site survey guide rev 8 - sys2u.com
TRANSCRIPT
Deployment Guide: Higher Education
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Technical Guide
Site Survey
Site Survey Guide
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TableofContents
Introduction .................................................................................................................................3
TypesofSiteSurveys ....................................................................................................................3
SurveyRequirements....................................................................................................................5
EquipmentRequired.....................................................................................................................7
PerformingtheSurvey..................................................................................................................8
GettingStarted.............................................................................................................................9
Summary ....................................................................................................................................11
Wi‐FiTools..................................................................................................................................11
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Introduction Thepurposeofthisguideistoserveasanintroductionandeducationonthebasics,thevalues,andbest
practicesassociatedwithperformingWi‐Fisitesurveys.WewilldescribetheprocessXirrususesforsitesurveysanddemonstratehowthesesameprocessescanbeusedbyanyonewithreadilyavailabletools.
Poorlyperformedsitesurveyscanresultinnotonlycoveragegapsandreducedperformance,butalso
increasedcostsassociatedwithidentifyingandresolvingtheseissuesafterthefact.Thegoalofanysitesurveyistodeterminethenumberandlocationofaccesspoints(APs)requiredtomeetwirelessdesigngoals(suchascoverage,performanceandusercapacity).
Gettingthesitesurveyaccurateisjustasimportantasselectingtheproperhardware.Ifthesitesurveyis
toooptimisticandcallsfortoofewaccesspoints,thefinalinstallationwillyieldpoorcoverageand/orperformance.Thisinturnwillrequireafollow‐upsurveytodeterminewhatchangesmayberequiredtothenumberorlocationofdeployedAPs.TheendresultwillbeincreasedcostsnotonlyinadditionalAPs,but
alsotheassociatedcostsofpullingcable,equipment,contractors,andinstallationeffort.Conversely,ifthesurveyistooconservative,moreaccesspointsthanareneededwillbespecifiedandagainmoneyiswastedonunneededequipmentandlaborcharges.
Types of Site Surveys Active vs. Predictive Therearetwoprimarymethodsinwhichsitesurveyscanbeperformed:ActiveandPredictive.Activesite
surveys,alsocalledlivesurveysuseanactivelytransmittingaccesspointandaWi‐FienabledlaptoporothertooltomeasureWi‐Fisignalstrengthintheactualenvironmenttodeterminehowmanyandwhereaccesspointsarerequired.Predictivesitesurveysusesoftwarepackagestoemulatetheenvironment.Floorplans
ofthesiteareimportedandallowtheusertoassignattenuationvalues(howmuchRFenergyisabsorbed)foreachwallandobjectinthebuilding(mosttoolstypicallyhaveadatabaseofmaterialstochoosefrom),theapplicationwillthenpredictthenumberandlocationofaccesspointsrequiredtomeetthedesired
coverageandperformancegoals.
Active site surveys–measurestherealperformanceofeachaccesspointlocationandinnatelytakesintoaccountthephysicalcharacteristicsandcontentsofthebuilding.Thereisnoneedtoestimatethedensityofthewallsorfloors.Anactivesitesurveyisalsoabletodetectanysourcesofinterferenceand
applythisinformationtodetermineSNR(signaltonoiseratio).Thistypeofsurveynotonlyprovidesthemostaccurateperformanceinformationforeachaccesspoint,italsoallowsforthephysicalinspectionofthesitetoassuretheaccesspointcanbemountedintheselectedlocation.Thedownsideofthistypeof
surveyisitislaborintensive,requiresphysicalaccesstothebuildinganddemandsahigherlevelofRFknowledgetoperform.
