HARGRAVE’S
`COMMUNICATIONS DICTIONARY
`
`Frank Hargrave
`
`@ IEEE
`
`PRESS
`
`@
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`TheInstitute of Electrical and Electronics Engineers, Inc., New York
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`Printed in the United States of America.
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`ISBN 0-7803-6020-6
`IEEE Order No. PC5869
`
`Library of Congress Cataloging-in-Publication Data
`
`Hargrave, Frank.
`Hargrave’s communications dictionary.
`/ Frank Hargrave.
`p.
`cm.
`Includes index.
`ISBN 0-7803-6020-6
`1. Telecommunication—Dictionaries.
`TK5102.H37 2000
`621.382'03—dc21
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`I. Title.
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`00-061416
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`“|
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`directed transmission
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`160
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`magnetic communications, a method in whicha signal is aimed at a
`central reflective target and read by receiving nodes as the signal
`bouncesoff the target. This is in contrast to a diffuse transmission in
`whichthe transmission travels in multiple directions (and therefore is
`much weakerin anydirection).
`directional antenna Anantennain which the radiation pattern is not
`uniform in all directions. Also called a nonisotropic antenna.
`directional coupler A multiport device inserted into a transmission
`line for either (1) Separately sampling either the forward (incident)
`wave and the backward (reflected) wave in transmission lines, or
`(2) It may beused to inject a signal into the transmissionlinein ci-
`ther the forward or backwarddirection.
`directional phase shifter A passive phase shifting device in which
`the phase shift for signal transmission in one direction is different
`from the phase shift in the other direction. Also called a directional
`phase changer ot a nonreciprocalphaseshifter.
`directory The nameofa storage area on the medium where files are
`stored.
`
`Ona large storage device,it is possible to have 10,000 to 100,000 (or
`more) files available. It would be difficult or impossible to locate a
`desired file if they were randomly arrangedin a singlelist (aflat di-
`rectory). To makeit easier to find files, the computer operator breaks
`the list of files into smaller lists where each item is related in some
`manner.Thelist, called a directory, may be broken further into sub-
`lists, called subdirectories. A directory may contain both subdirecto-
`ries and data files. When drawn,this structure resembles an inverted
`tree; hence, it is called a directory tree. The top directory (list) is
`called the root directory. This arrangementoffiles and directories is
`called a hierarchical directory system. The diagram depicts one pos-
`sible relationship of 15 directories in a typical computer.
`
`(ROOT)
`
`OS SPREADSHEET
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`COMM
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`—--->
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`WORDPROC
`PROGRAM
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`.
`DATA
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`PROGRAM
`PROGRAM
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`RX
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`1X
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`LETTERS
`ADS
`SPECS
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`iTPAYROLL
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`directory information tree (DIT)
`commonly used directory entries. As the directory cachefills up, the
`least used directory entries are eliminated from the cache.In addition
`to directory caching,file caching may beusedto reduce information
`access timefurther. Directory caching is used in Novell’s NetWare.
`directory entry table (DET) In Novell’s NetWare, one of two tables
`used to keep track of directory information. The othertableis thefile
`allocation table (FAT). The DET, stored on a hard disk, contains in-
`formation about a volume’sfile, directory names, and properties. For
`example, an entry might contain the following:
`¢ File name
`¢ File owner
`* Date andtimeoflast update
`¢ Trustee assignments(or user rights)
`¢ Locationofthefile’s first block on the network hard disk
`The contentsof the DETarestoredin special storage allocation units
`called directory entry blocks (DEBs), each of whichis 4 kilobytes.
`NetWare can support up to 65,536 of these blocks. To improve per-
`formance, NetWare can use directory caching or hashing. Directory
`caching keepscurrently used directory blocks and the FATin a re-
`served area of RAM.Frequently used directory entries will be loaded
`into a cache memory.Directory hashing is the indexingofthe direc-
`tory entries, which speeds accessto directory information.
`directory hashing A method for organizing/indexing directory en-
`tries to minimize the search time for an entry. The hashing provides
`guided accessto the desired entry, so that fewer entries need to be
`checked along the way.
`directory ID In an AppleTalk network, a unique value associated
`with a directory whenthe directory is created.
`directory information base (DIB) The bodyofdirectory-related in-
`formation in the ITU-T X.500 Directory Services model. Directory
`system agents (DSAs) access the DIB on behalf of directory user
`agents (DUAs).
`directory information tree (DIT) Information about a directory in-
`formation base (DIB) in the ITU-T X.500 Directory Services (DS)
`model. Since information in a DIT can get quite large,it is generally
`distributed. This provides faster access to the informationat the dis-
`tributed locations and helps keep down the size of the DIT materials
`at any single location.
