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FogNetworking:AnOverviewonResearchOpportunities MungChiang ArthurLeGrandDotyProfessorofElectricalEngineering PrincetonUniversity December2015 A.Introduction Thepast15yearshaveseentheriseoftheCloud,alongwithrapidincreaseinInternet backbonetrafficandmoresophisticatedcellularcorenetworks.Therearethree differenttypesof“Clouds:”(1)datacenter,(2)backboneIPnetworkand(3)cellular corenetwork,responsibleforcomputation,storage,communicationandnetwork management.NowthefunctionsofthesethreetypesofCloudsare“descending”tobe amongorneartheendusers,i.e.,totheedgeofnetworks,as“Fog.” WetakethefollowingasaworkingdefinitionofFogNetworks:“Itisanarchitecturethat usersoneoracollaborativemultitudeofend-userclientsornear-useredgedevicesto carryoutasubstantialamountofstorage,communicationandmanagement.” Architectureallocatesfunctionalities.EngineeringartifactsthatmayuseaFog architectureinclude5G,home/personalnetworking,andtheInternetofThings. TohighlightthecontrastbetweenCloudandFog,wecancompareFogarchitecturewith thecurrentstandardpracticealongthefollowingthreedimensions: • Carryoutasubstantialamountofstorageatorneartheend-user(ratherthan storedprimarilyinlarge-scaledatacenters). • Carryoutasubstantialamountofcommunicationatorneartheend-user(rather thanallroutedthroughthebackbonenetwork). • Carryoutasubstantialamountofmanagement,includingnetwork measurement,controlandconfiguration,atorneartheend-user(ratherthan controlledprimarilybegatewayssuchasthoseintheLTECore). ItisnotabinarychoicebetweenCloudandFogeither:theyformamutuallybeneficial, inter-dependentcontinuum.Itisacontinuum:tothewearabledevices,amobilephone maybeviewedastheCloud.Theyareinter-dependent,e.g.,coordinationamong devicesinaFogmayrelyontheCloud.Theyarealsomutuallybeneficial:certain functionsarenaturallymoreadvantageoustocarryoutinFogwhileothersinCloud.The interfacebetweenCloudandFogisindeedakeyaspectofFogR&D. Fogarchitecturesmaybefullydistributed,mostlycentralizedorsomewhereinbetween.Theymayrelyonhardware,software,orcombinationofboth.Thecommon denominatoristhattheydistributetheresourcesandservicesofcomputation, communication,control,andstorageclosertodevicesandsystemsatorneartheusers. Thereisalreadyalargeandincreasingrangeofsuchclientandedgedevicestoday:from smartphonestotabletsandfromset-topboxestosmallcellbasestations.Someof themhavebecomedramaticallymorepowerfulincomputation,communication, storageandsensingcapabilitieswithinthepastseveralyears,whilestilllimitedinother wayssuchasenergysupply.AsdifferentsegmentsofInternetofThings(IoT),Internetof Everything(IoE)orInternetofMe(IoM)starttotakeoff,e.g.,consumer,wearable, industrial,enterprise,automobile,healthcare,building,energy,etc.,therewillbean evenmoreimpressivesurgeinthediversity,volume,andcapabilitiesofsuch“Fog nodes.”Indeed,Fog’sfirstapplicationcontextswasconnectedcarsasproposedseveral yearsago[1].Information-transmittinglight-bulbs,computersonastick,andbuttonsizedRFtunersfurtherunderscoretheopportunitiesofFognodes. Concurrently,wirelessnetworksareincreasinglyusedlocally,e.g.,withinconnected cars,smart-buildings,andpersonalbody-areanetworks;anddatageneratedlocallyis increasinglyconsumedlocally.Whatcanacrowdofsuchdevicescollectively