`INTERNATIONALCONFERENCEONUNIVERSALPERSONALCOMMUNICATIONS,TOKYO,JAPAN, 
`SWAN:AnIndoorWirelessATMNetwork
`E.Hyden,J.Trotter,P.Krzyzanowski,M.SrivastavaandP.Agrawal
`AT&TBellLaboratories
`MountainAvenue
`MurrayHill,NJ 
`feah,trotter,paul,mbs,pag@research.att.com
`Abstract|TheSWAN projectinvestigatesarchitectural
`vidingindoor,wirelessaccesstomobilehostsviaawiredlo-
`aspectsofnetworkscontainingmobilehosts.Thenetwork
`calareainfrastructure.Thenetworktopologyisrestricted
`modelincludesbasestationsconnectedviaawired,ATM
`tooneprovidingawirelesslasthop.Figure depictsasys-
`infrastructureandawireless,ATMlasthoptoanumber
`ofmobilehosts,rangingincomputationalandfunctional
`abilitiesfrompersonaldigitalassistantstonotebookcom-
`puters.TheFAWNnetworkinterfacecardwasdeveloped
`aspartoftheimplementationofasmallSWANnetwork.It
`provideswireless,ATMchannelsusingo(cid:11)-the-shelfFHSS
`modemswhichoperateinthe.GHzindustrial,scienti(cid:12)c
`andmedicalband,anduseasequenceofradiochannelsof
` MHzbandwidthtoprovideuptokb/Srawbitrate.
`The(cid:12)rstphaseoftheimplementationhasbeencompleted
`andprovidesbasicwirelessATMconnectivity.Thispaper
`presentsanoverviewoftheSWANnetwork,followedbya
`descriptionoftheimplementationwhichhasbeenbuiltto
`validateourinitialarchitecturaldesign.
`Keywords|WirelessNetworks,AsynchronousTransfer
`Mode,MobileComputing.
`I.Introduction
`StationFig. .Networkingenvironment.
`CURRENTwirelesstechnologycanprovidedatalinks
`temrepresentativeofatypicalSWANnetwork;twolocal
`ranginginspeedsfromtensofkilobitstoalmosta
`areadomainsareconnectedbyawideareafabric.Theaim
`gigabitpersecondtomeettheneedsofapplicationsasdi-
`istoprovideuninterruptednetworkconnectivitytomo-
`verseaspagingandlocalareanetworkconnectivity.The
`bilehostsastheyroam,movingbetweenthebasestations
`basictechnologyisstilldeveloping,buttrendscanbeiden-
`withinalocalareadomainandevenbetweendomains.The
`ti(cid:12)ed;infrared(IR)appearswellsuitedtoperipheralcon-
`lattercasemayresultinperiodsofweakconnectivityor
`trolandinterconnectiononthedesktoporwithinasmall
`evendisconnection.ASWANbasestationprovidescover-
`room,andspreadspectrumtechniquessuchasDirectSe-
`ageforanareafrom tometersindiameter,servicing
`quence(DS)andFrequencyHopping(FH)arepopular
`typicallyoneortwoo(cid:14)cesorasectionofcorridorwithina
`withinthetelephonyandcomputerindustries.
`building.Highdataratesandfrequenthando(cid:11)sarechar-
`Miniaturisation,lowpowerelectronicsandevolvingdis-
`acteristicofsuchserviceareasizes.
`playtechnologiesallowincreasingfunctionalitytobepack-
`Endpointsinthenetworkrangeinfunctionalityandmo-
`agedintoeasilyportabledevicessuchasPersonalDigital
`bilityfromPDAstonotebookcomputersandincludeenti-
`Assistants(PDA)andnotebookcomputers.Theeasewith
`tiessuchasprintservers,whichmayseldombemoved.
`whichthesesmall,lightweightdevicescanbetransported
`Whilemobilehostsmayhavesigni(cid:12)cantcomputational
`andthedesiretointegratethemasseamlesslyaspossible
`power,itislikelythattheywillbeusedmoreforcommuni-
`intoauser'scomputingenvironmentusingwirelesstech-
`catingthanforcomputing.Powerusagerestrictionswillbe
`nologyisdrivingcurrentresearchinmobilecomputing.
