Transport System Architectures for High-Performanc

TransportSystemArchitecturesforHigh-PerformanceCommunicationsSubsystemsDouglasC.SchmidtandTatsuyaSudaDepartmentofInformationandComputerScience,UniversityofCalifornia,IrvineIrvine,CA92717,U.S.A.AnearlierversionofthispaperappearedintheIEEEJour-nalonSelectedAreasinCommunication,Vol.11,No.4,May1993.AbstractProvidingend-to-endgigabitcommunicationsupportforbandwidth-intensivedistributedapplicationsrequireshigh-performancetransportsystems.Thispaperdescribesandclassifiestransportsystemmechanismsthatintegrateoper-atingsystemresources(suchasCPU(s),virtualmemory,andnetworkadapters)togetherwithcommunicationpro-tocols(suchasTCP/IPandXTP)tosupportapplicationsrunningonlocalandwideareanetworks.Ataxonomyispresentedthatcomparesandevaluatesfourwidelyavailabletransportsystemsintermsoftheirsupportforprotocolpro-cessing.ThesystemscoveredinthispaperincludeSystemVUNIXSTREAMS,theBSDUNIXnetworkingsubsystem,thex-kernel,andtheConduitframeworkfromtheChoicesoper-atingsystem.Thispaperisintendedtohelpresearchersnavi-gatethroughthetransportsystemdesignspacebydescribingalternativemechanismsfordevelopingtransportsystems.1IntroductionThedemandformanytypesofdistributedapplicationsisexpandingrapidly,andapplicationrequirementsandusagepatternsareundergoingsignificantchanges.Whencoupledwiththeincreasedchannelspeedsandservicesofferedbyhigh-performancenetworks,thesechangesmakeitdifficultforexistingtransportsystemstoprocessapplicationdataatnetworkchannelspeeds.1Thispaperexaminestransportsystemmechanismsthatsupportbandwidth-intensivemul-timediaapplicationssuchasmedicalimaging,scientificvi-sualization,full-motionvideo,andtele-conferencing.Theseapplicationspossessquality-of-servicerequirementsthatare1Atransportsystemconsistsofprotocolfunctions(suchasconnectionmanagement,end-to-endandlayer-to-layerflowcontrol,remotecontextmanagement,segmentation/reassembly,demultiplexing,messagebuffering,errorprotection,andpresentationconversions),operatingsystemservices(suchasmessagebuffering,asynchronouseventinvocation,andprocessmanagement),andhardwaredevices(suchashigh-speednetworkadapters)thatsupportdistributedapplications.significantlydifferentfromconventionaldata-orientedappli-cationssuchasremotelogin,email,andfiletransfer.Multimediaapplicationsinvolvecombinationsofrequire-mentssuchasextremelyhighthroughput(full-motionvideo),strictreal-timedelivery(manufacturingcontrolsystems),lowlatency(on-linetransactionprocessing),lowdelayjitter(voiceconversation),capabilitiesformulticast(collabora-tiveworkactivities)andbroadcast(distributednameres-olution),high-reliability(medicalimagetransfer),tempo-ralsynchronization(tele-conferencing),andsomedegreeoflosstolerance(hierarchically-codedvideo).Applicationsalsoimposedifferentnetworktrafficpatterns.Forinstance,someapplicationsgeneratehighlyburstytraffic(variablebit-ratevideo),somegeneratecontinuoustraffic(constantbit-ratevideo),andothersgenerateshort-duration,interactive,request-responsetraffic(networkfilesystemsusingremoteprocedurecalls(RPC)).Applicationperformanceisaffectedbyavarietyofnet-workandtransportsystemfactors.Networksprovideatransmissionframeworkforexchangingvarioustypesofin-formation(suchasvoice,video,text,andimages)betweengateways,bridges,andhosts.ExamplenetworksincludetheFiberDistributedDataInterface(FDDI),theDistributedQueueDualBus(DQDB),theAsynchronousTransferMode(ATM),X.25networks,andIEEE802LANs.Ingeneral,thelower-layer,link-to-linknetworkprotocolsareimplementedinhardware.Transportsystemsintegratehigher-layer,end-to-endcom-municationprotocolssuchasTCP,TP4,VMTP,XTP,RPC/XDR,andASN.1/BERtogetherwiththeoperatingsys-tem(OS)mechanismsprovidedbyendsystems.Thetasksperformedbythetransportsystemmaybeclassifiedintosev-erallevelsofabstraction.Thehighestlevelprovidesanappli-cationinterfacethatmediatesaccesstoend-to-endcommuni-cationprotocols.Theseprotocolsrepresentanintermediatelevelofabstractionthatprovidespresentationandtransportmechanismsforvariousconnectionless,connection-oriented,andrequest-responseprotocols.Thesemechanismsareim-plementedviaprotocoltaskssuchasconnectionmanage-ment,flowcontrol,errordetection,retransmission,encryp-tion,andcompressionschemes.Boththeapplicationin-terfaceandtheprotocolsoperatewithinanOSframeworkthatorchestratesvarioushardwareresources(e.g.,CPU(s),1primaryandsecondarystorage,andnetworkadapters)andsoftwarecomponents(e.g.,virtualmemory,processarchitec-tures,messagemanagers,andprotocolgraphs)tosupporttheexecutionofdistributedapplications.Performancebottlenecksareshiftingfromtheunderlyingnetworkstothetransportsystem.ThisshiftisoccurringduetoadvancesinVLSItechnologyandfiberoptictransmissiontechniquesthathaveincreasednetworkchannelspeedsbyseveralordersofmagnitude.Increasingchannelspeedsac-centuatecertainsourcesoftransportsystemoverheadsuchasmemory-to-memorycopyingandprocessmanagementoper-ationslikecontextswitchingandscheduling.Thismismatchbetweentheperformanceofnetworksandthetransportsys-temconstitutesathroughputpreservationproblem,whereonlyaportionoftheavailablenetworkbandwidthisactuallydeliveredtoapplicationsonan