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1 SDLSpecicationandVericationofaDistributedAccess GenericOpticalNetworkInterfaceforNetworks ydepartmentofelectricalandcomputerengineering SharifM.ShahrieryRoyM.Jeneveinz zdepartmentofcomputersciences UniversityofTexasatAustin Austin,TX ofeachlineissharedbyallthenodesintheclustertomakemoreecientuseofbandwidth. allowsclustersofnodestobeconnectedtoannetworkviaber-opticlines.thecapacity nameddragon(distributedaccessgenericopticalnetwork)fornetworks.theuni ofmessagearrivals,byconsideringagloballydistributedqueue.anovelschemeisproposed ThispaperpresentsthedesignandspecicationofaBISDNuser-to-networkinterface(UNI) Withineachcluster,transmissionsarescheduledonrst-come-rst-served(FCFS)order Abstract reservationchanneliscontrolledbythereservationring:atokenringnetwork.allaccessesfor thequeueslotsarecompletelyfairandthebandwidthattainableisindependentofthepositionofthenodewithinthecluster.unlikepreviousdistributedqueueprotocols,thedragosagetransmissionscanproceedindependentlyandconcurrently.thereservationchannelisa facilitatesbothxed-sizedandvariablesizedtransmissions. broadcastchannelfornotifyingnodeswithintheclusterwhentoreserveaslot.accesstothe forcontrollingaccesstotheber-optictransmissionnetwork.byusingtwologicallyseparate subnetworkscalledthereservationchannelandthereservationringslotreservationsandmes- IndexTerms{computernetworks,BISDN,,UNI,SDL. dardspecicationanddescriptionlanguage(sdl).themodelwassimulatedandvalidated acertaincorrectlogicalbehavior.themodelwasthenindependentlyveriedusingtwodierent algorithms:bit-stateandrandomwalk.theresultsshowedthatthedesignwasveriedtoa highdegreeofcoverage. usingthesdt3.02toolsetfromtelelogic.anextensivesetofsimulationswereconductedto Weconstructedanextendednitestatemodel(EFSM)oftheDRAGONusingITUstan-

2 1Introduction BroadbandIntegratedServicesDigitalNetworks(BISDN)havebeenanactiveareaofresearchover thelastdecade.bothlocalandmetropolitanareanetworks(lans&mans)haveappearedin academicsites.tosupportthediverseapplicationsrequiredofbisdnnetworks,alargenumberof greatproliferationinthemarketplace,andalargenumberhavebeendeployedincommercialand protocolshavebeendeveloped,forexampleatm[1],sonet[2],[3],framerelay[4],x.2[], allowtransmissionathundredsofmegabytespersecond.recently,internationalstandardsfor BISDNhasbeenproducedbytheInternationalTelecommunicationsUnion(ITU)sothatequipment andmanyothers.opticalbersprovidethetransmissioninfrastructureforbisdnnetworksto producedbydierentmanufacturerswerecompatiblewithoneanother. andminimizesthedelayanddelayjitter.itisalsopossibletodeterminetheupperdelayboundof delayanddelayvarianceofallothertransmissionpolicies[7].thus,itmaximizesthethroughput ofmessagearrivals.thisisanoptimaltransmissionpolicyinthesensethatithasthesmallest interfacebetweenthehostnodeandthebroadbandnetwork.inthispaper,wedesignedaswitched Network).TheDRAGONallowsaclusterofnodestosharethesametransmissionmediumatthe UNI,byschedulingtransmissionsinagloballydistributedFirst-Come-First-Served(FCFS)order MultimegabitDataServices()UNIcalledDRAGON(DistributedAccessGenericOptical Animportantpartofbroadbandnetworksisthetheuser-to-networkinterface(UNI)[6]:the inequalitytoestimatetheupperdelaybound.thishadbeenillustratedin[8]. cells.onemethodistoestimatethemeanandvarianceofthecelldelayandthenusechebyshev's ofthisschemehavebeenimplementedinothernetworks,forexampledqdb[9],hangman[10]and S++[11].Oneofourmainobjectivewastoimproveonthepreviousdistributedqueuedesigns. andcannotbeapplieddirectlytomultiplenodeclustersconnectedtoasinglehigh-speedber-optic Recently,therehadnotbeenagreatdealofinterestintheDQDBtypeofprotocols.Wehopethat theimprovementswe'veproposedtothedistributedqueuearchitecturewillgeneratemoreinterest. ThedistributedqueueintheDRAGONiscalledareservationqueue(RESVQ).Othervariants line,asisthecaseinourdesign.ourdesignisalsodierentinthatslotreservationsandmessage transportingslotreservationinformation.dqdbands++usesthesamechannelfortransmissions thetransmissionbandwidthcanbeutilizedfortransmittingmessages,andnoneofitisutilizedfor thesameopticalmedium,bymeansofwavelengthdivisionmultiplexing(wdm).thismeansall andslotreservations.accesstotheslotsinthedragonarecompletelyfairandisindependent transmissionscanproceedindependentlyandconcurrentlyonseparatelogicalchannels,bysharing Mostofthepreviousdistributedqueueprotocolsweredevelopedfordualslotted-busnetworks aslot,andconsequentlythebandwidthattainabletoanodeisdependentonitspositioninthe ofthenodespositionwithinthecluster,whereasindqdbthenodesclosesttotheslotgenerators haveagreaterchanceofreservingaslot.hence,downstreamnodeshavefewerchancesofacquiring network.thisproblemdoesnotarisewiththedragon. directlyfortransmittingvariable-sizedpacketssuchasx.2andframerelay.thedragon,however,issuitableforbothxed-sizedpacketandvariable-sizedpackettransfers.wehavedeveloped aandframerelayversionsofthedragontoillustratethispoint,andperformanceresults DQDBandS++transmitsonlyxed-sizedsynchronouspackets.Thus,theycannotbeused 1

