the internet of things - cs.unibo.it · 4 ipv4 protocol ip-based network layer solutions l. bononi,...

TheInternetofThings:IP-basedNetworkLayerSolu<ons

[email protected]

MASTERDEGREEINCOMPUTERSCIENCEDEPARTMENTOFCOMPUTERSCIENCEANDENGINEERING,UNIVERSITYOFBOLOGNA,ITALY

[email protected]

Coursewebsite:h8p://www.cs.unibo.it/projects/iot/

2

IoTProtocolStack

IP-BASEDNETWORKLAYERSOLUTIONS L.BONONI,M.DiFELICE,DEPARTMENTOFCOMPUTERSCIENCEANDENGINEERING,UNIVERSITYOFBOLOGNA,ITALY

3

IoTProtocolStack

IEEE802.3 IEEE802.11 IEEE802.15 IEEE802.16

IPv4andIPv6+6LoWPAN

TCP UDP

MQTT CoAP AMQP HTTP OTHERS

PHY/MACPROTOCOLS

NETWORKPROTOCOLS

TRANSPORTPROTOCOLS

MESSAGINGPROTOCOLS

PROPRIETARYSTACKS

OTHERS

TCP/IPSTACK


4

IPv4Protocol


q  IPversion4(IPv4)²  FirstversiondeployedbytheARPANETprojectin1983²  Uses32-bitnetworkaddresses(addressspaceà4294967296values).²  IPv4canbepublic(i.e.routableovertheInternet)orprivate²  EachIPv4addresscontainstwoparts:the(i)networkiden^fier

andthe(ii)hostiden^fier.Thenetworkmaskindicatesthenumberofbits(overthe32)usedtorepresentthenetworkiden^fier.

192 168 10 3

NETWORKIDENTIFIER HOST

PRIVATEADDRESS /24

MASK

5

IPv6Protocol


q  Themigra<onprocesstoIPv6involves:networkinfrastructures,routers,applicaôns

q  Completemigraônexpectedby2025

q  IPversion6(IPv6)²  DevelopedbytheInternetEngineeringTaskForce(1998).²  ReplaceIPv4andaddresstheIPv4addressexhausônproblem.²  Addiônalrou^ngfuncônaliês(notincludedinIPv4).²  Notcompa^blewiththeIPv4protocol.

6

IPv6Protocol


q IPversion6(IPv6)adop^onworldwide

7

IPv6Protocol


q  NovelfeaturesoftheIPv6protocol(comparedtoIPv4)1.Extendedaddressingcapabili<es

IPv4address:32bit,IPv6address:128bità2128combina<onsavailable!

3FFE:085B:1F1F:0000:0000:0000:00A9:1234

8groupsof16-bithexadecimalnumbersseparatedby“:”

Leading zeros can be removed à 3FFE:85B:1F1F::A9:1234

8

IPv6Protocol



ThreetypesofIPv6addresses:

²  Unicast:one-to-onecommunicaôn² Mul<cast:one-to-manycommunicaôn²  Anycast:one-to-a-group,andasingledes^naônischosen²  Broadcast:notsupported

9

IPv6Protocol



Link-Local Site-Local Global

Anetworkinterfacecanhavemul^pleaddresses

LINK-LOCALADDRESSES

² Startusingalink-localprefixFE80::/10² Containtheinterfaceiden^fier(e.g.MACaddress)inthemodifiedEUI-64format.² Canbeusedtoreachtheneighboringnodesa8achedtothesamelink²  IPv6routersmustnotforwardpacketshavinglink-localsource/des^na^on² AllIPv6enabledinterfaceshavealink-localunicastaddress.

10

IPv6Protocol



Link-Local Site-Local Global

Anetworkinterfacecanhavemul^pleaddresses

SITE-LOCALADDRESS

² Startusingalink-localprefixFC00::/7² Similarproper^esasIPV4privateaddresses

GLOBALADDRESS

² CanbeusedtorouteIPdatagramsovertheInternet² Variableprefix,definedfromrouteradver^sements.SomeIPaddressescanbereserved.

