Ch09-Wireless Embedded Internet

1Telecomm.Dept.FacultyofEEEWSN2013

HCMUT

WirelessSensorNetworks

Dr.Ing.VoQueSonEmail:[email protected]


HCMUT

Chapter9:WirelessEmbeddedInternet ICMPv6AutoconfigurationNeighborDiscovery IProutinginWSNs:RPLEmbeddedweb REST/CoAP

Chapter10:Lab/DemoProgrammingwithTinyOS/ContikiRoutinginWSNsDataCollectionIPv6/6LoWPAN

Content


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IPv6review IPv4andIPv6comparison 6LoWPAN:IPv6Header

Compression:supportL3routing(RouteOver)

6LoWPANNeighborDiscovery


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ICMPv6 InternetControlMessage

Protocolv6 ModificationfromICMPfor

IPv4 NeighborDiscovery(ND)

ReplaceARP,ICMP ReachabilityofNeighbors Hostsusetodiscoveryrouters,

autoconfigurationofaddresses

DuplicateAddressDetection(DAD)

5NDmessages: RouterSolicitation(type133) RouterAdvertisement(type134) NeighborSolicitation(type135) NeighborAdvertisement(type

136) Redirect(type137)


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Autoconfiguration


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IPRoutinginWSNs LowpowerandLossyNetwork(LLN)consistsofanedge

router(alsocalledasLLNBorderRouterLBR),Router(R)andHost(H): Hchoosesonlythedefaultrouter Rforwardstraffic ROLLoperatesonlywithinLoWPAN andterminatesatLBR


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RPL:newtrendinWSNRoutingProtocolforLowpowerandLossy Network(LLNs)LLN:LowpowerandLossy networks(LLNs)aretypically

composedofmanyembeddeddeviceswithlimitedpower,memory,andprocessingresourcesinterconnectedbyavarietyoflinks,suchasIEEE802.15.4orLowPowerWiFi.ThereisawidescopeofapplicationareasforLLNs,includingindustrialmonitoring,buildingautomation(HVAC,lighting,accesscontrol,fire),connectedhome,healthcare,environmentalmonitoring,urbansensornetworks,energymanagement,assetstrackingandrefrigeration


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LLNs:Fact LLNshavenottobeconfusedwithWirelessSensorNetworks

AWSNisanLLN,butnottheopposite! LLNsarenotnecessarilywireless.

Industrialautomationnetworksarewired. LLNswilluseIPv6.Nodiscussionsaboutthis.

IPv4isadeadhorse. LLNnodescannotbeeasilyconfigured.

Typicallytheyrecheap,smallandwithverylimitedmemory/CPU


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LLNs:OpenIssues Transmissionefficiency(6lowpan)

Nodesrunonbattery.Savingenergyisapremium.IPv6Headersmustbecompressed.

Nodebootstrap(6lowpannd) Configurationisanightmare,andnormalIPv6autoconfigurationis

toochatty,NS/NAaswell,etc,.

Routing(ROLL) Routingrequirementsarescenariobased.Mainly:

onetoone(configuration,datareading) manytoone(datagathering) onetomany(datadissemination)


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DAGandDODAG DAG:DirectedAcyclicGraph(Fig.B)DAGroot:anodewithintheDAGthathasnooutgoingedgeAllpathsterminatedataDAGrootAlledgesareorientedinsuchawaythatnocyclesexist(Fig.Ais

notaDAG) DODAG:DestinationOrientedDAG(Fig.C)DefinesaDAGthatformspathstoasinglelogicalroot


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WhyDODAGforRPL?TrafficinLLNMainlyforP2MPandMP2Ptrafficflows

Asopposedtoatreetopology,DODAGenables(re)routearoundloss/interferenceandeasilyadaptstransientchanges

RPLorganizesatopologyasaDirectedAcyclicGraph(DAG)thatispartitionedintooneormoreDestinationOrientedDAGs(DODAGs)TherootinDAGactsasasinkP2MPandMP2Ptraffic