3 arepresentedin[12].andnally,weincludedareservationfifowithinthedragonsothat slotreservationsformultiplenumberofmessagescanbemade.thisfeaturewasnotsupportedby thedqdbands++protocols,thustheycanonlyreserveonemessageslotatatime. AdaptationLayer3/4ConvergenceSublayer-ProtocolDataUnit).Layer2takestheseframes layerprotocolsandconvertsitintovariablesizedframesreferredtoasaal3/4cs-pdu(atm SONET/STS-1payload.ThecellsarethentransportedviaSONETtoanswitchingnetwork. TheSIPisorganizedintothreelayers.Thehighestlayer,layer3,acceptsdatafromthehigher themtothesonet/interface(ssi)atarateof49.4mbits/sec,i.e.thecapacityofthe andconvertsitintoxedsizedcellsof48bytepayloadandbyteheaderreferredtoasaal3/4 formofxedsizedcells.theinterfaceprotocol(sip)convertsdataintocellsandtransmits AnnetworkarchitectureisshowninFig.1.Dataistransmittedinthenetworkinthe destinationcluster. cellsareagainremappedontothests-1payloadandtransportedovertheber-opticlinetothe areextractedfromthests-1payloadandroutedviatheswitches.beforeleavingthenetwork,the SAR-PDU(ATMAdaptationLayer3/4SegmentationAndReassembly-ProtocolDataUnit).The AAL3/4cellsareencapsulatedontoaSTS-1payloadbytheSSIandtransmittedovertheberopticlineatarateof1.84Mbits/sectothenetwork.Attheswitchingnetwork,thecells Upper Upper layers layers SIP SIP Upper Upper layers layers SIP SSI with SSI SIP switches Upper Upper layers layers SIP SIP areseveraltoolsforsdl,butweenteredacompletesetofsdl/gr(graphicalrepresentation) Figure1:networkwith4nodeclusters Upper Upper layers layers SIP SIP Upper Upper layers layers ensurethatthesdlmodelofthedragonconformstotheoriginalspecication.thiswasdoneby testingwereperformedtoensurethatthedesignfunctionedcorrectly.conformancetestingwasto proprietaryinternationalstandardnotationbasedonextendedfinitestatemachines.there waspresentedinsdl(specicationanddescriptionlanguage)[13,14,1,16].thisisanon- diagramsintothesdt(sdldesigntool)fromtelelogic.finally,conformanceandvalidation cycleconsistsofadualtrackapproach.intherstphase,aformalspecicationofdragon AdiagramdepictingthedevelopmentstepsoftheDRAGONisshowninFig.2.Thedevelopment SIP SSI SSI SIP simulatingthesdlsystemusingaknownsetofinputsandobservingtheoutputs.validationwas performedusingtwowellestablishedalgorithmscalledbit-stateandrandom-walk[17,18].these Upper Upper layers layers SIP SIP methodswereprovidedbythesdlvalidator.thesecondphaseofdevelopmentconsistsofan RTLimplementationmodelofDRAGONinVHDL.Extensivetimingsimulationswereperformed 2 RESERVATION RING RESERVATION RING RESERVATION BUS RESERVATION BUS SONET SONET SONET SONET RESERVATION BUS RESERVATION BUS RESERVATION RING RESERVATION RING

4 completesetofsdlspecicationdiagramsofthedragon.section4providesadescriptionof Section2providesaninformaldescriptionoftheDRAGONarchitecture.Section3presentsa anintegratedmixofvideoanddatatracusingactualtracesprovidedbybellcore.thispaper isconcernedwiththesdlmodelingandvalidationofdragon.thertldevelopmentaspects weretreatedinaseparatepublication[8,19].theremainderofthepaperisorganizedasfollows. usingconcurrentvideoanddatatrac.tracedrivenperformancesimulationwasperformedusing arepresentedinsection.thepaperisconcludedinsection6. thetwovalidationmethodsusedinthiswork.theconformancetestandvalidationcoverageresults CONFORMANCE TESTING PERFORMANCE ANALYSIS Figure2:DevelopmentstepsoftheDRAGONinSDL VHDL MODEL USER SPECIFICATION MODEL understanding.theinterconnectionofthenodeswithinaclusterisshowninfig.3.allaccessesto thenetworkmustbecontrolledsothattherearenocollisions.thisisdoneinpartbytwodierent ThissectionprovidesaninformalpresentationoftheDRAGONarchitecturefortheclarityof 2.1TheClusterOrganization 2TheDRAGONOverview CONFORMANCE VALIDATION TESTING asfollows. (RESVQ).Onlyonenodeatatimecansendonthereservationbus.Thus,topreventmorethan1 nodetransmittingsimultaneously,areservationringisused.thereservationringisahigh-speed, broadcastchannelusedfornotifyingallnodeswhentoreserveoneslotinthereservationqueue single-bittokenringnetworkforcontrollingaccesstothereservationchannel.thechannelsoperate subnetworks:thereservationbusandthereservationring.thereservationbusisasingle-bit afterthetokenisreceived,thenodeisonlyallowedtoreserveaslotintheresvq;itcannot Thereservationringhasbasicallyasingle-bittokenringarchitecture.Thedierenceisthat 3