11

IPv6Protocol


IPv4header,20Byte

Version Traffic Class Flow Label

Payload Length Next Header Hop Limit

Source Address

Destination Address

IPv6heade

r,40Byte

q  NovelfeaturesoftheIPv6protocol(comparedtoIPv4)2.IPHeaderre-newed

Version IHL Type of Service Total Length

Identification Flags Fragment Offset

Time to Live Protocol Header Checksum

Source Address Destination Address

Options Padding

12

IPv6Protocol



Version IHL Type of Service Total Length

Identification Flags Fragment Offset

Time to Live Protocol Header Checksum

Source Address Destination Address

Options Padding

IPv4header,20Byte

FieldsremovedintheIPv4header:

²  ChecksumàreplicatedinMACandTSPheader,notneededattheIPlayer.

²  Fragmenta<onàfragmenta^onisperformedbyend-points,whilemightnotbesupportedbyrouters.

²  Op<onsàreplacedbypointertonextheaderextension(nextheader).

13

IPv6Protocol



Version Traffic Class Flow Label

Payload Length Next Header Hop Limit

Source Address

Destination Address IPv6heade

r,40ByteIden^fypossibleQoSrequirements

Iden^fyasource-des<na<ontrafficflow

Pointertonextheaderextension(op^onal)

IPv6headerNextheader=TCP TCPheader+data

IPv6headerNextheader=Rou^ng

Rou^ngheaderNextheader=TCP TCPheader+data

14

IPv6Protocol


q  NovelfeaturesoftheIPv6protocol(comparedtoIPv4)3.IPAddressassignmentprocess,threeways

² Manualconfiguraônàlikeusingthe“ifconfig”u^lity

² StatefulconfiguraônàusingDHCPv6protocol

² Statelessautoconfigura<onànoDHCP,IPv6nodescanconnecttoanetworkandautoma<callygenerateglobalIPv6addresseswithouttheneedformanualconfiguraônorhelpofaserver.

ROUTERADVERTISEMENT(RA)

IPv6address=interfaceiden<fier+RAprefix

15

IPv6Protocol


q  NovelfeaturesoftheIPv6protocol(comparedtoIPv4)3.IPAddressassignmentprocess,threeways

² Manualconfiguraônàlikeusing“ifconfig”u^lity

² StatefulconfiguraônàusingDHCPv6protocol

² Statelessautoconfigura<onànoDHCP,IPv6nodescanconnecttoanetworkandautoma<callygenerateglobalIPv6addresseswithouttheneedformanualconfiguraônorhelpofaserver.

ROUTERADVERTISEMENT(RA)IPv6address

CheckforpossibleIPduplicates,usingtheNeighbourDiscoveryProtocol(NDP)

16

IPv6Protocol


²  Dual-stackapproach SomerouterswillsupportbothIPv4andIPv6protocols

²  GRETunnellingapproachCommunicaôntunnelsenablecommunicaônbetweenIPv6subnetworksoverIPv4links

IPv6networkIPv6network IPv4networkD-S D-S

q ManagingtransiônfromIPv4toIPv6

17

IPv6ProtocolandtheIoT


q  BenefitsofusingIPv6protocolsonIoTscenarios:²  Address/manage/accessanyIoTdevicefromtheInternet.²  EasilyconnecttootherIPnetworkswithouttheneedfor

transla<ongatewaysorproxies.²  Usewell-knownsocketAPIforthedeploymentofnetwork

applica^on.²  Easilyre-usetoolsformanaging,commissioninganddiagnosing

IP-basednetworks.²  LeverageontheaddressingcapabilityoftheIPv6protocol.

18



q  Atthesame^me,suppor^ngIPv6overIoTscenariospresentseveralchallenges:²  IPv6datagramsarenotanaturalfitforIEEE802.15.4networks

²  MTUsizeofanIEEE802.15.4frameis127bytes,whiletheminimumIPv6framesizeis1280bytes;

²  TheIPv6headersize(40bytes)canoccupy1/3oftheMTU²  IPv6assumesthatalinkisasinglebroadcastdomain,whiletheassumpôn

doesnotholdinmul^-hopwirelesssensornetworks.²  IPv6includesop<onalsupportforIPsecurity(IPsec),authen^caônand

encrypônbutthesetechniquesmightbetoocomplexforIoT-devices.