DODAGroot>LBR Informationstoredandprocessingatothernodescanbereduced


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UpwardandDownwardRoutes Upward:thedirectionfromleafnodes

towardstheDODAGroot DataflowtowardstheDAGrootMP2P

trafficflows

Downward:thedirectionfromtheDODAGroottowardsleafnodes DataflowawayfromtheDAGroot

P2MPtrafficflows

Pointtopointdataflowviaupanddownroute

UpwardRoute


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RankvsOF Rank:node'sindividualpositionrelativetoothernodeswith

respecttoaDODAGroot IncreasesintheDowndirectionanddecreasesintheUpdirection RankcomputeddependsontheObjectiveFunction (OF)e.g.

calculatedasasimpletopologicaldistance(hopcounts)ormayalsobecalculatedasafunctionoflinkmetrics

ObjectiveFunction(OF):DefinestheoptimizationobjectivestocomputetheRank Optimizationobjectives:minimizingenergy,minimizinglatency,or

satisfyingsomeconstraints,etc Dictateshowrouters(parents)insidetheDODAGareselected


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RPLInstance RPLInstance:ComposedofoneormoredisjointDODAGs,eachof

whichhasanuniqueDODAGID AllDODAGsinthesameRPLInstance usethesameOF(Objective

Function)

RPLInstanceID:identifiesasetofoneormoreDestinationOrientedDAGs(DODAGs) RPLinstanceID canbeusedtoidentifydifferentOFs

RPLInstanceID andDODAGID uniquelyidentifiesasingleDODAGinthenetwork differentDODAGID=differentrootnode


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DAGConstruction DistanceVector

advertisepathcost(routingmetric)

chooseaparent(defaultrouter/nexthop)thatminimizepathcost

Avoidsloops&counttoinfinity Assigneverynodearank

NodeRank:RelativepositionwithinaDODAG

Rankstrictlydecreasingtowardstheroot

Parents&Siblings Parentsnodeswithlowerranks Siblingsnodeswithsameranks


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DataPathValidation&LoopDetection PPLpacketinformation(Up/Downroute)is

transportedwithadatapacket Ondemandloopdetectionusingdata

packetsmaintainingauptodateroutingtopologycan

wasteenergyforLLNswithinfrequentdata Aninconsistencybetweentherouting

decisionforapacket(upwardordownward)andtheRankrelationshipbetweenthetwonodesindicatesapossibleloop E.g.ifS3receivesapacketflaggedasmoving

intheupwarddirection,andifthatpacketrecordsthatthetransmitter(S2)isofalowerRank thanthereceivingnode(S3)

S3shouldinitiatealocalrepairRPLdoesnotguaranteetheabsenceofloopsbutrathertriestoavoidthemandspecifiesmechanismstodetectloopsviadatapathvalidation


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CreationofUpwardroutes DIOmessages SomenodesareconfiguredtobeDODAG

roots DODAGrootsadvertisetheirpresence

(affiliationwithaDODAG,routingcost,andrelatedmetrics)bysendinglinklocalmulticast DIOmessagestoallRPLnodes

NodeslistenforDIOs tojoinanewDODAG(thusselectingDODAG

parents),ortomaintainanexistingDODAG,according

tothespecifiedObjectiveFunctionNodesupdateroutingtableentries,forthe

destinationsspecifiedbytheDIOmessageNodescandecidetojoinoneormoreDODAG

parentsasthenexthopforthedefaultroute


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CreationofDownwardRoutes:DAOMessages RPLusesDestinationAdvertisementObject

(DAO)messagestoestablishdownwardroutes

DAOmessagesareanoptionalfeatureforapplicationsthatrequireP2MPorP2Ptraffic

RPLsupportstwomodesofdownwardtraffic Storing(fullystateful) Nonstoring(fullysourcerouted)


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StoringModevsNonStoringmode Storingmode

Creationofroutes DAOpropagatestowardstherootvia

therouters Eachroutermaintainsroutestoeach

routerinWSNs Datagoeshopbyhop(eachrouter

forwardsthepackettotherightnexthop)

Nonsoringmode Onlytherootstoresroutestotheall

routersinWSNs Calculatesroutestoalldestinationby

piecingtogethertheinfo(addressoftherouters)collectedfromDAOmessages

Dataforwardsusingsourcerouting


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StoringModevsNonStoringmode Storingmode:

Requiresmorestoragecapacitiesandmemoryoneachrouter Efficientcommunications Extramechanismtoavoidloops(e.g.useofRPLpacketinformation)

Nonstoringmode: Doesnotrequireadditionalstateontherouters,butincreasesthe

messageoverhead Trafficthroughtherootnodeincreasesforinternaltraffic(e.g.P2P

trafficwithina6LoWPAN) Loopcanbeavoidedbycheckingheaders?

