glossaries of it terms

8/7/2019 GLOSSARIES of IT terms

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Geek Speak v2.0:

A Glossary of

Common IT Terms


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Copyright 2010 Global Knowledge Training LLC. All rights reserved. 2

Geek Speak v2.0:

A Glossary of Common IT Terms

10Base5 (10 Mbps, baseband, 500 meter): one oseveral physical media specied by IEEE 802.3 oruse in an Ethernet local area network (LAN); consistso Thickwire coaxial cable with a maximum segmentlength o 500 meters.

10Base2 (10 Mbps, baseband, 185 meter): one o

several physical media specied by IEEE 802.3 oruse in an Ethernet local area network (LAN); consistso Thickwire coaxial cable with a maximum segmentlength o 185 meters .

10BaseT (10 Mbps, baseband, unshielded twisted-pair): one o several physical media specied by IEEE802.3 or use in an Ethernet local area network (LAN);is ordinary telephone twisted pair wire.

100BaseT (100 Mbps, baseband, unshielded twisted-pair): one o several physical media specied by IEEE802.3 or use in an Ethernet local area network (LAN);reerred to as Fast Ethernet because o its highertransmission speed.

10 GbE (10 Gigabit Ethernet): an IEEE 802.3 Ethernetlocal area network protocol with a data transer rateo 10,000 Mb/s (10 Gb/s); disruptive technology thatprovides high-speed data exchange between storagenetworks using FC technology.

3G: third-generation cell phone technology designedor data transer and streaming services, such as video.

4G: ourth-generation cell phone technology suite thatwill be ully based on TCP/IP; all voice communicationwill be packetized or transer as data.

AAL (ATM adaptation layer): adapts PDUs passeddown rom higher layers onto ATM cells.

Absorption: type o signal intererence that relates tothe ability o some objects to absorb radio and datawaves and thereore reduce the distance, or possiblystop entirely, a transmission.

Access Control: the manner in which devices aregranted or denied access to the resource in caseswhere two or more devices simultaneously attempt touse a shared resource (e.g., telecommunications circuitbetween two sites, specic printer).

Access Control List (ACL): the database that keepstrack o and controls access to network servicesthrough assigned privileges or users and groups. Alsocalled authorization prole.

Access Point (AP): a stand-alone hardware deviceor a computer with a wireless adaptor and sotware,which acts as a wireless communication hub. Itenables wireless devices to connect to each other andto link wireless devices to the cabled portion o the

network.

Active Hub: allows multiple devices to be wired to acentral location to share the same media and regener-ate the signal; also reerred to as multiport repeater.


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Address Resolution: a process used to associate net-work addresses with media access control addresses.

ADSL (asymmetric digital subscriber line): typical ormo xDSL telephone companies oer to residences;

digital service designed to provide high data transerrates over traditional telephone cable.

AES (advanced encryption standard): popular encryp-tion used primarily or Wi-Fi systems; considered to bea very secure encryption system and is used or somegovernment data.

Agent: a sotware tool used to collect inormationabout a device and make that inormation availableto a network management system. Agents operate in

managed devices on the network (e.g., hubs, switches,servers, stations).

AGP (accelerated or advanced graphics port): a high-speed, point-to-point channel or attaching a graphicscard to a computers motherboard, primarily to assistin the acceleration o 3D computer graphics.

ALU (arithmetic logic unit): a digital circuit that calcu-lates an arithmetic operation (e.g., addition, subtrac-

tion) and logic operations between two numbers; theundamental building block o the Central ProcessingUnit (CPU) or a computer.

AM (amplitude modulation): a technique used ortransmitting inormation via a radio carrier wave byaltering the power (amplitude).

Amplitude: height o the wave at any point in thewave.

Analog Signal: signal that uses continuous physicalvariables (e.g., amplitude or requency variations) totransmit inormation; is analogous to the source trans-mission, such as a human voice; as the voice changesin tone and volume the waves change as well.

ANSI (American National Standards Institute): a vol-untary organization that coordinates the developmentand use o consensus standards in the United Statesand represents the needs and views o U.S. stakehold-ers in standardization orums around the globe.

Antenna: a conductive structure specically designedto couple or radiate electromagnetic energy. In radiorequency systems, the antenna may be used to bothtransmit and receive electromagnetic energy.

API (application programming interace): prewrit-ten unctions or set o routines to call on underlyingnetwork services used to make sotware programmingeasier and less likely to have errors.

Application Layer: responsible or providing mecha-nisms that enable sotware applications on dierentsystems to use the services o a network to exchangeinormation; perorms the unctions o le transer,e-mail, etc. (see OSI Model); also known as Layer 7.

Architecture: how a system is designed; includes howthe components are connected to and operate witheach other.

ARP (address resolution protocol): network layerprotocol provided with TCP/IP; used to map an IP(internet protocol) address to a MAC (media accesscard) address.

ARPANET (Advanced Research Projects Agency Net-work): developed by DARPA in 1983; Internet basis.

AS (autonomous system): collection o IP networksunder the control o a single entity.

ASCII (American Standard Code or Inormation Inter-change): relates a number rom 0 to 255 in the binary(base 2) orm to keyboard characters; 7-bit binary codecreated to allow compatibility among various types ocomputer equipment.


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ASIC (application-specic integrated circuit): an inte-grated circuit designed or a particular use (e.g., a chipdesigned solely to run a cell phone).

Asynchronous Communication: describes when

devices, such as computers, rely on their own internalclocks; it provides connectivity to printers, modems,ax machines, etc.

Asynchronous Signaling: a orm o signaling inwhich each data character is coded as a string o bits.The bits are separated by start character and stopcharacter bits.

Asynchronous Transmission: a data transmissionmethod that does not require a clock synchronization

signal or maintaining data integrity. Transmission ischaracterized by individual characters, surrounded bystart and stop bits.

ATM (asynchronous transer mode): high bandwidth,cell-switching technology; designed to carry manydierent types o inormation, including voice, video,image, data, and graphics; another orm o STDM(statistical time division multiplexing).

Attenuation: the decrease in magnitude or the powerloss o a signal that propagates between points, otenexpressed in decibels as the ratio o received signalto transmitted signal level; reers to loss in signalstrength, due to resistance, absorption, capacitance orany characteristics o the medium.

AUI (attachment unit interace): a 15-pin connec-tion that provides a path between a nodes Ethernetinterace and the medium attachment unit (MAU); alsoknown as a transceiver.

Authentication: security mechanism that veries ausers identity; consists o three actors: something youknow, something you have, and something you are.

Authorization: process o establishing and enorcingnetwork activities that are permitted or a given user.

AUTONEG (Autonegotiation): a eature that deter-mines link options and optimal settings or a given

Ethernet connection. When AUTONEG is enabled, anetwork interace card or a switch port can determinethe capabilities o the device at the ar end o the linkand select the best mode o operation.

Availability: in security terms, ensuring that the datacan actually be used by, and only by, the users whoneed it; measure o network response time or absenceo operating ailure (downtime) during a given periodo time.

B Channel (bearer channel): carries voice, video, im-age, or data trac, depending upon the equipmentand applications available.

Backbone: a acility (e.g., pathway, cable, conductors)between any o the ollowing spaces: telecommunica-tions rooms, telecommunications enclosures, commontelecommunications rooms, foor-serving terminals,entrance acilities, equipment rooms, and commonequipment rooms.

Backup: a copy o the data stored on a device.

Backup Storage: a redundant storage mechanismthat provides the means to recover rom primary stor-age ailure and the corresponding loss o data; alsoreerred to as disaster recovery.

Balanced Cable: two or more insulated pairs owiresidentical in composition, size, and lengthuniormly twisted together.

Balun: a balanced-to-unbalanced circuit-couplingdevice, used to convert rom unbalanced to balancedtransmission, and provides impedance matching orconnecting twisted-pair to coaxial cable.


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Bandwidth: range o requencies available or signal-ing; inormation transport capacity o a medium, alsocalled analog capacity; expressed in hertz.

Base 2 System: binary number system, only two dis-

crete values (0 and 1) are possible and all numbers area combination o these two characters; digital signalsare numbers sent in the Base 2 system.

Base 10 System: the decimal numbering system.

Baseband: describes signals and systems whoserange o requencies is measured rom 0 to a maxi-mum bandwidth or highest signal requency; some-times used as a noun or a band o requenciesstarting at 0.

Baseband signaling: method o signal transmissionwhere the entire bandwidth o the medium is used tosend a single signal. Contrast with broadband signaling.

Baselining: uses monitoring and reporting sotwareto record network utilization and trac patterns dur-ing smooth operation.