19



q Worstcasescenariocalcula^ons.²  MaximumfrasesizeinIEEE802.15.4à127bytes²  Reducedbythemaxframeheader(25bytes)à102bytes²  Reducedbythehighestlinklayersecurity(21bytes)à81bytes²  ReducedbystandardIPv6header(40bytes)à41bytes²  ReducedbystandardUDPheader(8bytes)à33bytes²  Only33bytesledfordatapayload!

FRAMEHEADER(25) LLSEC(21) IPv6HEADER(40) UDP(8) PAYLOAD(33)

20

6LoWPAN


q  SetofstandardsdefinedbytheInternetEngineeringTaskForce(IETF)enablingtheefficientuseofIPv6overlow-power,low-ratewirelessnetworksonsimpleembeddedIoTdevices.Itprovides:²  AnovelAdapta<onLayer;²  Severalop<miza<onofIPv6funcônaliês.

²  RFC4919(firstspecificaôn,2007)²  RFC4944(auto-configuraôn)²  RFC6282(headercompression)²  RFC7400(headercompression)²  …

21

6LoWPANMarketShare


Source:h8ps://www.ee^mes.com/document.asp?doc_id=1324664

22

6LoWPAN


RR R

HH H

R R RR

H H H H H

INTERNET

Edgerouter

Edgerouter Edgerouter

Backhaullink

RouterRouter

R

RR

H

H

H

SimpleLoWPAN

ExtendedLoWPANAd-HocLoWPAN

ThreeNetworkArchitectures

23

6LoWPAN


RR R

HH H

R R RR

H H H H H

INTERNET

Edgerouter

Edgerouter Edgerouter

Backhaullink

RouterRouter

R

RR

H

H

HSimpleLoWPAN

ExtendedLoWPAN Ad-HocLoWPAN

Threetypesofnodes:Hostsàend-usersleepydevice,RoutersàforwarddatainsidetheLoWPANEdgeRoutersàconnectaLoWPANtoan

externalIPv6network

24

6LoWPAN


q 6LoWPANProtocolStackvsEthernetProtocolStack

ETHERNETPHY

ETHERNETMAC

IPv6

TCP UDP ICMP

APPLICATIONS

ETHE

RNETPRO

TOCO

LSTAC

K

IEEE802.15.4PHY

IEEE802.15.4MAC

LOWPAN

UDP ICMP

APPLICATIONS

6LoW

PANPRO

TOCO

LSTAC

K

6LoWPANcanworkwithotherlink-layerprotocolsbesideIEEE802.15.4.Requirements:²  Uniqueaddressing²  Unicasttransmissions² MTUsize>30bytes

UDPisthemostcommonTSPprotocolwith6LOWPAN,sinceitsheadercanbeeasilycompressed…

25

6LoWPAN


q Use-cases:Large-scaleIoTDeploymentSM

ARTLIGH

TINGSYSTEM

WAS

TEM

ANAG

EMEN

TSYSTEM

26

6LoWPAN


q Use-cases:Interoperable,SmartEnvironmentsSM

ARTOFFICE

SMAR

TBU

ILDING

h8ps://iot6.eu/iot6_%20use_cases

27

Digression:IEEE802.15.4


q Low-power,low-costtechnologyforWirelessPersonalAreaNetworks(WPANs)

Source:h8p://file.scirp.org/Html/1-4000110_65802.htm

28



q  IEEE802.15.4àstandardforthedeploymentofWPAN.Characteris^cs:lowcomplexity,low-powerforlow-dataratewirelessconnec^vityamongfixedandportabledevices.

Thespecifica^onsdefinethePHYtechniquesandMAClayer,whiletheupperlayersaredefinedbytheZigbeestack.

