AC – Alternating current. A signal which 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.

ACR – Attenuation to Crosstalk Ratio. ACR is a comparison of signal strength to noise interference and is used as a “bandwidth” indicator. The ratio is not a test but a comparison between two previous test results. I compares signal loss (attenuation) to noise interference (NEXT). The larger the ACR, the better the transmission will be.

ADDRESS – The destination of a message sent through a data communications system. A series of digits identifying a component or device attached to a network.

AI – Artificial Intelligence. The basis behind current Expert or Knowledge based systems, it is the ability to update stored reference material and adapt to new information automatically.

ANALOG – An electrical signal comprised of many different and constantly changing voltage levels.

ANALOG/DIGITAL CONVERTER – A device which converts analog signals to a digital representation. Also called “A to D converter” or ADC (see above).

ANSI – American National Standards Institute. An organization which develops standards for voluntary use in the United States.

API – Applications Programming Interface. A software interface provided by network operating system vendors to promote the development of third-party applications which function under direct control of the operating system.

APPLETALK – A proprietary network designed for Apple Computer Corp. Macintosh computers and peripherals. (See Topologies Section)

APPLICATIONS LAYER – The highest layer of the OSI network model. This is the level that user interaction with the network occurs.

ARCNET – Attached Resources Computing Network. Developed by Datapoint, San Antonio, Texas, it is a 2.5 Mbps (soon to be optionally 20 Mbps) logical token-bus network configured in either a physical star or daisy chain. (See Topologies Section)

ARPANET – A network developed by the Advanced Research Projects Agency of the Department of Defense which connects many defense oriented research sites. The forerunner of several of today’s packet switching technologies.

ASCII – American Standard Code for Information Interchange. Developed by ANSI, it is a seven data bit code representing 128 different characters. Widely used as a common data exchange format between like and unlike computer systems.

ASIC – Application Specific Integrated Circuit.

ASYNCHRONOUS BALANCED MODE – Used in IBM’s Token Ring Logical Link Control, it allows access to the data link by network attached devices.

ASYNCHRONOUS TRANSMISSION – Also called “start-stop transmission”, it is a non-continuous data stream with each data element framed by tags called start and stop bits. This eliminates the need for precise clocking at both ends. Speed and bandwidth are sacrificed, however, due the excess information required. A seven bit data element will typically have one start bit, one parity bit and one or two stop bits needing a maximum of 11 bits to get the original seven transmitted and properly received. This is the type of communication that personal computers most often use when they communicate via telephone lines.

ATM – Asynchronous Transfer Mode. A high speed form of packet switching being developed for the commercial sector and now used in LAN’s. High speed (155 Mbps)
throughput can be achieved on Category 5 UTP. Most designers use ATM as a backbone technology connecting the switches and hubs with either Category 5 UTP (limited to 100 meters maximum) or fiber optic cable (up to 2000 meters distance).

ATTENUATION – Degradation of signal level along the cable due to losses in the cable. Attenuation is typically measured in decibels (dB) and represents the overall signal loss in the link. Excessive attenuation may cause a receiver to misinterpret electrical pulses and the larger the loss, the greater the attenuation. The dB values are expressed in negative numbers and by industry convention, the negative sign is omitted.
Attenuation is the measured loss of signal strength from one end of a cable to the other. A “Swept Frequency” measurement is taken to insure the cable’s integrity. This measurement starts at a low frequency and incrementally steps, making measurements, up to the maximum frequency for the selected cable type.

AUI – Attachment Unit Interface. Most often used with 10BASE-5 networks, this is the name for the 15 pin cable which connects a transceiver to the network interface card (NIC) in the node. 10 BASE-T networks use hubs and switches that have AUI ports on the back and they are directly connected to the network bus.

AVERAGE IMPEDANCE – Testing that can be performed to identify physical damage to the cable (much like a capacitance test), connector defects, or cable segments with incorrect characteristic impedance.

AVERAGE NOISE – Detects rms. voltage on each pair of wires using a broadband detector. Available only on the PRO-XL model.

AWG – American Wire Gauge. A method for measuring the thickness of the conductive portion of a piece of metallic cable. The numbers assigned are inversely proportional to the cable’s size. A cable with a rating of 24 AWG will be much thinner than one rated 18 AWG.

B-ISDN – Broadband ISDN.

BACKBONE – A term used to describe the main segment connecting several smaller subnetworks. This main segment is usually designed for maximum data throughput, sometimes at significantly higher speeds than the subnets.

