Dictionary of networking


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Dictionary of networking

  1. 1. IntroductionNetworks are currently one of the fastest growing and most important developments inthe computer industry. Not only are more and more PCs becoming parts of networks, butnetworked PCs are being incorporated into larger enterprise-wide applications so that ev-eryone in a company can access and share data.With the expanding technology of networking comes the terminology to describe it.This Dictionary of Networking provides definitions for all the terms you will encounterwhen dealing with networks of any type.Who Should Use This Book?This book is designed to meet the needs of people who work with networks, communica-tions, and mobile computing systems. Whether you are networking previously uncon-nected computers or downsizing from a mainframe, this book is for you. And if you arestudying for one of the network certification exams, you will find this book to be an es-sential reference.Network users of all levels are barraged with an almost bewildering array of terms, ab-breviations, and acronyms in books, magazine and newspaper articles, advertisements,and their day-to-day conversations. Jargon is a useful shorthand, but it can easily becomeincomprehensible and unmanageable, even to the most seasoned network administrator.What You’ll Find in This BookAlong with clear explanations of the jargon and slang associated with networking, you’llfind definitions of more than 3,000 networking technical terms, abbreviations, and acro-nyms. The list that follows gives you a brief overview of the topics that this book covers:IAcronyms and abbreviationsIActive DirectoryIActiveXIApplication softwareICables, cards, and connectorsICertification schemesIChips, memory, and adaptersICommunications2461book Page i Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  2. 2. IntroductioniiIConnectivity tools, products, and equipmentIDisks and storage mediaIE-mailIHardwareIFile systemsIIndustry standardsIInternet organizationsIInternet terms and abbreviationsIIntranet terms and abbreviationsIJavaILeading hardware and software companiesILinux, Free Software Foundation, GNUIMicroprocessorsIMicrosoft WindowsIMicrosoft Windows NT and NT ServerIMicrosoft Windows 2000IMobile computingINetworking theory and conceptsINovell NetWareINovell Directory ServicesIOperating systems and environmentsIThe OSI Reference ModelIPopular networking productsIProtocols and interfacesISecurity and network administrationISystem architecturesITrade associations2461book Page ii Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  3. 3. iiiIntroductionIUnix shells, tools, and utilitiesIThe World Wide WebIWorkstationsHow This Book Is OrganizedThis book is organized for easy reference. Entries are arranged in letter-by-letter alphabeticorder, ignoring punctuation and spaces, with terms that begin with an uppercase letter (orare all in uppercase) before those in all lowercase letters. So Internet comes before internet,and link level comes before link-state routing algorithm. Numbers and symbols are listedat the beginning of the book in ascending numeric order. If an entry begins with a letter orletters, but contains a number, it is listed alphabetically according to the letter, and then ac-cording to numerical order, so V.42 bis comes between V.42 and V.54.The information within each entry is always presented in the following order:IEntry nameIAbbreviation or acronymIPronunciation, if it isn’t obviousIDefinition, written in clear standard EnglishIURL pointing to further resources available on the Internet.ICross-references to other entries that provide additional or related information on thetopic; more on the cross references in a moment.If an entry has multiple definitions, each one is numbered to separate it from the next,and some of the entries also contain illustrations.Extensive Cross-ReferencingThe Dictionary of Networking is the most extensively cross-referenced dictionary of com-puting and networking terms available today. It contains two kinds of cross references:IA See reference points to another entry that contains the information you are lookingfor. Thus, you can start with an abbreviation, such asPPTP, or with the complete term,such as Point-to-Point Tunneling Protocol, and be sure that you will arrive at the cor-rect definition. You don’t have to know what an abbreviation stands for to be able tolook up a term. Some terms or concepts can be referred to by more than one name, suchas dialback modem and callback modem; you will find both here, so you can alwaysfind your way to the appropriate definition.2461book Page iii Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  4. 4. IntroductionivIA See also reference points to one or more entries that contain additional informationabout a topic. This kind of cross-reference allows you to follow through a related setof entries, broadening your search as you move from entry to entry.We have also added an extra element in this dictionary to help you find information,and that is the pronunciation of an acronym or abbreviation that is pronounced differ-ently from the way it is spelled. For example, if you are reading a magazine article andcome across the abbreviation SCSI, you can look up the abbreviation, which will pointto the main entry term, Small Computer System Interface. But if you are discussing harddisk interfaces with a colleague and hear the term scuzzy, you can look that up too, andyou will also find your way to the main entry, Small Computer System Interface.The AppendicesThis book contains four appendices to provide additional reference material:Appendix A: Internet Resources Collects together URLs under a wide variety of head-ings to cut down on the amount of time you have to spend with your favorite search en-gine. Using this appendix, you can go straight to the right Web site every time.Appendix B: Certification Resources Provides a guide through the complex and con-fusing world of computer and networking certification programs.Appendix C: ASCII Charts Contains both the standard and the extended AmericanStandard Code for Information Interchange charts.Appendix D: EBCDIC Chart Contains the most widely accepted Extended BinaryCoded Decimal Interchange Code chart.A Note about the URLs in This BookNothing is more annoying than a dead URL, and link rot is all pervasive. (If you don’tknow what link rot is, go look it up.) All the URLs in this book have been individuallychecked by our Technical Editor; and at the time of writing, they are all active, they allwork, and they all contain the information that I say they contain. But that is not to say thatsome of them won’t have changed by the time you try them out.The better-organized sites will simply post a link to the new site if they make substantivechanges, and you can use that new link to go right to the new or reorganized site. Othersites, such as the Microsoft Web site, reorganize themselves periodically as a part of theirhousekeeping; the information you want is still available, but you have to look in anotherplace to find it, or use the site’s built-in search engine to find it.2461book Page iv Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  5. 5. vIntroductionSome of the sites that contain the most advanced technical information belong to the.edu domain and are usually computer science departments at the major universities. I havetried to keep the number of such sites to a minimum in this book. Although they can be ex-tremely useful, they usually have a lifespan that closely resembles that of the average grad-uate student. Once the student maintaining the information graduates, the site becomesneglected and is usually removed soon after. Another dead URL.To be consistent with current usage, I have not specified the protocol used to access eachWeb site; unless a different protocol is specified, you can simply assume that HTTP willwork in all cases. Just add http:// to the beginning of each Web address in your browserwhen you access a site.And finally, we have tried very carefully not to break a URL across a line; you shouldbe able to type the characters you see without having to worry about whether to type thathyphen. If a URL has to break, the break is before a period (.) or after a slash (/).About the Companion CDThe companion CD contains an electronic version of this entire book. You can use it to findentries quickly and follow cross-references without a great deal of page flipping.And Finally…Through more than 25 years of hands-on involvement in practical computer applications,including the management of minicomputer systems, PC-based networks, large-scale datacommunications systems, software development, and technical support, I have become in-timately familiar with computer and networking terminology. TheDictionary of Network-ing is a direct result of that experience, and it represents a practical and down-to-earthapproach to computers and computing.Everyone who has worked on this dictionary has tried to make sure that it is as completeand accurate as possible. But if you think that we have missed a word or two that shouldbe included in a future edition, or if you think that an entry doesn’t contain enough infor-mation, please write to the following address:Dictionary of Networkingc/o SYBEX Inc.1151 Marina Village ParkwayAlameda, CA 94501-1044USA2461book Page v Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  6. 6. 14.4BSD LiteSymbols and Numbers! See bang.& See ampersand.* See asterisk.*.* See star-dot-star.. See period and double-perioddirectories... See period and double-perioddirectories./ See slash.// See double-slash.: See colon.<> See angle brackets.> See right angle bracket.? See question mark.@ See at symbol. See backslash.| See vertical bar.1/4-inch cartridge See quarter-inchcartridge.2B+D Common abbreviation for BasicRate ISDN, which has two B, or bearer,channels and one D, or data, channel.See also 23B+D; Basic Rate ISDN.3+ A network operating system, originallydeveloped by 3Com, that implemented Xe-rox Network System (XNS) transport pro-tocols and Microsoft MS-Net file sharing.3Com Corporation One of the largestmanufacturers of network hardware in theworld, particularly known for LAN andWAN products, including remote accessproducts, hubs, network interface cards,Gigabit Ethernet, and multimedia over net-works. The company’s PalmPilot hand-held computer has proved to be extremelypopular, with more than one million unitssold to date. In 1997, 3Com merged withU.S. Robotics in a deal worth $6.6 billion.For more information on 3Com, seewww.3com.com.4B/5B encoding A data-translationscheme used to precede signal encoding inFDDI (Fiber Distributed Data Interface)networks. In 4B/5B, each group of four bitsis represented as a five-bit symbol, which isthen associated with a bit pattern, which inturn is encoded using a standard method,often NRZI (non-return to zero inverted).See also Manchester encoding.4.4BSD Lite A version of the 4.4 Berke-ley Software Distribution (BSD) Unix fromwhich all the AT&T code has been re-moved in an attempt to avoid licensingconflicts. It is not possible to compile andthen run 4.4BSD Lite without a preexistingsystem because several important utilitiesand other files from the operating systemare missing.The 4.4BSD Lite version has served as thebasis for several other important Uniximplementations, including FreeBSD andNetBSD.2461book Page 1 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  7. 7. 