final.txt

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final.txt
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2012-12-02 18:12:00
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CompTIA Network
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Just the Glossary from one of the books;)
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  1. 10Base2
    An IEEE 802.3 specificationfor Ethernet at 10Mbps overthin coaxial cable. The maximumlength of a 10Base2 segment is 185meters (607 feet). 10Base2 operatesat 10Mbps and uses a basebandtransmission method.
  2. 10Base5
    The IEEE 802.3 specificationfor 10Mbps Ethernet usingthick coaxial cable. The maximumlength of a 10Base5 segment is 500meters (1,640 feet).
  3. 10BaseFL
    The IEEE 802.3 specificationfor running Ethernet at10Mbps over fiber-optic cable. Themaximum length of a 10BaseFLsegment is 2,000 meters.
  4. 10BaseT
    The IEEE 802.3i specificationfor running Ethernet at10Mbps over twisted-pair cabling.The maximum length of a 10BaseTsegment is 100 meters (328 feet).
  5. 10GbaseER
    A 10Gbps Ethernetnetworking standard that can beused up to 40,000 meters.
  6. 10GbaseEW
    Both the ER and EWGigabit standards deploy with extralong-wavelength single-mode fiber.This medium provides transmissiondistances ranging from 2 meters to40 kilometers. 10GbaseER deploysover dark fiber, but the EW standardis used primarily with SONETequipment.
  7. 10GbaseLR
    A 10Gbps Ethernetnetworking standard that can beused up to 10,000 meters.10GbaseLR uses single-mode fiberopticcabling.
  8. 10GbaseLW
    The 10GbaseLWEthernet standard is over singlemodefiber. Both the LR and LWstandards are designed to be usedover long-wavelength single-modefiber, giving it a potential transmissionrange of anywhere from 2meters to 10 kilometers. The LWstandard is designed to connect toSONET equipment.
  9. 10GbaseSR
    A 10Gbps Ethernetnetworking standard that can beused over relatively short distances,up to 300 meters.
  10. 10GbaseSW
    Both SR and SW aredesigned for deployment over shortwavelengthmultimode fiber. Thedistance range for both classificationsranges from as little as 2meters to 300 meters. The differencebetween the two classificationsis that SR is designed for use overdark fiber. The 10GbaseSW standardis designed for longer-distancedata communications and connectsto SONET equipment.
  11. 10GbE
    A term commonly used torefer to the 10Gbps Ethernet networkingstandards such as10GbaseER, 10GbaseLR, and10GbaseSR. 10 Gigabit Ethernet isdefined in the IEEE 802.3ae standard.
  12. 100BaseFX
    The IEEE 802.3 specificationfor running Fast Ethernetat 100Mbps over fiber-optic cable.The maximum length of a100BaseFX segment is 2,000 meters(6,561 feet) in full-duplex mode.
  13. 100BaseT
    The IEEE 802.3 specificationfor running Ethernet at100Mbps over twisted-pair cabling.The maximum length of a100BaseT segment is 100 meters(328 feet).
  14. 100BaseTX
    An IEEE 802.3u specification,also known as FastEthernet, for running Ethernet at100Mbps over STP or UTP. Themaximum length of a 100BaseTXsegment is 100 meters (328 feet).
  15. 1000BaseT
    An IEEE 802.3abstandard that specifies GigabitEthernet over Category 5 UTPcable. The standard allows for fullduplextransmission using four pairsof twisted cable.
  16. 568A/568B standards
    Telecommunications standards fromthe Telecommunications IndustryAssociation (TIA) and theElectronics Industry Association(EIA). These 568 standards specifythe pin arrangements for the RJ-45connectors on UTP or STP cables.The number 568 refers to the orderin which the wires within the UTPcable are terminated and attached tothe connector.
  17. AAA
    Authentication, authorization,and accounting. Authenticationis the process to determine if someoneis authorized to use the network�if he can log on to the network.Authorization refers to identifyingthe resources a user can accessafter he is authenticated. Accountingrefers to the tracking methods usedto identify who uses the networkand what they do on the network.
  18. access point
    A transmitter andreceiver (transceiver) device commonlyused to facilitate communicationbetween a wireless client and awired network. Wireless APs areused with the wireless infrastructurenetwork topology to provide a connectionpoint between WLANs anda wired Ethernet LAN.
  19. ACK
    The acknowledgment messagesent between two hosts duringa TCP session.
  20. ACL (access control list)
    The listof trustees assigned to a file ordirectory. A trustee can be anyobject available to the security subsystem.The term ACL is also usedwith routers and firewall systems torefer to the list of permitted computersor users.
  21. Active Directory
    Used in Windowsnetwork environments, this is adirectory services system thatenables network objects to be storedin a database. This database canthen be divided and distributedamong different servers on the network.
  22. active hub
    A hub that has powersupplied to it for the purposes ofregenerating the signals that passthrough it.
  23. ad hoc topology
    Defines a wirelessnetwork layout whereby devicescommunicate directly betweenthemselves without using an accesspoint. Sometimes called an unmanagedor peer-to-peer wirelesstopology.
  24. address
    A set of numbers used toidentify and locate a resource ordevice on a network. An example isan IP address such as 192.168.2.1.
  25. administrator
    A person responsiblefor the control and security ofthe user accounts, resources, anddata on a network.
  26. Administrator account
    On aWindows system, the defaultaccount that has rights to accesseverything and to assign rights toother users on the network. Unlikeother user accounts, theAdministrator account cannot bedeleted.
  27. ADSL (Asymmetric DigitalSubscriber Line)
    A service thattransmits digital voice and data overexisting (analog) phone lines.
  28. AES (Advanced EncryptionStandard)
    An encryption algorithmfor securing sensitive networksused by U.S. Governmentagencies. Has become the encryptionstandard for corporate networks.
  29. AH (Authentication Header)
    Oneof the two separate protocols IPSecconsists of (the other being ESP).AH provides the authentication andintegrity checking for data packets.
  30. AM (Amplitude Modulation)
    Oneof the earliest forms of radio modulation,this is a technique used incommunication to transmit informationover a radio wave.
  31. ANSI (American National StandardsInstitute)
    An organization thatpublishes standards for communications,programming languages, andnetworking.
  32. antivirus software
    A softwareapplication that detects and removesvirus programs.
  33. AP (wireless access point)
    A networkdevice that offers connectivitybetween wireless clients and (usually)a wired portion of the network.
  34. APIPA (Automatic Private IPAddressing)
    A technology implementedon certain Windows platformsthrough which a systemassigns itself an IP address in theabsence of a DHCP server.Addresses are assigned from the169.254.x.x address range.
  35. application layer
    Layer 7 of theOSI model, which provides supportfor end users and for applicationprograms using network resources.
  36. application-level firewall
    Application-layer firewalls operateat the application layer of the OSImodel. Application layer firewallscan inspect data packets traveling toor from an application.
  37. application log
    A log file on aWindows system that providesinformation on events that occurwithin an application.
  38. archive bit
    A flag that is set on afile after it has been created oraltered. Some backup methods resetthe flag to indicate that it has beenbacked up.
  39. ARIN (American Registry forInternet Numbers)
    The regionalInternet registry responsible formanaging both IPv4 and IPv6 IPnumber distribution.
  40. ARP (Address Resolution Protocol)
    A protocol in the TCP/IP suite usedto resolve IP addresses to MACaddresses. Specifically, the ARPcommand returns a Layer 2 addressfor a Layer 3 address.
  41. ARP ping
    The ARP utility thatresolves IP addresses to MACaddresses. The ARP ping utilitytests connectivity by pinging a MACaddress directly.
  42. ARP table
    A table of entries usedby ARP to store resolved ARPrequests. Entries can also be manuallystored.
  43. array
    A group of devices arrangedin a fault-tolerant configuration. Seealso RAID.
  44. ASP (Application Service Provider)
    A vendor who provides computerbasedservices over the network.
  45. attenuation
    The loss of signalexperienced as data transmits overdistance and across the networkmedium.
  46. ATM (Asynchronous Transfer Mode)
    A packet-switching technology thatprovides transfer speeds rangingfrom 1.544Mbps to 622Mbps.
  47. authentication
    The process bywhich a user�s identity is validatedon a network. The most commonauthentication method is a usernameand password combination.
  48. B (bearer) channel
    In ISDN, a64Kbps channel that carries data.See also D (delta) channel.
  49. backbone
    A network segment thatacts as a trunk between other networksegments. Backbones typicallyare high-bandwidth implementationssuch as fiber-optic cable.
  50. backup schedule
    A document orplan that defines what type of backupsare made, when, and what datais backed up.
  51. bandwidth
    The width of the rangeof electrical frequencies, or howmany channels the medium can support.Bandwidth correlates to theamount of data that can traverse themedium at one time, but other factorsdetermine the maximum speedsupported by a cable .
  52. baseband
    A term applied to anymedium that can carry only a singledata signal at a time. Compare withbroadband.
  53. baseline
    A measurement of performanceof a device or system forthe purposes of future comparison.Baselining is a common serveradministration task.
  54. baud rate
    The speed or rate ofsignal transfer. Baud rate bandwidthis measured in cycles per second, orHertz (Hz). The word baud isderived from the name of Frenchtelegraphy expert J. M. Baudot.
  55. BDF (Building Distribution Frame)
    A network wiring closet typicallyhousing wiring distribution equipmentand hardware. Two commonnetwork BDFs are the IntermediateDistribution Frame (IDF) and theMain Distribution frame (MDF).
  56. beaconing
    In a wireless network,beaconing refers to the continuoustransmission of small packets (beacons)that advertise the presence ofa base station (access point).
  57. BERT (Bit-Error Rate Test)
    A testto see the number of received bits ofa data stream that has changed dueto noise, interference, or other distortion.
  58. BGP
    Border Gateway Protocol.Used between gateway hosts on theInternet. BGP examines the routingtable, which contains a list of knownrouters, the addresses they canreach, and a cost metric associatedwith the path to each router so thatthe best available route is chosen.BGP communicates between therouters using TCP.
  59. binary
    A base 2 numbering systemused in digital signaling. It uses onlythe numbers 1 and 0.
  60. binding
    The process of associatinga protocol with a NIC.
  61. biometrics
    The science and technologyof measuring and analyzingbiological data. Biometrics is usedfor security purposes to analyze andcompare characteristics such asvoice patterns, retina patterns, andhand measurements.
  62. BIOS (Basic Input/Output System)
    A basic set of instructions that adevice needs to operate.
  63. bit
    An electronic digit used in thebinary numbering system. Bit is acontraction of the terms binary anddigit.
  64. blackout
    A total loss of electricalpower.
  65. Bluetooth
    A low-cost, short-rangeRF technology designed to replacemany of the cords used to connectdevices. Bluetooth uses 2.4GHz RFand provides transmission speeds upto 24Mbps.
  66. BNC (Bayonet Neill Concelman)connector
    A family of connectorstypically associated with thin coaxialcabling and 10Base2 networks. BNCconnectors use a twist-and-lockmechanism to connect devices tothe network.
  67. BOOTP
    Bootp is a TCP/IP protocolused by a network device toobtain an IP address and other networkinformation such as serveraddress and default gateway.
  68. bound medium
    Describes anymedium that has physical constraints,such as coaxial, fiber-optic,and twisted pair. Compare withunbound medium.
  69. boundless medium
    See unboundmedium.
  70. BPDU (Bridge Protocol Data Unit)
    Identifies the status of ports andbridges across the network. BPDUsare simple data messages exchangedbetween switches. They containinformation on ports and providethe status of those ports to otherswitches.