Batch File: MSDOS text le that contains one or moreDOS commands; .BAT extension is used to identiy abatch le.

BAUD: unit measuring the signaling speed o the datatransmission device.

BGP (border gateway protocol): an interautono-mous system routing protocol; a network or group onetworks under a common administration and withcommon routing policies.

Bidirectional Signaling: signals that pass in oppositedirections between two transmitters. In a twisted-paircable, this may be on the same or dierent pairs.

Binary: simple numbering system that alternatesbetween two states, a 1 and a 0.

Bit (b): contraction o the expression binary digit;smallest unit o data in a computer.

Bits Per Second (b/s or bps): common measure odata speed (transer rate) o a device, system, or com-munications channel; also called bit rate.

Biometrics: security method that relies on physicallyveriying that you are who you say you are; examplesinclude retinal scans, nger and palm prints.

BIOS (basic input/output system): the rmware code

run by an IBM-compatible PC when rst powered on,known as booting up; primary unction is to preparethe machine so other sotware programs can load,execute, and assume control o the PC.

Blade Server: sel-contained computer servers,designed or high density in a small ootprint; Non-core components are removed or space, power andother considerations leaving the unctional compo-nents to be considered a computer.

Blade System Server: enclosure that holds multipleBlade servers containing centralized power, cooling,networking, various interconnects and managementservices shared by the Blade servers.

Bootable Disk: a bootable disk contains the bootles o an operating system and is used to boot acomputer.

Bluetooth: low-speed wireless communication

protocol used or short-range data transer; allowsmobile phones, computers, and PDAs to be connectedwirelessly over short ranges.


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Bridge: a Layer 2 networking device used to connectseparate local area network collision domains (ornetwork segments) to extend network reach or selec-tively isolate network trac. Bridges restrict collisiondomains but orward broadcasts.

Broadband: A high-speed wide area network digitalsignal.

Broadband Signaling: the simultaneous transmissiono multiple signals over a medium (e.g., video signalsmultiplexed into channels with a bandwidth o 6 MHzeach).

Broadcast: a technique or sending data simultane-ously to all devices attached to a network with a

single transmission.

Broadcast Domain: the span o a network as repre-sented by the devices capable o receiving a Layer 2rame or Layer 3 datagram addressed to all devices.

Broadcast Group: the group o devices receiving abroadcast transmission.

Broadcast Storm: a series o retransmitted broad-casts caused by uncontrolled duplication o theoriginal message.

Browser Mode: a orm o remote access where theremote station accesses LAN resources through a Webserver on the LAN and obtains access to resourcesdesigned to operate in a Web browser environment.

BRI (basic rate interace): an integrated servicesdigital network conguration, usually intended or the

home and small enterprise (see also PRI).

Bricks and Clicks: business that existed pre-Internetthat now uses e-commerce technology to sell on theInternet.

Bridge: interprets the LAN hardware adapter addresscontained in MAC and decide whether to lter ororward the rame; does not change the rame in anyway.

Browsers: client applications that access World WideWeb servers.

Buer: a block o RAM or other temporary storagearea in a networking device used to temporarily holdincoming data until it can be processed or transeredrom one device to another.

Building Backbone: connects LANs within a building.

Burst Mode: a data transmission mode in which datais sent aster than normal.

Bus: electrical connection between any two compo-nents in a computer; electrical path used to transmitcontrol, data and address signals.

Bus Topology: networking layout where electricalsignals generated by a device connected anywhere onthe bus are received by all other connected devices;all devices are connected along a single wire with twoendpoints.

Byte (B): the standard size o data in a computer;8-bits; also called an octet.

Cable Tester: troubleshooting tool that consists o atwo-piece system with a tester on one end and a re-sponder on the other; tool that tests each cabling wireor breaks plus ensures that they are wired properly.

Cabling System: a specic system o telecommu-nications cables, equipment/patch cords, connectinghardware, and other components that is supplied as asingle entity.


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Cache: keeps data the processor is likely to needquickly close at hand; increases processor operationspeed.

Cache Memory: buer o high-speed memory that

temporarily holds data that is being read rom or writ-ten to the disk drives.

Caching: a technique that provides aster access todata by storing a copy o recently used or likely to beused data in ast, accessible memory.

Campus Area Network (CAN): a network that linkslocal area networks located in two or more buildingsin close proximity to each other.

CAD/CAM: computer-aided design/computer-aidedmanuacturing: sotware used to design products suchas electronic circuit boards in computers.

Campus Backbone: connects building LANs together.

CAP (competitive access provider): company thatprovides network links between the customer and theIntereXchange carrier or directly to the internet serviceprovider (ISP); CAPs operate private networks inde-pendent o local exchange carriers.

Carrier Sense: CSMA principle that a network devicelistens to the medium (wired or wireless) and onlytransmits i it isnt busy.

Cat 3 Cable (category 3 cable): twisted-pair cabletypically used or phones; consists o two twistedpairs.

Cat5 Cable (cat 5 or category 5 cable): twisted-paircable typically used or data communication. Allowsor higher speeds o data transer than Cat 3 cable;consists o our twisted pairs.

CD-R (compact disc recordable): special type o CD-ROM that can be written onto by any computer with arecording drive; can only be written onto once.

CD-ROM (compact disc read-only memory): optical

storage device read by lasers; can hold up to 700megabytes o data.

CD-RW (compact disc rewritable): special type oCD-ROM that can be written onto by any computerwith a recording drive; can be written onto more thanonce.

Cell Style Architecture: reuses requencies withoutletting them interere with each other; also known asa cellular network.

Central Connectivity Device: required device in aEthernet LAN; can be a hub or a switch.

Channel Service Unit (CSU): a customer premisesdevice that physically connects the data terminalequipment to a digital line rom the public networkservice provider; provides a loopback unction ortelephone company testing, and checks bipolar signalgeneration.

Chat: a basic text display application that allows twoor more users to communicate in real-time over anetwork. A text message typed by any user is instantlydisplayed on the screens o all users.

Checksum: a count o the number o bits in a trans-mission unit that is included with the unit so thereceiver can check to see whether the same number obits arrived.

Chipping: encoding system that uses a string o 11bits to represent either a 1 or a 0 to counteract poten-tial transmission loss.


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CIA Triad: acronym or data security; stands or Con-dentiality, Integrity, Availability

Circuit Gateway: a rewall that permits an inboundor outbound connection to take place on the basis o

authentication and authorization criteria. This type orewall does not inspect each datagramonce a de-vice is granted access to the communications channel,it can send and receive any type o message.

Circuit-Switched Network: WAN providing a dedi-cated circuit path between the source device and enddevice; packets are sent over one path and in order.

Circuit Switching: communications method in whicha dedicated communications path is established be-

tween two devices prior to message transer.

CIR (committed inormation rate): describes the userinormation transer rate the network supports duringnormal network operations.

CLEC (competitive local exchange carrier): a UStelecommunications provider company (carrier) thatcompetes with other, already established carriers (thelocal telephone company; e.g., GTE, Bell South).

CLI (command line interace): allows precise controlo a unction, but requires remembering all the correctcommands and switches necessary or a task; used inDOS; a way o interacting with computers.

Client/Server Architecture: network where somecomputers are clients (workstations) and some areservers; inormation is centralized on the server, andan administrator sets policies and manages it.

Client: network device that requests server services.

Clock Speed: timing pattern generated by the proces-sor to synchronize the operation o the microproces-sor; measured in megahertz (MHz).

Cloud Computing: service that allows you to reservespace on the Internet or storage and applicationprocessing; reerred to as cloud computing becausethe Internet is commonly represented by a cloud innetwork diagrams.

Cluster: a collection o servers and associated stor-age devices interconnected using a dedicated, high-speed network that appears as a single device to thenetwork; composed o one or more sectors and is thesmallest unit o disk space or data storage.

Cold Boot: reloading a computers operating systemby turning the power to the computer o, then on.

CMOS RAM (complementary metal-oxide semicon-

ductor RAM): requires very little power; maintainsinormation even when the computer is o.

Converged Network Interace Card (C-NIC): NICthat combines storage, management and data tracon a single device.

Coaxial Cable: copper cabling used primarily orcable or satellite TV.

Codec: a device that can transorm an analog signalinto a digital bit stream (coder) and digital bit streaminto an analog signal (decoder).

Coding: mathematical technique o repeating inor-mation to increase reliability; used to provide redun-dancy or digital communication.

Collapsed Backbone: an internetwork connectioncontained in one device; individual networks are con-

nected to this central device and can then communi-cate with one another.

Collision: occurs when network users communicate atsame time and interere (collide) with one another.