5B/6B encoding2See also Berkeley Software DistributionUnix; FreeBSD; NetBSD; Unix.5B/6B encoding A data-translationscheme used to precede signal encoding in100BaseVG networks. In 5B/6B, eachgroup of five bits is represented as a six-bitsymbol, which is then associated with a bitpattern, which in turn is encoded using astandard method, often NRZI (non-returnto zero inverted).See also Manchester encoding.9-track tape A tape storage format thatuses nine parallel tracks on 1/2-inch, reel-to-reel magnetic tape. Eight tracks are usedfor data, and one track is used for parity in-formation. These tapes are often used asbackup systems on minicomputer andmainframe systems; digital audio tapes(DATs) are more common on networks.See also quarter-inch cartridge.10/100 A term used to indicate that a de-vice can support both Ethernet (at a datatransfer rate of 10Mbps) and Fast Ethernet(at a data transfer rate of 100Mbps).See also Ethernet.10Base2 An implementation of the 802.3Ethernet standard on thin Ethernet (RG-58)coaxial cable; sometimes called thinnet orcheapernet wire. The 10Base2 specificationhas a data-transfer rate of 10Mbps and amaximum cable-segment length of 185meters (610.5 feet). A T-connector attachesthe thin coaxial cable to the BNC connectoron the Ethernet adapter.10Base5 An implementation of the802.3 Ethernet standard on thick Ethernetcoaxial cable; sometimes called thicknet.The 10Base5 specification has a data-trans-fer rate of 10Mbps and a maximum cable-segment length of 500 meters (1650 feet),over a bus topology. The cable attaches tothe Ethernet adapter with a vampire, orpiercing, connector and a transceiver.See also bus network.10BaseF An implementation of the802.3 Ethernet standard over fiber-opticcable. This specification allows throughputof a maximum of 10Mbps and is separatedinto these three categories:I10BaseFP (fiber passive) Used for desk-top connectionsI10BaseFL (fiber link) For intermediatehubs and workgroupsI10BaseFB (fiber backbone) Used forcentral facility lines between buildings10BaseT An implementation of the802.3 Ethernet standard over UTP wir-ing—the same wiring and RJ-45 connectorsused with telephone systems. The standardis based on a star topology, with each nodeconnected to a central wiring center and amaximum cable-segment length of 100meters (330 feet).See also star network.23B+D Common abbreviation for Prima-ry Rate ISDN, which has 23 B, or bearer,channels and 1 D, or data, channel.See also 2B+D; Primary Rate ISDN.24/7 Abbreviation for round-the-clockavailability, implying that the service isavailable 24 hours a day, 7 days a week.2461book Page 2 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  8. 8. 3802.x56K modem standard See V.90.100Base-FX A specification for FastEthernet over fiber-optic cable.See also Fast Ethernet100Base-T4 A specification for FastEthernet over four pairs of Category 3, 4, or5 untwisted-pair wiring.See also Fast Ethernet100Base-TX A specification for FastEthernet over two pairs of Category 5unshielded twisted-pair or Category 1shielded twisted-pair cable. The 100Base-TX specification requires two pairs ofwires.See also Fast Ethernet100VG-AnyLAN A term applied to theIEEE 802.12 standard, originally developedby Hewlett-Packard and supported by Nov-ell, Microsoft, AT&T, and many others.The 100VG-AnyLAN specification modi-fies the existing Ethernet standard to allowspeeds of 10 or 100Mbps and uses thedemand priority access method ratherthan Carrier Sense Multiple Access/Colli-sion Detection (CSMA/CD). A speed of100Mbps transmission is supported overCategory 3 four-pair unshielded twisted-pair cabling.See also demand priority; Fast Ethernet.680x0 A family of 32-bit microproces-sors from Motorola, used in Macintoshcomputers and many advanced worksta-tions. The 680x0 is popular with program-mers, because it uses a linear-addressingmode to access memory, rather than thesegmented-addressing scheme used by Intelcoprocessors.Several models have been developed:I68000 The first microprocessor in thisfamily, which used a 32-bit data wordwith a 16-bit data bus and could address16MB of memory. It was used in the firstApple Macintosh computers as well as inHewlett-Packard’s LaserJet printers.I68020 A 32-bit microprocessor thatruns at 16MHz, 20MHz, 25MHz, or33MHz and is capable of addressing asmuch as 4GB of memory. The 68020 wasused in the Macintosh II computer, buthas been replaced by the 68030.I68030 Has a paged memory manage-ment unit built-in and, therefore, does notneed external hardware to handle thisfunction. The 68030 is used in the Mac-intosh II and SE computers.I68040 Incorporates a built-in floating-point processor and memory manage-ment unit, along with independent 4KBdata and instruction caches. It can per-form parallel execution by using multiple,independent instruction queues. The68040 is used in the Macintosh Quadraline of computers.See also PowerPC.802.x A set of communications standardsdefining the physical and electrical connec-tions in LANs, originally defined by the In-stitute of Electrical and ElectronicsEngineers (IEEE).A number followed by an uppercase letterindicates a stand-alone standard; a num-ber followed by a lowercase letter indicates2461book Page 3 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  9. 9. 802.14either a supplement to a standard or a partof a multiple-number standard.Many of the IEEE standards have also beenadopted by the International Organizationfor Standardization(ISO), whose standardsare accepted all over the world; IEEE stan-dards 802.1 to 802.11 are now also knownas ISO 8802.1 to 8802.11. You will seeboth designations in networking books andmagazines; it will take a while for everyoneto get used to these numbers.See also IEEE standards.802.1 An IEEE standard that specifiesthe media-access-control level for bridgeslinking 802.3, 802.4, and 802.5 networks.It includes a spanning-tree algorithm forEthernet media-access-control layer bridg-es and the heterogeneous LAN manage-ment specification for Ethernet and token-ring hubs.See also IEEE standards.802.2 An IEEE standard that specifies thelogical linksublayerof the data-link layer inthe OSI protocol stack. The data-link layerin the OSI protocol stack is divided into thelogical link layer and the media-access-con-trol layer. The logical link layer providesframing, addressing, and error-controlfunctions.See also IEEE standards.802.3 An IEEE standard for CSMA/CD(Carrier Sense Multiple Access/Collision De-tection) LANs, including both baseband andbroadband networks. The baseband versionis based on the Ethernet network, originallydeveloped by Xerox Corporation.The 802.3 standard includes the following:I10Base2 An implementation of theEthernet standard on thin Ethernet cable,with a data-transfer rate of 10Mbps and amaximum cable-segment length of 185meters (600 feet).I10Base5 An802.3Ethernetstandardonthick Ethernet cable, with a 10Mbps data-transfer rate and a cable-segment lengthof a maximum of 500 meters (1650 feet),over a bus topology.I10BaseT Establishes a standard forEthernet over UTP wiring, the same wir-ing and RJ-45 connectors used with tele-phone systems. The standard is based ona star topology. Each node is connected toa wiring center, with a cable-length limi-tation of 100 meters (330 feet).I1Base5 A 1Mbps network standardwith twisted-pair cable based on AT&T’sStarLAN.I10Broad36 Defines a long-distanceEthernet with a 10Mbps data-transferrate and a maximum cable-segmentlength of 3600 meters (11,880 feet).I10BaseF Explicitly specifies fiber-opticcable in three settings; 10Base-FP (fiberpassive) for desktops, 10Base-FL (fiberlink) for intermediate hubs and work-groups, and 10Base-FB (fiber backbone)for central facility lines between buildings.I100BaseVG A 100Mbps Ethernet net-work developed by Hewlett-Packard andAT&T Microelectrics.I100BaseT A 100Mbps Ethernet devel-oped by Grand Junction Networks.See also 100VG-AnyLAN; Ethernet; FastEthernet; Gigabit Ethernet; IEEE standards.2461book Page 4 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  10. 10. 51394802.4 An IEEE standard for bus topolo-gy networks that use token passing to con-trol access and network traffic, running at10Mbps a second. Token-bus networksare sometimes used in manufacturing set-tings, but they are not often found in officenetworks.See also ARCnet; IEEE standards; Techni-cal and Office Protocol.802.5 An IEEE standard that defines ringnetworks using token passing to control ac-cess and network traffic, running at 4 or16Mbps. It is used by IBMs Token Ringnetwork over STP, UTP, or fiber-opticcabling. Also known as ANSI 802.1-1985.See also IEEE standards.802.6 An IEEE standard for metropoli-tan-area networks (MANs). It describes aDQDB (Distributed Queue Dual Bus) usedfor transmitting voice, video, and data overtwo parallel fiber-optic cables, with signal-ing rates in excess of 100Mbps per second.See also IEEE standards; Switched Multi-megabit Data Services.802.7 An IEEE Technical Advisory Group(TAG) report on broadband networks car-rying voice, data, and video traffic.See also IEEE standards.802.8 An IEEE Technical AdvisoryGroup (TAG) report on the use of fiber op-tics as alternatives to copper-based cable inLANs.See also IEEE standards.802.9 An IEEE advisory committee on in-tegrated data, voice, and video networking.The specification has been called IVD (In-tegrated Voice and Data), but is now morecommonly referred to as Iso-Ethernet.See also IEEE standards; Iso-Ethernet.802.10 An IEEE Technical AdvisoryGroup (TAG) working on the definition ofa standard security model for use over a va-riety of network types that incorporates au-thentication and encryption methods.See also IEEE standards.802.11 A proposed IEEE standard thatwill define wireless LANs, includingspread-spectrum radio, narrowband radio,infrared transmission, and transmissionover power lines.See also IEEE standards.802.12 An IEEE working group definingthe 100Mbps Ethernet 100VG-AnyLANoriginally developed by Hewlett-Packardand several other vendors.See also 100VG-AnyLAN; IEEE standards.802.14 An IEEE working group definingstandards for data transmission over tra-ditional cable TV networks using cablemodems.See also IEEE standards.1394 An IEEE standard for a digital plug-and-playbus,originallyconceivedbyAppleComputer in 1986. The 1394 standard sup-ports a maximum of 63 nodes per bus anda maximum of 1023 buses.Three speeds for device connections areavailable:I100Mbps2461book Page 5 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  11. 11. 32706I200MbpsI400MbpsAll devices are hot pluggable, and both self-powered and bus-powered devices can beattached to the same bus. Also known asFireWire, 1394 uses six-pair shieldedtwisted-pair cable and is intended for high-end applications such as digitized video.See also Universal Serial Bus.3270 A general description for the familyof products from IBM that includes termi-nals, printers, and terminal cluster control-lers.Theseproductsallcommunicatewithamainframe computer using the SNA (Sys-tems Network Architecture) protocol.80286 Also called the 286. A 16-bit mi-croprocessor from Intel, first released inFebruary 1982, used by IBM in the IBM PC/AT computer in 1984. Since then, it hasbeen used in many other IBM-compatiblecomputers.The 80286 uses a 16-bit data word and a16-bit data bus, with 24 bits to addressmemory. It has two modes:IReal mode effectively limits performanceto that of an 8086 microprocessor and canaddress 1MB of memory.IProtected mode prevents an applicationfrom stopping the operating system be-cause of an error and can address 16MBof memory.80386 Also called the 386DX and the386. A full 32-bit microprocessor intro-duced by Intel in October 1985 and used inmany IBM and IBM-compatible comput-ers. The 80386 has a 32-bit data word, cantransfer information 32 bits at a time overthe data bus, and can use 32 bits in address-ing memory. It has the following modes:IReal mode effectively limits performanceto that of an 8086 microprocessor and canaddress 1MB of memory.IProtected mode prevents an applicationfrom stopping the operating system be-cause of an error, and it can address 4GBof memory.IVirtual 8086 mode allows the operatingsystem to divide the 80386 into severalvirtual 8086 microprocessors, all runningwith their own 1MB of space, and all run-ning a separate program.80486 Also called the 486 or i486. A 32-bit microprocessor introduced by Intel inApril1989.The80486addsseveralnotablefeatures to the 80386, including an on-board cache, a built-in floating-point pro-cessor, and a memory management unit(MMU), as well as advanced provisions formultiprocessing and a pipelined executionscheme.2461book Page 6 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  12. 