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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.