apply to data communications.

COMMUNICATIONS SERVER - A device which acts as a gateway to communication lines outside normal building boundaries or to a different communicating device. The server may allow access to several lines by any number of users on a network. Sometimes called a modem pool.

CONCENTRATOR - A device used in LAN applications to attach several nodes to one AUI or bus attachment point. Often this term is used mistakenly in place of hub.

CONNECTING BLOCK - An interconnecting device used in telecommunications and LAN applications consisting of multiple points for wire attachment. Some common connecting blocks are the 66 block, 110 block, the BIX block and the Krone block.
(also see Cross-Connect)

CONSOLIDATION POINT - A location for interconnection between horizontal cables extending from a telecommunications room and horizontal cables extending to telecommunications outlet/connectors.

CORE - The central light carrying part of a fiberoptic cable. It has a higher index of refraction than that of the surrounding cladding

COUPLER - An optical device that splits or combines light from more than one fiber.

CPS - Characters Per Second.

CPU - Central Processing Unit

CRC - Cyclic Redundancy Check. A common form of error checking for data communications and other situations where blocks of data are moved from one location to another. All bits in a block are divided by a predetermined binary number and the result is compared with what the actual number should be.

CROSS-CONNECT - A facility enabling the termination of cable elements and their interconnection or cross-connection.

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 - Crosstalk is the measure of noise induced to one pair by another pair of conductors. Crosstalk measured from the near end is "NEXT" and Crosstalk measured from the far end is "FEXT". Crosstalk is expressed in dB and the smaller the number, the greater the inductive noise effect. ANSI/TIA/EIA-568-B.2 requires bidirectional NEXT measurements to verify performance in both directions.

CSMA/CD - Carrier Sense Multiple Access/Collision Detection (an Ethernet Media Access Mechanism).


CTS - Clear To Send

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D-CHANNEL - A sort of status line in the ISDN arena. A 16 Kbps line carrying control signals and call data in the BRI interface. A 64 Kbps line in the PRI interface.

D TYPE - A description for the 9, 15 and 25 pin connectors widely used for data communications and microcomputer peripherals. It looks very loosely like a "D" when viewed vertically.

DASD - Directly Accessible Storage Device. IBM's term for local hard disk.

DATA GRADE CIRCUIT - A telephone line capable of carrying high-speed data. The line is specially conditioned to accommodate this.

DATA SERVICE UNIT - DSU. A device for transmitting data on digital transmission facilities. Sometimes incorporated with a CSU.

DATA SET - Another term for modem.

dB - the abbreviation for decibel. A unit of measurement to compare an output signal to an input signal. A relative term. (See also text on ATTENUATION for more information)

DC - Direct Current. A steady state voltage, either positive or negative with respect to ground, but not both. Batteries are a source of DC.

DC RESISTANCE - Provides an effective check on cable and connector integrity. Both cabling and connectors have inherent DC resistance. Loop resistance is the combined resistance of each individual wire in a two-wire pair. It is tested for each pair by placing a known DC voltage on one wire in the pair, shorting the Remote Handset and reading the voltage loss at the Display Handset. DC loop resistance testing is essential to isolating poor connector punch downs, cable damage and shorts.

DEAD ZONE - In OTDR measurements, if a subsequent event occurs at a distance less than the pulse width generated by the OTDR, the subsequent event will not be "seen" by the OTDR because it occurs within a "dead zone."

DELAY SKEW - Also known as Propagation Delay/Delay Skew. Delay Skew is a measurement of the signaling delay difference from the fastest pair to the slowest. Delay Skew is calculated from Propagation Delay measurements.

DENSE WAVELENGTH DIVISION MULTIPLEXING (DWDM) - A method of increasing the amount of data that can be transmitted over an optical fiber.

DIGITIZE - The conversion of an analog or continuous signal into a data stream of binary digits.

DISOSS - Distributed Office Support System by IBM.

DISTRIBUTED PROCESSING - A system or network whereby the processing is done at each individual workstation and not at a central device. A LAN is an example of distributed processing.

DMA - Direct Memory Access.

DNA - Digital Equipment Corporation's Network Architecture.

DOMAIN - An area including all peripherals and nodes under control of a single computer or server in a network.

DOWNLINE IMPEDANCE - LAN Cable Testers perform this function using a Time Domain Reflectometer (TDR) that samples and analyzes the impedance of a link. Relative Impedance is measured as a function of length and each cable can be viewed in graphical format along its length to ascertain where the anomalies are located, whereas Characteristic Impedance is usually measured in a laboratory with complex test equipment such as an expensive network analyzer. The TDR measures relative impedance in the field to find crimps, kinks and/or stretched cable that would show up as a blips, peaks or valleys on the otherwise flat line graph of a good link. (also see FAULT FIND)

DRAIN WIRE - In a cable, it is an uninsulated wire included in the sheath with the insulated wires. Typically used for grounding.

DROP CABLE -A cable connecting a workstation or peripheral to the main network cable.

DS-0 - Digital Service Level 0, a 64 Kbps digitized voice line.

DS-1 - Digital Service Level 1, a 1.544 Mbps line carrying 24 DS-0 lines.

DS-1C - Digital Service Level 1C, a 3.152 Mbps line also called T-1.

DS-2 - Digital Service Level 2, a 6.312 Mbps line also called T-2.

DS-3 - Digital Service Level 3, a 44.736 Mbps line also called T-3.

DS-4 - Digital Service Level 4, a 273 Mbps line also called T-4.

DUAL NEAR END CROSSTALK - Near end Crosstalk (NEXT) is the amount of transmitted signal on one pair that is induced electromagnetically onto adjacent pairs. High levels can cause excessive retransmission rates. An AutoTest generates swept signals for NEXT from 1 to 250 MHz for Category 6/CLASS E and it measures the induced noise on adjacent pairs at precise intervals. The AutoTest performs Dual NEXT tests from both ends.


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EBCDIC - Extended Binary Coded Decimal Interchange Code. An 8-bit code developed by IBM for data transfer between their computers.