`thegoverningforcefortheforeseeablefuture,sothebulk
`TheSWANproject[ ]wasinitiatedwithintheNet-
`ofanyprocessingwillbedonebyserversattachedtothelo-
`workedComputingResearchdepartmentatAT&TBell
`calinfrastructure,whiletheprocessorsinthemobilehosts
`Laboratoriestostudythisnewaspectofcomputing.
`willbeusedprimarilyforinformation(cid:12)ltering,compression
`Broadly,theaimsoftheprojectaretogainsomefamil-
`anddecompression,encryptionanddecryptionandcapture
`iaritywiththeaspectsofcomputingwhicharerelatedto
`andpresentation.Audiovisualdataareimportantcommu-
`mobilityand,inthelongerterm,toidentifyprinciplesand
`nicationsmediaandmultiservicesnetworkswhichusethe
`engineeringguidelineswhichcanbeusedbydevelopersto
`AsynchronousTransferMode(ATM)[ ]arewellsuitedto
`buildsuccessfulwirelessnetworks.
`carryingthesetypesoftra(cid:14)c,soATMhasbeenadopted
`Initially,wehavechosentofocusontheproblemofpro-
`asthenetworkingparadigmforusewithinSWAN.
` Seamless,WirelessATMNetwork.
`WhileSWANhasanobviousroleinprovidingthewire-
`FlexibleArchitectureforWirelessNetworks
`lesslasthopinanATMnetworkinghierarchy,themajority
`
`Compute
`Server
`
`Media
`Server
`
`Base
`
`Wide Area
`
`Local Area
`
`Wired
`Host
`
`PDA
`
`Notebooks
`
`Ericsson Exhibit 1018
`Page 1
`
`

`

`INTERNATIONALCONFERENCEONUNIVERSALPERSONALCOMMUNICATIONS,TOKYO,JAPAN, 
`
`implementedusingaDualPortRAMinterfacewhichal-
`ofapplicationswhichareavailablerelyonInternetproto-
`lowsfastaccesstoasharedareaofmemory.Mostofthe
`colssuchasIP,UDPandTCP.Duringtheplanningofthe
`physicallevelfunctionsareimplementedinanFPGAwhich
`project,anearlymilestonewassetafterwhichitwould
`containspacketbu(cid:11)ers,arealtimeclockandprovidesan
`bepossibletouseSWAN'sATMlinkstotransferIPdata-
`interfacetothereceivedsignalstrength.TheFAWNcard
`grams.AchievingthisraisesissuessuchashowIP-over-
`canbeadaptedforuseinmanydi(cid:11)erentsystems.Inabase
`ATMoughttobeimplementedinawirelessATMsetting.
`stationseveralFAWNcardsareusedtoprovidethemulti-
`Oncethismilestonehasbeenachieved,mobilehostswithin
`plechannelaccessforFHSSmobilesystems.Inanotebook
`ournetworkimmediatelyhaveaccesstoaplethoraofIP-
`orPDAonecardispluggedintoaPCcardslotandina
`basedapplicationssuchasmosaicandthembonetoolsnv
`peripheral,suchasaprinter,aFAWNcardisembeddedin
`andvat.
`thedevicetoprovidethewirelessconnectivity.
`Thispaperdescribesthesystemasitexistsafterreach-
`ingthe(cid:12)rstmilestone.Apoint-to-pointMediumAccess
`TheARM ontheFAWNimplementsasimple,point-
`protocol(MAC)transferscellsbetweenamobileanda
`to-pointmediumaccessprotocol,andmanagesthecell
`basestation,anATMAdaptationLayer(AAL)converts
`queuesintheDPRAM.Thisrequiresapproximately KB
`betweenIPdatagramsandcells,andIPtra(cid:14)cistrans-
`ofcode,whichisorganisedasthreeconcurrentprocesses.