accomplish,throughadense,distributedandunder-organizednetworkontheedge? Whatcantheyaccomplishtoenableultra-lowanddeterministiclatency,dataminingin realtimewithstreamingdata,andcyberphysicalnetwork’sactuationandcontrol functionswithinstringenttemporalconstraints? Ithasbecomebothfeasibleandinterestingtoaskthequestion:“Whatcanbedoneon thenetworkedge?”Forexample,whatistheset-topboxinyourlivingroomreplaces thedeepinspectionboxesinoperatornetwork?Andthedashboardinyourcarisyour primarycachingdevice?Whatifyourphoneandphonesofotherscollectivelyactas controllersimilartoanS-GWorPDN-GW?Whiletheanswerstoquestionssuchasthese maynotbepositiveinallcases,ithasfinallybecomeworthwhileaskingthequestions. Wemaycontrasttheseclients,edgedevices,and“things”withthelarge,expensive, hard-to-innovate“boxes”intheCloud:S-GWandPDN-GWinLTEcore,largeserversand switchesinsideadatacenter,andmetroandcoreroutersinwide-area-network backbone.Thetraditionalviewisthatedgeusesthecorenetworkanddatacenters.The Fogviewisthatedgeisthecorenetworkandadatacenter.Inthetensionbetweenthe “brick”versusthe“click,”thependulumisstartingtoswingbacktowardthe“brick,” wherephysicalinteractionswiththecyber-systemisbecomingonceagainimportant. B.WhyFogandWhyNow? WhywouldwebeinterestedintheFogviewnow?Therearefourmainreasons: 1. Time:Realtimeprocessingandcyber-physicalsystemcontrol.Edgedata analytics,aswellastheactionsitenablesthroughcontrolloops,oftenhave stringenttimerequirementandcanonlybecarriedoutontheedge,“hereand now.”ThisisparticularlyessentialforTactileInternet:thevisionofmillisecond reactiontimeonnetworksthatenablevirtual-reality-typeinterfacesbetween humansanddevices. 2. Cognition:AwarenessofClient-centricobjectives.Followingtheend-to-end principle,someoftheapplicationscanbebestenabledbyknowingthe requirementsontheclients.Thisisespeciallytruewhenprivacyandreliability cannotbetrustedintheCloud,orwhensecurityisenhancedbyshorteningthe extentoverwhichcommunicationiscarriedout. 3. Efficiency:Poolingoflocalresources.Therearetypicallyhundredsofgigabytes sittingidleontablets,laptopsandset-topboxesinahouseholdeveryevening,or acrossatableinaconferenceroom,oramongthepassengersofapublictransit system.Similarly,idleprocessingpower,sensingabilityandwirelessconnectivity withintheedgemaybepooledwithinaFognetwork. 4. Agility:Rapidinnovationandaffordablescaling.Itisusuallymuchfasterand cheapertoexperimentwithclientandedgedevices.Ratherthanwaitingfor vendorsoflargeboxesinsidethenetworktoadoptaninnovation,intheFog worldasmallteammaytakeadvantagesofsmartphoneAPIandSDK, proliferationofmobileapps,andofferanetworkingservicethroughitsownAPI. Therearealsotwomore“defensive”reasonsfortheriseoftheFog: Feasibilitytooperateonencryptedandmultipathtraffic.Amajortrendthesedaysis thatbythetimetrafficleavestheedgeandentersthebackbonenetwork,itisalready encryptedandpossiblytraversingmultiplepaths,makingitexpensiveifnotimpossible tooperateonsuchdata. InUnitedStates,implicationsofFCCTitleIIRuling.TheFCCvoteinFebruary2015to classifyInternetservices,includingmobileservices,asa“utility”underTitleIIregulatory mandate,mayfurtherpushnetworkinnovationtotheedgeintheUS.Anewregulatory