DistributedSystems

MobilenetworkingRikSarkar

UniversityofEdinburgh

Fall2015

Distributed Systems, Edinburgh, 2014

Howdomobilephoneswork?

•  CellularbasestaEons(antennas+cpu)withhexagonalcells

Distributed Systems, Edinburgh, 2014

Channelassignments

•  EachbasestaEonusesasetof“channels”(e.g.frequencies)tocommunicatewithmobilenodesinitscell

•  Usuallyadjacentcellsdonotusesamechannel– Toavoidinterference

Distributed Systems, Edinburgh, 2014

SpaEalReuse

•  Thisfeatureofusingthesamechannelindifferentcellsiscalled“spaEalreuse”– Samechannelcanbeusedindifferentpartsof“space”

•  DistancebetweenbasestaEonscanvary– Fewhundredmetersinurbanregion– Severalkilometersinopenspaces/ruralregions

Distributed Systems, Edinburgh, 2014

•  Oneantennahasafixednumberofchannels•  Ifitscellislarge,theremaybemanypeopleinit,andtheantennamaynotbeabletohandle

•  HencecloserantennaplacementinciEes•  ButsElllimitedcapacityduetointerferencefromotherantennasusingsamechannel

Distributed Systems, Edinburgh, 2014

Channelassignments

•  Inaregion,theremaybedifferentmobileoperators

•  Theyusuallybidforrightstousedifferentpartsofthespectrum– Dependingonwheretheyneedmorechannelsorlessetc

– SpectrumaucEons– Thendecidewhichchanneltouseinwhichcell

Distributed Systems, Edinburgh, 2014

Therealmobilityissue

•  Whathappenswhenamobilephonemovesfromonecelltoanothercell?

Distributed Systems, Edinburgh, 2014

Terminology•  Mobilenode•  Homenetwork

–  Thenetworkthat“owns”themobilenumber•  Eg.EEorvodafoneorO2…•  Local

•  HomelocaEonregister–  Databaseofprofile,currentlocaEonetcofmobilenumbers

•  Visitednetwork– Wherethemobilecurrentlyresides–  VisitorlocaEonregister:databaseofnodescurrentlyinregion

Distributed Systems, Edinburgh, 2014

Call

•  Goesfirsttohomenetwork•  WhichreturnsthecurrentlocaEonofthemobile(itsvisitednetwork)

•  ThenthecallgoestotheactuallocaEon

Distributed Systems, Edinburgh, 2014

Handoff

•  Whenmobilemovesfromonecelltoanother–  It’scommunicaEonishandedofftothenewcell

•  Detectedbyweaksignalfromcell1butstrongsignalforcell2

•  Orforloadbalancing•  ExecutedbybasestaEonsandMSC

Distributed Systems, Edinburgh, 2014

Mobile Switching Center + VLR

Internetissues

Distributed Systems, Edinburgh, 2014

Internetissues

•  Cellularsystemsarefineforcalling,notforinternet

•  InternetrouEngisIP–based•  IPisgeographybased•  Whathappenswhenamobilephonemovestoadifferentarea?Orsimplytoadifferentcell?

Distributed Systems, Edinburgh, 2014

Internetissues

•  SocommunicaEonfromMNisdisrupted.•  MNmaybeabletore-iniEalizeeverything,butthatisundesirable

•  WewantapacketforIPXtosEllbedeliveredtoMN

Distributed Systems, Edinburgh, 2014

Internetissues

•  SupposeanMNhadIPaddressXinitsiniEalsubnet(localareanetwork)s1(incell1)

•  NowtheMNmovestoadifferentsubnets2– Xisnotavalidaddressins2– RoutersontheinternetwillsendpacketsforIPXtos1,nevertos2.