5 RESERVATION RING RESERVATION BUS passesthetokentoitssuccessornode.ifhowever,amessagehasarrivedatanode,thenode transmitpacketsimmediatelyafterreceivingthetokenasinnormaltokenringnetworks.asignal calledtokencirculatesaroundthereservationring,passingfromonenodetothenext.ifno Figure3:LANconguration NODE NODE NODE / FROM SOFI subnetworksandmaysharethesameber-opticmediumbywdmtechnique. newmessageshavearrivedatanode,thenodedoesn'treserveanyslotsintheresvq.itsimply waitsforthetoken,reservesaslotinitsresvqandnotiesallothernodestoalsoreserve channel,andthusnocollisions.thereservationchannelandthereservationringareindependent aslotbytransmittingaresvsignalonthereservationchannel.thetokenisthenpassed guaranteethattherewillbenomultiplesimultaneoustransmissionsofresvonthereservation toitssuccessor.hence,byrequiringanodetoownthetokenbeforebroadcastingresvwill / FR routesarebidirectional.thesonettransmitandreceivelinkstoandfromtheswitchingnetwork indicatedbythesignalnamesplacedinsidesquaredbrackets.thedirectionofthesignalisindicated 2.2TheDRAGONPrototypeandDatapath eachofthefunctionalunitswithinthedragonprototype.acompletedescriptionofthesignals byarrowheads.someofthesignalrouteshavearrowheadsatbothends,inwhichcasethesesignal thedragontothesofiarelabeledpktxmtandpktrcvrespectively.next,weshalldiscuss WeshallnowprovidethelayoutoftheindividualfunctionalunitswithintheDRAGON.Ablock arecalledsonetxmtandsonetrcvrespectively.thetransmitandreceivelinesconnecting diagramofthedragonprototypeanditsdatapathsignalsareshowninfig.4.signalsare andtransitiontablesforthenitestatemachinesareprovidedin[8]. nodesmustbeupdated.thebasicblocksoftheresvqconsistofthereservationqueue,the alsoanexternalinterfacenamedsofiwhichissharedbyallthenodesinthecluster. arrives,aslotmustbereservedinthereservationqueue.consequently,theresvqsofallthe reservationqueuecontroller,thereservationringcontrollerandthetransmitter/receiver.thereis Everynodeinthenetworkcontainsareservationqueue.Asexplainedpreviously,afteramessage 2.3TheReservationQueue(RESVQ)Operation 4

6 SONETrcv SONETxmt SONET/STS-1 fiber optic line. SOFI PKTxmt Connections to/from other nodes in the cluster. RESV.chl DRAGON Figure4:TheDRAGONprototypeanditsdatapath HEAD_CTR HEADctrl RESV SNTX PKTrcv HEADstat FIFOstat RESERVATION RESV_ FIFOctrl NTX TRANSMITTER QUEUE AND FIFO CONTROLLER RECEIVER TAILstat PKTinp TAILctrl TAIL_CTR PKTout ReservationQueueController:FSMforcontrollingtheoperationoftheRESVQ,includingassigningtransmissionslotsandupdatingthequeueforschedulingthenexttransmission. Containsup/downslotCOUNTER. ReservationQueue:ReservesFCFSslotspertainingtotheorderofmessagetransmissions. Containsanup/downcounternamedTAILCTR,adowncounternamedHEADCTRanda SLOTgnt RING CONTROLLER RESV TOKin TOKout ACKin ACKout VidReq DatReq Transmitter/Receiver:TransmitsandreceivesmessagestoandfromtheSONET/STS-N ReservationRingController:FSMtoperformallfunctionsofthetokenaccesscontrol. FIFOnamedRESVFIFO. RESET START SONETFiber-OpticInterface(SOFI):Externalinterfacesharedbyalltheclusternodes. network.messagesmayconsistofasequenceofcellsorfrframe. provideanoverviewoftheentiresystem. Inthefollowingsections,weshallprovideanoverviewofeachfunctionalunit.Butrst,we toallthenodesattheendofeverymessagetransmission. ItperformsmappinganddemappingofmessagepacketsontoSONETframes[20].Itinsets stu(idle)bytesintothesonetpayloadwhennecessary.italsobroadcastssignalsntx

7 Initially,everynodeintheclusterwaitstoreceiveaTOKen.Afteritisreceived,thenodechecks whetherithasanymessageswaitingtobescheduledfortransmission.ifitdoesn't,thetoken AowdiagramdepictingtheentireoperationoftheslotreservationprocedureisshowninFig. 2.4SystemsOverview issimplypassedontoitssuccessor.if,however,amessageiswaiting,theinterfacebroadcaststhe signalresvtoalltheothernodesintheclusteroverthereservationbus.everynodemonitors forthemessage.thetokenisthensenttothesuccessornode,andtheprocessrepeats. thereservationbus,andwhenitdetectstheresv,theresvqisupdatedandaslotisreserved andtheresvqcontrollerhasbeengroupedtogetherintoasingleowchart,andlikewisethe describeeachofthe4functionalunitsofdragonandthesofiusingow-charts.theresvq Transmitter/ReceiverandSOFIhavealsobeengroupedtogether. Transmitterwillthenbeginsendingcells/framestotheSOFI.Inthefollowingsections,weshall received,thenodesupdatetheresvqtodeterminewhichnodeistotransmitnext.whichever nodeisthenexttotransmit,itsresvqwillsendthesignalntxtoitstransmitter.the SOFI.SNTXisbroadcasttotheclusterattheendofeverymessagetransmission.IfSNTXis IfaTOKenisn'treceived,theinterfacecheckswhetherthesignalSNTXhadbeensentbythe slot.whenanewmessagearrivesatthedragon,thecounterisincrementedby1,and TheCOUNTERregistersthenumberofoutstandingmessageswaitingtobeallocatedaRESVQ toreceiveatokenfromitspredecessor.itthenacknowledgesitspredecessorbysendingthe acknowledgementacksignal.thenodethencheckswhetheritscounterislargerthanzero. 2.TheReservationRingController anytimeitiszeroitmeanstherearenopendingmessagessothetokensimplypassedtothesuccessornode.otherwise,thecontrollersendssignalslotgnttotheresvqandthecounter isdecremented.thereservationbusismonitored,andaftersignalresvhadbeenbroadcastby Theowchartforthereservationring(RESVRING)controllerisshownin6.Eachnodewaits theresvq,tokensignalissenttothesuccessornode. 2.6TheReservationQueue compositevaluesofalltheresvfifoelementsisthenumberofmessageswhichmustbeserviced hadreceivedslotgntfromtheresvringcontroller,andifso,itbroadcastsresvoverthe theresvfifoandclearsthetailctr.thedowncounternamedheadctrvalueplusthe reservationbus.subsequently,itincrementsitstailctr,writesthetailctrcontentsinto TheowchartforreservingaslotisshowninFig.7.Everynodeintheclustercheckswhetherit 2.6.1ReservingaSlot beforethecurrentlyreservedmessagecantransmit. Forexample,supposethatallthemessageshaveequalpriority.Further,supposethatatthis 6