  71. BRI (Basic Rate Interface)
    AnISDN digital communications linethat consists of three independentchannels: two B channels each at64Kbps and one D channel at16Kbps. ISDN BRI is often referredto as 2B+D. See also ISDN and PRI.
  72. bridge
    A device that connects andpasses packets between two networksegments that use the same communicationsprotocol. Bridges operateat the data link layer of the OSImodel. A bridge filters, forwards, orfloods an incoming frame based onthe packet�s MAC address.
  73. bridging address table
    A list ofMAC addresses that a bridge keepsand uses when it receives packets.The bridge uses the bridging addresstable to determine which segmentthe destination address is on before itsends the packet to the next interfaceor drops the packet (if it is on thesame segment as the sending node).
  74. broadband
    A communicationsstrategy that uses analog or digitalsignaling over multiple communicationschannels.
  75. broadcast
    A packet-delivery systemin which a copy of a packet istransmitted to all hosts attached tothe network.
  76. broadcast storm
    An undesirablecondition in which broadcasts becomeso numerous that they bog down theflow of data across the network.
  77. brouter
    A device that you can useto combine the benefits of bothrouters and bridges. Its commonusage is to route routable protocolsat the network layer of the OSImodel and to bridge nonroutableprotocols at the data link layer.
  78. brownout
    A short-term decrease inthe voltage level, usually caused bythe startup demands of other electricaldevices.
  79. BSSID (Basic Service SetIdentification)
    The BSSID is theMAC address of the wireless accesspoint (AP).
  80. buffer
    An area of memory in adevice used to temporarily store databefore it is forwarded to anotherdevice or location.
  81. bus topology
    A linear LAN architecturein which all devices connectto a common cable, called a bus orbackbone.
  82. butt set
    The butt set is typicallyassociated with telephony systems. Itis used to test and access the phoneline using clip wires that attach tothe phone cable.
  83. byte
    A set of bits (usually 8) thatoperate as a unit to signify a character.
  84. cable modem
    A device that providesInternet access over cable televisionlines.
  85. cable stripper
    A tool used to stripthe sheathing from copper cabling.
  86. cable tester
    A device used tocheck for electrical continuity alonga length of cable. Cable tester is ageneric term that can be applied todevices such as volt/ohm meters andTDRs.
  87. caching-only server
    A type ofDNS server that operates the sameway as secondary servers except thata zone transfer does not take placewhen the caching-only server isstarted.
  88. CARP (Common AddressRedundancy Protocol)
    A protocolthat enables multiple hosts on thesame network to share a set of IPaddresses and thus provides failoverredundancy. It is commonly usedwith routers and firewalls and canprovide load balancing.
  89. carrier
    A signal that carries data.The carrier signal is modulated tocreate peaks and troughs, whichrepresent binary bits.
  90. change control
    A process in whicha detailed record of every changemade to the network is documented.
  91. channel
    A communications pathused for data transmission.
  92. CHAP (Challenge HandshakeAuthentication Protocol)
    A protocolthat challenges a system to verifyidentity. CHAP is an improvementover Password AuthenticationProtocol (PAP) in which one-wayhashing is incorporated into a threewayhandshake. RFC 1334 appliesto both PAP and CHAP.
  93. checksum
    A basic method oferror checking that involves calculatingthe sum of bytes in a sectionof data and then embedding theresult in the packet. When the packetreaches the destination, the calculationis performed again to makesure that the value is still the same.
  94. CIDR (classless interdomain routing)
    An IP addressing scheme thatenables a single IP address to designatemany unique IP addresses.CIDR addressing uses an IP addressfollowed by a / and the IP networkprefix. An example of a CIDRaddress is 192.168.100.0/16. CIDRis sometimes called supernetting.
  95. circuit-level firewall
    A type of networksecurity system whereby networktraffic is filtered based onspecified session rules and may berestricted to recognized computersonly.
  96. circuit switching
    A method ofsending data between two parties inwhich a dedicated circuit is createdat the beginning of the conversationand is broken at the end. All datatransported during the session travelsover the same path, or circuit.
  97. Class A network
    A TCP/IP networkthat uses addresses from 1 to126 and supports up to 126 subnetswith 16,777,214 unique hosts each.
  98. Class B network
    A TCP/IP networkthat uses addresses from 128 to191 and supports up to 16,384 subnetswith 65,534 unique hosts each.
  99. Class C network
    A TCP/IP networkthat uses addresses from 192to 223 and supports up to 2,097,152subnets with 254 unique hosts each.
  100. client
    A node that uses the servicesfrom another node on a network.
  101. client/server networking
    A networkingarchitecture in which frontend,or client, nodes request andprocess data stored by the back-end,or server, node.
  102. cloud computing
    The hosting,storage, and delivery of computingas a service rather than a product.The end user accesses remotelystored programs and other resourcesthrough the Internet without theneed for expensive local networkingdevices, services, and support.
  103. clustering
    A technology thatenables two or more computers toact as a single system to provideimproved fault tolerance, load balancing,and failover capability.
  104. CNAME (canonical name)
    Specifies an alias or nickname for acanonical hostname record in adomain name system (DNS) database.CNAME records are used togive a single computer multiplenames (aliases).
  105. coaxial cable
    A data cable, commonlyreferred to as coax, that ismade of a solid copper core insulatedand surrounded by braided metaland covered with a thick plastic orrubber covering. Coax is the standardcable used in cable televisionand in older bus topology networks.
  106. cold site
    A disaster recovery sitethat provides office space, but thecustomer provides and installs allthe equipment needed to continueoperations.
  107. cold spare
    A redundant piece ofhardware stored in case a componentshould fail. Typically used forserver systems.
  108. collision
    The result of two framessimultaneously transmitting on anEthernet network and colliding,thereby destroying both frames.
  109. collision domain
    A segment of anEthernet network between managingnodes, where only one packetcan be transmitted at a time.Switches, bridges, and routers canbe used to segment a network intoseparate collision domains.
  110. collision light
    An LED on networkingequipment that flashes toindicate a collision on the network.A collision light can be used todetermine whether the network isexperiencing many collisions.
  111. communication
    The transfer ofinformation between nodes on anetwork.
  112. concentrator
    A device that combinesseveral communications channelsinto one. It is often used tocombine multiple terminals into oneline.
  113. connectionless communication
    Packet transfer in which delivery isnot guaranteed.
  114. connection-oriented communication
    Packet transfer in whichdelivery is guaranteed.
  115. connectivity
    The linking of nodeson a network for communication totake place.
  116. convergence
    When a change inthe network routing is made, it takessome time for the routers to detectand accommodate this change
  117. copy backup
    Normally, a backupof the entire hard drive. A copybackup is similar to a full backup,except that the copy backup doesnot alter the state of the archive bitson files.
  118. cost
    A value used to encourage ordiscourage the use of a certain routethrough a network. Routes that areto be discouraged are assigned ahigher cost, and those that are to beencouraged are assigned a lowercost. See also metric.
  119. cracker
    A person who attempts tobreak software code or gain accessto a system to which he or she is notauthorized. See also hacker.
  120. cracking
    The process of attemptingto break software code, normallyto defeat copyright protection oralter the software�s functioning. Alsothe process of attempting to gainunauthorized access to a computersystem. See also hacking.
  121. CRAM-MD5
    A challenge-responseauthentication mechanism.
  122. CRC (cyclical redundancy check)
    A method used to check for errorsin packets that have been transferredacross a network. A computationbit is added to the packet andrecalculated at the destination todetermine whether the entire contentof the packet has been correctlytransferred.
  123. crimper
    A tool used to join connectorsto the ends of networkcables.
  124. crossover cable
    A cable that canbe used to directly connect twodevices�such as two computer systems�or as a means to expand networksthat use devices such as hubsor switches. A traditional crossovercable is a UTP cable in which thewires are crossed for the purposes ofplacing the transmit line of onedevice on the receive line of theother. A T1 crossover is used toconnect two T1 CSU/DSU devicesin a back-to-back configuration.
  125. crosstalk
    Electronic interferencecaused when two wires are too closeto each other, and the adjacent cablecreates interference.
  126. CSMA/CA (carrier sense multipleaccess with collision avoidance)
    Acontention media access method thatuses collision-avoidance techniques.
  127. CSMA/CD (carrier sense multipleaccess with collision detection)
    Acontention media access methodthat uses collision-detection andretransmission techniques.
  128. CSU/DSU (Channel ServiceUnit/Data Service Unit)
    Acts as atranslator between the LAN dataformat and the WAN data format.Such a conversion is necessarybecause the technologies used onWAN links are different from thoseused on LANs.
  129. cut-through packet switching
    Aswitching method that does notcopy the entire packet into theswitch buffers. Instead, the destinationaddress is captured into theswitch, the route to the destinationnode is determined, and the packetis quickly sent out the correspondingport. Cut-through packetswitching maintains a low latency.
  130. Data field
    In a frame, the field orsection that contains the data.
  131. data link layer
    Layer 2 of the OSImodel, which is above the physicallayer. Data comes off the cable, goesthrough the physical layer, and goesinto the data link layer. The datalink layer has two distinct sublayers:MAC and LLC.
  132. datagram
    An information groupingtransmitted as a unit at the networklayer. See also packet.
  133. DB-25
    A 25-pin connector used forserial port or parallel port connectionbetween PCs and peripheral devices.
  134. DB-9
    A nine-pin connector usedfor serial port or parallel port connectionbetween PCs and peripheraldevices.
  135. D (delta) channel
    The channelused on ISDN to communicate signalingand other related information.Use of the D channel leavesthe B channels free for data communication.See also B (bearer) channel.
  136. DDNS (Dynamic Domain NameService)
    A form of DNS thatenables systems to be registered andderegistered with DNS dynamically.DDNS is facilitated by DHCP,which passes IP address assignmentsto the DNS server for entry into theDNS server records. This is in contrastwith the conventional DNSsystem, in which entries must bemanually made.
  137. DDoS (Distributed Denial of Service)
    A DoS attack that utilizes more thanone computer in the attack. See DoS(Denial of Service).
  138. DDS (digital data storage)
    A formatfor storing computer data on aDAT. DDS-formatted tapes can beread by either a DDS or DAT drive.The original DDS standard specifieda 4mm tape cartridge with a capacityof 1.3GB. Subsequent implementationsof DDS have taken the capacityto 40GB with compression.
  139. dedicated line
    A dedicated circuitused in WANs to provide a constantconnection between two points.
  140. default gateway
    Normally arouter or a multihomed computer towhich packets are sent when theyare destined for a host on a differentnetwork.
  141. demarcation point
    The point atwhich communication lines enter acustomer�s premises. Sometimesshortened to simply demarc.
  142. destination address
    The networkaddress to which data is sent.
  143. DHCP (Dynamic Host ConfigurationProtocol)
    A protocol that providesdynamic IP addressing to DHCPenabledworkstations on the network.
  144. dialup networking
    Refers to theconnection of a remote node to anetwork using POTS.
  145. differential backup
    A backup ofonly the data that has been createdor changed since the previous fullbackup. In a differential backup, thestate of the archive bits is notaltered.
  146. dig
    On a Linux, UNIX, orMacintosh system, you can use thedig command to perform manualDNS lookups.
  147. directory services
    A system thatenables network resources to beviewed as objects stored in a database.This database can then bedivided and distributed among differentservers on the network. Examplesof directory services systems includeNovell Directory Services andMicrosoft Active Directory.
  148. disaster recovery plan
    A plan forimplementing duplicate computerservices if a natural disaster, ahuman-made disaster, or anothercatastrophe occurs. A disaster recoveryplan includes offsite backups andprocedures to activate informationsystems in alternative locations.