Thedatapackettravelsuptoacommonancestoratwhichpointitisforwardedinthedowndirectiontothedestination


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RouteConstructionandForwarding Uproutestowardsnodesofdecreasing

rank ViaDAGparents(alwaysforwardtolower

rankwhenpossible)mayforwardtosiblingifnolowerrank

exists

Downroutestowardsnodesofincreasingrank Nodesinformparentsoftheirpresenceand

reachability Forwardhopbyhop(storingmode)orusing

sourcerouting(nonstoringmode)


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Summary:BuildingDODAG RouterssendsDIO(DODAGInformationObject)messagesUseslinklocalmulticasting Indicatesarespectiverank(=position),accordingtoametric

(e.g.hopcount)w.r.t.therootUpwardroutes(pathstowardstheroot)arecreatedDefinestheoptimizationobjectivewhenformingupwardroute

Linkproperties:(Reliability,Latency),Nodeproperties:(Poweredornot)

Objective:optimizepathsbasedononeormoremetricsNodeissuesDAO(DestinationAdvertisementObject)

messagesPropagatesviaDAOparentsdiscoveredduringDIOpropagationDAOcanbeacknowledgedDownwardroutesarecreate


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DAGConstruction LLNlinksaredepicted LBRisconfiguredbythe

systemadministrator(TherecouldbeseveralLBR)

Linksareannotatedw/ETX RPLusesnewCMPv6

messages DIO:DODAGInformationObject DAO:DestinationAdvertisement

Object DIS:DODAGInformation

Solicitation

A B C

EDF

G H I

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LBR1


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DAGConstruction ObjectiveCodePointfor

exampleMetric:ETX Objective:MinimizeETX Depthcomputation:Depth~ETX

Notethatapracticalcomputationmaybemorecoarse

A B C

EDF

G H I

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3

2

11

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LBR1


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DAGConstruction LBR1multicastsRADIO NodesA,B,Creceiveand

processRADIO NodesA,B,Cconsiderlink

metricstoLBR1andtheoptimizationobjective

TheoptimizationobjectivecanbesatisfiedbyjoiningtheDAGrootedatLBR1

NodesA,B,CaddLBR1asaDAGparentandjointheDAG

A B C

EDF

G H I

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LBR1

RA:RouteAdvertisement


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DAGConstruction NodeAisatDepth1inthe

DAG,ascalculatedbytheroutineindicatedbytheexampleOCP(Depth~ETX)

NodeBisatDepth3,NodeCisatDepth2

NodesA,B,Chaveinstalleddefaultroutes(::/0)withLBR1assuccessor

A B C

EDF

G H I

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3

2

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LBR1

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C

DAGConstruction TheRAtimeronNodeC

expires NodeCmulticastsRADIO LBR1ignoresRADIOfrom

deepernode NodeBcanaddNodeCas

alternateDAGParent,remainingatDepth3

NodeEjoinstheDAGatDepth3byaddingNodeCasDAGParent

A B

EDF

G H I

1

3

2

11

LBR1

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Ifanodeisconfiguredtoactasarouter,itstartsadvertisingthegraphinformationtoitsneighborsAleafnode,itsimplyjoinsthegraphanddoesnotsendanyDIOmessage


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DAGConstruction LBR1multicastsDIO NodeAisatDepth1,andcan

reach::/0viaLBR1withETX1

NodeBisatDepth3,withDAGParentsLBR1,andcanreach::/0viaLBR1orCwithETX3

NodeCisatDepth2,::/0viaLBR1withETX2

NodeEisatDepth3,::/0viaCwithETX3

A B C

EDF

G H I

1

3

2

11

LBR1

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DAGConstruction

C

TheRAtimeronNodeAexpires NodeAmulticastsRADIO LBR1ignoresRADIOfrom

deepernode NodeBaddsNodeA NodeBcanimprovetoamore

optimumpositionintheDAG NodeBremoves LBR1,NodeC

asDAGParents NodeBremoves (keepsas

backup) ::/0viaLBR1withETX3 ::/0viaCwithETX3

Adds: ::/0viaAwithETX2

A B

EDF

G H I

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LBR1

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DAGConstruction NodeAisatDepth1,::/0via

