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F !B--- %BBEFGHHII I H H GB--% C E F H H HGFECC ---$ KKQQLLQQ L L Q QK---% KKQQLLQQ L L Q QK---V$)S T T V W X X X X W V T TSSSTUVWXYYXXWVTTTVW X Y Y Y XVUS S ---V%)S T T V W X X X X W V T TSSSTUVWXYYXXWVTTTVW X Y Y Y XVUS S ---$ [[aa\\aa \ \ a a[---% [[aa\\aa \ \ a a[---F$!g g k k jgdd c c cddfghijjiigedd d f g h i j j g ---F%!g g k k jgdd c c cddfghijjiigedd d f g h i j j g ---$$llmp p p sttsspomml---$%llmp p p sttsspomml---$ vv||ww|| w w | |v---% vv||ww|| w w | |v---$ ~~ ~---% ~~ ~---$ ---% ---$     ---%     --- ! ! ! ! ! ! ! ! ! !  !  !  !  !  !  !  !  !  !  ! !---4%           --% ---B$JKKIGEEDDDEEFGIJKKJIGFEEEFGHIJJ---B%JKKIGEEDDDEEFGIJKKJIGFEEEFGHIJJ--- !Q !P !N !R !M !S !M !T !M !T !M !T !M !T !M !T !M !S !N !R !O---*%MMNPQRSTTUUUTSQONMM--"%NNPQRTTTSSRQPNN---$ VVW\\]]\WWV---% VVW\\]]\WWV---$ __`eeffe``_---% __`eeffe``_---$ ggmmhhmmhhmmg---% ggmmhhmmhhmmg---@$uvvtsppoooqrstuvvutsqppprsttuu---@%uvvtsppoooqrstuvvutsqppprsttuu---$ zzww~~{{z---% zzww~~{{z---$---%--- ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !---*%--"%---$ ---% ---^$----^%-------$o\o,q,q\o\--(%$  1  Level 1Level 2Level 3Level 4Level 5 =y#  U Figure  1   0SuggestedalternatediagramfortheDFWProtocol  StackshowninFigure35ofP802.1193/190.( $ Figure  1  ((2OW$ 5!   d ( $0 WAZ=[@A<< BLevel 1Level 2Level 3Level 4Level 5(P$ Table  1  HTABLE ALevel 1Level 2Level 3Level 4Level 5 T /t'  .3\ .March1994@VV//7/doc:IEEEP802.1194/12A X  66*' xd6 l #. 3\=##..##$%]]]]]]]]]]]$@]d@]>@]]]@]@]$@]?TABLE A]  K4$   1    3\3\3\0` D" DFWMAC DistributedFoundationWirelessMediumAccessControl,"W.DiepstratenNCR X WCNDUtrecht,G.EnnisSymbolTechnologies,P.BelangerXircom;IEEEP802.1193/190;November'93.Seealso802.1193/191,802.1193/192and802.1193/193.) Z<Century Schoolbook Regular  Cy"  e;MOTIONBY802.11PLENARYONMACMETHOD 󀀄November11,1993    TheplenarysessiondirectstheMACsubgrouptoaccepttheDFWMACasthedirectionofthe802.11workinggroup.1.0XProceedtostudyandenhancethisproposalbyvote.DDX X  2.XAnswerandresolvequestionsrelativetoperformance.  3.0XWhenasubgrouphassomethingthatcanpassbyasimplemajority,thatitbeoffered  backtotheplenarysessionfor75%approval.h2#.e;# % Cy"    3.2PointCoordinationFunction   DFWMACoptionallysupportsaPointCoordinationFunction(PCF)whichcanprovideContentionFreeservices.TheuseofthisPCFisrestrictedbecauseitcanonlybeusedincertainenvironments.ThebasicrestrictionisthataPCFcannotoverlapwithanotherPCFonthesamechannel,sosufficientisolationbetweenmultiplePCF'sisneeded.Thisisbecausecontentionbetween  multipleoverlappingPCF'scannotberesolvedbythe[this]protocol.Thiswilllimittheuseability \\ ofthePCFtoeitheroperationinasingleBSSofanESS,ortomultiplechannelenvironmentsthatcanassuresufficientisolationbetweenneighboringPCF's. =y#  ?