Intel® Technology Journal | Volume 14, Issue 1, 2010

ENSEMBLE COMPUTING: OPPORTUNITIES AND CHALLENGES

Contributors

Roy Want Abstract Intel Corporation SSinceince tthehe aadventdvent ooff tthehe fi rrstst ppracticalractical mmobileobile ccomputersomputers mmoreore tthanhan 2200 yyearsears aago,go, aadvancesdvances inin thethe uunderlyingnderlying ttechnologyechnology hhaveave mmovedoved ooutut ooff rresearchesearch aandnd EEveve SchoolerSchooler ddevelopmentevelopment aandnd iintonto bbothoth tthehe eenterprisenterprise aandnd tthehe aarearea ooff cconsumeronsumer eelectronics.lectronics. IIntelntel CCorporationorporation TToday,oday, mmobileobile nnetworkedetworked ccomputersomputers aarere uubiquitous.biquitous. TTrendsrends tthathat hhaveave eenablednabled Lenka Jelinek tthishis rrevolutionevolution iincludenclude iimprovedmproved pprocessorrocessor pperformance,erformance, eexponentiallyxponentially Intel Corporation iincreasingncreasing sstoragetorage ddensity,ensity, aandnd hhigh-bandwidthigh-bandwidth sstandardizedtandardized rradios:adios: aallll ooff tthesehese ccomputersomputers cconsumeonsume lessless powerpower aandnd aarere ppackagedackaged iinn ssmallermaller fform-factorsorm-factors tthanhan JJaeyeonaeyeon JungJung ttheirheir ppredecessors.redecessors. HHowever,owever, tthehe fformationormation ooff mmobileobile ccollectionsollections ofof ddevices,evices, IIntelntel CCorporationorporation oorr eensembles,nsembles, ccanan furtherfurther bbuilduild oonn tthehe nnetworketwork eeffff eectct ttoo aamplifymplify eensembles’nsembles’ uusefulness,sefulness, a propertyproperty fi rrstst oobservedbserved wwithith ttelephony,elephony, aandnd llaterater tthehe IInternet.nternet. Dan Dahle EEnsemblesnsembles ccanan bbee ccreatedreated bbyy uusingsing nnowow ccommonlyommonly aavailablevailable wwirelessireless aandnd Intel Corporation wwiredired sstandards,tandards, pprovidingroviding anan aggregateaggregate vvaluealue ttoo a uuserser tthathat iiss ggreaterreater tthanhan tthehe ssumum ooff tthehe ccomponentomponent pparts.arts. IInn tthishis aarticle,rticle, wwee eexaminexamine tthehe oopportunitiespportunities forfor UUttamttam SenguptaSengupta eensemblensemble computing;computing; classifyclassify thethe mainmain usagesusages andand applicationapplication domains;domains; reviewreview IIntelntel CCorporationorporation eenablingnabling componentcomponent technologies,technologies, andand pointpoint outout thethe rresearchesearch cchallengeshallenges thatthat nneedeed ttoo bbee aaddressedddressed ttoo rrealizeealize tthehe ffullull ppotentialotential ooff tthehe eensemblensemble cconcept.oncept.

Introduction Index Words Th e hhistoryistory ooff mmodernodern ccomputingomputing ccanan bbee ddividedivided iintonto tthreehree ddistinctistinct eeras,ras, eeachach EEnsemblesnsembles ccharacterizedharacterized bbyy tthehe nnumberumber ooff ccomputersomputers aavailablevailable ttoo aann aaverageverage uuser.ser. DuringDuring MMobileobile ComputingComputing tthehe fi rrstst eera,ra, ddominatedominated bbyy tthehe mmainframeainframe ((1960-1980),1960-1980), ttherehere wwereere ttypicallyypically DDistributedistributed SystemsSystems mmanyany ppeopleeople uusingsing a ssingleingle computer.computer. IInn tthehe PPersonalersonal CComputeromputer ((PC)PC) eraera CContext-awareontext-aware ((1980-2000),1980-2000), mmostost ppeopleeople hhadad ttheirheir oownwn PPC.C. TToday,oday, wwee aarere iinn tthehe tthirdhird eerara WWirelessireless NetworkingNetworking ((20002000 oonwards)nwards) iinn wwhichhich iitt iiss nnowow ccommonommon fforor ppeopleeople ttoo oownwn andand uusese manymany ccomputers,omputers, ssometimesometimes rreferredeferred ttoo aass tthehe eerara ooff uubiquitousbiquitous ccomputingomputing [[1].1].

IInn aadditionddition ttoo tthehe ttrendrend ooff iincreasingncreasing nnumbersumbers ooff ccomputingomputing ddevicesevices pperer ppersonerson pperer yyear,ear, wwee hhaveave sseeneen iimprovedmproved pprocessorrocessor pperformanceerformance ((drivendriven bbyy MMoore’soore’s Law)Law) andand greatergreater nnetworketwork cconnectivityonnectivity fforor mmobileobile ccomputersomputers tthathat hhaveave bbeeneen mmadeade ppossibleossible tthroughhrough iinnovationsnnovations inin sstandardizedtandardized wwirelessireless ttechnologies.echnologies. Th e esese sstandardstandards pproviderovide hhigh-bandwidthigh-bandwidth ddata-transmission,ata-transmission, aallowingllowing sseamlesseamless ccoordinationoordination bbetweenetween aapplications,pplications, andand theythey enableenable ffullyully distributeddistributed aandnd rreplicatedeplicated pprogrammingrogramming mmodels.odels. BByy a mmeasureeasure ccalledalled tthehe nnetworketwork eeffff eect,ct, oorr MMetcalfe’setcalfe’s LLawaw [[2],2], N ddevicesevices cconnectedonnected iinn tthishis wwayay ccreatereate a ttotalotal nnetworketwork vvaluealue pproportionalroportional ttoo tthehe nnumberumber ooff cconnectionsonnections ttheyhey ccanan mmakeake mmultipliedultiplied bbyy tthehe nnumberumber ooff ddevicesevices pparticipating;articipating; tthishis rresultsesults iinn tthehe nnetworketwork vvaluealue ggrowingrowing aatt OO(N(N2)).. OOrchestratedrchestrated ccollectionsollections ooff ccomputersomputers ccanan tthushus pproviderovide ggreaterreater aaggregateggregate vvaluealue ttoo uuserssers tthanhan wwouldould bebe expectedexpected ffromrom a ssimpleimple ssumum ooff tthehe ccomponentomponent pparts.arts.

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AAlthoughlthough ddistributedistributed programmingprogramming hhasas bbeeneen tthehe ssubjectubject ooff rresearchesearch fforor ““WeWe ccallall dynamicallydynamically coordinatedcoordinated ssomeome ttimeime wwithith iitsts ffoundationoundation iinn nnetworksetworks ooff ttraditionalraditional serversservers oror desktopdesktop ccomputers,omputers, mobilemobile ccomputingomputing bbringsrings ddynamicallyynamically cchanginghanging ttopologies,opologies, ccollectionsollections ofof computers,computers, whichwhich includeinclude ccontext-awareness,ontext-awareness, aandnd mmoreore diversediverse ccollectionsollections ofof computingcomputing rresources,esources, bbothoth mmobileobile andand infrastructureinfrastructure aaddingdding a newnew ddimensionimension ttoo tthishis fi eeld.ld. WWee ccallall ddynamicallyynamically ccoordinatedoordinated ccollectionsollections ooff computers,computers, wwhichhich iincludenclude bbothoth mmobileobile aandnd iinfrastructurenfrastructure ccomponents,omponents, DDeviceevice EEnsemblesnsembles..”” ccomponents,omponents, DDeviceevice EEnsemblesnsembles [[3],3], aandnd tthehe ttechniquesechniques fforor pprogrammingrogramming aandnd oorchestratingrchestrating ttheirheir aapplications,pplications, EEnsemblensemble CComputingomputing.

TV/STB Cell Tower

Den PC Smart Phone Server

Laptop

Localized Ensemble in the Digital Home Internet Wide-area Ensemble Across a City

Figure 1: Ensembles of Devices a) Localized: Based on Wireless Local Area Network (WLAN), b) Wide-area: Based on Wireless Wide-area Network (WWAN), Properties: Dynamic Confi guration/Heterogeneous/Context-aware Source: Intel Corporation, 2010

EEnsemblesnsembles ccanan bbee ccreatedreated fforor ddiffiff eerentrent sscalescales ooff uuse,se, pprimarilyrimarily ddeterminedetermined bbyy ggeographiceographic sseparation.eparation. InIn closeclose proximityproximity (localized(localized eensembles—Figurensembles—Figure 11a),a), a ccomputeromputer ccanan bebe eenhancednhanced bbyy ddynamicallyynamically aaddingdding nnewew wwirelessireless peripherals,peripherals, ee.g.,.g., a wwirelessireless hheadset.eadset. AAlternatively,lternatively, ccomputersomputers ccanan mmutuallyutually shareshare theirtheir oownwn ssystemystem rresourcesesources ssuchuch aass ddisplays,isplays, nnetworks,etworks, aandnd ddisks.isks. PProcessorrocessor ssharingharing bbetweenetween ddevicesevices iiss aalsolso ppossibleossible tthroughhrough tthehe mmigrationigration ooff aapplicationspplications eencapsulatedncapsulated inin a virtualvirtual machinemachine image,image, migratingmigrating themthem bbetweenetween llow-ow- aandnd hhigh-performanceigh-performance computers.computers. SharingSharing rresourcesesources inin thisthis wayway effeff eectivelyctively bbuildsuilds llogicalogical computerscomputers byby wirelesslywirelessly ppiecingiecing ttogetherogether nnewew ccomponentsomponents oonn tthehe fl yy,, ““SharingSharing rresourcesesources iinn tthishis wwayay tthushus eenablingnabling a uuserser ttoo oovercomevercome tthehe ddesignesign llimitationsimitations ooff ttheirheir oownwn ccomputeromputer bbyy uusingsing wwhateverhatever ccanan bbee ffoundound nnearbyearby [[4].4]. IInn llocalizedocalized eensembles,nsembles, pproximityroximity eeffff ectivelyectively buildsbuilds llogicalogical ccomputersomputers iiss a pprerequisitererequisite fforor ccomponentsomponents tthathat ssupportupport a uuserser iinterfacenterface ((e.g.,e.g., ddisplay,isplay, bbyy wwirelesslyirelessly piecingpiecing togethertogether newnew ccamera,amera, kkeyboard,eyboard, mmouse),ouse), aass iitt oonlynly mmakesakes ssenseense ttoo ssharehare tthesehese ccomponentsomponents wwhenhen ttheyhey aarere pphysicallyhysically aaccessibleccessible ttoo a uuser.ser. ccomponentsomponents onon thethe fl y.”y.”

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IInn ccontrast,ontrast, eensemblensemble applicationsapplications basedbased onon highlyhighly distributeddistributed ssetsets ofof hheterogeneouseterogeneous ddevicesevices mmayay ttakeake aadvantagedvantage ooff ggeographiceographic ddiversityiversity ((wide-areawide-area eensembles—Figurensembles—Figure 11b),b), wwhilehile sstilltill dynamicallydynamically adaptingadapting theirtheir membershipmembership aandnd ttakingaking aadvantagedvantage ooff ttheirheir ccontextontext ooff uuse.se. Th i iss iinformationnformation ccanan bbee uusedsed ttoo ccreatereate eensemble-widensemble-wide iinferencesnferences bbasedased oonn ttheirheir pphysicalhysical sseparationeparation tthathat wwouldould hhaveave bbeeneen iimpossiblempossible ffromrom a llocalizedocalized viewpoint.viewpoint. ForFor example,example, a smart-phonesmart-phone vvehicularehicular ttraffiraffi cc-monitoring-monitoring aapplicationpplication [[5]5] ccanan bebe ddesignedesigned ssoo tthathat eeachach ssmartmart pphonehone eenrollednrolled iinn tthehe ttaskask iiss pprogrammedrogrammed ttoo pperiodicallyeriodically rrelayelay iinformationnformation aaboutbout itsits locationlocation toto a server,server, whichwhich inin turnturn buildsbuilds upup a real-timereal-time vviewiew ooff ttraffiraffi c fl ooww acrossacross aallll tthehe ccityity hhighways,ighways, aandnd tthushus ccanan hhighlightighlight aareasreas ooff ccongestion.ongestion. Th e traffitraffi cc-service-service rrelayselays tthishis iinformationnformation bbackack ttoo eeachach ooff tthehe ssmartmart pphoneshones rrunningunning a ttraffiraffi cc-monitoring-monitoring cclient,lient, tthushus eenablingnabling uuserssers ttoo mmakeake ddecisionsecisions aaboutbout ttheirheir ppreferredreferred ddrivingriving rroutes.outes. Th e rresultingesulting aapplicationpplication hhasas ggreaterreater uutilitytility tthanhan wwouldould bebe ppossibleossible withwith a setset ofof ccontextuallyontextually isolatedisolated devicesdevices originallyoriginally ddesignedesigned fforor tthehe pprimaryrimary ttaskask ooff mmakingaking pphonehone ccalls.alls. ““InIn tthehe casecase ooff WWLANs,LANs, uunlikenlike wwiredired LLocalizedocalized aandnd wwide-areaide-area eensemblensemble aapplicationspplications ofof thethe ttypesypes ddescribedescribed herehere existexist ttoday,oday, bbutut ttherehere iiss nnoo cconsistentonsistent pprogrammingrogramming sstrategytrategy oorr architecturearchitecture thatthat cancan nnetworks,etworks, therethere isis nono cconnectivityonnectivity bbee uusedsed ttoo ccapitalizeapitalize oonn llessonsessons learnedlearned fromfrom ttheirheir ddesignesign aandnd iimplementation.mplementation. bbetweenetween aanyny ooff tthehe ppeereer llayersayers iinn tthehe Th i iss lleaveseaves eengineersngineers ttoo rreinventeinvent tthehe wwheelheel aacrosscross mmanyany ooff tthehe aapplicationpplication ddomains.omains. Furthermore,Furthermore, tthesehese llessonsessons aarere rrarelyarely ccapturedaptured iinn tthehe ttool-chainsool-chains uusedsed pprotocolrotocol sstacktack uuntilntil a llayer-2ayer-2 ddiscoveryiscovery ttoo iimplementmplement tthem,hem, aandnd tthereforeherefore ddevelopersevelopers ddoo nnotot pprogressivelyrogressively bbuilduild bbetteretter pprocessrocess hashas takentaken place.”place.” ttoolsools forfor eacheach generationgeneration ooff ssystemystem ddesign.esign. IInn tthehe rremainderemainder ooff tthishis aarticlerticle wwee eexaminexamine bbackgroundackground aandnd rrelatedelated wwork,ork, eenablingnabling technologiestechnologies aandnd oopportunitiespportunities forfor eensemblensemble ccomputing,omputing, aandnd wewe ddiscussiscuss tthehe cchallengeshallenges tthathat nneedeed ttoo bbee aaddressed.ddressed.