EIA - Electronis Industry Association. A trade organization of manufacturers which sets and defines standards for its members. This group works with the TIA on standards pertaining to both industries. The originator of the "RS" series of interfaces (RS232, RS-449, etc.)

EISA - Extended Industry Standard Architecture. An independent alternative to IBM's Micro-channel for 32 bit computers.


EMI - Electromagnetic Interference.

EPROM - Erasable Programmable Read Only Memory.

EQUAL LEVEL FAR-END CROSSTALK (ELFEXT) - A measure of the unwanted signal coupling from a transmitter at the near-end into a neighboring pair measured at the far-end relative to the received signal level measured on that same pair.

EQUIPMENT CABLE CORD - A cable or cable assembly used to connect telecommunications equipment to horizontal or backbone cabling.

ESDI - Enhanced Small Device Interface.

ETHERNET - A LAN operating under the guidelines of the IEEE 802.3 document defining physical and data link layer behavior.


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FANOUT - A device similar to a concentrator in that it provides multiple access to a single backbone tap.

FARAD - A unit for measuring capacitance. One farad is a one-coulomb charge with one-volt potential difference between the plates. A 50-volt, one farad capacitor is roughly the size of a quart milk container. (also see CAPACITANCE)

FAR-END CROSSTALK LOSS (FEXT) - A measure of the unwanted signal coupling from a transmitter at the near-end into a neighboring pair measured at the far-end.

FAT - File Allocation Table. The location of all names and addresses of data files stored on a disk.

FAULT FIND - A diagnostics feature on the IDEAL LAN Testers that allows you to determine where in a link a fault is located. (also see DOWNLINE IMPEDANCE)

FCC - Federal Communications Commission.

FC CONNECTOR - A connector type used primarily for Singlemode fiberoptic cable. It offers precise alignment of the cable with respect to the transmitter and detector. Using a threaded receptacle and a locator notch, once installed the position is maintained with absolute accuracy.

FCS - Frame Check Sequence. An error-checking field found in bit oriented protocols.

FDDI - Fiber Distributed Data Interface. A dual counter-rotating ring topology based on fiber optics operating at 100 Mbps.

FDM - Frequency Division Multiplexing. A technique in which several signals are transmitted on the same cable simultaneously at different frequencies. Used in Broadband.

FDX - An abbreviation for Full Duplex transmission. Gigabit Ethernet will use full duplex transmission on all four pairs. This is analogous to being on an 8-lane highway and any car can go any direction, at any time!

FEP - Front End Processor. A preprocessor for devices attached to a larger, faster computer.

FERRULE -The component of a connector that holds a fiberoptic cable in place and maintains its alignment. Cylindrical in shape with a hole in the middle, the ferrule is sometimes described as a sleeve.


FIBER - A thin filament of glass capable of carrying information in the form of light.

FIBEROPTICS (FO) - Light transmission through flexible fibers for communications or lighting.

FIBEROPTIC TEST PROTOCOLS - A series of test procedures defined by the FO 6.2 committee of TIA. The procedures cover a wide number of situations, for example, verification by manufacturers of cable specifications, cable bend radius, connector manufacturing, fire rating, and field testing of fiber optic installations.

FIBEROPTICS LAN SECTION - Known as FOLS, a group operating within the trade association operation of TIA. FOLS is dedicated to promoting the common interests of TIA members involved in fiberoptic telecommunications.

FILE SERVER - A device found on local area networks which sends requested files and programs to requesting nodes and stores files sent from nodes.

FIRMWARE - Operating instructions for a processor permanently stored in devices such as EPROM's, and ROM's which are hardware.

FLASH MEMORY - Flash Erasable Programmable Read-only Memory is a form of computer semiconductor storage. It allows data in electronic format to be held without loss (unlike RAM) for an indefinite period (like ROM), and for the contents to be changed. It is a popular type of removable storage used for transporting data between recording devices and a PC.




FOUR-WIRE CIRCUIT - A transmission circuit using a transmit pair and a receive pair, or four wires altogether.

FREQUENCY - The rate, at which an electrical current alternates, usually measured in Hertz, or cycles per second, which are the same.

FTP - File Transfer Protocol. A file sharing protocol often used in conjunction with TCP/IP. It operates in layers 5 through 7 of the OSI network model.

FULL DUPLEX - The ability of a circuit to carry signals in two directions simultaneously. (also see FDX and GIGABIT ETHERNET)

FUSION SPLICER - An instrument that splices fiber by fusing or welding the fibers, typically by an electric arc.

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GATEWAY - For LAN's, a connection between two dissimilar network topologies, i.e., Token-Ring and Ethernet.

GIGA - A prefix for one billion.

GIGABIT ETHERNET - Gigabit Ethernet is defined by three standards generated by IEEE 802.3 working groups.

· 1000Base-T supports Gigabit Ethernet over 100 meters of Category 5e balanced copper cabling.
· 1000BASE-SX supports the use of short wavelength Vertical Cavity Side-Emitting Lasers (VCSELs) to transmit data over fiber optic cable. The lasers specified by the Standard operate over Multimode Fiber in the wavelength range of 770 to 860 nanometers.
· 1000BASE-LX supports the use of long wavelength lasers to transmit data over fiber optic cable. The lasers specified by the Standard operate over either Multimode or Singlemode Fiber in the wavelength range of 1270 to 1355 nanometers.

GROUND LOOP - This occurs when a segment is grounded at more than one point. It creates a situation for a potential voltage difference between the grounds, causing the network cable to conduct unwanted electricity. A bad thing.

GUI - Pronounced "gooey", it's the abbreviation for Graphical User Interface

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HALF DUPLEX - The ability of a circuit to carry signal in one direction at a time. Ethernet and Fast Ethernet use half duplex with one pair transmitting and the other pair receives.

HARDWARE - A generic term describing all computing and peripheral machinery.

HARDWIRE - A permanent connection between two devices, usually not easily disconnected.