environmentdoesnotmeannetworkscannotbeengineeredandmanagedanymore, butwemayneeddifferentvantagepointsofcontrol:notfrominsidethenetworkbut fromaroundtheendusers.Forexample,todaynetworkoperatorscanpickwhichlane (WiFi,Macro-cellular,Femtocell)auserdeviceshouldbein.Sincedifferentlaneshave differentspeedsanddifferentpaymentsystem/amount,suchpracticemaynotbe allowedanymoreintheUS.Instead,weneedtobetterdesignsystemwhereeachuser devicemustchoosewhichlanetobeinforitself.ThechallengeresultingfromTitleII regulationisa“hangingsword”thatchillsthedeploymentofnetworkinfrastructure innovations,asrisk-Returnbalancenowtipstowards“keepthenetworkasis.” However,aslongasthegovernmentdoesnotprohibitend-userchoices,thenwecan runnetworkingfromtheedge,throughclient/home-drivencontrol/configuration. C.CaseStudies 5G Internet CyberMobile ofThings Physical Edge-driven dataplane Data analy<cs Edge-driven Control-plane Figure1:DataplaneandcontrolplaneofFognetworksenabledifferentapplications ArchitecturalR&Dasksthequestionof“whodoeswhat,atwhattimescale,andhowto putthemodulesbacktogether?”Asanarchitecture,Fognetworkingconsistsofboth dataplaneandcontrolplane,eachwitharapidlygrowingnumberofexamplesacross protocollayersfromthephysicallayertotheapplicationlayer: • ExamplesofDataplaneofFog: o Poolingofclientsidlecomputing/storage/bandwidthresourcesandlocal content o Contentcachingattheedgeandbandwidthmanagementathome o Client-drivendistributedbeam-forming o Client-to-clientdirectcommunications(e.g.,FlashLinQ,LTEDirect,WiFi Direct,AirDrop) o Cloudletsandmicrodata-centers • ExamplesofControlplaneofFog: o OvertheTop(OTT)contentmanagement o Fog-RAN:Fogdrivenradioaccessnetwork o Client-basedHetNetscontrol o Client-controlledCloudstorage o Sessionmanagementandsignalingloadattheedge o Crowd-sensinginferenceofnetworkstates o Edgeanalyticsandreal-timestream-mining Data-planeofFoghasbeenmoreextensivelystudied,e.g.,[2].Inthefollowing,we highlightafewparticularcasesthatillustratethepotentialandchallengesofFogcontrol plane,suchastheinference,control,configurationandmanagementofnetworks: Case1:Crowd-sensingLTEstates(incommercialdeployment).Throughacombinationof passivemeasurement(e.g.,RSRQ),activeprobing(e.g.,packettrain),application throughputcorrelationandhistoricaldatamining,acollectionofclientdevicesmaybe ableto,inreal-timeandusefulaccuracy,inferthestatesofaneNBsuchasthenumber ofResourceBlocksused[3]. Case2:OTTnetworkprovisioningandcontentmanagement(incommercial deployment).Thetraditionalapproachtoinnovatingnetworksistointroduceanother boxinsidethenetwork,possiblyavirtualizedboxbutaboxnonetheless.Fognetworking directlyleveragesthe“things”andphonesinstead,andremovesthedependenceon boxes-in-the-networkaltogether.WithSDKssittingbehindappsonclientdevices, throughtaskssuchasURLwrapping,contenttagging,locationtracking,behavior monitoring,networkservicescanbeinnovatedmuchfaster. Figure2:SDKsittinginsideclientscanenablenetworkinferenceandconfiguration Case3:Client-basedHetNetscontrol(in3GPPstandards).Coexistenceofheterogeneous networks(e.g.,LTE,femto,WiFi)coexistenceisakeyfeatureincellularnetworkstoday. Ratherthanthroughnetworkoperatorcontrol,eachclientcanobserveitslocal conditionsandmakedecisiononwhichnetworktojoin.Throughrandomizationand