12. 7accelerator boardAA+ Certification Acertificationprogramfrom the CompTIA (Computer TechnologyIndustry Association) designed to measurecompetence in basic computer repair andaimed at the computer technician. Certifi-cation requires passing two tests: a coreexam to test general knowledge of PCs, in-cluding configuration, installation and up-grading, diagnosis, repair, maintenance,customer interaction, and safety, and atleast one specialty exam that tests operatingsystem knowledge.A+B signaling A type of in-band signal-ing used in T1 transmission; 1 bit from eachof the 24 subchannels in every sixth frame isused to carry dialing and other control infor-mation. A+B signaling reduces the T1 band-width from 1.544Mbps to 1.536 Mbps.See also T1.a-b box A switching box that allows twoor more computers to share a peripheral de-vice such as a printer. It can be switchedmanually or through software.A/UX A version of the Unix operatingsystem that runs on the Macintosh. A/UX isbased on the System V release 2 of Unix andincludes a number of Apple features, suchassupportfortheMacintoshToolbox.Thissupport allows applications running underA/UX to use the familiar Macintosh user in-terface. You need a Macintosh II with aMotorola 68020 or higher microprocessorand at least 4MB of memory to use A/UX.See also Unix.AAL See ATM Adaptation Layer.AASE See Associate AccreditedSystems Engineer.ABCP See Associate BusinessContinuity Professional.abend Contraction of abnormal end. Amessage issued by an operating system whenit detects a serious problem, such as a hard-ware failure or major software damage.ABI See Application Binary Interface.ABR See Available Bit Rate.ABUI See Association of Banyan UsersInternational.accelerator board An add-in, printedcircuit board that replaces the main proces-sor with a higher-performance processor.Using an accelerator board can reduce up-grading costs substantially, because youdon’t need to replace the monitor, case,keyboard, and so on. However, the mainprocessor is not the only component that af-fects the overall performance of your sys-tem. Other factors, such as disk-access timeand video speed, contribute to a system’sperformance.See also graphics accelerator board.2461book Page 7 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  13. 13. access8access To use, write to, or read from afile, or to log in to a computer system ornetwork.AccessBuilder Remote access softwarefrom 3Com Corporation that lets you ac-cess network resources over a dial-up con-nection from a remote location.access control entry AbbreviatedACE. The basic unit of security in Mi-crosoft Windows 2000 that controls accessto the file system, to Active Directory ob-jects, to printers and other network re-sources, and to the Registry.An ACE consists of a security identifier(SID) and an access mask that defines theaccess rights of that SID. A collection ofACEs that control access to an object isknown as an access control list.See also access control list; securityidentifier.access control list Abbreviated ACL. Alist or table containing information aboutthe users, processes, and objects that can ac-cess a specific file or object. ACLs are usu-ally attached to file-system directories, andthey specify access permissions such asread, write, execute, delete, and so on.ACLs are implemented in Novell NetWare,Microsoft Windows 2000, and Unix:IIn Novell Directory Services, ACLs are as-sociated with every object in the NDS tree,storing the list of rights for each trusteethat can access the object.IIn the Unix Network File System, ACLsinclude the name of the user or group,along with the rights granted to that useror group.IInWindows2000, everythingisanobject,and every object has an associated ACL.See also Active Directory; authentication;NDStree;NovellDirectoryServices;rights;security.access method The set of rules that de-termines which node in a network has ac-cess to the transmission media at anymoment.Attempts at simultaneous access are eithermanaged by a collision detection mecha-nism such as CSMA/CD or prevented byuse of a token-passing method.access protocol The set of rules thatworkstations use to avoid collisions whensending information over shared networkmedia. Also known as the media access con-trol protocol.access rights See rights.access server A computer that providesaccess for remote users who dial in to thesystem and access network resources asthough their computers were directly at-tached to the network.See also communications/modem server;mobile computing.access time The period of time thatelapses between a request for informationfrom disk or memory and the arrival of thatinformation at the requesting device.Memory-access time refers to the time ittakes to transfer a character between mem-ory and the processor. Disk-access time2461book Page 8 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  14. 14. 9ACFrefers to the time it takes to place the read/write heads over the requested data. RAMmay have an access time of 80 nanosecondsor less, while hard-disk access time could be10 milliseconds or less.access token In Microsoft Windows2000, an object that contains the securityidentifier (SID) of a running process.When a process is started by another pro-cess, the second process inherits the startingprocess’s access token. This access token isthen checked against each object’s accesscontrol list to confirm that the appropriatepermissions are in place to permit any ser-vices requested by the process.See also access control list; permissions;process; rights.account OnLANsormultiuseroperatingsystems, an account is set up for each user.Accounts are usually kept for administrativeor security reasons. For communicationsand online services, accounts identify a sub-scriber for billing purposes.See also user account.accounting The process of tracking theresources on a network. The network ad-ministrator can charge for files accessed,connect time, disk space used for file stor-age, and service requests by assigning ac-count balances to users. The users can thendraw from their account balances as theyuse network services.account lockout In Microsoft Windows2000 and other operating systems, a countof the number of invalid logon attempts al-lowed before a user is locked out.See also authentication; user account.account policy On networks and mul-tiuser operating systems, the set of rulesthat defines whether a new user is permittedaccess to the system and whether an exist-ing user is granted additional rights or ex-panded access to other system resources.Account policy also specifies the minimumlength of passwords, the frequency withwhich passwords must be changed, andwhether users can recycle old passwordsand use them again.Accredited Systems Engineer Abbre-viated ASE. A certification from Compaqdesigned to evaluate and recognize exper-tise in installing and administering Compaqworkstations and servers running both Mi-crosoft Windows 2000 and Novell Net-Ware network operating systems.See also Associate Accredited SystemsEngineer.ACE See access control entry.Acer Group One of the top five PC mak-ers in the world, with factories in Malaysia,the Netherlands, the Philippines, Taiwan,and the United States. The Acer Groupbought Texas Instrument’s notebook com-puter business in 1997 and has formed busi-ness alliances with companies, including3Com and Hitachi, for the development ofadvanced digital consumer products suchas PC-ready televisions and DVD systems.For more information on the Acer Group,see www.acer.com.tw.ACF See Advanced CommunicationsFunction.2461book Page 9 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  15. 15. ACK10ACK See acknowledgment.acknowledgment Abbreviated ACK. Incommunications, ACK is a control code,ASCII 06, sent by the receiving computer toindicate that the data has been receivedwithout error and that the next part of thetransmission may be sent.See also NAK.ACL See access control list.ACONSOLE A Novell NetWare 3.xworkstation utility that controls a modemattached to the workstation. ACONSOLE isused to establish an asynchronous remoteconsole connection to a server. The RS232NetWare Loadable Module (NLM) must beloaded on the server to which you want toconnect. In NetWare 4.x, use RCONSOLEto perform this function.acoustic coupler A modem that in-cludes a pair of rubber cups that fit over themouthpiece and earpiece of a standard tele-phone handset (to prevent external noisefrom being picked up). An acoustic couplerallows you to connect your computer to atelephone system that does not have thestandard RJ-11 connections used with con-ventional modems.ACPI See Advanced Configuration andPower Interface.ACR See Available Cell Rate.across-the-wire migration A methodof migrating file-server data, trustee rights,and other information to a Novell Net-Ware server using the NetWare Migrationutility. You can also use across-the-wiremigration to upgrade from LAN Manager,LAN Server, and earlier versions of Net-Ware; a similar process known as BMI-GRATE allows users to migrate fromBanyan VINES.ACS See Advanced CommunicationsService.ACTE See Ascend Certified TechnicalExpert.Active Desktop In Microsoft Windows,a user interface feature that makes the Desk-top look and behave just like a Web page,with underlined icons and a hand mousepointer. Active Desktop is offered as an al-ternative to the classic Windows user inter-face; you can use Active Desktop, you canuse the classic Windows interface, or youcan swap back and forth between the two.Active Directory InMicrosoftWindows2000, a system for large-scale networkmanagement that views the network as a hi-erarchy of objects. Active Directory doesthe following:IProvides a hierarchy for the managementof all network objects, including users,servers, services, file shares, Web pages,printers, and so on.IDivides administration and security intosubdomains, domains, and trees ofdomains.IScales to 10 million users per domain.IImplementsMIT’sKerberosauthenticationsystembasedonprivatekeyencryptionandalso supports public key encryption forauthentication of clients and businesspartners.2461book Page 10 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  16. 16. 