`ferredonVirtualCircuits(VCs)reservedforcarryingthat
`Themainlineprogramcodeinitialisesthehost/fawn
`particulartypeoftra(cid:14)c.
`DPRAMinterfaceandRFmodemhardware,thenbecomes
`theidleloop.ThemodemhardwareassertstheARM 's
`II.NetworkInterfaceCard
`FastInterruptrequest(FIQ)inputwheneveratransmit
`bu(cid:11)erhasbeenemptied,thereceivedsignalstrengthex-
`WirelesshopconnectivityisprovidedbytheFAWN
`ceedstheprogrammedthreshold,areceivebu(cid:11)erhasbeen
`(FlexibleAdapterforWirelessNetworking)card[]which
`providesaninterfacebetweenaPCcard busandanRF
`(cid:12)lled,orthecountdowntimerhasexpired.Theseevents
`areusedtodrivethemodemmanagementprocesswhich
`modem.TheRFmodemwaschosenbecauseofavailabil-
`controlsthebidirectional(cid:13)owofcellsbetweenthecell
`ity,costandlicensingconditions.TheFAWNcardonly
`queuesintheDPRAMandtheRFmodembu(cid:11)ers.Host
`requiresaccesstotransmitandreceivedatastreamsand
`softwarecanassertthelowpriorityInterruptRequest
`canmakeuseofareceivedsignalstrengthindication,so
`(IRQ)inputtoindicatethatcellshavebeenplacedinthe
`thechoiceofmodemisnotcriticalandfutureversionswill
`DPRAMfortransmission,andtheARM cangenerate
`likelytakeadvantageofnewer,fastermodemsastheybe-
`aninterruptonthehosttosignalthatreceivedcellsare
`comeavailable.APCcardinterfacewaschosensothesame
`availableintheDPRAM.
`III.CellFormat
`Themodemcontrolhardwareprovidestwo,-octetcell
`bu(cid:11)ersforfeedingthemodemtransmitstream,andtwofor
`drainingthereceivestream.Thisimplementationsuggests
`awirelesscellsizeofoctets,whichissu(cid:14)cienttoac-
`commodateastandardBISDNcellconsistingofa-octet
`headeranda-octetpayload,leaving octetsspare.It
`hasbeensuggestedthatthisspacemightbeusedtocon-
`tainForwardErrorCorrection(FEC)informationwhich
`couldbeusedtorecoverfrombiterrors,butinabusy
`FHSSenvironment,bursterrorswillbeinducedwhentwo
`hoppingpatternscollide,scramblingmultipleconsecutive
`CardFig..Fawnnetworkinterfaceadaptor.
`cellsandrenderingFECine(cid:11)ective.Wirelessbandwidthis
`apreciousresource,soforthepurposeofthe(cid:12)rstproject
`cardcanbeusedinmanyapplicationsincludingPDAsand
`milestone,thecellformatchosenhasa-octetheaderand
`notebooksaswellasinbasestations.Becausemobilityis
`a-octetpayload.Figure showstheformatofaSWAN
`animportantaspectofthisresearchtheprototypeFAWN
`wirelesscell.The(cid:12)rstoctetcontainsaframestart(FS)bit
`cardwasdesignedtobeeasilyportable.
`Itsdimensions
`whichindicatesthe(cid:12)rstcellinasegment.Thesequence
`are .cm(W)(cid:2) . cm(H)(cid:2) .cm(D)andit(cid:12)ts
`(SEQ)(cid:12)eldcontainstheordinalofthecellinasegment
`intothebaywhichholdstheremovable(cid:13)oppydriveinan
`andcountsbackwardssothatthe(cid:12)rstcellinasegment
`AT&TSafari  orsimilarnotebookcomputer.Thear-
`hasasequence(cid:12)eldofonelessthanthetotalnumberof
`chitectureoftheFAWNcardisshownin(cid:12)gure.The
`cellsinthesegment,andasequencevalueofzeroindicates
`cardincludesanembeddedprocessor,theARM ,which
`thelastcellinasegment.TheVCI(cid:12)eldidenti(cid:12)esthevir-
`providestheprocessingpowertoimplementtheMACas
`tualcircuittowhichthiscellbelongsandtheCRC(cid:12)eld
`wellassomeATMqueuemanagementfunctions.Com-
`containsan-bitCRCgeneratedfromtheheaderdata.