  149. disk duplexing
    A fault-tolerantstandard based on RAID 1 that usesdisk mirroring with dual disk controllers.See also RAID.
  150. disk mirroring
    A fault-tolerantstandard that is defined as RAID 1and mirrors data between two disksto create an exact copy.
  151. disk striping
    An implementationof RAID in which data is distributedacross multiple disks in a stripe.Some striping implementations provideperformance improvements(RAID 0), whereas others providefault tolerance (RAID 5).
  152. distance-vector routing
    A type ofrouting in which a router usesbroadcasts to inform neighboringrouters on the network of the routesit knows about. Compare with linkstaterouting.
  153. DLC (Data Link Control)
    The serviceprovided by the data link layer ofthe OSI model.
  154. DMZ (Demilitarized Zone)
    An areafor placing web and other serversthat serve the general public outsidethe firewall, therefore isolating themfrom internal network access.
  155. DNS (Domain Name Service)
    Asystem used to translate domainnames, such aswww.quepublishing.com, into IPaddresses, such as 165.193.123.44.DNS uses a hierarchical namespacethat enables the database of hostname-to-IP address mappings to bedistributed across multiple servers.
  156. DOCSIS (Data-Over-Cable ServiceInterface Specification)
    Atelecommunications standard fortransmitting high-speed data overexisting cable TV systems.
  157. domain
    A logical boundary of anActive Directory Structure onWindows servers. Also, a section ofthe DNS namespace.
  158. domain name server
    A server thatruns application software thatenables the server to perform a roleassociated with the DNS service.
  159. DoS (denial of service) attack
    Atype of hacking attack in which thetarget system is overwhelmed withrequests for service, which keeps itfrom servicing any requests�legitimateor otherwise.
  160. downtime
    A period of time duringwhich a computer system or networkis unavailable. This may bedue to scheduled maintenance orhardware or software failure.
  161. DSL (Digital Subscriber Line)
    Apublic network technology thatdelivers high bandwidth over conventionalcopper wiring over limiteddistances.
  162. DSU (data service unit)
    A networkcommunications device that formatsand controls data for transmissionover digital lines. A DSU is usedwith a CSU.
  163. DTE (data terminal equipment)
    Adevice used at the user end of a usernetwork interface that serves as adata source, a destination, or both.DTE devices include computers,protocol translators, andmultiplexers.
  164. dumb terminal
    A keyboard/monitorcombination that enables accessto a multiuser system but providesno processing or storage at the locallevel.
  165. duplexing
    In RAID, a RAID 1mirror set in which each drive isconnected to a separate controller toeliminate the single point of failurethat the controller created.
  166. DWDM (Dense Wavelength DivisionMultiplexing)
    A form of multiplexingoptical signals that replacesSONET/SDH regenerators witherbium doped fiber amplifiers(EDFAs) and can also amplify thesignal and allow it to travel a greaterdistance. The main components of aDWDM system include a terminalmultiplexer, line repeaters, and aterminal demultiplexer.
  167. dynamic routing
    A routing systemthat enables routing information tobe communicated between devicesautomatically and that can recognizechanges in the network topologyand update routing tables accordingly.Compare with static routing.
  168. dynamic window
    A flow controlmechanism that prevents the senderof data from overwhelming thereceiver. The amount of data thatcan be buffered in a dynamic windowvaries in size, hence its name.
  169. E1 (E-Carrier Level 1)
    An E1 linkthat operates over two separate setsof wires, typically twisted-pair cable.
  170. EAP (Extensible AuthenticationProtocol)
    An extension of PPPthat supports authentication methodsmore secure than a standardusername and password combination.EAP is commonly used as anauthentication protocol for tokencards, smart cards, and digital certificates.
  171. EDNS (Extension Mechanisms forDNS)
    As specified by the InternetEngineering Task Force as RFC2671, EDNS increases the size ofthe flags fields, return codes andlabel types available in basic DNS.
  172. EGP (Exterior Gateway Protocol)
    The exterior gateway protocoldefines distance vector protocolscommonly used between hosts onthe Internet to exchange routingtable information. BGP is an exampleof an EGP. See BGP.
  173. EIGRP (Enhanced Interior GatewayRouting Protocol)
    A protocol thatenables routers to exchange informationmore efficiently than earliernetwork protocols. Routers configuredto use EIGRP keep copies oftheir neighbors� routing informationand query these tables to help findthe best possible route for transmissionsto follow.
  174. EMI (electromagnetic interference)
    External interference of electromagneticsignals that causes a reductionin data integrity and increased errorrates in a transmission medium.
  175. encapsulation
    A technique usedby protocols in which header andtrailer information is added to theprotocol data unit as it is passeddown through the protocol stack ona sending system. The reverseprocess, decapsulation, is performedat the receiving system as the packettravels up through the protocolsuite.
  176. encryption
    Modifying data forsecurity purposes prior to transmissionso that the data cannot be readwithout the decryption method.
  177. ESD (electrostatic discharge)
    Acondition created when two objectsof dissimilar electrical charge comeinto contact with each other. Theresult is that a charge from theobject with the higher electricalcharge discharges itself into theobject with the lower-level charge.This discharge can be harmful tocomputer components and circuitboards.
  178. ESP (Encapsulated SecurityPackets)
    One of the two separateprotocols IPSec consist of (the otherbeing AH). ESP provides encryptionservices.
  179. ESS (Extended Service Set)
    Theextended service set (ESS) refers totwo or more BSS sets connected,therefore using multiple APs. TheESS would be used to createWLANs or larger wireless networksand is a collection of APs andclients. See BSS.
  180. ESSID (Extended Service SetIdentifier)
    The terms ESSID andSSID are used interchangeably, butthey are different. The SSID is thename used with BSS networks, andthe ESSID is the network nameused with an ESS wireless networkdesign. With an ESS, not all APsnecessarily use the same name.
  181. Ethernet
    The most common LANtechnology. Ethernet can be implementedusing coaxial, twisted-pair,or fiber-optic cable. Ethernet typicallyuses the CSMA/CD mediaaccess method and has variousimplementation standards.
  182. Event Viewer
    A utility available onWindows Server systems and clientsystems including Windows7/Vista/XP. It is commonly used togather systems information and alsois used in the troubleshootingprocess.
  183. failover
    The automatic switchingfrom one device or system to another.Servers can be configured in afailover configuration so that if theprimary server fails, the secondaryserver automatically takes over.
  184. Fast Ethernet
    The IEEE 802.3uspecification for data transfers of upto 100Mbps over twisted-pair cable.See also 100BaseFX, 100BaseT, and100BaseTX.
  185. fault tolerance
    The capability of acomponent, system, or network toendure a failure.
  186. FDDI (Fiber Distributed DataInterface)
    A high-speed data transfertechnology designed to extendthe capabilities of existing LANs byusing a dual-ring topology and atoken-passing access method.
  187. FDM (Frequency-DivisionMultiplexing)
    A technology thatdivides the output channel into multiplesmaller-bandwidth channels,each of which uses a different frequencyrange.
  188. FHSS (Frequency Hopping SpreadSpectrum)
    A multiple access methodof transferring radio signals in the frequency-hopping code division multipleaccess (FH-CDMA) scheme.
  189. fiber-optic cable
    Also known asfiber optics or optical fiber, a physicalmedium that can conduct modulatedlight transmissions. Comparedwith other transmission media, fiberopticcable is more expensive, but itis not susceptible to EMI orcrosstalk, and it is capable of highdata rates and increased distances.
  190. Fibre Channel
    A technology thatdefines full gigabit-per-second datatransfer over fiber-optic cable.Commonly used with storage areanetwork (SAN) implementations.
  191. firewall
    A program, system, device,or group of devices that acts as abarrier between one network andanother. Firewalls are configured toenable certain types of traffic to passwhile blocking others.
  192. flow control
    A method of controllingthe amount of data transmittedwithin a given period of time.Different types of flow control exist.See also dynamic window and staticwindow.
  193. FM (Frequency Modulation)
    Oneform of radio modulation, this communicationtechnique transmitsinformation over a radio wave.
  194. FQDN (fully qualified domain name)
    The entire domain name. It specifiesthe name of the computer, thedomain in which it resides, and thetop-level DNS domain (for example,www.marketing.quepublishing.com).
  195. fragment-free switching
    A switchingmethod that uses the first 64bytes of a frame to determinewhether the frame is corrupted. Ifthis first part is intact, the frame isforwarded.
  196. frame
    A grouping of informationtransmitted as a unit across the networkat the data link layer of theOSI model.
  197. Frame Length field
    In a dataframe, the field that specifies thelength of a frame.
  198. Frame Type field
    In a data frame,the field that names the protocolbeing sent in the frame.
  199. frequency
    The number of cyclesof an alternating current signal overa unit of time. Frequency isexpressed in hertz.
  200. FTP (File Transfer Protocol)
    A protocolthat provides for the transferof files between two systems. FTP ispart of the TCP/IP suite and operatesat Layer 7 of the OSI model.
  201. F-type connecter
    A screw-typeconnector used with coaxial cable.In computing environments, it ismost commonly used to connectcable modems to ISP equipment orincoming cable feeds.
  202. full backup
    A backup in whichfiles, regardless of whether theyhave been changed, are copied tothe backup medium. In a full backup,the files� archive bits are reset.
  203. full duplex
    A system in which datasimultaneously transmits in twodirections. Compare with halfduplex.
  204. gateway
    A hardware or softwaresolution that enables communicationsbetween two dissimilar networkingsystems or protocols. Agateway can operate at any layer ofthe OSI model but is commonlyassociated with the application layer.
  205. Gb (gigabit)
    1 billion bits, or1000Mb.
  206. GBIC (Gigabit Interface Converter)
    A Gigabit Ethernet and fibre channeltransceiver standard.
  207. Gbps (gigabits per second)
    Thethroughput of a given networkmedium in terms of 1 billion bps.
  208. GFS (grandfather, father, son)
    Atape rotation backup strategy ofmaintaining backups on a daily,weekly, and monthly schedule.Backups are made on a 5-day or 7-day schedule. A full backup is performedat least once a week. On allother days, full, incremental, or differentialbackups (or no backups atall) are performed. The daily incremental,or differential, backups areknown as the son. The father is thelast full backup in the week (theweekly backup). The grandfather isthe last full backup of the month(the monthly backup).
  209. Gigabit Ethernet
    An IEEE 802.3specification that defines standardsfor data transmissions of 1Gbps. Seealso 1000BaseX.
  210. GPG (GNU Privacy Guard)
    AnIETF RFC 4880-compliant alternativeto the PGP suite of cryptographicsoftware.
  211. guaranteed flow control
    A methodof flow control in which the sendingand receiving hosts agree on a rateof data transmission. After the rateis determined, the communicationtakes place at the guaranteed rateuntil the sender is finished. Nobuffering takes place at the receiver.
  212. hacker
    A person who carries outattacks on a computer software program.See also cracker.
  213. half duplex
    A connection in whichdata is transmitted in both directionsbut not simultaneously.Compare with full duplex.
  214. handshake
    The initial communicationbetween two data communicationdevices, during which theyagree on protocol and transfer rulesfor the session.
  215. hardware address
    The hardwareencodedMAC address burned intoevery NIC.
  216. hardware loopback
    A deviceplugged into an interface for thepurposes of simulating a networkconnection. This enables the interfaceto be tested as if it is operatingwhile connected.
  217. HDLC (High-Level Data LinkControl)
    An ISO developed bitorientedsynchronous data link layerprotocol used for point-to-point orpoint-to-multipoint connections.
