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

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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

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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?

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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:

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

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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