distributed systems mobile networking€¦ · mobile networking rik sarkar university of edinburgh...
TRANSCRIPT
DistributedSystems
MobilenetworkingRikSarkar
UniversityofEdinburgh
Fall2016
Distributed Systems, Edinburgh, 2016
Howdomobilephoneswork?
• CellularbasestaEons(antennas+cpu)withhexagonalcells
Distributed Systems, Edinburgh, 2016
Channelassignments
• EachbasestaEonusesasetof“channels”(e.g.frequencies)tocommunicatewithmobilenodesinitscell
• Usuallyadjacentcellsdonotusesamechannel– Toavoidinterference
• ButsamechannelcanbeusedatdistantbasestaEons
Distributed Systems, Edinburgh, 2016
SpaEalReuse
• Thisfeatureofusingthesamechannelindifferentcellsiscalled“spaEalreuse”– Samechannelcanbeusedindifferentpartsof“space”
• DistancebetweenbasestaEonscanvary– Fewhundredmetersinurbanregion– Severalkilometersinopenspaces/ruralregions
Distributed Systems, Edinburgh, 2016
• Oneantennahasafixednumberofchannels• Ifitscellislarge,theremaybemanypeopleinit,andtheantennamaynotbeabletohandle
• HencecloserantennaplacementinciEes• ButsElllimitedcapacityduetointerferencefromotherantennasusingsamechannel
Distributed Systems, Edinburgh, 2016
Channelassignments
• Inaregion,theremaybedifferentmobileoperators
• Theyusuallybidforrightstousedifferentpartsofthespectrum– Dependingonwheretheyneedmorechannelsorlessetc
– SpectrumaucEons– Thendecidewhichchanneltouseinwhichcell
Distributed Systems, Edinburgh, 2016
Therealmobilityissue
• Whathappenswhenamobilephonemovesfromonecelltoanothercell?
Distributed Systems, Edinburgh, 2016
Terminology• Mobilenode• Homenetwork
– Thenetworkthat“owns”themobilenumber• Eg.EEorvodafoneorO2…• Local
• HomelocaEonregister– Databaseofprofile,currentlocaEonetcofmobilenumbers
• Visitednetwork– Wherethemobilecurrentlyresides– VisitorlocaEonregister:databaseofnodescurrentlyinregion
Distributed Systems, Edinburgh, 2016
Call
• Goesfirsttohomenetwork• WhichreturnsthecurrentlocaEonofthemobile(itsvisitednetwork)
• ThenthecallgoestotheactuallocaEon
Distributed Systems, Edinburgh, 2016
Handoff
• Whenmobilemovesfromonecelltoanother– It’scommunicaEonishandedofftothenewcell
• Detectedbyweaksignalfromcell1butstrongsignalforcell2
• Orforloadbalancing• ExecutedbybasestaEonsandMSC
Distributed Systems, Edinburgh, 2016
Mobile Switching Center + VLR
Internetissues
Distributed Systems, Edinburgh, 2016
Internetissues
• Cellularsystemsarefineforcalling,notforinternet
• InternetrouEngisIP–based• IPisgeographybased• Whathappenswhenamobilephonemovestoadifferentarea?Orsimplytoadifferentcell?
Distributed Systems, Edinburgh, 2016
Internetissues
• SocommunicaEonfromMNisdisrupted.• MNmaybeabletore-iniEalizeeverything,butthatisundesirable
• WewantapacketforIPXtosEllbedeliveredtoMN
Distributed Systems, Edinburgh, 2016
Internetissues
• SupposeanMNhadIPaddressXinitsiniEalsubnet(localareanetwork)s1(incell1)
• NowtheMNmovestoadifferentsubnets2– Xisnotavalidaddressins2– RoutersontheinternetwillsendpacketsforIPXtos1,nevertos2.