HARMONICA - A cable adapter used to change an Amphenol type 50 pin Telco connector into multiple RJ-45's or RJ-11's.

HDLC - High Level Data Link Control. A bit oriented protocol developed by the International Standards Organization (ISO).

HEADROOM - Headroom is the sum of the natural margin, or ACR, of the cabling and the additional margin between the worst case NEXT and the limit for NEXT. Headroom is calculated using a power sum ACR on the worst pair after the attenuation for that pair has been normalized to 100 meters (328 ft).

HERTZ (Hz) - An equivalent to cycles per second for defining frequency.

HIT - Slang for an induced electrical impulse. (also see IMPULSE NOISE section)

HOME RUN - A cable run going from a workstation or office directly back to a wiring closet with no other connections. Physical star topologies consist exclusively of home runs.

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

HOST - Term describing a Host computer. A central computer responsible for the control of time-share terminals and other peripherals. Usually associated with minicomputers and mainframes.

HUB - 1. A central point of connection for several circuits. 2. A device which electrically converts a logical topology to a different physical topology. An ARCNET hub enables physically star-wired nodes to be seen as a logical, token-passing bus. Hubs can be active (powered), or passive (non-powered). Active hubs sometimes are capable of allowing longer cabling lengths than passive units.

HUB ACTIVATION - Hub activation tests transmit a signal to a 10 BASE-T hub to verify it is operational.

HYBRID CABLE - An assembly of two or more cables, of the same or different types or categories, covered by one overall sheath.

Hz - See Hertz.

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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.

I/O - Input/Output.

I/O CHANNEL - A high-speed bus used to interconnect peripherals with the CPU.

I/O CONTROLLER - A device that arbitrates the I/O channel and controls data transfer between devices attached to the channel.

IBM TOKEN RING - A token passing network topology that conforms to the IEEE 802.5 definition and documents. Operating at 4 Mbps or 16 Mbps, it is the chief topology used to interconnect small and mid-size equipment from IBM and other vendors.

IDC - Insulation Displacement Connector. A type of connector in which the insulated wire is pushed down between two sharp blade-like pieces of metal so that the conductor touches the connector and there is no exposed bare wire. Modular telephone plugs (RJ series) are examples of insulation displacement connectors.

IDF - Intermediate Distribution Frame as it was called previous to being changed to "IC" or intermediate cross-connect in TIA/EIA 568-A. Also known as a wiring closet, the IDF is a cross connection point for horizontally attached devices to riser media. Provides the wiring interface between the end-user and the Main Distribution Frame. The MDF was change to "MC", which stands for main cross-connect.

IEEE - Institute of Electrical and Electronic Engineers. A standards setting and publishing body responsible for such guidelines as the 802 series for LAN's.

IEEE 802.X - Guidelines describing the physical and data link layers of the OSI network model for various topologies.

IMPEDANCE - The complex opposition to current flow dynamically in a transmission medium. Including components of resistance, capacitance and inductance when driven by a voltage source. (also see CHARACTERISTIC IMPEDANCE for more detailed information)

IMPEDANCE MATCHING - An operation to assure maximum transfer of signal power over the operating frequency range by proper selection of all elements of a transmission system. A properly impedance matched system transfers maximum signal power to the load with no signal distortion.

IMPULSE NOISE - Intermittent, short, high frequency, high amplitude pulses that are induced into a transmission line. Can cause data corruption and in some cases hardware damage.

INDUCTANCE - The tendency for an electrical current to build a magnetic field around a conductor and cause a portion of that current to be induced or generated on an adjacent conductor. (also see NEAR-END CROSSTALK).

INSERTION LOSS - The signal loss resulting from the insertion of a component, or link, or channel, between a transmitter and receiver (often referred to as attenuation).

INSULATION - A non-conductive material used to separate conductors to prevent electrical short circuits. Cables are insulated and rated for different applications. Plenum rated cables can be used anywhere inside a building and riser rated cables are only used between floors.

INTELLIGENT TERMINAL - A computer terminal or personal computer/workstation having the ability to process data independently from the host computer.

INTERCONNECTION - A connection scheme that employs connecting hardware for the direct connection of a cable to another cable without a patch cord or jumper.

INTERFACE - The point at which two different items come together. They might be mechanical, electronic or software.

INTERNET PROTOCOL (IP) - Used at OSI Level 3 and above to connect networks through gateways.

INTERNETWORKING - The connection of multiple networks for data interchange. This is normally accomplished with interface devices such as bridges, brouters and gateways.

IPL - Initial Program Load. A fancy term for "booting" a large computer.

IRQ - Interrupt ReQuest. A form of peripheral prioritization for microcomputers.

ISO - International Standards Organization. Based in Paris, this body develops open industry standards for the world. A key standard is the Open Systems Interconnection Network Model (OSI model) which forms a general definition for all LAN's. ISO 11801 is similar to ANSI/EIA/TIA/568-B but uses different terms and values in some instances.

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JABBERING, JABBER - The continuous transmission of meaningless data, usually due to a failure of some sort. The network slows tremendously when burdened with this excess traffic.

JACK - A receptacle for a modular device. Mates with a plug.

JACKET - The outer protective sheath of a cable.

JITTER - The skewing of a transmitted pulse so as to cause its edge to become poorly defined and difficult to correctly detect.

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

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K - A short form for the metric "Kilo" or 1000. Often appended to measurements of things like frequency (KHz), storage (KBytes), and bit rate (Kbps).

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

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LAN - Local Area Network. A distributed processing environment usually located within the confines of a single building.

LAUNCH CABLE - A known good fiber optic jumper cable attached to a source and calibrated for output power used for loss testing. This cable must be made of fiber and connectors of a matching type to the cables being tested.

LAY - From cable manufacturing. A term describing the length of one conductor in a twisted pair in making one complete turn.

LAYER - A subdivision of a complete model comprising software and/or hardware elements to complete a specific and related set of tasks.

LCD - Liquid Crystal Display.




