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Research on Protocol Migration

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Research on Protocol Migrationon,RESEA

    Research on Protocol Migration

V_01.11No.6J.ofComput.

    ;Sci.&Techno1.November1996

    ;ResearchonProtocolMigration

    ;WangYun(汪芸),GuGuanqun(顾冠群)andDuiJiyin(兑继英)

    ;DepartmentofComputerScience&Engineering,SoutheastUniversity,Nanjing210096

    ;ReceivedMay21,1994;revisedMarch25,1996.

    ;Abstract

    ;Thispaperelaboratestheconceptandmodelofprotocolmigrationinnet

    ;workinterconnection.Migrationstrategiesandprinciplesarediscussedand ;severalcases3xestudiedindetailwhichshowthebasicprocedureandtech. ;niquesusedinprotocolmigration.

    ;Keywords:Protocolmigration,interconnection.

    ;Nowadays.therequestforinterconnectionbecomesmoreurgentwiththewider

    ;useofcomputernetworks.Moreandmore”informationislands’’appearbecause

    ;ofvariousfeaturedhardware,softwareandnetworkproductssuppliedbyvarious

    ;vendors.Inordertosolvetheproblemof”informationislands”.networktechniques

    ;aredemandedtobeopen,integratedandstandardized.Confrontingheter0gene0us

    ;networkinterconnection.protoco1migrationisoneeff~!ctiveway. ;1ConceptofProtocolMigration

    ;Protocolisoneofthemostimportantconceptsinnetworktechnique.Itisaset ;ofrulestocontrolinformationexchangebetweentwoentities.Becauseoftheisola-

    ;tionamongcomputerandcommunicationvendorsandlargenetworkorganizations,

    ;thereareseveraldifferentcommunicationprotocolsandcommunicationsystemar-

    ;chitecturessuchasTCP/IPofDoD,SNAofIBM,DECNetofDEC,whichcannot

    ;communicatewitheachotheroriginally.Intheearly80’S,ISOissuedOSI/RMfISo

    ;74981,whichformsthecommonbasistocoordinatethedevelopmentofsysteminter-

    ;connectionstandards.Sincethen.TCP/IPsuitehasbecomethe”defactostand

    ard’’

    ;andhasgotvastapplicationsandusers.However,OSIsuiteisfarfromperfecti

on.

    ;MigrationtechniquesmustbestudiedbecausequiteafeWprotocolscoexistandthey

    ;needtocooperate.

    ;Protocolmigration,inbrief,isaproceduretoaccomplishcommunicationamong

    ;differentprotocolsbyusingcertainmeans.Therearetwoviewpointstheuse

    r’S

    ;view.andtheprotoco1designer’Sview.SupposethattherearetwosystemsAand

    ;B.whichusePAandPBastheircommunicationprotocolsrespectively.Acannot

    ;communicatewithBbecauseofthedifferencesandincompatibilitiesbetweenAand

    ;BinspitethattheirservicesSAandSBsupportedbvPAandPBrespectivelyare ;TheprojectissupportedbyNational”863”High

    ,IlechProgrammeandNationalNaturalScience

    ;FoundationofChina.

    ;

    ;602J.ofComput.Sci.&TechnolV01.11

    ;thesameorsimilar.ThenAismigratedtoB.Intheuser’sviewpoint.theavailable

    ;communicationareaofusersinAisexpandedwithoutanychange,whileinthe ;protocoldesigner’sviewpoint,anewandpossiblestackPM(A,B)issetupbetween

    ;AandB.Fig.1showsthemodelofprotocolmigration.

    ;Thekeyfeatureofprotocolmigrationisthatlogicallythereisnochangein ;theendsystems,nonethelesstheycancommunicateinsteadofmismatchingand

    ;misunderstanding.

    ;SA

    ;LA

    ;(IA)

    ;SystemAM(A,B)SystemB

    ;SB

    ;LB

    ;fIB

    ;Note:Pxx:theprotocolwhosefunctionisxx;Lx:thelowerlayers’servicesofx:

    ;Ix:theinterconnectionlayerinsystemx;PM:thenewmigrationprotocol ;Fig.1.Themodelofprotocolmigration.

    ;2MigrationStrategiesandPrinciples

    ;2.1TheStrategiesofCompleteandPartialMigration

    ;SupposethatAismigratedtoB.Completemigrationistoimplementallthe ;servicesinSAwhichcanbesupportedbySBinthenewprotocolstack.while

    ;partialmigrationisjusttoimplementpartofservicesinSAnecessarytoguarantee

    ;theappointedcommunication.

    ;Itisveryimportantforprotocoldesignerstodeterminethetypeofmigration. ;Generally,completemigrationhastheadvantagethatthegapbetweenAandB ;canbebridgedmostly,butthedevelopingloadmaybehugeandthewholesystem

    ;efficiencymbereduced.Astopartialmigration,itissuitableforsomeinstancesin

    ;whichsupportingalltheservicesinSAisnotnecessary.Andinsuchcircumstances.

    ;itisquiteeasytorealizethemigrationalthoughservicesoutofthescopeofmigration

    ;servicesarenotsupported.

    ;Wecanfindmanyexamplestowhichprotocolmigrationisapplied.Ifthetwo ;endsystemsarehomogeneous,partialmigrationisoftenused.Thereasonsarethat

    ;theheterogeneousnetworkswhicharepassedjustprovideapathfortheendsystem

    ;communication,andtherelaysystemsarenotrequiredtoexplainthemeaning ;oftransferreddata.Productssuchasrouters,bridgesandrepeatersarepopular ;examplesofpartialmigration.What’smore.theinterconnectionsoftwareord

evices

    ;appearinpairsinsystems.