`A DITdoesnotcontain actual objects—just information about them
`and a pointerto the actual bodyof information. Therefore, an object
`that appears at multiple locations in the DIT will have only one body
`of information associated with it. Each location in the tree has pre-
`definedattributes associated with it; the attributes will depend on the
`object class to which the entry belongs. An object class such as coun-
`Frequently, directories contain additional information aboutthe file
`try or organization determines which attributes are mandatory and
`suchasfile size, creation date, date of the last modification, and num-
`which are optional for objects belonging to that class. Objects in the
`ber of attributes (read only, system, archived, hidden,etc.) See also
`tree will have specific values associated with these attributes. Two
`access rights.
`generalclasses of operations are possible in a DIT:retrieval (reading)
`and modification (creating and writing). Furthermore, a given DIT
`directory access protocol (DAP) An X.500 protocol used to commu-
`nicate between a Directory User Agentand a Directory System Agent.
`operation may applytoa single entry or to a groupofentries; hence,
`four operation classes are possible. The X.500 model supports three
`directory assistance call In telephony, a call placed to request the
`of the four possible operation classes:
`station number(directory number) of a customer.
`e Retrieve a single entry.
`directory caching A methodof decreasing the timeto find the loca-
`© Retrieve a groupofentries.
`tion ofafile on the disk drive.
`© Modify a single entry.
`The fourth operation class, modify a group of entries, is not sup-
`ported in X.500. Both end users and processes can access the infor-
`mation in the DIT by either of two procedures:
`
`TAX
`
`To speed up the process,it uses a fast memory area (from whichin-
`formation can be quickly retrieved) to store the file allocation table
`(FAT) anddirectory entry table (DET)information about the most
`
`a
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`540
`traffic path
`traffic path A channel, circuit, frequency band, line, switch, time
`slot, or trunk over which individual communicationspass.
`traffic shaping Allowsthe station sending information into an asyn-
`chronoustransfer mode (ATM) networkto:
`* Specify the priority and throughputof information goinginto the
`network, and
`¢ Monitor performance to meet requiredservicelevels.
`traffic unit A synonym for erlang (E).
`
`transfer time
`transfer (1) The movement of data from one location to another,
`(2) Thepassing ofcontrol from one device to another, (3) In teleph-
`ony, a switching system featurethat allowsa userto reassigna call to
`different end station.
`
`transfer characteristics Those intrinsic parametersofan entity (sys-
`tem, subsystem, or device) which, when applied to the input of the
`entity, will fully describe its output. See also transferfunction.
`transfer delay A performance characteristic that expresses the
`amountofelapsed time required to send a messagethrougha system.
`It includes not only the link’s propagation time but any signal pro-
`cessing time required at either endofthe link.
`transfer function (1) A mathematical statement that describes the
`transfer characteristics of a system, subsystem,or device. (2) A rule
`(the transfer characteristic) describing how the outputsignalofcir-
`cuit, device or system respondsto an input signal. The rule may be
`stated in mathematical, graphical, or tabular terms. A transferfunc-
`tionis essentially the complex ratio of the output signalofthe entity
`to the inputsignal.
`
`traffic usage recorder A device (or system) used to sample and
`record the occupancy of equipment, i.e., the amount of telephone
`traffic carried by a group, or several groups, of switchesor trunks.
`-trailer Information occupying the last several bytes of a block or
`packet. Trailers often contain checksumsorothererror control infor-
`mation.
`
`train (1) A sequenceof events or items, such as a pulse train. (2) To
`modify the behavior of a device based on external conditions, as in
`the training of an echo canceler for each new connected path.
`transaction (1) An interaction between a client and a server. A se-
`quence of messages between a masterandclient station required to
`perform a specific function. (2) The smallest complete action when
`using the Structured Query Language (SQL) to search or modify a
`database. (If any step in the transaction cannot be completed, the en-
`tire transactionfails, andall the intermediate steps in the transaction
`are undone.) (3) An entry in a database.
`
`transaction code An identifier or symbol associated with a specific
`transaction and representing the action to be carried out.
`For example,the letter A may beusedas a transaction code for the
`operation “add,” D maybe “delete;’ and so on.
`transceiver (1) A contraction of TRANSmitter and reCEIVER. A de-
`vice that can both transmit and receive signals, such ascellular tele-
`phones, modems, and network interface controllers (NICs). Often
`NICs provide some form ofcollision detection as well. Also known
`as a medium attachment unit (MAU) in IEEE specifications. (2) In
`military communications, the combination of transmitting and re-
`ceiving equipment which:
`* Is housed in a commonchassis or enclosure,
`* Is usually designed for portable or mobile use,
`* Uses commoncircuit components for both transmitting and re-
`ceiving, and
`+ Provides half-duplex operation.