LENGTH - The distance of a communications link measured by a tester with a TDR. For TIA/EIA 568-B.2, the Permanent Link is limited to 90 meters of horizontal cabling embedded in the walls and ceiling plenum. Length is one of the ANSI/EIA/TIA-568-B.2 required tests for a Category 5e UTP cable limited to a total distance of 100 meters including the Permanent Link of 90 meters + 10 meters allowance of line cords, patch cords and up to two cross-connects in a link. (also see NOMINAL VELOCITY OF PROPAGATION)

LIGHT-EMITTING DIODE (LED) - A semiconducting device that emits light when stimulated by an electrical current. Used in transmitters for multimode fiber links.

LINE - A term used loosely to describe a connection between two communicating devices.

LINEMAP - A term referring to the termination pinout pairs of cable. (also see CONTINUITY and WIREMAP)

LINE SPEED - The maximum rate of data transfer for a given line.

LINK - A transmission path between two points, not including terminal equipment, work area cables, and equipment cables.

LLC - Logical Link Control. A protocol developed by the IEEE for end-system addressing and error checking. Operates in Layer 2 of the OSI model.

LISTED - Equipment included in 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 satiable for use in a specified manner.

LOCAL DISTRIBUTION FRAME - LDF. Another name for an Intermediate Distribution Frame or "IC" as the ANSI/EIA/TIA-568-B.2 standard specifies.

LONG WAVELENGTH - A commonly used term for light in the 1300 and 1550 nm ranges.

LONGITUDINAL CONVERSION LOSS - A ratio expressed in dB, of measured differential voltage relative to the common mode voltage on a conductor pair applied at the same end.

LONGITUDINAL CONVERSION TRANSMISSION LOSS - A ratio expressed in dB, of measured differential voltage relative to the common mode voltage on a conductor pair applied at the opposite end.

LOSS BUDGET - Sometimes known as dB LOSS BUDGET, it is the amount of light available to overcome attenuation in a fiberoptic link and maintain performance specifications.

LRC - Longitudinal Redundancy Check. Another term for parity checking.

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M - Short form of the metric "Mega" or 1,000,000. Used as a prefix for frequency (MHz), storage (MBytes) and line speed (Mbps).

m - Representation of the metric "milli" or 1/1000th .

MAC - Media Access Control. A control protocol designed for specific media with variations for different media. Works in conjunction with LLC.

MACHINE LANGUAGE - The binary digits that the computer hardware processes without interpretation. Also called machine code.

MAIN DISTRIBUTION FRAME - the MDF has been changed to "MC" (main cross-connect) in ANSI/EIA/TIA-568-B.2. The MC is the point at which outside service lines interface to inside service and then to IC's or to TC's.

MAINFRAME - A large computer system.

MAN - Metropolitan Area Network. A Network operating within the confines of a single city or community.

MANCHESTER ENCODING - An encoding method which involves a digital state change (0 to 1 or vice versa) for every bit representation occurring in the middle of the transmitted bit. Useful in local area networks because it is self-clocking. The receiver can develop the data clock from the transmitted data stream. Used in Token Ring and Ethernet systems. Standard Ethernet uses Manchester encoding which results in 10 Mbps throughput at 10 MHz frequency (one-for-one).

MAPPING - The act of associating logical representations with their physical counterparts.

MAU - Media Access Unit. Another name for an Ethernet transceiver. MAU was also the abbreviation for a Token Ring Multi-station Access Unit. This has been changed recently to MSAU to avoid confusion.

MCA - Micro-Channel Architecture. IBM's 32-bit peripheral bus for microcomputers.

MDF - Main Distribution Frame, which has been changed to "MC" (main cross-connect) by ANSI/EIA/TIA-568-B. The connecting point in a building where outside services interface to internal services. All networking components are "star-wired" back to the MC.

MECHANICAL SPLICE - A semi-permanent connection between two fibers, made with an alignment device and refractive index matching fluid or adhesive.

MEDIA (Telecommunications) - Wire, cable or conductors used for telecommunications.

MEDIUM - Material used for the transmission of signals.

MIB - Management Information Base. An information database used in conjunction with the Simple Network Management Protocol.

MICRO (µ) - Prefix for one millionth. Used as a prefix for capacitance.

MICROFARAD (µf) - One millionth of a farad.

MIPS - Millions of Instructions per Second. A speed rating for computers and workstations.

MJ - Modular Jack. A term describing plug-in IDC connectors used in telephone and data communications. The connectors usually are configured with 4, 6 or 8 pins.

MMJ - Modified Modular Jack. Developed by Digital Equipment Corp. (DEC), it is an RJ-12 (6 pin) modular jack with the bottom-locking tab offset to one side.

MODAL DISPERSION - The temporal spreading of a pulse in an optical waveguide caused by modal effects.

MODEM - MOdulator DEModulator. A device which converts digital data to a modulated form which can be transmitted over telephone lines and reverses the process when receiving.

MODULAR PLUG - A series of connectors designed for ease of use and flexibility. They are characterized by locking plastic tabs on the bottom and typically appear in three configurations: RJ-11 (4-conductor), RJ-12 (6-conductor) and RJ-45 (8-conductor).

MSAU - Multi-Station Access Unit. The new abbreviation for a Token Ring wiring center. The units can be active or passive. They typically have eight ports for device (or lobe) attachment and a RI (ring-in) and RO (ring-out) port for network attachment.

MS-NET - Microsoft NETworks. The predecessor to LAN Manager. First introduced in MS-DOS version 3.1.

MTBF - Mean Time Between Failures. The average operational time of a device.

MULTIMODE FIBER - A fiber with a core diameter (commonly 50 or 62.5 microns) much larger than the wavelength of light transmitted that allows many modes of light to propagate. Commonly used with LED light sources for lower speed, short distance links. More recently used with VCSEL laser light sources for Gigabit Ethernet.