11active terminationIEmulates Windows NT 4.x directory ser-vices for backward compatibility.IUses DNS rather than WINS, and requiresall user and host names to be in DNSform.IUses LDAP rather than a proprietary pro-tocol so that non-Microsoft applicationscan query the name database.IInteroperates with Novell NetWare Di-rectory Services.See also forest; Kerberos; Lightweight Di-rectory Access Protocol; NetWare Directo-ry Services; Microsoft Windows 2000; tree.Active Directory Service InterfaceAbbreviated ADSI. In Microsoft Active Di-rectory, an application programming inter-face (API) designed to simplify access toActive Directory objects.See also Active Directory; application pro-gramming interface.Active Directory Users andComputers Abbreviated ADUC. In Mi-crosoft Windows 2000 Server, the main ad-ministrative tool used to manage useraccounts, security groups, organizationalunits, and policies.ADUC is a Microsoft Management Con-sole (MMC) snap-in and replaces WindowsNT User Manager.See also Active Directory; Microsoft Man-agement Console; snap-in.active hub A device that amplifies trans-mission signals in a network, allowing sig-nals to be sent over a much greater distancethan is possible with a passive hub.An active hub may have ports for coaxial,twisted-pair, or fiber-optic cable connec-tions, as well as LEDs to show that eachport is operating correctly.See also repeater.Active Monitor The first station to bestarted on a Token Ring network. The Ac-tive Monitor is responsible for passing andmaintaining the token and detects error con-ditions. The Active Monitor’s performanceis constantly monitored by the StandbyMonitorSee also Standby Monitor.Active Server Pages Abbreviated ASP.In Microsoft Internet Information Server, ascript interpreter and execution environ-ment that supports VBScript and Java-Script and is compatible with other script-ing languages such as Perl, REXX, Tcl, andPython through add-ins from third-partydevelopers.ASP allows you to combine HTML, scripts,and ActiveX components on the same Webserver; all the code runs on the server andpresents the results of this dynamic processto the client browser as a standard HTMLpage.See also JavaScript; Perl; Tcl; VBScript.active termination A technique used toterminate a SCSI. Active termination reduc-es electrical interference in a long string ofSCSI devices.See also forced perfect termination; pas-sive termination.2461book Page 11 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  17. 17. active window12active window The window currentlyaccepting mouse clicks and keyboard input.The title bar of the active window is alwaysa different color from that of the other openwindows.ActiveX The latest development of Mi-crosoft’s COM, the foundation that sup-ported OLE. By adding network capabilities(and so creating DCOM, or DistributedCOM) and by reducing the scope of OLE tocreate ActiveX, Microsoft has created acomprehensive set of component-basedInternet- and intranet-oriented applications.In an attempt to promote ActiveX as a stan-dard, in 1996 Microsoft turned over con-trol of ActiveX to the Open Group tomanage future developments.See also ActiveX control; Distributed Com-ponent Object Model; Java.ActiveX control The basic buildingblock of Microsoft’s ActiveX specification.An ActiveX control is a software modulethat cannot run by itself, but requires an Ac-tiveX container such as a Web browser, aword processor, or a spreadsheet. Eachcontrol delivers a specific function such asdatabase access, user-interface elements, orfile access and can communicate with an-other ActiveX control, an ActiveX contain-er, or the underlying Windows operatingsystem.Unlike Java applets, which for security rea-sons run in a sandbox designed to protectthe file system from unauthorized access,ActiveXcandirectlyaccessfiles.Toprovidea measure of security, ActiveX controls arepackagedwithdigitalcertificatesthatprovethe origin of the control.See also ActiveX; certificate; Java; Javaapplet; Java Virtual Machine; sandbox.AD See Active Directory.Adaptec, Inc. A leading manufacturer ofhigh-performance networking and connec-tivity products, including SCSI adapters,RAID products, Fast Ethernet adapters,ATM network interface cards, and servermanagement software. In 1998, Adaptecacquired Ridge Technologies, a manufac-turer of RAID and other storage solutionsfor Microsoft Windows 2000.For more information on Adaptec, seewww.adaptec.com.adapter A printed circuit board thatplugs into a computer’s expansion bus toprovide added capabilities.Common adapters include video adapters,joy-stick controllers, and I/O adapters, aswell as other devices, such as internal mo-dems, CD-ROMs, and network interfacecards. One adapter can often support sev-eral different devices. Some of today’s PCdesigns incorporate many of the functionspreviously performed by these individualadapters on the motherboard.adaptive equalization See adaptivespeed leveling.adaptive routing A mechanism that al-lows a network to reroute messages dynam-ically, using the best available path, if aportion of the network fails.See also alternative route.adaptive speed leveling A modemtechnology that allows a modem to respond2461book Page 12 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  18. 18. 13address classesto changing line conditions by changing itsdata rate. As line quality improves, the mo-dem attempts to increase the data rate; asline quality declines, the modem compen-sates by lowering the data rate. Also knownas adaptive equalization.ADCCP See Advanced Data Communi-cations Control Procedures.address 1. The precise location in mem-ory or on disk where a piece of informationis stored. Each byte in memory and eachsector on a disk has its own unique address.2. The unique identifier for a specific nodeon a network. An address may be a physicaladdress specified by switches or jumpers onthe network interface card hardware, or itcan be a logical address established by thenetwork operating system.3. To reference or manage a storagelocation.4. In Unix, an IP address as specified in the/etc/hosts file.5. Information used by a network or the In-ternet to specify a specific location in theform username@hostname; username isyour user name, logon name, or accountname or number, and hostname is the nameof the Internet Service Provider (ISP) orcomputer system you use. The hostnamemay consist of several parts, each separatedfrom the next by a period.See also address bus; Domain Name Ser-vice; e-mail address; Internet Service Pro-vider; IP address; memory address.address bus The electronic channel,usually from 20 to 64 lines wide, used totransmit the signals that specify locations inmemory.The number of lines in the address bus de-termines the number of memory locationsthat the processor can access, because eachline carries one bit of the address. A 20-lineaddress bus (used in early Intel 8086/8088processors) can access 1MB of memory, a24-line address bus can access 16MB, and a32-line address bus can access more than4GB. A 64-line address bus (used in theDEC Alpha APX) can access 16EB.address classes In a 32-bit IP address,which is shown in the accompanying illus-tration, the number of bits used to identifythe network and the host vary accordingto the network class of the address, asfollows:IClass A is used only for very large net-works. The high-order bit in a Class Anetwork is always zero, leaving 7 bitsavailable to define 127 networks. The re-maining 24 bits of the address allow eachClass A network to hold as many as16,777,216 hosts. Examples of Class Anetworks include General Electric, IBM,Hewlett-Packard, Apple Computer,Xerox, Digital Equipment Corporation,and MIT. All the Class A networks are inuse, and no more are available.IClass B is used for medium-sized net-works. The 2 high-order bits are always10, and the remaining bits are used to de-fine 16,384 networks, each with as manyas 65,535 hosts attached. Examples ofClass B networks include Microsoft andExxon. All Class B networks are in use,and no more are available.2461book Page 13 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  19. 19. addressing space14IClass C is for smaller networks. The 3high-order bits are always 110, and the re-maining bits are used to define 2,097,152networks, but each network can have amaximum of only 254 hosts. Class C net-works are still available.IClass D is a special multicast address andcannot be used for networks. The 4 high-order bits are always 1110, and the re-maining 28 bits allow for more than 268million possible addresses.IClass E is reserved for experimental pur-poses. The first four bits in the address arealways 1111.See also Classless Inter-Domain Routing;IP address; subnet mask.IP ADDRESS STRUCTUREaddressing space The amount of RAMavailable to the operating system runningon a server.address mask See subnet mask.Address Resolution Protocol Abbrevi-ated ARP. A protocol within TCP/IP(Transmission Control Protocol/InternetProtocol) and AppleTalk networks that al-lows a host to find the physical address of anode on the same network when it knowsonly the target’s logical or IP address.Under ARP, a network interface card con-tains a table (known as the address resolu-tion cache) that maps logical addresses tothe hardware addresses of nodes on the net-work. When a node needs to send a packet,it first checks the address resolution cacheto see if the physical address information isalready present. If so, that address is used,and network traffic is reduced; otherwise, a2461book Page 14 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  20. 20. 15Advanced Communications Servicenormal ARP request is made to determinethe address.See also IP address.address translation gateway Abbrevi-ated ATG. A function in Cisco DECnetrouting software capable of establishing auser-specified address translation mecha-nism for certain selected nodes on the net-work.adjacency A term describing the rela-tionship formed between certain neighbor-ing routers for the purpose of swappingrouting information. Adjacency is based onthe use of a common network segment.administrative alerts In Windows2000, informational messages sent to spe-cific accounts, groups, or computers to an-nounce security events, impendingshutdown due to loss of server power, per-formance problems, and printer errors.When a server generates an administrativealert, the appropriate message is sent to apredefined list of users and computers.See also Alerter service.administrative distance A term usedby Cisco Systems, Inc., to express theintegrity of a routing-information source.Administrative distance is expressed as avalue in the range 0 through 255; the higherthe value, the lower the quality of the rout-ing information.Administrator account In MicrosoftWindows 2000, a special account with themaximum authority and permissions thatcan assign any permission to any user orgroup.The Administrator account cannot be delet-ed, but it can be renamed, which is probablya good security policy.See also permissions.ADMIN object A NetWare DirectoryServices User object, created during the in-stallation of NetWare, that has special priv-ileges, including the supervisory rights tocreate and manage other objects.ADMIN has Supervisor rights and can,therefore, manage the NetWare DirectoryServices tree and add or delete Directoryobjects.ADSI See Active Directory ServiceInterface.ADSL See Asymmetric Digital Sub-scriber Line.ADUC See Active Directory Users andComputers.Advanced CommunicationsFunction Abbreviated ACF. A set ofprogram packages from IBM that allowscomputer resources to be shared overcommunications links using the concepts ofSAA (Systems Application Architecture).For example, ACF/TCAM (Advanced Com-munications Functions/Telecommunica-tions Access Method) and ACF/VTAM(Advanced Communications Functions/Vir-tual Telecommunications Access Method)allow the interconnection of two or more do-mains into one multiple-domain network.Advanced Communications ServiceAbbreviated ACS. A large data-communi-cations network established by AT&T.2461book Page 15 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  21. 