Distributed Systems, Edinburgh, 2016
SoluEon:IPinIPencapsulaEon
• WhenMNmoves,itinformsvisitednetworkofitsIPX
• Homeagent– AprocessonhomenetworkthatinterceptspacketsforIPX
– SendsittoIPY(IPofforeignagent)• Foreignagent(correspondingprocessonvisitednetwork)– Receivespacket– UnpackstoseeitisintendedforX– DeliversthroughMAClayeraddress
Distributed Systems, Edinburgh, 2016
data X
Y data X
MobileIP
• SolvestherouEngproblem• However,oniniEalmove,somepacketsoracksmaygetlost/delayed– TransportlayerthinksthereiscongesEon– Slowsdown– …
Distributed Systems, Edinburgh, 2016
Moreadvancedthings
• Withadvancingtechnology• Newfeaturesarecroppingupinmobilenets• Newissuesareappearing
Distributed Systems, Edinburgh, 2016
LocalizaEoninwirelessnetworks
• Canbedonebasedonsignalstrengths– Decreaseswithdistance
• TrilateraEon–threedistancessufficetolocateapoint– SignalstrengthfromthreeormorewirelesstransmiherswithknownlocaEon
– ApproximatelocalizaEonduetovariaEoninsignalpropagaEon,noiseetc
Distributed Systems, Edinburgh, 2016
LocaEoninmobilenets
• Canbedoneusingthreecellulartowers– Eitheratthemobilephone– Oratcellnetwork
• NewpossibiliEes– PredicthandoffsfrommoEon,makepreparaEonsearly
– Learn/predictuserbehavior– GivelocaEonbasedrecommendaEonsetc…
Distributed Systems, Edinburgh, 2016
Privacyissues• LocaEonisconsideredprivateinformaEon• TrackinglocaEonalltheEmeisconsideredintrusive
• Nowaytopreventcellcompaniesfromdoingit…• Atthemobilephoneend,effortsarebeingmadetofuzzlocaEons– GivesomeinformaEonforlocaEonbasedservicestorun
– AvoidsomeotherinformaEon,oravoidpreciselocaEons
• Context/acEvityinformaEonisalsoprivate…
Distributed Systems, Edinburgh, 2016
Femto-cellnetworks
• Smallpersonalizedcellantennas(~10mrange)– Plugintoyourwirelessrouter
• EvenbeherspaEalreuse• Lessorganized,trickiertocoordinatechannelassignmentetc
• Possibilityofchannelclashwithmacrocells
Distributed Systems, Edinburgh, 2016
BeamformingdirectedcommunicaEon
• SendssignalsinaparEculardirecEon– UsesmulEpleantennastogethertransmijngstdifferentphases
– DestrucEveinterferenceensuresthatsignaldoesnottravelinotherdirecEons
– EasytochangedirecEonsquickly• Anglecanrangefrom20or30degreestoafewdegrees(narrowbeam)
Distributed Systems, Edinburgh, 2016
BeamformingdirectedcommunicaEon
• Usuallyaround60GHzfrequency• Highsupportedbandwidth• Goodforhidefvideo,largedatavolumesetc• Atthisrange,signalhashighahenuaEonfromair– Shortrange(fewmetersto100meters)
• TogetherwithdirecEonalityimpliesveryeffecEvespaEalreuse
Distributed Systems, Edinburgh, 2016
BeamformingdirectedcommunicaEon
• Challenges– Easilyaffectedbyobstacles– Bothtransmiherandreceiverneedtobe“looking”ateach-otherattherightEme
• Mediumaccessbecomesharder
– Mobilitycancreateachallengeof“tracking”adevice
Distributed Systems, Edinburgh, 2016
MobilecompuEng
• Mobilewirelessdevicesaregoingtobeevenmorepopular
• Moreapps/services/media• Greatneedforwirelessbeandwidth
– Currentinfrastructureisnotsufficient• Newtechnologies• Simultaneously,detecEonofcollecEvecontext,groupsetcforbeheradapEveservices
Distributed Systems, Edinburgh, 2016