PHYLAYER

MACLAYER

NETWORKLAYER

PROFILES

APPLICATIONS

}}}

IEEE

ZIGBEE

USER-DEFINED

29




Feature Descrip<onSpectrumbands 2.4GHz,915MHzor868MHz

Data-rate Upto250Kbs(2.4GHz)

Range <30meters

Channels 16(2.4GHz)

Channelaccess CSMA/CAorslo8edCSMA/CA

30




STARTOPOLOGY ADHOCTOPOLOGYPANCOORDINATOR

31



NetworkBEACON,sendbythePANcoordinator,andcontainingnetwork-relatedinfo.Usedalsoforsynchronizingeachdevicewiththestartofthecontenôn-freeoperaôns.

Contenôn-periodslots.AccessedbyusingCSMA/CAprotocol.

Contenôn-Freeperiodslots.ReservedbyPANcoordinatortoapplicaônswithQoSrequirements.

Inac^veperiods(neededforenergysavingonba8ery-constraineddevices)

ContenônPeriod CFPeriod Inac^ve

32



q PerformanceofIEEE802.15.4networks(ArduinoXbeetestbed).

Source:www.arduino.cc

33

6LoWPAN


q Mainopera<ons:

²  DeviceAddressing²  Rou^ng(differentfromforwarding)²  HeaderExtensions²  Headercompression²  Fragmenta^on²  Bootstrapping&Devicediscovery² …

34

6LoWPAN:Addressing


q IPv6addressesaretypicallyformedautoma<callyfromtheprefixoftheLoWPANedgerouter,andtheMACaddressofthewirelesscard.

q TheIEEE802.15.4supportstwoMACaddressformat:²  64-bitEUI-64addressACDE:4812:3456:7890+2001:ODB8:0BAD:FADE EUI-64MACaddress NetworkPrefix

² 48-bitEUI-64addressPANNetworkIden^fier(16bits)+16bits(zeros)+PANAddress(16bits)

35

6LoWPAN:Rou<ng


q 6LoWPANsupportstwodifferentrou<ngmodesMESH-UNDERROUTING

APPLICATIONS

UDP

LoWPAN

MAC802.15.4

PHY802.15.4

APPLICATIONS

UDP

LoWPAN

MAC802.15.4

PHY802.15.4

LoWPAN

MAC802.15.4

PHY802.15.4

² Usesthelayer-two(MAClayer)addressestoforwarddatapackets.

² Amesh-undernetworkisasingleIPsubnetwithasingleedgerouter.

² Usefulforsmallorlocalnetworks.

36

6LoWPAN:Rou<ng


q 6LoWPANsupportstwodifferentrou<ngmodesROUTEOVERROUTING

APPLICATIONS

UDP

LoWPAN

MAC802.15.4

PHY802.15.4

APPLICATIONS

UDP

LoWPAN

MAC802.15.4

PHY802.15.4

LoWPAN

MAC802.15.4

PHY802.15.4

² Usesthelayer-three(IPv6)addressestoforwarddatapackets.

²  IPv6addressesmustberoutable(Globalonly).² Deployscalable,large-scalenetworks.

37

6LoWPAN:ExtensionHeaders


q AnalogouslytoIPv6,6LoWPANusestheExtensionHeadersfortheop^onaldataandforspecificuse-cases.

q Two6LoWPANExtensionHeadersaredefined:FRAGMENTHEADERàusedincaseofpacketfragmenta^on,seenextslides

MESHHEADERàusedbyMESH_UNDERrou^ng,itcontains:<ORIGINATOR_MAC,DESTINATION_MAC,NUM_HOPS_LEFT>

J.Olsson,6LoWPANDemys^fied,Whitepaperh8p://www.^.com/lit/wp/swry013/swry013.pdf

38

6LoWPAN:Fragmenta<on


q AllIPv6subnetworkshavetoprovideaminimumMTUof1280bytes(recommended:1500bytes).²  IPV6doesprovideitsownfragmentaônfor

datagramslargerthantheminimumMTU(1280bytes).² 6LoWPANprovidesfragmentaôninordertofitthe

sizeof802.15.4MTU(127bytes)² Mesh-Underàfragmentsarereassembledatthedes^naôn.