21. Advanced Configuration and Power Interface16Advanced Configuration and PowerInterface Abbreviated ACPI. An inter-face specification developed by Intel, Mi-crosoft, and Toshiba for controlling poweruse on the PC and all other devices at-tached to the system. A BIOS-level hard-ware specification, ACPI depends onspecific hardware that allows the operat-ing system to direct power managementand system configuration.See also Advanced Power Management.Advanced Data Communications Con-trol Procedures Abbreviated ADCCP.A bit-oriented, link-layer, ANSI-standardcommunications protocol.See also High-level Data Link Control.Advanced Interactive ExecutiveAbbreviated AIX. A version of Unix fromIBM that runs on its RS/6000 workstationsand on minicomputers and mainframes.Although AIX is based on Unix System VRelease 3, it contains many of the featuresavailable in System V Release 4, isPOSIX-compliant, and meets the TrustedComputer Base (TCB) Level C2 security.One of the major enhancements of AIX isVisual Systems Management (VSM), agraphical interface into the older SystemsManagement Interface Tool (SMIT). VSMcontains four main elements: Print Manag-er, Device Manager, Storage Manager, andUsers and Groups Manager.Advanced Micro Devices, Inc. Abbre-viated AMD. The fifth largest manufactur-er of integrated circuits, flash memory, andmicroprocessors, specializing in clones ofIntel’s popular PC chips, including theAMD386, AMD486, AMDK5, and theAMDK6.For more information about AMD, seewww.amd.com.See also Cyrix; Intel Corporation; Pentium;Pentium II; Pentium III.Advanced Mobile Phone Service Ab-breviated AMPS. Currently the cellulartelephone standard in the United States; ananalog, cellular communications system de-veloped by AT&T. AMPS uses frequency-division multiplexing (FDM) and operatesin the 825 to 890MHz range.See also Cellular Digital Packet Data.Advanced Peer-to-Peer Internet-working An SNA routing scheme pro-posed by Cisco Systems and eventuallyabandoned.Advanced Peer-to-Peer NetworkingAbbreviated APPN. IBM’s SNA (SystemsNetwork Architecture) protocol, based onAPPC (Advanced Program-to-ProgramCommunications). APPN allows nodes onthe network to interact without a main-frame host computer and implements dy-namic network directories and dynamicrouting in an SNA network.APPN can run over a variety of network me-dia, including Ethernet, token ring, FDDI,ISDN, X.25, SDLC, and higher-speed linkssuch as B-ISDN or ATM.See also Asynchronous Transfer Mode;Customer Information Control System;Systems Network Architecture.Advanced Power Management Ab-breviated APM. An API specification from2461book Page 16 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  22. 22. 17Aggregate Route-Based IP SwitchingMicrosoft and Intel intended to monitorand extend battery life on a laptop comput-er by shutting down certain system compo-nents after a period of inactivity.See also Advanced Configuration andPower Interface.Advanced Program-to-ProgramCommunications AbbreviatedAPPC.Aset of protocols developed by IBM as a partofitsSNA(SystemsNetworkArchitecture),designed to allow applications running onPCs and mid-range hosts to exchange dataeasily and directly with mainframes. APPCcan be used over an SNA, Ethernet, X.25,or Token Ring network and is an open,published communications protocol.APPC/PC is a PC-based version of APPCused over a Token Ring network.advanced run-length limitedencoding Abbreviated ARLL. A tech-nique used to store information on a harddisk that increases the capacity of run-length limited (RLL) storage by more than25 percent and increases the data-transferrate to 9Mbps.See also RLL encoding.Advanced Technology AttachmentAbbreviated ATA. The ANSI X3T10 stan-dard for the disk-drive interface usuallyknown as Integrated Drive Electronics(IDE).See also Integrated Drive Electronics.advertising The process by which servic-es on a network inform other devices on thenetwork of their availability. Novell Net-Ware uses the Service Advertising Protocol(SAP) for this purpose.AFP See AppleTalk Filing Protocol.AFS See Andrews File System.aftermarket The market for relatedhardware, software, and peripheral devicescreated by the sale of a large number ofcomputers of a specific type.agent 1. A program that performs a taskin the background and informs the userwhen the task reaches a certain milestone oris complete.2. A program that searches through ar-chives looking for information specified bythe user. A good example is a spider thatsearches Usenet articles. Sometimes calledan intelligent agent.3. In SNMP (Simple Network Manage-ment Protocol), a program that monitorsnetwork traffic.4. In client-server applications, a programthat mediates between the client and theserver.Aggregate Route-Based IPSwitching Abbreviated ARIS. A schemefrom IBM used to establish switched pathsthrough networks that act as virtual cir-cuits, transmitting data packets through thenetwork without the need to make routingdecisions at every step. ARIS uses taggingtechniques to add information to the datapackets that can be used to guide the pack-ets through the virtual circuits based on in-formation already established by protocolssuch as Open Shortest Path First (OSPF)and Border Gateway Protocol (BGP).2461book Page 17 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  23. 23. AIX18AIX See Advanced InteractiveExecutive.alert log In Microsoft Windows 2000, aSystem Monitor log used to monitorcounters that exceed user-specified limits.When such a limit is exceeded, the event islogged into the alert log.See also counter log; System Monitor;trace log.Alerter service A Microsoft Windows2000 service that warns a predefined list ofusers and computers of an administrativealert. The Alerter service is used by theServer service and requires the Messengerservice.See also administrative alerts; Messengerservice; service.Alias object In Novell NetWare, a leafobject that references the original locationof an object in the directory. Using Alias ob-jects, one object can appear in several con-tainers at the same time, allowing users tolocate and use the object quickly and easily.See also leaf object.Allowed Cell Rate See Available CellRate.alphanumeric Consisting of letters,numbers, and sometimes special controlcharacters, spaces, and other punctuationcharacters.See also American Standard Code forInformation Interchange; Extended BinaryCoded Decimal Interchange Code;Unicode.alpha testing The first stage in testing anew hardware or software product, usuallyperformed by the in-house developers orprogrammers.See also beta testing.alternative route A secondary commu-nications path to a specific destination. Analternative route is used when the primarypath is not available.See also adaptive routing.alt newsgroups A set of Usenet news-groups containing articles on controversialsubjects often considered outside the main-stream. Alt is an abbreviation for alternative.These newsgroups were originally createdto avoid the rigorous process required tocreate an ordinary newsgroup. Some altnewsgroups contain valuable discussionson subjects ranging from agriculture towolves, others contains sexually explicitmaterial, and others are just for fun. Not allISPs and online services give access to thecomplete set of alt newsgroups.See also mailing list; moderatednewsgroup; newsgroup; unmoderatednewsgroup.AMD See Advanced Micro Devices, Inc.American National StandardsInstitute AbbreviatedANSI.Anonprofitorganization of more than 1000 businessand industry groups, founded in 1918,devoted to the development of voluntarystandards.ANSI represents the United States in the In-ternational Organization for Standardiza-tion (ISO) and is affiliated with CCITT.2461book Page 18 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  24. 24. 19analogANSI committees have developed many im-portant standards, including the following:IANSI X3J11: Standard for the C pro-gramming language, including languagesemantics, syntax, execution environ-ment, and the definition of the library andheader files.IANSI X3J16: Standard for the C++ pro-gramming language.IANSI X3J3: Definition of the Fortran pro-gramming language compiler.IANSI X3.131-1986: Definition of theSCSI standard. The X3T9.2 standard con-tains the extensions for SCSI-2.IANSI X3T9.5: The working group for theFDDI definition.American Standard Code for Informa-tion Interchange Abbreviated ASCII,pronounced “as-kee.” A standard codingscheme that assigns numeric values to let-ters, numbers, punctuation characters, andcontrol characters to achieve compatibilityamong different computers and peripheraldevices. In ASCII, each character is repre-sented by a unique integer value in the range0 through 255. See Appendix C.See also ASCII extended character set;ASCII file; ASCII standard character set;double-byte character set; ExtendedBinary Coded Decimal Interchange Code;Unicode.American Wire Gauge AbbreviatedAWG. A measurement system that specifiescopper wire by thickness; as thicknessincreases, the AWG number decreases.Some common conductor gauges are:IRS-232-C: 22 or 24 AWGIThick Ethernet: 12 AWGIThin Ethernet: 20 AWGSee also cabling standards; EIA/TIA 586;Type 1–9 cable.America Online, Inc. AbbreviatedAOL. The world’s largest online service,headquartered in Vienna, Virginia, withmore than 15 million subscribers. AOLprovides a gateway to the Internet, as wellas its own news, sports, e-mail, chat rooms,and other fee-based services. In 1997, AOLbought CompuServe, and in 1998,Netscape Communications.For more information about America On-line, see www.aol.com.ampersand (&) 1. In Unix, a commandsuffix used to indicate that the precedingcommand should be run in the background.2. In Unix, a root user command used tostart a daemon that is to keep running afterlogout.3. In HTML, a special character entry in adocument.See also daemon; HyperText MarkupLanguage.AMPS See Advanced Mobile PhoneService.analog Describes any device that repre-sents changing values by a continuouslyvariable physical property, such as a volt-age in a circuit. Analog often refers to trans-mission methods developed to transmitvoice signals rather than high-speed digitalsignals.2461book Page 19 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  25. 25. Andrews File System20Andrews File System AbbreviatedAFS. A protocol developed at CarnegieMellon University; used to share remotefiles across systems using TCP/IP.AFS has certain advantages over NFS inthat it only allows users to access fileslinked to AFS rather than giving access toall files, it has a built-in cache that helps toreduce the demands made on the system,and system administrators can allocate diskspace on the fly as required.See also Distributed File System; NetworkFile System; Transmission Control Proto-col/Internet Protocol.angle brackets The less-than (<) andgreater-than (>) symbols used to identify atag in an HTML document.Also used to identify the return address inan e-mail message header.See also HyperText MarkupLanguage; tag.ANI See automatic numberidentification.anonymous FTP A method used to ac-cess an Internet computer that does not re-quire you to have an account on the targetcomputer system. Simply log on to the In-ternet computer with the user name anon-ymous, and use your e-mail address as yourpassword. This access method was original-ly provided as a courtesy so that system ad-ministrators could see who had logged onto their systems, but now it is often requiredto gain access to an Internet computer thathas FTP service.You cannot use anonymous FTP with everycomputer on the Internet, only with thosesystems set up to offer the service. The sys-tem administrator decides which files anddirectories will be open to public access,and the rest of the system is considered offlimits and cannot be accessed by anony-mous FTP users. Some sites only allow youto download files; as a security precaution,you are not allowed to upload files.See also File Transfer Protocol; Telnet.anonymous posting In a Usenet news-group, a public message posted via an anon-ymous server in order to conceal theidentity of the original sender.anonymous remailer See anonymousserver.anonymous server A special Usenetservice that removes from a Usenet post allheader information that could identify theoriginal sender and then forwards the mes-sage to its final destination. If you use ananonymous server, be sure to remove yoursignature from the end of the message; notall anonymous servers look for and thenstrip a signature. Also known as an anony-mous remailer.ANSI SeeAmericanNationalStandardsInstitute.answer mode A function that allows amodem to answer an incoming call, detectthe protocol being used by the calling mo-dem, and synchronize with that protocol.See also auto-answer; auto-dial.2461book Page 20 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  26. 