hysteresis,suchlocalactionsmayemergegloballytoconvergetoadesirable configuration[4]. Figure3:Co-existenceofheterogeneousnetworksmaybemanagedinpartbyclients Case4:Client-controlledCloudstorage(inbetatrial).Bydecouplingmassivecheap storage(intheCloud)fromclientsidecontrolofprivacy(intheFog),wecanachievethe bestofbothworlds.Forexample,byspreadingthebytes,inaclientshimlayer,ofa givenfileacrossmultipleCloudstorageproviders,itcanbeassuredthatprivacyofthe dataismaintainedevenifencryptionkeyisleakedbyanygivenCloudprovider[5]. Figure4:ShredandSpread(CYRUSproject)storesinCloudbutcontrolsinFog Case5:Real-timestreammining(inbetatrial).Considervirtualrealitytasksassociated withGoogleGlass.Someoftheinformationretrievalandcomputationtasksmaybe carriedoutontheGlass(a“wearablething”),someontheassociatedphone(aclient device),someonthehomestorage(anedgedevice),andtherestintheCloud.An architectureofsuccessiverefinementmayleverageallofthesedevicesatthesame time,withanintelligentdivisionoflaboracrossthem[6]. Case6:BorrowingbandwidthfromneighborsinD4D(inbetatrial).Whenmultiple devicesbelongingtothesameperson,torelativesortoemployeesofthesame companyarenexttoeachother,onecanasktheotherstosharetheirLTE/WiFi bandwidthbydownloadingotherpartsofthesamefileandtransmitting,viaWiFiDirect, clienttoclient[7]. Figure5:IdleresourcesinclientdevicescanbepooledinD4Dformoreefficientuse Case7:Bandwidthmanagementathomegateway(inbetatrial).Byadaptingthehome set-topbox/gateway,thelimitedbroadbandcapacityisallocatedamongcompeting usersandapplicationsessions,accordingtoeachsession’spriorityandindividual preferences.Aprototypeonacommodityrouterdemonstratesascalable,economical andaccuratecontrolofcapacityallocationontheedge[8]. Case8:Distributedbeam-forming(inlabdemonstration).Fogcanalsohappeninthe physicallayer,forexample,byexploitingmulti-userMIMOtoimprovethroughputand reliabilitywhenaclientcancommunicatewithmultipleWiFiaccesspoints.Foruplink, wecanusemulti-userbeam-formingsothattheclientcansendmultipledatastreams tomultipleAPssimultaneously.Fordownlink,wecanuseinterferencenullingsothat theclientcandecodeparallelpacketsfrommultipleAPs.Thesecanbedoneentirelyon theclientside[9]. Someoftheabovecasestudiesarecoretopicsinwhatmanypeopleimaginewould partiallydefine“5G:”HetNets/smallcell/densification,overthetopserviceprovisioning, cognitiveradioandcrowd-sensing.Othercasestudiespointtowardarchitectural thinkingforIoTservices,questionsaboutownership,controlandvisibilityofpersonal areanetworks,suchas“shouldAppleWatchandthelikehavetheirowndataplan?” thatwillhelpdefinethebalanceofpowerbetween“AT&T”sand“Apple”softheworld. Ifthenetworkinoraroundtheendusershavealogicaltopologythatlookslikeastar, withafixedgateway(e.g.,iPhone),thevisibility,control,andvalue-addedbynetwork operatorswillbedrasticallydifferentthaninthealternativescenariowherethe gatewaysaredynamicallychosenortheThingscansometimeshavedirect communicationpathswithoutagateway. Formorereferencesfortheseexamplesandmoreexamples,pleaseseeaninitiallistof over100recentpublicationsoneightdifferenttopicsunderFogNetworkingat http://fogresearch.org D.OpenQuestionsandResearchChallenges AsistypicalofanyemergentareaofR&D,manyofthethemesinFogNetworkingare