MULTIMODE PROPAGATION - A method of introducing a light pulse with multiple light rays (modes) into an optical fiber. Multimode is typically used for short-haul applications of less than 2 KM using relatively inexpensive light sources usually operating at a 850 or 1300 nanometer wavelength. Gigabit Ethernet uses an 850 VCSEL laser while most other applications use Light Emitting Diode (LED) light sources.

MULTIPROCESSING - The ability of a system to run two or more processors simultaneously.

MULTIPLEXER - A device which causes two or more signals to use the same communications medium. Multiplexing can occur in either the frequency or the time domain.

MUTUAL CAPACITANCE - The capacitance between two conductors with all other conductors shorted to ground.

MUX - A short form slang of multiplex. Also MUXED, MUXING.

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NAK - No Acknowledgment. A data communications negative response.

NEAR-END CROSSTALK (NEXT) - The coupling of power from the transmitted signal pair to an adjacent pair at the same transmitting end of the LAN cable.

NETBIOS - Network Basic Input/Output System.

NETVIEW - A network management offering from IBM.

NETWARE - A popular network operating system from Novell Inc.

NETWORK ADDRESS - A number giving a specific identification to a network attached device.

NETWORK INTERFACE CARD - NIC. A circuit card providing the hardware interface between a network device and the transmission medium.

NETWORK OPERATING SYSTEM - NOS. The software component of a network. The NOS contains all instructions pertinent to data transfer, file manipulation and services and interfacing routines.

NETWORK TOPOLOGY - The physical layout and interconnection of a network.


NODE - A connection point into a network. The node may perform several functions (i.e., file server, workstation, print server, bridge, etc.).

NOMINAL VELOCITY OF PROPAGATION - "NVP" is the relative speed a signal travels on a conductor that is proportionate to the speed of light in a vacuum. Length measurements are determined by sending a signal down a line and measuring the reflected signal that comes back and factoring in the amount of time that it took to make the return trip. (also see c and LENGTH)

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OCTOPUS - A cable adapter that transforms a 25-pair feeder into individual modular plugs.

ODD PARITY - An error checking method in which binary 1's or zeroes are added to a character so that the number of 1's is always odd.

OHMS - A measure of resistance. One ohm allows one ampere of current to flow across a one volt potential.

OPEN CIRCUIT - An incomplete circuit. A cable connected at one end only is an example of an open circuit. The opposite of a short circuit.

OPEN OFFICE - A floor space division provided by furniture, moveable partitions or other means instead of by building walls.

OPERATING SYSTEM - A software program or collection of programs that manage the computer's hardware and provide an interface to that hardware for the end-user.

OPTICAL LOSS TEST SET - A measurement instrument for optical loss that includes both a meter and a light source.

OPTICAL POWER - The amount of radiant energy per unit time expressed in linear units of Watts or on a logarithmic scale in dBm (where 0 dB equals 1 mWatt) or dB* (where 0 dB = 1 microwatt).

OPTICAL RETURN LOSS (ORL) - Light reflected from the cleaved or polished end of a fiber caused by the difference of refractive indices of air and glass.

OPTICAL TIME DOMAIN REFLECTOMETER (OTDR) - A device that uses an emitted light pulse of known power and width and measuring the light that is scattered back from events along the length of the fiber. Distance to splices, connectors, faults and the end of the cable can then be calculated and displayed.

OS - Abbreviation for Operating System.

OSI - Open Systems Interconnect. A seven layer model defining the different levels of data communications in a network environment. Developed by the International Standards Organization. Cables comprise the Physical Layer of the OSI model.


OUTLET BOX (Telecommunications) - A metallic or nonmetalic box mounted within a wall, floor or ceiling and used to hold telecommunications outlets/connectors or transition devices.

OUTLET CABLE - A cable placed in a residential unit extending directly between the telecommunications outlet/connector and the distribution device.

OUTLET/CONNECTOR (Telecommunications) - A connecting device in the work area on which horizontal or outlet cable terminates.

OUTSIDE PLANT - Telecommunications infrastructure designed for installation exterior to buildings.

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PACKET - A group of data in an organized form with a distinct header, control information and a destination address.

PACKET SWITCHING - The transmission of packetized data through a network. Each packet has information linking it to the rest of the total message or file as well as the destination address. This form of communication is efficient because each packet can take a different route if necessary to maximize throughput.

PACKET SWITCHING NETWORK - A network constructed to move data packets. An X.25 network is an example of a packet switching network.

PAIR - Two wires, usually twisted around each other.

PAIRED CABLE - Cable in which all conductors are arranged in color-coded pairs usually twisted around each other and then surrounded by a sheath.

PARALLEL DATA - Multiple bits of data transmitted each on its own line simultaneously.

PARITY CHECK - The addition of a bit to a character to aid in error checking.

PATCH CORD - A Length of cable with a plug on one or both ends.

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

PDN - Public Data Network.

PDS - Premise Distribution system.

PEER-TO-PEER NETWORK - A network in which all devices have equal status and abilities for file transfer, printer sharing, etc.

PERMANENT LINK - The Channel Link includes up to 90 m (295 ft) of horizontal cable and one connection at each end and may also include an optional transition/consolidation point connection. The permanent link configuration excludes both the cable portions of the test cord and the connection to the testing device.

PHYSICAL LAYER - The bottom layer of the OSI model, concerning physical interconnect hardware and electrical interface between devices.

PICO - 1 X 10 -12 . Used as a prefix usually for capacitance (pF) values.

PICOFARAD (pF) - One-trillionth (10 -12) of a farad. A common unit used in measuring mutual capacitance in cable.

PLENUM CABLE - Cable that can meet the UL 910 (Steiner Tunnel) test by using fire retardant insulation that inhibits fire propagation and toxic fumes. These cables can be used in horizontal runs in open air ceiling returns and will be clearly indicated with a "P" suffix (such as CMP) as certified by UL, ETL or other third party testing firms. It is typically coated with TEFLON®.

POLL - In LAN applications, it is a query to a node looking for information to be transferred on the network.