8 Receive TOKen? message waiting? Receive SNTX? Broadcast RESV Update RESVQ Detect Receive Figure:TheDRAGONsystemsoverview RESV NTX? Update transmit RESVQ message Send TOKen 7

9 Receive TOKen? Send ACK to predecessor COUNTER>0 Send SLOTgnt to RESVQ Decrement COUNTER Figure6:Reservationringcontroller Monitor reservation bus Detect RESV? Send TOKen 8 to successor

10 element.thus,thenewlyarrivedmessagewillhavetowaituntil17(3+7+2+)messageswhich instantheadctr=andresvfifo=f3,7,2g,where`2'istheheadelementand`3'isthetail hadarrivedbeforeittobeservicedbeforeitcantransmit.intheexample,thenodehadscheduled prioritymessagewillbetransmittedwhentheheadctrcountsdowntozero,irrespectiveofthe aslotallocatedtoahighprioritymessageandtheremaining3arelowprioritymessages,thehigh HEADCTR>0. vationsarestillmadeintheusualway:butthehigherprioritymessagewillalwaysbetransmitted 4messagesfortransmission.ThisisgivenbythenumberofRESVFIFOelementsplusone,ifthe therebyreservingaslotforsomeothernodewithinthecluster. receiveslotgnt,butdetectsresvonthereservationbus:itwillincrementitstailctr, factthattheslotwasallocatedtoalowprioritymessage.further,supposethatthenodedoesn't aheadofallthelowerprioritymessages.forinstance,ifthetailelement`3'intheresvfifois Now,ifthereweretwodierentprioritiesofmessages,asinthecaseofvideoanddata,slotreser- Receive SLOTgnt? Send RESV Detect RESV? Figure7:Reservingaslot Increment Increment TAIL_CTR TAIL_CTR Write TAIL_CTR to RESV_FIFO andifso,itdecrementstheheadctr.thenewheadctrvalueisnow4anditsignies checkingthevalueoftheheadctr.first,considerthepreviousexamplewhereheadctr= andresvfifo=f3,7,2g.theresvqcheckswhetherithasreceivedsntxfromthesofi, Theowchartforschedulingamessagefortransmissionisshownin8.Theprotocolinitiatesby 2.6.2SchedulingaTransmission Clear TAIL_CTR thenumberofothernodesthatmustbeservicedbeforethisnodecantransmit.thus,afterthe 9

11 nodecantransmit.ifresvfifoisemptyandheadctriszeroandsntxis,the thenumberoftransmissionsthatmustbemadebytheothernodeswithintheclusterbeforethis TAILCTRisdecrementedifitsvalueisnon-zero.WhenHEADCTRandRESVFIFOareboth HEADCTRreacheszero,signalNTXissenttotheTransmitter/Receiverblockinformingitto sinceitsnotempty,thetopelement`2'isloadedintotheheadctr.asbefore,thisvalueis begintransmission. butnotthisnode. empty,anon-zerotailctrsigniesthenumberofmessagesscheduledforotherclusternodes: Next,considerthecasewhereHEADCTRisequaltozero.TheRESVFIFOischecked,and HEAD_CTR >(0) =(0) not_empty Receive RESV_FIFO SNTX? empty Decrement Receive Load HEAD_CTR SNTX? HEAD_CTR 2.7TheTransmitter/Receiver >(0) =(0) TheowchartdeningtheTransmitter/ReceiverandSOFIcombinationisshowninFig.9and10. Figure8:Schedulingatransmission HEAD_CTR TAIL_CTR =(0) >(0) missionofpackets.fig.10describeshowpacketsareextractedfromincomingsonetframesand TheowchartinFig.9showshowtheSOFIinteractswiththenodesforschedulingthetrans- transportedtothedestinationclusternode. Send NTX to Decrement Transmitter TAIL_CTR 2.7.1TransmittingPackets aclusternode,itcheckswhetherthemessageconsistsofcellsorfrframe.ifthemessage Fig.9showstheprocedurefortransmittingpackets.AftertheSOFIreceivesamessagepacketfrom 10

