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Chapter 6. Wiring the NetworkCables, Connectors, Concentrators, and Other Network Components

Chapter 6. Wiring the NetworkCables, Connectors, Concentrators, and Other Network Components

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network.Althoughthedefinitionsandothermaterialyou'llfind

inthischaptermightseemoverwhelmingatfirst,thischapteris

agoodreferencewhenyouencountersomeofthesetermslater

inthebook.



StructuredWiring

Inthe1980s,theTelecommunicationsIndustryAssociation

(TIA)andtheElectronicsIndustriesAssociation(EIA)formeda

taskforcetoestablishasetofstandardsforinstallingnetwork

wiringinbuildings.Thefirstdraftwascompletedin1991and

becameknownasEIA/TIA-568(referredtointhischapteras

568).AmorerecentstandardisnamedANSI/TIA/EIA-569-A

(referredtointhischapteras569-A).Thesestandards

documentsencompassstructuredwiring,cables,network

topology,connectorsandhardware,electricalperformance

specifications,physicaltermination,andsupportmechanisms.



Note

ANSIisanacronymforAmericanNationalStandards

Institute.ANSIwasfoundedin1918andisthe

majorstandardsorganizationfortheUnitedStates.

ANSIisalsoamemberofotherstandards

organizations,suchasISO.Programmersmight

recognizeoneofthestandardsthatANSIadopted

manyyearsago:AmericanStandardCodefor

InformationInterchange(ASCII).Unicodeandother

standardshavebeendevelopedtoaddsupportfor

otherlanguagecharactersets.YoucanfindANSI

onlineatwww.ansi.org.



The568and569-Astandardsdescribethephysicallayoutand

specificationsforthephysicalplantasitrelatestothevarious

topologicalstandards.Thephysicalplant,inthiscontext,

compriseseverythinghavingtodowithwhatleadsuptoyour

desktop,fromrouters,cables,patchpanels,andsoon.



Thesearethebasictopicscoveredinthestandards:

TheworkareaTheterminationpointofthenetworkata

user'sworkspace.

ThebackbonecablingsystemstructureConnections

betweenmultipletelecommunicationrooms,equipment

rooms,andentrancefacilities.

ThehorizontalcablingsystemstructureConnection

fromthetelecommunicationsoutletintheworkarea,

terminatinginthetelecommunicationsroom.

ThetelecommunicationsclosetThecentralwiringpoint

forafloor.Thetelecommunicationsclosetcancontainboth

networkdevicesandconcentrators(suchasswitches),as

wellastelephoneequipment.

OtherspecificationsSuchissuesasintrabuilding

connectionsandsuchfactorsaselectromechanical

interference.

Inthefollowingsectionsyouwilllearnaboutthesetopics,as

wellasothers.Foramorecompleteexplanationofthe

standards,itissuggestedthatyouobtainthestandardsand

readthem.Itisbeyondthescopeofthisbooktodescribethe

standardsindetail.Instead,thosethatapplytonetworksare

discussed.Inaddition,severaltermsaredefinedforthosewho

arenotwellversedintheterminologyusedbythesestandards.

Manyofthesetermsarealsousedthroughoutotherchaptersin

thisbook.Betweenthischapterandtheglossary,youshouldbe

abletolocatethedefinitionofalmostanywordusedbynetwork

administrators,andthosewhoputtogetherLANs,MANs,and

WANs.



TheWorkArea

Theworkareaincludesthetelecommunicationsoutlet(thatis,

thefaceplateintowhichyouplugyourcomputer'snetwork

cableatyourdesk),whichservesastheworkareainterfaceto

theentirenetworkcablingsystem.Workareaequipment

includescablesusedtoconnecttothetelecommunications

outlet.Thefollowingaretheworkareacablingspecifications:

Equipmentcordsareassumedtohavethesame

performanceaspatchcords(inthetelecommunications

closet)inthesametypingcategory,forexample,Category

5,5e,and6networkcables.

Whenused,adaptersareassumedtobecompatiblewith

thetransmissioncapabilitiesoftheequipmenttowhichthey

connect.

Horizontalcablelinksarespecifiedwiththeassumptionthat

amaximumcablelengthof5meters(16feet)isusedfor

equipmentcordsintheworkarea.Thiscandependonthe

actuallengthofcablingusedtoconnecttheworkareaback

tothetelecommunicatonscloset.Theimportantfactorto

rememberisthatthereisamaximumdistancethatall

cablescanaddupto,dependingonyourtopology.Thus,if

thecablefromthetelecommunicationsclosetislessthan

thespecifiedlengthallowedbythestandards,youcanuse

alongercablefromtheterminationpointattheworkarea.



TheBackboneCablingSystemStructure

Thebackbonecablingsystemofthestandardprovides

interconnectionsbetweentelecommunicationrooms,equipment

rooms,andentrancefacilities(seeFigure6.1).



Figure6.1.Thebackboneofthenetworkincludes

thecablesthatconnectdifferentareasofthe

network.



Thiscablingsystemincludesbackbonecables,intermediateand

maincrossconnects,mechanicalterminations,andpatchcords

orjumpersusedforbackbone-to-backbonecrossconnections.

Thebackbonealsoextendsbetweenbuildingsinacampus

environment.

Therearesomepointsspecifiedforthebackboneofthecabling

system:

Equipmentconnectionstothebackbonecablingshouldbe

madewithcablelengthsof30metersorless.



Thebackboneofcablingshouldbeconfiguredasastar

topology.

Thebackboneislimitedtonomorethantwohierarchical

levelsofcrossconnectsmainandintermediate.Nomore

thanonecrossconnectcanexistbetweenamainanda

horizontalcrossconnect,andnomorethanthreecross

connectscanexistbetweenanytwohorizontalcross

connects.