  218. hop
    The means by which routingprotocols determine the shortestway to reach a given destination.Each router constitutes one hop. Ifa router is four hops away fromanother router, for example, threerouters, or hops, exist between thefirst router and the destination. Insome cases, the final step is alsocounted as a hop.
  219. horizontal cross-connect
    Ties thetelecommunication room to the enduser. Specifically, the horizontalcabling extends from the telecommunicationsoutlet, or network outletwith RJ-45 connectors, at theclient end. It includes all cable fromthat outlet to the telecommunicationroom to the horizontal crossconnect.The term horizontal crossconnectrefers to the distributionpoint for the horizontal cable.
  220. host
    Typically refers to any deviceon the network that has beenassigned an IP address.
  221. host firewall
    A firewall systeminstalled and configured on andused for an individual host. Contrastto a network firewall that providesfirewall services for all networknodes.
  222. host ID
    An identifier used touniquely identify a client orresource on a network.
  223. hostname
    A name assigned to asystem for the purposes of identifyingit on the network in a moreuser-friendly manner than by thenetwork address.
  224. HOSTS file
    A text file that containshostname-to-IP address mappings.All commonly used platformsaccommodate static name resolutionusing the HOSTS file.
  225. hot site
    A disaster recovery termused to describe an alternative networksite that can be immediatelyfunctional in the event of a disasterat the primary site.
  226. hot spare
    In a RAID configuration,a drive that sits idle untilanother drive in the RAID arrayfails, at which point the hot sparetakes over the role of the faileddrive.
  227. hotspot
    An area in which anaccess point provides public wirelessbroadband network services tomobile visitors through a WLAN.Hotspots are often located in heavilypopulated places such as airports,hotels, and coffee shops.
  228. hot swap
    The removal andreplacement of a component in asystem while the power is still onand the system is functioning.
  229. HSRP (Hot Standby RouterProtocol)
    A Cisco proprietary protocolused for establishing redundantgateways.
  230. HTTP (Hypertext Transfer Protocol)
    A protocol used by web browsers totransfer pages, links, and graphicsfrom the remote node to the user�scomputer.
  231. HTTPS (Hypertext Transfer ProtocolSecure)
    A protocol that performsthe same function as HTTP butdoes so over an encrypted link,ensuring the confidentiality of anydata that is uploaded or downloaded.Also referred to as S-HTTP.
  232. hub
    A hardware device that acts asa connection point on a networkthat uses twisted-pair cable. Alsoknown as a concentrator or a multiportrepeater.
  233. HyperTerminal
    A Windows-basedcommunications program thatenables users to establish host/shellaccess to a remote system.
  234. Hz (Hertz)
    Equivalent to cycles persecond, hertz is the unit of frequencydefined as the number ofcycles per second of a periodicphenomenon.
  235. IANA (Internet Assigned NumbersAuthority)
    An organization responsiblefor IP addresses, domainnames, and protocol parameters.Some functions of IANA, such asdomain name assignment, have beendevolved into other organizations.
  236. ICMP (Internet Control MessageProtocol)
    A network layer Internetprotocol documented in RFC 792that reports errors and providesother information relevant to IPpacket processing. Utilities such asping and tracert use functionalityprovided by ICMP.
  237. ICS (Internet Connection Sharing)
    The use of one device with access tothe Internet as an access point forother devices to connect.
  238. IDF
    Some networks use multiplewiring closets. When this is thecase, the wiring closet, known as themain distribution frame (MDF),connects to secondary wiring closets,or intermediate distributionframes (IDFs). See also MDF.
  239. IDS (Intrusion Detection System)
    A software application or hardwaredevice that monitors a network orsystem for malicious or nonpolicyrelated activity and reports to a centralizedmanagement system.
  240. IEEE (Institute of Electrical andElectronics Engineers)
    A professionalorganization that, amongother things, develops standards fornetworking and communications.
  241. IEEE 1394
    A standard that definesa system for connecting up to 63devices on an external bus. IEEE1394 is commonly used with consumerelectronic devices such asvideo cameras and MP3 players.IEEE 1394 is based on a technologydeveloped by Apple Computerscalled FireWire.
  242. IEEE 802.1
    A standard that definesthe OSI model�s physical and datalink layers. This standard allows twoIEEE LAN stations to communicateover a LAN or WAN and is oftencalled the internetworking standard.
  243. IEEE 802.1X
    An IEEE securitystandard designed for authenticatingwireless devices. This standard usesExtensible Authentication Protocol(EAP) to provide a central authenticationserver to authenticate eachuser on the network.
  244. IEEE 802.2
    A standard that definesthe LLC sublayer of the data linklayer for the entire series of protocolscovered by the 802.x standards.This standard specifies the addingof header fields, which tell thereceiving host which upper layersent the information.
  245. IEEE 802.3
    A standard that specifiesphysical layer attributes, such assignaling types, data rates, andtopologies, as well as the mediaaccess method used. It also definesspecifications for the implementationof the physical layer and theMAC sublayer of the data link layer,using CSMA/CD. This standard alsoincludes the original specificationsfor Fast Ethernet.
  246. IEEE 802.4
    A standard that defineshow production machines shouldcommunicate. It establishes a commonprotocol for use in connectingthese machines. It also defines specificationsfor the implementation of thephysical layer and the MAC sublayerof the data link layer, using token ringaccess over a bus topology.
  247. IEEE 802.5
    A standard used todefine token ring. However, it doesnot specify a particular topology ortransmission medium. It providesspecifications for the implementationof the physical layer and the MACsublayer of the data link layer, usinga token-passing media access methodon a ring topology.
  248. IEEE 802.6
    A standard that definesthe distributed queue dual-bus technologyto transfer high-speed databetween nodes. It provides specificationsfor the implementation ofMANs.
  249. IEEE 802.7
    A standard that definesthe design, installation, and testingof broadband-based communicationsand related physical media connectivity.
  250. IEEE 802.8
    A standard that definesthe Fiber Optic Technical AdvisoryGroup, which advises the other 802standards committees on various fiberoptictechnologies and standards.
  251. IEEE 802.9
    A standard that definesthe integration of voice and datatransmissions using isochronousEthernet.
  252. IEEE 802.10
    A standard that focuseson security issues by defining astandard method for protocols andservices to exchange data securelyby using encryption mechanisms.
  253. IEEE 802.11
    The original IEEEwireless standard, which definesstandards for wireless LAN communication.
  254. IEEE 802.11a
    A wireless networkingstandard operating in the 5GHzband. 802.11a supports a maximumtheoretical data rate of 54Mbps.Depending on interference, 802.11acould have a range of 150 feet at thelowest speed setting. Higher-speedtransmissions would see a lowerrange. 802.11a uses the CSMA/CAmedia access method and is incompatiblewith 802.11b and 802.11g.
  255. IEEE 802.11b
    A commonlydeployed IEEE wireless standardthat uses the 2.4GHz RF range andoffers speeds up to 11Mbps. Underideal conditions, the transmissionrange can be as far as 75 meters.
  256. IEEE 802.11g
    An IEEE wirelessstandard that is backward compatiblewith 802.11b. 802.11g offers adata rate of 54Mbps. Like 802.11b,802.11g uses the 2.4GHz RF range.
  257. IEEE 802.11n
    The 802.11n standardsignificantly increase throughputin both the 2.4GHz and 5GHzfrequency range. The baseline goalof the standard reaches speeds of100Mbps, but given the right conditions,802.11n speeds may reach600Mbps. In practical operation,802.11n speeds are much less.
  258. IEEE 802.12
    A standard thatdefines 100BaseVG-AnyLAN,which uses a 1Gbps signaling rateand a special media access methodthat enables 100Mbps data trafficover voice-grade cable.
  259. IETF (Internet Engineering TaskForce)
    A group of research volunteersresponsible for specifying theprotocols used on the Internet andthe architecture of the Internet.
  260. ifconfig
    A command used onLinux, UNIX, and OS/2 systems toobtain configuration for and configurenetwork interfaces.
  261. IGMP (Internet Group ManagementProtocol)
    A protocol used forcommunication between deviceswithin the same multicast group.IGMP provides a mechanism forsystems to detect and make themselvesaware of other systems in thesame group.
  262. IGP
    The interior gateway protocol(IGP) identifies the protocols usedto exchanging routing informationbetween routers within a LAN orinterconnected LANs. See EGP.
  263. IIS (Internet Information Services)
    A web server application and supportingservices created byMicrosoft for Microsoft Windows.
  264. IKE (Internet Key Exchange)
    AnIPSec protocol that uses X.509 certificatesfor authentication.
  265. IMAP4 (Internet Message AccessProtocol version 4)
    A protocolthat enables email to be retrievedfrom a remote server. It is part ofthe TCP/IP suite, and it is similarin operation to POP3 but offersmore functionality.
  266. incremental backup
    A backup ofonly files that have been created orchanged since the last backup. In anincremental backup, the archive bitis cleared to indicate that a file hasbeen backed up.
  267. infrared
    A wireless data communicationmethod that uses light pulses inthe infrared range as a carrier signal.
  268. infrastructure topology
    A wirelesstopology that defines a wireless networkcomposed of an access pointconnected to a wired LAN. Wirelessdevices communicate with the wiredLAN through the access point (AP).
  269. inherited rights
    The file system ordirectory access rights valid at agiven point as a result of those rightsbeing assigned at a higher level inthe directory structure.
  270. intelligent hub/switch
    A hub orswitch that contains some managementor monitoring capability.
  271. intelligent UPS
    A UPS that hasassociated software for monitoringand managing the power provided tothe system. For information to bepassed between the UPS and thesystem, the UPS and system must beconnected, which normally isachieved through a serial or USBconnection.
  272. interface
    A device, such as a cardor plug, that connects pieces ofhardware with a computer so thatinformation can be moved fromplace to place (for example, betweencomputers and printers, hard disks,and other devices, or between two ormore nodes on a network). Also, thepart of an application or operatingsystem that the user sees.
  273. interference
    Anything that cancompromise a signal�s quality. Onbound media, crosstalk and EMI areexamples of interference. In wirelessenvironments, atmospheric conditionsthat degrade a signal�s qualitywould be considered interference.
  274. internal loopback address
    Functionality built into the TCP/IPstack that enables you to verify thecorrect functioning of the stack. Youcan ping any IPv4 address in the127.x.x.x range, except the networkaddress (127.0.0.0) or the broadcastaddress (127.255.255.255). Theaddress 127.0.0.1 is most commonlyused. In IPv6, the localhost (loopback)address is 0:0:0:0:0:0:0:1.
  275. Internet domain name
    The nameof an area of the DNS namespace.The Internet domain name normallyis expressed along with the topleveldomain to which it belongs(for example, comptia.org).
  276. Internet layer
    In the TCP/IParchitectural model, the layerresponsible for addressing, packaging,and routing functions.Protocols that operate at this layerare responsible for encapsulatingpackets into Internet datagrams. Allnecessary routing algorithms are runhere.
  277. internetwork
    A group of networksconnected by routers or other connectivitydevices so that the networksfunction as one network.
  278. intrusion detection
    The process orprocedures that warn you about successfulor failed unauthorized accessto a system.
  279. IP (Internet Protocol)
    A networklayer protocol, documented in RFC791, that offers a connectionlessinternetwork service. IP providesfeatures for addressing, packet fragmentationand reassembly, type-ofservicespecification, and security.
