Today’s model of networking primarily concentrates intelligence at the end hosts with the network itself offering a simple“best-effort”,“data agnostic ” communication medium. However, this paradigm has proven to be insufficient to meet todays needs co
terthenetwork.Approachesbasedonpacket lteringandheadercheckingcannotofferthislevelof exibilitysincetheylackinferencecapabilities.Likewise,applicationsrun-ningontopofourframeworkcanspecifytheirresourceneeds,withthisinputvaryingindetailfrombeinghighlyspeci ctojustcommunicatinghighlevelsemanticinfor-mationlikethe“ owoftypeJPEGwithframeratexandqualityy”.OurframeworkrunningontopofanIntservorDiffServnetworkwillbeabletoconverttheapplicationrequesttothecorrespondingrealizationmechanismsuchassignallinganRSVPreservationormappingthedatapacketstothecorrespondingDSCPasthecasemaybe.
3.1Node
Level
2.5SemanticMarkup
ResourceDescriptionFramework(RDF)[3]isaframe-workforrepresentingmetadataregardingwebcontentusingXMLastheencodingmechanism.RDFprovidesastan-dardframeworkforinterchanginginformationacrossappli-cations.RDFisbasedontheideaofidentifyingobjectsusingUniformResourceIdenti ers(URI)anddescribingresourcesintermsofsimplepropertiesandpropertyvalues.Astatementisatriplespecifyingasubject(usingURI),apredicate(representingaproperty)andanobject(repre-sentingthevalue).Thisresultsinstructuredgraphswithnodesforsubjectsandobjectswitharcsrepresentingthepredicates.RDFSchema[2]isthemechanismforspecify-ingvocabulariesthatcanbeusedtoformRDFstatements.Thevocabularygivestheactualmeaningtothestatement.Throughthis,objectsandtheirpropertiesandwhattheyre-fertocanbespeci ed.Morepowerfulschemade nitioncanbeprovidedusingOWL.
Providingmarkupforcontentisprevalentinmanyotherar-easalbeitnotalwaysusingastandardmachineprocessablemeanssuchasRDF.SessionDescriptionProtocol(SDP)-Anytimeisaspeci cationforaudio-videocontentmarkup.ID3tagsappliedtoMP3 lescanconveymetadatasuchastitlesandcomposers.ManyoftheseapproachesuseunstructuredXMLwhichisdif culttouseforconveyingknowledge.WehavechosentouseRDFforourframe-workmainlytoprovideastandardandsimplemechanismthroughwhichdatastreamscanbedescribed.Themainob-jectiveistokeepourframework exibletoallowfortheintroductionofnewconceptsasneededratherthanenforcearigidschematobefollowedbyallparticipants.
Figure1.CoCoNetNodeFramework
Atthenodelevel,thearchitectureweproposeintroducesourNodeFrameworkasanadditionallayercalledtheCo-CoNetlayerbetweentheapplicationandthetransportlayer.Thislayerisresponsibleforinterceptingsocketcallsmadebyapplicationstothetransportlayer.TheAPIisenhancedtoallowtheapplicationtoprovidesemanticlevelinforma-tionformessagestransmittedoverthisinterface.ALocalPolicyDecisionPoint(LPDP)isusedtodeterminewhatpoliciestoenforcebasedonthecontent.Inourframework,eachPolicyEnforcementPoint(PEP)isateverylayerinthenetworkingstackwhile[36]treatsthePEPatanodelevel.PlacementofthePEPateverylevelofthestackal-lowsustoimplementcoordinatedcrosslayerinteractionsinitiatedandcontrolledbyourframework.ThePEPex-posestheinterlayeroptimizationpointsthatanyparticularlayersupports.TheframeworkutilizesthepoliciesstoredintheLPDPtodrivethesettingstobeappliedtoeachofthePEPsinthestack.Essentially,weareproposingtoex-poseanetworkstackasacollectionofswitchesanddialsandallowanexternalpolicytodeterminetheexactsettingsofeachofthesedials(basedoncontentandcontext).Wewanttoexposefunctionality,notnecessarilythemechanismofhowitisachieved(thisfallsunderintra-layeroptimiza-tion).Forexample,aMACcanadvertisetwodifferentdataratesandtheirassociatedpacketerrorprobabilitieswith-outexposingtheFECschemeusedtoachievetheserates.Thepoliciescanbespeci edasproductionrules(if(condi-tion)then(action))orevent-condition-actionrules(oneventif(condition)then(action)).Inessence,theNodeFrame-workprovidesarich,extensibleoptionforrealizingpolicycontrolledcross-layerinteractionswithinanode’snetworkstack.Byparameterizingthepossiblesetofinteractions5
3ProposedApproach
Thissectionpresentsanoverviewofourproposedframework.Webreakitdownintotwocomponents;atanodelevelandatasystemlevelthatspansthenetwork.