Predictive site surveys–maytakelesstimebutstillrequire“seattime”infrontofacomputerprogramversusthe“legtime”neededforanactivesurvey.Asthenameimpliesthesoftwareperformsapredictive
analysisofthebuilding,oncefloorplansareimporteditusesindustrydefinedattenuationvaluesforwalls,
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doors,windows,etc.ThedifficultyhereisthecommonGIGO(GarbageIn‐Garbageout)problemassociatedwithtryingtoaccuratelymodelthecontentsandmakeupofthebuilding(especiallyonesthathavechanged
orremodeledovertime).
SurveyComparison
Active(live)Survey PredictiveSurvey
SurveyEffort Higher PotentiallyLower
AccessPointPlacement ExactLocationschosen Finallocationsstillneedbechosen
WirelessCoverage Measured/Known Predictive:MayrequiremoreAPs
WirelessPerformance Measured/Known Estimated:MayrequiremoreAPs
CablingandEquipment TypicallyAccurate Mayrequirecablestobeaddedormoved
Installation Simplified MayrequiremovingAPsoraddingmoreAPs
Remotevs.On‐SiteSurvey
AlthoughthefollowingdiscussiongoeshandinhandwithActivevs.Predictivesurveys,itisimportanttoidentifytheadditionalvaluebeyondRFanalysisofanon‐siteactivesurveyvs.apredictivesoftwareanalysis.
Thekeypointistounderstandthevalueofwalkingthefacilityasthesurveyisperformedandknowingwhattolookfor.
Theactivesurveynotonlyprovidesthemostaccurateperformanceinformationforeachaccesspoint,italsoallowsforthephysicalinspectionofthesitetoassuretheaccesspointcanbemountedintheselected
location.IfAPplacementisbasedjustonthemarkingonafloorplantheactualinstallersmayfindthelocationunacceptableforinstallation,asitmaynotbephysicallymountableatthepredictedlocation.
Aphysicalwalkthroughoftheinstallationsiteenablesidentificationandaddressingofthefollowingtypesofissuesbeforeinstallationday,wheredelayscanbecostly:
Identifying AP locations – Thisiswillgreatlyassistthosepullingdata/powercablingandavoidcostlychanges.Physical restrictions–AretheremountingissuesthatpreventanAPbeinginstalledwhereitwouldbestbelocated,suchaslighting,airconditioningducts,sprinklers,appropriatemountingpoints,etc.Italsoallowsinstallerstoidentifyalltoolsandanyspecialmountinghardwarerequiredfortheinstall.RF Interference issues–Aretherenearbynon‐802.11devicesthatemitRFenergy(microwaveovens,medicalequipment,airconditioningunits,etc.)thatmayinterferewiththeproperoperationoftheAP?Inaddition,whatotherWi‐Finetworksarelocatedintheenvironment?Ifother5GHznetworksarenearby
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thereistypicallysufficientavailablechannelstoavoidinterference,howeverwith2.4Ghz(11b/g)thereareonly3usablechannelsandanearbynetworkalsousingthesecouldresultininterference.AtthispointthereshouldbesomediscussionbetweenITstaffstosetchannelsandpowertoavoidinterferencethatcoulddegradebothnetworksperformance.Aesthetic Issues–Aretherecorporatepoliciesthatrestrictthelocation,color,shape,etc.,oftheAccessPoint.Regulations/Codes/Policies–Aretheirspecificrulesthatthedeploymentmustconfirmto,suchasACpowerdistribution,cablingruns,RFpowerlimits,plenumrating,orotherissues.Arrivingonsitewithinappropriatecomponentscanaddexpensivedelays. Flexibility of environment–Manyenvironments‐especiallyschools,conferencecenters,warehouses,manufacturingfacilities–canbeveryphysicallydynamic.Fromonedaytothenext,wallscanbemoved,equipmentshuffled,racksrearranged,etc.Avisualwalkthroughandon‐sitediscussioncanidentifyandaddresstheseissuespriortotheinstallandavoidpostinstallcomplications.