`transceiver cable In Ethernet, a cable that attaches a terminal device
`to an Ethernet backbonecable (either 10Base2 or 10BaseS5).
`transcoder A device that directly converts one digital code into an-
`other digital code, i.e., without returning the original code to an ana-
`log form before generating the new code.
`For example, the conversion of £255-law encoded pulse code modu-
`lation (PCM) to A-law PCMfortransmission from the United States
`to countries in Europe.
`transducer A device for converting energy from one form (heat,
`light, sound, temperature,electrical, etc.) to another for either mea-
`surement of a physical quantity or information transfer.
`Examples oftransducers include devices that:
`* Convert sound pressure levels into electrical signals (micro-
`phones).
`* Convert electrical signals into sound pressure waves (speakers).
`
`Whenthe transferfunction (T) operates on the input(e), the output
`(€,)
`is obtained. Given any twoofthese three entities (T, e, and o)>
`the third can be obtained,that is,
`T=6,/€;, @ =T+e, or ej =e,/T
`
`Simple transferfunctions express the ratio of output to input signals
`whenthe imaginary part of the signals can be ignored, examples are
`voltage and currentgains,reflection coefficients, transmission coef-
`ficients, andefficiency ratios. Complex transferfunctionsinclude the
`imaginary part and are frequency dependent, examplesincludefilter
`response and envelope delay distortion. Transfer functions are fre-
`quently expressed in terms of amplitude vs. frequency and phasevs.
`frequency. (3) In an opticalfiber, the complex mathematical function
`that expressesthe ratio of the variationof the instantaneous powerof
`the optical signal at the output of the fiber (P,) to the instantaneous
`powerof the optical signal that is launchedinto the fiber (P;), as a
`function of modulation frequency.
`transfer mode In telecommunications, the mannerin which data are
`transmitted and/or switched in a network,i.e., synchronousvs. asyn-
`chronous,circuit switched vs. packet switched, and so on.
`transfer rate The rate at which information is conveyed across a
`communicationschannelorcircuit. Transfer rate is expressed in units
`per second(e.g., bits per second, characters per second,bytes per sec-
`ond,andso on). It may representeither the maximum numberofunits
`per second possible or the average numberof units per second(in-
`cluding headers,trailers, and gaps betweenblocks). See also baud.
`transfer rate of information bits (TRIB) The average transfer rate
`of actual, error-free, useful information (not including overhead,er-
`ror bits, or retransmitted bits) through a device orseries of devices.
`Mathematically, TRIB can be expressed as:
`
`B= Numberof information bits properly received
`TRIB =
`Totaltime required to getthe bits
`Data compressionincreasesthe transfer rate by reducing the number of
`bits to be transmitted so that more information can be transferredin the
`sametime. TRIBis also called the throughput or data transfer rate.
`transfer ratio A dimensionlesstransfer function.
`
`transfer time (1) The timeit takes to switch from oneprocess or de-
`vice to an alternate. (2) In gas tube surge protectors, the amount of
`time required for the voltage across the gap to drop into the areTe-
`gion after theinitial gap conduction begins. (3) The amountoftime
`required to transmit and receive a complete message.
`
`4
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`

`

`wirehead
`581
`WOM Anacronym for Write Only Memory. Usefulin FINO(First In
`wirehead Jargon(1) ‘ hanware expert, especially one who concen-
`Never Out) buffers.
`trates on communications
`hardware, (2) An e
`i
`aes LANS).
`‘Xpert in local area net-
`WOMBATAnacronym for Waste Of Money, Brains, And Time. De-
`A wirehead ae be a network software wizard too but will always
`scribes problemsthat are both profoundly uninteresting in them-
`have the ability to deal with network hardware, downto the smallest
`selves and unlikely to benefit anyone, even if solved.
`component.
`-
`wordAset ofbits or characters treated as a single unit within a system.
`wireless access modeIn a personal communications service (PCS),
`+ In computers, although a binary word length can be anyfixed or
`interfacing with a network access point by means of a standardized
`variable length, in computer-based systems,it is generally fixed at
`air interface protocol without the use of a physical connection to the
`8, 16, or 32 bits depending on the particular computer.
`network.
`In telegraphy, six characterintervals are defined as a word when
`computing traffic capacity in words per minute, which is com-
`puted by multiplying the data signaling rate in baud by 10 anddi-
`viding the resulting product by the numberof unit intervals per
`character.
`
`wireless cable A term referring to the use ofradio networksto trans-
`mit cable-like TV programming to homes andbusinesses.