Background DDistributedistributed pprogrammingrogramming hhasas bbeeneen a ssubjectubject ooff rresearchesearch aandnd ddevelopmentevelopment ssinceince tthehe 11970s970s wwithith mmanyany wwell-understoodell-understood pprogrammingrogramming mmodelsodels ddevelopedeveloped aandnd inin ccommonommon useuse today.today.

AAlthoughlthough wwirelessireless eensemblesnsembles ccanan makemake useuse ofof manymany provenproven ddistributed-istributed- ccomputingomputing aabstractionsbstractions suchsuch asas sockets,sockets, remoteremote procedureprocedure callcall (RPC),(RPC), messagemessage ppassing,assing, sstreaming,treaming, andand cclient/serverlient/server modelsmodels inin commoncommon useuse today,today, ttheyhey ddiffiff eerr iinn sseveraleveral iimportantmportant ways.ways. IInn tthehe ccasease ooff WWLANs,LANs, uunlikenlike wwiredired nnetworks,etworks, ttherehere iiss nnoo cconnectivityonnectivity bbetweenetween aanyny ooff tthehe ppeereer llayersayers iinn tthehe pprotocolrotocol sstacktack uuntilntil a layer-2layer-2 ddiscoveryiscovery pprocessrocess hhasas ttakenaken pplace,lace, aandnd uuntilntil a mmobileobile ddeviceevice iiss iinstructednstructed ttoo cconnectonnect ((manuallymanually oorr aautomatically).utomatically). InIn thethe casecase ofof WWANs,WWANs, ddevicesevices aarere aalwayslways connectedconnected bbutut peer-to-peerpeer-to-peer mmessagingessaging aandnd ddiscoveryiscovery

120 | Ensemble Computing: Opportunities and Challenges Intel® Technology Journal | Volume 14, Issue 1, 2010 pprotocolsrotocols aarere rrestrictedestricted bbyy tthehe rrulesules ooff a pparticulararticular sserviceervice pprovider,rovider, llimitingimiting ““InIn tthehe ccasease ooff WWWANs,WANs, ddevicesevices aarere tthehe ttypesypes ooff pprotocolsrotocols iinn uuse.se. HHowever,owever, iinn eeitherither ttypeype ooff wwirelessireless nnetwork,etwork, eensemblesnsembles ooff ddevicesevices ccanan aaugmentugment tthehe ddiscoveryiscovery pprocessrocess ffurtherurther bbyy iincludingncluding aalwayslways connectedconnected butbut peer-to-peerpeer-to-peer mmetadataetadata tthathat cancan bebe derivedderived fromfrom theirtheir currentcurrent contextcontext (e.g.,(e.g., llocation,ocation, oorr mmessagingessaging andand discoverydiscovery protocolsprotocols aarere pphysicalhysical sensorsensor data),data), andand ddeviceevice ccapabilitiesapabilities ((e.g.,e.g., ssupportedupported ccommunicationommunication pprotocols).rotocols). BBasedased oonn tthesehese mmetadata,etadata, ddecisionsecisions ccanan bbee mmadeade aaboutbout tthehe ddeviceevice rrestrictedestricted byby tthehe rrulesules ooff a pparticulararticular ggroupingsroupings tthathat cancan form.form. ContextContext informationinformation cancan alsoalso bebe derivedderived ffromrom uuserser sserviceervice pprovider,rovider, limitinglimiting thethe typestypes ofof iinput,nput, aautomaticallyutomatically sensed,sensed, oorr inferredinferred fromfrom thethe behaviorbehavior ofof applications.applications. SSharedhared mmetadataetadata ooff tthishis ttypeype ccanan ddefiefi nnee aandnd ddynamicallyynamically mmodifyodify cconnectionsonnections aass pprotocolsrotocols inin use.”use.” tthehe ccontextontext cchanges.hanges. WWee nownow llookook iinn mmoreore ddetailetail aatt ssomeome ooff tthehe ssolutionsolutions tthathat ggiveive rriseise ttoo eensemblesnsembles iinn bbothoth tthehe llocalocal aandnd wwide-areaide-area eenvironment.nvironment.

Localized Ensembles RRadioadio ttechnologiesechnologies tthathat aarere ddesignedesigned fforor sshort-rangehort-range ooperationperation iimplicitlymplicitly ddefiefi nnee a llocalizedocalized ensembleensemble ofof devicesdevices byby thethe naturenature ofof thethe proximateproximate connectionsconnections theythey ccanan eestablish.stablish. Th e fi rrstst ddigitaligital rradioadio sstandardtandard ttoo aachievechieve tthishis wwasas BBluetooth*,luetooth*, pprovidingroviding aann eeffff eectivective rreplacementeplacement fforor wwiredired pperipheralseripherals ((upup ttoo 1100 mm).). BBluetooth’sluetooth’s mmostost ppopularopular aapplicationpplication hhasas bbeeneen ttoo cconnectonnect a ccellell pphonehone ttoo a wwirelessireless hheadset,eadset, bbutut tthehe pprotocolrotocol ccanan iinn ffactact llinkink uupp ttoo 8-slave8-slave peripheralsperipherals toto a ccomputer;omputer; tthereby,hereby, sservingerving aass tthehe mmasteraster ddeviceevice [[6]6]. BBluetoothluetooth applicationapplication eexamplesxamples includeinclude on-body,on-body, in-room,in-room, andand in-carin-car networksnetworks supportingsupporting anan eensemblensemble ooff ddevicesevices iinn tthosehose ccontexts.ontexts.

SShort-rangehort-range rradioadio ssystemsystems hhaveave rrecentlyecently eenablednabled nnewew oopportunitiespportunities fforor ppatientatient ccare.are. MMonitoringonitoring ooff cchronicallyhronically illill patientspatients whilewhile ooutut ofof a hhospital,ospital, aandnd hhenceence mmobileobile ((ambulatoryambulatory mmonitoring),onitoring), hhasas bbeeneen a ggoaloal ooff pphysicianshysicians fforor mmanyany yyears.ears. InIn recentrecent years,years, inexpensiveinexpensive BodyBody SensorSensor NetworksNetworks (BSNs)(BSNs) hhaveave bbecomeecome vviable.iable. Th i iss iiss bbecauseecause ppowerower cconsumptiononsumption hhasas bbeeneen rreducededuced ttoo a ppointoint wwherehere iitt iiss ppossibleossible ttoo pperformerform ssignalignal pprocessing,rocessing, aandnd tthehe rresultsesults ccanan bbee wwirelesslyirelessly ccommunicatedommunicated wwithinithin a ppowerower eenvelopenvelope tthathat ccanan bbee ssustainedustained bbyy a ssmallmall battery-poweredbattery-powered ddeviceevice fforor sseveraleveral ddaysays [[7].7]. BBSNsSNs ccanan wwirelesslyirelessly cconnectonnect a hheterogeneouseterogeneous ssetet ooff ssensorsensors tthroughhrough a BBodyody AArearea NNetworketwork ((BAN)BAN) [[8]8] ttoo a ccentralentral processorprocessor tthathat ccanan sstore,tore, oorr wwirelesslyirelessly oofflffl ooad,ad, tthehe rresultsesults ttoo a hhospital,ospital, fforor eexample,xample, tthroughhrough a ssecondaryecondary rradio,adio, ssuchuch aass WWiFiiFi oorr a GGeneraleneral PPacketacket RRadioadio ServiceService ((GPRS)GPRS) [[9].9]. HHowever,owever, sspecialpecial ccareare nneedseeds ttoo bbee ttakenaken wwithith tthehe aantennantenna ddesign,esign, bbecauseecause iitsts bbasebandaseband ffrequencyrequency iiss 22.4.4 GGHz,Hz, wwhichhich iiss rreadilyeadily aabsorbedbsorbed bbyy wwater,ater, aandnd tthereforeherefore wwirelessireless ssignalsignals ccannotannot ttravelravel tthroughhrough tthehe bbodyody wwithoutithout bbeingeing sseverelyeverely attenuated.attenuated. SSensors,ensors, iincludingncluding EEKGs,KGs, ppulse-ulse- ooximeters,ximeters, aandnd bblood-pressurelood-pressure mmonitors,onitors, aarere nnowow aalsolso rreadilyeadily aavailablevailable aass ccommercialommercial productsproducts aandnd ccanan bbee iintegratedntegrated iintonto a BBAN.AN. ““BluetoothBluetooth applicationapplication examplesexamples iincludenclude on-body,on-body, in-room,in-room, andand in-carin-car nnetworksetworks ssupportingupporting anan ensembleensemble ofof ddevicesevices inin thosethose contexts.”contexts.”

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““AnAn ensemble,ensemble, bbasedased oonn body-body- AAnothernother uusese ooff BBSNs,SNs, ootherther tthanhan mmonitoringonitoring tthehe bbody’sody’s vvitalital ssigns,igns, iiss toto mmonitoronitor pphysicalhysical activity.activity. InIn rrecentecent years,years, therethere hashas beenbeen cconsiderableonsiderable iinterestnterest wwornorn devices,devices, ssuchuch aass a wwatchatch oror iinn uusingsing ttechnologyechnology ttoo aallowllow a largerlarger fractionfraction ofof thethe eelderlylderly ppopulationopulation a ccellell pphone,hone, iinn ccombinationombination withwith ttoo rremainemain inin theirtheir hhomesomes aass llongong aass possiblepossible withoutwithout needingneeding ttoo resortresort ttoo iinstitutionalnstitutional care,care, oftenoften rreferredeferred ttoo aass aging-in-place.aging-in-place. Th e pproblemroblem iiss tthathat aagingging eenvironmentalnvironmental mmonitorsonitors iinn tthehe hhome,ome, mmayay bbee aaccompaniedccompanied bbyy a sslowlow mentalmental decline,decline, andand itit isis oftenoften notnot cclearlear toto ccanan pproviderovide ccaregiversaregivers wwithith tthehe ddataata ffamilyamily aandnd ffriendsriends wwhenhen aann eelderlylderly ppersonerson bbecomesecomes a ddangeranger ttoo hhimim oorr hherselferself [[10]10]. AAnn eensemble,nsemble, bbasedased oonn bbody-wornody-worn ddevices,evices, aandnd eembeddedmbedded iinn dday-to-dayay-to-day ttheyhey need.”need.” aaccessoriesccessories suchsuch asas a watchwatch oror a cellcell phone,phone, inin combinationcombination withwith environmentalenvironmental mmonitorsonitors inin tthehe hhome,ome, ccanan pproviderovide ccaregiversaregivers wwithith tthehe ddataata ttheyhey nneed.eed. FForor eexample,xample, wwhenhen ddailyaily aactivityctivity ppatternsatterns cchangehange aandnd bbecomeecome iincreasinglyncreasingly ssedentaryedentary oorr eerratic,rratic, tthesehese ddevicesevices ccanan pproviderovide vvitalital cclueslues tthathat a ppersonerson iiss nnoo llongeronger bbehavingehaving iinn a hhealthfulealthful wway,ay, aandnd tthathat sshehe nneedseeds ffurtherurther eevaluation.valuation. Th e vvaluealue ppropositionroposition fforor tthehe eelderlylderly iiss tthathat iinn mmostost ccasesases ttheyhey rreadilyeadily wwantant ttoo bbee aableble ttoo staystay inin theirtheir oownwn homehome aass longlong asas theythey areare able,able, andand a BSNBSN providesprovides ccaregivers,aregivers, tthehe pphysicians,hysicians, aandnd tthehe eelderlylderly wwithith tthehe iinformationnformation nneededeeded ttoo mmakeake tthishis ppossible.ossible.

Th e WWiFiiFi rradioadio sstandardtandard aandnd iitsts vvariousarious ggenerationsenerations ((b/a/g/n)b/a/g/n) aalsolso ssupportupport a nnetworketwork ooff pproximateroximate wwirelessireless ddevices,evices, bbutut tthesehese sstandardstandards aarere ttypicallyypically ccenteredentered oonn aann iinfrastructurenfrastructure nnode,ode, oorr aaccessccess ppoint.oint. AAlthoughlthough tthesehese nnetworksetworks ccanan bbee bbridgedridged ttoo bbuilduild a wwirelessireless nnetworketwork ooff aarbitraryrbitrary ssize,ize, a ccommonommon cconfionfi ggurationuration mmakesakes useuse ofof a singlesingle accessaccess pointpoint servingserving oonene llocationocation uupp ttoo a rradiusadius ooff 110000 mm.. FForor eexample,xample, iin-homen-home nnetworksetworks ttypicallyypically onlyonly needneed oonene accessaccess ppoint,oint, aandnd aallll devicesdevices tthathat ddiscoveriscover aandnd cconnectonnect ttoo iitt ccanan tthenhen ccommunicateommunicate wwithith eeachach oother.ther. Th e ““digitaldigital hhome”ome” iiss aanothernother eexamplexample ooff wwherehere a ccoordinatedoordinated eensemblensemble ofof devicesdevices ccanan bbetteretter sserveerve a uuserser tthanhan a ssetet ooff iisolatedsolated ddevices.evices. ByBy ccoordinatingoordinating tthehe aaccessccess aandnd pplaybacklayback ofof digitaldigital mediamedia ccapturedaptured aandnd cconsumedonsumed oonn a widewide vvarietyariety ooff cconsumeronsumer ddevices,evices, a uuserser ccanan sseeee oorr llistenisten ttoo ttheirheir mediamedia onon a ddeviceevice tthathat iiss mmostost cconvenient,onvenient, oorr hhasas tthehe bbestest pphysicalhysical ccapabilitiesapabilities (e.g.,(e.g., size,size, rresolution,esolution, andand fi ddelity).elity).