Bottom line–Apredictivesurveyisofteneasiertoaccomplishbuthasthepotentialtomaketheactual
installmorecomplexduetounknownsthatcouldbeencountered.Anactivesitesurveythatincludesaphysicalwalkthroughismorecomplex,howeverwillmaketheinstallgosmootherbyidentifyingpotentialissuesupfrontandultimatelyresultinamoresuccessfuldeployment.
Survey Requirements Beforestartingasitesurvey,itisofcriticalimportancetodefinethepurposeofthesurvey.Itmayseemverybasictoincludethisasarequirement,howeveritisamazinghowmanysurveysareconductedwiththefocusonlyonRFcoverageandnoconsiderationgiventothereasonsforinstallingWi‐Fiinthefirstplace.
Thefollowingcomponentsshouldbeconsideredbeforeselectingavendororperformingasurveyastheywillhelpdeterminetheproductandsurveyrequirements.Business Requirements–Whatisthepurposeofadding/upgradingtheWi‐Fiservices?IsthegoaltojustaddWi‐Fihotspots,connectivityintheconferencerooms,orisitabuilding/campus‐widepervasiveWi‐Fiservicethatprovidesseamlesscoverageandroamingthroughouttheenterprise.Theanswertothisquestionwillhelpdeterminethevendors,productsandWi‐Fiarchitectureyouselect.Application Requirements–BandwidthandQoScapabilitiesdefinetheproductspurchased,howeverminimumRFsignalstrengthmustalsobeconsideredforvoiceoverWi‐Fisolutions.ThemajorityofWi‐Fiphonevendorsrequirea‐68dBmRSSI(receivedsignalstrengthindicator)orstrongersignal.Surveyingtothislevelavoidshavingtore‐surveyandaddAPs/cablingatalatertime.Security Requirements–Anothertopicoftenoverlookedduringasitesurveyissecurity.ControllingtheamountofRFenergytransmittedbeyondtheenterpriseboundaries(parkinglots,etc.)shouldalwaysbeaconsideration.WithproperAPplacement,powerlevels,anduseofdirectionalantennas,RFleakagecanbeminimized.ToclearlydefinetheedgeofRFcoverage,varypowerlevelsandrecordsignalstrengthreadingsoninsideandoutsidewallsoffacility.DirectionalantennacanalsobeusedforRFshaping.
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Coverage vs. Capacity–Mostvendorsofferseparatesurveyproceduresforcoverageorcapacitymodels.CoveragesurveysaredesignedtogenerateasolutionwiththeminimumnumberofAPstoguaranteeclientassociation.Capacitysurveysaredesignedtosupportlargernumbersofstationsandofferhigherdataratestoclients;thesetypicallygroupmoreAPsinasinglearea,resultinginsmallercellsandwithmoreradiochoicesforclients.Theresultistypicallystrongersignalstrengthconnectionsforclients,whichresultsinhigherdatarates.Cell Size Planning‐Wi‐Fiinthe5GHzband(802.11a/n)hasslightlysmallercellsthanWi‐Fiinthe2.4GHzband(802.11b/g/n).Designfor5GHzanditwillprettymuchensurecoverageforall802.11a/b/g/nclients.LargercellssizescanreducenumberofAPsrequired,butcouldresultinclientconnectivityproblems.Choosing Between 2.4 GHz or 5 GHz–BothbandsarecommonlydeployedinWi‐Finetworkstodayanditisstronglyrecommendedtoperformthesurveyforbothbands.