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Collision Detection: the process initiated when twoor more network devices on an Ethernet network at-tempt to send a message at the same time and theirmessages collide.

Collision Domain: logical network segment wheredata packets can collide with one another or beingsent on a shared medium

Compression: The coding or modication o datarom its original orm in order to save storage space ortransmission time.

Computer: any machine that perorms unctionsbased on a set o instructions.

Computer Networking: a combination o hardwareand sotware that allows the various computers in anorganization communicate with one another.

Computer Room: the space that serves the purposeo providing a secure environment or the equipmentand cabling directly related to the critical load; is usu-ally part o the data center.

Concentrator: device that unwraps data sent viaVPN and sends it to the LAN; device that combinesdata rom several active inputs into one shared chan-nel that can be separated ater transmission.

Conerencing: the process o communicating amongusers over a network in real-time, using any combina-tion o text, voice, and video.

Condentiality: in security terms, ensuring that onlythe proper individuals have access to the data.

Congestion: state in which the volume o messagesexceeds the designed capacity o a communicationschannel or network abric, resulting in transer delaysor ailures.

Connection-Oriented Protocols: ensure that data isreceived properly, usually by the receiver transmittingan acknowledgement o data receipt.

Connectionless Protocols: data is sent to the desti-

nation with no regard or whether it is received.

Connectivity Devices: bring users o the networkinto contact with one another.

Constant Bit Rate (CBR): transmission that uses a setamount o network capacity on a continual basis; usedwhen the arrival o the inormation is time-sensitive.

Content Acceleration: the process o loading data

accessed requently by a large number o users ontodevices capable o transerring the data more rapidlythan the existing servers can transer.

Content Access: the process o providing remoteusers the means to connect to a network to obtainspecic inormation.

Content Filtering: the process o restricting the entryor exit o unauthorized or unwanted data (e.g., e-mailattachments) to and rom a network.

Contention: network access method in which devicescompete or use o available communications channel.

Control Mode: orm o remote access where a net-work administrator uses the remote station to monitoror modiy a specic network device or general net-work operations.

Convergence: the merging and sometimes clashingo voice and data networks.

Converter: a device that changes a signal rom onetransmission medium type to another (e.g., rom cop-per to optical ber).


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CPE (customer premises equipment): telephones, DSLor cable modems, or purchased set-top boxes or usewith communication service providers services.

CPS (cycles per second): measure o how requently

an alternating current changes direction; has beenreplaced by the term hertz (Hz).

CPU (central processing unit): the brain o the com-puter system where calculations and decisions aremade; also reerred to as the processor.

CPU Speed: how ast the CPU works.

CRC (cyclic redundancy check): method o checking or

errors in data that has been transmitted on a commu-nications link; a unction used to produce a Checksumagainst a block o data.

Crosstalk: the unwanted transer o signal rom oneor more circuits to other circuits as a result o electro-magnetic intererence.

CS (convergence sublayer): particular protocols thatgather and ormat higher layer inormation so it canbe processed by the lower layers.

CSMA (carrier sense multiple access): data coordina-tion rules or communication; based on the principleso carrier sense and multiple access and the collisiondetect or avoidance decision.

CSMA/CA (carrier sense multiple access collisionavoidance): set o rules or determining how networkdevices respond to avoid a collision.

CSMA/CD (carrier sense multiple access collision de-tect): set o rules or determining how network devicesresponsd when two devices collide; when a collision isdetected, each device stops transmitting and waits arandom amount o time beore proceeding.

Cut-Through: a switching method in which messagesare orwarded as soon as the destination address isreceived, without error checking.

D Channel (data channel): used or common channel

signaling by both the telephone company switch andthe customer equipment; provides the call signals thatset up B channel connections.

DACS (digital access and cross-connect system): apiece o telecommunications equipment used orrouting T1 lines; can cross-connect any T1 line in thesystem with any other T1 line in the system.

DARPA (Deense Advanced Research Project Agency):began developing and testing TCP/IP in the early

1970s.

DAS (direct-attached storage): storage system that isdirectly attached to a workstation or server withoutthe use o a network; combination o a high-speedinterace and shared disk drives, where the disk drivesare connected directly to the servers internally orexternally; primary advantage is high access speed.

Data: inormation manipulated inside the computer in

the orm o bits and bytes.

Data Center: a physical space that contains dataequipment; typically has generator backup, is tem-perature controlled, and physically protected.

Data Integrity: the assurance that a given data lehas not been deleted, modied, duplicated, or orgedwithout detection.

Data Service Unit (DSU): a customer premises devicethat rames and channelizes the users data or trans-mission on the digital network.


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Data Transer Rate: the rate at which inormation istranserred between network devices over a commu-nications channel; also called throughput or operatingspeed.

Data Link Layer: responsible or ormatting dataaccording to the medium it will be sent over (see OSIModel); provides data transer in the orm o rameson a local area network; also called Layer 2.

Datagram: packet sent over an IP network; associatedwith the network layer when communication proto-col is connectionless; contains the data and controlinormation necessary to transer a message romone network to another; created at Layer 3 o the OSIModel; also called a packet.

DCE (data communications equipment ordata circuit-terminating equipment): a device that communicateswith a data terminal equipment (DTE) device in aparticular standard; equipment that establishes, main-tains, and terminates a connection, and perorms theconversion necessary or communications.

Dynamic Data Exchange (DDE): method o inter-process communications that allows you to exchangecommands and data between two applications run-

ning simultaneously.

DDP (datagram delivery protocol): a member o theAppleTalk networking protocol suite, mainly respon-sible or socket-to-socket delivery o datagrams overan AppleTalk network.

DE (discard eligibility): signal used to identiy lessimportant data trac that can be dropped duringperiods o congestion on the system.

Decibel (dB): a logarithmic unit or measuring therelative voltage, current, or power (in watts) o asignal.

Demultiplexing: the process o reconstituting theindividual channels rom the composite signal.

Dialer: the sotware used by remote stations to con-nect to the network over telecommunications circuits.

Digital Certicate: a security tool used to authenti-cate a message. It ensures the recipient that the mes-sage originated rom a source whose identity has beenveried by the issuer o the certicate.

Digital Key: a bit sequence used by a security toolto encrypt a message prior to transmission to keepits contents condential and used by the recipient torestore the encrypted message.

Digital Signal: transmission o inormation in theorm o a sequence o discrete pulses, specically 1sand 0s.

Digital Signature: a bit sequence used by a securitytool to authenticate a message; It ensures the recipi-ent that the message was not modied ater beingtransmitted by the sender.

Directional Antenna: antenna characterized by acoverage zone that preerentially sends or receivessignals in a specic direction; common example isthe wall mounted patch antenna that is physicallyfat and generally mounted on a wall to cover a widehallway or the oces on one side o a foor; generatesa wide and tall signal that extends outward rom theantenna and looks like a rectangle.

Directory: a database o the resources available ona network. Typically, it contains records or devices,sotware applications, data les, users, and groups.

Disaster Recovery: the procedures and actions takento restore network operations ater an event thatdestroys or disables some or all o the network.


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Disk Fragmentation: a disk is said to be ragmentedwhen the data o a le span several sectors, and thesesectors are scattered all around the disk.

Disk Mirroring: simultaneous writing o all data to be

stored onto two hard disks, where both disks are con-nected to same controller card. I one o the hard disksails, the other continues to provide storage services.

Diskless Workstation: a personal computer thatdepends upon a network server or loading data andapplications. Diskless workstations are conguredwithout a foppy or hard disk drive, thereby providingadditional security.

Diversity Reception: a technique used to improve

the reception ability o a wireless network device (e.g.,access point) by combining or selecting signals romtwo or more independent antennas. Used to mitigatethe eects o ading.

DHCP Server (dynamic host conguration protocol):network server that provides automatically conguredIP address inormation to a client computer rom aprecongured pool o IP addresses.

DLCI (data link connection identier): a channel num-ber that tells the network how to route the data.

DMA (direct memory access): a eature that allowscertain hardware subsystems in a computer to ac-cess system memory or reading/writing and/or datatranser independently o the CPU, reducing overheadon the CPU; can include disk drive controllers, graphicscards, network cards, and sound cards.

Domain Name: a human-riendly name given to one

or more IP addresses.

DOS (disk operating system): a amily o closelyrelated operating systems (COS) that ran on IBM PC-type hardware.

DNA (digital network architecture): a set o speci-cations or protocols created by Digital EquipmentCorporation (DECnet) that evolved into one o the rstpeer-to-peer network architectures.

DNS (domain name system): worldwide system oservers that maps a domain name to an IP address.