notcompletelynew,andinsteadareevolvedversionofaccumulatedtransformationsin thepastdecadeortwo: • Comparedtopeer-to-peer(P2P)networksinthemid-2000s,Fogisnotjustabout contentsharing(ordataplaneasawhole),butalsonetworkmeasurement, control&configuration,andservicedefinition. • Comparedtomobileadhocnetwork(MANET)researchadecadeago,wehave muchmorepowerfulanddiverseoff-the-shelfedgedevicesandapplications now,togetherwiththestructure/hierarchythatcomeswithcellular/broadband networks. • Comparedtogenericedge-networkinginthepast,Fognetworkingprovidesa newlayerofmeaningtotheend-to-endprinciple:notonlydoedgedevices optimizeamongthemselves,buttheycollectivelymeasureandcontroltherest ofthenetwork. Alongwithtwoothernetworkarchitecturethemes:ICNandSDN,eachwithalonger history,Fogisrevisitingthefoundationofhowtothinkaboutandengineernetworks, i.e.,howtooptimizenetworkfunctions:whodoeswhatandhowtogluethemback together: • Information-CentricNetworks:Redefinefunctions(tooperateondigitalobjects ratherthanjustbytes) • Software-DefinedNetworks:Virtualizefunctions(throughcentralizedcontrol plane) • FogNetworks:Relocatefunctions(tothenetworkedge) WhileFognetworksdonothavetohaveanyvirtualizationortobeinformation-centric, onecouldalsoimagineaninformation-centric,software-definedFognetwork(since thesethreebranchesarenotorthogonal). Asinanemergentareainitsinfantage,thereisnoshortageofchallengingquestionsin Fognetworking,someofwhichcontinuefromearlierstudyofP2P,MANETandCloud, whileothersaredrivenbyaconfluenceofrecentdevelopmentsinnetworkengineering, devicesystemsanduserexperience: • Cloud-Foginterface:Thefundamentalquestionofarchitectureis“whodoes what,atwhattimescale,andhowtoputthembacktogether?”Cloudwillremain usefulasFogarises.ThequestioniswhattasksgotoFog(e.g.,thosethatrequire real-timeprocessing,enduserobjectivesorlow-costleverageofidleresources) andwhatgotoCloud(e.g.,massivestorage,heavy-dutycomputation,orwideareaconnectivity),andwhatwillbetheFog-CloudandFog-Foginterfaces:the specificationofinformationpassage,fromitsfrequencytogranularity,across theseinterfaces. • Interactionswithclient/thinghardwareandOS:Oncetheactionsaretakenon theclientsorthings,theinterfacewiththeiroperatingsystemsandhardware becomeessential.MorethanjustusingD4Dforpoolingidleedgeresources, thereisalsothepossibilityofspecializedprotocolstackjustfornetworking withinanedge. • Trustworthinessandsecurity:WhileFogmayhelpenhancesecurityinsome cases,itmaypresentnewsecuritychallengesinothercases.Giventhatitis ofteneasiertohackintoclientsoftware,perhapssecurityathardwarelevelon clientdevices.Atthesametime,becauseoftheproximitytoendusersand localityontheedge,nodesinFognetworkscanoftenactasthefirstnodeof accesscontrolandencryption,providecontextualintegrityandisolation,and enablethecontrolofaggregatingprivacy-sensitivedatabeforeitleavesthe edge. • Incentivizationofclientparticipation:Sometimesitisnottoomanyuntrustworthyclientsthatcreateconcernbuttoofewclientswillingtoparticipate. Marketsystemsandincentivemechanismswillbecomeuseful. • Convergenceandconsistencyarisingoutoflocalinteractions:Typicalconcernsof distributedcontrol,divergence/oscillationandinconsistencyofglobalstates, becomemoreacuteinamassive,under-organized,possiblymobilecrowdwith