Wireless Bridging (WDS) Requirements–WillAPtoAPwirelessbridgingbeused?Thisquestionmaycomeupinoutdoordeployments,inwarehouseswhereintra‐APdistancescouldexceed100metersorevenbuilding‐to‐buildinglinks.Aspartofthesurvey,examinepoint‐to‐pointpathloss.Specialattentionshouldbepaidtoanytreesorfoliageinthepathasseasonalgrowthcouldimpactthelink.Wired Infrastructure –Don’toverlooktheexistingwiredinfrastructure,asitscapabilitiesorlackthereofcanseverelyimpactWi‐Fiperformance.Forexampleifdeploying802.11nWi‐Fi,theuplinkswillrequireGigabitlinks.VerifythecableplantandswitchesarecapableofGigabitEthernetorifawirednetworkupgradewillberequired.Inaddition,verifyAPpoweringoptions.IfPoEwillbeused,verifythatneworexistingPoEproductsprovidesufficientpower(802.3af,802.3at,orother)fortheWi‐Fitobedeployed(forexample802.11nrequiresincreasedpower). The 802.11n Site Survey –Theintroductionof802.11nhasaddedsomeconfusionandcaveatstothetraditionalsitesurvey.802.11nisnotabouthighertransmitpower,butaboutbetterreceiversensitivity(abilitytolisten).802.11nrangeimprovementsrequire11nradiosatbothendsoftheconnection‐thestationandAccessPoint.Themajorityofnetworksdeploymentswillincludeamixofclienttypes(802.11nandnon‐802.11n)andcellsizesshouldthereforeremainthesame.Somerecommendationsforperforming11nsurveysinclude:
• Alwayssurveyforboth2.4/5Ghz‐Thisisthesameasfor802.11a/b/gsurveysandisrecommendedsobothbandswillbeproperlysupported
• Usean802.11abgadapterforsitesurvey–Thisisrecommendedevenfor11nAPsassupportforlegacy802.11a/b/gdeviceswillcontinueforsometime
• Usean802.11abgnadapteronlyifallnetworkdeviceswillbe11ncapable–Althoughsomenetworksmaymeetthiscriteria,thevastmajorityofWi‐Finetworkswillbemixed11a/b/g/nenvironmentsforsometime
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Equipment Required Thissectionidentifiesspecificequipment,tools,andsoftwareXirrusrecommendsforperformingaprofessionalqualitysitesurvey.
Array/APs/Radios: UsethetypeofArrayorAPtobedeployed.Allsurveysshouldbeperformedusingproductsidenticaltothosethatwillbeinstalled;thisapproachhelpstoguaranteeinstalledcoveragematchesthatofthesurvey.Usingdifferentproductsforsurveyandproductioncouldresultinsignificantvariabilityinactualcoverage.
Support Equipment:
• Multiplecopiesofthefloorplanshouldbeavailabletotrackmountinglocations,recordobstructions,andindicatemountingoptionsandgeneralnotetaking.
• SurveysshouldbeconductedwithArrays/APslocatedascloseaspossibletowheretheywillbe
installed.XirrususestripodstolocateArrays.IfusingstandardAPs,itisrecommendtopolemountthemforeasierplacement.
• GeneralpurposeequipmentsuchasACextensioncords,Ethernetcabling,consolecables,ladders,flashlights,etc,shouldbeavailabletoassistonthesurvey.
• Acameraisdesirabletorecorduniquemountingobstaclessoappropriatemountscanbedefined.• Someformoflocationidentifiers(e.g.stickers)toindicatewhereArray/APswillbeplaced.
Software/Firmware Tools
Alaptopwiththefollowingtoolswillberequiredforthesurvey:• RFsurveytool,forexampleAirMagnetSurveyorsimilar.Alternativelyformoresimplesurveys,free
toolsthatreadWi‐Fisignalstrengthcanbeused.TheXirrusWi‐FiMonitorgadgetisafreetoolthatcanbeusedandisavailableathttp://www.xirrus.com/library/wifitools.php.
• OptionallysomeformofRFmonitoringtoolthatwillidentifynearbyAPsandperformSpectrumAnalysistoidentifypotentialnoisesources.TheXirrusWi‐FiArrayhasthesecapabilitiesbuilt‐inandcanbeleveragedduringthesurveyprocess.