SSmartmart sspacespaces, oorr ssmartmart rroomsooms, aarere a ffertileertile aarearea fforor eexperimentationxperimentation tthathat mmakeake uusese ooff tthehe ttenetsenets ooff eensemblensemble ccomputing.omputing. Th e eessencessence ooff a ssmartmart sspacepace iiss oonene iinn wwhichhich llocalocal iinfrastructurenfrastructure iiss rreadilyeadily mmadeade aavailablevailable aass a sserviceervice ttoo uuserssers aandnd ttheirheir mmobileobile ccomputingomputing ddevices.evices. UUsually,sually, tthishis iiss iinn tthehe fformorm ooff ssupportupport fforor mmultimediaultimedia ccapabilitiesapabilities ttoo eenhancenhance mmeetingseetings aandnd ppresentations,resentations, bbutut mmayay eextendxtend ttoo hhighly-ighly- sspecializedpecialized ccapabilities,apabilities, ddependingepending oonn tthehe oorganizationrganization tthathat ddevelopedeveloped iit.t. MManyany ooff tthehe cconceptsoncepts tthathat uunderlienderlie ssmartmart sspacespaces aarere eexemplifixemplifi eedd iinn tthehe EEasyLivingasyLiving pprojectroject aatt MMicrosofticrosoft [[11],11], aandnd tthehe SStanfordtanford iiRoomRoom pprojectroject [[12].12]. FForor eexample,xample, tthehe iiRoomRoom ssupportsupports mmultiple,ultiple, wwall-sizedall-sized sscreenscreens tthathat ccanan bbee llinkedinked ttogetherogether iintonto oonene ccontiguousontiguous ddisplay,isplay, aandnd aatt tthehe ssameame ttime,ime, iiss wwirelesslyirelessly iintegratedntegrated wwithith llaptopsaptops aandnd ““ThTh e essenceessence ooff a ssmartmart sspacepace iiss oonene iinn ootherther hheterogeneouseterogeneous mmobileobile ddevicesevices bbroughtrought iintonto tthehe sspace.pace. Th e ssystemystem ccanan aalsolso bbee ccommandedommanded tthroughhrough ttangibleangible oobjectsbjects ddesignedesigned ttoo bbee mmanipulated,anipulated, oorr ggesturedestured wwhichhich llocalocal iinfrastructurenfrastructure iiss rreadilyeadily wwith,ith, ttoo pproviderovide iintuitiventuitive uuserser ccontrols.ontrols. Th i iss ssmartmart sspacepace ddemonstratedemonstrated eeffff eectivective mmadeade availableavailable aass a sserviceervice toto usersusers uusese ooff tthehe eensemblensemble ccomputingomputing cconceptoncept iinn ssupportupport ooff ggrouproup ccollaboration.ollaboration. Th e EEasyLivingasyLiving pprojectroject hhadad ssimilarimilar pproperties,roperties, bbutut aalsolso mmadeade uusese ooff ccamerasameras aandnd aandnd ttheirheir mmobileobile ccomputingomputing ddevices.”evices.” iimagemage pprocessingrocessing ttoo iinfernfer aactivitiesctivities ggoingoing oonn iinn tthehe ssmartmart sspace.pace.

122 | Ensemble Computing: Opportunities and Challenges Intel® Technology Journal | Volume 14, Issue 1, 2010

Wide-Area Ensembles EEnsemblensemble ccomputingomputing hashas iitsts ooriginrigin iinn GGridrid [[13]13] aandnd CCloudloud CComputingomputing ““EnsembleEnsemble computingcomputing hashas itsits originorigin fframeworksrameworks [14][14]. Th e esese ttechniquesechniques ccanan bbee uusedsed ttoo ssupportupport eensemblensemble aapplications,pplications, andand itit isis llikelyikely thatthat nnewew pprogrammingrogramming paradigmsparadigms willwill bebe iinn ggridrid andand cloudcloud computingcomputing ddiscoverediscovered tthathat ffurtherurther eenhancenhance tthehe vvaluealue ooff eensemblesnsembles iinn tthehe ffuture.uture. HHowever,owever, fframeworks.”rameworks.” mmanyany eensemblensemble aapplicationspplications ccanan aalsolso bbee bbuiltuilt bbyy uusingsing sstandardtandard ddistributedistributed ccomputingomputing ttechniquesechniques tthathat aarere aaugmentedugmented ttoo ttakeake aadvantagedvantage ooff mmobileobile ppropertiesroperties ssuchuch aass ccontext.ontext.

SSocialocial nnetworkingetworking fforor mmobileobile ddevicesevices iiss aann eexamplexample wwherehere ddistributedistributed ccomputingomputing mmergeserges wwithith mmobileobile aandnd ccontext-awareontext-aware computingcomputing aandnd cclearlylearly ddefiefi nesnes valuevalue fforor ddeviceevice eensembles.nsembles. CConsideronsider ssomeome ooff tthehe llatestatest llocation-basedocation-based ccomputingomputing aapplications,pplications, ssuchuch aass LLooptoopt* oorr OOverhereverhere* tthathat rrunun oonn aann iiPhone*,Phone*, aandnd uusese ccell-tower-basedell-tower-based ((oror GGPS-based)PS-based) ppositionosition fi nnding.ding. IInn tthesehese ssystems,ystems, a ggrouproup ooff friendsfriends decidedecide toto shareshare ttheirheir llocationocation iinformation,nformation, bbyy aallowingllowing ttheirheir ddevicesevices ttoo bbee ttracked.racked. EEffff eectively,ctively, aann eensemblensemble ooff ddevicesevices hhasas bbeeneen ddeclaredeclared tthathat iiss a proxyproxy fforor groupgroup mmembers.embers. Th e rresultingesulting ssystemystem lletsets yyouou kknownow iiff yyourour ffriendsriends areare nnearbyearby ssoo tthathat yyouou ccanan sserendipitouslyerendipitously mmeeteet uupp ooverver ccoffoff eeee oorr ssharehare a mmeal.eal. IInn tthehe ccasease ooff LLoopt,oopt, yyouou cancan alsoalso periodicallyperiodically keepkeep ttrackrack ooff youryour ffriends’riends’ sstatustatus tthroughhrough ssecondaryecondary sserviceservices ssuchuch aass TTwitter*witter* notifinotifi ccations.ations. SSensorensor NNetworksetworks aarere aanothernother eexamplexample ooff wwide-areaide-area eensemblensemble ccomputingomputing iinn ““ManyMany ssensorensor networksnetworks aarere ccomposedomposed wwhichhich tthehe uunderlyingnderlying ggoaloal iiss fforor aann eensemblensemble ooff ddevicesevices ttoo wworkork togethertogether toto ssharehare eenvironmentalnvironmental ddataata iinn oorderrder ttoo mmakeake ssenseense ooff tthem,hem, aandnd uunderstandnderstand ooff hhighlyighly ccustomizedustomized nodesnodes (often(often llargerarger sscalecale ttrendsrends [[15].15]. EExamplesxamples iincludenclude mmicro-weathericro-weather mmonitoringonitoring iinn oorderrder rreferredeferred ttoo aass mmotes)otes) tthathat ssenseense aandnd ttoo mmakeake betterbetter wweathereather forecasts,forecasts, sseismiceismic aactivityctivity mmonitoringonitoring ttoo uunderstandnderstand tthehe eeffff eectscts ooff ccity-wideity-wide eearthquakearthquake ddamageamage oonn bbuildingsuildings aandnd sstructures,tructures, aandnd rrelayelay informationinformation aacrosscross a wwirelessireless wwide-areaide-area ppollutionollution mmonitoringonitoring toto aadvisedvise oonn ttravel.ravel. ManyMany sensorsensor networksnetworks areare mmeshesh ooff ddevicesevices towardstowards a collectioncollection ccomposedomposed ofof highlyhighly customizedcustomized nodesnodes (often(often referredreferred toto asas motes)motes) thatthat sensesense aandnd rrelayelay iinformationnformation aacrosscross a wwirelessireless mmeshesh ooff ddevicesevices ttowardsowards a collectioncollection ppoint.”oint.” ppoint,oint, oorr ssink.ink. FFromrom ttherehere iitt iiss rroutedouted ttoo mmoreore ccapableapable pprocessorsrocessors tthathat ccanan sstoretore aandnd aanalyzenalyze tthehe ddata,ata, aandnd iinn tturnurn iinfernfer tthehe ddominantominant ttrends.rends. Th rroughough nnetworketwork sserverservers tthehe rresultsesults ccanan bbee rredistributededistributed ttoo uuserssers rrunningunning cclientlient pprograms,rograms, therebythereby aallowingllowing tthemhem ttoo ttakeake aappropriateppropriate aaction.ction. AAnn eexamplexample ooff a ssensorensor nnetworketwork iinn aactionction iiss tthehe CCommonommon SSenseense pprojectroject [[16]16] iinn IIntelntel LLabsabs tthathat pprovidesrovides uuserssers wwithith a ddeviceevice ttoo monitormonitor atmosphericatmospheric pollutionpollution basedbased onon carboncarbon mmonoxide,onoxide, nnitrogenitrogen ooxides,xides, aandnd oozone.zone. Th e eentirentire ssystemystem ccomprisesomprises bbothoth a llocalocal eensemblensemble aandnd a wide-areawide-area eensemble.nsemble. LLocally,ocally, pollutionpollution measurementsmeasurements areare ccombinedombined withwith locationlocation iinformationnformation ffromrom thethe monitormonitor hardwarehardware viavia BluetoothBluetooth ttoo a cellcell pphone.hone. Th e enn bbyy uusingsing GGPRS,PRS, tthehe ccellell pphonehone pperiodicallyeriodically ttransmitsransmits tthesehese ddataata ooverver tthehe wwide-areaide-area nnetworketwork ttoo a sservererver wwherehere tthehe iinformationnformation iiss aaggregated;ggregated; tthereby,hereby, pprovidingroviding a sserviceervice tthathat ssupportsupports aallll ooff tthehe pparticipatingarticipating pphones.hones. IInn tthishis wway,ay, uuserssers ccanan bbee aadviseddvised aaboutbout ttravelravel ooptions,ptions, aandnd tthehe aairborneirborne ppollutionollution llevelsevels ccurrentlyurrently ccontaminatingontaminating pparticulararticular rroutes.outes. SuchSuch a ssystemystem bbecomesecomes valuablevaluable whenwhen a largerlarger numbernumber ofof devicesdevices areare pparticipatingarticipating iinn pparallelarallel aacrosscross a largelarge distributeddistributed area.area.

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Enabling Technology and Trends EEnsemblesnsembles hhaveave bbeeneen eenablednabled bbyy sseveraleveral ttechnologyechnology ttrends,rends, eeachach aadvancingdvancing tthehe ccapabilitiesapabilities ooff mmobileobile ddevices.evices. Th e kkeyey aadvancesdvances aarere iincreasingncreasing pprocessorrocessor pperformanceerformance ((FigureFigure 22a)a) aatt llowerower ppower,ower, iincreasingncreasing pportableortable mmemoryemory ddensityensity ((FigureFigure 22b),b), aandnd iincreasingncreasing wwirelessireless nnetworkingetworking bbandwidthandwidth ((FigureFigure 22c),c), aandnd aallll aatt ssmallermaller formform factorsfactors forfor eacheach newnew generationgeneration ofof ddevice.evice.

Vacuum-tube Era Transistor Era Microprocessor Era 1.E+16 Current Laptops Sicortex SC5832 1.E+15 Dell Dimension 2400 Gateway P3 (733 MHz) 1.E+14

Dell Optiplex GXI 1.E+13 IBM PS/2E & Sun SS1000 1.E+12 Intel 486/25 & 486/33 Computations per Kilowatt-Hour if they 1.E+11 Macintosh 128K followed Moore’s Law, doubling every IBM PC-AT two years 1.E+10 IBM PC IBM PC-XT Cray 1 Apple IIe 1.E+09 Commodore 64 DEC PDP-11/20 1.E+08 Altair 8800 SDS 920 1.E+07

1.E+06 UNIVAC III

Computations per Kilowatt-Hour 1.E+05 UNIVAC II 1.E+04 UNIVAC I 1.E+03 EDVAC ENIAC 1.E+02 1940 1950 1960 1970 1980 1990 2000 2010 Year The complete study is available from the Intel Web site at http://download.intel.com/pressroom/pdf/computertrendsrelease.pdf.

Figure 2a: Trends in Processor Instructions per kWhr by Year Source: Intel Corporation, 2010

FFigureigure 22aa sshowshows tthehe ddramaticramatic pprogressrogress tthathat hhasas bbeeneen aachievedchieved iinn iincreasingncreasing pprocessorrocessor pperformanceerformance iinn ttermserms ooff eeverver iincreasingncreasing nnumbersumbers ooff iinstructionsnstructions tthathat ccanan bbee pperformederformed wwithith tthehe ssameame aamountmount ooff eenergy.nergy. Th e iimplicationmplication iiss tthathat llow-powerow-power pprocessorsrocessors ccanan ddoo mmoreore eeachach yyearear ggiveniven tthehe aamountmount ooff eenergynergy tthathat ccanan bbee sstoredtored iinn a ssmallmall portableportable battery—abattery—a technologytechnology whosewhose energyenergy densitydensity isis iimprovingmproving aatt a ffarar llowerower rrate.ate.