LBR1withETX2 NodeBisatDepth2,::/0via

AwithETX2 NodeCisatDepth2,::/0via

LBR1withETX2 NodeEisatDepth3,::/0via

CwithETX3

A B C

EDF

G H I

1

3

2

11

LBR1

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DAGConstruction DAGConstruction

continues Andiscontinuously

maintained Thisripplingeffectbuildsthe

graphedgesoutfromtheroottotheleafnodeswheretheprocessterminates

Eachnodeofthegraphhasaroutingentrytowardsitsparentinahopbyhopfashion

Theleafnodecansendapacketallthewaytorootofthegraphbyjustforwardingthepackettoitsimmediateparent

A B C

EDF

G H I

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3

2

11

LBR1

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A

EDF

G H

MP2PTraffic viaUpwardRouteMP2Ptrafficflowsinwards

alongDAG,towardDAGRoot DAGRootmayalsoextend

connectivitytootherprefixesbeyondtheDAGroot,asspecifiedintheDIO

NodesmayjoinmultipleDAGsasnecessarytosatisfyapplicationconstraints

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LBR1

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B C


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DownwardRouteandDestinationAdvertisements

DestinationAdvertisementsbuilduproutingstateinsupportofP2MPtrafficflowsoutward,fromthesinktoothernodes

DAusesthesameDAG Forsimplicity,wewillfocusona

subsetofDAintheexample Nodesinformparentsoftheir

presenceandreachabilitytodescendantsbysendingaDAOmessage

Nodecapableofmaintainingroutingstate>Aggregateroutes

Nodeincapableofmaintainingroutingstate>attachanexthopaddresstothereverseroutestackcontainedwithintheDAOmessage

A B C

EDF

G H I

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LBR1

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DestinationAdvertisements Somenodesmaybeableto

storeroutingstateforoutwardflows(LBR1,A,F)

Somenodesmaynot(B,D) Somenodesmayhavea

limitedability;DAsmayindicateapriorityforstorage

A B

DF

G H

1

LBR1

1

1

1

1

1

1


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DestinationAdvertisements DAsmaybetriggeredbyDAG

rootornodewhodetectsachange

DAtimersconfiguredsuchthatDAsstartatgreaterdepth,andmayaggregateastheymoveup

A B

DF

G H

1

LBR1

1

1

1

1

1

1


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DestinationAdvertisements LBR1triggersDestination

AdvertisementmechanisminDIO GemitsNAtoFwithDAO

indicatingreachabilitytodestinationprefixG::

FstoresG::viaG HemitsNAtoFfordestination

prefixH:: FstoresH::viaH

1

LBR1

1

1

1

1

1

1H

A B

DF

G

NA:NeighborAdvertisement


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G

DestinationAdvertisements SupposeinthisexampleFhasa

prefixF*::capableofaggregating{F::,G::,H::} Themethodtoprovisionsuchaprefixis

beyondthescopeofRPL

FemitsNAtoDwithDAOindicatingreachabilitytodestinationprefixF*::

Dcannotstore

(continued)

A B

DF

H

1

LBR1

1

1

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F

G

A

H

DestinationAdvertisements DaddsFtotheReverseRouteStack

intheDAO,andpassesDAOontoBforF*::[F]

DalsoemitsaDAOindicatingprefixD::toB

Bcannotstoreroutingstate

(continued)

1

LBR1

1

1

1

1

1

1

B

D


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DestinationAdvertisements BaddsDtotheReverseRoute

StackintheDAOforD::,andpassesDAOD::[D]ontoA

AstoresD::viaB,withthepiecewisesourceroute[D]

BalsoemitsaDAOindicatingprefixB::toA

AstoresB::viaB

(continued)

1

LBR1

1

1

1

1

1

1

DF

G H

BA


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DestinationAdvertisements AemitsDAOstoLBR1for

destinationprefixesA::,B::,D::,andF*

LBR1storesA::viaA,B::viaA,D::viaA,andF*::viaA

AstoredB::viaB,D::viaB[D],F*viaB[D,F]

B,Dstorednothing FstoredG::viaG,H::viaH

1

1

1

1

1

1

1

B

LBR1

DF

G H

A


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P2MPTraffic Theroutingstatesetupby

DestinationAdvertisementisusedtodirectP2MPtrafficoutward

LBR1directstrafficforG(F*::)toA Aaddssourceroutingdirective,[D,

F],andforwardstoB Busessourceroutingdirectiveto

forwardtoD...