12 network.foreverycell,itstypeasindicatedbythesteldinthepayloadischecked.ifthecell typeisbomorcom,itmeansthatthemessagetransferisnotcomplete.thus,thenextcellis transmitted. is,theneachcellofthemessageistransmittedtothesofi,whereitismappedonto thesynchronouspayloadenvelope(spe)ofasonetframeandtransmittedoverthesonet themessagetypeisfr. thesofibroadcaststhesignalsntxtothenodestonotifythemofthiscondition.eachnode willthenupdateitsresvqbydecrementingtheirrespectiveheadctrsorthetailctrsas Transmitter,andthenextmessagetransferwillbegin.Asimilarsequenceofeventsoccurswhen explainedearlier.thenodewhoseheadctrdecrementsfrom1!0willissueanntxtoits IfthecelltypeisSSMorEOMitmeansthatthemessagetransmissioniscomplete,andso Receive NTX? message type? FR point to next (first) message cell transmit frame to SOFI transmit cell to SOFI map frame onto SONET SPE map cell onto SONET SPE transmit over SONET network Figure9:Transmittingpackets Send SNTX transmit over to all SONET network RESVQs 11 cell type? BOM/COM SSM/EOM Send SNTX to all RESVQs

13 2.7.2ReceivingPackets IDwiththeMultiplexingIdentier(MID)valueofthecells,(b)FR:comparingitsIDwiththe TheowchartdescribingthemethodforreceivingpacketsisshowninFig.10.AfteraSONET frameisreceivedfromtheswitchingnetwork,thesofidemapsthepacketsfromthespeofthe Thenodescandeterminewhetheritistherecepientofthepacketby:(a):comparingits incomingframe.allthestubytesareignoredandvalidpacketsarebroadcasttoallthenodes. DataLinkConnectionIdentier(DLCI)oftheframe.Ifamatchoccursthepacketisaccepted, otherwiseitisrejected.conn monitor SONET network SONET frame? message type? FR Demap cell(s) from SONET SPE Demap frame(s) from SONET SPE Broadcast cells to Broadcast frame cluster nodes to cluster nodes ID=MID? ID=DLCI? AcompletesetofSDLdiagramsoftheDRAGONprototypeisprovidedinFigs.3to16.These diagramsspecifythebehaviorofthesysteminatopdownmanner;startingwiththesystem 3DRAGONPrototypeSDLSpecication Figure10:Receivingpackets Reject cells Accept cells Accept frame Reject frame 12 conn

14 fortransmittingsignalsresvandtokentoalltheblockswithinthedragonsblockset. ThenumberofinstancesofDRAGONisspeciedbytheparametercalledNoOfNodes.The CLUSTERalsocontainsthe/SONETinterface(SSI)andtheBROADCASTblockresponsible CLUSTERconsistsoftheblocksetDRAGONscontaininganumberofblocksoftypeDRAGON. denition,thentotheleveloftheblocks,andnallydowntotheprocessdenitionsusingextended broadcastoverallthes1channels,andlikewisethetokenisbroadcastoverallthes2channels. ThesetofchannelsS1andS2arecalledthereservationbusandthereservationringrespectively. FiniteStateMachine(EFSMs)notation.EachnodehasitsownDRAGONblocktype.Thesystem ThereareNoOfNodesofchannelswithineachchannelset.WheneveraRESVsignalissent,itis DRAGONs.InordertoaddresseachRESVQCTLRprocessindividually,itsPIdmustbeknown.The thiswayinsdl. oneoftheresvqctlrprocessessendssignalslottothebroadcastprocess.afterthat,the ThereservationringismodeledasanIEEE8802-4tokenbus[21],becauseitwaseasiertodoit executedthestartsymbol.thebroadcastprocessstoresthepidvaluesinarrayidarray1. EachRESVQCTLRprocessinstancessendsId1totheBroadcastprocessimmediatelyafterithas PIdswereobtainedafterconsumingtheId1signalsandthenapplyingthePId-expressionsender. BroadcastprocessbroadcaststheRESVsignaltoeachoftheRESVQCTLRprocesseswithinthe TheSDLprotocolforbroadcastingtheRESVsignalconsistsoftwostages.Intherststage, similarwaytoabove.asmentionedearlier,thetokenpassingschemewasimplementedin SDLusingthetokenbusprotocol.ThisworksbybroadcastingtheTOKensignalstoallthe RINGCTLRprocesseswithintheDRAGONsblockset.TheTOKenconveysthePIdofthenext thepidsoftheringctlrprocessesmustalsobeknownbythebroadcastprocess,andlikewise RINGCTLRprocesswhichisdesignatedtheTOKen.AfterconsumingtheTOKensignal,each thenthetokenisaccepted,otherwisethetokenisrejected.aswiththeresvqctlrprocess, oftheringctlrprocessescheckswhetherthispidmatchesitsownpidvalue.ifamatchoccurs TheSDLprocedureforpassingtheTOKensignalaroundthereservationringworksina theyareextractedafterconsumingthesignalid2.theringctlrprocesspisarestoredinarray Theseconsistsofthereservationqueue(RESVQ)andthecelltransmitter/receiver(TXRCV)blocks. cellsenterthetxrcvblockinsequentialorderovertheinpchannel.received IdArray2. cellswhicharedestinedforthenodeareacceptedandsentviaoutchannelforreassembly. blockforthedesiredtransmissionprotocol.theresvqblockremainsunchanged. protocolsalsosuchasatm,x.2andframerelay.thismerelyinvolvesrespecifyingthetxrcv AlthoughtheDRAGONhasbeenmodeledfortheprotocol,itcanbeadaptedforother TheDRAGONblocktypecontainsthemaincomponentsoftheuser-to-networkinterface. namedreservationfifo(resvfifo).whenanewmessagearrivesatthetransmitter,aslotreq thereservationringcontroller(ringctlr). controlledbytwonitestatemachinesnamedthereservationqueuecontroller(resvqctlr)and signalisgeneratedtorequestthereservationofaslotinresvqforthemessage.thisoperationis namedtailcounter(tailctr),adowncounternamedheadcounter(headctr)andafifo ApartoftheslotreservationistheTOKenaccesscontrolandthisisperformedbythe TheRESVQblockisshowninFig.(a).Itcontainsthreebasicelements:anup/downcounter 13