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Performing the Survey ThissectiondescribesproceduresusedbyXirrustoperformasitesurvey.UsingthismethodologyandreadilyavailableWi‐Fitools,anITadministratorwithamoderatedegreeofWi‐Fiknowledgecanperformareasonablyaccuratesurveyoftheirown.Aspreviouslydiscussed,thesitesurveyisoneofthemostcrucialstepsinasuccessfulWi‐Finetworkdeployment.WithmanytechniquescommonlyusedforWi‐Fisitesurveysandthemanymodesof802.11a/b/g/n,ensuringthesurveyisdonerightismoreimportantthanever.Apoorlyperformedsitesurveydoesnotonlyimpactyounetworktoday,itcanresultinacostlyredesignwhenit’stimetoupgradeto802.11n.Componentsofaprofessionalsitesurveyperformedbyvendor‐qualifiedindividualsshouldinclude:
• Completeon‐sitesurveyofallareastobecovered,usingsameproductsthatwillbedeployed.
• On‐siteRFspectrumanalysistoidentifypotentialinterferenceissues.
• PostsurveyanalysisandreportincludingcoveragemapsandRSSIvalues.
• PostinstallsurveytoconfirminstalledWi‐Fiequipmentmeetsproposalrequirements.
Recommended Site Survey Parameters
• SignalStrength‐70dBmRSSI(orstronger)inallareastosupportfulldatarates• SignalStrength‐68dBmRSSI(orstronger)inallareastosupportWi‐Fivoicehandsets• Clientshouldbeabletoseeatleast2‐3radiosateverylocationthesesignallevels
Before Arriving On-site
• DiscussbusinessrequirementswithallwhohaveastakeintheWi‐Fisolution• Obtaindigitalfloorplansoffacilitytobecovered(e.g..jpg,.bmp,.png)• Ensureaccesswillbeavailableonthedayofthesurveytoallarea,orarepresentativesubsetof
area,thatistobecoveredbyWi‐Fi
Tips Before Starting
Thissectionincludesanumberoftipsandrecommendationstohelpensureasuccessfulandaccurate
survey.• ItisagoodideatodeployasmanyArraysasreasonable,asthiswillsimplifythesurveyprocessand
providesuperiorsurveymeasurementsvs.justusingjustoneArrayandcontinuallymovingandtakingmeasurements.
• SetupTripod/ArrayinsuchawaythatitcorrectlyrepresentshowtheArraywillbemounted• ForeachArrayandArraylocationduringthesurvey,useaseparateSSIDsospecificcoverageofeach
Arraycanbeeasilydistinguished.• SetArraybeaconrateto20ms‐thisenablesthesurveysoftwaretoreceivemanymorebeacons.
Afterthesurvey,don’tforgettoresetbeaconratetodefault.• Performsurveysunderworst‐caseusageconditionsfortheenvironment,forexampledoorsclosed,
curtainsdrawn,etc.• Beawarethateachclient(laptop/Wi‐Ficard/driver)willhaveslightlydifferentreadings.Thisisa
goodreasontobeconservativewhenperformingWi‐Fisurveys.
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• Performthesurveyatboth5GHzand2.4GHz.• Donotsurveyfor802.11nonlyunlessyouare100%surenolegacy(802.11a/b/g)clientswillbe
supported(notcommon)• Takemeasurementswhereuserswillbelocated:desks,tables,etc.• Takemultiplereadingsineachroom• ConsideradditionalsignalattenuationifArrays/APswillbeplacedinenclosuresoraboveceilings.• Inmulti‐floorbuilding,checkforfloor‐to‐floorbleed‐through.Ifsignificant,planforcoverageof
areasfromArrays/APsplacedabove/belowagivenfloor.StaggerthefinalplacementsoftheArrays/APsbetweenfloorstoaccountforthis.
• Constantlyconsiderinstallationconcernswhensurveyingandprepareaccordingly• Don’trush!
Getting Started ThissectiondemonstratesaprocessthatXirrushasfoundtobesuccessfulandaccurate.