POLYVINYL CHLORIDE - PVC. A common insulation material sheathing many types of paired and axial cable. Emits very toxic gases when burned so it may not be used in free-air plenums or risers in premises applications. (also see also PLENUM CABLE)

POTS - Plain Old Telephone Service. Slang term to describe unknown, older, generic telephone wire.

POWER BUDGET - The difference (in dB) between the transmitted optical power (in dBm) and the receiver sensitivity (in dBm).

POWER METER (Fiberoptic) - An instrument that measures optical power emanating from the end of a fiber.

POWER SUM - Pair-to-Pair measurements are used to measure one pair against another. Power Sum measurements select a pair and then measure the disturbances from other pairs within the same sheath. This can be used in a 4-Pair or other high pair count (25, 50, 100 and up) to determine the effects of all the cables (of course testers only test 4-Pair at a time). Power Sum ACR, ELFEXT, and bidirectional NEXT measurements are made with the LT8000 Series. In general, this results in an approximately 3-dB loss limit when compared to pair-to-pair test values.

POWER SUM ATTENUATION TO CROSSTALK RATIO (PSACR) - A ratio expressed in dB, determined by subtracting the insertion loss from the POWER SUM NEAR-END CROSS TALK LOSS.

POWER SUM EQUAL LEVEL FAR-END CROSSTALK (PSELFEXT) - A computation of the unwanted signal coupling from multiple transmitters at the near-end into a pair measured at the far-end relative to the received signal level on that same pair.

POWER SUM NEAR-END CROSSTALK LOSS (PSNEXT) - A computation of the unwanted signal coupling from multiple transmitters at the near-end into a pair measured at the near-end.

PREMISES DISTRIBUTION SYSTEM - A multifunction wiring system designed by AT&T for integration of voice, data, video and graphics. It includes cables, adapters, electronic modules, wall jacks and protective covers. It is scalable from a single floor to a campus environment.

PRIMARY RATE INTERFACE (PRI) - An ISDN service consisting of either 23 B-channels + 1 D-channel (1.544 Mbps) or 30 B-channel + 1 D-channel (2.048 Mbps). (also see B-CHANNEL and D-CHANNEL) .

PROPAGATION DELAY - Propagation Delay is the time it takes for a signal to propagate from one end of a conducting pair in cabling, cables or connecting hardware to the opposite end of that pair. (also see DELAY SKEW).

PROPAGATION RATE - The speed at which electricity travels in a transmission medium. Expressed as a percentage of the speed of light that is represented as a lowercase "c".

PROTOCOL - A set of rules governing all aspects of communicated data.

PROTOCOL ANALYZER - A device capable of capturing, monitoring, decoding and analyzing various communications protocols. A high level troubleshooting and analysis tool.


PUNCH-DOWN BLOCK - A device used to terminate and cross-connect premises wiring. (also see also CONNECTING BLOCK)


PULL TENSION - The pulling force that can be applied to a cable.


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RACEWAY - A metal or plastic trough used to guide and carry installed cabling.

RECEIVER - Any device which receives communications. The opposite of a transmitter.

RECEIVER (Optical) - A device containing a photodiode and signal conditioning circuitry that converts light into an electrical signal in fiberoptic links.

RESISTANCE - The blockage or obstruction of current flow. A property of all conductors, it is measured in ohms.

RETURN LOSS - A measure of impedance mismatch indicated by a return echo signal reflection. It is often referred to as "RL" and it measures the ratio between the transmitted signal strength and the signal reflected back to the transmitting end. Like attenuation, excessive return loss indicates reduced signal strength at the receiver end and it can indicate a mismatched impedance at some point along the cable link. Return Loss is reported as a dB value for each pair, from each end. A value of 20 dB or higher for UTP is very good and a value below 10 dB causes a large reflection of signal back to the source and is not good. The IDEAL LT8000 Series provides this measurement.

REVERSED PAIR - See also SPLIT PAIR and TRANSPOSED PAIR. A situation that occurs when the one end of a twisted pair has its connections reversed. This condition is detected by a LAN Cable Tester's Wiremap test. (also see SPLIT PAIR and TRANSPOSED PAIR).

RISER - The path between floors of a building carrying cables which interconnect the floors.

ROUTER - A device used to connect LAN's utilizing different communications protocols. It directs traffic within networks and offers security by restricting access to those that don't belong. Routers require intensive programming instructions and are used mostly for WAN (wide area network) interface to outside services.

RS232-C - A standard developed by the EIA defining signal levels and pin assignments for serial data communications. Much misused and modified, it no longer represents a standard, but a general guideline to follow when interfacing DTE and DCE.

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SAA - Systems Application Architecture. Specifications designed by IBM to insure compatibility at the application (highest) level between all newly developed software packages.

SAG - The downward curvature of a wire or cable due to its weight. The TIA/EIA 569 Pathways and Spaces Standard requires Category 5 cable to be supported at 48" to 60" intervals and the sag cannot exceed 12" between supports.

SC CONNECTOR - The SC (Subscriber Carrier) fiber optic connector is one of three connectors (the other two are ST and SFF) approved by ANSI/TIA/EIA 568-B.3. The SC Connector's main advantage is polarization since the connectors can be paired and keyed.

SCATTERING - The change of direction of light after striking small particles that causes loss in optical fibers.

SCREEN - An element of a cable formed by a shield

SCSI - Small Computer Systems Interface. A high-speed semi-intelligent peripheral interface for microcomputers.

SDLC - Synchronous Data Link Control. A bit oriented synchronous communications protocol developed by IBM for use within SNA.

SEGMENT - A cable run. Its maximum length is determined by the topology. A 10BASE2 segment may be up to 605 feet long. A 10BASE-T segment may be up to 328 feet long.

SERIAL TRANSMISSION - The sending of multiple data bits down a single line in a stream.

SERVER - A network device which provides a service to other network devices. Services include file, printer, communications or gateway.

SESSION LAYER - The fifth layer of the OSI model dealing with network processing, linking and unlinking users from their chosen service.