  280. IP address
    The unique addressused to identify the network numberand node address of a device connectedto a TCP/IP network. IPv4addresses typically are expressed indotted-decimal format, such as192.168.1.1. A typical IPv6 addresslooks like 2001:0:4137:9e76:18d1:2094:b980:a30.
  281. IPS (Intrusion Prevention System)
    A network device that continuallyscans the network, looking for inappropriateactivity.
  282. ipconfig
    A Windows commandthat provides information about theconfiguration of the TCP/IPparameters, including the IPaddress.
  283. IPSec (IP Security)
    A protocolused to provide strong security standardsfor encryption and authenticationon virtual private networks.
  284. IPv4 (Internet Protocol version 4)
    A suite of protocols used for communicationon a local area networkand for accessing the Internet.
  285. IPv6 (Internet Protocol version 6)
    The new version of IP, which has alarger range of usable addresses thanthe current version of IP, IPv4, andenhanced security.
  286. IrDA
    A wireless networking technologythat uses infrared beams tosend data transmissions betweendevices.
  287. ISAKMP (Internet SecurityAssociation and Key ManagementProtocol)
    Defined by RFC 2408,ISAKMP is a protocol typically usedby IKE for key exchange.
  288. ISDN (Integrated Services DigitalNetwork)
    An internationallyadopted standard for providing endto-end digital communicationsbetween two points. ISDN is adialup technology allowing data,voice, and other source traffic to betransmitted over a dedicated link.
  289. ISDN terminal adapter
    A devicethat enables communication over anISDN link.
  290. IS-IS
    Intermediate System-to-Intermediate System. A link-stateprotocol that discovers the shortestpath for data to travel using theshortest path first (SPF) algorithm.IS-IS routers distribute topologyinformation to other routers, allowingthem to make the best pathdecisions.
  291. ISO (International Organization forStandardization)
    A voluntaryorganization founded in 1946 that isresponsible for creating internationalstandards in many areas, includingcommunications and computers.This also includes the developmentof the OSI model.
  292. ISP (Internet service provider)
    Acompany or organization that providesfacilities for clients to accessthe Internet.
  293. IV (Initialization Vector)
    A fixedsize input used in cryptography. Thelarger initialization vector, the moreit increases the difficulty in crackingand minimizes the risk of replay.
  294. jumpered (or jumpering)
    Refers tothe physical placement of shortingconnectors on a board or card.
  295. jumperless
    A term used todescribe devices configured via asoftware utility rather than by physicaljumpers on the circuit board.
  296. Kb (kilobit)
    1,000 bits.
  297. KB (kilobyte)
    1,000 bytes.
  298. Kerberos
    A network authenticationprotocol designed to ensure that thedata sent across networks is encryptedand safe from attack. Its primarypurpose is to provide authenticationfor client/server applications.
  299. L2F (Layer 2 Forwarding)
    A Ciscotunneling protocol designed tospecifically tunnel point-to-pointprotocol (PPP) traffic.
  300. L2TP (Layer 2 Tunneling Protocol)
    A VPN protocol that defines itsown tunneling protocol and workswith the advanced security methodsof IPSec. L2TP enables PPP sessionsto be tunneled across anarbitrary medium to a home gatewayat an ISP or corporation.
  301. LACP (Link Aggregation ControlProtocol)
    An IEEE specificationthat provides a control method ofbundling several physical ports intoone single channel.
  302. LAN (local area network)
    A groupof connected computers located in asingle geographic area�usually abuilding or office�that share dataand services.
  303. latency
    The delay induced by apiece of equipment or device usedto transfer data.
  304. LC connector
    A media connectorused with fiber-optic cabling.
  305. LDAP
    A protocol used to accessand query compliant directory servicessystems such as MicrosoftActive Directory and NovellDirectory services.
  306. learning bridge
    A bridge thatbuilds its own bridging address tableinstead of requiring someone tomanually enter information. Mostmodern bridges are learningbridges. Also called a smart bridge.
  307. legacy
    An older computer systemor technology.
  308. line conditioner
    A device used tostabilize the flow of power to theconnected component. Also knownas a power conditioner or voltageregulator.
  309. link light
    An LED on a networkingdevice such as a hub, switch, orNIC. The illumination of the linklight indicates that, at a hardwarelevel, the connection is completeand functioning.
  310. link-state routing
    A dynamic routingmethod in which routers tellneighboring routers of their existencethrough packets called linkstateadvertisements (LSAs). Byinterpreting the information inthese packets, routers can createmaps of the entire network.Compare with distance-vectorrouting.
  311. Linux
    A UNIX-like operating systemkernel created by LinusTorvalds. Linux is distributed underan open-source license agreement,as are many of the applications andservices that run on it.
  312. LLC (logical link control) layer
    Asublayer of the data link layer of theOSI model. The LLC layer providesan interface for network layerprotocols and the MAC sublayer.
  313. LMHOSTS file
    A text file used in aWindows network environment thatcontains a list of NetBIOS hostname-to-IP address mappings usedin TCP/IP name resolution.
  314. logical addressing scheme
    Theaddressing method used in providingmanually assigned node addressing.
  315. logical topology
    The appearanceof the network to the devices thatuse it, even if in physical terms thelayout of the network is different.See also physical topology.
  316. loop
    A continuous circle that apacket takes through a series ofnodes in a network until it eventuallytimes out.
  317. loopback plug
    A device used forloopback testing.
  318. loopback testing
    A troubleshootingmethod in which the output andinput wires are crossed or shorted ina manner that enables all outgoingdata to be routed back into the card.
  319. MAC (Media Access Control)address
    A six-octet number,described in hexadecimal, thatuniquely identifies a host on a network.It is a unique number burnedinto the network interface.
  320. MAC layer
    In the OSI model, thelower of the two sublayers of thedata link layer. It is defined by theIEEE as being responsible for interactionwith the physical layer.
  321. Mac OS X
    Version 10 of an operatingsystem designed for Macintoshcomputer systems. Mac OS X representsa complete shift in Appleoperating systems because it is basedon UNIX code and as such can bemanaged using UNIX utilities andprocedures.
  322. MAN (metropolitan area network)
    A network that spans a defined geographiclocation, such as a city orsuburb.
  323. master name server
    The supplyingname server that has authorityin a DNS zone.
  324. Mb (megabit)
    1 million bits. Usedto rate transmission transfer speeds.
  325. MB (megabyte)
    1 million bytes.Usually refers to file size.
  326. Mbps (megabits per second)
    Howmany millions of bits can travelacross a given medium in a second.
  327. MDF
    The main distribution frameis a type of wiring closet. The primarywiring closet for a networktypically holds the majority of thenetwork gear, including routers,switches, wiring, servers, and more.This is also typically the wiring closetwhere outside lines run into thenetwork. This main wiring closet isknown as the MDF. One of the keycomponents in the MDF is a primarypatch panel. The network connectorjacks attached to this patchpanel lead out to the building fornetwork connections. See also IDF.
  328. MDI (medium-dependent interface)
    A type of port found on Ethernetnetworking devices such as hubs andswitches in which the wiring isstraight through. MDI ports aresometimes called uplink ports. Theyare intended for use as connectivitypoints to other hubs and switches.
  329. MDI-X (medium-dependent interfacecrossed)
    A type of portfound on Ethernet networkingdevices in which the wiring iscrossed so that the transmit line ofone device becomes the receive lineof the other. MDI-X is used to connecthubs and switches to clientcomputers.
  330. media converter
    Network mediaconverters are used to interconnectdifferent types of cables within anexisting network. For example, themedia converter can be used to connectnewer Gigabit Ethernet technologieswith older 100BaseT networks.
  331. media tester
    Defines a range ofsoftware or hardware tools designedto test a particular media type.
  332. memory address
    The labelassigned to define the location inmemory where information isstored.
  333. mesh
    A type of network topologyin which each node connects toevery other node. The mesh networkprovides a high level of redundancybecause it provides alternativeroutes for data to travel should asingle route becomes unavailable.
  334. metric
    A value that can beassigned to a route to encourage ordiscourage the use of the route. Seealso cost.
  335. MIB (Management InformationBase)
    A data set that defines thecriteria that can be retrieved and seton a device using SNMP.
  336. microsegmentation
    The processof using switches to divide a networkinto smaller segments.
  337. microwaves
    A wireless technologysometimes used to transmit databetween buildings and across vastdistances.
  338. mirroring
    A fault-tolerant techniquein which an exact duplicate ofdata on one volume is created onanother. Mirroring is defined asRAID 1. See also RAID.
  339. MMF (Multimode Fiber)
    A type offiber in which many beams of lighttravel through the cable, bouncingoff the cable walls. This strategyactually weakens the signal, reducingthe length and speed at which thedata signal can travel. See also SMF.
  340. modem (modulator-demodulator)
    A device used to modulate anddemodulate the signals that passthrough it. It converts the directcurrent pulses of the serial digitalcode from the controller into theanalog signals compatible with thetelephone network.
  341. MPLS (Multiprotocol LabelSwitching)
    A technology designedto speed up network traffic flow bymoving away from the use of traditionalrouting tables. Instead ofrouting tables, MPLS uses shortlabels to direct packets and forwardthem through the network.
  342. MSAU (multistation access unit)
    Adevice used in an IBM Token-RingNetwork. It organizes the connectednodes into an internal ring and usesthe RI and RO connectors toexpand to other MSAUs on the network.Sometimes referred to asMAU.
  343. MT-RJ connector
    A media connectorused with fiber-optic cabling.
  344. multicast
    A single-packet transmissionfrom one sender to a specificgroup of destination nodes.
  345. multihomed
    A term used to referto a device that has more than onenetwork interface.
  346. multimeter
    A tool used to measurevoltage, current and resistance.
  347. multiplatform
    A term used to referto a programming language, technology,or protocol that runs on differenttypes of CPUs or operatingsystems.
  348. multiplexing
    A technique of combiningmultiple channels over atransmission path and then recoveringor demultiplexing the separatechannels at the receiving end.Examples include FDM, TDM,CDM, and WDM.
  349. NaaSC (Network as a Service)
    Acloud computing model offered bymany telecom providers provided ondemand in a pay-as-you-go model.
  350. NAC (Network Access Control)
    Acomputer networking security solutionthat uses a set of network protocolswith the goal to unify endpointsecurity solutions such asantivirus, vulnerability assessment,and authentication.
  351. name server
    A server that containsa database of name resolutioninformation used to resolve networknames to network addresses.
  352. NAT (Network Address Translation)
    A standard that enables the translationof IP addresses used on onenetwork to a different IP addressthat is acceptable for use on anothernetwork. This translation enablesmultiple systems to access an externalnetwork, such as the Internet,through a single IP address.
  353. NAS (Network attached Storage)
    A specialized file level computerstorage device connected to a network.
  354. nbtstat
    A Windows operating systemcommand-line utility that displaysprotocol statistics and currentTCP/IP connections usingNetBIOS over TCP/IP (NBT).
  355. NetBEUI (NetBIOS Extended UserInterface)
    A nonroutable,Microsoft-proprietary networkingprotocol designed for use in smallnetworks.
  356. NetBIOS (Network BasicInput/Output System)
    A softwareapplication that enables differentapplications to communicatebetween computers on a LAN.
  357. netstat
    A Windows operating systemcommand-line utility that displaysprotocol statistics and currentTCP/IP network connections.
  358. network card
    See NIC.
  359. network ID
    The part of a TCP/IPaddress that specifies the networkportion of the IP address. The networkID is determined by the classof the address, which in turn isdetermined by the subnet maskused.
  360. network interface layer
    The bottomlayer of the TCP/IP architecturalmodel, which is responsible forsending and receiving frames.