If any fragment ismissing, the complete packetmust be re-transmikedbythesourcenode.

39



q AllIPv6subnetworkshavetoprovideaminimumMTUof1280bytes(recommended:1500bytes).²  IPV6doesprovideitsownfragmenta^onfor

datagramslargerthantheminimumMTU(1280bytes).² 6LoWPANprovidesfragmenta^oninordertofitthe

sizeof802.15.4MTU(127bytes)²  Route-overà fragments are reassembled at every hop (and

fragmented again). If is fragment is missing, the completepacketmustbere-transmikedbythepreviousnode.

40



q FragmentinfoarecontainedintheFragmentHeader.q AllFragmentscarrythesametagvalue,assigned

sequentuallybythesourceoffragmenta^on.

11000 SIZE TAG

11000 SIZE TAG OFFSET

FIRSTFRAGMENT

OTHERFRAGMENTs

41

6LoWPAN:HeaderCompression


q 6LoWPANcanusestate-lessorshared-contextheadercompressionmechanisms.


42





43





44

6LoWPAN:DeviceDiscovery


q TheIPv6NeighbourDiscoveryProtocolisusedbyIPv6nodestofindrouters,todeterminetheirlink-layeraddressandtomaintainreachibilityinfoaboutthepaths.² RouterssendAnnouncementmessages(RA)in

mul^cast,a8achingtheirnetworkprefix.²  IPv6nodescansolicitaRAmessagebyusingaRouter

Solicita<on(RS)message.² EachIPv6nodebuildsitsownaddress:<Prefix,MAC>

45



q DifferencescomparedtothestandardNDPv6protocol²  In802.15.4networks,6LoWPANnodesmightbelongto

differentbroadcastdomains(e.g.mul^-hopscenarios).²  RAmessagesmustbefloodedintheen^re6LoWPAN.

R H

R

R

R

H

H

H

6LoWPAN

EDGEROUTERRAfromtheIPv6ROUTER

RAfromtheER

RAfromeach6LoWPANrouter

46



q DifferencescomparedtothestandardNDPv6protocol.²  The6LoWPANEdgeRoutermaintainsawhiteboardofallthe

IPv6addressregisteredinthe6LoWPAN.²  ItalsoperformsDuplicateAddressDetec<on(DAD).

HEDGEROUTER

ROUTERSOLICITATION

ROUTERADVERTISEMENT

NODEREGISTRATION

NODECONFIRMATION

HEDGEROUTER

RRS

RA

NRNR

NCNCSI

NGL

E-HO

PTO

POLO

GY

MULTI-H

OPTO

POLO

GY

47

RPLProtocol:Rou<ngover6LoWPAN


q RPLàIPv6Rou^ngProtocolforLow-PowerandLossyNetworks

² StandardizedbytheIETFin2011(currentdraz:RFC6550)² DeFactostandardrou<ngprotocolforIoTscenarioscharacterizedbythepresenceof

low-power,resource-constraineddevices.²  Itsupports:point-to-point,point-to-mul^pointandmul^point-to-pointcommunicaôns.²  Itseparatespacketprocessingandforwardingfromtherou^ngop^mizaônobjec^ve

(e.g.minenergy,maxthroughput,mindelay,etc).²  ItcanbeusedtodisseminateIPv6or6LoWPANspecificinfo(e.g.neighbourdiscovery).²  Itdoesnotrelyonanyspecificlink-layerprotocol(althoughitiscommonlycoupledwith

theIEEE802.15.4standard).

RPLIETFspecificaôns(RFC6550)--h8ps://tools.ie{.org/html/rfc6550

48



q RPLcreatesarou^ngtopologyintheformofaDes<na<on-OrientedDirectedAcyclicGraph(DODAG)² Directedgraphwithoutcycles,orientedtowardsaroot

node(theedgerouter).

