Politecnico di MilanoAdvanced Network Technologies Laboratory

6LowPAN

o Slide/Figures Sourcesn IPSOAlliance Webinar “6LowPANfor IPSmart

Objects”n 6LoWPAN:TheWirelessEmbeddedInternet,

Shelby&Bormann,ISBN:978-0-470-74799-5,(c)2009JohnWiley&SonsLtd

ACKs

o AnAdaptationLayertofitIPv6overLow-PowerwirelessAreaNetworks

o DefinedbyIETFstandardsn RFC4919,4944n draft-ietf-6lowpan-hcand-ndn draft-ietf-roll-rpl

Whatis6LoWPAN?

IPv6

o Low-powerRF+IPv6=TheWirelessEmbeddedInternet

o 6LoWPANmakesthispossibleo Thebenefitsof6LoWPANinclude:

n Open,long-lived,reliablestandardsn Easy learning-curven TransparentInternet integrationn Networkmaintainabilityn Globalscalabilityn EnablesastandardsocketAPIn Minimaluseofcodeandmemoryn Directend-to-endInternetintegration

o Multipletopologyoptions

Benefitsof6LoWPANTechnology

EvolutionofWirelessSensorNetworks

ScalabilityPrice

Cabling

Cables

Proprietaryradio + network

20001980s 2006

Vendorlock-in

IncreasedProductivity

ZigBee

Complex middleware

6lowpanInternet

Open developmentand portability

Z-Wave, prop. ISM etc.

ZigBee andWHARTAny vendor

6lowpanISA100

2008 ->

Architecture

o LoWPANs arestubnetworkso SimpleLoWPAN

n SingleEdgeRoutero ExtendedLoWPAN

n MultipleEdgeRouterswithcommonbackbonelinko Ad-hocLoWPAN

n NorouteoutsidetheLoWPANo InternetIntegrationissues

n Maximumtransmissionunitn Applicationprotocolsn IPv4interconnectivityn FirewallsandNATsn Security

Architecture

IPv6-LoWPAN Router Stack

o Efficientheadercompressionn IPv6baseandextensionheaders,UDPheader

o Fragmentationn 1280byteIPv6MTU->127byte802.15.4

frames

AdaptationFeatures

o Supportfore.g.64-bitand16-bit802.15.4addressing

o Usefulwithlow-powerlinklayerssuchasIEEE802.15.4,narrowbandISMandpower-linecommunications

o Networkautoconfiguration usingneighbor discoveryo Unicast,multicastandbroadcastsupport

n Multicastiscompressedandmappedtobroadcasto SupportforIProuting(e.g.IETFRPL)o Supportforuseoflink-layermesh(e.g.802.15.5)

Additional Features

o IPv6(RFC2460)=thenextgenerationInternetProtocoln CompleteredesignofIPaddressingn Hierarchical128-bitaddresswithdecoupledhostidentifiern Statelessauto-configurationn Simpleroutingandaddressmanagement

o MajorityoftrafficnotyetIPv6but...n MostPCoperatingsystemsalreadyhaveIPv6n GovernmentsarestartingtorequireIPv6n MostroutersalreadyhaveIPv6supportn SotheIPv6transitioniscoming

o 1400%annualgrowthinIPv6traffic(2009)

InternetProtocolv6

IPv4vs.IPv6Addressing

Image source: Indeterminant (Wikipeida) GFDL

IPv4: 7x10-6[addresses/m2] IPv6: 666x1021 [addresses/m2]

IPv4vs.IPv6Header

Image source: Bino1000, Mkim (Wikipeida) GFDL

o 6LoWPANisanadaptationheaderformatn EnablestheuseofIPv6overlow-powerwirelesslinksn IPv6headercompressionn UDPheadercompression

o FormatinitiallydefinedinRFC4944o Updatedbydraft-ietf-6lowpan-hc (workinprogress)

The6LoWPANFormat

o Statelesscompressiono Flow-independentcompressiono SimpletricksonIPv6/UDP

headern Commonvaluesforheader

fields=>compactformsn Version is always 6n TrafficClassandFlowLabel

arezeron PayloadLengthalwaysderived

fromL2headern SourceandDestination

Addressescanbeelided(link-local)and/orcompresseddependingonthe“context”ofthetransmission