  361. network layer
    Layer 3 of the OSImodel, which is where routing basedon node addresses (IP addresses)occurs.
  362. network operating system
    Anoperating system that runs on theservers on a network. Networkoperating systems include WindowsServer 2008, UNIX, and Linux.
  363. newsgroup
    A discussion groupthat focuses on a specific topic andis made up of a collection of messagesposted to an Internet site.Newsgroups are useful resources forsupport personnel.
  364. NFS (Network File System)
    A filesharing and access protocol mostcommonly associated with UNIXand Linux systems.
  365. NIC (network interface card)
    Ahardware component that serves asthe interface, or connecting component,between a network and thenode. It has a transceiver, a MACaddress, and a physical connectorfor the network cable. Also called anetwork adapter or network card.
  366. NIPS (Network Intrusion PreventionSystem)
    A network security systemthat monitors, blocks, andreports malicious network activity.
  367. NMS (Network ManagementSystem)
    An application that acts asa central management point for networkmanagement. Most NMS systemsuse SNMP to communicatewith network devices. See alsoSNMP.
  368. NNTP (Network News TransferProtocol)
    An Internet protocolthat controls how news articles areto be queried, distributed, and posted.NNTP uses port 119.
  369. noise
    Another name for EMI. Seealso EMI.
  370. nslookup
    Windows andLinux/UNIX command-line utilityused to query Domain NameSystem (DNS) servers and clients toobtain DNS information.
  371. NTP (Network Time Protocol)
    Aprotocol used to communicate timesynchronization informationbetween devices on the network.NTP is part of the TCP/IP suite.NTP uses port 123.
  372. OS (operating system)
    The maincomputer program that managesand integrates all the applicationsrunning on a computer. The OShandles all interactions with theprocessor.
  373. OSI (Open Systems Interconnect)reference model
    A seven-layermodel created by the ISO to standardizeand explain the interactionsof networking protocols.
  374. OSPF (Open Shortest Path First)
    Alink-state routing protocol used onTCP/IP networks. Compare withdistance-vector routing.
  375. OTDR
    A tool used to locate problemswith optical media, such ascable breaks.
  376. packet
    A packet refers to a unit ofdata that travels in communicationnetworks.
  377. packet filtering
    A firewall methodin which each packet that attemptsto pass through the firewall is examinedto determine its contents. Thepacket is then allowed to pass, or itis blocked, as appropriate.
  378. packet sniffer
    A device or applicationthat enables data to be copiedfrom the network and analyzed. Inlegitimate applications, it is a usefulnetwork troubleshooting tool.
  379. PAN (personal area network)
    Anetwork layout whereby deviceswork together in close proximity toshare information and services, commonlyusing technologies such asBluetooth or infrared.
  380. PAP (Password AuthenticationProtocol)
    A simple authenticationprotocol in which the username andpassword are sent to the remoteaccessserver in clear text, making itpossible for anyone listening to networktraffic to steal both. PAP typicallyis used only when connectingto older UNIX-based remote-accessservers that do not support any additionalauthentication protocols.
  381. passive hub
    A hub that has nopower and therefore does not regeneratethe signals it receives.Compare with active hub.
  382. password
    A set of characters usedwith a username to authenticate auser on a network and to provide theuser with rights and permissions tofiles and resources.
  383. PAT (Port Address Translation)
    Avariation on NAT (Network AddressTranslation). With PAT, all systems onthe LAN are translated into the sameIP address, but with a different portnumber assignment. See also NAT.
  384. patch
    A fix for a bug in a softwareapplication. Patches can be downloadedfrom the Internet to correcterrors or security problems in softwareapplications.
  385. patch cable
    A cable, normallytwisted pair, used to connect twodevices. Strictly speaking, a patchcable is the cable that connects aport on a hub or switch to the patchpanel, but today people commonlyuse the term to refer to any cableconnection.
  386. patch panel
    A device in which thecables used in coaxial or twisted-pairnetworks converge and are connected.The patch panel is usually in acentral location.
  387. peer-to-peer networking
    A networkenvironment that does nothave dedicated servers, where communicationoccurs between similarlycapable network nodes that act asboth clients and servers.
  388. permissions
    Authorization providedto users that allows them toaccess objects on a network.Network administrators generallyassign permissions. Permissions areslightly different from but oftenused with rights.
  389. physical address
    The MACaddress on every NIC. The physicaladdress is applied to a NIC by themanufacturer. Except for rare occurrences,it is never changed.
  390. physical layer
    Layer 1 of the OSImodel, where all physical connectivityis defined.
  391. physical network diagram
    A diagramthat displays the physical layoutof a network including placementof systems and all networkcabling.
  392. physical topology
    The actualphysical layout of the network.Common physical topologiesinclude star, bus, and ring. Comparewith logical topology.
  393. ping
    A TCP/IP stack utility thatworks with ICMP and that usesecho requests and replies to testconnectivity to other systems.
  394. PKI (Public Key Infrastructure)
    Acollection of software, standards,and policies combined to enableusers from the Internet or otherunsecured public networks tosecurely exchange data. PKI uses apublic and private cryptographic keypair obtained and shared through atrusted authority.
  395. plenum
    The space between thestructural ceiling and a drop-downceiling. It is commonly used forheating, ventilation, and air conditioningsystems and to run networkcables.
  396. plug and play
    An architecturedesigned to enable the operatingsystem to detect hardware devicesand for the driver to be automaticallyloaded and configured.
  397. PoE (Power over Ethernet)
    Atechnology that enables electricalpower to be transmitted over twisted-pair Ethernet cable. The poweris transferred, along with data, toprovide power to remote devices.
  398. point-to-multipoint (PtMP)
    A wirelessconnection designed to linkmultiple wired networks. Signals inpoint-to-multipoint networks travelfrom a central node such as a basestation of a cellular system, an accesspoint of a WLAN, or a satellite.
  399. point-to-point (PtP)
    Refers to awireless topology configuration. Itidentifies the communication linkfrom one node directly to one othernode. Wireless point-to-point systemsare often used in wireless backbonesystems such as microwaverelay communications, or as areplacement for a single wired communicationcable.
  400. policies and procedures
    Policiesrefer to an organization�s documentedrules regarding what is to bedone, or not done, and why.Network procedures differ frompolicies in that they identify the wayin which tasks are to be performed.
  401. polling
    The media access methodfor transmitting data in which acontrolling device is used to contacteach node to determine whether ithas data to send.
  402. POP3 (Post Office Protocol version3)
    A protocol that is part of theTCP/IP suite used to retrieve mailstored on a remote server. The mostcommonly used version of POP isPOP3. POP is an application layerprotocol.
  403. port
    In physical networking terms,a pathway on a networking devicethat enables other devices to be connected.In software terms, a port isthe entry point into an application, asystem, or a protocol stack.
  404. port mirroring
    A process by whichtwo ports on a device, such as aswitch, are configured to receive thesame information. Port mirroring isuseful in troubleshooting scenarios.
  405. POTS (plain old telephone system)
    The current analog public telephonesystem. See also PSTN.
  406. PPP (Point-to-Point Protocol)
    Acommon dialup networking protocolthat includes provisions for securityand protocol negotiation. Provideshost-to-network and switch-toswitchconnections for one or moreuser sessions.
  407. PPPoE (Point-to-Point Protocol overEthernet)
    An Internet connectionauthentication protocol that uses twoseparate technologies, Ethernet andPPP, to provide a method for multipleusers to share a common DigitalSubscriber Line (DSL), cablemodem, or wireless connection tothe Internet.
  408. PPTP (Point-to-Point TunnelingProtocol)
    A protocol that encapsulatesprivate network data in IP packets.These packets are transmittedover synchronous and asynchronouscircuits to hide the Internet�s underlyingrouting and switching infrastructurefrom both senders andreceivers.
  409. presentation layer
    Layer 6 of theOSI model, which prepares informationto be used by the applicationlayer.
  410. PRI (Primary Rate Interface)
    Ahigh-level network interface standardfor use with ISDN. PRI is defined ashaving a rate of 1.544Mbps, and itconsists of a single 64Kbps D channelplus 23 T1 B channels for voiceor data. See also BRI and ISDN.
  411. primary name server
    The DNSserver that offers zone data from filesstored locally on the machine.
  412. private network
    A network towhich access is limited, restricted, orcontrolled. Most corporate networksare private networks. Compare withpublic network.
  413. proprietary
    A standard or specificationcreated by a single manufacturer,vendor, or other private enterprise.
  414. protocol
    A set of rules or standardsthat control data transmission andother interactions between networks,computers, peripheral devices, andoperating systems.
  415. protocol analyzer
    Protocol analyzerscan be hardware- or software-basedwith their primary function being toanalyze network protocols such asTCP, UPD, HTTP, FTP and more.
  416. proxy
    A device, application, orservice that acts as an intermediarybetween two hosts on a network,eliminating the capability for directcommunication.
  417. proxy server
    A server that acts as ago-between for a workstation andthe Internet. A proxy server typicallyprovides an increased level of security,caching, NAT, and administrativecontrol.
  418. PSTN (public switched telephonenetwork)
    A term that refers to allthe telephone networks and servicesin the world. The same as POTS,PSTN refers to the world�s collectionof interconnected public telephonenetworks that are both commercial-and government-owned. Allthe PSTN is digital, except the connectionbetween local exchanges andcustomers (which is called the localloop or last mile), which remainsanalog.
  419. public network
    A network, such asthe Internet, to which anyone canconnect with the most minimal ofrestrictions. Compare with privatenetwork.
  420. punchdown block
    A device usedto connect network cables fromequipment closets or rooms to otherparts of a building. Connections tonetworking equipment such as hubsor switches are established from thepunchdown block. Also used intelecommunications wiring todistribute phone cables to theirrespective locations throughout thebuilding.
  421. punchdown tool
    A hand tool thatenables the connection of twistedpairwires to wiring equipment suchas a patch panel.
  422. PVC (permanent virtual circuit)
    Apermanent dedicated virtual linkshared in a Frame Relay network,replacing a hardwired dedicatedend-to-end line.
  423. QoS (quality of service)
    Describesthe strategies used to manage andincrease the flow of network traffic.QoS features enable administratorsto predict bandwidth use, monitorthat use, and control it to ensurethat bandwidth is available to theapplications that need it.
  424. RADIUS (Remote AuthenticationDial-in User Service)
    A securitystandard that employs a client/servermodel to authenticate remotenetwork users. Remote users areauthenticated using a challenge-andresponsemechanism between theremote-access server and theRADIUS server.
  425. RAID (Redundant Array ofInexpensive Disks)
    A method tostore data on multiple hard drives,enabling the overlapping of I/Ooperations. The RAID levels offereither fault-tolerance or performanceadvantages.
  426. RAID 0
    A RAID configuration thatemploys data striping but that lacksredundancy because no parity informationis recorded (see RAID 5). Asa result, RAID 0 offers no fault tolerance,but it does offer increasedperformance. Requires a minimumof two disks.
  427. RAID 1
    A fault-tolerant methodthat uses disk mirroring to duplicatethe information stored on a disk.Also called disk duplexing when thetwo drives in a RAID 1 array areconnected to separate disk controllers.
  428. RAID 5
    A fault-tolerant methodthat uses disk striping with distributedparity. Striping is done acrossthe disks in blocks.
  429. RAID 10
    Also called RAID 1/0. ARAID configuration in which stripesets (RAID 0) are mirrored (RAID1). This combination provides thefault-tolerant aspects of RAID 1 andthe performance advantages ofRAID 0.