diversecapabilitiesandvirtualizedpoolofresourcessharedunpredictably.Use casesinedgeanalyticsandstreamminingprovideadditionalchallengesonthis recurrentchallengeindistributedsystems. • Ingeneral,thetradeoffbetweendistributedandcentralizedarchitectures, betweenwhatstaysonlocalandwhatgoesonglobal,andbetweencareful planningandresiliencethroughredundancy.Onthistopic,weneedtobe sensitivetotheopportunitywheremanydifferent,ordynamic,logicaltopologies mayarisefromthesameunderlyingphysicalconfigurationofaFognetwork. Toaddresstheabovechallenges,weneedboth • Fundamentalresearch,acrossnetworking,devicehardware/OS,pricing,HCIand datascienceasshowninFigure6,and • Industry-academiainteractions,asexemplifiedintheOpenFogConsortium,a global,non-profitconsortiumlaunchedinNovember2015withfounding membersfromARM,Cisco,Dell,Intel,MicrosoftandPrincetonUniversity. Figure6:Arangeoffieldsisneededforaninter-disciplinarystudyofFognetworks Indeed,FogNetworkingisstartingtoshapethefutureofthebalanceofpowerand distributionofdrivinginnovationacrosstheentireindustryfoodchain,includingthe following: • Enduserexperienceprovider(e.g.,GE,Toyota…) • Networkoperators(e.g.,AT&T,Verizon,Comcast…) • Networkequipmentvendors(e.g.,Cisco,Nokia,Ericsson,Huawei…) • Cloudserviceproviders(e.g.,VMWare,Amazon…) • Systemintegrators(e.g.,IBM,HP…) • Edgedevicemanufacturers(e.g.,Linksys…) • Client/IoTdevicemanufacturers(e.g.,Dell,Microsoft,Apple,Google…) • Chipsuppliers(e.g.,Intel,ARM,Qualcomm,Broadcom…) 2015isaninterestingyeartostartsystematicallyexploringwhatFogmightlooklikeand thedifferencesitwillmakeintheworldofnetworkingandcomputinginthenext15 years. Acknowledgements: Theauthorisgratefulfortheinspiringconversationswithmanycolleaguesinindustry andacademia,especiallyFlavioBonomi,RussellHsing,BharathBalasubramanian, AakankshaChowdhery,YanSchvartzshnaider,SangtaeHa,JunshanZhang,RajSavoor, JohnSmee,ChonggangWangandrepresentativesofARM,Cisco,Dell,Inteland MicrosoftinOpenFogConsortium. Reference:(morereferencescanbefoundathttp://Fogresearch.org) [1]F.Bonomi,R.Milito,P.NatarajanandJ.Zhu,“Fogcomputing:AplatformforInternetof ThingsandAnalytics,”inBigDataandIoT,Springer2014. [2]M.Satyanarayanan,P.Bahl,R.Caceres,andN.Davies,“ThecaseforVM-basedCloudletsin mobilecomputing,”IEEETransactionsonPervasiveComputing2009. [3]A.Chakraborty,V.Navda,V.N.PadmanabhanandR.Ramjee,“Coordinatingcellular backgroundtransfersusingLoadSense,”ProceedingsofACMMobicom2013. [4]E.Aryafar,A.Keshavarz-Haddard,M.WangandM.Chiang,“RATselectiongamesin HetNets,”ProceedingsofIEEEINFOCOM2013. [5]J.Chong,C.Joe-Wong,S.HaandM.Chiang,“CYRUS:Towardclient-definedCloudstorage,” ProceedingsofEuroSys2015. [6]L.CanzianandM.vanderSchaar,“Realtimestreammining:Onlineknowledgeextraction usingclassifiernetworks,”IEEENetworksSpecialIssueonNetworkingforBigData2014. [7]Z.Zhang,J.ZhangandL.Ying,“Multimediastreamingincooperativemobilesocial networks,”Preprint. [8]F.M.F.Wong,S.Ha,C.Joe-Wong,Z.LiuandM.Chiang,“Mindyourownbandwidth: Adaptivetrafficmanagementonnetworkedge,”ProceedingsofIEEEIWQoS2015. [9]Y.Du,E.Aryafar,J.CampandM.Chiang,“iBeam:Intelligentclient-sidemulti-user beamforminginwirelessnetworks,”ProceedingsofIEEEINFOCOM2014.