$   2   0XZFrompage27,802.1193/190(Italicsforemphasis)[authorcomment]^G^^^^^^^ ?^ @^ @^ @^^Y@^I@^I@^A@^^^^^^ @^@^@^@^@^^ B@^ 0@^ "@^ @^^ ?^ @^ @^ @^^ L7A`?^ ?^ "~j?^ ?^ @^I@^i@^i@^@^  @^  ffffff:@^  9@^  333333F@^  @^ ^ ^ ^  @^  ?^  @^  ?^ ^ ^ ^ @^  Q%@^  9@^  333333V@^   @^ ^  ?^ @^ @^ @TABLE A^  Cy"  +TomBaumgartner: " Conclusions: Forstationtostationtrafficusingapointcoordination  functiontorelaydataisthemosteffectivemethodbyafactorof2.Forstationtoaccesspointtrafficthepointcoordinationfunctionsisabout4timemoreeffectivethanothermethods.""TheWattsperkilobytehectaremethodofevaluatingwirelessmaynotyieldexactnumbersbutcanyieldratios.""Allproposalsforbatterypowerconservation,shortofsimplyshuttingdownforaperiodoftime,utilizeacoordinationfunction.Sincepowersavingoperationbythemobilestationissovitalthisalonepresentsanoverridingcaseforacoordinationfunction." =y#  ?$   3   0XZFrom"AMeasureofPerformance:WattsperKilobyteHectare,"T.Baumgartner,Spectrix,  IEEEP802.1193/214,Nov'93 J K4$   2    3\3\3\0` D"AnalysisofReturnson'IEEE802.11DesignGoalsQuestionnaireP802.1191/82B,"C. X Rypinski,March92(Questionnaire91/82BbyL.vanderJagtandC.Rypinski)  Cy"    DaleBuchholz: "CSMAasanaccessmethodworkswellunderlightloads,eitherwhenthe  numberofusersissmallortheapplicationsbeingusedgeneratelittletraffic.Whilethismaybetypicalof'quicklycreatedanddisbanded'workgroups,itisnottypicalofsomeoftheloadsgeneratedbysomedesktopapplicationsthatrunonfixedorportablecomputers."XX"Thetrendisratherapparent:asthethroughputforaparticularCSMAtechnique  increasestowardthemaximumforthatmethod,thedelayincreasesexponentiallytowardinfinity."  [referringtoFig9.23fromKleinrocketal]   =y#  ?$   4   0XZFrom"CommentsonCSMA,"D.Buchholz,Motorola,IEEEP802.11/9149  Cy"  @ "DYNAMICPOWERCONTROLPOTENTIAL   *X<Problemaddressed  XEnvironmentisINTERFERENCELIMITED  X0Insinglechannelenvironment,mediumneedstobesharedwithasignificant LL numberofdifferentBSA's    X0Inmultichannelenvironmentalargenumberofchannelsmaybeneededforre  useisolation,    XForlargecells,need610channels \\ XForsmallcells,needaround20channels    *X<Proposedsolution   XReducethecochannelinterference.   XLimitTXPowerleveltoavalueneededforreliablereception. ll  XLearnproperlevelperindividualDestination. 0 0  XUseDeferthresholdasfunctionofpowerlevel." =y#  ?$   5   0XZFrom"ThePotentialofDynamicPowerControl,"W.Diepstraten,NCR,July92,P802.11    92/76 K4$   3    3\0` D3\3\"ThePotentialofDynamicPowerControl,"W.Diepstraten,NCR,July92,P802.1192/76 y Cy"  Dr.KCChen: 󀀀"WeanalyzethenonpersistentCSMAwithimperfectsensing(thushidden  terminal)andoverlappingcellcoverageininfrastructurebasedwirelessLANs.TheresultswhichhavebeenjustifiedbysimulationsshowthatCSMAdeliversmuchlowerthroughput(unstablepeakvalue)thanknownbytraditionalanalysis." $ =y#  ?