SHORT WAVELENGTH -A commonly used term for light in the 665, 790, and 850 nm ranges.

SINGLEMODE FIBER - A fiber with a small diameter (commonly 8-10 microns) core, only a few times the wavelength off light transmitted that only allows one mode of light to propagate. Commonly used with laser sources for high-speed, long-distance links.

SMALL FORM FACTOR CONNECTOR (SFF) - The SFF CONNECTOR is a term used to describe a group (rather than a single) of fiberoptic connectors approved by ANSI/TIA/EIA 568-B.3 (along with ST and ST Connectors). They are not presently used for Singlemode connections. They are designed to reduce the size of patch panels, thereby reducing the number and cost of telecommunication closets to make fiber-to-the-desktop more competitive with copper. Popular SFF connectors include SC/DC, LC, MT-RJ, Volition and Fiber Jack.

SHARED LOGIC - The simultaneous use of resources in a computer by several users.

SHEATH - See cable sheath

SHIELD - A metallic layer placed around a conductor or group of conductors.

SHIELDED PAIR - A pair of wires, twisted together and covered with a conductive material to provide any potentially induced noise a quick path to ground.

SINGLEMODE PROPAGATION - A method of introducing a light pulse into a single light ray (mode) into an optical fiber. Singlemode is typically used for long-haul applications of 2 to 50 kilometers using relatively expensive laser light sources usually operating at a 1310 or 1550 nanometer wavelength.

SHORT CIRCUIT - A condition that exists when two conductors are connected ahead of where they normally should be in a circuit. This causes reduced resistance and sometimes the undesirable side effects.

SIGNAL GROUND - A common point of reference for all other signals in a communications interface.

SIGNAL TO NOISE RATIO - (SNR) The ratio of received signal to existing system noise. In LAN applications it is the attenuation to NEXT ratio. Both are expressed in decibels.

SILVER SATIN - Flat, untwisted cable used typically as a telephone extension cord. It should never be used in a Local Area Network.

SIMPLEX - Transmission in one direction only.


SNA - Systems Network Architecture. Developed by IBM as a path to interconnect all of its computer products. Very common and very successful.

SNMP - Simple Network Management Protocol. A popular network management protocol that is incorporated into many intelligent hubs and concentrators. Originally designed for TCP/IP, it now functions independently and with most topologies and network operating systems.

SONET - Synchronous Optical NETwork.

SOURCE - A laser diode or LED used to inject an optical signal into a fiber.

SPACE - Another name for a binary "0" in data communications.

SPLICE - A splice describes the connection of two fibers in a permanent joint. A splice may be formed by "fusion splicing," wherein the two fibers are welded together, usually with an electric arc. Alternatively, a splice may be formed by "mechanical splicing" that uses a mechanical alignment fixture and a matching gel or epoxy to minimize back reflection.

SPLIT PAIR - A situation that occurs when a twisted pair is misconnected so that it becomes ½ of two separate pairs. The noise immunity of the twists is lost and an impedance mismatch is created. This wiring error will not show up as an error on a Wiremap, but will be indicated by very high NEXT. (also see also REVERSED PAIR and TRANSPOSED PAIR).

ST CONNECTOR - The ST (Straight Through or alternatively Straight Terminus) fiber optic connector is one of three connectors (the other two are SC and SFF) approved by ANSI/TIA/EIA 568-B.3. The ST Connector is the most widely used connector for Multimode fiberoptic cable.

STAR TOPOLOGY - A physical layout in which each device is wired back to a central point.

START BIT - In asynchronous communications, a start bit and stop bit delimits each character to indicate to the receiver the character's location.

START/STOP TRANSMISSION - Another term for Asynchronous Communication.

STOP BIT - The trailing bit in an asynchronous character sequence.

STP - Shielded Twisted Pair. Cable constructed of pairs of insulated wire twisted around each other surrounded by shielding material made of foil or braid or both. The entire group of wires may have a common shield or as found in Category 7 cables, each pair may be shielded individually with another shield around the entire group just under the sheath.

STRANDED CONDUCTOR - A wire or cable constructed of several small strands of conductor instead of one larger solid piece. This configuration provides for more flexibility in certain applications. Patch cords are made out of stranded conductors and the NEXT values are degraded up to 20% to allow for them in a link.

SURFACE EMITTER LED - An LED that emits light perpendicular to the semiconductor chip. Most LEDs used in data communications are surface emitters.

SWITCH - Multi-port device used to connect a quasi-exclusive 10/100/1000 Mbps connection between any two-end systems using the source and destination addresses of the packet via the internal bus. Switches work at the MAC (Media Access Control) Layer and above and use either "store and forward" or "cut-through" technology. Switches are "plug-and-play " devices that can be used to segment a network when it starts to slow down. Each port can function at the rated speed of the switch and some are auto-sensing for 10/100 Mbps. Ethernet switches are offered as standalone systems or as modules for existing hubs.

SYNCHRONOUS TRANSMISSION - Transmission between devices with a common clock. Data can be sent at a much higher speed because there is no need to frame each character.

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T CONNECTION - A connector fanning out in three directions and looking like a "T". Commonly used is a BNC T connector for 10BASE2 applications.

TAP - An electrical connection to a bus to enable access. A tap may be invasive (requiring a cable splice), or non-invasive (a "vampire" tap).

TCP/IP - Transmission Control Protocol/Internet Protocol. A suite of protocols designed by the Department of Defense to enable communications between dissimilar computer systems. Now widely used by the commercial and academic sectors.

TDR - Time Domain Reflectometer. A piece of test equipment used to measure metallic cable length and impedance.

TELECOMMUNICATIONS - Any transmission, emission, and reception of signs, signals, writings, images and sounds, that is information of any nature by cable, radio, optical or other electromagnetic systems.

TELECOMMUNICATIONS INDUSTRY ASSOCIATION - Known as TIA, this association is made up of two autonomous parts. The first operates as a traditional trade association structured to promote the common interests of its members. The second operates as the Standards Development organization for the telecommunications industry in North America.