1

1

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F

G H

A B

LBR1

D


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P2MPTraffic Dusessourceroutingdirectiveto

forwardtoF FusesroutingstatetoforwardtoG Notetheuseofsourceroutingto

traversethestatelessregionoftheLLN Thedetailsofthesourcerouting

mechanismarestilltobedefined

1

1

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1

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1

DF

G H

A B

LBR1


HCMUT

Bydefault,P2Ptrafficfollowsthedefaultrouteuntilanodeisencounteredwhohasamoreexplicitroute

P2PtrafficflowsinwardsalongtheDAGuntilacommonnodeisreachedtodirectthetrafficoutwards

P2PTraffic

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A

EDF

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LBR1

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B C


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ThedefaultschemeallowsP2Ptrafficwithminimalstaterequiredofnodes butisnotappropriateinallcases

MoreoptimalP2Proutesmaybecomputedandinstallediftheapplicationrequires RPLdoesnotspecifynor

precludesuchamechanismatthistime

P2PTraffic

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A

EDF

G H

LBR1

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B C


HCMUT

ConsiderthecasewherethelinkBDgoesbad

NodeDwillremoveBfromitsDAGparentset

NodeDnolongerhasanyDAGparentsinthegroundedDAG,soitwillbecometherootofitsownfloatingDAG

DAGMaintenance:FloatingDAG

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EDF

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LBR1

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B C


HCMUT

NodeDmulticastsanRADIOtoinformitssubDAGofthechange

NodeIhasanalternateDAGParent,E,anddoesnothavetoleavetheDAGrootedatLBR1.

NodeIremovesNodeDasaDAGParent

DAGMaintenance:FloatingDAG

1

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11

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A

E

G H

LBR1

B C

F

I

D


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NodeFdoesnothaveanoptiontostayintheDAGrootedatLBR1(noalternateDAGParents),soNodeFfollowsNodeDintothefloatingDAG

NodeFmulticastsanRADIO NodesGandHfollowNodeF

intothefloatingDAG

DAGMaintenance:LocalRepair

1

3

2

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A

E

LBR1

B C

IG H

F D


HCMUT

ThesubDAGofnodeDhasnowbeenfrozen

NodescontainedinthesubDAGhavebeenidentified,andbyfollowingnodeDintothefloatingDAG,alloldroutestoLBR1havebeenpurged

ThefloatingDAGseekstorejoinagroundedDAG

DAGMaintenance:LocalRepair

1

3

2

11

11

1

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1

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A

E

LBR1

B C

IG H

F D


HCMUT

NodeImulticastsanRADIO NodeDseesachanceto

rejoingroundedDAGatdepth5throughNodeI

NodeDstartsaDAGHoptimerofduration 4associatedwithNodeI

DAGMaintenance

1

3

2

11

11

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A

LBR1

G H

F E

B C

D

I


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SupposealinkAFbecomesviable

NodeAmulticastsanRADIO NodeFseesachanceto

rejoingroundedDAGatdepth2throughNodeA

NodeFstartsaDAGHoptimerofduration 1associatedwithNodeA

DAGMaintenance

1

3

2

11

11

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4

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I

A

LBR1

G H

F E

B C

D


HCMUT

NodeFsDAGHopTimerexpires

NodeFjoinstothegroundedDAGatdepth2byaddingAasaDAGparent,andremovingD

NodeFmulticastsanRADIO NodesGandHfollowNodeF

tothegroundedDAG

DAGMaintenance:LoopAvoidance

1

3

2

11

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LBR1

E

B CA

G H

F D


HCMUT

NodeDseesachancetorejoinDAGLBR1atdepth3throughNodeF

NodeDstartsaDAGHoptimerofduration 2associatedwithNodeF,inadditiontheDAGHoptimeralreadyrunningwithduration 4associatedwithNodeI