  430. RARP (Reverse Address ResolutionProtocol)
    A protocol, part of theTCP/IP suite, that resolves MACaddresses to IP addresses. Its relativeARP resolves IP addresses toMAC addresses. RARP resides onthe network layer of the OSI model.
  431. RAS (Remote Access Service)
    AWindows service that enables accessto the network through remote connections.
  432. RDP (Remote Desktop Protocol)
    Apresentation layer protocol that supportstraffic between a WindowsTerminal Client and WindowsTerminal Server.
  433. regulations
    Regulations areactual legal restrictions with legalconsequences.
  434. remote control
    In networking,having physical control of a remotecomputer through software.
  435. remote node
    A node or computerconnected to a network through aremote connection. Dialing in tothe Internet from home is an exampleof the remote node concept.
  436. repeater
    A device that regeneratesand retransmits signals on a network.Repeaters usually are used tostrengthen signals going long distances.
  437. resolver
    A system that requeststhe resolution of a name to an IPaddress. This term can be applied toboth DNS and WINS clients.
  438. restore
    To transfer data frombackup media to a server. Theopposite of backup.
  439. RFC (Request for Comments)
    Theprocess by which standards relatingto the Internet, the TCP/IP suite,and associated technologies are created,commented on, and approved.
  440. RG-6/8/58/59
    Designations for thecoaxial cable used in thin coaxialnetworks that operate on theEthernet standard.
  441. rights
    An authorization providedto users that allows them to performcertain tasks. The network administratorgenerally assigns rights.Slightly different from but oftenused with the term permissions.
  442. RIP (Routing Information Protocol)
    A protocol that uses hop count as arouting metric to control the directionand flow of packets betweenrouters on an internetwork.
  443. RJ-11 connector
    A connectorused with telephone systems. Canhave up to six conductors.
  444. RJ-45 connector
    A connectorused with twisted-pair cable. Cansupport eight conductors for fourpairs of wires.
  445. route
    The entire path betweentwo nodes on a network.
  446. router
    A device that works at thenetwork layer of the OSI model tocontrol the flow of data betweentwo or more network segments.
  447. RSA
    An algorithm for public-keycryptography. Can be used forencryption purposes. RSA is used asa secure solution for e-commerce.
  448. RTP
    Real-time Transport Protocol(RTP). The Internet-standard protocolfor the transport of real-timedata, including audio and video.
  449. sag
    A momentary drop in thevoltage provided by a power source.
  450. SC connector
    The SC connectoris a type of connector used withfiber cabling.
  451. SCP (Secure Copy Protocol)
    Abasic file-copying protocol that usesSecure Shell (SSH) technology toprovide security to the transfer.
  452. SDSL (Symmetrical DigitalSubscriber Line)
    A DSL implementationthat offers the samespeeds for uploads and downloads.It is not widely implemented in thehome/small business environmentand cannot share a phone line.
  453. secondary name server
    A type ofDNS server that gets its zone datafrom another DNS name server thathas authority in that zone.
  454. Security log
    A log located in theWindows Event Viewer that providesinformation on audit eventsthat the administrator has determinedto be security-related. Theseevents include logons, attempts tolog on, attempts to access areas thatare denied, and attempts to log onoutside normal hours.
  455. segment
    A physical section of anetwork.
  456. server
    A network node that fulfillsservice requests for clients. Usuallyreferred to by the type of service itperforms, such as file server, communicationsserver, or print server.
  457. server-based application
    Anapplication run from a networkshare rather than from a copyinstalled on a local computer.
  458. server-based networking
    A networkoperating system dedicated toproviding services to workstations,or clients. See also client/server networking.
  459. service pack
    A software updatethat fixes multiple known problemsand in some cases provides additionalfunctionality to an application oroperating system.
  460. session
    How long the dialogremains open between two nodes.
  461. session layer
    Layer 5 of the OSImodel, which establishes, manages,and terminates sessions betweenapplications on different nodes.
  462. SFTP (Secure File Transfer Protocol)
    An implementation of File TransferProtocol (FTP) that uses SecureShell (SSH) technology to provideadditional authentication andencryption services for file transfers.
  463. shared system
    The infrastructurecomponent routed directly into aninternetwork�s backbone for optimalsystems access. It provides connectivityto servers and other sharedsystems.
  464. shell
    An interface, graphical orotherwise, that enables a user toaccess the functionality of an operatingsystem.
  465. SIP
    An application layer protocoldesigned to establish and maintainmultimedia sessions such as Internettelephony calls.
  466. SMF (Single-mode fiber)
    A type offiber that uses a single direct beamof light, thus allowing for greaterdistances and increased transferspeeds. See also MMF.
  467. SMTP (Simple Mail TransferProtocol)
    An Internet protocolused for the transfer of email messagesand attachments.
  468. SNAT (Static NAT)
    A simple formof NAT. SNAT maps a private IPaddress directly to a static unchangingpublic IP address. See also NAT.
  469. SNMP (Simple NetworkManagement Protocol)
    Providesnetwork devices with a method tomonitor and control networkdevices
  470. SNMP agent
    A software componentthat enables a device to communicatewith, and be contacted by,an SNMP management system.
  471. SNMP trap
    An SNMP utility thatsends an alarm to notify the administratorthat something within thenetwork activity differs from theestablished threshold, as defined bythe administrator.
  472. SOA (start of authority)
    A recordof information containing data onDNS zones and other DNS records.A DNS zone is the part of a domainfor which an individual DNS serveris responsible. Each zone contains asingle SOA record.
  473. SOHO (Small Office / Home Office)
    A small network typically serving 1to 10 users.
  474. SONET (Synchronous OpticalNetwork)
    A U.S. standard for datatransmission that operates at speedsup to 2.4Gbps over optical networksreferred to as OC-x, where x is thelevel. The international equivalentof SONET is Synchronous DigitalHierarchy (SDH).
  475. source address
    The address ofthe host that sent the frame. Thesource address is contained in theframe so that the destination nodeknows who sent the data.
  476. source-route bridge
    A bridge usedin source-route bridging to send apacket to the destination nodethrough the route specified by thesending node.
  477. spike
    An instantaneous, dramaticincrease in the voltage input to adevice. Spikes are responsible formuch of the damage done to networkhardware components.
  478. SPS (Standby Power Supply)
    Atype of power supply in which theSPS monitors the power line andswitches to battery power as soon asit detects a problem. During thetime it takes to switch to batterypower, the computer does notreceive any power and may powerdown. This is in contrast to anonline UPS, which constantly providesbattery power.
  479. SSH (Secure Shell)
    An application,such as Telnet, that enables a sessionto be opened on a remote host. SSHdiffers from Telnet in that it providesadditional authenticationmethods and encryption for data asit traverses the network. SSH usesTCP/IP port 22.
  480. SSID (Service Set Identifier)
    Aunique client identifier sent over theWLAN that acts as a simple passwordused for authenticationbetween a wireless client and anaccess point. The SSID is used todifferentiate between networks.Therefore, the client system and theAP must use the same SSID.
  481. SSL (Secure Sockets Layer)
    Amethod of securely transmittinginformation to and receiving informationfrom a remote website. SSLis implemented through HTTPS.SSL operates at the presentationlayer of the OSI model and usesTCP/IP port 443.
  482. STA (Spanning Tree Algorithm)
    Astandard defined by IEEE 802.1 aspart of STP to eliminate loops in aninternetwork with multiple paths.
  483. star
    A type of physical networkdesign is which all nodes connect toa centralized device�in most cases anetwork switch.
  484. static IP address
    An IP addressmanually assigned to a networkdevice, as opposed to dynamicallyvia DHCP.
  485. static routing
    A routing method inwhich all routes must be enteredinto a device manually and in whichno route information is exchangedbetween routing devices on thenetwork. Compare with dynamicrouting.
  486. static window
    A mechanism usedin flow control that prevents thesender of data from overwhelmingthe receiver. The amount of datathat can be buffered in a static windowis configured dynamically bythe protocol.
  487. ST connector
    ST refers to a typeof fiber connector.
  488. storage area network (SAN)
    Asubnetwork of storage devices, usuallyfound on high-speed networksand shared by all servers on a network.
  489. store-and-forward
    A fast-packetswitchingmethod that produceshigher latency than other switchingmethods because the entire contentsof the packet are copied into theswitch�s onboard buffers. CRC calculationsare performed before thepacket can be passed on to the destinationaddress.
  490. STP (shielded twisted pair)
    Twisted-pair network cable that hasshielding to insulate the cable fromEMI.
  491. STP (Spanning Tree Protocol)
    Aprotocol developed to eliminate theloops caused by the multiple pathsin an internetwork. STP is definedin IEEE 802.1.
  492. subdomain
    A privately controlledsegment of the DNS namespacethat exists under other segments ofthe namespace as a division of themain domain. Sometimes also calleda child domain.
  493. subnet
    A logical division of a network,based on the address to whichall the devices on the network areassigned.
  494. subnet mask
    A 32-bit addressused to mask, or screen, a portion ofan IP address to differentiate thepart of the address that designatesthe network and the part that designatesthe host.
  495. subnetting
    The process of usingparts of the node portion of anassigned IP address to create morenetwork IDs. Although subnettingincreases the number of networkIDs, it decreases the number ofnode addresses available for eachnetwork ID.
  496. supernetting
    The process ofaggregating IP network addressesand using them as a single networkaddress range.
  497. surge
    A voltage increase that isless dramatic than that of a spike butcan last much longer. Sometimescalled a swell. The opposite of abrownout.
  498. surge protector
    An inexpensiveand simple device placed between apower outlet and a network componentto protect the component fromspikes and surges. Also known as asurge suppressor.
  499. SVC (switched virtual circuit)
    Avirtual circuit dynamically establishedon demand to form a dedicatedlink. It is broken when transmissionis complete.
  500. switch
    A Layer 2 networkingdevice that forwards frames basedon destination addresses.
  501. SYN
    A message sent to initiate aTCP session between two devices.The full term is synchronizationpacket.
  502. synchronous transmission
    A digitalsignal transmission method thatuses a precise clocking method anda predefined number of bits sent at aconstant rate.
  503. system log
    A log, accessedthrough Event Viewer on WindowsServer platforms, that providesinformation and warnings on eventslogged by operating system componentsand hardware devices. Theseevents include driver failures, deviceconflicts, read/write errors, timeouts,and bad block errors.
  504. T1/E1
    T1 lines are a form of TCarrierlines that offer transmissionspeeds of 1.544Mbps. E1 refers tothe European equivalent of T1. Seealso T-carrier.
  505. T1 crossover
    See also crossovercable.
  506. T3/E3
    T3 carrier lines offer transmissionspeeds of up to44.736Mbps, using 672 64Kbps Bchannels. See also T-carrier.
  507. TACACS+ (Terminal AccessController Access Control SystemPlus)
    A security protocol designedto provide centralized validation ofusers who are attempting to gainaccess to a router or NetworkAccess Server (NAS). TACACS+ is aset of security protocols designed toprovide authentication, authorization,and accounting (AAA) ofremote users. TACACS uses TCPport 49 by default.
  508. T-carrier
    T-carrier lines are highspeeddedicated digital lines that canbe leased from telephone companies.T-carrier lines can supportboth voice and data transmissionsand are often used to create pointto-point private networks.
  509. TCP (Transmission ControlProtocol)
    A connection-oriented,reliable data transmission communicationservice that operates at thetransport layer of the OSI model.TCP is part of the TCP/IP suite.
  510. TCP/IP (Transmission ControlProtocol/Internet Protocol)
    A suiteof protocols that includes TCP andIP. TCP/IP was originally designedfor use on large internetworks buthas now become the de facto protocolfor networks of all sizes.