DRAM (dynamic random access memory): primarychoice or holding large amounts o inormation dueto its inexpensive cost; must be rereshed or rewrittenrequently (about every 386 milliseconds).

Driver: sotware that helps the OS communicate withhardware.

DS0 (digital signal, level 0): basic digital signalingrate o 64 kbit/s, corresponding to the capacity o onevoice-requency-equivalent channel.

DS1 (digital signal, level 1): also known as T1; widelyused to transmit voice and data between devices.

DSL (digital subscriber line): technology that deliv-ers digital data transmission over the wires o a localtelephone network.

DSSS (direct sequence spread spectrum): modulationtechnique that takes data and spreads it across theentire 22 MHz channel and uses a chipping code torepresent the bits or data encoding.

DSU (data service unit): transorms digital signal roma unipolar DTE to a bipolar digital network signal onthe transmitting side and vice versa on the receivingside.

DTE (data terminal equipment): device that perormsunctions at network end o communications line; seeDCE (data communications equipment); device pro-ducing data to be transmitted across an internetwork.


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Dual-Ring Topology: a ring topology that allowseach device or network to have two connections toeach adjacent device or network.

DVD (digital versatile disc): can hold over seven times

as much inormation as CDs; drives are backward-compatible with CD-ROM drives.

DWDM (dense wavelength-division multiplexing): anoptical technology used to increase bandwidth overexisting ber optic backbones (see building backbone,campus backbone).

EBCDIC (extended binary coded decimal interchangecode): 8-bit character encoding table used by ISMmainrames.

EGP (exterior gateway protocol): a protocol commonlyused between hosts on the Internet to exchange rout-ing table inormation.

EMI (electromagnetic intererence): radiation thatcauses unwanted signals (intererence or noise) to beinduced in other circuits; also called radio requencyintererence or RFI.

Emulation: the technique o modiying a device withhardware or sotware to make it operate in the samemanner as another device.

Encapsulation: process that enables message transerover dissimilar networks; used when messages initi-ated by network devices must be transported over anintermediate network using dierent protocols.

Encryption: act o transorming raw data using an

algorithm called a cipher into an unreadable ormatto all except those who possess the key; mathematicalmethod o turning real data into data that is unus-able without the proper math key; modication o abit stream to make it appear random and to controlemissions.

Enterprise Network: connects many types onetworks.

Equipment Room: an environmentally controlledcentralized space or telecommunications equipment

that usually houses a main or intermediate cross-connect.

Error Control: a process that veries that a messageis transerred successully between devices.

Ethernet: most commonly used protocol designed tochange the packets into electrical signals that can besent out over the wire; originally based on a logicalbus structure and carrier sense multiple access withcollision detection.

Exterior Protocol: routing protocol used betweenautonomous systems.

Fabric: an interconnection scheme that enables com-munications between any two connected devices ornetworks through a series o interlinked switches.

Fabric Manager: sotware application that simpliesSAN management and conguration and ensures SANavailability; provides a single location or zone control.

Failover: the automatic transer o control rom aprimary to a backup system as a strategy or aulttolerance.

FAT (le allocation table): table that the operatingsystem uses to locate les on a disk; because a lemay be divided into many sections that are scatteredaround the disk, the FAT keeps track o all the pieces.

Fault Management: the detection, isolation, andcorrection o hardware or sotware conditions thatdisrupt network operations.


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Fault Tolerance: the ability o a system to continueoperations ater the ailure o one or more compo-nents or communications paths.

FDDI (ber distributed data interace): a set o ANSI

protocols or sending digital data over ber opticcable; ault-tolerant token-passing network protocolbased on single or dual optical ber rings.

FDM (requency-division multiplexing): permits arange o input signals to be carried over a communi-cation line that uses separate carrier requencies oreach signal channel; mostly used or analog inorma-tion but can carry digital.

Fibre Channel (FC): high-speed, point-to-point

network protocol utilized to transport data betweenservers and storage or High Perormance Computing(HPC) and to dene a Storage Area Network (SAN);allows concurrent communications among worksta-tions, mainrames, servers, storage drives and otherperipherals, using SCSI and IP protocols.

Fibre Channel Identier (FCID): 24-bit port addressidentication; consists o three parts (domain, area,and port); typically assigned dynamically by the switchduring start-up.

Fibre Channel over Ethernet (FCoE): FCP stack ortransporting SCSI using the Ethernet inrastructure.

Fibre Channel Protocol (FCP): Protocol or transport-ing SCSI commands over Fibre Channel networks.

Fiber Optics: a communications system that usesoptical ber as media.

Field-Programmable Gate Array: hardware devicethat can be congured, using sotware, to perormunctions, including logic gates or combination unc-tions not dened by the original device manuacturer.

File Management System: way to store and retrieveinormation rom disk drives; controls how les can becreated, accessed, retrieved, and deleted.

Filtering: a process device that examines all incoming

trac or specic characteristics (e.g., source address,destination address, protocol, virus) and determineswhether to accept, orward, or discard that tracbased on the established criteria.

Firewall: a sotware or hardware barrier between anetwork and the Internet through which only autho-rized users can pass; set o security policies to screenincoming and outgoing messages; also used to isolateone part o a network rom another.

FireWire: the Apple implementation o IEEE 1394;largely been replaced by USB 2.0.

Fixed Mobile Convergence: a technolgoy that al-lows a single phone device to operate on any network:home, cellular, oce or other.

Floppy Drive: early versions were actually foppy;today, they use hard 3.5-inch disk; also reerred to asremovable drive.

Flooding: the process used by switches/bridges androuters to direct a message to all outgoing ports, withthe exception o the port or interace on which thetrac was received. Flooding is used typically whenthe destination address o the message is not recog-nized or or multicast and broadcast messagedistribution.

FM (requency modulation): blending data into acarrier signal; a modem modulates data by convert-

ing it to audible tones that can be transmitted on atelephone wire, and demodulates received signals toget the data.


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Forwarding: the transerring o a message to anothernetwork by an internetworking device. See alsoltering.

Forwarding Logic: the set o rules used by an inter-

networking device to transer a received message toanother network.

Fragment-Free Switching: a switching technique inwhich messages are orwarded as soon as the re-ceived rame as been determined not to be a collisionragment (i.e., longer than 64 bytes). Also called modi-ed cut-through. See also cut-through and store-and-orward.

Frame: data structure that collectively represents the

transmission stream (headers, data, and the trailer)and provides the data, control, and error-checkinginormation necessary or the correct delivery o thedata.

Frame Check Sequence (FCS): an error-detectingcode normally inserted as the nal eld in a block otransmitted data.

Frame Relay: network protocol designed to transport

messages over extended distances via a mesh net-work, using virtual circuits and switches.

FRAD (rame relay access device): sotware thatrames the customers payload with the Frame Relayoverhead inormation, including the rst DLCI (datalink connection identier) address, to prepare it ordelivery to the network.

Free Path Loss: concept that the arther away a sig-nal moves rom its transmission point, the weaker it is.

Frequency: number o times a wave repeats a cycle ina one-second period; measured in cycles per second,or hertz; requency is inversely proportional to wave-length.

Frequency: the number o cycles that a periodic sig-nal completes in a given time; i the unit o time is onesecond, the requency is stated in hertz (Hz).

FTP (le transer protocol): application used to

transer a copy o a le rom one computer to anothercomputer with one acting as client and the other asserver; a login with a user name and password is typi-cally required.

Full-Duplex Link: enables both sides to simulta-neously send and receive data; could require twoseparate cables, one in each direction or a singlemultiplexed cable.

Full-Duplex Signaling: the transmission o data in

opposite directions simultaneously.

Gateways: a node on a network that translates (con-verts protocol) rom one operating system environ-ment to another.

Gateway Routers: used to implement exterior proto-cols and interconnect autonomous systems.

Gbps (gigabits per second; billions o bits per second):a data transer speed measurement or high-speednetworks.

Geosynchronous Orbit: the satellite is always ina xed position in relation to the ground because itmoves at the same speed at which the earth rotates.

GPS (global positioning system): calculates location byusing a system o satellites that are constantly trans-mitting timing inormation; three satellites calculate

location, and a ourth includes altitude.

Guest Operating System: an operating systemrunning in a virtual machine environment that wouldotherwise run directly on a separate physical system.


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GUI (graphical user interace): allows users to interactwith the computer by manipulating icons instead otyping in commands; pronounced gooey.

Hal-Duplex Signaling: a bidirectional signaling

method in which data transer can take place in eitherdirection, but in only one direction at a time; inor-mation only fows in one direction at a time using acontrol procedure to mediate.