1

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LBR1

E

B CA

G H

F D


HCMUT

NodeDsDAGHoptimerofduration 2tendstoexpirefirst

NodeDjoinsthegroundedDAGatdepth3byaddingNodeFasaDAGParent

ThebreakingoffandrejoiningofthebrokensubDAGisthuscoordinatedwithloopavoidance


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B CA

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F D


HCMUT

Twomechanismstoavoidcounttoinfinity

FloatingDAGLeaveDAG,colorsubDAG,thenlookfornewroutesOperationlocaltonodesthatmustincreasetheirdepthDoesnotguaranteeloopfreedom

SequencenumberchangeLoopfreedom,butexpensivenetworkwideoperationUsedinfrequentlyifpossible

Loop Avoidance


HCMUT

RPL:summaryWorkingwith6LoWPAN SupportIPbasedApplication SupportP2MP,MP2Ptraffic Routingstateisminimized:statelessnodeshavetostoreonly

instance(s)configurationparametersandalistofparentnodes

Takesintoaccountbothlinkandnodepropertieswhenchoosingpaths

Linkfailuresdoesnottriggerglobalnetworkreoptimization


HCMUT

ProtocolStackforWSNsWhatdoesmissingintheprotocolstack?

PHY/MAC802.15.4 Adaptation:6LoWPAN Routing:RPL Transport:UDP ApplicationProtocol?

IPprovidespacketnetworkingoverheterogeneouslinks UDP:Besteffort(packetsmaybesilentlydropped,duplicatedor

delayedandmayarriveoutoforder) thefastestandmostsimplewayoftransmittingdata

TCP:Reliableconnectionoriented IPusesSocketCommunication:endpointsaredefinedby16bit

sourceanddestinationportsandsourceanddestinationIPaddresses


HCMUT

IPbasedApplicationProtocols Widelyusedinternetprotocols(TCP,HTTP,FTP;SIPand

SOAP) Considerableworkhastobedoneforadaptingto6LoWPAN

ExistingprotocolsforWSNs(mainlybasedonUDP)MQTT:MessageQueueTelemetryTransportisdevelopedby

IBM CAP:ZigBeeCompactapplicationProtocol SLP:simpleServiceLocationProtocol Etc..


HCMUT

IPbasedApplicationProtocolsIPbasedapplicationprotocolsover6LoWPAN6LoWPANsupportsthecompressionofUDPportsdowntoarangeof16

shouldbeenoughforlimitednumberofapplicationsthatcanberun

TCPheaderisnoteasytocompressTCPisnotefficientoverlossywirelessmultihopnetworks

WhyUDPfor6LoWPAN?Simple,compressibleandsuitsmostapplicationprotocolsneeds

MulticastsupportReliability?


HCMUT

ApplicationProtocolsforWSNsMQTT(MessageQueueTelemetryTransport)byIBM Lightweightpublish/subscribeprotocoloverTCP/IP

Fixedlengthheader(2bytes)Onetomanymessagedistribution3QoS formessagedelivery(Atmostonce,atleastonce,exactly

once)Applications,e.g.FacebookMessenger

XMLbasedprotocols(SOAP)M2MXML

MessagesarestrictASCII Devicesareidentifiedby128bitUUID BiTXml

RESTful protocolsHTTPCoAP


HCMUT

DesignIssues LinkLayer

Payloadsize,limitedbandwidth,lossy

Multicastsupport Networking

LimitedcompressedUDPport Hostissues

Sleepingcycles Identification(64bit,16bit

addresses) Compression

Headerandpayloadcompression

Endtoendorbyanintermediatenode

Security Applicationlayersecurity Firewallingattheedgerouter


HCMUT

WebServiceDefactoforinterservercommunications

AllInternetserversspeakHTTP/XMLSOAPorRESTarchitectureAdvantagesFormalmessagesequencesInternetwidesupportMostInternetapplicationsusewebservices,whichdependonthebasicRepresentationalStateTransfer(REST)architecture

DisadvantagesforembeddedservicesInefficient,complex


HCMUT

RESTArchitecture RepresentationalStateTransfer(REST)

Describesclientserverandcacheablecommunicationsprotocol,suchasHTTP,tomakesimplecallsbetweennetworkdevices