    ;Ifthetwoendsystemsareheterogeneous,completemigrationisusuallyputinto

    ;usebecauseapartfromthedifferenceofprotocolsyntax,semanticsisdifferentand

    ;theinterconnectionpartneedstoexplainpackets.Inaddition,ifapplicationsof ;theendsystemsarethesameorsimilar,butthesupportingnetworkprotocolsare

    ;clearlydifferent,completemigrationimplementationusuallyfindsitselfabovethe

    ;toplayeroftheheterogeneousprotocols.Thustheinterconnectionsoftwareand

    ;devicesoftenmanifestthemselvesasgateways.

    ;

    ;No.6ResearchesonProtocolMigration603

    ;Ifthesamemigrationstrategyisusedinthesamecircumstance,thelowerthe ;interconnectionlayeris,themoreworkisnecessarytobedone.Thereasonsareas

    ;follows:theexpressionabilityisstrongerinhigherlayer;theimplementationdetail

    ;oflowerlayersisshieldedinhigherlayer;andtheinterfaceiseasiertobeusedin

;higherlayer.

    ;Therefore,thefollowingformulacanbegot:C(A)<C(B)<c(c)ifZ(A)&lt;

    ;I(B)<(),inwhichc(x)standsfortheconvenienceofmigrationX,andz(x) ;standsfortheinterconnectionlayerof.

    ;2.2TheImplementationStrategies

    ;Protoco1migrationwil1naturallyinvolvetwoormorecommunicationprotocols

    ;inheterogeneousenvironment.Generally,amigrationmachineisspeciallyconnected

    ;withcertainprotocols.IfoneoftheprotocolsiSchangedorsubstitutedbyanother

    ;protocol,themigrationmachinehastobeimplementedagain.Thereasonforthis

    ;isthattherelationshipbetweenamigrationmachineanditsconcerningprotocols

    ;isoneto-onemapping.

    ;Followingaresomeimplementationstrategiesweshouldpaymoreattentionto:

    ;a)Modulardesign

    ;Amigrationmachinewillcoverthemappingfunctionsinthreeaspects:connec

    ;tion,datatransmissionanddisconnection.Differenceamongprotocolsislargelyin

    ;connectionanddisconnectionstyles.ExtractthesepartsinseparatemodulesSOas

    ;toconfinethepotentialchangesin1oca1modules.

    ;b)Generalmigrationmachine

    ;Toturntheonetoonerelationshiptomanyto-onerelationship,agener

    almi

    ;grationmachinemaybeimplemented.Itisaservicebasedstrategy.Inthege

    neral

    ;migrationmachine,asetofbasiccommunicationservicesisprovided.Whenproto-

    ;CO1AwantstomigratetoprotocolB,whatisneededtodoistoinformthemachine

    ;formatsofpacketsofbothprotocolsAandB.AwayfromAtoBiseasilybuiltup. ;Fig.2.Theimplementationenvironmentofthegateway

    ;2.3DeterminationoftheStrategy

    ;Notalltheservicesinprotocolsareabletobemigratedfromeachother.Ifa ;serviceinSAcannotbesupportedbySB,thentheinterconnectionisimpossibleto

    ;realizethetransformationoftheservice.Forinstance,ifTCP/IPwantstomigrate

    ;toX.25,andtheexpresstransmissionisprovidedbyTCP/IPratherthanbyX.25,

    ;theexpresstransmissionserviceisnotavailableinX.25networkscopeinspiteofthe

    ;

    ;604J.ofComput.

    ;Sci.&Technol

    ;interconnection.Therefore,theprerequisiteforprotocolmigrationisthattheinter

    ;sectionsetofservicesprovidedbytwoendsystemsisnotNULLandthemigration

    ;servicesareincludedbytheintersectionset.Wecandistinguishcompletemigration

    ;frompartialmigrationinthisway:whetheral1theservicesintheintersectionset

    ;areimplementedornot.

    ;Inordertochoosetheinterconnectionlayerappropriately,wemustfirsthave ;agoodknowledgeoftherequirements,thedifferencesbetweenprotocols, ;andthe

    ;implementationenvironment.Intermsofthese,decisionscanbemade. ;3CaseStudy

    ;case1:MMSgateway

    ;IntheNational”863”High—TechProgramme”MMSCommunicationSystemin

    ;HeterogeneousNetworks”,agatewayisimplementedtomigrateTCP/IPsuiteto

    ;OSIsuite.ItisabridgebetweenMAPnetworkandTOPnetwork. ;TheimplementationenvironmentisshowninFig.2.

    ;Intheproject,therequirementisthattheMMSinformationcanflowfrom ;TCP/IPtoMAP.ItisanimportantsteptotransfercommandsanddataofCADor ;CAMinTOPtorealmachinesinMAP.BothEthernet/TCP/IPandMAPprovide

    ;basictransportservicesalthoughtheyaretwoquitedifferentprotocolsandhave

    ;upt04and6layersrespectively.CompleP

    ;Fig.3.Themigrationstructureofthegateway

    ;Whatthenewprotocolstackneedstodoisactuallythemappingofstatus ;betweenTCP/IPandMAP.Themostdistinctdifferenceliesintheconnection ;procedure.InTCP/IP.threetimehandshakingisusedwhileinMAP.four

    time

    ;handshaking.Thus,thenewprotocolstackmustknowthatwhenaneventoccurs

    ;inTCP/IP,itwillleadtoanewTCP/IPstatuscorrespondingtothestatusMAP ;shouldbeinandtheeventMAPshouldgenerateandoccur.

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