`wireless in-building network (WIN) A wireless networkthatis con-
`fined to a single building.
`
`world newsgroups
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`wireless LAN (WLAN) A local area network (LAN)architecture ra-
`diated transmissions (such as radio or light) rather than conducted
`transmissions (including twisted pair, coax, or fiber optic cables).
`wireless local loop (WLL) Theuseofa radiolink to provide service
`to a remotelocation orto locations whereitis too expensiveto install
`copper loops.
`wireless modem A modem that transmits over a wireless network
`rather than over telephonelines.
`wireless packet network A switching network designed specifically
`for handling packet data communications. The network, like most
`telephonic systems, is a hierarchical topology. Thatis, at the lowest
`level, a base station exchangeswireless packets with nearby devices.
`Thebase stations then route these packets via traditional local area
`network (LAN)techniques to the destination user.
`wireless switching center (WSC) Thesecondofthe twocellular sys-
`tems in every market, it always belongsto the local telephone com-
`pany. The frequencies used are in the 869-894 MHz band. Also
`called the Block B carrier.
`
`wireline A term for a communications system that uses wire cable
`rather than radio for communicationslinksto its customers.
`wireline common carrier Commoncarriers that are in the business
`of providing landline local exchange telephone service.
`wiring center (J) In general, a term for any of several components
`that serve as commontermination points for one or more nodes
`and/or other wiring centers. The wiring center frequently connects to
`either an intermediate distribution frame (IDF)or a maindistribution
`frame (MDF). (2) The IEEE 802.5 namefor a token ring node con-
`centrator, Called a multistation access unit (MAU) by IBM.See also
`multistation access unit (MAU).
`
`wiring closet The termination point for customer premises cabling.
`These cables connectthe variousareasin an office or building to the
`central wiring, and to the telephone or power company wiring. Usu-
`ally a physical box, room,or even a closet in which the cabling on a
`particular floor is terminated,typically on a wiring frame.
`wiring frame A frame used to organize and managethe termination
`and connection and cross connection of multiple cables.
`WLANAnacronym for Wireless LAN.
`WLL Anabbreviation of Wireless Local Loop.
`WN Anabbreviation of Wrong Number.
`
`word length Thetotal numberofbits ina symbol(or character) with-
`outstart, stop, or parity bits.
`work space In computers and data processing systems,that portion of
`mainstorage used by a computer program for temporarily storing data.
`workflow automation The flow of documents around an organiza-
`tion in a prescribed order (workflow) which can be automated,deliv-
`ering an hierarchical and controlled form of workgroup computing.
`workgroup A collection of network nodes grouped for administrative
`purposesbut not sharing security information. Each workgroup has a
`unique name.See also domain anduser.
`workgroup computing A method of organizing a business around
`productive teams using computer support
`to enable cooperative
`working and to eliminate time/space restrictions. An extension of
`conventional local area network (LAN) working.
`workstation (1) A networked computertypically dedicated for end-
`user applications(i.e. it does not provide any resourcesthat can be
`shared on a network). See also mainframe, microcomputer, micro-
`processor, minicomputer, and personal computer. (2) A term used
`freely to mean a PC,node,terminal, or high-end desktop processor
`(for computer aided design or computer aided manufacturing
`(CAD/CAM)andsimilar computerintensive applications). (3) In au-
`tomated systems, such as computer, communications, and control
`systems, the inpuoutput, display, and processing equipment that
`provides the operator to system interface.
`World Geodetic System 1984 (WGS84) A geodetic reference system
`that includes a geocentric referenceellipsoid, a coordinate system, and
`a gravity field model. Theellipsoid attempts tofit the shape of the en-
`tire Earth as well as is possible with a single ellipsoid. Although WGS
`84 is often used as the worldwide reference, other models are used lo-
`cally to provide a betterfit to the Earth in a specific region.
`WGS 84 defines the Earth-centered ellipsoid coordinates such that
`the Z-axis is collinear with the Earth’s spin axis, the X-axis is through
`the intersection of the prime meridian and the equator, and the Y-axis
`is rotated 90° east of the X-axis about the Z-axis. WGS84 is the geo-
`detic coordinate system and ellipsoid commonly used by the Global
`Positioning System (GPS). See also ECEF (Earth Centered Earth
`Fixed) and GlobalPositioning System (GPS).
`world newsgroups The seven major newsgroup categories that are
`automatically distributed to every USENetsite on the Internet. The
`seven categories are comp, news, rec, sci, soc, talk, and misc.
`Two other classifications of newsgroups are also available in
`USENet: alternative newsgroups and local newsgroups. The alterna-
`tive newsgroups (whichare notcarried by all USENetsites) are cre-
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