26. 21Apple Computer, Inc.antivirus program A program that de-tects or eliminates a computer virus. Someantivirus programs can detect suspiciousactivity on your computer as it happens;others must be run periodically as part ofyour normal housekeeping activities.An antivirus program locates and identifiesa virus by looking for characteristic pat-terns or suspicious activity in the system,such as unexpected disk access or .EXE fileschanging in some unusual way. It recogniz-es the virus by comparing information fromthe system against a database of known vi-ruses, which is kept on disk.Be sure you test an antivirus program care-fully on your network before you employit everywhere; some programs impose anenormous overhead on normal networkoperations.See also file-infecting virus; macro virus;multipart virus; polymorphic virus; stealthvirus; Trojan Horse; vaccine; virus.AnyNet A family of gateway productsfrom IBM used to integrate SNA, TCP/IP,and NetBIOS networks with products run-ning on IBM’s AIX/6000, OS/2, and OS/400 and with Microsoft Windows.AOL See America Online, Inc.Apache HTTP Server A freeware Webserver, supported by the Unix community,in use on almost half of the Web sites on theInternet. So called because the original uni-versity-lab software was patched with newfeatures and fixes until it became known as“a patchy server.”Apache dominates the Web because of itslow cost, excellent performance, good scal-ability, and great flexibility. Don’t expecteasy graphical configuration programs andhypertext help; you’ll get the command lineand the man pages instead, so it certainlyhelps to have staff with Unix experience.Apache Server is available as part of the RedHat Software Linux distribution, whichalso provides developers with full supportfor CGI, Perl, Tcl, a C or C++ compiler, anApache server API, and a SQL database.For more information on Apache Server,see The Apache Group Web site atwww.apache.org.See also Linux; Red Hat Software.API See application programminginterface.APM See Advanced PowerManagement.app See application.APPC See Advanced Program-to-Pro-gram Communications.APPI See Advanced Peer-to-Peer Inter-networking.Apple Computer, Inc. Manufacturer ofthe successful Macintosh and Quadra seriesof computers based on Motorola chips. Thecompany was founded by Steve Wozniakand Steve Jobs in a garage on April 1, 1976.In 1993, Apple entered the consumer elec-tronics marketplace with a personal digitalassistant known as Newton, combiningfax, electronic mail, and other functionsinto a unit small enough to fit into a pocket.2461book Page 21 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  27. 27. Apple Desktop Bus22In 1994, Apple launched a new series ofcomputers called the Power Macintosh (orPower Mac), based on the PowerPC, capa-ble of running either the Macintosh operat-ing system or Windows programs undersoftware emulation.Apple always kept the architecture of theMac proprietary, a move that has cost thecompany considerable market share; never-theless, Apple has always had a strong fol-lowing among musicians and graphicaldesigners.In 1997, Steve Jobs rejoined Apple and, af-ter realigning Apple’s product line, led thedevelopment and launch of the popular andcapable Internet-ready iMac computer.For more information on Apple Computer,Inc., see www.apple.com.Apple Desktop Bus A serial communi-cations link that connects low-speed inputdevices, such as a mouse or a keyboard, tothe computer on the Macintosh SE, II, IIx,IIcx, and SE/30.Light pens, trackballs, and drawing tabletsmay also be connected via the Apple Desk-top Bus. Most Apple Desktop Bus devicesallow one device to be daisy-chained to thenext, up to a maximum of 16 devices.Apple Macintosh See Macintosh.AppleShare Network software fromApple Computer that requires a dedicatedMacintosh computer acting as a central-ized server and includes both server andworkstation software. AppleShare uses theAppleTalk Filing Protocol (AFP).AppleTalk AnAppleMacintoshnetworkprotocol, based on the OSI Reference Mod-el, which gives every Macintosh network-ing capabilities. AppleTalk can run underseveral network operating systems, includ-ing Apple Computer’s AppleShare, NovellNetWare for the Macintosh, and TOPSfrom Sun Microsystems.AppleTalk includes specifications for thedata-link layer as LocalTalk, EtherTalk,FDDI-Talk, or TokenTalk, and the networklayer as Datagram Delivery Protocol. Thetransport layer contains four protocols:IRouting Table Maintenance Protocol(RTMP)IAppleTalk Echo Protocol (AEP)IAppleTalk Transaction Protocol (ATP)IName Binding Protocol (NBP)The session layer includesIAppleTalk Data Stream Protocol (ADSP)IAppleTalk Session Protocol (ASP)IPrinter Access Protocol (PAP)IZone Information Protocol (ZIP)The presentation layer adds the AppleTalkFiling Protocol (AFP) for access to remotefiles on shared disks.AppleTalk Filing Protocol Abbreviat-ed AFP. AFP is located in the presentationand application layers of the AppleTalkprotocol stack. AFP lets users access remotefiles as though they were local, as well asproviding security features that can restrictuser access to certain files.2461book Page 22 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  28. 28. 23applicationAPPLETALK PROTOCOL STACKapplication Abbreviated app, or if theapplication is a small one, it is referred to asan applet. A computer program designed toperform a specific task, such as accounting,scientific analysis, word processing, ordesktop publishing.In general, applications can be distinguishedfrom system software, system utilities, andcomputer language compilers, and they canbe categorized as either stand-alone ornetwork applications. Stand-alone applica-tions run from the hard disk in an indepen-dentcomputer,soonlyoneuseratatimecanaccess the application. Network applica-tions run on networked computers and canbe shared by many users. Advanced applica-tions such as groupware and e-mail allowcommunications between network users.See also application metering; client/server architecture; LAN-aware.2461book Page 23 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  29. 29. Application Binary Interface24Application Binary Interface Abbrevi-ated ABI. A specification that aims to ensurebinary compatibility between applicationsrunning on the same family of processors orCPUs using Unix System V Release 4.Applications developed using ABI can runon hardware from different manufacturerswithout being recompiled; any system callsneeded for specific hardware are main-tained in libraries.The specification was originally developedby AT&T and Sun Microsystems and in-cludes a test and verification suite used todetermine if a system complies with thestandard.See also application programminginterface.application layer The seventh, or high-est, layer in the OSI Reference Model forcomputer-to-computer communications.This layer uses services provided by thelower layers but is completely insulatedfrom the details of the network hardware. Itdescribes how applications interact withthe network operating system, includingdatabase management, electronic mail, andterminal emulation programs.See also OSI Reference Model.application-level filter A category offirewall that provides a high degree of secu-rity but at the cost of lower speed and great-er complexity. Typical application-levelfilters can provide proxy services for appli-cations and protocols such as Telnet, FTP,HTTP, and SMTP.See also firewall; packet-level filter; state-less filter.application log In Microsoft Windows2000, a system log that contains events gen-erated by applications or by alert logs. Youcan use the Event Viewer to display the con-tents of the application log.See also Event Viewer; security log; sys-tem log.application metering The process ofcounting the number of executions of thecopies of an application in use on the net-work at any given time and ensuring thatthe number does not exceed preset limits.Application metering is usually performedby a network management application run-ning on the file server. Most applicationmetering software will allow only a certainnumber of copies (usually that numberspecified in the application software li-cense) of an application to run at any onetime and will send a message to any userswho try to exceed this limit.See also concurrent license.Application object In Novell DirectoryServices (NDS), a leaf object that representsa network application in a NetWare Direc-tory tree.See also Computer object; container ob-ject; leaf object; Novell Directory Services.application programming interfaceAbbreviated API. The complete set of alloperating system functions that an applica-tion can use to perform such tasks as man-aging files and displaying information.An API provides a standard way to write anapplication, and it also describes how theapplication should use the functions it pro-vides. Using an API is quicker and easier2461book Page 24 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  30. 30. 25archive filethan developing functions from scratch andhelps to ensure some level of consistencyamong all the applications developed for aspecific operating system.In operating systems that support a graphi-cal user interface, the API also defines func-tionstosupportwindows,icons,drop-downmenus, and other components of the inter-face. In network operating systems, an APIdefines a standard method that applicationscan use to take advantage of all the networkfeatures.application server A special-purposefile server that is optimized for a specifictask, such as communications or a databaseapplication, and that uses higher-end hard-ware than a typical file server.See also superserver.application-specific integratedcircuit Abbreviated ASIC. A computerchip developed for a specific purpose, de-signed by incorporating standard cells froma library rather than created from scratch.Also known as gate arrays, ASICs are foundin all sorts of appliances, including mo-dems,securitysystems,digitalcameras,andeven microwave ovens and automobiles.APPN See Advanced Peer-to-Peer Net-working.ARB See Area Border router.arbitration The set of rules used to man-age competing demands for a computerresource, such as memory or peripheral de-vices, made by multiple processes or users.See also contention.Archie A system used on the Internet tolocate files available by anonymous FTP.Once a week, special programs connect toall the known anonymous FTP sites on theInternet and collect a complete listing of allthe publicly available files. This listing offiles is kept in an Internet Archive Database,and when you ask Archie to look for a file,it searches this database rather than thewhole Internet; you then use anonymousFTP to retrieve the file.See also anonymous FTP.architecture 1. The overall design andconstruction of all or part of a computer,particularlytheprocessorhardwareandthesize and ordering sequence of its bytes.2. Theoveralldesignofsoftware,includinginterfaces to other software, the operatingsystem, and to the network.See also client/server architecture; closedarchitecture; complex instruction set com-puting; open architecture; reduced instruc-tion set computing.archive 1. To transfer files to some formof long-term storage, such as magnetic tapeor large-capacity disk, when the files are nolonger needed regularly but must be main-tained for periodic reference.2. On the Internet, a site containing acollection of files available via anonymousFTP.3. A compressed file.archive file A single file that contains oneor more files or directories that may havebeen compressed to save space. Archives areoften used as a way to transport large num-bers of related files across the Internet.2461book Page 25 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  31. 