TERMINAL SERVER - A device that allows connection of several terminals and multiplexes them onto a LAN cable.

TERMINATE - To connect a wire or wires to a device or a matching impedance connection.

THICKNET - Another term for IEEE 802.3 10BASE-5 systems.

THIN ETHERNET - Normally describes a 10BASE-2 system. Also called Cheapernet.


TOKEN - A unique combination of bits that passes from station to station in a token passing network. When a station has the token, it may communicate with the network.

TOKEN BUS - A bus topology that uses token passing as its contention method.

TOKEN PASSING - Moving a special combination of bits from station to station in a ring or bus when there is no traffic. When a workstation has the token, it may then use the network channel for communications.

TOKEN RING - A logical ring topology that passes a token in one direction around the ring. A given device must possess the token to communicate with any other device. If it does not gain control of the token as it passes, it must wait until the token goes around the ring.

TOPOLOGY - The geometric form describing a network's logical and physical layout.


TRAFFIC - A measure of the activity on a network at a given time. Network analyzers can monitor traffic and when Ethernet segments start to exceed 30% to 40% utilization, they run much slower and need to be segmented with switches.

TRANSCEIVER - A device which can transmit and receive information, typically to a workstation from a network connection.

TRANSFER IMPEDANCE - A measure of shielding performance determined by the ratio of the voltage on the conductors enclosed by a shield to the surface currents on the outside of the shield.

TRANSPORT LAYER - Level 4 of the OSI model, this layer deals with end-to-end control of the transmitted information and provides results to the session layer.

TRANSPOSED PAIR - A transposed pair occurs when the ends of two twisted pairs are interchanged. This condition is detected by a LAN Cable Tester's Wiremap test. (also see SPLIT PAIR and REVERSED PAIR).

TRANSVERSE CONVERSION LOSS - A ratio expressed in dB, of measured common mode voltage on a pair relative to the differential mode voltage on the same pair applied at the same end.

TSB - 67, TSB - 95 - Technical Service Bullets that augmented the ANSI/EIA/TIA-A Standard. TSBs were incorporated into the body of ANSI/EIA/TIA-B, and further updates are issued as updated Standards.

TWINAXIAL CABLE - Cable constructed of two insulated center conductors surrounded by a braided shield. Widely used in midrange IBM systems (AS 400's).

TWISTED PAIR - Two insulated wires twisted around each other at regular intervals. May be shielded or unshielded. The number of twists per foot directly relates to the relative noise immunity of the pair.

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UNDERWRITERS LABORATORIES (UL) - A testing body formed primarily to certify fire safety of electrical equipment dealing with voltages greater than 48 VAC or DC. UL has the most recently assumed the responsibility for certification of data grade unshielded twisted pair media for conformance to EIA/TIA and NEMA specifications. The cable categories III through V from the EIA/TIA TSB 36 document serve as the basis for UL cable LEVELS 2 through 5. Cable certified by the UL to meet these standards would bear a marking indicating.

UNIVERSAL SERVICE ORDERING CODE - USOC. A wiring standard for telephone service to an individual phone. In a modular plug, the two center conductors are the primary pair, and supplementary pairs radiate out concentrically. For example, in an RJ-45 (eight pin) plug, pins 4,5 are the primary pair with pins 3,6 - 2,7 - 1,8 forming the supplementary pairs. Note that this is not compatible with TIA/EIA 568-A's recommendation of T-568A or T-568B.

UNIVERSAL SYSTEMS BUS (USB) - A bus for transmitting data between computing devices. Rated at 11 Mbits per second, it offers about 100 times the throughput of a Serial bus.

USART - Universal Synchronous/Asynchronous Receiver Transmitter.


UTP - Unshielded Twisted Pair. Cable constructed of typically multiple twisted pairs of wires, unshielded in a PVC- or plenum-rated sheath.

µV - Microvolt. One millionth of a volt.

µm - A "micro-meter" equals one millionth of a meter.

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VAMPIRE TAP - A tap system for 10BASE5 systems that does not require cutting and splicing the cable. This system uses a sharp pin that pierces the insulator and contacts the center conductor of the thick 10BASE5 cable.


VERTICAL CAVITY SIDE-EMITTING LASER (VCSEL) - A type of light source usually operating at 850 nm and used for Gigabit Ethernet applications.

VOICE GRADE - A designation for a facility capable of carrying signals with a frequency range of 200 - 4000 Hertz.

VOLTAGE - The potential difference in energy between two points.

VTAM - Virtual Telecommunications Access Method. A software suite designed by IBM for their 370 line to manage remote communications for the host and users.

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WAN - Wide Area Network. A network typically spanning a continent or the globe and connected by routers.

WATS - Wide Area Telecommunications Service.

WAVELENGTH DIVISION MULTIPLEXING - WDM is a method encoding data for transmission over an optical fiber.


WIRING CLOSET - Typically called a telecommunications closet (TC). It is a central point for horizontal floor wiring to connect to vertical riser cable or to backbones running to an IC or MC.

WIREMAP - A test performed in the suite of ANSI/EIA/TIA-B.2 requirements that determines the pinout configuration of the wiring pairs. This is the first test a Category 5 tester runs and it looks for opens, shorts, reversals, split pairs and any other miswiring. TIA/EIA 568-B.2 specifies that all four pairs are terminated for Category 5 UTP. Each respective protocol has different pinouts as shown by the WIREMAP test results. Ethernet uses pins 1,2 and 3,6 and Token Ring uses 3,6 and 4,5. (also see LINEMAP)

WORD - The number of bits transmitted in parallel on a data bus.

WORK AREA (work station) - A building space where the occupants interact with telecommunications terminal equipment.

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X-ON/X-OFF - A basic form of information flow control for data communications, the receiving device would issue an X-OFF to the transmitter while it emptied its buffer to disk or performed another operation. When the receiver was ready for more data, it would then issue an X-ON.

XC - Abbreviation for cross-connect.