`municationbetweentheFAWNandPCcardinterfaceis
`Thepayloadcontainsuptobytesofuserdata.Thiscell
` AlsoknownasPCMCIA.
`formatwillbealteredinfutureversionsoftheMACwhere
`
`RF
`Modem
`Modem
`Control
`
`Host
`Processor
`
`FAWN
`
`PCMCIA
`Controller
`
`Wired LAN
`Adaptor
`
`PCMCIA
`Interface
`
`ARM610
`
`Peripheral
`Interface
`
`Ericsson Exhibit 1018
`Page 2
`
`

`

`
`
`0
`
`1
`
`2
`
`3
`
`4
`
`5
`
`6
`
`7
`
`FS
`
`SEQ
`
`SWAN:ANINDOORWIRELESSATMNETWORK
`Fig. .Wirelesscellformat.
`interworkingwithwiredATMLANsismoreimportant;a
`-octetpayloadwillreducetheamountofe(cid:11)ortrequired
`totranslatecellsbetweencircuits.
`IV.MediumAccess
`TheMACdividesthewirelessbandwidthbetweenre-
`ceiveandtransmitandallowsthemobilesystemstoes-
`tablishandcontinuecommunicationwithabasestation.
`Themobilesandbasestationsoperateononeofseveral
`channelswhichcanbehoppingsequencesforthecaseof
`ourfrequencyhoppingmodem.TheMACcommunicates
`usingframesof cellseach.Eachcellisbyteslongand
`takesabout mStosendandaframetakesabout mS.
`Thetimetoturnthechannelbetweenreceiveandtransmit
`isapproximately mS.These(cid:12)gureswerechosenbecause
`themaximumtransmittimeofourmodemis mS[].
`
`VCI 0:7
`
`VCI 8:15
`
`CRC
`
`PAYLOAD
`(60 BYTE)
`
`Transmit
`
`Receive
`
`64 byte cell
`(1mS)
`
`Time
`
`

`

`INTERNATIONALCONFERENCEONUNIVERSALPERSONALCOMMUNICATIONS,TOKYO,JAPAN, 
`
`VII.Performance
`Figureshowsthetopologyofthenetworkuseddur-
`ingexperimentation.tunisa MHzPentium/PCIPC,
`Fig..Networkcon(cid:12)guration.
`con(cid:12)guredasagatewaybetweenswan-netandthede-
`partmentalethernet;nipandtotarerespectivelyaNEC
`VERSA /andanAT&TSafari  notebooks.
`In
`theresultswhichfollow,TCPthroughputwasmeasured
`usingttcptotransfera MB(cid:12)lefromtuntonipover
`thewirelesslink,withnoothertra(cid:14)conthelink.Thean-
`tennaswereplacedsu(cid:14)cientlyclosetoeachotherthatthe
`errorrateonthechannelwasminimal.Anearbyspectum
`analysershowedthatnoabnormalinterferencewaspresent
`atthetimeoftheexperiments.Usingthestandardframe
`sizeof cellsforbothtransmitandreceiveframes,the
`test(cid:12)lewastransferredin . seconds,yieldingaTCP
`transferrateof. KB/S(Kb/S).
`A.MACFrameSize
`MACframesizeisanimportantparameteroverwhich
`thesystemdesignershavesigni(cid:12)cantcontrol.Figure
`showsthee(cid:11)ectthatvaryingMACframesizehasonTCP
`transferrate.This(cid:12)gurerevealsthatsmallframesizes
`giverisetolowtransferrates.Thisistobeexpectedbe-
`causeittakessometime(approximately mS)toturnthe
`wirelesslinkfromtransmitmodetoreceivemodeandvice
`versa,andsmallframesizesdothismorefrequently,yield-
`inglowerdatarates.Thegraphshowsthatachoiceof
`cellsperframeisquiteacceptable;transferratedropso(cid:11)
`rapidlyforsmallerframesizes,butmuchlargerframesizes
`donotobtainsigni(cid:12)cantlyhighertransferrates.