31. ARCNet26An archive file created under Unix may havethe filename extension .TAR (for tape ar-chive), .GZ (for gzip), or .Z (for compress orpack). Those created in Windows may havethe filename extension .ZIP from the PKZIPor WinZip programs. Archive files createdon a Macintosh will have the filename exten-sion .SAE or .SIT from the StuffIt program.An Internet host that provides access tolarge numbers of archive files is known asan archive site.ARCNet Acronym for Attached Resourc-es Computing Network. A network avail-able from the Datapoint Corporation andother vendors that can connect a wide vari-ety of PCs and workstations (up to a maxi-mum of 255) on coaxial, twisted-pair, orfiber-optic cable. ARCnet uses a proprietarytoken-passing access method at speeds of2.5Mbps. ARCNet Plus is Datapoint’s pro-prietary product that runs at 20Mbps.ARCNetwaspopularforsmallernetworks,because it is relatively easy to set up and tooperate and also because the componentsare inexpensive and widely available. Thesedays, however, it is showing its age and isno longer sold by the major vendors.See also Token Ring network.Area Border router Abbreviated ARB.In an internetwork that uses link state rout-ing protocols such as Open Shortest PathFirst (OSPF) protocols, a router that has atleast one connection to another router in adifferent part of the internetwork. Alsoknown as a Border router.See also Autonomous System Borderrouter; Open Shortest Path First.ARIS See Aggregate Route-Based IPSwitching.ARLL See advanced run-length limitedencoding.ARP See Address Resolution Protocol.ARPAnet Acronym for Advanced Re-search Projects Agency Network. A re-search network funded by the DefenseAdvanced Research Projects Agency(DARPA) to link universities and govern-ment research agencies, originally built byBBN, Inc., in 1969. It was the backbonefor the now huge Internet. TCP/IP proto-cols were pioneered on ARPAnet. In 1983,the military communications portion wassplit off into the MILnet.article An e-mail message posted to oneof the Usenet newsgroups, accessible byanyone with a newsreader and a connectionto the Internet. Also called a post.See also newsreader.AS/400 A series of mid-range mini-computers from IBM, first introduced in1988, that replaces the System/36 and Sys-tem/38 series of computers. The AS/400can serve in a wide variety of network con-figurations: as a host or an intermediatenode to other AS/400 and System/3x com-puters, as a remote system to System/370-controlled networks, or as a network serv-er to a group of PCs.ASBR See Autonomous System Bor-der router.Ascend Certified Technical ExpertAbbreviated ACTE. A certification schemefrom Ascend Communications, Inc., aimed2461book Page 26 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  32. 32. 27ASPat technical professionals with experiencein installing, configuring, and trouble-shooting Ascend remote-access products.Two written exams, the Networking andTelecommunications exam, and the Re-mote Access exam, are followed by a hands-on lab test administered at Ascend’s head-quarters in Alameda, CA.Ascend Communications, Inc. A lead-ing provider of solutions for telecommuni-cations carriers, ISPs, and corporatecustomers, Ascend manufactures productsfor remote access, for wide area network-ing, and for linking telephone switches, net-work connections, and videoconferencingfacilities to phone company networks.Ascend recently acquired Cascade Commu-nications, establishing the company as oneof the largest suppliers of frame-relay andATM equipment. In 1999, Ascend wasbought by Lucent Technologies.For more information on Ascend, seewww.ascend.com.ASCII See American Standard Code forInformation Interchange.ASCII extended character set The sec-ond group of characters, from 128 through255, in the ASCII character set. The extend-ed ASCII character set is assigned variablesets of characters by computer hardwaremanufacturersandsoftwaredevelopers,andit is not necessarily compatible between dif-ferent computers. The IBM extended char-acter set used in the PC (see Appendix C)includes mathematics symbols and charac-ters from the PC line-drawing set.See also American Standard Code for In-formation Interchange; ASCII file; ASCIIstandard character set; double-byte char-acter set; Extended Binary Coded DecimalInterchange Code; Unicode.ASCII file A file that contains only textcharacters from the ASCII character set. AnASCII file can include letters, numbers, andpunctuation symbols, but does not containany hidden text-formatting codes. Alsoknown as a text file or an ASCII text file.See also American Standard Code for In-formation Interchange; ASCII extendedcharacterset;ASCIIstandardcharacterset;binary file.ASCII standard character set A char-acter set that consists of the first 128 (from0 through 127) ASCII characters. The val-ues 0 through 31 are used for nonprintingcontrol codes (see Appendix C), and therange 32 through 127 is used to representthe letters of the alphabet and commonpunctuation symbols. The entire set from 0through 127 is referred to as the standardASCII character set. All computers that useASCII can understand the standard ASCIIcharacter set.See also American Standard Code for In-formation Interchange; ASCII file; ASCII ex-tended character set; double-bytecharacter set; Extended Binary Coded Dec-imal Interchange Code; Unicode.ASCII text file See ASCII file.ASE See Accredited Systems Engineer.ASIC See application-specificintegrated circuit.ASP See Active Server Pages.2461book Page 27 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  33. 33. assembly language28assembly language A low-level pro-gramming language in which each programstatement must correspond to a single ma-chine language instruction that the proces-sor can execute.Assembly languages are specific to a givenmicroprocessor and, as such, are not porta-ble; programs written for one type of pro-cessor must be rewritten before they can beused on another type of processor.You use assembly language for two reasons:ITo wring as much performance out of theprocessor as possibleITo gain access to specific characteristicsof the hardware that might not be possiblefrom a higher-level languageSee also compiler; interpreter; machinelanguage; microcodeAssociate Business ContinuityProfessional Abbreviated ABCP. A cer-tification from Disaster Recovery InstituteInternational (DRII) that covers basic in-formation on business continuity planningand disaster recovery.See also Certified Business ContinuityProfessional; Master Business Continu-ity Professional.Associated Accredited SystemsEngineer Abbreviated AASE. A certifica-tionfromCompaqdesignedtoevaluateandrecognize basic knowledge of PC architec-ture and operations. An AASE may choosetospecializeinMicrosoftWindows2000orNovell NetWare operation.See also Accredited Systems Engineer.Association of Banyan UsersInternational Abbreviated ABUI. TheBanyan user group, with 1700 membersworldwide, concerned with all hardwareand software related to the Banyan system,including Banyan VINES.See also Banyan VINES.asterisk In several operating systems,you can use the asterisk (*) as a wildcardcharacter to represent one or more un-known characters in a filename or filenameextension.See also question mark; star-dot-star.AST Research One of the world’s topten computer manufacturers, AST Re-search makes desktop, laptop, notebook,and hand-held computers, as well as moni-tors, graphics cards, and memory products.A subsidiary of Samsung Electronics Com-pany Limited.FormoreinformationonASTResearch,seewww.ast.com.asymmetrical multiprocessing A mul-tiprocessing design in which the program-mer matches a specific task to a certainprocessor when writing the program.This design makes for a much less flexiblesystem than SMP (symmetrical multipro-cessing) and may result in one processor be-ing overworked while another stands idle.SMP allocates tasks to processors as theprogram starts up, on the basis of currentsystem load and available resources. Need-less to say, asymmetrical multiprocessingsystems are easier to design, code, and testthan symmetrical multiprocessing systems.2461book Page 28 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  34. 34. 29asynchronous transmissionAsymmetric Digital Subscriber LineAbbreviated ADSL. A high-speed datatransmission technology originally devel-oped by Bellcore and now standardized byANSI as T1.413. ADSL delivers high band-width over existing twisted-pair coppertelephone lines. Also called AsymmetricDigital Subscriber Loop.ADSL supports speeds in the range of 1.5 to9Mbps in the downstream direction (fromthe network to the subscriber) and supportsupstream speeds in the range of 16 Kbps to640 Kbps; hence, the term asymmetric.See also Digital Subscriber Line; High-Bit-Rate Digital Subscriber Line; Rate-AdaptiveDigital Subscriber Line; Single-Line Digi-tal Subscriber Line; Very-High-Bit-RateDigital Subscriber Line.Assymetric Digital Subscriber LoopSee Assymetric Digital Subscriber Line.asynchronous communications Seeasynchronous transmission.asynchronous communicationsserver A LAN server that allows a net-work user to dial out of the network intothe public switched telephone system or toaccess leased lines for asynchronous com-munications. Asynchronous communica-tions servers may also be called dial-in/dial-out servers or modem servers.asynchronous time-divisionmultiplexing Abbreviated ATDM. Anasynchronous and adaptive version of time-division multiplexing in which time slots areallocated dynamically based on demand.See also time-division multiplexing.Asynchronous Transfer Mode Abbre-viated ATM. A method used for transmit-ting voice, video, and data over high-speedLANs and WANs. ATM uses continuousbursts of fixed-length packets called cells totransmit data. The basic packet consists of53 bytes, 5 of which are used for controlfunctions and 48 for data.ATM is a connection-oriented protocol,and two kinds of connections are possible:IPermanent virtual circuits (PVCs), inwhich connections are created manuallyISwitched virtual circuits (SVCs), in whichconnections are made automaticallySpeeds of up to 2.488Gbps have beenachieved in testing. ATM will find wide ac-ceptance in the LAN and WAN arenas as asolution to integrating disparate networksover large geographical distances. Alsoknown as cell relay.See also permanent virtual circuit;switched virtual circuit.asynchronous transmission Amethodof data transmission that uses start bits andstop bits to coordinate the flow of data sothat the time intervals between individualcharacters do not need to be equal. Parityalso may be used to check the accuracy ofthe data received.See also communications parameters;data bits; synchronous transmission.2461book Page 29 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  35. 