$   6   0XZFrom"PerformanceofNonpersistentCSMAwithCellInterferenceandImperfectSensing,"  KwangChengChen,NationalTsingHuaUniversity(Taiwan),IEEEP802.11/93195,Sep'93 ^ K4$   4    3\3\3\0` D"WirelessLocalAreaNetworkRequirements,"(Version1.0)K.Biba,Editor;IEEEP802.11/92 X  X 20,Jan'92see"3.4.2Performance"pages2125TABLE A  K4$   5    3\3\3\*,XX XX*0` D"RTS"and"CTS"asusedintheDFWhavealonguseprecedentaspartoftheRS232interface. X Inthiscontext,theirvalueisBoolean.Whenthefunctionismorecomplexrequiringassociationwithsourceanddestinationaddressaswellastrafficdescriptors,RTSandCTSbecomemultipleoctetmessageswhicharebettercalled "request"and"grant." InthecontextofanIntegrated L Servicesdocument,thisnomenclatureisusedinthepresentIEEE802.9draftstandard.UseofRTSandCTSmaymisleadsomeindividualswithexperienceinotherfields. ~ K4$   6    3\0` D3\3\"Superframe"isproperlyusedforframetoframedifferenceswithinaregularpattern.Justframe X wouldbepreferredfortheperiodofonebeaconinterval.Thesubdivisionsmaybeandareherecalledsubframes.  K4$   7    3\3\3\0` DInthe19641980IMTSmobiletelephonesystem(BellMJandMK),idletonewastransmitted X onthenextchanneltobeusedforaconnection.Ifallchannelswerebusytherewasnoidletoneuntiloneofthechannelsdisconnected.Thestationlogicspecifiedarandomizeddelayafterappearanceofidletonetoreducesimultaneousaccessrequests.Afterseveralyearsofserviceandthesystemsbecamefullyloaded,entrepreneursdevisedabypassforthebackoffdelayandmarketedthemodificationas"channelgrabber." 5!  ,XX1a % \  @*5 .7ś .IEEE802.11   @R5802LANAccessMethodforWirelessPhysicalMedium66*' xd6 C4 7Xś X 7ś DATE: ` March1,1994 F 7 66*' _ xd6 &   AUTHOR: ` ChandosA.Rypinski, )    `  ` ChiefTechnicalOfficer ` LACE,Inc.=5Tel:+014153896659     ` 655RedwoodHighway#340=5Fax:+014153896746    ` MillValley,CA94954USAp#:5Em:rypinski@netcom.com   66*' xd6    TITLE:` EVALUATIONOFTHEDFWMAC0p.  p!p! 66*' {xd6    3X\X X7Xś3\X3X\ NOTE: Adraftpresentationwiththistitlewasdistributedtomanyactivevotingmembersof802.11inDec'93.The  JanuarysubmissionP802.1194/12wasasummaryintheformofbulletlistsandslides.CertainmisunderstandingsoftheoperationoftheDFWMACappearinginthesepapershavebeencorrectedinthispaperinsectionsmarked[revised].Newtexthasbeen[added].Thispaperisofferedasanattachmenttothebasecontribution.3%\%3\ zi SUMMARY  wh TheDFWMACisdeficientandflawedifmeasuredagainstthestatedobjectivesofthe802.11Committeedefinedinitsfirstyearofexistence.Oneapproachtoaremedyistoamendtherequirementsuntilthereisapartialfittothecapabilities.Toaidinfurtheranalysisofthisassertion,manyofthedeficienciesareidentifiedanddescribed.Thegeneralthrustofthepointschosen,arethosewhicharearchitecturalratherthandetailed.ExaminationoftheseobjectionswillshowfundamentalphilosophicaldifferenceswithmuchoftheconstituencyfortheDFWMACspecifically:78  Theprimaryservicerequirementisnot"peertopeer."Moreapplicationswillgenerate ?!0" trafficthatis"clientserver"oriented,andlargegainsmaybemadebytakingadvantageofthisfact.Thisassertiondoesnotexcludepeertopeerfordefaultorsecondaryuse.  