BALUN – Balanced/Unbalanced. A passive line matching transformer designed to match the impedance of the transmission medium with that of the communicating device. Frequently used to implement communications on twisted pair media that would normally require 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 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 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.

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. Using current data compression and modulation techniques, however, 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). Absolutely critical that this be maintained so as to not affect a cable’s impedance (metallic) or refractive index (fiber optic).
BER – Bit Error Rate. The ratio of errored bits of data to the total number of bits transmitted.

BINARY – Information contained in one of two states, either 0 (zero) or 1 (one). A numbering system based on 2’s. Digital computers a 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, really).

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. They may or may not have the same topology.

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.

BUS – An electrical connection tying two or more points together. A bus can be serial or parallel and can carry 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 speed range.

BYTE – Eight data bits or two nibbles.

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

c – Symbol representing the Speed of Light (See Propagation Rate and NVP).

CABLE – Metallic or fiber optic transmission medium used to interconnect electrical and data communications devices. Common metallic types used in LAN interconnects are axial (coaxial, twinaxial, triaxial, quadraxial), shielded twisted-pair (STP) and unshielded twisted-pair (UTP). Cable comes in many varieties and ratings for particular applications. See text for additional information.

CABLE EXPERT – Runs the Autotest, but automatically diverts to assistance screens with advice to help you troubleshoot the problem found. Cable Expert should be used when Autotest indicates a failure.

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 horizontal installed cable segment with its unique path. The “Star Wired” cable run is the cable that is “home-run” from work outlet to cross-connect or patch panel.

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 interference. It may be constructed of metal foil or braided strands.

CAMPUS ENVIRONMENT – A relatively large geographical area encompassing multiple buildings and involving the interconnections between all devices therein.

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 106), nanofarads (nF = X 109) and picofarads (pF = X 1012).

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, like Ethernet.

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

CAT 3 – “category three” 4 Pair UTP cable and associated connecting hardware whose transmission characteristics are specified up to 16 MHz. (EXISTING TIA/EIA; SEE ISO 11801 CLASSES A, B, C)

CAT 4 – “category four” 4 Pair UTP cable and associated connecting hardware whose transmission characteristics are specified up to 20 MHz. (EXISTING TIA/EIA; SEE ISO 11801 CLASSES A,B,C)

CAT 5 – “category five” 4 Pair UTP cable and associated connecting hardware whose transmission characteristics are specified up to 100 MHz. (EXISTING TIA/EIA; SEE ISO 11801 CLASS D)

CAT 5E – “category five e” 4 Pair UTP cable and associated connecting hardware whose transmission characteristics are specified up to 100 MHz (FUTURE PROPOSED TIA/EIA) Has approximately 3dB stronger signal strength than standard CAT 5.

CAT 6 – “category six” 4 Pair UTP cable and associated connecting hardware whose transmission characteristics are specified up to 200 MHz.(FUTURE PROPOSED TIA/EIA; SEE ISO 11801 CLASS E)

CAT 7 – “category seven” 4 Pair STP cable and associated connecting hardware whose transmission characteristics are specified up to 600 MHz.(FUTURE PROPOSED TIA/EIA; SEE ISO 11801 CLASS F)

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.

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.

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

CHARACTERISTIC IMPEDANCE – 1. The measure of a transmission medium’s impedance throughout its length and over a swept frequency spectrum. Often conversion is done to the frequency data to put it in the time domain. 2. A resistive termination matching that of the transmission medium being used to effectively minimize reflections due to structural variations in the medium.

CHARACTER ORIENTED PROTOCOL – A communications protocol which 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. (see Thin Ethernet)

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

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 – When data from two devices attached to a common bus is placed on the bus at the same time. In Ethernet this typically generates a re-transmission.

COMMUNICATIONS PROTOCOL – Rules governing 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 communications 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.
(see Cross-Connect)

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-CONNECTION – Linking two physically different connections together.

CROSS-CONNECT – A block or patch panel used to cross-connect or patch (make changes) to a network backbone or a user’s horizontal cable run.
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. TSB-67 requires bi-directional 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.

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 – Actually, dB or 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.

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 – The PRO-XL performs this function using a 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. 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. This TDR is a powerful diagnostic tool that not only gives you a pass/fail criteria required by TSB-67, but it tells you where the problem is and saves you a great amount of time that would be spent troubleshooting cables and connectors to determine where the problem could be found. (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 electro-magnetically onto adjacent pairs. High levels can cause excessive retransmission rates. An Autotest generates swept signals for NEXT from 1 to 100 MHz and it measures the induced noise on adjacent pairs at precise intervals. The Autotest performs Dual NEXT tests from both ends.