124 | Ensemble Computing: Opportunities and Challenges Intel® Technology Journal | Volume 14, Issue 1, 2010

Areal Density of Magnetic HDD and DRAM 100000 100% CGR Travelstar 30GT Travelstar 18GT Microdrive II 10000 Travelstar 6GN Ultrastar 60% CGR Ultrastar 36ZX 36LZX 25% = 2X per 3 years Ultrastar 36XP 1000 40 2 Ultrastar 18XP 60 1.5 Ultrastar 2XP 1024M 100 1 Ultrastar XP 256M Corsair 100 3390 2 64M 3380K 3380E 16M 40% CGR 25% CGR 10 4M 1M

1 Areal Density (Mbits/inch2) 0.1

0.01 1970 1980 1990 2000 2010 AREAL 98E.PRZ Year Ed Grochowski at Almaden

Figure 2b: Trends in Magnetic and Semiconductor Storage Density by Year Source: Intel Corporation, 2010

FFurther,urther, tthehe yyearlyearly rrateate ooff iincreasencrease iinn sstoragetorage ddensityensity fforor mmagneticagnetic mmedia,edia, a rrateate wwhichhich hhasas bbeeneen oout-pacingut-pacing MMoore’soore’s LLaw,aw, hhasas bbeeneen aapproximatelypproximately ddoublingoubling eeveryvery yyearear ((FigureFigure 22b),b), aandnd tthishis iincreasencrease hhasas aalsolso bbeeneen a kkeyey eenablernabler fforor eensembles.nsembles. AAss a result,result, ssmallmall mmobileobile ddevicesevices aarere aableble ttoo sstoretore thethe ggigabytesigabytes ooff ddataata requiredrequired bbyy mmodernodern ooperatingperating ssystemsystems aandnd ttheirheir aapplications,pplications, andand atat anan aaffff oordablerdable ppricerice ppoint.oint. TToday,oday, mmanyany mmobileobile ccomputersomputers aarere aass ccapableapable aass ssomeome ooff tthehe mmostost ppowerfulowerful desktopdesktop ccomputersomputers iinn uusese ttenen yyearsears aagogo wwhilehile aalsolso rrunningunning ccomparableomparable operatingoperating systems.systems.

10000

802.11ac 1000

802.11HR 802.11n 100 802.11a 802.11g 802.11b

Bandwidth (Mbps) Bandwidth 10

1 1998 2000 2002 2004 2006 2008 2010 2012 Year

Figure 2c: Trends in Wireless Bandwidth for WLANS by Year Source: Intel Corporation, 2010

Ensemble Computing: Opportunities and Challenges | 125 Intel® Technology Journal | Volume 14, Issue 1, 2010

FFinally,inally, iinter-devicenter-device ccommunication,ommunication, aann eessentialssential ccomponentomponent ooff eensemblensemble ccomputing,omputing, hhasas aalsolso improvedimproved ddramatically.ramatically. IItt wwasas oonlynly iinn 11999999 tthathat tthehe fi rrstst ddraftraft ooff tthehe BBluetoothluetooth sstandardtandard aandnd tthehe fi rrstst iimplementationsmplementations ooff tthehe IIEEEEEE 8802.11b02.11b WWiFiiFi [[17]17] ((1111 MMbps)bps) sstandardtandard wwereere eestablished.stablished. TToday,oday, 8802.11HR02.11HR aapproachespproaches 445050 MMbps,bps, wwithith ffurtherurther eextensionsxtensions pplannedlanned ((FigureFigure 22c).c). WWide-ide- aarea,rea, wireless-datawireless-data ttransportransport sserviceservices ssuchuch aass GGPRS,PRS, aandnd llaterater 33GG [[18],18], aalsolso bbecameecame aavailablevailable duringduring thisthis ttime.ime. EEachach ttechnologyechnology ssupportsupports ccommunicationommunication aatt ddiffiff eerentrent ggeographiceographic sscalescales aandnd bbandwidthandwidth aandnd ccanan bbee cclassifilassifi eedd iintonto vvariousarious ttypesypes ooff nnetworksetworks nnowow commonlycommonly availableavailable toto supportsupport ensembleensemble computing:computing:

• Personal Area Networks (PANs) connecting computers and peripheral components over a short range (10 m) e.g., Bluetooth 1.0 (1 Mbps). • WLANs connecting computers to local infrastructure and other nearby computers (100 m) e.g., WiFi/802.11g (54 Mbps). • WWANs connecting mobile computers to cell towers networked across a city, e.g., GPRS (2000 m) 20/80kbps.

1600 1400 1200 1000 Cell phones 800 Smart Phones 600 Laptops

Shipments (M) 400 200 0 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Year

Figure 3: Shipments of Mobile Devices by Year: Actual 2004-2009 and Forecast 2010-2014 Source: Intel Corporation, 2010

FFurthermore,urthermore, tthehe vvaluealue ppropositionroposition fforor mmobileobile uuserssers hhasas ccontinuedontinued ttoo iincrease;ncrease; ii.e.,.e., mmoreore ccapabilityapability aatt llowerower cost,cost, resultingresulting iinn tthehe sspectacularpectacular iincreasencrease iinn mmarketarket ssizeize fforor ccellell pphones,hones, ssmartmart pphones,hones, aandnd llaptopaptop ccomputersomputers tthathat wewe havehave wwitnesseditnessed dduringuring tthehe llastast fi vvee yyears.ears. MMoreover,oreover, tthehe ttrendrend iiss sstilltill fforecastedorecasted ttoo ccontinueontinue ddespiteespite tthehe rrecentecent rrecessionecession iinn 22009009 ((FigureFigure 33).). Th e llarge-scalearge-scale pproliferationroliferation ooff tthesehese ddevicesevices hhasas bbecomeecome a kkeyey eenablernabler fforor a wwideide vvarietyariety ooff eensemblensemble applications.applications.

126 | Ensemble Computing: Opportunities and Challenges Intel® Technology Journal | Volume 14, Issue 1, 2010

Opportunities IInn tthishis ssectionection wwee cconsideronsider tthreehree mmajorajor oopportunitiespportunities fforor rrealizingealizing ggreaterreater vvaluealue fforor eensemblensemble ssolutionsolutions iinn tthehe ffollowingollowing aareas:reas: cconvertibleonvertible rresources,esources, ssuper-uper- cchargingharging pperformance,erformance, andand aaddeddded vvaluealue ffromrom newnew emergentemergent bbehaviors.ehaviors.

Convertible Resources AAlthoughlthough sshort-rangehort-range wirelesswireless standardsstandards provideprovide a corecore ccapabilityapability ttoo eenablenable ““ThTh e DDCCCC ccompositionomposition fframeworkramework llocalizedocalized eensembles,nsembles, a hhigher-leveligher-level cconstructonstruct iiss nneededeeded ttoo ttakeake aadvantagedvantage ooff tthem.hem. Th e DDynamicynamic CComposableomposable CComputingomputing ((DCC)DCC) pprojectroject aatt IIntelntel [[4]4] iiss uutilizestilizes mmanyany existingexisting solutionssolutions forfor a oonene mmodelodel fforor oovercomingvercoming thethe resourceresource llimitationsimitations ooff a ccomputer,omputer, eespeciallyspecially ccategoryategory ofof peripherals,peripherals, advertisingadvertising a ssmallmall mmobileobile device,device, aaugmentingugmenting itsits capabilitiescapabilities byby utilizingutilizing tthehe rresourcesesources ooff mmoreore ccapableapable ddevicesevices nnearby.earby. Th e mmodelodel fforor DDCCCC iiss ttoo aabstractbstract aawayway tthehe ttheirheir ppresence,resence, aandnd ccoordinatingoordinating uunderlyingnderlying ddevicesevices bbyy uusingsing a cclient/serverlient/server sserviceervice mmodelodel eenablingnabling a rremoteemote ooperationsperations forfor thethe useruser viavia aann iintuitiventuitive pperipheraleripheral ttoo aappearppear aass iiff llocal.ocal. Th e erere aarere sseveraleveral iindustryndustry ssolutionsolutions ttoo eenablenable nnetworketwork aaccessccess ttoo rremoteemote ddisplays,isplays, ssuchuch aass VVirtualirtual NNetworketwork CComputingomputing ((VNC)VNC) GGUI.”UI.” [[19],19], sstoragetorage [[20],20], aandnd UUSBSB pperipheralseripherals [[21],21], bbutut nnoneone tthathat ccoordinateoordinate aallll tthesehese sserviceservices iintonto a uunifinifi eedd ssystem.ystem. Th e DDCCCC compositioncomposition fframeworkramework uutilizestilizes mmanyany eexistingxisting ssolutionsolutions fforor a ccategoryategory ooff pperipherals,eripherals, aadvertisingdvertising ttheirheir ppresence,resence, aandnd ccoordinatingoordinating ooperationsperations fforor tthehe uuserser vviaia aann iintuitiventuitive GGUI.UI. Th e oopportunitypportunity fforor ccomposableomposable systemssystems iiss fforor eeveryvery ccomputeromputer ttoo bbee aableble ttoo cconvertonvert iitselftself iintonto a mmuchuch mmoreore ccapableapable devicedevice byby usingusing tthehe bbestest ooff tthehe aavailablevailable resourcesresources nearby.nearby.

Super-Charging Performance IItt iiss aalsolso possiblepossible toto useuse high-performancehigh-performance ccomputersomputers ttoo aaugmentugment tthehe pprocessingrocessing ccapabilitiesapabilities ofof nearbynearby ssmallmall mmobileobile ddevices,evices, tthushus ggoingoing bbeyondeyond ssharingharing ssystemystem pperipherals,eripherals, ttoo ssharingharing a pprocessorrocessor aamongmong aann eensemblensemble ooff ddevices.evices. HHowever,owever, uunlikenlike pperipheraleripheral ssharingharing mmechanismsechanisms ssuchuch aass VVNC,NC, ssuper-uper- cchargingharging pprocessingrocessing hashas nnotot bbeeneen widelywidely exploredexplored toto datedate inin ssupportupport ofof mobilemobile ccomputing.omputing.

OOnene ooff tthehe mmostost ppromisingromising aapproachespproaches ttoo eenablenable tthishis ccapabilityapability iiss iinn tthehe rrealmealm ooff vvirtualirtual mmachineachine ((VM)VM) mmigration.igration. IItt hhasas oonlynly rrecentlyecently bbeeneen ppracticalractical ttoo rrunun a VVMM oonn a handheldhandheld mobilemobile computercomputer withwith thethe adventadvent ooff llow-powerow-power mmobileobile xx8686 pprocessorsrocessors ((i.e.,i.e., tthehe IIntel®ntel® AAtom™tom™ familyfamily ofof processors).processors). MobileMobile InternetInternet DDevicesevices ((MIDs)MIDs) aandnd NNetbooks,etbooks, bbothoth bbasedased oonn tthehe IIntelntel AAtomtom pprocessor,rocessor, aalsolso rrunun sstandardtandard operatingoperating ssystemsystems bbasedased oonn WWindows*indows* andand Linux*.Linux*. Th e ““ThTh e nnextext ggenerationeneration ooff IIntelntel AAtomtom nnextext ggenerationeneration ooff IIntelntel AtomAtom processorsprocessors willwill targettarget smartsmart pphones,hones, aandnd rrunun sstandardtandard operatingoperating ssystemsystems bbyy uusingsing xx8686 aapplicationspplications wwithoutithout modifimodifi ccation.ation. pprocessorsrocessors willwill targettarget smartsmart pphones,hones, Th e rresultingesulting ccommonommon iinstruction-setnstruction-set aallowsllows tthehe ssameame ccodeode ttoo rrunun oonn mmobileobile ccomputersomputers thatthat areare basedbased oonn thethe IntelIntel AtomAtom processor,processor, asas itit doesdoes onon mostmost aandnd runrun standardstandard operatingoperating systemssystems ddesktopesktop ccomputers,omputers, aandnd tthushus sstandardtandard VVMM hhypervisors,ypervisors, aandnd tthehe aassociatedssociated bbyy uusingsing x86x86 applicationsapplications withoutwithout VVMM mmigrationigration ttechniques,echniques, ccanan bbee eemployedmployed ttoo ssupportupport tthehe mmigrationigration ooff ccomputationomputation betweenbetween thethe two.two. mmodifiodifi cation.”cation.”

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CConsideronsider tthehe bbenefienefi ttss ooff VVMM mmigrationigration iinn aann eeverydayveryday sscenariocenario ((FigureFigure 44)) iinn wwhichhich a mmobileobile pprofessional,rofessional, Jane,Jane, wisheswishes toto maintainmaintain a consistentconsistent computingcomputing eexperiencexperience aass hherer ccomputingomputing aactivitiesctivities fl ooww bbetweenetween hhome,ome, ooffiffi cce,e, aandnd mmobileobile wworking.orking. WWhilehile iinn hherer hhomeome ooffiffi cce,e, JJaneane wwasas ssendingending ee-mail,-mail, ssurfiurfi nngg tthehe WWeb,eb, aandnd rreferringeferring ttoo ddocumentsocuments aaboutbout a pproductroduct sshehe wwantedanted ttoo rresearch.esearch. WhenWhen mmobile,obile, sshehe wwouldould llikeike toto continuecontinue thesethese ttasksasks onon herher ssmartmart phonephone eevenven whilewhile wwaitingaiting fforor a ffriendriend iinn a pparkingarking llot.ot. LLaterater sshehe fi nndsds tthehe pproductroduct iinn a sstoretore aandnd ttakesakes ssomeome ppicturesictures wwithith hherer mmobileobile ssoo sshehe ccanan sstudytudy iitt mmoreore bbeforeefore bbuyinguying it.it. AAss isis oftenoften tthehe ccasease wwithith ssmartmart pphones,hones, tthehe ccameraamera hhasas ppooroor rresolution,esolution, aandnd ssoo sshehe eemploysmploys a ssuper-resolutionuper-resolution [[22]22] aapplicationpplication inin whichwhich severalseveral picturespictures aarere ttakenaken iinn qquickuick succession,succession, andand thenthen ttheyhey aarere ccombinedombined ttoo ccreatereate a hhigherigher rresolutionesolution picturepicture ((aa ccompute-ompute- aandnd ppower-intensiveower-intensive aactivity).ctivity).