35. ATA30ASYNCHRONOUS TRANSMISSIONATA See Advanced TechnologyAttachment.AT command set A set of standard in-structions used to activate features on a mo-dem. Originally developed by HayesMicrocomputer Products, the AT com-mand set is now used by almost all modemmanufacturers.See also modem.ATDM See asynchronous time-divisionmultiplexing.ATG See address translation gateway.ATM See Asynchronous Transfer Mode.ATM25 A low-cost version of Asynchro-nous Transfer Mode (ATM) that runs onCategory 3 unshielded twisted-pair cableand provides 25Mbps transmissions inboth directions.See also Asynchronous Transfer Mode; IPover ATM; LAN Emulation; Multiprotocolover ATM.ATM Adaptation Layer AbbreviatedAAL. A service-dependent layer in Asyn-chronous Transfer Mode (ATM) that pro-vides the protocol translation betweenATM and the other communications servic-es involved in a transmission.AAL has several service types and classes ofoperation to handle different kinds of traf-fic, depending on how data is transmitted,the bandwidth required, and the types ofconnection involved.See also convergence sublayer; segmen-tation and reassembly sublayer.ATM LAN Emulation An Asynchro-nous Transfer Mode (ATM) variation thatuses software to make the network operat-ing system see an ATM adapter as an Ether-net or Token Ring adapter.See also IP over ATM; LAN Emulation;Multiprotocol over ATM.2461book Page 30 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  36. 36. 31AUDITCONat symbol The separating character (@)betweenaccountnameanddomainnameinan Internet e-mail address.See also bang path.AT&T The parent company of Bell Labo-ratories, the original developers of Unix.For many years Bell Labs was one of thetwo major development centers for Unix(the other being the Computer Systems Re-search Group at the University of Califor-nia at Berkeley), but in 1990, AT&Tformed Unix Systems Laboratories, or USL,to continue the development of Unix. In1993, USL was sold to Novell, and in 1995,Novell sold the rights to SCO (Santa CruzOperation).See also Baby Bells; Regional Bell Operat-ing Companies.attach To establish a connection be-tween a workstation and a network fileserver; particularly, to access additionalservers after logging on to one server.attachment See enclosure.Attachment Unit Interface Abbreviat-ed AUI. A 15-pin socket used by someEthernet devices. AUI connections adaptbetween two different cabling types andwork with a wide range of wiring schemes.Also known as a DIX (for Digital, Intel,Xerox) connector.attack An attempt to circumvent the se-curity measures in place on a network eitherto gain unauthorized access to the system orto force a denial of service.See also brute-force attack; dictionary at-tack; social engineering.attenuation The decrease in power of asignal with increasing distance. Attenua-tion is measured in decibels, and it increasesas the power of the signal decreases. Thebest cables (those exhibiting the least atten-uation) are fiber-optic lines, and the worstcables are unshielded, untwisted-pair lines,such as the silver, flat-satin cables used inshort-run telephone and modem lines.In a LAN, attenuation can become a prob-lem when cable lengths exceed the statednetwork specification; however, the usefullength of a cable may be extended by the useof a repeater.attribute 1. A file attribute is a tech-nique for describing access to and proper-ties of files and directories within a filesystem. You may see the termattribute usedinterchangeably with the term property.2. A screen attribute controls a character’sbackground and foreground colors, as wellas other characteristics, such as underlining,reverse video, and blinking or animation.3. In operating systems, a characteristicthat indicates whether a file is a read-onlyfile, a hidden file, or a system file or haschanged in some way since it was lastbacked up.4. InmarkuplanguagessuchasHTMLandSGML, a name-value pair within a taggedelement that modifies certain characteris-tics of that element.5. In a database record, the name or struc-ture of a field.See also tag.AUDITCON A Novell NetWare and In-tranetWare workstation utility that creates2461book Page 31 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  37. 37. audit policy32a log file to allow an independent auditor toverify that network transactions are accu-rate and that confidential information is se-cure. When auditing is enabled, an auditorcan track when files or directories are cre-ated, deleted, modified, salvaged, moved,or renamed. Changes to security rights canalso be tracked.audit policy In Microsoft Windows2000, the policy that defines the securityevents to track and report to the networkadministrator.See also security log.audit trail An automatic feature of cer-tain programs or operating systems thatcreates a running record of all transactions.An audit trail allows you to track a piece ofdata from the moment it enters the systemto the moment it leaves and to determinethe origin of any changes to that data.auditing The process of scrutinizing net-work security-related events and transac-tions to ensure that they are accurate,particularly reviewing attempts to create,access, and delete files and directories andreviewing security violations. Records ofthese events are usually stored in a securitylog file, which can only be examined by us-ers with special permissions.AUI See Attachment Unit Interface.authentication In a network operatingsystem or multiuser system, the process thatvalidates a user’s logon information.Authentication may involve comparing theuser name and password to a list of autho-rized users. If a match is found, the user canlog on and access the system in accordancewith the rights or permissions assigned tohis or her user account.See also authorization; Kerberos; pass-word; user; user account.authoring The process of preparing amultimedia presentation or a Web page.This involves not only writing the text ofthe presentation or Web page, but also theproduction of the slides, sound, video, andgraphical components.authorization The provision of rights orpermissions based on identity. Authoriza-tion and authentication go hand in hand innetworking; your access to services is basedon your identity, and the authenticationprocesses confirm that you are who you sayyou are.See also authentication.auto-answer A feature of a modemthat allows it to answer incoming callsautomatically.See also answer mode; dialback modem.auto-dial A feature of a modem that al-lows it to open a telephone line and start acall. To auto-dial, the modem sends a seriesof pulses or tones that represent a storedtelephone number.See also callback modem.AUTOEXEC.BAT A contraction of Au-tomatically Executed Batch. A specialMS-DOS batch file, located in the root di-rectory of the startup disk, that runs auto-matically every time you start or restartyour computer. The commands contained2461book Page 32 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  38. 38. 33Available Cell Ratein AUTOEXEC.BAT are executed one byone, just as if you typed them at the systemprompt. An AUTOEXEC.BAT file can beused to load hardware device drivers, setthe system prompt, change the defaultdrive to the first network drive, and log theuser in to the file server.In OS/2, you can select any batch file to beused as AUTOEXEC.BAT for a specificMS-DOS session, so you can tailor specificenvironments for separate MS-DOS sessions,each using a different AUTOEXEC.BAT file.SeealsoAUTOEXEC.NCF;boot;bootstrap;CONFIG.SYS.AUTOEXEC.NCF A Novell NetWarebatch file usually located on the NetWarepartition of the server’s hard disk, used toset the NetWare operating system configu-ration. AUTOEXEC.NCF loads the LANdrivers, the NLMs, and the settings for thenetwork interface boards and then bindsthe protocols to the installed drivers.Automatic Client Upgrade A mecha-nismusedtoupgradeNovellclientsoftwareduring the logon process by executing fourseparate programs called by the logonscript. Automatic Client Upgrade can bevery useful when all client workstations usestandard configurations.automatic forwarding A feature ofmany e-mail programs that automaticallyretransmits incoming messages to anothere-mail address.automatic number identification Ab-breviated ANI. A method of passing a call-er’s telephone number over the network tothe recipient so that the caller can be iden-tified. ANI is often associated with ISDNand is sometimes known as caller ID.automatic rollback In a Novell Net-Ware network, a feature of the TransactionTracking System (TTS) that abandons thecurrent transaction and returns a databaseto its original condition if the network failsin the middle of a transaction. Automaticrollback prevents the database from beingcorrupted by information from incompletetransactions.See also backing out.Autonomous System Border routerAbbreviated ASBR. In an internetwork thatuses link state routing protocols such asOpen Shortest Path First (OSPF) protocols,a router that has at least one connectionto a router in an external network.See also Area Border router; Open Short-est Path First.AutoPlay A feature of Microsoft Win-dows that automatically executes an appli-cation from a CD-ROM or automaticallyplays an audio CD when the disk is insertedinto the CD-ROM drive.Available Bit Rate A Type 3 or Type 4Asynchronous Transfer Mode AdaptionLayer (AAL) service designed for non–time-criticalapplicationssuchasLANemulationand LAN internetworking.See also Constant Bit Rate; Unspecified BitRate; Variable Bit Rate.Available Cell Rate Abbreviated ACR.A measure of the bandwidth in Asynchro-nous Transfer Mode (ATM) networks. TheACR value represents the number of ATM2461book Page 33 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  39. 39. avatar34cells available or allowed per second for aspecific quality of service (QoS) class.Available Cell Rate is also known as Al-lowed Cell Rate.See also Asynchronous Transfer Mode;Minimum Cell Rate; Peak Cell Rate; Sus-tainable Cell Rate.avatar 1. In Unix, another name for thesuperuser account; an alternative to thename root.2. A visual representation of a user in ashared virtual-reality environment.AWG See American Wire Gauge.2461book Page 34 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com
  40. 40. 35back-end systemBBaan Advanced Certification Abbrevi-ated BAC. A certification from Baan avail-able in four specialties covering the BaanIV suite of products: Enterprise Logistics,Enterprise Finance, Enterprise Tools,and Enterprise Modeler.See also Baan Basic Certification.Baan Basic Certification AbbreviatedBBC. A certification from Baan designed toevaluate basic proficiency with the Baan IVsuite of products; a prerequisite qualifica-tion to taking the Baan Advanced Certifica-tion exams.See also Baan Advanced Certification.Baan Company A leading provider ofenterprise and inter-enterprise businesssoftware used for managing finance, man-ufacturing, inventory, distribution, trans-portation, and administrative functions forlarge companies.For more information on Baan, seewww2.baan.com.Baby Bells A slang term for the 22 Re-gional Bell Operating Companies (RBOC),formed when AT&T was broken up in 1984.See also Bell Labs.BAC See Baan Advanced Certification.backbone That portion of the networkthat manages the bulk of the traffic. Thebackbone may connect several locations orbuildings, and other, smaller networks maybe attached to it. The backbone often usesa higher-speed protocol than the individualLAN segments.back-end processor A secondary pro-cessor that performs one specialized taskvery effectively, freeing the main processorfor other, more important work.back-end system The server part of aclient/server system that runs on one ormore file servers and provides services tothe front-end applications running on net-workedworkstations.Theback-endsystemaccepts query requests sent from a front-end application, processes those requests,and returns the results to the workstation.Back-end systems may be PC-based serv-ers, superservers, midrange systems, ormainframes.See also client/server architecture.2461book Page 35 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA. www.sybex.com