15 totheresvqctlrprocess.thenxttokrnd(nexttokenround)signalisthensenttothe RINGCTLRprocess.AftertheRINGCTLRprocessreceivestheTOKen,itchecksifthePId accessthetokenandsothetokenisaccepted,otherwisethetokenisrejected.afteracceptingthetoken,iftheprocesshasaslotreqsignalpending,theslotgntsignalisissued Broadcastprocesssothatitcanstartthenexttokenbusoperation. itconveysisequaltotheprocessesownpid.ifitis,itimpliesthatthenodeisthenextoneto alsopushesthecontentsofitstailctrintotheresvfifo.thetailctristhencleared. Interface(FIOT)sendsthesignalSTXtoalltheRESVQCTLRprocesses.Followingthis,the ThisisdonebytheBroadcastprocessasdescribedearlier.AfterconsumingtheRESVsignal,the itreceivesaslotgntsignalfromtheringctlr,theresvsignalisbroadcasttoallthenodes. nodesincrementtheirtailctrs.inadditiontothis,thenodethathadissuedtheslotsignal Afterthetransmissionofamessagecellsequenceiscompleted,theFiber-OpticTransmitter TheRESVQCTLRprocesscontrolstheoperationsoftheHEADCTRandtheTAILCTR.After \0"thesignalNTXissenttotheTransmitterprocess,informingittobegintransmission. mentedifitsvalueisgreaterthanzero.ifatthisstage,theheadctrcountsdownfrom\1"to HEADCTRsaredecrementedifitsvalueisgreaterthanzero,otherwisetheTAILCTRisdecre- transitionwherebythestxsignalisbroadcasttoalltheresvqctlrprocesses.subsequently, theresvqctlrprocessesinarrayidarray1.asbefore,thepidsareextractedafterconsuming theid1signals.afterthis,theprocessentersthexmitcellstate.then,oneoftwoeventsmay timerexpiresduetoinactivityinthexmtchanneloveratimedurationd.thisresultsina occur.firstly,thetimeoutsignalmaybereceivedfromthetimerprocess.thiswilloccurifthe considertheactionsofthefiotprocesses.thisprocessstartsobyrecordingthepidvaluesofall FIOTandFIORprocessesrespectively.BoththeseprocessesresidewithintheSSIblock.Werst ThetransmissionandreceptionofcellstoandfromtheSONETchannelsisperformedbythe andretransmittedoverthesonetxmtchannel:thesonettransmitchannel.thetimeristhen otherpossibleeventisthatacellmaybereceivedviathexmtchannel.thiscellisconsumed \freezed"untilthenalcellofthemessagehasbeentransmitted,afterwhichitisagainrestarted. Finally,theSchedulerbroadcastsSTXtoallthenodestoschedulethenexttransmission. thereservationqueueisupdatedandthenextmessage(ifany)isscheduledfortransmission.the set.todetermineifaparticularreceiverprocessisthedestinationofthecell,eachoneofthemis callingprocesswillreturnedadierentinteger.themideldextractedfromeachincomingcell goestothercvcellstateandwaitsforcellstoarriveviathesonetreceivechannelsonetrcv. assignedanidenticationnumbercalledmyid.theassignmentisdonebytheremoteprocedure Afterreceivingeachcell,itisbroadcasttoalltheReceiverprocesseswithintheDRAGONsblock namedserverwhichreturnsadistinctintegervaluetoeachcallingprocess.theintegersaredistinct becausethecallstotheremoteprocedureareserializedinsdl,andthusitisimpliedthateach TheFIORprocessstartsobystoringthePIdsoftheReceiverprocessinarrayIdArray3.Itthen andcheckedwhetheritmatchesthenode'smyidvalue.ifitdoes,thecellisacceptedandsent outviatheoutchannelforreassembly.incaseofamismatch,thecellisrejected. 14