Th i iss sscenariocenario ccanan bebe implementedimplemented bbyy rrunningunning JJane’sane’s eentirentire ooffiffi ccee PPC’sC’s ccomputationalomputational statestate inin a VMVM thatthat cancan bebe suspended,suspended, aandnd tthenhen ttransferredransferred toto hherer ssmartmart pphonehone wwherehere iitt iiss rresumed.esumed. WWhilehile mmobile,obile, hherer ee-mail-mail aandnd ddocumentsocuments ccanan bbee aaccessedccessed aass before,before, aandnd tthehe mmobileobile pphone’shone’s ccameraamera ccanan bebe uusedsed toto taketake pphotos.hotos. WWhenhen rreturningeturning hhome,ome, oorr aatt hherer wworkplace,orkplace, hherer ssmartmart pphonehone ccanan ssuspenduspend iitsts VVMM aagaingain aandnd ttransferransfer iitt bbackack ttoo a ddesktopesktop PPCC wwherehere iitt ccanan rresumeesume aandnd eexecutexecute aatt hhigherigher pperformance.erformance. IInn tthishis eexample,xample, VVMM mmigrationigration eenablesnables eeffff eectivective mmobilityobility bbyy pprovidingroviding ssessionession ttransferransfer aandnd bbyy ssuper-charginguper-charging pprocessorrocessor pperformanceerformance fforor CCPU-PU- aandnd ppower-intensiveower-intensive ooperations.perations. BByy uutilizingtilizing a mmains-ains- ppoweredowered ddesktopesktop ccomputer,omputer, iitt iiss ppossibleossible ttoo rreduceeduce pprogramrogram eexecutionxecution ttimeime oonn tthehe ssmartmart pphone,hone, wwhilehile aalsolso savingsaving powerpower onon a battery-constrainedbattery-constrained ddevice.evice.

INTERNET

Den Computer Office PC WIMAX

VM Resync Intermittent Connectivity WLAN WLAN VM Migration VM Migration PC to Phone Phone to PC

HOME MOBILE OFFICE

Figure 4: A Smart Phone Migrating Processing Between Home, Offi ce PC, and Mobile Use, Encapsulated in a Virtual Machine Source: Intel Corporation, 2010

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SSmartmart pphones,hones, bbasedased oonn tthehe IIntelntel AAtomtom pprocessor,rocessor, mmakeake tthishis mmobileobile uusese mmodelodel ““VMVM mmigrationigration iiss nnotot a ppracticalractical a rreality.eality. IInn a collaborationcollaboration bbetweenetween tthehe UUniversityniversity ooff TTorontooronto aandnd CCarnegiearnegie MMellonellon UUniversityniversity ((CMU),CMU), tthehe HHoratiooratio ssystemystem [[23]23] hhasas bbeeneen ddevelopedeveloped ooptionption asas thethe largelarge imageimage sizesize eexpandingxpanding thethe eearlierarlier wworkork oonn IInternetnternet SSuspenduspend RResumeesume ((ISR)ISR) [[24]24] ttoo iincludenclude ((4-20GB)4-20GB) resultsresults inin transfertransfer timestimes mmigrationigration ttoo a ssmartmart phone.phone. Th i iss ssystemystem ddemonstratesemonstrates tthehe oopportunitypportunity fforor uusingsing eeitherither a nnetworketwork sserver,erver, oorr a mmobileobile ddevice,evice, ttoo ttransferransfer a VVMM iimagemage ttoo a tthathat wwouldould likelylikely taketake tootoo longlong overover a ssecondaryecondary PC.PC. HHowever,owever, tthehe fi rrstst vversionersion ooff tthehe HHoratiooratio ssystemystem uusedsed AAdvanceddvanced WWWANWAN oorr ootherther llong-haulong-haul network.”network.” RRiskisk MMachinesachines ((ARM)ARM) bbasedased ssmartmart pphoneshones aandnd tthereforeherefore ccouldould nnotot rresumeesume tthehe VVMM iimagemage wwhilehile mmobile.obile. IInn a ffewew yyears,ears, xx8686 ssmartmart pphoneshones wwillill becomebecome mmoreore ccommon,ommon, tthushus enablingenabling thethe moremore completecomplete useuse model.model.

IInn aadditionddition ttoo llocalocal iinfrastructure,nfrastructure, ccloudloud ccomputingomputing [[14]14] ooffff eersrs aanothernother oopportunitypportunity ttoo ssuper-chargeuper-charge tthehe eexecutionxecution pperformanceerformance ooff a mmobileobile ddevice.evice. IInn tthishis ccasease ccomputationomputation ccanan bbee mmovedoved ffromrom a mmobileobile ttoo a hhigh-performanceigh-performance ccomputingomputing ((HPC)HPC) ccenter.enter. However,However, VVMM mmigrationigration iiss nnotot a ppracticalractical ooptionption aass tthehe llargearge iimagemage ssizeize ((4-20GB)4-20GB) rresultsesults iinn ttransferransfer ttimesimes tthathat wwouldould llikelyikely ttakeake ttoooo llongong ooverver a WWWANWAN oorr ootherther llong-haulong-haul nnetwork.etwork. OOnn tthehe ootherther hhand,and, eensemblesnsembles tthathat aarere ddesignedesigned fforor sspecializedpecialized ttasksasks mmayay iincludenclude HHPCPC sservices,ervices, iinn ccombinationombination withwith mobilemobile devicesdevices thatthat sendsend onlyonly selectedselected ddataata eelements.lements. Th e esese mmightight iincludenclude media,media, ddocuments,ocuments, aandnd ccontextontext sentsent toto servicesservices iinn tthehe ccloudloud forfor pprocessing,rocessing, e.g.,e.g., photosphotos sentsent toto thethe cloudcloud forfor imageimage iidentifidentifi ccation,ation, oorr ddocumentsocuments translatedtranslated fformorm oonene languagelanguage toto aanother.nother. IInn bbothoth ccasesases tthesehese sserviceservices aarere iimprovedmproved bbyy uutilizingtilizing ccontextontext kknowledgenowledge aaboutbout tthehe mmedia’sedia’s ccreation,reation, wwhichhich ccanan bbee providedprovided bbyy tthehe eensemble.nsemble.

Added Value from Emergent Behaviors AAlthoughlthough tthehe nnumberumber ooff ccompute-capableompute-capable ddevicesevices iinn uusese iiss ppredictedredicted ttoo rreacheach ““Increasingly,Increasingly, ddevicesevices fi ndnd tthemselveshemselves 1155 bbillionillion bbyy 22015015 [[25],25], aandnd tthehe nnumberumber ooff ddevicesevices cconnectedonnected ttoo tthehe IInternetnternet wwillill mmoreore tthanhan ddoubleouble ffromrom 20102010 toto 20132013 [26],[26], thethe sheersheer aavailabilityvailability ofof devicesdevices iinn a sseaea ooff otherother devices,devices, eacheach ooff wwhichhich ttoo ccommunicateommunicate doesdoes nnotot equateequate withwith theirtheir intelligentintelligent coordination.coordination. Th e hhasas tthehe aabilitybility ttoo measuremeasure itsits oownwn oopportunitypportunity ttoo hharnessarness tthehe ccollectiveollective rresourcesesources ooff mmultipleultiple ddevicesevices hhasas bbeeneen mmaturingaturing fforor ssomeome ttime,ime, yetyet thethe opportunityopportunity toto harnessharness thethe ccollectiveollective wwisdomisdom bbehaviors,ehaviors, ttoo sensesense thethe eenvironmentnvironment ooff ggroupsroups ooff ddevicesevices aawaitswaits uus.s. oorr ccontextontext inin whichwhich itit iiss operating,operating, IIncreasingly,ncreasingly, ddevicesevices fi nndd tthemselveshemselves iinn a sseaea ooff ootherther ddevices,evices, eeachach ooff wwhichhich aandnd toto shareshare itsits fi ndingsndings wwithith ootherther hhasas tthehe aabilitybility ttoo mmeasureeasure iitsts oownwn bbehaviors,ehaviors, ttoo ssenseense tthehe eenvironmentnvironment oorr ccontextontext iinn wwhichhich iitt iiss ooperating,perating, aandnd ttoo ssharehare iitsts fi nndingsdings wwithith ootherther ddevices.evices. ddevices.”evices.” AAss a consequenceconsequence ofof gossipinggossiping data,data, notnot onlyonly areare devicesdevices ableable toto buildbuild locallocal aapproximatepproximate iimagesmages ooff ggloballobal ssystemystem sstate,tate, bbutut aalsolso ttoo eexhibitxhibit ggloballobal ppropertiesroperties tthathat eemergemerge ffromrom llocalocal pproperties.roperties. IInn tthesehese eemergentmergent ccollaborativeollaborative systems,systems, mmetricsetrics hhaveave bbeeneen sshownhown ttoo iimprovemprove wwithith tthehe ssizeize ooff tthehe ggroup.roup. IInn tthehe ssecurityecurity rrealm,ealm, eensemblesnsembles ooff eend-hostsnd-hosts ccollaborativelyollaboratively ddefendefend tthehe eenterprisenterprise nnetwork,etwork, ooffff eeringring iimprovedmproved aaccuracyccuracy aandnd ssensitivityensitivity ooff mmalwarealware ddetectionetection [[27].27]. IInn tthehe wwirelessireless wworld,orld, eensemblesnsembles hhaveave bbeeneen uusedsed ttoo ggreatreat eeffff eectct ttoo mmitigateitigate wwirelessireless iinterferencenterference [[28].28]. AAdditionally,dditionally, iinn tthehe aarenarena ooff nneighborhood-leveleighborhood-level nnetworking,etworking, ddistributedistributed ttrustrust mmodelsodels hhaveave ddemonstratedemonstrated tthehe ssimplifiimplifi ccationation ooff sself-elf- cconfionfi ggurationuration [[29].29].

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Challenges DDespiteespite tthehe mmanyany aattractivettractive oopportunities,pportunities, ttherehere iiss a vvarietyariety ooff cchallengeshallenges wwhenhen aapplyingpplying eensemblensemble cconceptsoncepts ttoo ppracticalractical problems.problems. HereHere wewe considerconsider diffidiffi ccultiesulties iinn mmanageability,anageability, nnewew programmingprogramming models,models, wirelesswireless networknetwork limitations,limitations, uusability,sability, power,power, andand securitysecurity andand privacy.privacy.

Manageability Challenges OOnene cchallengehallenge ooftenften ffacedaced bbyy wwide-areaide-area eensemblesnsembles iiss tthehe sstringenttringent rrequirementequirement fforor hhomogeneity,omogeneity, ii.e.,.e., tthathat aallll mmachinesachines aagreegree oonn tthehe ssameame ssoftware,oftware, pprotocols,rotocols, fformats,ormats, aandnd vversioning.ersioning. Th u us,s, mmachineachine ffederationsederations aarere ooftenften mmanagedanaged bbyy oonene oowner,wner, whowho isolatesisolates thethe solutionssolutions fromfrom oonene aanothernother aandnd ccanan tthwarthwart eeffff oortsrts ttoo ssupportupport a moremore broadlybroadly generalizedgeneralized sserviceervice [[30].30]. HHowever,owever, pproprietaryroprietary ssolutionsolutions oftenoften rreduceeduce ssecurityecurity aandnd pprivacyrivacy cconcernsoncerns tthathat aariserise wwhenhen ddeviceevice ffederationsederations sspanpan multiplemultiple ownersowners and/orand/or multiplemultiple administrativeadministrative domains,domains, eveneven tthoughhough ttheyhey mmayay nnotot hhaveave tthehe mmostost eeffff eectivective ssolutions.olutions.

WWithith tthehe pproliferationroliferation ooff mmobileobile aandnd eembeddedmbedded ddevices,evices, ttherehere iiss aann oopportunitypportunity ttoo rrevisitevisit hhowow wwee mmanageanage tthem.hem. IInn tthehe aabsencebsence ooff aann IITT ddepartment,epartment, ccomputersomputers aarere aatt llibertyiberty ttoo bbootstrapootstrap sserviceservices ffromrom nnearbyearby [4,[4, 31]31] oorr llike-mindedike-minded ddevicesevices [[32,32, 333,3, 334],4], aand/ornd/or ffromrom rreputableeputable ppeerseers [[35],35], rratherather tthanhan ffromrom ppreconfireconfi gguredured sserverservers oorr pproxies.roxies. IInn ootherther wwords,ords, eensemblesnsembles ccanan ttakeake aadvantagedvantage ooff ppeer-to-peereer-to-peer mmechanismsechanisms iinn a ccontextontext wwherehere nnoo iinfrastructurenfrastructure eexists.xists. However,However, eensemblesnsembles aalsolso uunderscorenderscore tthehe cchallengeshallenges iinherentnherent iinn eestablishingstablishing ddeviceevice ttrustworthinessrustworthiness [[36],36], aandnd tthehe cchallengehallenge ooff ppreservingreserving a ddevice’sevice’s iidentitydentity aalonglong wwithith iitsts ddataata ((seesee llaterater ssectionection oonn SSecurityecurity aandnd PPrivacy).rivacy). FForor wwideide aacceptance,cceptance, tthesehese iissuesssues nneedeed ttoo bbee rresolved,esolved, aandnd tthehe llevelevel ooff ssharingharing nneedseeds ttoo bbee aadapteddapted ttoo tthehe ccontextontext bbeforeefore eenterprisenterprise IITT ddepartmentsepartments wwillill aallowllow ttheirheir mmobileobile ccomputersomputers ttoo pparticipatearticipate iinn ggeneralizedeneralized eensemblensemble aapplications.pplications.