6LowPANHeader Compression ataGlance

o 128-bitIPv6address=64-bitprefix+64-bitInterfaceID(IID)o The64-bitprefixishierarchical

n Identifiesthenetworkyouareonandwhereitisgloballyo The64-bitIIDidentifiesthenetworkinterface

n Mustbeuniqueforthatnetworkn Typicallyisformedstatelessly fromtheinterfaceMACaddress

o CalledStatelessAddressAutoconfiguration (RFC2462)o TherearedifferentkindsofIPv6addresses

n Loopback(0::1)andUnspecified(0::0)n Unicast withglobal(e.g.2001::)orlink-local(FE80::)scopen Multicastaddresses(startswithFF::)n Anycast addresses(special-purposeunicast address)

IPv6Addressing

o IPv6addressesarecompressedin6LoWPANo Prefix

n Addresseswithin6LoWPANtypicallycontaincommonprefixn Nodestypicallycommunicatewithoneorfewcentraldevicesn Establishstate(contexts)forsuchprefixes– onlystate

maintenancen Supportforupto16contexts6LoWPANcompressesIPv6

addressesbyo InterfaceID

n TypicallyderivedfromL2addr duringautoconfigurationn ElidewhenInterfaceIdentifiercanbederivedfromL2header

6LoWPANAddressing

AddressingExample

o TF(TrafficClassandFlowLabel)n 0:Carried Inline (ECN+DSCP+Flow),1:ECN+Flow,2:ECN+DSCP,3:All zero

o NH(Next Header compression)n 0:CarriedInline,1:NextHeaderiscompressed

o HLIM(HopLimit=Inline,1,64,255)n 0:CarriedInline,1:1,2:64,3:255

o CID(Context Identifier Extension)n 0:No1-byteCIDidentifier, 1:1-byteidentifier follows

o SAC/DAC(Source/Destination Address Compression)n 0:Stateless,1:Context-based

o SAM/DAM(Source/Destination AddressMode)n 0:16bytes inline,1:8bytes inline,2:2 bytes inline,3:elided

o M(Multicast Destination)n 0:Destination isnotmulticast,1:Destination ismulticast

TheHeader Compression header

Traffic Class andFlowLabelCompression

o Next Header Field

o HopLimit Field

Next Header andHoplimitcompression

o Source/Destination Address Compression modes

o Stateless Mode(SAC/DAC=0)n Prefixislink-local(fe80::/10)

o Context-Based (SAC/DAC=1)n Prefixtakenfromstoredcontexts(upto16contexts)n CID=0,use ContextID =0n CID=1,include4-bitContextID forsource&destination

Addresses Compression

Multicast Addresses Compression

UDPHeader Compression

o Assumecommonvaluesforheaderfieldsanddefinecompactformsn Portswithin61616to61632(4bits)n Lengthderived from IPv6Lengthn Checksummaybeelidedifotherintegritychecksareinuse(e.g.Ipsec)

n C(Checksum):0:Inline,1:Eliden P(Ports):

o 0:Inlineo 1:Elide first8bitsofDest Porto 2:Elide first8bitsofSourcePorto 3:Elide first12bitsofSourceandDest Ports

UDPHeader Compression

LinkLocal

GlobalUnicast

o IPv6requires aminimum2-PDUof 1280byteso 802.15.4has amaximum payload of 127byteso IPv6packets should be fragmented by

6LowPANadaptation layer

Fragmentation

o dgram_size:size of thefragment inbyteso dgram_tag:fragmentation ID(commonto all

fragments)o dgram_offset:fragmentation offset(wordof 8

bytes).Elided inthe1° fragment

Fragmentation Header

o TheperformanceoflargeIPv6packetsfragmentedoverlow-powerwirelessmeshnetworksispoor!n Lostfragmentscausewholepackettobe

retransmittedn Low-bandwidthanddelayofthewirelesschanneln 6LoWPANapplicationprotocolsshouldavoid

fragmentationn Fragmentationhandledattheapplicationlayer

(COAP)n CompressionshouldbeusedonexistingIP

applicationprotocolswhenusedover6LoWPANifpossible

Fragmentation inPractice

o Autoconfiguration isimportantinembeddednetworkso Inorderfora6LoWPANnetworktostartfunctioning:

n Link-layerconnectivitybetweennodes(commissioning)n Networklayeraddressconfiguration,discoveryof

neighbors,registrations(bootstrapping)n Routingalgorithmsetsuppaths(routeinitialization)n Continuousmaintenance