O.Iova,G.P.Picco,T.Istomin,andC.Kiraly,RPL,theRou^ngStandardfortheInternetofThings...OrIsIt?,Communica^onMagazine:54(12),16-22,2016

ER

R R R

R R

R

ER

R R R

R R

R

PHYSICALLINKS

RPLDO

DAG

49



q IncaseofExtendedLoWPANs(i.e.presenceofmul^pleEdgeRouters),RPLmightcreatemul<pledisjointDODAGs,routedatdifferentER.


ER

R R R

R R

R

RPLDO

DAG

ER

R R R

R R R

BACKBONELINK

50



q InordertocreateandmaintaintheDODAG,theRPLprotocolintroducesthefollowingcontrolpackets:²  DIO(DODAGInformaônObject)àusedtoenstablishthe

upwardpath(fromleafstoroot)²  DAO(Des^naônAdver^smentObject)àusedtoenstablishthe

downlinkpath(fromroottoleafs)²  DIS(DODAGInformaônSolicitaôn)àusedbyaninternalnode

inordertosolicitatethetransmissionofDIOmessages²  DAO-ACK(Des^naônAdver^sementObjectAcknowledgement)

51



q Twomodesofoperaôn:storingandnon-storing²  Storingàeachnodekeepsarou<ngentryforallthe

des^naônsreachableviaitssub-DODAG.²  Non-Storingàtherootistheonlynetworknodemaintaining

rou^nginformaôn;sourcerou^ngisusedfordownwardrou^ng.


ER

1 2 3R44

5SOURCE DESTINATION

StoringMode:²  Node4forwards

datatowardNode2²  Node2stores

rou<nginfoforallitssubgraph(nodes4and5)

ER

1 2 3R44

5SOURCE DESTINATION

Non-storingMode:²  Node4always

forwardsdatatowardtheroot

Containstheinfoaboutnext-hops

52



q EachnodeoftheDODAGhasitsownrankvalue.

ER

R R R

R R

R

Rank0

Rank1

Rank2

Rank8

Rank4

Rank6

Rank1

² Abstractnumericvalue,expressionofarela^veposi^onwithinaDODAGVersion.

² RankofthenodesmustmonotonicallydecreasetowardstheDODAGdes^na^on.

² Rankisusedtoavoidanddetectloops.

PROPERTIES

HOWTOCOMPUTEIT?

²  RankiscomputedaccordingtotheObjec<veFunc<oninuse(seenextslides)

53



q Crea^onoftheupwardpaths(assumedatstart-up)

ER

R R R

R R

R

DIOmessage

1.  TheEdgeroutercreatestheDIOmessage,containingitsrankandDODAGid,andsendsitinmul<cast.

RECEIVINGNODES

2.Eachnodeestablishestheupwardlinktowardthesender.

3.Eachnodecomputesitsownrankvalue,basedontheroot’srankandontheObjec<veFunc<on.

4.EachnoderebroadcaststheDIOmessage(followingtheTricklealgorithm),byincludingitsowncomputedrank.

Rank:2

54



q Crea^onoftheupwardpaths(assumedatstart-up)

ER

R R R

R R

R

Anodereceivingmul^pleDIOmessages(e.gthebluenode)

2.BasedontheusedmetricandconstraintsdefinedbytheObjec^veFunc^on,itchoosesanappropriateparent:

Ø  Mul^pleparentscanbeestablished,butapreferredparentisselected;

Ø  Ifthenodehasalreadyitsownrank,andthereceivedoneisgreaterthanthelocalrank,theDIOmessageisdiscarded(loopavoidance)

3.Asbefore,eachnoderebroadcaststheDIOmessage(followingtheTricklealgorithm),byincludingitsown computedrank.

Rank:2 Rank:3

Therou^ngprocedureendswhenreachingtheleafnodes.

55



q Crea^onofthedownwardpaths(fromleaftoedgerouter)

1.EachnodeperiodicallygeneratesaDAOmessageandsendsittothedes^na^on,byusingtheupwardpathestablishedthroughtheDIOmessage.