New Programming Models PPlatform-independentlatform-independent pprogrammingrogramming ssuchuch aass JJava*,ava*, FFlash*,lash*, aandnd SSilverlight*ilverlight* ccanan bbee aadapteddapted ttoo eensemblensemble pprogrammingrogramming iinn wwhichhich aapplicationspplications runrun acrossacross devicesdevices wwithith ddiffiff eerentrent ooperatingperating ssystemsystems aandnd hheterogeneouseterogeneous hhardwareardware pplatforms.latforms. HHowever,owever, eensemblensemble ccomputingomputing iiss inherentlyinherently ddistributedistributed aacrosscross mmultipleultiple ddevicesevices ((unlikeunlike tthehe ttraditionalraditional cclient-serverlient-server mmodel),odel), aandnd iitt sshouldhould ddynamicallyynamically aadaptdapt ttoo tthehe ppresenceresence ooff nnearbyearby rresources.esources. Th i iss eenvironment,nvironment, uunlikenlike tthehe sstatictatic cconfionfi ggurationuration ooff wwiredired ccomputeromputer nnetworks,etworks, eextendsxtends eexistingxisting pplatform-latform- iindependentndependent pprogrammingrogramming mmodelsodels tthathat ccurrentlyurrently mmayay nnotot ssuffiuffi ccee ttoo ttakeake ““EnsembleEnsemble ccomputingomputing isis inherentlyinherently aadvantagedvantage ooff aallll thethe ppotentialotential benefibenefi ttss ooff aann eensemble.nsemble. ddistributedistributed aacrosscross mmultipleultiple ddevicesevices aandnd iitt sshouldhould ddynamicallyynamically aadaptdapt ttoo tthehe ppresenceresence ooff nnearbyearby rresources.”esources.”

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WWee eenvisionnvision thatthat requirementsrequirements fforor nnewew pprogrammingrogramming mmodelsodels ttoo ssupportupport eensemblensemble ssystemsystems wwillill bbearear ssimilaritiesimilarities ttoo tthosehose fforor ddata-parallelata-parallel technologies,technologies, ssuchuch aass Globus*Globus* [37][37] oror MapReduce*MapReduce* [[38]38] wwithith aadditionaldditional supportsupport forfor runningrunning aalgorithmslgorithms effieffi ccientlyiently oonn aann uunreliable,nreliable, hheterogeneouseterogeneous ccollectionollection ooff mmobileobile ddevices.evices. FForor iinstance,nstance, wwhenhen a ffailureailure ooccursccurs e.g.,e.g., a participatingparticipating devicedevice ssuddenlyuddenly lleaveseaves tthehe aarea,rea, tthehe ddepartingeparting ccodeode sshouldhould bbee rre-executede-executed oonn a ddeviceevice tthathat iiss sstilltill ppresent.resent.

SSecond,econd, ccontext-awareontext-aware pprogrammingrogramming mmodelsodels [[39,39, 440]0] ccanan aalsolso bbee uusefulseful ttoo wwriterite eensemblensemble aapplications.pplications. Th e esese pprogrammingrogramming mmodelsodels aallowllow ddevelopersevelopers ttoo ddefiefi nnee ttuplesuples tthathat cconnectonnect a ccurrenturrent ccontext,ontext, dderivederived ffromrom ssensorensor ddata,ata, ttoo a correspondingcorresponding aactionction tthathat aallowsllows pprogramsrograms ttoo nnaturallyaturally adaptadapt toto theirtheir eenvironment,nvironment, aandnd ttoo tthehe ddynamically-changingynamically-changing mmembershipembership ooff aann eensemble.nsemble. A ffriend-firiend-fi nnderder aapplicationpplication iiss a ggoodood eexamplexample aass iitt uusesses ssensedensed llocation-dataocation-data ttoo iinitiatenitiate aann aactionction tthathat nnotifiotifi eess uuserssers tthathat aarere nnearear oonene aanothernother iinn a ccity.ity.

Wireless Limitations WWhilehile wwirelessireless cconnectivityonnectivity pprovidesrovides ggreatreat bbenefienefi ttss iinn cconvenienceonvenience aandnd uusability,sability, iitt aalsolso ppresentsresents ssignifiignifi ccantant cchallengeshallenges iinn rreliabilityeliability aandnd fformorm ffactor.actor.

Reliable Connectivity Th e rreliabilityeliability ooff a cconnectiononnection bbetweenetween eensemblensemble ddevicesevices iiss iimpactedmpacted bbyy a nnumberumber ooff factorsfactors inin thethe ensemble’sensemble’s environment.environment. PPhysicalhysical oobjectsbjects ccanan bblocklock tthehe wwirelessireless ssignalignal bbetweenetween ensembleensemble devicesdevices andand dropdrop thethe connection,connection, mmuchuch llikeike a ddroppedropped cellularcellular ccall.all. WWhenhen eensemblesnsembles iincludenclude mmobileobile nnodes,odes, rreliableeliable ccommunicationommunication cancan bebe problematic.problematic. Also,Also, radioradio frequencyfrequency interferenceinterference (RFI)(RFI) mmayay bbee ccausedaused bbyy ootherther wirelesswireless ddevicesevices wwithinithin rrangeange ooff tthehe eensemble.nsemble. Th e hhouseholdousehold mmicrowaveicrowave oovenven isis a ttypicalypical eexample,xample, ccontributingontributing iinterferencenterference iinn tthehe llicense-freeicense-free 22.4.4 GGHzHz bband,and, iinn wwhichhich mmostost hhomeome aandnd cconsumeronsumer wwirelessireless ddevicesevices aaroundround tthehe wworldorld ooperate.perate. FForor wwide-areaide-area eensemblesnsembles ttherehere aarere a llargerarger nnumberumber ooff otherother devicesdevices toto ccooperateooperate withwith (and(and interfereinterfere wwith)ith) tthanhan fforor llocal-areaocal-area ensembles,ensembles, aandnd tthishis ssituationituation ccanan aalsolso lleadead ttoo ppotentialotential ssecurityecurity rrisksisks ((seesee SSectionection oonn SSecurityecurity aandnd PPrivacy).rivacy). FFurthermore,urthermore, llargearge ddistancesistances bbetweenetween eensemblensemble ddevicesevices ccanan aaffff eectct tthehe qqualityuality aandnd rreliabilityeliability ooff cconnection.onnection. DDevicesevices tthathat cconnectonnect nnearear tthehe limitslimits ooff ttheirheir rrangeange mmustust pprocessrocess wweakereaker ssignalsignals tthathat aarere mmoreore ddiffiiffi ccultult ttoo ddecodeecode rreliably.eliably. RResearchesearch oonn DDelayelay TTolerantolerant NNetworkingetworking [[41]41] ssuggestsuggests ttechniquesechniques ttoo mmitigateitigate ccommunicationommunication llinkink ffailureailure aandnd boostboost rreliabilityeliability iinn tthesehese ssituations.ituations.

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““AchievingAchieving ggreaterreater rrangeange ttypicallyypically AAnothernother aapproachpproach fforor iincreasingncreasing tthehe rreliabilityeliability ooff wwirelessireless communicationcommunication iiss ttoo ddesignesign ddevices,evices, oorr iinfrastructuralnfrastructural ccommunicationommunication hubs,hubs, withwith greatergreater rrequiresequires a mmoreore ppowerfulowerful ttransmitterransmitter ooperationalperational range.range. However,However, aachievingchieving ggreaterreater rrangeange ttypicallyypically rrequiresequires a mmoreore tthathat ttranslatesranslates ttoo llargerarger batteries,batteries, ppowerfulowerful ttransmitterransmitter tthathat ttranslatesranslates ttoo largerlarger bbatteries,atteries, biggerbigger aantennas,ntennas, aandnd a llargerarger pphysicalhysical device.device. Th e esese ffactorsactors aarere a cchallengehallenge wwhenhen ddesigningesigning mmobileobile bbiggerigger antennas,antennas, aandnd a llargerarger pphysicalhysical ddevices,evices, rresultingesulting iinn a ccompromiseompromise ooff uutilitytility vversusersus formform ffactor.actor. ddevice.”evice.” Form Factor BByy ddefiefi nnition,ition, ggiveniven tthehe ddynamicynamic nnatureature ooff eensemblesnsembles aandnd ggrouproup fformation,ormation, a ssignifiignifi ccantant nnumberumber ooff pparticipatingarticipating ddevicesevices aarere llikelyikely ttoo bbee hhighlyighly mmobile,obile, wwithith ssmallmall user-friendlyuser-friendly fformorm ffactors.actors. Th e esese uultra-mobileltra-mobile ddesignsesigns pproviderovide ssignifiignifi ccantant cchallengeshallenges wwhenhen aaccommodatingccommodating tthehe aantennantenna aandnd ppowerower rrequirementsequirements ooff a rradioadio ssubsystemubsystem thatthat providesprovides ddiscoveryiscovery aandnd cconnectivity.onnectivity. HHigh-capacityigh-capacity bbatteriesatteries tthathat ccanan ssupportupport hhigh-powerigh-power rradios,adios, oorr llongong ttransmissionransmission times,times, incurincur aadditionaldditional ddeviceevice wweighteight aandnd ssize.ize. IIncreasingly,ncreasingly, mmobileobile ddevicesevices aalsolso ssupportupport sseveraleveral ccommunicationommunication technologiestechnologies (3G,(3G, BT,BT, WiFi)WiFi) iinn tthehe ssameame ppackage,ackage, ooperatingperating aatt a vvarietyariety ooff ffrequencies.requencies. IInn tturn,urn, tthishis iincreasesncreases thethe ccomplexityomplexity ofof aantennantenna ddesigns,esigns, aalsolso requiringrequiring sshieldinghielding bbetweenetween eeachach rradio,adio, aandnd tthesehese ffactorsactors ccontributeontribute ttoo llargerarger ppackagingackaging rrequirementsequirements fforor a mmobileobile ddevice.evice.

Usability Issues ““DevicesDevices tthathat ttransmitransmit wweakeak ssignalsignals Th e bbroadroad aavailabilityvailability aandnd sspectrumpectrum ooff ddevicesevices tthathat ccanan fformorm aann eensemble,nsemble, aandnd ddoo ssoo wwithith mminimalinimal uuserser iinterventionntervention, wwillill dictatedictate tthehe uusabilitysability aandnd ppervasivenesservasiveness mmayay frequentlyfrequently ddroprop cconnectionsonnections wwithith ooff tthehe ttechnology.echnology. A ssuccessfuluccessful wwiredired pprecedentrecedent ccameame wwithith tthehe iintroductionntroduction ootherther eensemblensemble ddevices,evices, ttherebyhereby ccausingausing ooff tthehe uuniversalniversal sserialerial bbusus ((USB),USB), wwhichhich aallowedllowed uuserssers toto painlesslypainlessly transfertransfer ddataata bbetweenetween ddevices.evices. NNotablyotably aatt CCESES 22010,010, mmanufacturersanufacturers sstartedtarted sshowinghowing llostost ddataata aandnd sslowlow rresponseesponse ttimes.”imes.” cconceptsoncepts fforor wwirelesslyirelessly pairingpairing mmobileobile devicesdevices wwithith CConsumeronsumer EElectroniclectronic (CE)(CE) eequipmentquipment ((suchsuch aass TTVs)Vs) ttoo shareshare ccontentontent andand executeexecute aapplications.pplications. WeWe cancan eeasilyasily imagineimagine tthishis nnotionotion eevolvingvolving ttoo iincludenclude eensemblesnsembles bbetweenetween ((andand wwithin)ithin) aautomobiles,utomobiles, peripherals,peripherals, aandnd hhomeome aappliances.ppliances. KeyKey iingredientsngredients fforor mmakingaking anan eensemblensemble computingcomputing paradigmparadigm wworkork wwellell areare minimalminimal andand consistentconsistent user-user- iinterfacesnterfaces ((UI),UI), ppreference-basedreference-based conficonfi ggurationuration aandnd iintelligentntelligent sset-up,et-up, aandnd ccontext-basedontext-based aadaptationdaptation aandnd cconnection.onnection. FFurther,urther, iinn aann ooptimalptimal world,world, thesethese wwouldould allall requirerequire minimalminimal useruser interventionintervention toto discover,discover, cconnect,onnect, aandnd ssharehare rresourcesesources aamongmong participatingparticipating ccomputers.omputers.

SSomeome ooff tthehe pprimaryrimary aadvantagesdvantages ooff wwirelessireless ssystemsystems aalsolso ccreatereate aadditionaldditional cchallengeshallenges iinn uusagesage ccomparedompared wwithith wwiredired nnetworks.etworks. AAss describeddescribed iinn tthehe ssectionection oonn WirelessWireless Limitations,Limitations, devicesdevices tthathat transmittransmit weakweak ssignalsignals mmayay ffrequentlyrequently ddroprop cconnectionsonnections wwithith ootherther eensemblensemble ddevices,evices, ttherebyhereby ccausingausing llostost ddataata aandnd sslowlow rresponseesponse times,times, andand thesethese ffurtherurther llimitimit cconnectiononnection qquality,uality, tthroughput,hroughput, aandnd rreliability.eliability. Th e esese ddisruptionsisruptions iinterruptnterrupt nnaturalatural uusagesage tthathat nnegativelyegatively aaffff eectscts tthehe uuserser eexperience.xperience. WWirelessireless ddeviceevice cconnectionsonnections llackack tthehe vvisualisual pphysicalhysical iindicatorsndicators ((i.e.,i.e., a vvisibleisible ccable)able) ooff wwiredired cconnections.onnections.