6LoWPANSetup&Operation

o IPv6istheformat- NDisthebrainsn “One-hoproutingprotocol”definedinRFC4861

o Definestheinterfacebetweenneighborso FindingNeighbors

n NeighborSolicitation/NeighborAcknowledgemento FindingRouters

n RouterSolicitation/RouterAdvertisemento AddressresolutionusingNS/NAo DetectingDuplicateAddressesusingNS/NAo NeighborUnreachability DetectionusingNS/NAo DHCPv6maybeusedinconjunctionwithND

IPv6NeighborDiscovery

IPv6NeighborDiscovery

o StandardNDforIPv6isnotappropriatefor6LoWPAN:n AssumptionofasinglelinkforanIPv6subnetprefixn Assumptionthatnodesarealwaysonn Heavyuseofmulticasttraffic(broadcast/floodin6LoWPAN)n Noefficientmultihop supportovere.g.802.15.4

o 6LoWPANNeighborDiscoveryprovides:n Anappropriatelinkandsubnetmodelforlow-powerwirelessn Minimizednode-initiatedcontroltrafficn NodeRegistration(NR)andConfirmation(NC)n DuplicateAddressDetection(DAD)andrecoveryn SupportforextendedEdgeRouterinfrastructures

o NDfor6LoWPANhasbeenspecifiedindraft-ietf-6lowpan-nd(workinprogress)

6LoWPANNeighborDiscovery

o InnormalIPv6networksRAsaresenttoalinkbasedontheinformation(prefixetc.)configuredforthatrouterinterface

o InNDfor6LoWPANRAsarealsousedtoautomaticallydisseminaterouterinformationacrossmultiplehops

PrefixDissemination

o 6LoWPAN-NDOptimizesonlythehost-routerinterfacen RFC4861=signalingbetweenallneighbors(distributed)

o Nodesregisterwiththeirneighboringroutersn ExchangeofNR/NCmessagesn Bindingtableofregisterednodeskeptbytherouter

o Noderegistrationexchangeenablesn Host/routerunreachabilitydetectionn Addressresolution(apriori)n Duplicateaddressdetection

o Registrationsaresoftbindingsn PeriodicallyrefreshedwithanewNRmessage

NodeRegistration

0 1 2 30 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Type (NR)/(NC)| Code | Checksum |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| TID | Status |P|_____________________________|+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Binding Lifetime | Advertising Interval |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |+ Owner Interface Identifier +| |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Owner Nonce |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Registration option(s)...+-+-+-+-+-+-+-+-+-+-+-+-+-+

NR/NCFormat

Typical6LoWPAN-NDExchange

o Shortest-pathrouteso Avoidsoverlapo Minimumenergyconsumptiono Needsglobaltopologyinformation

WhatshouldbetheOptimum“Ideal”RoutingProtocolforWSNs

B

D E

FG

C

A

o Algorithmclassesn Distance-vector

Linksareassociatedwithcost,usedtofindtheshortestroute.Eachrouteralongthepathstorelocalnext-hopinformationabout itsroutetable.

n Link-stateEachnodeacquirescompleteinformationaboutthenetwork,typicallybyflooding.Eachnodecalculatedashortest-pathtreecalculatedtoeachdestination.

o TypesofSignalingn Proactive

Routinginformationacquiredbeforeitisneeded.n Reactive

Routinginformationdiscovereddynamicallywhenneeded.o Routemetricsareanimportantfactor

TypesofRoutingProtocols

o HereweconsiderIProuting(atlayer3)

o RoutinginaLoWPANn Single-interfaceroutingn Flataddressspace(exact-match)n Stubnetwork(notransitrouting)

6LoWPANRouting

o IPisagnostictotheroutingprotocolusedn Itforwardsbasedonroutetableentries

o Thus6LoWPANisroutingprotocolagnostico SpecialconsiderationforroutingoverLoWPANs

n Singleinterfacerouting,flattopologyn Low-powerandlossy wirelesstechnologiesn Specificdataflowsforembeddedapplications

o MANETprotocolsusefulinsomead-hoccasesn e.g.AODV,DYMO

o NewIETFworkinggroupformedn Routingoverlow-powerandlossy networks(ROLL)n Developedspecificallyforembeddedapplications