2.AlltheintermediateparentsextendtheDAOmessagebyaddingtheirIPv6addressintheTransitInforma<onOp<on.

NON-STORINGMODE

ER

1 2 3

4 5

6

DAOmessage

6-4

6-4-1

56



q Crea^onofthedownwardpaths(fromleaftoedgerouter)

1.EachnodeperiodicallygeneratesaDAOmessageandsendsittoallparentsnode(differentlytothepreviouscase,themessageisnotforwardedtowardtheroot).

2.Eachparentmaintainsaddi^onalrou^ngtablesforallthenodesofitssub-DODAG.

STORINGMODE

ER

1 2 3

4 5

6

DAOmessage

57



q  Tricklealgorithmàdatadisseminaônschemeforlossysharedmedium(e.g.low-powerandlossynetworks).

²  Itcanbeappliedtoawiderangeofprotocoldesignproblems(besideourtopic,i.e.theDIOmessagedisseminaôninRPL)

² Threeconfigura<onparameters:theminimumintervalsizeImin,themaximumintervalsizeImax,andaredundancyconstantk.

² Inaddiôn,Tricklemaintainsthreevariables:ü  Iàthecurrentintervalsize.ü  tàa^mewithinthecurrentinterval.ü  càacounter.

Tricklealgorithm–IETFspecificaôns:h8ps://tools.ie{.org/html/rfc6206

58



q  TheTrickleexecu^onfollowsfiverules:1.  Atstartup,itsetsItoavalueintherangeof[Imin,Imax],cto0andttoa

randompointintheinterval,[I/2,I];2.  WheneverTricklehearsatransmissionthatis"consistent",itincrements

thecounterc;3.  At^met,Trickletransmitsifandonlyifthecountercislessthanthe

redundancyconstantk.4.  WhentheintervalIexpires,Trickledoublestheintervallength(I).5.  IfTricklehearsatransmissionthatis"inconsistent"andIisgreaterthan

Imin,setsItoIminandttoarandompointintheinterval[I/2,I](step1).

Themeaningofconsistentandinconsistentdependsonthespecificuse-case!


59



q  TheTrickleexecu^onfollowsfiverules:1.  Atstartup,itsetsItoavalueintherangeof[Imin,Imax],cto0andttoa

randompointintheinterval,[I/2,I];2.  WheneverTricklehearsatransmissionthatis"consistent",itincrements

thecounterc;3.  At^met,Trickletransmitsifandonlyifthecountercislessthanthe

redundancyconstantk.4.  WhentheintervalIexpires,Trickledoublestheintervallength(I).5.  IfTricklehearsatransmissionthatis"inconsistent"andIisgreaterthan

Imin,setsItoIminandttoarandompointintheinterval[I/2,I](step1).

EXAMPLE:CONSISTENCYofTOPOLOGYinRPL-DIOmessages…


60



q  TheObjec<veFunc<on(OF)definesthespecificmetrics/constraintstouseforfindingminimumcostpaths.

² Howtocomputetherank;² Howtoselecttheparents(andthepreferredparent);² Howtocomputethepathcost.

Ø  EXAMPLE1.Determinetheshortestroute(METRIC)byavoidinglow-energynodes(CONSTRAINT).

Ø  EXAMPLE2.Determinethelowestend-to-enddelay(METRIC)byavoidinglow-qualitylinks(CONSTRAINT).

61



q  Twoobjec^vefuncônshavebeendefinedsofar:² OF0:Objec^veFuncônZeroà

usehopcountasdefaultrou^ngmetric.

² OF1:MinimumRankwithHysteresisObjec^veFuncônàSelectrouteswhichminimizeanaddi^vemetric.DefaultMetric:ExpectedTransmissionNumber(ETX)

MinimumRankwithHysteresisObjec^veFuncôn–IETFspecificaôns:h8ps://tools.ie{.org/html/rfc6719

the internet of things - cs.unibo.it · 4 ipv4 protocol ip-based network layer solutions l. bononi,...

Documents