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

EIA – Electronic Industry Associates. 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 (RS-232C, RS-449, etc.)

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

ELFEXT – Equal Level Far End Crosstalk, is a measure of crosstalk noise between pairs at the receive end of the transmission line, adjusted for attenuation. This noise measurement is important to the performance of newer applications which will transmit on multiple pairs (Gigabit Ethernet).

EMI – Electro-Magnetic Interference.

EPROM – Erasable Programmable Read Only Memory.

ESDI – Enhanced Small Device Interface.

ETHERNET – 1. A LAN operating under the guidelines of the IEEE 802.3 document defining physical and data link layer behavior. 2. What you use to catch the Ether Bunny.

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. (see also CAPACITANCE)

FAR-END CROSSTALK – A less accurate measurement of the amount of a signal which is induced into an adjacent pair of wires. (see also CROSSTALK)

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 LT8155/8600 that allows you to determine where in a link a fault is located. (see DOWNLINE IMPEDANCE)

FCC – Federal Communications Commission.

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 a 16 lane highway and any car can go any direction, at any time!

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

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 – Devices such as EPROM’s, and ROM’s which are hardware, but permanently store operating instructions for a processing device.

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.

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

GIGA – A prefix for one billion.

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.

HALF DUPLEX – The ability of a circuit to carry signal in one direction at a time.
Ethernet and Fast Ethernet uses 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 – An equivalent to cycles per second for defining frequency.

HIT – Slang for an induced electrical impulse. (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.

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.

I/O – Input/Output.

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

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

IBM TOKEN RING – A token passing network topology which 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. See also TOPOLOGIES section for specifications.

IDC – Insulation Displacement Connector. A type of connector in which the insulated wire is pushed down between two sharp bladelike 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. See TOPOLOGIES Section for a description of each.

IMPEDANCE – The complex opposition to current flow dynamically in a transmission medium. Including components of resistance, capacitance and inductance. (See IMPEDANCE for more detailed information)

IMPEDANCE MATCHING – The verification that all elements of a transmission system exhibit very similar impedance characteristics at operating frequency. A properly impedance matched system introduces very little signal distortion.

IMPULSE NOISE – Intermittent, high frequency (short), high amplitude pulses that are induced into a transmission line. Can cause data corruption and in some cases hardware damage. (see also ELECTRICAL NOISE TESTING Section)

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. (see also ELECTRICAL NOISE TESTING and NEAR-END CROSSTALK TESTING Sections)

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.

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 TIA/568-A but uses different terms and values. (see NETWORK TROUBLESHOOTING TOOLS for a copy of the OSI model)

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 its width to be variable, causing data errors.

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).

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

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-A, the basic link is limited to 90 meters of horizontal cabling embedded in the walls and ceiling plenum, plus 2 meters of test equipment cords on each end. Length is one of the TSB-67 required tests for a Category 5 UTP cable limited to a total distance of 100 meters including the basic link of 90 meters + 10 meters allowance of line cords, patch cords and up to two cross-connects in a link. (see NOMINAL VELOCITY OF PROPAGATION)

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

LINEMAP – A term referring to the termination pinout pairs of cable. (see CONTINUITY & WIREMAP)

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

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.

LOCAL DISTRIBUTION FRAME – LDF. Another name for an Intermediate Distribution Frame or “IC” as the
TIA/EIA 568-A standard specifies.

LRC – Longitudinal Redundancy Check. Another term for parity checking.
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 the TIA/EIA 568-A 1995 revision. 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. 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 the

TIA/EIA 568-A Standard. The connecting point in a building where outside services interface to internal services. All networking components are “star-wired” back to the MC.

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 – Prefix for one millionth. Used as a prefix for capacitance.

MICROFARAD – 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.

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.

MULTI-PROCESSING – 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.

NAK – No Acknowledgment. A data communications negative response.

NEAR-END CROSSTALK – The induction of transmitted signal onto the receive pair at the transmitting end of the medium (NEXT). (see also NEAR-END CROSSTALK TESTING)

NETBIOS – Network Basic Input/Output System.

NETVIEW – A network management offering from IBM.

NETWARE – A popular network operating system from Novel Inc., Provo, Utah.

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. See TOPOLOGIES Section for examples.