Protocolsfor6LoWPAN

o RoutingOverLowpowerandLossy networks(ROLL)n WorkinggroupattheIETF

o Standardizingaroutingalgorithmforembeddedapps

o Applicationspecificrequirementsn Homeautomationn Commercialbuildingautomationn Industrialautomationn Urbanenvironments

o Analyzedallexistingprotocolso SolutionmustworkoverIPv6and6LoWPANo Protocolin-progresscalledRPL“Ripple”

n Proactivedistance-vectorapproach

IETFROLL

o Constraineddevices!(fewKbytesofRAM,dozensofKbytesofFlash,8/16-bitmicro-controller)

o Low-speedhighlyunstablelossy links(oscillationavoidance isakey)

o Potentiallyverylargescale(10-100sKnodes)

o Unattendeddevicesinharshenvironments

Background

o General Principle:“DoNot Overact”

RPLPhylosophy

ROLLRPL“Ripple”

o Unicast/Anycast/Multicasto Adaptive Routing

n Different metricso Constraint-Based Routing

n Parallel Pathso Scalabilityo Goal:RPLbuilds upaDestination-Oriented

Directed Acyclic Graph (DODAG)o What DODAGdepends onthespecific

Objective Function (OF)

Requirements/Objectives

o Metric:scalarto capture thelink/pathperformance(reliability, interference,throughput,etc.)

o Constraint:criteria to eliminatelinks from aDODAG

o Routing OFcombines metric andconstraintsn Es:“find thepath with themaximum reliability

that does not traverseany non-encrypted link”

Metrics &Constraints

o Noden Residual Energy(node)n CPU,Storage,WorkLoad,Battery/Mains

o Linkn Troughput (local/globalmetric)n Latency (local/globalmetric)n Reliability (local/globalmetric)

o Expected Transmission Count (ETX)o LinkQuality Level (LQL)

o HopCount

TheMost CommonRouting Metric

o “Theaverage number of packettransmissions to successfully transmit apacket”

o Ex:n Being thepacket error probability from Ato B

andfrom Bto Ap andq,respectively,theETXis:1/[(1-p)(1-q)]

n p andqcanbe estimated through periodicbeaconing

TheETX

A B

o DODAGInformationObject (DIO)n LinkLocal Messages to Advertise/Build UpDODAGn Contains all theinformationto exchange

metrics/setconstraintso Destination Advertisment Object (DAO)

n Used to propagateinformationondestination(prefixes)

n Support to ptp andptmp traffico DODAGInformationSolicitation (DIS)

n Used to solicit DIOs

RPLMessages

DODAGConstruction

Step 1and2

Step 3

Final DODAG

o Thevery same networkmay support differentapplicationsn Es:networkwith battery- andmain-operated

devices,highandlowbandwidth links,andtwoapplications (telemetry andalarming)

n One “time sensitivepath”for alarms (lowlatency,highreliability,noconstraints onenergy)

n One “non-time-sensitive path”for telemetryenergy optimized (donot traversebattery-operated nodes)

MultipleRouting OFcalls forMultipleDODAGs

o OF1: use the LQL asa global metric,minimize thenumber of low andfair quality links,avoid non-encrypted links

o OF2: find the bestpath in terms oflatency whileavoiding poorquality links andbattery-operatednodes

o DATACENTRICPROTOCOLSn Flooding,Gossiping,SPIN,Directed Diffusion,SAR

(Sequential Assignment Routing),RumorRouting,Constrained Anisotropic Diffused Routing,COUGAR,ACQUIRE,ZigBee,RPL

o HIERARCHICALPROTOCOLSn LEACH,PEGASIS,TEEN(Threshold SensitiveEnergy

Efficient Sensor NetworkProtocol)o LOCATIONBASED(GEOGRAPHIC)PROTOCOLS

n MECN,SMECN(Small MinimumEnergyComNetw),GAF(Geographic Adaptive Fidelity),GEAR,Distributed Topology/Geographic,

TaxonomyofRoutingProtocolsforWirelessSensorNetworks