Mobile and Wireless Compu2ng CITS4419 Week 3 MAC...
Transcript of Mobile and Wireless Compu2ng CITS4419 Week 3 MAC...
MobileandWirelessCompu2ngCITS4419Week3MACProtocols
AssociateProfessorRachelCardell-OliverSchoolofComputerScience&So;wareEngineering
semester-22018
WhystudyMAC?(shouldCSstudentsstudyWSNMACprotocols)
• ControllingwhentosendapacketandwhentolistenforapacketareperhapsthetwomostimportantoperaKonsinawirelessnetwork– Especially,idlewaiKngwasteshugeamountsofenergy
• CommunicaKoninasensornetworkischallengingbecause– Powerislimited– Thechannelisshared
• MACprotocolsforsensornetworksaimtosharethechannelinanenergyefficientmanner
What
• LastweekwesawhowdatacouldbetransmiQedonwirelesschannel
• ThisisthePhysicalLayerofasensornetwork• Thisweekwewillconsiderthenextlayer:theMAClayer
• TheMAClayerisresponsibleformanagingtheexchangeofmessagesbetweenpairsofnodesinasensornetwork
Overview
• WSNMACchallenges• ContenKonMACs–Aloha• ScheduledMACs–SMAC,FlexiMAC• HybridMACs-IEEE802.15.4MAC• LoRaWAN
SharedChannelChallenges
• Energy– Tosaveenergyneedtominimisecollisions,overhearing,re-transmissions,hiddenterminal
• Latency– ApplicaKondependent–deliverdataassoonaspossible
RecommendedReading
A.Bachir,M.Dohler,T.WaQeyne,andK.Leung,MACEssen)alsforWirelessSensorNetworks,CommunicaKonsSurveysandTutorials12(2)2010
WhatisaMACprotocol?
• Thetermprotocolreferstotherulesthatgovernwhateachnodeinanetworkisallowedtodoandhowitshouldoperate
• MACprotocolsdefinehowmulKplenodescontroltheiraccesstoasharedmedium
• Theyaretermedmediaaccess(MAC)protocolsormul)pleaccessprotocols.
WSNMACRequirements• DesignConstraints
– Transmissionsarecostly– Receivingaboutasexpensiveastransmi`ng– IdlingcanbecheaperbutissKllexpensive
• Energyproblems– Collisions–wastedeffortwhentwopacketscollide– Overhearing–wasteeffortinreceivingapacketdesKnedforanothernode
– Idlelistening–si`ngidlyandtryingtoreceivewhennobodyissending
– Protocoloverhead• Alwaysnice:LowcomplexitysoluKon
Ad hoc & sensor networs - Ch 5: MAC protocols
SS 05 Ad hoc & sensor networs - Ch 5: MAC protocols 14
Main wireless MAC options Wirelessmediumaccess
Centralized
Distributed
ContenKonSchedule
Fixedassignment
Demandassignment
ContenKonSchedule
Fixedassignment
Demandassignment
Aloha(1968Hawaii)
Byhelix84-Ownwork,CCBY2.5,hQps://commons.wikimedia.org/w/index.php?curid=1374485ByOriginal:KyurimVector:flThisvectorimageincludeselementsthathavebeentakenoradaptedfromthis:AlohaSvG.PNG.-AlohaSvG.PNG,CC0,hQps://commons.wikimedia.org/w/index.php?curid=27793990
Protocol=Whenreadythensendmessage(Distributed,ContenKon)
ScheduledMACprotocols
Idea: Coordinate node schedules
Advantages: Turn off radio when not needed (allocated time slot) Limits collision, idle listening, overhearing
Disadvantages: Rigidity – fixed sleep times Not flexible to changes in sensor density or movements Sleep delays increase packet delivery time (latency)
S-MAC
Strategy:Eachnodebroadcastsandfollowsitslisten/sleepscheduleTotalktoyourneighbour,wakeupwhensheislisteningUseRTS/CTStoresolveconflictPeriodicallylistenforallnodes’schedulesSYNCpktssynchronisenodes’clocksYeetal,MediumAccessControlwithCoordinatedAdap)veSleepingforWSNs,IEEETransacKonsonNetworking2004
FlexiTP
FlexiTP:AFlexible-Schedule-BasedTDMAProtocolforFault-TolerantandEnergy-EfficientWirelessSensorNetworks,Lee,WinnieLouis;DaQa,Amitava;Cardell-Oliver,Rachel,InIEEETransac2onsonParallelandDistributedSystems,vol.19,no.6,pp.851-864,June2008
22Sep2010 22MannheimSummerSchool
IEEE802.15.4Standard
• Forlow-ratewirelesspersonalareanetworks• 10mcommsrange,datarate250kbit/s• DefinesphysicallayerandMACprotocols• Usedasbaseprotocolsfor
– ZigbeeIoTmeshprocotol– ISA100.11aProcessandfactoryautomaKon– WirelessHARTreal-KmeautomaKonandindustryapps– MiWi,SNAP– 6LoWPANforIPv6overpersonalareanets
• Home Networking
• Automotive Networks
• Industrial Networks
• Interactive Toys
• Remote Metering
• Environmental Monitoring sensor networks
• Infrastructure monitoring sensor networks
IEEE 802.15.4 Applications Space
Joe Dvorak, Motorola 9/27/05 22Sep2010 26MannheimSummerSchool
Features
• Networkbeaconsforcommsmanagement• GuardedKmeslots(foreg.alarms)• Securitysupport• Frequencybands:868/915/2450MHz
Topologies
• MACsupportspeertopeerorstarnetworks• Peertopeerforselfmanaging,adhocnetworks(meshnetworks)
• StarpaQernhascoordinators,fullfuncKondevices(clusterheads)andreducedfuncKondevices(leafnodes)
• FullfuncKondevice(FFD)– Anytopology– Networkcoordinatorcapable– Talkstoanyotherdevice
• ReducedfuncKondevice(RFD)– Limitedtostartopology– Cannotbecomeanetworkcoordinator– Talksonlytoanetworkcoordinator– VerysimpleimplementaKon
IEEE 802.15.4 MAC Overview Device Classes
Slide 29 Joe Dvorak, Motorola 9/27/05 22Sep2010 29MannheimSummerSchool
Sensornode
Basenodeorclusterhead
Full function device
Reduced function device
CommunicaKonsflow
Master/slave
PANCoordinator
IEEE 802.15.4 MAC Overview Star Topology
Slide 30 Joe Dvorak, Motorola 9/27/05 22Sep2010 30MannheimSummerSchool
Full function device Communications flow
Point to point Cluster tree
IEEE 802.15.4 MAC Overview Peer-Peer Topology
Slide 31 Joe Dvorak, Motorola 9/27/05 22Sep2010 31MannheimSummerSchool
Full function device
Reduced function device
Communications flow
Clusteredstars-forexample,clusternodesexistbetweenroomsofahotelandeachroomhasastarnetworkforcontrol.