Hando: the process that occurs when a mobile usermoves rom one cell or zone to another cell or zone ina wireless network; accomplished without disruptiono the exiting connection.

Hard Drive: large data storage devices permanently

mounted in the computers case; hermetically sealedunit containing multiple platters that are spun at highRPM (revolutions per minute), a magnetic readinghead is attached to a motor that moves to dierentareas o the platters as needed.

HDD (hard disk drive): a layered system o hard diskscontained in a housing; typically used or separatestorage rom the main computer unit.

Hardware: physical devices located on a desk or in aserver-room rack.

Hardware-Level Virtualization: virtualization ap-proach where the virtualization layer sits on top o thehardware exporting the virtual machine abstraction;the virtual machine looks like the hardware, all thesotware written or it will run in the virtual machine.

HDMI (high-denition multimedia interace): the stan-dard or high quality video transmission; very popular

in the home theater industry and is slowly becoming astandard or video in computers.

Header: the initial part o a message, typically con-taining identication and control inormation.

Hexadecimal: base-16 numbering system that uses0 through 9 to represent values rom 0 through 9 andA through F to represent values 10 through 15; allowyou to represent large numbers in a compact ormat.

Hierarchical Topology: a topology that links devicesor networks using a series o levels, similar to anorganizational chart.

High-Level Language Virtual Machines: the virtual-ization layer sits as an application program on top oan operating system. The layer exports an abstractiono the virtual machine that can run programs writtenand compiled to the particular abstract machine de-nition. Any program written in the high-level languageand compiled or this virtual machine will run in it.

Host: term used to describe any network-attacheddevice that provides application-level services; genericterm used to describe mainrames and minicomputers.

Host-to-Host Layer: part o TCP/IP model that per-orms same unction as transport layer in OSI model.

Host Address: part o an IP address that is uniquelyassigned by an administrator; also known as host

identication or hosted.

Host Bus Adapter (HBA): Connects a server via FiberChannel to a storage drive; improves the servers per-ormance by relieving the data storage and retrievaltasks rom the CPU.

Hosted Virtualization: virtualization approach wherepartitioning and virtualization services run on top oa standard OS (the host); the virtualization sotwarerelies on the host OS to provide the services to talk

directly to the underlying hardware.

HTTP (hypertext transer protocol): protocol usersinteract with (by means o a browser) to access Webpages over an internet or intranet.


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Hub: simple central connectivity device that thatrequires no programming or conguration; receives asignal on any physical port and repeats it out all otherports.

Hybrid Mesh Network/Topology: mesh network/to-pology where redundant connections exist, but unlikea true mesh not all nodes are required to connect toevery other node.

Hypervisor: thin layer o sotware that generally pro-vides virtual partitioning capabilities that runs directlyon hardware, but underneath higher-level virtualiza-tion services; sometimes reerred to as a bare metalapproach.

Hz (hertz): unit o requency; one hertz simply meansone cycle per second, applied to any periodic event(e.g., one tick o a clock is 1 Hz; the human heartbeats at 1.2 Hz).

ICANN (Internet Corporation or Assigned Names andNumbers): non-prot corporation created to overseeInternet-related tasks previously perormed or theU.S. Government by other organizations; tasks includemanaging the assignment o domain names and IPaddresses, and introducing new generic top-level

domains; pronounced I can.

ICMP (Internet control protocol message protocol):network layer protocol provided with TCP/IP; used toreport errors and provide other inormation relevant toIP packet processing.

IEEE (Institute o Electronic and Electrical Engineers):international voluntary organization o engineers thatcreates consensus standards or network wiring and

other technologies; pronounced eye-triple-E.

IGMP (Internet group management protocol): a com-munications protocol used to manage the membershipo IP multicast groups.

IGP (interior gateway protocol): set o routing proto-cols used within an autonomous system.

IGRP (interior gateway routing protocol): developedby Cisco to provide a robust protocol or rerouting

within an autonomous system (AS); a type o IGP.

ILEC (incumbent local exchange carrier): a telephonecompany providing local service when the Telecommu-nications Act o 1996 was enacted (see CLEC).

ILP (initial loader program): reads an existing le con-taining database records; also called a boot-loader.

IMAP (Internet message access protocol): retrieves e-

mail headers without downloading the entire messagerom the server.

Incident Handling: a term used to describe the orga-nizational response to a security-related event.

InniBand (IB): A single abric network that provideshigh-speed data transer and low latency or comput-ing and storage over a single, scalable abric.

Inrared: wireless technology that typically camewith laptops, PDAs, etc. in the 1990s; has been all butreplaced with Bluetooth technologies; lower requencythan what the human eye can see; used over shortdistances and requires line o sight.

Input/Output Management Routines (I/O manage-ment routines) management routines: provide orderlycontrol and fow o inormation between a computersmain memory and attached peripheral devices.

Instant Messaging: text-only, real-time conerencing.

Integrity: in security terms, maintaining the data asit should be, without allowing unauthorized users tomodiy or delete it.


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Interace: point in the system where the rules, controlcodes, ormats, and inormation direction (as dictatedby the protocol) are implemented; procedures, proto-cols, and codes that allow two devices to interact orthe purpose o exchanging inormation.

Intererence: the undesirable signals on a device,equipment, or system. See also electromagnetic inter-erence.

Interior Protocols: routing protocol used within/inte-rior to an independent/ autonomous system.

Internet Layer: part o the TCP/IP model that per-orms the same unction as the network layer o theOSI model.

iSCSI (Internet SCSI): Allows hosts to negotiate andexchange commands at high-speed over a network,utilizing existing switching and network inrastructure.

Internetwork: the communications system connect-ing two or more networks.

Internetworking: connecting one network to anothernetwork.

Interprocess Communication: allows programs toshare inormation dynamically, whether running lo-cally or remotely.

Intrusion Detection: the process o detecting andtracking actual or attempted unauthorized access to anetwork or a protected device.

I/O Devices (input/output devices): hardware used toenter and retrieve data rom the system.

I/O Memory Management Unit: MMU that connectsa DMA-capable IO bus to the main memory; It mapsdevice-visible virtual addresses to physical addresses.

IP (internet protocol): network layer protocol providedwith TCP/IP; connectionless, unreliable protocol thatprovides eatures or addressing, type or service speci-cation, ragmentation and reassembly, and security.

IP Address: logical address assigned to every work-station, server, printer, and router on any intercon-nected network; 4-byte, binary number.

IPsec (Internet Protocol Security): security protocolused or data encryption when communicating over anIP-based network.

IPTV: a technology that will allow you to get televi-sion transmissions as data, not signals.

IPX/SPX (internetwork packet exchange/sequencedpacket exchange): a networking protocol used by theNovell NetWare operating systems; it is a datagramprotocol used or connectionless communications.

IRC (Internet relay chat): allows groups to communi-cate interactively via keyboard and screen display.

ISDN (integrated services digital network): a circuit-switched telephone network system designed to allowdigital transmission o voice and data over ordinarycopper telephone wires; digital communications acil-ity designed to provide transparent end-to-end trans-mission o voice, data, audio/video, and still imagesacross the public switched telephone network.

ISDN PRI: switched-line service rom telephone com-panies that operates over T1 (or E1/J1) acilities.

IS-IS (intermediate system-to-intermediate system):

an interior gateway protocol (IGP) intended or usewithin an administrative domain or network.


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Isochronous Signaling: a signaling method where aset data transer rate within a communications chan-nel is guaranteed. Timing or synchronizing inormationis derived rom the signal carrying the data.

ISP (Internet service provider): business or organiza-tion that provide consumers with access to the Inter-net and related services.

IT (inormation technology): broad term that can reerto anything rom mainrames to PDAs; any technologythat moves inormation (voice, video, or data).

ITU-T (ITU Telecommunication Standardization Sector):coordinates standards or telecommunications on be-hal o International Telecommunication Union (ITU).

IXC (interexchange carrier): a telephone company thatprovides connections between local exchanges in di-erent geographic areas.

Jitter: distortion in a digital signal caused by a shit intiming pulses; can cause data interpretation errors.

JPEG (joint photographics experts group): a compres-sion technique or color images; pronounced jay-peg.

Jumper: series o pins protruding rom a circuit boardonto which a contact block is placed; used to selectvarious circuit options.

Kbps (thousands o bits per second): a measure odata transer speed.

KHz (kilohertz): a unit o measurement o requency,also known as cycles per second (e.g., one kilohertzequals 1,000 Hz, or cycles per second).

LAN (local area network): network that operateswithin a small geographic area, usually within a build-ing, oce, or department.

LAPB (link access protocol, balanced): a data linkprotocol in the X.25 stack.

