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  • The Citrix Administrators

    Technical Guide to Understanding and

    Troubleshooting Citrix ICA/HDX

    2017 Goliath Technologies. All Rights Reserved

    By Marius Sandbu, CTP & Goliath Support Team

    "IfyoureallyneedtoreadoneCitrixTroubleshootingdocumentthisyear,thisisit!GoliathTechnologiestakesyouthroughthedifferentaspectsoftheICA/HDXprotocol,whatcanbeutilized,andwhatstepscanbeusedtounderstandissuesyoumaybeexperiencing."

    -AlexanderErvikJohnsen,CTP

  • 2

    TableofContents

    INTRODUCTION....................................................................................................................................3

    DEFININGICA/HDX...............................................................................................................................3A. THEHISTORYOFICA.............................................................................................................................3B. HOWICAWORKS.................................................................................................................................4C. HDX...................................................................................................................................................6D. ICAANDNETSCALERGATEWAY..............................................................................................................7

    HDXADAPTIVETRANSPORTPROTOCOL...............................................................................................9

    FRAMEHAWK.......................................................................................................................................9

    HDX/ICAANDITSDEPENDENCIES.........................................................................................................9A. NETWORKING......................................................................................................................................9B. SERVERPERFORMANCE........................................................................................................................12

    MEASURINGICAPERFORMANCE........................................................................................................12A. ICALATENCY.....................................................................................................................................13B. ICARTT...........................................................................................................................................13C. FRAMESPERSECOND..........................................................................................................................14

    TROUBLESHOOTINGICASESSIONPERFORMANCE..............................................................................14A. OVERVIEW.........................................................................................................................................14B. IMPACTONUSEREXPERIENCE...............................................................................................................16C. TROUBLESHOOTING.............................................................................................................................18

    ICACHANNELS....................................................................................................................................21A. TROUBLESHOOTINGWITHICACHANNELS...............................................................................................23B. CORRELATINGICACHANNELUSAGETOICAPERFORMANCEMETRICSFORTROUBLESHOOTING.......................24

    SUMMARY.........................................................................................................................................26

  • 3

    Introduction

    ThegoalofthedocumentthatyouareabouttoreadistoprovideacomprehensiveunderstandingofICA/HDX,thecomponentsthatitsbuilton,howitworks,howitcanbeimpactedbynetworkconditions,andhowtotroubleshootit.Armedwiththisinformation,wehopethatyouwillbebetterequippedtotroubleshootandresolvewhatwehavecometoknowastheubiquitousCitrixisslowcomplaintfromendusers.

    Thisdocumentwasco-authoredbytheCitrixsupportteamfromGoliathTechnologiesandMariusSandbu,CTP.GoliathproductsareusedbysomeofthelargestandmostsophisticatedCitrixdeploymentsworldwide.And,inanenvironmentwheresupportdirectlyfromCitrixisnotalwayshelpfulwhensolvingcomplexenduserexperienceissues,oursupportteamstepsintoassistcustomersdirectly.ThisdocumentisaresultofthedeepexperienceandknowledgegainedthroughthousandsofhoursspentwithourcustomersinthepursuitofsolvingtheirCitrixproblems.

    DefiningICA/HDX

    A. TheHistoryofICA

    BeforewecanstartdiggingdeepintothetechnicalspecificsofICA/HDX,wemustfirstunderstandwhatitis.TheIndependentComputingArchitecture,orICAisaproprietaryprotocoldevelopedbyCitrixover20yearsago.Thepurposeofthetechnologywastoallowforthedeliveryofapplicationsanddesktopcomputingenvironmentsindependentoftheenduserscomputingplatform.Inotherwords,tocreateaclient/servercomputingexperiencelikehowUnixapplicationsweredeliveredduringthemainframeera.Thegoalwastohaveawaytoconsumecomputingresourcesfromanydeviceorplatformindependentofplatformortransportprotocol.

    WhatdoesICAstandfor?

  • 4

    Initiallydevelopedin1992,theprotocolwaslicensedwithMicrosoftWindowsNTasWinFrame.Themulti-winengineatitscoreallowedmultipleuserstoleverageapplicationsfromasingleWindowsoperatingsystemsimultaneously.In1997thistechnologywaslicensedtoMicrosoftandbecameknownasRemoteDesktopProtocol(RDP).

    FurtherdevelopmentfromCitrixfollowingtheintroductionofWindowsTerminalServicesenhancedthecapabilitiesofICA,separatingitfromthebasiccapabilitiesofferedbyMicrosoftRDP.TheenhancementstoICAallowedCitrixtosupportapplicationpublishing,lowbandwidthrequirements,encryptionandsessionreliabilityamongothers.ThisversionofICAiswhatformsthefoundationoftheprotocolthatXenAppandXenDesktoparedeliveredfromtoday.