16 CLUSTER DRAGON RESVQ HEAD_CTR RESV_FIFO RESVQ_CTLR RING_CTLR TAIL_CTR TX_RCV Receiver Transmitter Broadcast Broadcast NodeIdServer NodeIdServer Server SSI FIOR FIOT Scheduler thetimer x:y DRAGONs (...) : DRAGON (a)systemtreeorganization System CLUSTER 1(2) NodeIdServer DRAGON Broadcast SLOT, Id1 s2 NxtTokRnd, Id2 /*System CLUSTER consists of "NooNodes" node elements, each with its own DRAGON interface block connected to a SONET network via the /SONET Interface (SSI).*/ signal SLOT,RESV, /*slot reservation signals*/ STX, /*schedule transmission*/ Id1,Id2,Id3, /*PId notification signals*/ NxtTokRnd, /*next token passing round*/ TOKen(PId), /*token signal*/ SONETxmt(Celltype),SONETrcv(Celltype), /*SONET transmit & receive*/ xmt(celltype),rcv(celltype), /* transmit & receive*/ inp(celltype),out(celltype); /* input & output*/ (b)clustersystem remote procedure Server; returns Natural; /*remote procedure definition*/ synonym NoOfNodes Natural=10; /*Total node elements*/ synonym D Duration=6; /*Timer cycle duration*/ SSI SONETxmt SONETrcv s6 Id1 s7 Id3 s8 xmt s9 rcv STX RESV i h g f inp a DRAGONs e s1 (NoOfNodes): TOKen out b DRAGON d s11 s10 s s4 System CLUSTER 2(2) i h g f Block Type DRAGON 1(1) Id1 xmt syntype TwoBits =Natural constants 0:3 endsyntype TwoBits; syntype FourBits =Natural constants 0:1 endsyntype FourBits; Id3 syntype SixBits syntype EightBits =Natural constants 0:63 =Natural constants 0:2 endsyntype SixBits; endsyntype EightBits; s11 s14 s8 s9 rcv syntype TenBits =Natural constants 0:1023 endsyntype TenBits; STX synonym PayloadSize Natural=44; syntype idx=natural constants 0:PayloadSize endsyntype idx; s1 SLOT,Id1 newtype PayloadType array(idx,eightbits) endnewtype PayloadType; SLOT,Id1 NTX inp Figure11:SDLspecicationdiagrams RESV s2 RESV s12 synonym COM TwoBits=0; /*Continuation of Message*/ a s7 RESVQ TX_RCV synonym EOM TwoBits=1; /*End of Message*/ a s3 NxtTokRnd,Id2 s6 d synonym BOM TwoBits=2; /*Beginning of Message*/ s13 TOKen synonym SSM TwoBits=3; /*Single Segment Message*/ b out 1 (d)dragonblock SLOTreq b s4 TOKen newtype Celltype /* cell definition*/ NxtTokRnd,Id2 struct ST TwoBits; /*segment type*/ SN FourBits; /*sequence number*/ MID TenBits; /*multiplexing identifier*/ signal SLOTreq, /*slot request*/ PAYLOAD PayloadType; /*SAR-PDU payload*/ NTX; /*Next-To-Transmit*/ LI SixBits; /*length indicator*/ CRC TenBits; /*cyclic redundancy checksum*/ endnewtype Celltype;(c)Clustersystem i Id1 STX Id3 h xmt g f rcv inp e e d out

17 Block RESVQ 1(1) FIFOin FIFOout TAIL_CTR RESV_FIFO HEAD_CTR s12 s6 s11 read s9 NTX s14 s9 Block TX_RCV rcv s8 1(1) Id3 s14 s9 xmt s8 s11 s1 s2 Id1 SLOT, Id1 RESV s2 s3 s4 (Action) (a)reservationqueueblock dec s7 s SLOTreq STX NxtTokRnd, Id2 SLOTgnt RESVQ_CTLR RING_CTLR s8 s13 TOKen s14 signal FIFOin(Natural),FIFOout(Natural), /*FIFO input & output*/ inc,dec,incout, /*TAIL_CTR control*/ read, /*FIFO read*/ SLOTgnt; /*reservation slot grant*/ remote DCNTR Integer; /*exported HEAD_CTR value*/ signallist Action=inc,dec,incout; /*HEAD & TAIL counter control signals*/ s12 s13 s3 s4 (b)transmitter/receiverblock s7 out inp s6 s6 s7 NTX s12 SLOTreq s13 s12 s13 Process HEAD_CTR 1(1) Process TAIL_CTR 1(1) /*When HEAD_CTR is zero, the RESV_FIFO is popped and the value is loaded into HEAD_CTR. When HEAD_CTR counts from "1" to "0", signal NTX is issued, indicating the node is next to transmit.*/ dcl CTR Integer:=0; dcl exported CNTR as DCNTR Integer; /*counter valuue*/ /*TAIL_CTR is an up/down counter. It performs selected counting operations based on the value of the signallist "Action". inc: Increment counter. dec: Decrement counter. incout: Increment counter, push its contents to FIFO, and clear counter.*/ dcl CNT Integer:=0; /*counter value*/ idle ready (c)headcounter LDC FIFOout dec load_ctr Figure12:SDLspecicationdiagrams(cont.'d) CNTR:= FIFOout CNTR-1 (CTR) * export (CNTR) CNTR:=CTR 16 (d)tailcounter FIFOin(CNT) idle via s6 >(0) export CNTR (CNTR) <=(0) CNT:=0 NTX ready via s11 ready read via s9 idle LDC inc incout dec CNT:=CNT+1 CNT:=CNT+1 CNT else CNT:=CNT-1 idle (0)