Last Mile: the nal step in providing Internet accessto the customer; the connection between the ISP and

the customers home or oce network.

LATA (local access and transport area): In the US,reers to a geographic region assigned to one or moretelephone companies or providing communicationservices.

Latency: the time it takes or a signal to pass througha device or network (e.g., the delay between the timea switch receives a message on an input port andorwards it to an output port).

Layer 2 Switches: interpret and make switching deci-sions on the LAN hardware adapter address containedin the data link header o MAC rames; orward ramesonly to the destination hardware address contained inthe rame.

LCI (logical channel identier): used to dene requen-cies in use on M/A-COM EDACS (Enhanced DigitalAccess Communications System) systems and LTR

(logic trunked radio) systems; more commonly knownas logical channel number (see LCN); also known asvirtual channel.

LCN (logical channel number): used to dene requen-cies in use on M/A-COM EDACS (Enhanced DigitalAccess Communications System) systems and LTR(logic trunked radio) systems; also known as the logi-cal channel identier (see LCI); also known as virtualchannel.

LE (local exchange): a regulatory term in telecommu-nications or local telephone company.

Leased Lines: another name or private lines, dedi-cated lines, or permanent circuits.


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LEC (local exchange carrier): a public telephone com-pany in the US that provides local service.

LED (light-emitting diode): a light source used orsignal transmission over optical ber cabling.

Legacy: reers to hardware or sotware that is con-sidered to be out-o-date or has been surpassed bynewer and presumably better devices or applications.

LGN (logical channel group number): together withthe LCN (in the X.25 packet header), identies theactual logical channel number o the DTE-DCE link; a4-bit eld representing a number between 0 and 15.

Line Layer: layer o the OSI physical layer that is re-sponsible or synchronizing and multiplexing multiplestreams o data into one SONET stream within SONETrames; also monitors and administers SONET multi-plexers.

Link Aggregation: a mechanism that combines mul-tiple network communication channels into a singlelarge channel to allow or increased data transerrates.

Linux: operating system developed with the vision oan open-source operating system ree rom licensingor cost.

LLC (logical link control): standard interace allow-ing any combination o MAC techniques and physicalmedia to be used simultaneously in the same worksta-tions; shields higher layer protocols rom the peculiari-ties o the physical medium.

Load Balancing: mechanism or distributing incomingrequests among a collection o devices or circuits toreduce response times; technology that complementsserver clustering.

Logical Addresses: addresses used by the networklayer.

Logical Segmentation Devices: allow networkdesigners to maintain separate networks (oten or

security reasons) that can still communicate with oneanother.

Logical Topology: the path data will take to reach itsdestination; actual method (ring, bus, star) by whichdierent nodes in a network communicate with oneanother as compared with the physical connections.

Lossy: data compression method where compressingand then decompressing retrieves data that may wellbe dierent rom the original, but is close enough to

be useul in some way.

Low Pin Count Bus: Used to connect low-bandwidthdevices to the CPU in workstations; requires ewerpins than the equivalent ISA bus to route on themotherboard.

LU (logical unit): identies an end-user in IBMs Sys-tems Network Architecture (SNA).

LUN (Logical Unit Number) : used to identiy SCSIdevices connected to a workstation; each device is as-signed a LUN rom 0 to 7, which serves as the devicesunique address.

MAC (medium access control): set o protocols thatenables a device to access a network.

MACAddress (media access control): unique 6-byteaddress associated with and coded into each network

interace card (NIC); consists o the OUI (organization-ally unique identier) and the manuacturer ID.

MAN (metropolitan area network): connects sites inand around a large city.


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Managed Hub: network hub that can be monitoredand controlled through network management sotware.

MAU (medium attachment unit): converts signals onan Ethernet cable to and rom AUI signals.

MAU (multistation access unit): centralized connectiv-ity device, the key to the Token Ring network.

MB (megabyte): unit o inormation or computerstorage equal to either exactly one million bytes or, insome cases, 1,048,567 bytes, or more rarely, 1,024,000bytes; not to be conused with Mb, which stands ormegabits.

Mbps (megabits per second): a unit o inormationstorage; not to be conused with MB or megabytes.

Medium: transmission, or system that carries the mes-sage or data.

Memory: desk space o the computer system; micro-chips located on the motherboard that hold data andinstructions or the CPU (central processing unit).

Memory Management: allocates memory to sepa-rate tasks and protects data rom corruption.

Memory Virtualization: removes volatile random ac-cess memory (RAM) resources rom individual systems,and aggregates those resources into a virtualizedmemory pool available to any computer in the cluster.

Menu: used in some DOS shells and early versions oWindows; an improvement on the command line butcumbersome when a task requires the submenu o asubmenu o a submenu o a menu item.

Mesh Network/Topology: topology where all nodesare connected to every other node in the network;extremely rare because o the high cost involved.

Message: inormation content to be shared.

MHz (megahertz): one hertz is one cycle per second; amegahertz is equal to one million cycles per second.

MIB (management inormation base): a type o data-base used to manage the devices in a communicationsnetwork.

Microwave: any requency between 300 MHz and300 GHz.

Mirroring: a technique used to increase the aulttolerance o a system. A backup device is conguredidentically to the primary device and can replace the

primary device i it ails.

MMU (memory management unit): Responsible orhandling accesses to memory requested by the CPU;protects memory and reduces ragmentation.

Modem: a hardware device used by remote stationsor network access over public switched telephonenetwork telecommunications circuits; also calleddial-up lines; acronym or modulator/demodulator.Modems convert between digital signals and analogsignals.

Modied Cut-Through: a switching method in whichmessages are orwarded as they are received, withminimal error checking.

Modulation: the way binary bits are representedover a wave orm; can be simple (less corruption) orcomplex (more data).

Motherboard: a computer component that hasinternal and external communication ports to acilitatecommunication between internal devices.


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MPEG (motion picture experts group): digital videoormat identied by .mpg extension ater the lename; a working group o ISO/IEC charged with thedevelopment o video and audio encoding standards;pronounced m-peg.

MPLS (multiprotocol label switching): an initiativethat integrates Layer 2 inormation about networklinks (bandwidth, latency, utilization) into Layer 3 (IP)within a particular autonomous system to simpliy andimprove IP packet exchange.

Mpps (millions o packets per second): a measure-ment o inormation sent per second.

Multicast: a technique or sending content to a

selected group o devices on a network using a singlepoint o transmission.

Multimode Fiber: optical ber capable o highthroughput in shorter distance applications; primarilyused in buildings and between buildings in a campusenvironment.

Multiple Access: CSMA principle that multiple peopleor devices access a shared medium, but only one can

talk at a time.

Multiplexing: process o putting multiple signals on awire simultaneously; combining two or more com-munications channels into a common, high-capacitychannel rom which the original signals may be indi-vidually recovered.

Multiport Repeaters: allow multiple devices to bewired to a central location, share the same media,and regenerate (repeat) the signal; also reerred to as

active hubs.

Multitasking Routines: permit two or more distincttasks to be perormed concurrently by the computer.

Name Resolution: process by which the peer-to-peername used on each conversational level is related toother levels.

NAP (network access point): transitional data commu-

nications acilities at which Network Service Providers(NSPs) would exchange trac, in replacement o thepublicly-nanced NSFNet Internet backbone; nowreplaced by modern IXPs.

NAS (network-attached storage): storage systemconsidered to be on the ront end o the network;can be accessed by client devices or servers andapplications; bridges the connection between whatthe end user sees and the back-end storage services;orm o data storage where shared data is placed on

a high-capacity storage device with a built-in networkinterace card.

NAT (network address translator): involves re-writingthe source and/or destination addresses o IP packetsas they pass through a router or rewall; also callednetwork masquerading, native address translation, orIP-masquerading.

NetBIOS (network basic input/output system): allowsapplications on separate computers to communicate

over a local area network (LAN).

Network Access Device: equipment used to in-terconnect stations, servers, and shared peripheralsdevices on a local area network or internetwork.

Network Access Layer: allows a computer to ex-change data with another computer over a commonnetwork medium; part o the TCP/IP model that per-orms the same unctions as the data link and physical

layers o the OSI model.

Network Address: part o an IP address that isuniquely assigned by one o the ICANN-sanctionedagencies.


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Network Design: how the various clients and serversare arranged or purposes o connectivity, peror-mance, and security.

Network Diameter: the distance between the two

data terminal equipment devices arthest apart in thesame collision domain; also called a collision diameter.

Network Layer: where the packet is appended withan address that will help the packet get to its naldestination; also called Layer 3.

Network Resource: any device, le, or applicationthat is to be accessed rom another device.