RESTstylearchitecturesconsistofclientsandservers Clientsinitiaterequeststoservers Serversprocessrequestsandreturnappropriateresponses Requestsandresponsesarebuiltaroundthetransferof

representationsofresources Resources:mostlyidentifiedbyitsURI(Uniform

ResourcesIdentifier) Resourcesmaybewebaddress,aphysicalresourceorsimply

adocumentlocatedsomewhereonaserver Representations:tomanipulateresources

Representationdefinestheformatoftheresource TypicalrepresentationsareHTML,XMLorJSON, butmaybealsobinary,plaintext,MIMEtypes,etc

Methods:allowsclientstoretrieve,modifyordeleteresourcesbyuseoftheirrepresentations Thebasicoperations/methodsonaresourceareGET,PUT,

POSTandDELETE


HCMUT

Resource Protocols(e.g.HTTP,CoAP)

Sourcesofspecificinformation(e.g.sensors,webcontent)

IdentifiedbyanUniformResourceIdentifier(URI)

ManipulationthroughMethods(e.g.GET,PUT)

Representedasjpg,plaintext,etc


HCMUT

WebServicesforWSNs TodayswebservicesarenogoodforembeddedsystemsFTP,HTTP,XML,SOAP

WebservicesforembeddeddevicesRESTful architectureforgoodwebintegrationUDPbasedtransportwithmulticastsupportOverheadsuitableforconstrainednetworksComplexitysuitableforconstrainednodesBuiltinwebdiscoveryandsecurity

TheConstrainedRESTful Environments(CoRE)workinggroupaimsatrealizingtheRESTarchitectureforconstrainednodesandnetworkse.g.8bitmicrocontrollerswithlimitedRAMandROMnetworks(e.g.6LoWPAN)


HCMUT

CoAP:ConstrainedApplicationProtocol Aspecializedwebtransferprotocolforusewithconstrained

networksandnodes M2Mapplications(smartenergy,buildingautomation,etc) Tomonitorsimplesensors(e.g.temperaturesensors,lightswitches,and

powermeters) Tocontrolactuators(e.g.lightswitches,heatingcontrollers,anddoor

locks) Tomanagedevices

Embeddedwebtransferprotocol(coap://) Asynchronoustransactionmodel UDPbindingwithreliabilityandmulticastsupport GET,POST,PUT,DELETEmethods URIsupport Small,simpleheader


HCMUT

WhatisCoAP (andisnot)?CoAP isARESTful protocolBothsynchronousandasynchronousForconstraineddevicesandnetworksSpecializedforM2MapplicationsEasytoproxyto/fromHTTP

CoAP isnotAreplacementforHTTPGeneralHTTPcompressionSeparatefromtheweb


HCMUT

COREArchitecture UseofwebservicesontheInternet

dependsontheRepresentationalStateTransfer(REST)architecture

RESTful protocoltocaterthespecialrequirementsofaconstrainedenvironment SimpleRESTful protocoltransport Create,Read,Update,Delete,Notify

Small,simpleheader 4bytebaseheader TLVoptions,typically1270bytesper

option URIsupport:e.g.

coap://fec0::1:5683/temp Subsetofcontenttypes SubsetofHTTPcompatibleresponse

codes UDPbindings defaultport=5683

C:Constrainednode sensornodesNonconstrainednodes server,proxy,node,etc


HCMUT

CoAP Requirements


HCMUT

TheTransactionModelTransportCoAP isdefinedforUDP

MessagingSimplemessageexchangebetweenendpointsCON,NON,ACK,RST

RESTRequest/ResponsepiggybackedonmessagesMethod,ResponseCodeandOptions(URI,contenttypeetc.


HCMUT

MethodsofCoAP GET:retrievestheinformationoftheresourceidentifiedby

therequestURI PUT:requeststhatthefile/resourceidentifiedbytherequest

URItobeupdatedwiththeenclosedmessagebody.Ifdoesnotexsist,itcreatesanewresource

POST:Submitsdatatobeprocessedtotheidentifiedresource.Thedataisincludedinthebodyoftherequest.Thismayresultinthecreationofanewresourceortheupdatesofexistingresourcesorboth

DELETE:requeststhattheresourceidentifiedbytherequestURItobedeleted


HCMUT

CoAP MessageFormat Ver:Version, T:TransactionType

(CON,NON,ACK) OC:Numberofoptions Code:Methodor

ResponseCode MessageID:AuniqueID

assignedbytheoriginator

OptionDelta Differencebetweenthisoptiontypeandtheprevious!