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Th e eextentxtent ooff ssecureecure ccommunicationommunication iiss aalsolso uunclear,nclear, aass eeavesdroppingavesdropping oonn a wwiredired nnetworketwork rrequiresequires pphysicalhysical aaccessccess ttoo tthehe ccable,able, wwhereashereas eeavesdroppingavesdropping oonn a wwirelessireless nnetworketwork oonlynly rrequiresequires tthathat tthehe ddeviceevice bbee iinn rrange.ange. BBecauseecause wwirelessireless iiss iinvisible,nvisible, tthesehese iissuesssues nneedeed ttoo bbee aaddressedddressed tthroughhrough cconnectiononnection statusstatus aandnd cconfionfi ggurationuration iindicatorsndicators ttoo gguideuide aandnd ssupportupport tthehe uusabilitysability mmodelodel fforor a ddeviceevice aandnd tthehe eensemble.nsemble. UUserser iinterfacenterface sstandardstandards iinn tthesehese aareasreas havehave notnot beenbeen ddevelopedeveloped aatt tthishis ttime.ime. FFurthermore,urthermore, iiff a ddeviceevice iiss cconnectedonnected ttoo a wwire,ire, iitt ccanan bbee ddesignedesigned ttoo bbee ppoweredowered bbyy tthehe ssameame wwire,ire, ssimplifyingimplifying tthehe fformorm ffactoractor ddesignesign cconstraints,onstraints, oorr wwhenhen aann iinternalnternal bbatteryattery iiss ppresent,resent, pprovidingroviding a mechanismmechanism fforor cchargingharging tthehe ddevice.evice. EnsemblesEnsembles areare lessless likelylikely toto benefibenefi t ffromrom tthishis ddesignesign aapproach.pproach.

Power Constraints IInn tthehe ccasease ooff eensembles,nsembles, wwherehere vvaluealue iiss mmaximizedaximized bbyy tthehe sseamlesseamless oorchestrationrchestration ooff mmultipleultiple ddevices,evices, powerpower bbecomesecomes ccritical.ritical.

WWee hhaveave aallll eexperiencedxperienced tthehe ffrustrationrustration ooff uusingsing a ccellell pphonehone iinn a ccarar aandnd tthehe ““EavesdroppingEavesdropping oonn a wwirelessireless nnetworketwork pphonehone bbatteryattery ddiesies wwhenhen yyou’reou’re inin tthehe mmiddleiddle ooff ggettingetting ddirections.irections. IInn tthishis mmobileobile ssituationituation wwee aarere ffurtherurther ffrustratedrustrated bbecauseecause wwee cannotcannot easilyeasily useuse ourour oonlynly requiresrequires thatthat thethe devicedevice bebe inin hhandsands ttoo ppluglug iinn a cchargerharger andand rredial.edial. Th e rrealityeality ttodayoday iiss tthathat wwee iincreasinglyncreasingly rrange.”ange.” rrelyely oonn oourur mmobileobile battery-poweredbattery-powered ddevicesevices ttoo bbee ccontinuouslyontinuously aavailablevailable aandnd pproviderovide ccriticalritical ccommunication,ommunication, ccontentontent ccapture,apture, II/O/O ccontrol,ontrol, aandnd sstorage.torage. AAss tthehe iinterdependency,nterdependency, aandnd tthushus ccriticality,riticality, ooff tthesehese ddevicesevices ccontinuesontinues ttoo ggrow,row, tthehe eexpectationxpectation tthathat ttheyhey aarere ppoweredowered aandnd aavailablevailable iincreases.ncreases. Th e ssolutionolution iiss nnotot ssimple;imple; mmoreover,oreover, tthehe pproblemroblem iiss eexacerbatedxacerbated bbyy oourur eexpectationsxpectations ooff eever-ver- sshrinkinghrinking fformorm ffactors,actors, aandnd tthehe ddesireesire fforor mminimalinimal ddependencyependency oonn pplugginglugging iin.n. HHowever,owever, ddevicesevices ccanan aadaptdapt wwhenhen ttheyhey jjoinoin aann eensemble,nsemble, fforor eexample,xample, bbyy tturningurning ooffff uunnecessarynnecessary dduplicateuplicate pperipheraleripheral ccapabilitiesapabilities aalreadylready pprovidedrovided bbyy ppeereer ddevicesevices aacrosscross thethe wirelesswireless connection.connection.

Mobility of Tasks within Ensembles Based on Power Availability OOnene ooff tthehe aadvantagesdvantages ooff aann eensemblensemble iiss tthehe oopportunitypportunity fforor rreliabilityeliability tthroughhrough redundancy.redundancy. IInn tthehe ddroppedropped pphone-callhone-call eexamplexample jjustust ccited,ited, ttherehere iiss a ppotentialotential ssolution.olution. BByy ddetectingetecting tthehe cellcell phone’sphone’s llow-powerow-power sstatetate aandnd sseamlesslyeamlessly rreroutingerouting tthehe phonephone callcall (including(including headsetheadset rre-pairing)e-pairing) ttoo a VVOIPOIP [[42]42] ssystemystem runningrunning onon a laptoplaptop iinn tthehe ccar,ar, aann aautomaticutomatic hhandoverandover ccouldould bbee aachieved.chieved. CCharacterizationharacterization aandnd ddiscoveryiscovery ooff ddeviceevice ccapabilitiesapabilities iinn aann eensemble,nsemble, aandnd tthehe aabilitybility ttoo ccrossross ddeviceevice bboundariesoundaries ttoo ttakeake aadvantagedvantage ooff oopportunitiespportunities ssuchuch aass moremore availableavailable power,power, aarere kkeyey ccapabilitiesapabilities fforor eenablingnabling tthishis aapproach.pproach. TTechniquesechniques suchsuch asas VVMM mmigrationigration ((describeddescribed eearlier)arlier) ccanan aalsolso pproviderovide tthehe ““ByBy ddetectingetecting thethe cellcell phone’sphone’s llow-ow- iinfrastructurenfrastructure nneededeeded fforor pprocessrocess mmigrationigration ttoo ddevicesevices tthathat hhaveave ssuffiuffi ccientient ppowerower ttoo ccompleteomplete a ttask.ask. ppowerower sstatetate aandnd seamlesslyseamlessly reroutingrerouting tthehe pphonehone ccallall (including(including headsetheadset rre-pairing)e-pairing) toto a VVOIPOIP ssystemystem rrunningunning oonn a laptoplaptop inin thethe car,car, anan automaticautomatic hhandoverandover ccouldould bebe achieved.”achieved.”

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Mobility of Physical Power among Ensemble Members ““ToTo fformorm aann eensemble,nsemble, mmobileobile ddevicesevices AAnn aalternatelternate aapproachpproach usesuses powerpower asas a resourceresource ttoo bbee ssharedhared aamongmong ddevices.evices. IInn tthishis sscenario,cenario, ppowerower iiss ttransferredransferred ttoo tthehe mmostost ccriticalritical ppartart ooff tthehe eensemble.nsemble. sshouldhould bbee aableble ttoo ddiscoveriscover ootherther TToo ccontinueontinue wwithith tthehe ddroppedropped ccallall oonn tthehe ccellell pphonehone eexample,xample, tthehe eensemblensemble eensemble-capablensemble-capable devicesdevices asas theythey enterenter ddetectsetects tthehe llow-powerow-power sstatetate ooff tthehe ccellell pphone,hone, aandnd iitt mmovesoves ppowerower ffromrom tthehe uuser’sser’s laptop,laptop, oorr eevenven tthehe ccarar iitself,tself, ttoo tthehe ccellell pphone.hone. UUserssers ccanan ddoo tthishis ttodayoday mmutualutual communicationcommunication range.”range.” uundernder ssomeome cconditionsonditions bbyy uusingsing a UUSBSB ccable;able; ootherther ttechnologies,echnologies, ssuchuch aass wwirelessireless power,power, areare underunder development.development. WWirelessireless cchargingharging tthroughhrough iinductivenductive ccouplingoupling oorr sspatialpatial (longer(longer range)range) technologiestechnologies willwill increasinglyincreasingly bebe adaptedadapted aandnd iimprovedmproved fforor uusese iinn ccommercialommercial aapplications.pplications. HHowever,owever, iitt iiss oonlynly llikelyikely bbetweenetween llargerarger ppower-richower-rich ddevices,evices, aandnd nnearbyearby llow-powerow-power mmobileobile ccomputers,omputers, ddueue ttoo tthehe ccurrenturrent iineffineffi cciencyiency ooff ffree-spaceree-space ppower-transfer.ower-transfer.

Security and Privacy SSecuringecuring aann eensemblensemble ssystemystem aass a wwholehole requiresrequires mmoreore eeffff oortrt tthanhan ssecuringecuring iindividuallyndividually pparticipatingarticipating ddevices.evices. IInn tthishis ssectionection wwee ddiscussiscuss ssecurityecurity aandnd pprivacyrivacy iissuesssues thatthat areare uuniquelyniquely associatedassociated withwith implementingimplementing aandnd rrunningunning eensemblensemble systems.systems.

Ensemble Formation TToo fformorm aann eensemble,nsemble, mmobileobile devicesdevices sshouldhould bbee aableble ttoo ddiscoveriscover ootherther eensemble-capablensemble-capable devicesdevices aass theythey eenternter mmutualutual ccommunicationommunication range.range. FForor eexample,xample, anan accessaccess pointpoint periodicallyperiodically broadcastsbroadcasts itsits SSIDSSID toto allowallow otherother 802.11802.11 cclientslients ttoo fi nndd tthehe rresourceesource ((andand vviceice vversa).ersa). WWhilehile tthishis ttypeype ooff bbeaconingeaconing iiss ccommonlyommonly usedused forfor automaticautomatic resourceresource discovery,discovery, tthehe ddiscoveryiscovery pprotocolrotocol ccouldould iinadvertentlynadvertently eexposexpose tthehe ddevice’sevice’s iidentitydentity ttoo aattackersttackers wwhoho ssnoopnoop oonn bbroadcastroadcast ttraffiraffi c forfor thethe purposepurpose ofof trackingtracking thethe mobilitymobility patternspatterns ofof eacheach device.device. AAnn aapproachpproach fforor ssecuringecuring ddiscoveryiscovery pprotocolsrotocols iiss ttoo eemploymploy ccryptographicryptographic aalgorithmslgorithms toto limitlimit suchsuch risksrisks [43,[43, 44].44].

““AA nnewew aapproachpproach ttoo ccontrolontrol tthehe uusese ooff OOncence nnearbyearby ddevicesevices aarere llocated,ocated, tthehe nnextext ssteptep iiss ttoo eestablishstablish ttrustrust bbetweenetween tthehe ddevicesevices bbeforeefore eexecutingxecuting ccoordinatedoordinated ttasks.asks. GGiveniven tthathat mmanyany uusagesage ccasesases pprivaterivate sensitivesensitive ddataata isis viavia a trustedtrusted aassumessume littlelittle oror nono institutionalinstitutional supportsupport forfor thethe ensembleensemble infrastructure,infrastructure, vvirtualirtual domaindomain aaccessibleccessible ttoo tthehe rremoteemote bbothoth ccertifiertifi ccatesates aandnd ttrustrust vverifierifi ccationation pprocessesrocesses uusedsed iinn ttraditionalraditional nnetworksetworks wwouldould bebe iimpracticalmpractical oror tootoo heavyweightheavyweight ttoo bebe aappliedpplied ttoo ensembleensemble ssystems.ystems. pparties.arties. OOncence aann eensemblensemble ddissociates,issociates, HHowever,owever, eexistingxisting ssolutionsolutions forfor mmobileobile aad-hocd-hoc networksnetworks [[45]45] ccouldould bbee aadapteddapted ttoo eestablishingstablishing ttrustrust wwithith eephemeralphemeral ddevices,evices, bbutut tthehe hheterogeneityeterogeneity ooff aanyny cachedcached ccodeode oorr ddataata inin tthehe ttrustedrusted pparticipatingarticipating ddevicesevices ccomplicatesomplicates ddistributedistributed kkeyey mmanagement.anagement. ddomainomain ccanan aalsolso bbee ddeletedeleted fforor aaddeddded Ensemble Computation ssystemystem ssecurity.”ecurity.” IIff ssensitiveensitive ddataata aarere iinvolvednvolved iinn aann eensemblensemble ccomputation,omputation, oorr tthehe ccodeode iimplementingmplementing aapplicationspplications nneedseeds ttoo bbee pprotectedrotected ffromrom rreverseeverse eengineering,ngineering, itit iiss ppossibleossible toto buildbuild anan additionaladditional layerlayer ofof securitysecurity leveragingleveraging ttrustedrusted hhardware.ardware. FForor iinstance,nstance, a nnewew aapproachpproach ttoo ccontrolontrol tthehe uusese ooff pprivaterivate ssensitiveensitive ddataata iiss vviaia a ttrustedrusted vvirtualirtual ddomainomain aaccessibleccessible ttoo tthehe rremoteemote ppartiesarties [[46].46]. OOncence aann eensemblensemble ddissociates,issociates, aanyny cachedcached ccodeode oorr ddataata iinn tthehe ttrustedrusted ddomainomain ccanan aalsolso bebe deleteddeleted fforor aaddeddded ssystemystem ssecurity.ecurity.

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AAnothernother cchallengehallenge fforor eensemblensemble systemsystem ssecurityecurity iiss ttoo ddevelopevelop ddynamicynamic ssecurityecurity ppoliciesolicies tthathat ccanan aadaptdapt ttoo aavailablevailable ppower,ower, pplatformlatform rresources,esources, aandnd tthehe ccollectionollection ooff ddevicesevices ppresent.resent. HHowever,owever, tthehe ssecurityecurity ooff tthehe eensemblensemble iiss oonlynly aass sstrongtrong aass tthehe wweakesteakest mmemberember ddevice;evice; hence,hence, strikingstriking tthehe rrightight bbalancealance bbetweenetween fl eexibilityxibility aandnd ssecurityecurity iiss iimportantmportant ttoo ssecureecure tthehe eentirentire ssystem.ystem.