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 that a signal travels on a conductor which 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 it took to make the return trip. (see “c” and LENGTH)

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.

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

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.

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 PANEL – A board with multiple jacks installed for the purpose of connecting devices with modular jacks and cables.

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.

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 for capacitance (pF).

PICOFARAD – One trillionth 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. (see also PLENUM CABLE)

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

POWER SUM – Pair-to-Pair measurements are used to measure one pair against another. Power Sum measurements select a pair and then measures the disturbing 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 (equal level FEXT), and bi-directional NEXT measurements are made with the PRO-XL. In general, this results in an approximately 3 dB loss limit when compared to pair-to-pair test values.

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 scaleable 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). (see B-CHANNEL and D-CHANNEL)

PROPAGATION RATE – The speed at which electricity travels in a transmission medium. Expressed as a percentage of the speed of light which is represented as a lowercase “c”. (see also CABLE

PROTCOL – 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. (see also CONNECTING BLOCK)

PVC – Abbreviation for PolyVinyl Chloride.

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

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

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 Wavetek LT8155/8600 will provide this measurement.

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

ROUTER – A device used to connect LAN’s utilizing the same communications protocol. 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.

RS-232-C – A standard developed by the EIA defining signal levels and pin assignments for serial data communications. Misused and modified, it no longer represents a standard, but a general guideline to follow when interfacing DTE ad DCE.

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.

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 10BASET 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.

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

SHEATH – The outermost covering of a cable, usually an insulating material applied to protect the cable from environmental effects.

SHIELD – A conductive material installed between the insulated center conductor(s) and the sheath. Designed to provide increased immunity to interference caused by outside electrical noise. Usually constructed of metal foil or braided, stranded wire.

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.

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 being incorporated into many intelligent hubs and concentrators. Originally designed for TCP/IP, it now functions independently and with most topologies and NOS’s.

SONET – Synchronous Optical NETwork.

SPACE – Another name for a binary “0” in data communications.

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 wiremap, but will be indicated by very high NEXT.

STAR TOPOLOGY – A physical layout in which each device is wired back to a central point. (see also TOPOLOGIES Section)

START BIT – In asynchronous communications, each character is delimited by a start bit and a stop bit 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 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.

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.

T CONNECTION – A connector fanning 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. (see also CABLE LENGTH TESTING and IMPEDANCE TESTING Sections)

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. (see also
TOPOLOGIES Section for specifications)

TIA – Telecommunications Industry Associates.

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 which 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 which 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.

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.

TSB – 67 – Technical Service Bulletin released by TIA/EIA 568-A. It is entitled “Transmission Performance Specifications for Field Testing of Unshielded Twisted-Pair Cabling Systems.” TSB-67 specifies the electrical characteristics of field testers, test methods and minimum transmission requirements for UTP cabling. It describes the different categories of cable, four basic test requirements: wiremap, length, attenuation, and bi-directional crosstalk. In addition, tester accuracy limits are specified with Level II being the most accurate.

TSB – 95 – Technical Service Bulletin coming from TIA (draft 8A, June 22, 1998) “Additional Transmission Performance Specifications for 100 ohm 4-Pair Category 5 Cabling”. This TSB will govern the pass/fail requirements for Gigabit Ethernet over installed Category 5. It is expected to be released in late 1998 and defines additional parameters — return loss, ELFEXT, delay and delay skew — for installed Category 5 cabling. It is expected that every cable link will need to be tested to TSB-67 and TSB 95 to guarantee that it will support Gigabit Ethernet. TSB-95 also specifies Level II-E field tester requirements to measure these new parameters. Field re-certification using a Level II-E instrument will insure proper operation of 1000 BASE-T.

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.

UART – Universal Asynchronous Receiver Transmitter. A common integrated circuit used in many personal computer serial data ports.

UL – Underwriter’s Laboratories. 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 will bear a marking indicating such.

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.

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.
uV – Microvolt. One millionth of a volt.
µm – A “micro-meter” equals one millionth of a meter. 70 um is the approximate width of a human hair and the most common multi-mode fiber uses 62.5/125 µm core/cladding.

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

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.

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

WATS – Wide Area Telecommunications Service.

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 TSB-67 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 miswires. TIA/EIA 568-A specifies that all four pairs be 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. (see LINEMAP)

WORD – A collection of related data bits whose length is dependent upon the bus width of the computer doing the processing. For example, an 8-bit computer would use an 8-bit word, a 32-bit computer would use 4X8 bits or a 32 bit word.
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.

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