18 Process RESV_FIFO 1(1) /*The FIFO queue is implemented as an array, indexed by HEAD and TAIL pointers. HEAD points to the front of the queue, TAIL points to the end of the queue. Operations on HEAD and TAIL pointers are modulo MAX, where MAX is the maximum size of the queue. SIZE is the current queue size*/ syntype idx=integer constants 0:1000 endsyntype idx; newtype FIFOMEM /*FIFO memory type*/ array(idx,integer) endnewtype FIFOMEM; Process RESVQ_CTLR 1(1) Id1 via s2 /*Finite state machine to control the HEAD_CTR and TAIL_CTR operations.*/ dcl MyRESV Boolean:=; /*set to 1 after process outputs RESV signal*/ imported DCNTR Integer; dcl FIFO FIFOMEM, /*reservation FIFO*/ SIZE Integer:=0, /*current FIFO depth*/ Integer, /*FIFO input & output*/ DINP,DOUT HEAD,TAIL idx:=0; /*element head & tail pointers*/ Enables "Broadcast" block to determine sender process PId by consuming Id1 and then accessing "sender" PId-expression. Id1 via s3 WaitEvent (a)reservationfifo idleing FIFOin (DINP) read SIZE <1000 SIZE>0 FIFO(TAIL) DOUT:= :=DINP FIFO(HEAD) SIZE:= FIFOout SIZE+1 (DOUT) TAIL:= SIZE:= (TAIL+1) SIZE-1 mod 1000 HEAD:= idleing (HEAD+1) mod 1000 idleing SLOTgnt SLOT incout MyRESV:= WaitEvent Reservation queue slot granted. Send RESV to "Broadcast" block which broadcasts it to all the nodes. RESVQ counters already updated. Thus, no action. (b)reservationqueuecontroller Sent by the RESV "Broadcast" STX block. >(0) import MyRESV (DCNTR) <=(0) MyRESV:= inc dec via s7 dec via s WaitEvent WaitEvent WaitEvent WaitEvent TX_RCV sends signal STX to schedule next transmission. If HEAD_CTR>0, decrement HEAD- _CTR, else decrement TAIL_CTR. Process RING_CTLR 1(1) /*Implementation is similar to the IEEE Token Bus Access protocol.*/ dcl count Integer:=0; dcl ID PId; /*TOKen PId value*/ Process Receiver 1(1) dcl cell Celltype, /* cell*/ MyId Natural; /*PId of this process*/ imported procedure Server; /*NodeId Server*/ returns Natural; Enables "Broadcast" block to determine sender process PId by consuming Id2 and then accessing "sender" PId-expression. TOKen PId matches node s PId. Thus, TOKen is accepted. AcceptTOK Enables "thessi" block to determine sender process PId by consuming Id3 via s14 Id3 and then acessing "sender" (c)reservationringcontroller Id2 via s13 SLOTreq PId-Expression. MyId:= call Server SLOTgnt WaitTOK Figure13:SDLspecicationdiagrams(cont.'d) via s8 monitor TOKen NxtTokRnd rcv (ID) SLOTreq via s13 17 (d)receiverprocess (cell) () cell!mid () =MyId ID=self WaitTOK () If cell MID value matches the () out node s ID, then cell is accepted. Otherwise cell is rejected. (cell) TOKen PId does not AcceptTOK WaitTOK match node s PId. Thus, TOKen is rejected. monitor TOKen received with PId of next node to access the TOKen. Assign an unique ID to the node. cell received via SONET network.

19 Process Transmitter 1(1) WaitForCell dcl cell Celltype; Block Broadcast 1(1) /*Receives RESV and TOKen signals from a specific node and broadcasts it to every node in the cluster.*/ inp (cell) NTX (a)transmitterprocess (COM,EOM) cell!st (BOM,SSM) SLOTreq via s13 transmit NTX inp xmt (cell) WaitForCell Broadcast r1 SLOT,Id1 r2 (b)broadcastblocknxttokrnd,id2 RESV TOKen s1 s2 Process Broadcast 1(2) syntype Index=Natural constants 1:NoOfNodes endsyntype Index; newtype IdArrayType /*process PId array*/ Array(Index,PId) endnewtype IdArrayType; dcl IdArray1 IdArrayType, /*RESVQ_CTLR process PIds*/ IdArray2 IdArrayType, /*RING_CTLR process PIds*/ idx Natural:=1; /*PId array index*/ Process Broadcast 2(2) RESV signal received from the "Broadcast" process. wait SLOT dcl K,L Natural:=1, /*PId array index of the next node designated the TOKen*/ ID PId; /*PId of the next node designated the TOKen*/ NxtTokRnd TOKen signal received from the "Broadcast" process. SndRESV SndTOKen PId of each RESVQ_CTLR process is extracted and stored in array IdArray1. RcvId2s SLOT, SLOT, (c)broadcastprocess(1) NxtTokRnd NxtTokRnd RcvId1s RESV is sent to the RESVQ- RESV to TOKen Id2 _CTLR processes within every IdArray1(K) (IdArray2(L)) to node using the PId values IdArray2(K) Id1 Id2 stored in IdArray1. Figure14:SDLspecicationdiagrams(cont.'d) K:=K+1 K:=K+1 IId of each RING_CTLR IdArray2(idx) is extracted and :=sender IdArray1(idx) stored in array IdArray2. :=sender <(NoOfNodes+1) <(NoOfNodes+1) K K idx:=idx+1 =(NoOfNodes+1) =(NoOfNodes+1) 18 (d)broadcastprocess(2) idx:=idx+1 SndRESV K:=1 K:=1 SndTOKen =(NoOfNodes+1) idx =(NoOfNodes+1) wait L:=L+1 idx <(NoOfNodes+1) <(NoOfNodes+1) <(NoOfNodes+1) RcvId2s idx:=1 L RcvId1s idx:=1 =(NoOfNodes+1) SndTOKen wait L:=1 RcvId2s wait

20 Block NodeIdServer 1(1) Process NodeIdServer 1(1) ;signalset dummy; signal dummy; /*never used*/ dcl ID Natural:=0; (a)nodeidserverblock NodeIdServer Exported Server (b)nodeidserverprocess wait dummy dummy wait Exported Procedure Server; returns Natural 1(1) Block SSI 1(1) /*The /SONET Interface accepts cells sent by a cluster node and transmits them over the SONET network. It also receives cells sent over the SONET network and broadcasts them to all the nodes. The SSI also monitors the Timer and whenever it expires, broadcasts STX to the nodes to update the reservation queue and determine the next node for transmission.*/ signal hold, /*Timer is frozen and held*/ (c)nodeidserverprocedure restart, /*Timer is restarted*/ timeout; /*Timeout after Timer expires*/ Id1 Figure1:SDLspecicationdiagrams(cont.`d) ID:=ID+1 hold, restart timeout FIOT s2 19 (d)/sonetinterface(ssi)block thetimer FIOR s6 STX xmt s8 SONETxmt s11 rcv s9 SONETrcv s10 id3 s7 s6 s8 s11 s9 s10 s7

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