Conclusion EEnsemblensemble ccomputingomputing extendsextends thethe generalgeneral notionnotion ofof distributeddistributed ccomputingomputing wwithith tthehe iissuesssues tthathat aariserise ffromrom iintroducingntroducing collectionscollections ofof mobilemobile devicesdevices iintonto tthehe mmix.ix. KKeyey ddiffiff eerentiatorsrentiators aarere tthehe ddynamicynamic nnatureature ooff tthehe cconnectionsonnections bbetweenetween ddevices,evices, tthehe uusese ooff llocationocation aandnd ootherther ccontextontext iinformation,nformation, aandnd tthehe hheterogeneouseterogeneous nnatureature ooff ddevicesevices aandnd ttheirheir pprocessingrocessing aandnd ssystemystem rresources.esources.

AAss a result,result, ttherehere aarere mmanyany oopportunitiespportunities tthathat aariserise ffromrom tthehe eexistencexistence ooff ““ManyMany oopportunitiespportunities aariserise ffromrom tthehe eensemblesnsembles tthathat iincludenclude cconvertingonverting ((oror aaugmenting)ugmenting) a ccomputeromputer bbyy ssharingharing rremoteemote wwirelessireless rresources.esources. AAlternatively,lternatively, pprocessingrocessing ccanan bbee ssuper-chargeduper-charged eexistencexistence ooff ensemblesensembles thatthat includeinclude bbyy mmigratingigrating ccomputationomputation ffromrom uunder-powerednder-powered mmobileobile ddevicesevices ttoo hhigher-igher- cconvertingonverting ((oror aaugmenting)ugmenting) a pperformanceerformance infrastructureinfrastructure ccomputers.omputers. EmergentEmergent bbehaviorsehaviors inin anan ensembleensemble mmayay aalsolso ssolveolve pproblemsroblems tthathat ccannotannot bbee ssolvedolved llocally:ocally: ssomeome ssolutionsolutions willwill ccomputeromputer byby sharingsharing remoteremote wirelesswireless oonlynly bbee ffoundound bbyy ttakingaking aadvantagedvantage ooff tthehe ssharedhared wwisdomisdom ofof llargearge nnumbersumbers ooff ppeople.eople. rresources.”esources.”

EEnsemblensemble ssystemsystems aalsolso ffaceace mmanyany cchallenges:hallenges: mmanaginganaging llargearge nnumbersumbers ooff ddevices,evices, ddefiefi nninging nnewew ccontextualontextual pprogrammingrogramming mmodels,odels, llivingiving wwithith tthehe llimitationsimitations ooff wwirelessireless ccommunication,ommunication, ddesigningesigning iintuitiventuitive uuserser iinterfaces,nterfaces, mmitigatingitigating ppowerower cconstraints,onstraints, aandnd aallll tthehe wwhilehile eensuringnsuring ssecurityecurity aandnd pprivacy.rivacy. Th e esese pproblemsroblems aarere nnotot iintractable,ntractable, aandnd ttherehere aarere mmanyany ppromisingromising ssolutionsolutions tthathat wwillill mmoveove usus forwardforward iinn tthishis fi eeld.ld.

EEnsemblensemble ssystemsystems tthathat eexploitxploit tthehe aavailablevailable oopportunitiespportunities wwhilehile fi nndingding nnewew wwaysays ttoo eeffff eectivelyctively hhandleandle tthehe cchallengeshallenges aarere aann oongoingngoing ssubjectubject ooff rresearch.esearch. AAtt IntelIntel LLabsabs wewe ccontinueontinue ttoo ddefiefi nnee nnewew rresearchesearch pprojectsrojects tthathat eexplorexplore tthesehese iissues.ssues. TTimeime aandnd ttimeime aagain,gain, wwee fi nndd eexamplesxamples iinn wwhichhich tthehe aaggregateggregate vvaluealue ooff eensemblesnsembles iiss greatergreater tthanhan tthehe ssimpleimple ssumum ooff tthehe ccomponentomponent pparts.arts.

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[27] Dash, D., Kveton, B., Agosta, JM., Schooler, E. M., Chandrashekar, J., Bachrach, A. and Newman, A. “When Gossip is Good: Distributed Probabilistic Inference for Detection of Slow Network Intrusions.” AAAI, 2006.

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Acknowledgements WWee tthankhank DDinaina PPapagiannaki,apagiannaki, TTrevorrevor PPering,ering, JJohnohn GGustafson,ustafson, LLakshmanakshman KKrishnamurthy,rishnamurthy, AAnthonynthony JJoseph,oseph, aandnd HHermanerman DD’Hooge’Hooge fforor ttheirheir ttechnicalechnical ffeedback.eedback.

Author Biographies RRoyoy WantWant iiss a SeniorSenior PPrincipalrincipal EEngineerngineer aatt IIntelntel LLabs,abs, SSantaanta Clara,Clara, California,California, aandnd AAssociatessociate DirectorDirector forfor XTR.XTR. HisHis rresearchesearch iinterestsnterests iincludenclude mmobileobile aandnd uubiquitousbiquitous computing,computing, wirelesswireless protocols,protocols, embeddedembedded aandnd ddistributedistributed systems,systems, aautomaticutomatic identifiidentifi ccation,ation, aandnd MMEMS.EMS. WWantant rreceivedeceived hhisis PPhDhD ddegreeegree iinn CComputeromputer SSciencecience ffromrom CChurchillhurchill CCollege,ollege, CCambridge,ambridge, UUKK iinn 11983.983. HHee iiss ccurrentlyurrently tthehe CChairhair ooff AACMCM SSIGMOBILE,IGMOBILE, aandnd a FFellowellow ooff bbothoth tthehe IEEEIEEE andand AACM.CM.

EEveve SSchoolerchooler jjoinedoined IIntelntel iinn 22005.005. SShehe iiss a PPrincipalrincipal EEngineerngineer iinn IIntelntel LLabsabs wwithinithin iitsts nnewew EEnergynergy SSystemsystems RResearchesearch LLab,ab, wwherehere sshehe iiss ddesigningesigning aann iintelligentntelligent ccontrolontrol pplanelane forfor SSmartmart HomesHomes aandnd SSmartmart micro-Grids.micro-Grids. PreviouslyPreviously sshehe lleded tthehe DDistributedistributed DDetectionetection aandnd IInferencenference ((DDI)DDI) pproject,roject, aann eeffff oortrt tthathat ffocusedocused oonn ccollaborativeollaborative anomalyanomaly detectiondetection toto securesecure large-scalelarge-scale networks.networks. HHerer bbroadroad iinterestsnterests llieie aatt tthehe iintersectionntersection ooff nnetworking,etworking, ddistributedistributed ssystems,ystems, aandnd sscalablecalable groupgroup algorithmalgorithm design.design. EveEve sservederved oonn tthehe TTransportransport DDirectorateirectorate ooff tthehe IIETF,ETF, cco-foundedo-founded aandnd cco-chairedo-chaired tthehe IIETFETF MMMUSICMUSIC wworkingorking ggrouproup fforor mmanyany yyears,ears, aandnd iiss a cco-authoro-author ofof thethe SSIPIP pprotocolrotocol thatthat iiss widelywidely uusedsed forfor IInternetnternet ttelephony.elephony. EEveve oobtainedbtained aann BBScSc ddegreeegree ffromrom YYaleale UUniversity,niversity, aann MMScSc ddegreeegree ffromrom UUCLA,CLA, aandnd a PPhDhD ddegreeegree ffromrom CCaltech,altech, aallll iinn CComputeromputer SScience.cience. PPriorrior ttoo IIntel,ntel, sshehe hheldeld ppositionsositions aatt AApollopollo CComputers,omputers, IInformationnformation SSciencesciences IInstitutenstitute ((ISI),ISI), AAT&TT&T LLabs-Researchabs-Research aandnd PPollereollere LLLC.LC.

LLenkaenka JJelinekelinek. LLenka’senka’s ppassionassion isis incubatingincubating ttechnologies,echnologies, ggrowingrowing iideasdeas ffromrom anan inspirationinspiration intointo a marketmarket rreality.eality. HHerer mmostost rrecentecent ffocusocus hhasas bbeeneen oonn mmakingaking ppowerower ccordsords oobsoletebsolete tthroughhrough wwirelessireless ppower.ower. IInn hherer ppriorrior 1155 yyearsears ooff eexperiencexperience aatt IIntel,ntel, LLenkaenka lleded rresearchesearch oonn iintuitiventuitive ssystemsystems aandnd llow-powerow-power IIAA pplatforms.latforms. LenkaLenka wwasas a co-founderco-founder ofof thethe IIntelntel SSmartmart ToyToy LabLab aandnd a leadlead aarchitectrchitect oonn tthehe aaward-winningward-winning IIntel®ntel® PPlay™lay™ QQX3™X3™ CComputeromputer MMicroscope.icroscope. SShehe sservederved aass tthehe TTAA ttoo AAndrewndrew CChien,hien, VVPP aandnd DDirectorirector ooff IIntelntel RResearch.esearch. LLenkaenka hholdsolds ddegreesegrees iinn EElectricallectrical EEngineeringngineering aandnd CComputeromputer SSciencecience ffromrom tthehe UUniversityniversity ooff WWisconsin-Madison.isconsin-Madison.

140 | Ensemble Computing: Opportunities and Challenges Intel® Technology Journal | Volume 14, Issue 1, 2010

JJaeyeonaeyeon JJungung rreceivedeceived hherer PPhDhD ddegreeegree iinn CComputeromputer SSciencecience ffromrom MMITIT iinn 22006,006, aandnd herher BBachelor’sachelor’s andand MMaster’saster’s ddegreesegrees ffromrom tthehe KKoreaorea AAdvanceddvanced IInstitutenstitute ooff SSciencecience aandnd TTechnologyechnology ((KAIST).KAIST). HHerer rresearchesearch ffocusesocuses oonn mmanyany aaspectsspects ooff nnetworkedetworked ssystemsystems aandnd ssystemystem ssecurity.ecurity. PPriorrior ttoo jjoiningoining IIntelntel LLabs,abs, SSeattle,eattle, JJaeyeonaeyeon wworkedorked aatt MMazuazu NNetworksetworks aandnd iimplementedmplemented hherer sscan-can- ddetectionetection aalgorithmslgorithms iinn MMazu’sazu’s PProfirofi llerer pproduct.roduct. SShehe iiss aann aaffiffi lliateiate ffacultyaculty mmemberember aatt tthehe UUniversityniversity ooff WWashingtonashington aandnd KKAIST.AIST.

DDanan DDahleahle iiss a SSr.r. SStrategictrategic AArchitectrchitect iinn IIntelntel LLabsabs rresponsibleesponsible fforor ddevelopingeveloping aandnd eexecutingxecuting sstrategiestrategies fforor mmovingoving IIntelntel rresearchesearch ttechnologiesechnologies iintonto tthehe mmarketplace.arketplace. InIn thethe past,past, DDanan lleded a tteameam ccharteredhartered wwithith eenablingnabling ttechnologiesechnologies fforor anytime,anytime, anywhereanywhere computing.computing. Th e tteameam aalsolso wworkedorked iinn tthehe aareasreas ooff ccommunicationsommunications iinn mmobileobile nnetworks,etworks, iincludingncluding WWi-Fii-Fi ((802.11)802.11) hhotspots,otspots, WWiMax,iMax, andand ccellularellular nnetworks,etworks, aaddressingddressing ssecurity,ecurity, aauthentication,uthentication, aauthorizationuthorization aandnd aaccountingccounting ((AAA)AAA) fforor ssafer,afer, ssimpler,impler, sseamlesseamless aaccessccess fforor mmobileobile cclients.lients. PPriorrior ttoo IIntel,ntel, DanDan rranan hhisis oownwn mmarketingarketing cconsultingonsulting ccompany.ompany. HeHe startedstarted hhisis ccareerareer wwithith AAT&TT&T iinn pproductroduct eengineering,ngineering, pproductroduct mmanagement,anagement, wworldwideorldwide ssales,ales, aandnd bbusinessusiness ddevelopment.evelopment. A llicensedicensed pprofessionalrofessional engineer,engineer, DDahleahle hholdsolds a BBSS ddegreeegree iinn MMechanicalechanical EEngineeringngineering aandnd MMaterialaterial SSciencecience aandnd EEngineeringngineering ffromrom thethe UniversityUniversity ooff CCaliforniaalifornia atat BBerkeley,erkeley, aass wwellell aass aann MMBABA ffromrom IIndianandiana UUniversity.niversity.

UUttamttam SenguptaSengupta iiss a pprincipalrincipal eengineerngineer iinn tthehe UUltraltra MMobilityobility GroupGroup andand isis rresponsibleesponsible fforor ddefiefi nninging ssecurity,ecurity, mmanageabilityanageability aandnd vvirtualizationirtualization ccapabilitiesapabilities ooff hhandheldandheld platforms.platforms. UUttam’sttam’s ootherther iinterestsnterests iincludenclude eensemblensemble ccomputing,omputing, llocationocation & ccontextontext ssensingensing aandnd rrelatedelated ttechnologiesechnologies rrequiredequired fforor a sserviceervice rreadyeady pplatform.latform. PPriorrior ttoo IIntel,ntel, UttamUttam wwasas a pprincipalrincipal eengineerngineer aatt MMotorola,otorola, wworkingorking iinn tthehe aarearea ooff GGSMSM ccellularellular ttechnologies.echnologies. HHee rreceivedeceived a PhDPhD iinn ccomputeromputer ssciencecience ffromrom AArizonarizona SStatetate UUniversity.niversity. UUttamttam iiss a mmemberember ooff IIEEEEEE CComputeromputer SSociety.ociety.

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