NTP (network time protocol): synchronizes IP-baseddevices with master clocks.

Network Topology: the connection setup o a groupo computers, categorized as physical or logical.

NIC (network interace card): hardware adapter thatprovides communication capabilities; responsible orbuilding, transmitting, receiving, and decoding ramesin a LAN environment; serves as the interace betweenthe networked devices and the connecting wires.

Nonblocking: the ability o a device or network tosuccessully provide a communications path betweenall available devices.

Nonrepudiation Services: the network securityprocesses that provide proo that a message was sentrom a specic source, thereby preventing that sourcerom denying having sent the message.

NOS (network operating system): integrated collec-tion o sotware designed to optimize the client/serverarchitecture; provides and supports network servicessuch as le services, e-mail, Internet and intranetservices, and applications.

NNTP (network news transer protocol): makesUSENET possible; protocol or the distribution, inquiry,retrieval, and posting o news articles using a reliablestream-based transmission o news among the ARPA-Internet community.

Nonvolatile Memory: chips that hold inormationeven when the system is turned o.

Node: network device that can transmit and receiveinormation.

NRZ-L (non-return to zero level): orm o digital en-coding; negative voltage is used to represent binary 1,and a positive voltage is used to represent binary 0.

NSP (network service provider): a business or orga-nization that sells bandwidth or network access byproviding direct backbone access to the Internet, andusually access to its network access points (see NAP).

Null Modem: cable that interchanges wire positions,so that a DTE device looks like a DCE or vice versa.

OC1 (optical carrier, level 1): a ber optic connectioncapable o transerring data at 51.85 Mbps.

Octet: a data unit o eight bits; also called a byte.

OLE (object linking and embedding) - enhancementto DDE process that allows you to link data created inone application to a document created in another ap-plication; allows editing o data in the original applica-tion without leaving the compound document.

Omni-Directional Antenna: antenna that covers arelatively small area and radiates signals in all direc-tions equally, creating a coverage pattern shapedlike a doughnut; Its area is wider than it is high andis good or small indoor environments; also called adipole antenna.


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OOB (out o band): data transmitted with the primarydata stream that is considered a control signal andwhich demands immediate attention; receiving sidemust pass the out-o-band data to the appropriatesotware routine in ront o any other data that hasbeen buered and not yet processed, because the

command must be executed as soon as possible.

Open Source: sotware code that is ree or anyone toview, modiy, or copy.

Operating Environment: how the OS controls thehardware and application programs.

Operating System (OS): sotware interace betweenthe application (word processor, spreadsheet, etc.) and

the computer hardware; controls the execution o allprograms and the utilization o resources on a devicesuch as a personal computer.

Operating System-Level Virtualization: virtual-ization approach where the virtualization layer sitsbetween the operating system and the applicationprograms that run on the operating system. The virtualmachine runs applications, or sets o applications, thatare written or the particular operating system beingvirtualized.

Optical Fiber: clear glass or plastic strands that allowlight to move rom one end to another; aster alterna-tive to copper wiring.

Optoelectronics: the components or circuitry used toperorm the necessary conversions between light-based signaling and electricity-based signaling.

OSI Model (open systems interconnection): seven-

layer architecture developed to provide a view o thedistinct unctionalities that are required to implementeach protocol layer; denes a complete range o unc-tions that can be achieved with data communicationsequipment.

OSPF (open shortest path rst): a link-state hierarchi-cal interior gateway protocol (see IGP) or networkrouting protocol.

OUI (organizationally unique identier): unique

number ound in MAC addresses assigned to a cardmanuacturer by the IEEE.

Packet: data structure that collectively representsthe transmission stream (headers and data); associ-ated with the network layer when the communicationprotocol is connection-oriented.

Packet Filter: rewall that looks at each packet anduses an access control list to determine i it should bediscarded (ltered) or allowed to pass through.

Packet-Switched Network: WAN that sends the datapackets over any available path; packets are assem-bled into the original message at the end device basedon their numbers.

Packet Switching: a data communications switch-ing and transmission system in which an input datastream is broken into packets that are transerredbetween devices on dierent networks without rst

establishing a dedicated communications path be-tween the devices.

PAD (packet assembler/disassembler): device that as-sembles X25 packets on the sending end or transmis-sion over the X25 PSDN, or disassembles X25 packetson the receiving end or onward transmission to thelocal network.

PAN (personal area network): network that includesdevices that are close to the person (within a ew

meters range); can be wired or wireless and connectto each other or to a WAN; devices include PDAs (per-sonal digital assistants) and phones.


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Parabolic Dish Antenna: most common example arethose used or satellite TV service; generates a verynarrow radiation pattern; used to connect two physi-cally distant up to 25 miles networks together.

Parallel Communication: reers to sending multiplebits at one time parallel with each other.

Parallel Port: port where the bits travel down parallelpaths, arriving one byte at a time; can supply morebytes o data per unit time.

Passive Hubs: used in a LAN environment; specialorm o repeater that allow multiple devices to bewired into a central location and share the samemedia; do not regenerate (repeat) the signal; hub that

does not require electrical power to operate.

Para-Virtualization : virtualization approach that ex-ports a modied hardware abstraction, which requiresoperating systems to be explicitly modied and portedto run.

Parity: an error-dectecting scheme which uses anextra checking bit, called the parity bit, to allow thereceiver to determine whether there has been an error

in the received data bits.

Partition: electronic division o a hard disk that mustbe created beore the disk can be ormatted.

Partitioning: ability to run multiple operating systemson a single physical system and share the underlyinghardware resources.

Path Layer: layer o the OSI physical layer that is

responsible or reliable end-to-end transport andpayload delivery, including automatic recovery romailure points.

PBX (private branch exchange): a telephone exchangethat serves a particular business or oce.

PC (personal computer): a microcomputer whose price,size, and capabilities make it useul or individuals.

PCI (peripheral component interconnect): a computerbus or attaching peripheral devices to a computermotherboard.

PCIe (Peripheral Component Interace express): anindustry standard bus, consisting o a transactionlayer, a data link layer, and a physical layer; or attach-ing peripheral IO devices to a CPU, structured aroundpoint-to-point serial links.

PCM (pulse code modulation): process or convertingrom analog to digital.

PDA (personal digital assistant): hand-held computerwith a touch screen.

PDU (protocol data unit): inormation that is deliveredas a unit among peer entities o a network; in layeredsystems, a unit o data that is specied in a protocol oa given layer.

Peripheral Device: any hardware that is added to thecomputer to serve extra purposes.

Peer-to-Peer Network: network in which eachcomputer is capable o unctioning as a client and aserver; users on the network can reely share resourceson their computer or access shared resources on othercomputers.

Phase: where in the wave cycle the wave currently is;measured in degrees; a comparison o one signal toanother.


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Photonic Layer: layer o the OSI physical layer thatspecies ber cable with optical light sources andreceivers.

Physical Layer: creates the physical link between

two devices (see OSI Model); reerred to as the PHY,pronounced e; also called Layer 1.

Physical Medium Attachment (PMA): in Ethernet,the part o the Physical layer that controls transmis-sion, reception, collision detection, clock detection,and skew alignment.

Physical Segmentation Device: divides collisiondomains to improve network perormance.

Physical Topology: the physical connections betweenthe nodes on a network; or example the wiring andconnection devices used in the network.

Piconet: a single Bluetooth wireless personal areanetwork that can contain a maximum o eight activedevices, one o which is the master.

Ping: sonar concept implemented with the EchoRequest and Echo Reply application; basic connectivitytest between two TCP/IP network devices.

Point-to-Point Topology: two nodes are connectedby one single physical connection; the simplest o alltopologies.

Point-to-Multipoint Topology: nodes are connectedrom one point to several other points.

POP (points o presence): an articial demarcationpoint or interace point between communicationsentities.

POP (post oce protocol): how clients access theirmailboxes on the messaging server; set o rules orretrieving e-mail rom the e-mail server o your ISP(Internet service provider); usually done in its thirdversion, POP3.

Port: a physical connection point on a network accessdevice (e.g., a hub or switch).

Port Mirroring: the process o copying the datapassing through one or more ports o a switch to anetwork management port or monitoring purposes.

Port Number: tells the computer what type o data isbeing received; each type o data trac is assigned astandardized port number; examples are port 80: HTTP

(Web sites), port 110: POP3 (receiving e-mail).

POST (power-on sel-test): the pre-boot sequence ora computer, router, or printer.

POTS (plain old telephone service): standard tele-phone service, the basic orm o residential and smallbusiness telephone service.

Presentation Layer: responsible or presenting inor-mation to the application layer in the manner that it isexpecting (see OSI Model); also known as Layer 6.