`B.TransferSize
`Figureshowsaplotofpingtimesforarangeofpay-
`loadsizes.Thetimesaretheaveragetimescalculated
`from individualsamplesforeachpayloadsizemea-
`sured.Payloadsizesweremeasuredin-byteincrements.
`PayloadsizessmallerthanA(cid:12)tintoasinglecellandresult
`Availableasftp://ftp.sgi.com/sgi/src/ttcp/.
`Althoughframesizesgreaterthan mSdrivethemodemsbe-
`yondtheirdocumentedspeci(cid:12)cations,thelackofanydecreasein
`TCPthroughputshowsthatthepairusedinthisexperimentdidnot
`produceseriouserrorswhenoperatedwithframesizesofupto
`cells.
`
`Fig..Pingtimeinmillisecondsversuspayloadsizeinbytes.
`inaconstantpingtime.FromAtoB,increasingpayload
`sizescorrespondtoaproportionateincreaseinthenumber
`ofcellstransmittedincreasingpingtimeatarateofap-
`proximatelymSpercell.BtoCrepresentsanincrease
`inpingtimecausedbythepayloadstartingtospantwo
`frames.Theaveragepingtimeisincreasedbyabout
`mSbecausethetimetotransmitapayloadnowhasto
`includeanunusedreceiveframebetweenthetwotransmit
`frames.FromDtoEwecanexpectasimilarincreasedueto
`thetransmissionnowincludingtwounusedreceiveframes.
`SincetheMTUis bytes,payloadsizeatthisstageis
`increasedbyoneortwocellsduetoIPfragmentation.
`C.Delay
`TheMACframestructureinducesnoticeablee(cid:11)ectsin
`end-to-enddelaytimes.Figures and showthevari-
`
`Frame size (cells)
`
`E
`
`D
`
`C
`
`B
`
`400
`
`600
`
`800
`
`1000
`
`1200
`
`1400
`
`1600
`
`Payload size (Bytes)
`
`110
`
`100
`
`90
`
`80
`
`70
`
`60
`
`50
`
`40
`
`30
`
`20
`
`10
`
`0
`
`Ping time (Milliseconds)
`
`A
`
`200
`
`Fig..TCPthroughputversusframesize.
`
`2
`
`4
`
`6
`
`8
`
`10
`
`12
`
`14
`
`16
`
`18
`
`20
`
`30
`
`25
`
`20
`
`15
`
`10
`
`5
`
`0
`
`0
`
`TCP throughput (KB/S)
`
`casta-net
`
`swan-net
`
`tun
`
`nip
`
`tot
`
`Ericsson Exhibit 1018
`Page 4
`
`

`

`
` ,exceptthatinthisexperiment,thepingperiodof
`mScausesconsecutivetransmissionstooccuronalternat-
`ingtransmitandreceiveframes.Thisresultsinasequence
`ofalternatingshorterandlongerpingtimes.
`D.Discussion
`Ourearlyresultshighlightsomeinterestingchallenges.
`Firstly,aTCPtransferrateof. KB/Sshowsthatwe
`areutilisingaboutKb/Sor %ofour Kb/Sband-
`widthinasingledirection.Secondly,wirelessbandwidth
`isprecious,andtoutilizeitusingourhardwarewehave
`adoptedaparticularATMcellformat.Inournextgenera-
`tionMAC,weexpecttousea-bytepayloadforeaseofin-
`terworkingwithwiredATMnetworks,ATMnetworks,but
`fore(cid:14)cientuseofthewirelessbandwidth,wemayreduce
`thesizeofthecellheader.Thehardwarecellbu(cid:11)ersize
`willbealteredaccordingly.Thirdly,thewirelesschannel
`isimplementedwithinasharedmeduimandwehaveless
`controloveritthanwewouldhaveinawired,switchbased
`network,sotheprovisionofanyQualityOfService(QOS)
`guaranteeswhicharetypicallyassociatedwithATMnet-
`worksismademuchmoredi(cid:14)cult.Thepingtimesplotted
`in(cid:12)gures and aregoodexamplesofthetypesofchal-
`lengestobefaced.Thetimesareessentiallyanestimate
`ofend-to-enddelay,animportantQOSparameter.Even
`onasimplepoint-to-pointlinksuchastheoneusedfor
`ourexperiments,thee(cid:11)ectsofhavingtosharethewireless
`mediumbetweenjusttransmitandreceivechannelsshows
`amarkede(cid:11)ectonthedelaysachievable.