    B. HowICAWorks

    TheICAprotocoloperatesatthepresentationlayer(layer6)oftheOSImodel(wewilldetailtheOSImodellaterinthisdocument).Atthislayer,dataispreparedtobepresentedattheapplicationlayer(layer7).Itfunctionsbydeliveringinputfromtheclienttotheserver,aswellasprovidingoutputsuchasvideoandaudiofromtheserverbacktotheuser.Thispresentationlayertrafficflowsoverport1494(ICA)and2598(sessionreliability)bycreatingdynamicallyallocatedTCPportsforclient/servercommunication.Inside,theprotocolvirtualchannelsareusedforfunctionssuchasprinting,typing,video,audioandUSBamongothers.LaterinthisdocumentwewillprovidemoredetailaroundICAandHDXchannels,howtheywork,andhowtheyimpactoveralluserexperience.Inadditiontoleveragingvirtualchannelsformanagingtraffic,ICAalsomanagesuserexperiencewithSessionReliability.Thiscapabilityallowssessionstoremainactiveonthescreeneveniftheenduserssessionconnectivityisinterrupted.Thiscapabilityallowsforresiliencyandconsistencyevenwhenusersareonunreliablenetworkconnectionsormobile.Thespecificsonsessionreliabilityareshowninthegraphbelow.

    ICAinRealLife:

  • 5

    SessionreliabilityisreliantontheCommonGatewayProtocol,whichisaserversidereplaythatstripsawaytheCGPlayerandthenforwardsICAtraffictotheICAlisteneron1494.TheservicebufferstrafficifthenetworklinkbetweentheclientandtheXAorXDserverisbroken.Whileasessionisbuffering,thescreenfreezesandtheuserispresentedwithaspinninghourglassuntilthesessionsconnectivityreturns.ThisiswherethehourglassofdeatheffectcomesfromintheCitrixsessions.Whilesessionreliabilityisinconceptagoodidea,thespinninghourglassisgenerallyperceivedasanissueandoftenresultsinconfusionandfrustrationforusersthatdonothaveanyindicationastowhytheirsessionsuddenlylockedup.

  • 6

    Fromabandwidthperspective,theICAprotocolwasdesignedduringatimewhenthemostcommoninternetconnectionwasa56Kmodem.Needlesstosay,theprotocolisoptimizedforWANandhighlatencynetwork/internetconnections.ItalsosupportsQuality-of-Service(QoS)andothernetworkfeaturesforperformanceoptimization.Overtimeasapplicationsanduserexperiencehasbecomemoregraphicallyintensive,newfeatureshavebeenimplementedtohelpwithdeliveringaqualityexperienceoverlessthanreliableconnections.Off-loadingofgraphicsrenderingorvideodisplayhavebeenimplementedtohelpeasethestrainoftheICAsessionandimprovereliability.InthenetworksectionofthisdocumentwewilldiscussindetailhownetworkbandwidthaffectsICA/HDXtrafficandhowitcanbeoptimizedtominimizetheimpact.

    C. HDX

    HDXhasbecomethemodernacronymgiventothedeliveryprotocolforXenDesktopandXenApp.AlthoughmanyseethisastheevolutionofICA,thatdefinitionisabitofamisnomer.HDXinandofitselfdoesnotreplaceICA.Rather,itisasetofcapabilitiesdesignedtoenhancetheuserexperienceforsessionsdeliveredoverICA.TherearethreekeycapabilitiesthatcomprisetheunderpinningsforHDXperCitrix.Theyareintelligentredirection,adaptivecompressionanddatade-duplication.Eachcapabilityworkstogethertoenhancethequalityofuserexperiencewhilereducingsessionbandwidthdemands.

    Intelligentredirectionisanoff-loadingcapabilitythattakesseveralfactorsincludingscreenactivity,applicationcommands,endpointdevice,networkandservercapabilitiesintoconsiderationtodeterminehowandwhentobestoffloadprocessingtotheendpoint.Thissmarterformofredirectionalsoincludesdevicesandperipheralssuchaswebcams,printersandscannersthatalloperateatnativeUSBspeedsusingthiscapability.

    AdaptivecompressionisproprietarytoCitrixandICA,anditsetsthecodecsusedduringsessions.ItalsointelligentlyallocatesandmanagesthewaytheCPUandGPUresourcesareleveraged.

    De-duplicationisaformamulticastingandcachingthatallowsforthereductionofduplicatenetworkdatafromtraversingthenetwork.Multi-castisprimarilyusedformultimediastreamstoensureasingledeliveryofdatathatmaybeconsumedbymorethanasingleuser.Cashingde-duplicatesdatathatiscommonlyaccessedsuchasdocumentfiles,printjobsandbitmaps.

    HDXareenhancedcapabilitiesthatbringamorenativefeelanduserexperiencetoICA.Thesecapabilitieswerepurposebuiltandintroducedtoallowforg

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