Prioritization: a unction perormed by a networkinterace card (NIC) that makes it possible to assigndierent levels o priority to the requests made by ap-plications using the NIC.

Private Key Encryption: a security process in whichinormation is encrypted with a key that both the

sender o the inormation and the receiver possess.The parties involved are expected to agree on a keyin a way that does not compromise the establishedsecurity processes.


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PRI (primary rate interace): an integrated servicesdigital network (ISDN) conguration that consists otwenty-three 64 kb/s B channels and one 64 kb/s Dchannel using a T-1 line or thirty 64 kb/s B channelsand one 64 kb/s D channel using an E-1 channel, usu-ally intended or large users (see also BRI).

Process and Application Layer: part o the TCP/IPmodel that perorms the same unctions as the ap-plication, presentation, and session layers o the OSImodel.

Processor: brain o the computer system wherecalculations and decisions are made; also reerred toas the CPU.

Processor Memory: reerred to as the L1 (level 1), aninterace between the processor and the cache.

Propagation Delay: the time required or a signal totravel rom one end o the transmission path to theother end.

Proprietary Protocols: developed by vendors to al-low communication between their own products.

Protocol: set o rules used to control the exchange oinormation that is understood by the transmitter andreceivers.

Protocol Analyzer: troubleshooting tool that displaysthe actual protocol down to the binary level; userequires a specialized skill set; can be used on bothwired and wireless networks.

Protocol Stack: a comprehensive set o specications

that dene how network hardware and sotware in-teract at various levels to transer messages betweendevices on a network.

Proxy Server: rewall security mechanism that sitsbetween the network router and the Internet; talks tothe Internet on behal o a networks resources, allow-ing real network addresses to be hidden.

PS/2: most reerenced by its use as a mouse and key-board connector; widely replaced by USB.

PSDN (packet-switched data network): a publiclyavailable network supporting packet-switched data,separate rom PSTN.

PSTN (public switched telephone network): thenetwork o the worlds public circuit-switched tele-phone networks; in much the same way the Internetis the network o the worlds public IP-based packet-

switched networks.

Public Key Encryption: a security technique in whicha user is assigned two related keys, one held privatelyand the other distributed publicly. Anyone wishingto send a condential message to the user encryptsit with the users public key. When the message isreceived, the user decrypts it with the correspondingprivate key.

PU (physical unit): a value or magnitude convention-ally adopted as a unit or standard o physical mea-surements (e.g., length, mass, and time); identies anetwork node that supports communication sessionsbetween logical units (LU) which represent end usersin IBMs SNA.

Punch Card: one o the rst ways to store data ora computer; physical piece o cardstock with holespunched in to signiy bits or characters.

Pure Play: newly developed business built on advan-tages aorded by e-commerce.


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PVC (permanent virtual circuit): sotware-dened logi-cal connection in a switched network in which usersdene logical connections and required bandwidthsbetween end points while the switched network tech-nology achieves the dened connections and managesthe trac; uses a real, shared circuit in the service

providers backbone.

QoS (quality o service): the capability o a network toprovide better service to selected network trac overvarious technologies; commitment to perormance,based on predened service parameters; measure othe level o service provided on a network.

QWERTY Keyboard: a keyboard with the charactersQ, W, E, R, T, and Y on top row o alpha keys.

RADIUS (remote authentication dial-in user service):an authentication, authorization, and accounting ser-vice used to veriy identities prior to granting access tonetwork resources.

RAID (redundant array o independent disks): arrayo hard drives that act as one single hard drive; canbe sotware or hardware; classied into levels thateach provide a dierent balance o perormance andreliability.

RAM (random access memory): ast, temporary datastorage; chips capable o storing and later dumpingdata in preparation or other uses.

RARP (reverse address resolution protocol): protocolused to resolve an IP address rom a given hardwareaddress (e.g., an Ethernet address).

RAS (remote access service): allows users to access

the network through dial-up modem connections.

Reboot: the process o shutting down and restart-ing a device or group o devices on the network aterconguration changes.

Receiver: destination o the message or data.

Recovery Routine: enables a computer to resume op-eration ater encountering a problem, such as a poweroutage or program error.

Refection: type o signal intererence that happenswhen radio waves bounce o o something and travelin a dierent direction.

Remote Login: allows a user at one computer tointeract with another, as i the users computer isdirectly attached to the remote computer.

Removable Storage: a way to store inormation

on disks that can be removed and used on dierentsystems; most removable drives (also known as foppydrives) use a hard 3.5-inch disk.

Repeater: device that regenerates and reshapes digi-tal pulses and allows a signal to be transmitted urtherthan a single circuit can achieve.

RFID (remote requency identication): a method oidentiying objects, people, pets, and consumer goodswith radio requency.

RIP (routing inormation protocol): used by routersconnecting LANs to exchange routing table inorma-tion to determine the best path through the networkat any point in time.

Ring Topology: physical or logical network topologyin which nodes are connected along a single wire withno endpoints; similar to a network except with the lasttwo devices connected to each other.

Roaming: act o using a mobile or wireless deviceoutside a specied geographic area dened by theservice provider.


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ROM (read-only memory): chips that store data thatneeds to be maintained constantly.

Router: basic piece o network hardware necessaryto connect one network to another; makes decisions

about packet orwarding based on IP address inor-mation in the packet; directs trac between networksegments.

Router Table: a database containing inormation onthe routes a datagram can take.

RTMP (routing table maintenance protocol): a com-munication protocol used by AppleTalk to ensure thatall routers on the network have consistent routinginormation.

SAN (storage area network): specialized high-speednetwork o multiple hard drives that are directly orvirtually connected to servers.

SAP (service access point): represent internal sotwareaddresses in the sending or receiving computer.

SAR (segmentation and reassembly): the process usedto ragment and rebuild packets that allow them to betransported across asynchronous transer mode (ATM).

SATA (serial advanced technology attachment): onetype o internal connections to a DAS; serial connecteddisc drive interace used to control and transer dataand inormation rom a server or storage drive; SATAis less complex bus than SCSI but has a lower datatranser rate.

Satellite Phones: more reliable phone system used

when a clear view o the sky, rather than an Earth-based tower, is needed.

Scalability: the ability o a network to grow withoutdegradation o perormance

Scale-Out: Server architecture in which more serversare added to a group o servers sharing a workload,or example in a web server arm or through a cluster.

Scale-Up: Server architecture in which more comput-

ing power is added within a server to handle moreworkload.

Scattering: type o signal intererence that happenswhen a signal impacts objects that have many refec-tive or jagged edges.

Scripting: The process o determining which congu-ration tasks can be perormed unattended and thenautomating the process.

SCSI (small computer system interace): set o ANSIstandard electronic interaces that allows computersto communicate with peripheral hardware (e.g., diskdrives, tape drives, CD-ROM drives, printers, scanners);parallel connected disc drive interace or connectingworkstations and servers with peripheral devices suchas storage drives; It operates at higher transer ratesthan achievable with SATA.

SDH (synchronous digital hierarchy): international

counterpart o SONET.

SDRAM (synchronous dynamic random access memo-ry): version o DRAM that allows or increased speed.

SEAL (simple and ecient AAL): method o relayingATM (asynchronous transer mode) cells between ATMLayer and a higher layer.

Section Layer: layer o the OSI physical layer that

creates rames, monitors the conditions o the trans-mission between the SONET equipment, and convertsoptical signals to and rom electrical signals.


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Security Management: the protection o all networkresources, including physical devices, operating sys-tems, applications sotware, organizational data, andnetwork operations.

Security Plan: set o principles, rules, and practicesused to implement security in an organization.

Security Routines: protect data and applicationsrom unauthorized use, execution, or change.

Segment: an electrically continuous network createdwithin a hub; single collision domain on a networkconsisting o multiple collision domains.

Segmentation: the process o dividing a large colli-sion domain into multiple smaller collision domains toimprove overall network perormance.

Semaphores: messages sent when a le is openedthat prevent other users rom opening the same le atthe same time and compromising the integrity o thedata.

Serial-Attached SCSI: a serial-connected SCSI thatallows or higher data transer rates compared tostandard SCSI.

Serial Communication: inormation that is passedthrough a medium one bit at a time, in sequence.

Serial Port: handles data one bit at a time travelingsequentially across a single line rom one device to thenext.

Server: a network device that combines hardware andsotware to provide and manage shared services andresources on the network to the other workstations.

Server Farm: alternate name or a data center.

Session Layer: allows applications unctioning ondevices to establish, manage, and terminate a dialog(or session) through a network (see OSI Model); alsoknown as Layer 3.

glossaries of it terms

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