`VIII.Summary
`WehavepresentedthecurrentstatusofSWAN|a
`projectaimedatprovidingwirelessnetworkconnectivity
`inamobilecomputingenvironment.Theresultspresented
`representdelayandthroughputwhichmakealargenum-
`berofapplicationsusableonthemobilehosts.Interactive
`applicationssuchaseditorsandremoteshellssu(cid:11)ernoap-
`preciabledelay,andtheavailablebandwidthissu(cid:14)cientto
`supportNFSmounted(cid:12)lesystems,webbrowsingandau-
`dioandvideoclients.Workiscurrentlyunderwayona
`newMACwhichprovidesexplicitsupportformobilityand
`QOS.
`References
`[ ]P.Agrawal,A.Asthana,M.Cravatts,E.Hyden,P.Krzyzanowski,
`P.Mishra,B.Narendran,M.SrivastavaandJ.Trotter,AnIndoor
`NetworkedWirelessComputingSystem,ICC' 
`[]GECPlesseySemiconductor,WLANHandbook,GECPlessey
`Semiconductors,December, .
`[ ]D.RaychaudhuriandN.Wilson,ATM-BasedTransportArchi-
`tectureforMultiservicesWirelessPersonalCommunicationNet-
`works,IEEEJournalonSelectedAreasinCommunciations,Vol.
` ,No.,October, ,pp.  {  .
`[]J.TrotterandM.Cravatts,AWirelessAdapterArchitecturefor
`MobileComputing,ProceedingsoftheSecondUSENIXSym-
`posiumonMobileandLocation-IndependentComputing,Ann
`Arbor,Michigan,USA,April - , ,pp.{ .
`
`SWAN:ANINDOORWIRELESSATMNETWORK
`ationinpingtimesfortwosequencesofconsecutive
`packetstransmittedatintervalsofmSandmSre-
`spectively.Inbothcasesthepayloadconsistedoftwocells.
`InFigure ,thesmallestpingtimeisobservedwhenboth
`
`30
`
`25
`
`20
`
`15
`
`10
`
`5
`
`0
`
`0
`
`Ping time (Milliseconds)
`
`Fig. .Pingtimeinmillisecondsversuspacketnumber.Timebe-
`tweenconsecutivepacketsismilliseconds.
`pingcellsaregeneratedattheendofatransmitframe
`sothatthecorrespondingreplyarrivesatthestartofthe
`nextreceiveframe.Thepingperiodisnotperfectlysyn-
`chronisedwiththeframeperiod,soagradualdriftoccurs.
`Asthearrivalofthepingcellsisfurtherremovedfromthe
`endofthetransmitcycle,theobservedresponsetimesin-
`crease.Intheworstcase,thepingcellsaregeneratedat
`theextremeendofthetransmitframe,suchthatoneofthe
`cellsmissesthecurrentframeandhastowaitforthenext
`transmitframe.ThesameprocessisoccurringinFigure
`
`50
`
`100
`
`150
`
`200
`
`Packet number
`
`30
`
`25
`
`20
`
`15
`
`10
`
`5
`
`0
`
`0
`
`Ping time (Milliseconds)
`
`Pingtimeinmillisecondsversuspacketnumber.Time
`Fig. .
`betweenconsecutivepacketsismilliseconds.
`
`50
`
`100
`
`150
`
`200
`
`Packet number
`
`Ericsson Exhibit 1018
`Page 5
`
`