Length Lengthoftheoptionvalue(0270)!

Value ThevalueofLengthbytesimmediatelyfollowsLength

MessageFormat

OptionHeader


HCMUT

CoAP Code Structureofthe8bit

Responsecode:

3classes: 2 Success 4 Clienterror 5 Servererror

Example:"NotFound"iswrittenas4.04 indicatingavalueofdecimal132


HCMUT

ExampleofCoAP Message


HCMUT

TransactionMessagesofCoAP Confirmable(CON)

Toknowitdidarriveortodeliverthereply

ReturnmessagetypeACK/RST Acknowledgment(ACK)

ACKtotheCONmessage(identifiedbyamessageID)

Payloadcarriesmoredata Reset(RST)

TolettheclientknowtheCONmessageisreceived,butprocessingfailed

E.g.nodehasrebooted NonConfirmable(NON)

DonotrequireanACK E.g.repeatedreadingsfroma

sensor


HCMUT

CoAP OperationCoAP interactionissimilartotheclient/servermodel(CoAP endpoints)URIandContenttypesupport(likeinHTTP)

MessageexchangeissimilartoHTTPRequestactionisoriginatedbyaclient(usingaMethodcode)

RequestisforaResource(identifiedbyaURI)onaserverResponseissentwithaResponseCode


HCMUT

CoAP OperationUnlikeHTTP,CoAP dealsOperatesoverUDP,withreliableunicastandmulticastsupport

Retransmission(=reliableunicast)ACoAP endpointkeepstrackofopenConfirmablemessagesitsentthatarewaitingforaresponse

SimpleCongestionControl exponentialbackoffmechanism

Dealswithmessageinterchangesseperately

Servermightneedlongertimetoobtaintherepresentationofresource.Thisresultsintheclientretransmittingtherequest


HCMUT

CoAP Operation OperatesoverUDP,with

reliableunicastandbesteffortmulticastsupport

CONvsNONmessages? IfCON/NONmessages

cannotbeprocessed,ServersendsRSTmessage

WhyMID&Token?


HCMUT

CoAP Options ContentType:SpecifiestheformatoftheapplicationpayloadMaxAge:Maximumageforamessagetobecached ProxyUri:DefinesanabsoluteURItoaproxy Token:Matchesaseparateresponsetoarequest UriHost:SpecifiestheInternethostofaresource(onlyadded

ifnotrepresentingthedestinationIPaddressoftherequest) UriPath:Specifiestheresourceofthehost UriPort:Specifiestheportofthehost(onlyaddedifdiffers

fromthedestinationUDPportrequest) UriQuery:Indicatesadditionaloptionsfortherequest Etc..


HCMUT

RequestExampleRequestandResponseCONmessage

NONmessage

Dealingwithpacketloss


HCMUT

RequestExampleNormalresponse


HCMUT

Caching CoAP includesasimplecaching

model Cacheability determinedby

responsecode Freshnessmodel

MaxAgeoptionindicatescachelifetime

Validationmodel ValiditycheckedusingtheEtag

Option Aproxyoftensupportscaching

Usuallyonbehalfofasleepingnode,

andtoreducenetworkload


HCMUT

Observation TheObserveOption,when

present,modifiestheGETmethodsoitdoesnotonlyretrievearepresentationofthecurrentstateoftheresourceidentifiedbytherequestURI,butalsorequeststheservertoaddtheclienttothelistofobserversoftheresource.

Inaresponse,theObserveOptionidentifiesthemessageasanotification,whichimpliesthattheclienthasbeenaddedtothelistofobserversandthattheserverwillnotifytheclientoffurtherchangestotheresourcestate


HCMUT

BlockTransfer Transferslargerthancanbeaccommodatedinconstrainednetworklink

layerpacketscanbeperformedinsmallerblocks. Nohardtomanageconversationstateiscreatedattheadaptationlayer

orIPlayerforfragmentation.


HCMUT

ResourceDiscovery ResourceDiscoverywithCoRE

LinkFormat WeblinkingasperRFC5988 Discoveringthelinkshostedby

CoAP servers GET/.wellknown/core Returnsalinkheaderstyle

format URL,relation,type,interface,

contenttypeetc.

Documents

Ch09-Wireless Embedded Internet