IEEE 802.15.4 MAC Overview Combined Topology
Slide 32 Joe Dvorak, Motorola 9/27/05 22Sep2010 32MannheimSummerSchool
FrameTypes
• Data• Acknowledgement• Beacon• MACcommand
• SloQedorunsloQedCSMA/CA
• Datatransfer=beaconsync+datainslots+opKonalack=request+confirm+response
052004 MarcoNaeve,EatonCorp. Slide34
GeneralMACFrameFormat
Octets:2 1 0/2 0/2/8 0/2 0/2/8 variable 2Destination
PAN identifier
Destination address
Source PAN
identifier
Source address
MAC payload MAC footer
Frame check
sequence
MAC header
Addressing fields
Frame control
Sequence number
Frame payload
Bits: 0-2 3 4 5 6 7-9 10-11 12-13 14-15
Frame type Sequrity enabled
Frame pending
Ack. Req. Intra PAN ReservedDest.
addressing mode
ReservedSource
addressing mode
Framecontrolfield
052004 MarcoNaeve,EatonCorp. Slide35
BeaconFrameFormat
Bits: 0-3 4-7 8-11 12 13 14 15Beacon
orderSuperframe
orderFinal CAP
slotBattery life extension Reserved
PAN coordinator
Association permit
Octets:2 1 4 or 10 2 variable variable variable 2
MAC footer
Frame check
sequence
MAC header
Source address information
MAC payload
Superframe specification
GTS fields
Pending address
fields
Frame control
Beacon sequence number
Beacon payload
052004 MarcoNaeve,EatonCorp. Slide36
MACCommandFrame
• CommandFrameTypes– AssociaKonrequest– AssociaKonresponse– DisassociaKonnoKficaKon– Datarequest– PANIDconflictnoKficaKon
– OrphanNoKficaKon– Beaconrequest– Coordinatorrealignment– GTSrequest
Octets:2 1 4 to 20 1 variable 2
MAC footer
Frame check
sequence
Frame control
Data sequence number
Address information
MAC header MAC payload
Command type
Command payload
052004 MarcoNaeve,EatonCorp. Slide37
DataFrameFormat
Acknowledgement Frame Format Octets:2 1 2
MAC footer
Frame check
sequence
MAC header
Frame control
Data sequence number
Octets:2 1 4 to 20 variable 2
MAC Payload MAC footer
Data payloadFrame check
sequence
MAC header
Frame control
Data sequence number
Address information
MeshNetwork
• Meshnetwork:individualend-nodesforwardtheinformaKonofothernodestoincreasethecommunicaKonrangeandcellsizeofthenetwork.Whilethisincreasestherange,italsoaddscomplexity,reducesnetworkcapacity,andreducesbaQerylifeKme
LoRa-Alliance.org
StarNetwork• Singlehopefromsensornodestoagateway• LongrangestararchitecturemakesthemostsenseforpreservingbaQerylifeKmewhenlong-rangeconnecKvitycanbeachieved
LoRa-Alliance.org
End-devices
Eachend-deviceclasshasdifferentbehaviordependingonthechoiceofopKmizaKon:• BaQeryPowered–ClassA• LowLatency–ClassB• NoLatency–ClassC
LoRa-Alliance.org
BaQeryPowered–ClassA• BidirecKonalcommunicaKons
• Unicastmessages• Smallpayloads,longintervals• End-deviceiniKatescommunicaKon(uplink)• Servercommunicateswithend-device(downlink)duringpredeterminedresponsewindows:
LoRa-Alliance.org
LowLatency–ClassB• BidirecKonalwithscheduledreceiveslots• UnicastandMulKcastmessages• Smallpayloads,longintervals• Periodicbeaconfromgateway• Extrareceivewindow(pingslot)• ServercaniniKatetransmissionatfixedintervals
LoRa-Alliance.org
NoLatency–ClassC
• BidirecKonalcommunicaKons• UnicastandMulKcastmessages• Smallpayloads• ServercaniniKatetransmissionatanyKme• End-deviceisconstantlyreceiving
LoRa-Alliance.org