  511. TCP/IP socket
    A socket, or connectionto an endpoint, used inTCP/IP communication transmissions.
  512. TDM (Time-Division Multiplexing)
    Divides a single communicationchannel into multiple channels,enabling data signals to be transferredsimultaneously as subchannelsin one communication channel.Despite being only a single channel,data signals take turns sending data.
  513. TDR (time-domain reflectometer)
    A device used to test copper cablesto determine whether and where abreak is on the cable. For opticalcables, an optical TDR is used.
  514. Telnet
    A standard terminal emulationprotocol in the TCP/IP stack.Telnet is used to perform terminalemulation over TCP/IP via remoteterminal connections, enabling usersto log in to remote systems and useresources as if they were connectedto a local system.
  515. temperature monitor
    A deviceused to monitor temperature typicallyin a server room or wiringcloset.
  516. Terminal Services
    A service onWindows Server platforms thatenables clients to connect to theserver as if it were a multiuser operatingsystem. All the processing forthe client session is performed onthe server. Only screen updates anduser input are transmitted across thenetwork connection.
  517. TFTP (Trivial File Transfer Protocol)
    A simplified version of FTP thatenables file transfers but does notoffer any security or file managementcapabilities. TFTP usesTCP/IP port 69.
  518. thick coaxial
    The thick cable mostcommonly used as the backbone of acoaxial network. It is approximately.375 inches in diameter.
  519. thick Ethernet
    The IEEE 802.3standard 10Base5, which describesEthernet networking using thickcoaxial cabling. Also calledThickNet.
  520. thin client
    An application run froma back-end server system such asMicrosoft Terminal Services. Theprocessing tasks are all performed atthe terminal server rather than onthe client. In basic usage, onlyscreen updates are sent from theterminal server, and only keyboardand mouse data is sent to the terminalserver.
  521. thin coaxial
    Cable that is thinnerthan thick coaxial cable but stillabout .25 inches in diameter. It iscommonly used in older bus topologies.
  522. thin Ethernet
    The 802.3a standard10Base2, which describes Ethernetnetworking using thin coaxialcabling. Also called ThinNet.
  523. throughput tester
    A device used totest the actual data throughput of anetwork cable.
  524. TIA (Telecommunications IndustryAssociation)
    An organization that,along with the Electronic IndustriesAssociation (EIA), develops standardsfor telecommunications technologies.
  525. TKIP (Temporal Key IntegrityProtocol
    ) Designed to address theshortcomings of the WEP securityprotocol. TKIP is an encryptionprotocol defined in IEEE 802.11i.
  526. T-line
    A digital communicationline used in WANs. Commonlyused T designations are T1 (TrunkLevel 1) and T3 (Trunk Level 3). Itis also possible to use only part of aT1 line, which is known as fractionalT1. T1 lines support a data transmissionrate of up to 1.544 Mbps.
  527. TLS (Transport Layer Security
    ) Asecurity protocol designed to ensureprivacy between communicatingclient/server applications. When aserver and client communicate, TLSensures that no one can eavesdropand intercept or otherwise tamperwith the data message. TLS is thesuccessor to SSL.
  528. token
    A frame that provides controllinginformation. In a token ringnetwork, the node that possesses thetoken is the one that is allowed totransmit next.
  529. token ring
    An IBM-proprietarytoken-passing LAN topologydefined by IEEE standard 802.5. Itoperates at either 4Mbps or 16Mbpsin a star topology.
  530. token ring adapter
    Traditionallyan ISA or Microchannel device with4Mbps or 16Mbps transfer capabilityused to connect nodes to a tokenring network.
  531. tone generator
    A device used witha tone locator to locate and diagnoseproblems with twisted-paircabling. Commonly referred to asfox and hound.
  532. toner probe
    A network tool usedto locate the ends of a run of networkcable.
  533. topology
    The shape or layout of aphysical network and the flow of datathrough the network. See also logicaltopology and physical topology.
  534. trace route
    A function of theTCP/IP suite, implemented in utilitiessuch as traceroute and tracert,which enables the entire path of apacket to be tracked between sourceand destination hosts. It is used as atroubleshooting tool.
  535. tracert
    A Windows command-lineutility used to track the route a datapacket takes to get to its destination.
  536. transmit
    To send data using light,electronic, or electric signals. Innetworking, this is usually done inthe form of digital signals composedof bits.
  537. transparent bridging
    A situation inwhich the bridges on a network telleach other which ports on thebridge should be opened and closed,which ports should be forwardingpackets, and which ports should beblocking packets�all without theassistance of any other device.
  538. transport layer
    Layer 4 of the OSImodel. Protocols at this layer performfunctions such as segmentingdata so that it can be sent over thenetwork and then reassembling thesegmented data on the receivingend. The transport layer also dealswith some of the errors that canoccur in a stream of data, such asdropped and duplicated packets.
  539. transport protocol
    A communicationsprotocol responsible for establishinga connection and ensuringthat all data has arrived safely. It isdefined in Layer 4 of the OSImodel.
  540. Trojan
    A type of program thatappears legitimate but performssome illicit activity when it is run.
  541. TTL (Time To Live)
    A valueassigned to a packet of data to preventit from moving around the networkindefinitely. The TTL value isdecremented each time the packetcrosses a router, until it reaches 0, atwhich point it is removed from thenetwork.
  542. twisted pair
    A type of cable thatuses multiple twisted pairs of copperwire.
  543. UDP (User Datagram Protocol)
    Acommunications protocol that providesconnectionless, unreliablecommunication services and operatesat the transport layer of theOSI model. It requires a networklayer protocol such as IP to guide itto the destination host.
  544. unbound medium (or boundlessmedium)
    Any medium that doesnot have physical constraints.Examples of unbound media areinfrared, wireless, and microwave.Compare with bound medium.
  545. UNC (Universal Naming Convention)
    An industry-naming standard forcomputers and resources that providesa common syntax that shouldwork in most systems, includingWindows, UNIX, and NetWare. Anexample of a UNC name is\\servername\sharename.
  546. unicast
    Communication that takesplace over a network between a singlesender and a single receiver.
  547. UPS (uninterruptible power supply)
    A system that provides protectionagainst power surges and poweroutages. During blackouts, a UPSgives you time to shut down systemsor devices on the network beforethe temporary power interruptionbecomes permanent. A UPS is alsocalled battery backup.
  548. uptime
    How long a device hasbeen on and operating.
  549. URL (uniform resource locator)
    Aname used to identify a website andsubsequently a page on the Internet.An example of a URL iswww.quepublishing.com/products.
  550. USB (universal serial bus)
    A typeof interface between a computersystem and peripheral devices. TheUSB interface enables you to add orremove devices without shuttingdown the computer. USB supportsup to 127 devices. USB also supportsautodetection and plug andplay.
  551. UTP (unshielded twisted pair)
    Atype of cable that uses multipletwisted pairs of copper wire in a casingthat does not provide much protectionfrom EMI. The most commonnetwork cable in Ethernet networks,UTP is rated in categoriesincluding Category 1 throughCategory 6, as well as Category 5eand Category 6a.
  552. VDSL (Variable Digital SubscriberLine)
    An asymmetric version ofDSL that supports high-bandwidthapplications such as VoIP andHDTV. It is the fastest availableform of DSL and uses fiber-opticcabling.
  553. vertical cross-connect
    The mainor vertical cross-connect is the locationwhere outside cables enter thebuilding for distribution. This mayinclude Internet and phone cabling.
  554. virus
    A software program designedspecifically to adversely affect a systemor network. A virus is usuallydesigned to be passed on to othersystems with which it comes in contact.
  555. VLAN (virtual LAN)
    A group ofdevices located on one or more differentLAN segments, whose configurationis based on logical insteadof physical connections. Thisenables the devices to operate as ifthey were connected to the samephysical switch, regardless ofwhether they are connected to thesame switch.
  556. VNC (virtual network computing)
    Enables remote login, in whichclients can access their own desktopswhile being physically away fromtheir computers.
  557. VOIP (Voice over IP)
    Any of anumber of technologies that enablevoice communication across theInternet Protocol.
  558. volume set
    Multiple disks or partitionsof disks that have been configuredto read as one drive.
  559. VPN (virtual private network)
    Anetwork that uses a public networksuch as the Internet as a backbone toconnect two or more private networks.A VPN provides users withthe equivalent of a private network interms of security. VPNs can also beused as a means of establishingsecure remote connectivity between aremote system and another network.
  560. VTP (VLAN Trunking Protocol)
    ACisco proprietary protocol thatmanages the addition, deletion, andrenaming of VLANs for the entirenetwork. Information about changesto a VLAN or the addition of a newVLAN to a network is distributed toall switches on the network simultaneouslyand does not need to bedone one at a time.
  561. WAN (wide area network)
    A datacommunications network that servesusers across a broad geographicarea. WANs often use transmissiondevices such as modems orCSUs/DSUs to carry signals overleased lines or common carrier lines.
  562. warm site
    A disaster recovery siteoffering most equipment and applications.Compare to a cold site thatrefers to a disaster recovery site withlimited hardware and typically onlya reserved location. A hot site is onewith duplicate hardware and softwareand can be operational withinminutes of a disaster.
  563. web server
    A server that runs anapplication and makes the contentsof certain directories on that server,or other servers, available to clientsfor download, via a protocol such asHTTP.
  564. WEP (Wired Equivalent Privacy)
    Adata encryption method used toprotect the transmission between802.11 wireless clients and accesspoints. WEP security has comeunder scrutiny because it uses aninsufficient key length and providesno automated method for distributingthe keys.
  565. WiFi
    A voluntary standard thatmanufacturers can adhere to, whichaims to create compatibility betweenwireless devices. WiFi is an abbreviationfor wireless fidelity.
  566. WINS (Windows Internet NameService)
    A NetBIOS name-to-IPaddress resolution service that runson Windows Server platforms.
  567. WINS database
    A dynamicallybuilt database of NetBIOS namesand IP addresses used by WINS.
  568. wire crimper
    A tool used to createnetworking cables. The type of wirecrimping tool used depends on thecable being made.
  569. wireless channel
    The band of frequencyused for wireless communications.Each IEEE wireless standardspecifies the channels that canbe used.
  570. wireless networking
    Networkingthat uses any unbound media, such asinfrared, microwave, or radio waves.
  571. wiring schematics
    Network documentationdesigned to show thephysical wiring of a network. Thewiring schematic can often be usedin the troubleshooting process.
  572. WISP (Wireless Internet ServiceProvider)
    A service provider thatspecializes in offering users wirelessaccess to the Internet, often includinghotspot access.
  573. WLAN (wireless LAN)
    A local areanetwork created using wirelesstransmission methods such as radioor infrared rather than traditionalwired solutions.
  574. workstation
    A client computer ona network that does not offer anyservices of its own but that uses theservices of the servers on the network.
  575. worm
    A self-replicating programthat can perform destructive acts toa single computer or across a network,both wired and wireless.
  576. WPA (WiFi Protected Access)
    Adata encryption method used on802.11 wireless LANs. WPA is anindustry-supported standarddesigned to address WEP�s securityshortcomings.
  577. X.25
    An ITU-T standardized protocolsuite for packet switching networks.
  578. XDSL (Extended Digital SubscriberLine)
    All the variations of DSLavailable are lumped together underthe label XDSL.
  579. XML (Extensible Markup Language)
    A set of rules for the encoding ofdocuments in a machine readableformat.
  580. zone transfer
    The passing of DNSinformation from one name serverto a secondary name server.

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