Atotalcoaxbackbonedistanceof90metersisspecifiedfor

high-bandwidthcapabilityovercopper.Thisdistanceisfor

uninterruptedbackboneruns.

Thedistancebetweenterminationsintheentrancefacility

andmaincrossconnectshouldbedocumentedandmade

availabletoaserviceprovider.

Recognizedmediacanbeusedindividuallyorina

combination,asrequiredbytheinstallation.

Multipaircableisallowed,aslongasitsatisfiesthe

requirementofaminimumofcross-talk.

Theproximityofcablingtosourcesofelectromagnetic

interferenceshouldbetakenintoaccount.

Crossconnectsfordifferentcabletypesmustbelocatedin

thesamefacility.

Notethatinthesespecifications,bridgetapsandsplittersare

notallowed.



Caution



Abridgetapisanextraneouspieceofcablingthatis

leftoverfromapreviousconnectiontoa

communicationsline.Ifnotremoved,abridgetap

actssimilarlytoanantenna,andcausesimpedance

mismatchesandotherproblemswiththesignalthat

travelsdownthecopperwire.Bridgetapsareoneof

thereasonswhyitcanbedifficulttoobtainDSL

servicefromyourlocalphonecompany.Asphones

areaddedtoyourlocalloopandthendisconnected,

manydanglingwirescanbeleftbehindbecauseit's

simplytoocostlytoremovethem.Inaproperly

cablednetwork,bridgetapsshouldnotexist.



Tip

Splittersaredevicesthatareusedtoseparate

higherfrequenciesfromlowerfrequenciesona

copperwire.Again,splittersservenopurposeona

properlycabledLAN.However,onthepublic

switchedtelephonenetwork(PSTN),splitterscanbe

installedtomakeitpossibletoobtainvoice-grade

telephoneserviceandDSLserviceusingthesame

copperwirepair,withaminimumofinterference

betweenthefrequenciesusedonthewireforvoice

andDSLservices.

FormoreaboutDSL,seeChapter16,"Digital

SubscriberLines(DSL)Technology."



TheHorizontalCablingSystemStructure

Thehorizontalcablingsystem(showninFigure6.2)extends

fromthetelecommunicationsoutletintheworkareaand

terminatesinahorizontalcrossconnectinthe

telecommunicationsroom.Itincludesthetelecommunications

outlet.



Figure6.2.Thehorizontalcablingextendsfrom

thetelecommunicationsclosettotheuser'swork

area.



Thedistancecoveredbythehorizontalcablingislimitedbythe

networktopologychosenforyournetwork.Forexample,in

mostEthernetnetworks,thisdistanceis90meters.Token-Ring

hasvariousspecifications,dependingonthecablesused.For

moreinformationaboutToken-Ring,seethechapter"TokenRingNetworks,"locatedontheupgradingandrepairingpcs.com

Website.



TheTelecommunicationsCloset



Telecommunicationsroomsgenerallyareconsideredtobefloorservingfacilitiesforhorizontalcabledistribution.Theyalsoare

usedforintermediateandmaincrossconnects.The

telecommunicationsroomiswhereyouplacepatchpanels,as

wellashubsorswitchesthatareusedtoconnectindividual

workstationsorserverstothenetworkbackbone.







ImportantDefinitions

Indiscussingnetworkcablesandtroubleshootingwiring

problems,thereareseveralimportanttermsandconceptsto

understand.Thissectioncontainsdefinitionsofsomeofthe

termsusedearlierinthechapter.Thissectionshouldbe

consideredasanexpandedglossaryoftermsassociatedwith

thePhysicallayeroftheOSImodel(discussedinAppendixA,

"OverviewoftheOSISeven-LayerNetworkingReference

Model").Inotherchaptersyouwillfindreferencestothese

terms.Althoughitisnotrequiredreadingforthecasualreader,

thefollowingcanserveasaninvaluablereferencewhenmaking

purchasingdecisions,aswellasduringthedesignphaseofa

newnetworkorwhenupgradinganexistingone.



AttenuationtoCross-TalkRatio(ACR)

ACRisacriticalfactorindeterminingthecapabilityofan

unshieldedtwisted-paircableorshieldedtwisted-paircable.

Attenuationtocross-talkratio(ACR)isthevalueofthe

attenuationlessthecrosstalkvalue,bothexpressedindecibels

(db)ataparticularfrequency.Thisisaqualityfactorfor

cabling.Beforeyoucanunderstandthisratio,youneedto

understandwhatthetermattenuationmeans.



Attenuation

Attenuationisthedecreaseinmagnitudeofthesignalasit

travelsthroughanytransmittingmedium,suchaswireorglass.

Attenuationismeasuredasalogarithmoftheratiobetweenthe

inputandtheoutputpowerorbetweentheinputandtheoutput

voltageofthesystem.It'sexpressedindb.Allgoodthings



mustcometoanend,andthisisthecasewithelectricityas

wellaslight.Asthesignaltravelsdownthecopperwire(orthe

fiber-opticcable),someofthesignalislost.Thisiswhyitis

necessaryinanetworktopologytoimposespecificlimitsonthe

lengthsofcableyoucanuse.Afteryougetpastcertainlimits

imposedbyaparticulartopology,thesignalbecomesso

degradedthatthedatatransmittedcannotbereliablyrecovered

atthedestination.

Figure6.3showsthatattenuationoccursasthesignaltravels

downthewire.Theamplitudeoftheelectricalsignaldecreases

thefartherittravelsfromthetransmittingsideofthe

communicationschannel.



Figure6.3.Anelectricalsignaldegradesasit

travelsthroughacoppercable(attenuation).



Bandwidth



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