1. StartwithlaptopinafarcornerofthefacilityandtheArray/APplacednearby.MovetheArray/APawayfromthelaptopuntilsignalstrengthdropsto,butnotunder,thespecifiedRSSIvalue(e.g.‐70)
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2. FindtheotheredgeofcoverageareabymovingthelaptopawayfromtheArray/APandsurveying
untilthesignalstrengthdropsto,butnotbelow,thespecifiedsignalstrengthvalues.
3. ThisdefinesthecoverageareaforthesingleArray;identifythelocationbyrecordingtheinformationonafloorplanandalsowithsomeformofphysicaltagging(e.g.stickersontheceiling)toidentifytheexactlocationwheretheArraywillbelocated.
4. Continuetorepeatthisprocessasyoumoveacrossthebuildinguntilthecompletefacilityhasbeensurveyed.Ifsurveyingamulti‐storyfacility,makesuretoverifyfloor‐to‐floorcoveragebeforeturningmovingtheArray.
5. UsetheArray’sRFMonitor/IntrusionDetectionfunction(orsimilartool)tofindotherAPsinthearea.AlldetectedAPsshouldbeidentifiedasknownorunknowndevicesandconsideredintheoverallsurvey.
6. UsetheArray’sRFMonitor/SpectrumAnalyzerfunction(orsimilartool)toidentifysourcesofinterference,either802.11co‐channelinterferenceornon‐802.11noise.Onceanoisesourceisidentified,defineaplanforinterferenceavoidance.Insomecases,discussionswithneighboringWi‐
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FinetworksITstaffshouldbesetuptoarrangeforchannelplanningandpowersettingcoordination.
7. Finally,sharecompletesurveyinformationwithallstakeholders.Discusscoveredareas,RSSIvalues,weakspotsandindicatehowmanyradiosareavailabletomobileusersthroughoutthefacility.Thislastpartiskeyaswerecommendatleast2‐3strongradiostoallclientstoprovideresiliencyandtoreducethepossibilityofasingleradiofailuretakingdownanyarea.
Exampleof‘Active’SiteSurveyresults(usingAirMagnettool)
Summary PredictivesitesurveysmaybeacceptableinsomelesscomplexWi‐Fideployments,howeverthelargerandmorebusinesscriticalyourWi‐Fiprojectis,themoreessentialanactivesitesurveybecomes.RollingoutWi‐Fiforalargeofficebuildingorcampusenvironmentmandatesanaccuratesitesurvey.Withlargeprojects,
evenbeingoffbyasmallpercentagecouldresultinunacceptableadditionalcostsassociatedwithadditionalequipment,cabling,andmanpowerrequirements.
Anactive,on‐sitesurveyusingtriedandtruebestpracticemethodologiesisthemostaccuratetypeofsurveyandXirrusstronglyrecommendsitbemadearequirementofanyWi‐Fideployment.
FinalThought‐YouarebettingthesuccessofyourWi‐Finetworkonthesurvey,andmaybeyourjob!
Wi-Fi Tools • Wi-Fi Basics FAQ – www.xirrus.com/library/faq.php
o Useful Wi-Fi FAQ for understanding the components, requirements and goals associated with performing a site survey
• Wi-Fi Tools – www.xirrus.com/library/wifitools.php o XirrushasassembledseveralusefulWi‐Fitoolsfoundtobeofgreatvalueinplanning,
deploying,andmanagingWi‐Finetworks. • Xirrus Wi-Fi Reference Posters –
www.xirrus.com/posters o Educational/reference
information on Wi-Fi
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• Xirrus Wi-Fi Widgets/Gadgets – www.xirrus.com/library/wifitools.php o The Xirrus Wi-Fi Monitor provides detailed information about surrounding Wi-Fi
networks and your laptop’s current Wi-Fi connection, including SSID, signal strength, IP address, MAC address, security level, vendor, and network type. This free tool can be used to perform simple site surveys.
Guide