Distributed Systems, Edinburgh, 2014

SoluEon:IPinIPencapsulaEon

•  WhenMNmoves,itinformsvisitednetworkofitsIPX

•  Homeagent–  AprocessonhomenetworkthatinterceptspacketsforIPX

–  SendsittoIPY(IPofforeignagent)•  Foreignagent(correspondingprocessonvisitednetwork)–  Receivespacket–  UnpackstoseeitisintendedforX–  DeliversthroughMAClayeraddress

Distributed Systems, Edinburgh, 2014

data X

Y data X

MobileIP

•  SolvestherouEngproblem•  However,oniniEalmove,somepacketsoracksmaygetlost/delayed– TransportlayerthinksthereiscongesEon– Slowsdown– …

Distributed Systems, Edinburgh, 2014

Moreadvancedthings

•  Withadvancingtechnology•  Newfeaturesarecroppingupinmobilenets•  Newissuesareappearing

Distributed Systems, Edinburgh, 2014

LocalizaEoninwirelessnetworks

•  Canbedonebasedonsignalstrengths– Desreaseswithdistance

•  TrilateraEon–threedistancessufficetolocateapoint– SignalstrengthfromthreeormorewirelesstransmiherswithknownlocaEon

– ApproximatelocalizaEonduetovariaEoninsignalpropagaEon,noiseetc

Distributed Systems, Edinburgh, 2014

LocaEoninmobilenets

•  Canbedoneusingthreecellulartowers– Eitheratthemobilephone– Oratcellnetwork

•  NewpossibiliEes– PredicthandoffsfrommoEon,makepreparaEonsearly

– Learn/predictuserbehavior– GivelocaEonbasedrecommendaEonsetc…

Distributed Systems, Edinburgh, 2014

Privacyissues•  LocaEonisconsideredprivateinformaEon•  TrackinglocaEonalltheEmeisconsideredintrusive

•  Nowaytopreventcellcompaniesfromdoingit…•  Atthemobilephoneend,effortsarebeingmadetofuzzlocaEons– GivesomeinformaEonforlocaEonbasedservicestorun

– AvoidsomeotherinformaEon,oravoidpreciselocaEons

•  Context/acEvityinformaEonisalsoprivate…

Distributed Systems, Edinburgh, 2014

Femto-cellnetworks

•  Smallpersonalizedcellantennas(~10mrange)– Plugintoyourwirelessrouter

•  EvenbeherspaEalreuse•  Lessorganized,trickiertocoordinatechannelassignmentetc

•  Possibilityofchannelclashwithmacrocells

Distributed Systems, Edinburgh, 2014

BeamformingdirectedcommunicaEon

•  SendssignalsinaparEculardirecEon– UsesmulEpleantennastogethertransmijngstdifferentphases

– DestrucEveinterferenceensuresthatsignaldoesnottravelinotherdirecEons

– EasytochangedirecEonsquickly•  Anglecanrangefrom20or30degreestoafewdegrees(narrowbeam)

Distributed Systems, Edinburgh, 2014

BeamformingdirectedcommunicaEon

•  Usuallyaround60GHzfrequency•  Highsupportedbandwidth•  Goodforhidefvideo,largedatavolumesetc•  Atthisrange,signalhashighahenuaEonfromair– Shortrange(fewmetersto100meters)

•  TogetherwithdirecEonalityimpliesveryeffecEvespaEalreuse

Distributed Systems, Edinburgh, 2014

BeamformingdirectedcommunicaEon

•  Challenges– Easilyaffectedbyobstacles– Bothtransmiherandreceiverneedtobe“looking”ateach-otherattherightEme

•  Mediumaccessbecomesharder

– Mobilitycancreateachallengeof“tracking”adevice

Distributed Systems, Edinburgh, 2014

MobilecompuEng

•  Mobilewirelessdevicesaregoingtobeevenmorepopular

•  Moreapps/services/media•  Greatneedforwirelessbeandwidth

– Currentinfrastructureisnotsufficient•  Newtechnologies•  Simultaneously,detecEonofcollecEvecontext,groupsetcforbeheradapEveservices

Distributed Systems, Edinburgh, 2014