78  Negativeorabsenceofinformationcannotbeusedinaradiowirelesssystemasacriteria '$% permittingtransmissionwithoutgravelimitationsonreliabilityandcapacity  78  Interferencelimitedradiosystemdesignincludingtheaccommodationofcochanneluse 7&(!' isanabsoluterequirementforhighspectrumutilizationnotmetbyanyformofLBT.  78  TheDFWMACisaPHYlayermultiplexerwithaseparateMACforeachofthe G(8#) subdivisionservices,ratherthanacommonpacketMACforallservices.  Thosewhobelievethatthisproposalmustbeadequatebecauseoftheconstituencythatsupportsit,maygaininsightbyexaminingtheseobjectionsandbyconsideringalternativephilosophiesdescribedincontributionIEEEP802.11/9413.Theseissueswillberaisedaslongasthisproposalisintheprocessofdraftingandacceptance,soanticipationofthesequestionsmayresultinearlierresolution.  ,'. BXX zi@ L# EVALUATIONOFTHEDFWMAC    TableofContents NPage   b  @ ,& PartIPROLOGUE   MOTIONADOPTINGDFWMAC!!Q.!1 o` $  $0 0` !!`   Nonresponsiveto802.11FunctionalRequirements!!!Q.l A` !` !!1$݌ G 8 Ќ  $  $0 0` !!`   Consequences!!!Q. ` !` !!2$ ݌   Ќ  $  $0 0` !!`   RemedialPossibilities!!!Q.4 '` !` !!2$݌   Ќ  @ {  PartIIDFWMACOPERATINGCONCEPTS     SELECTIONOFPEERTOPEEROPERATIONASPRIMARYMODE!!Q.~?3  p  $  $g0 0` !!`   AutonomousAdHocGroups!!!Q.0)` !` !!3$g݌ WH  Ќ  $  $L0 0` !!`   MarketNeedforPeertopeerServices!!!Q.6` !` !!4$Lg݌ /  Ќ  $  $>0 0` !!`   AdvantagesofMakingClientServerPathPreeminent!!!Q.C` !` !!4$>Y݌   Ќ  #  #=0   INTERFERENCELIMITEDRADIOSYSTEMDESIGNNOTIMPLEMENTED!!!Q.C!!!5#=X݌   Ќ  #  #+0   PHYLAYERMULTIPLEXINGOFINTEGRATEDSERVICES[added]!!!Q.P@!!!5#+F5݌ gX Ќ   Figure1SuggestedAlternateDiagramfortheDFWProtocolStack ` showninFigure35ofP802.1193/190[added]!!Q.DC6   @%5PartIIIPROBLEMS   DISQUALIFYINGPROBLEMS!!Q. > !7  $  $q0 0` !!`   1.0` ` !` !AbsenceofFrequencyReusePlan$q݌wh` !` ! Ќ   ` NeedforECF(ExtendedareaCoordinationFunction)!!Q.`J7 O@ $  $0 0` !!`   2.0` ` !` !UseofNegativeInformation!!!Q.T:1` !` !!8$݌ ' Ќ  $  $0 0` !!`   3.` UnacceptableTransferDelayforConnectiontypeServices!!!Q.nN` !` !!9$݌  Ќ  %  %0 0` !!0 ` ` !` !`   SuperframeStructuralDelay!!!Q.T1 ! !!9%݌  Ќ  %  %0 0` !!0 ` ` !` !`   WLANRequirementsofJanuary1992!!!Q.(7 ! !!9%݌  Ќ  $  $ 0 0` !!`   TableISelectedResultsfromTables3.53.8inP802.11/9220!!!Q.<Q` !` !!9$  ݌ x Ќ  #  #!0   SERIOUSPROBLEMS!D!H!P.x !!!10#!)!݌ 7( Ќ  $  $!0 0` !!`   4.0` ` !` !NAV(networkaccessvector)FunctionalityinContentionSpace[revised]!D!H!P. .]` !` !!10$!!݌    Ќ  $  $ #0 0` !!`   5.0` ` !` !WaitstateinContentionfreePacketTransfers[revised]!D!H!P.N` !` !!11$ #%#݌  ! Ќ  $  $*$0 0` !!`   6.0` ` !` !SegmentationandMaximumPacketLength!D!H!P.E<` !` !!11$*$E$݌ !" Ќ  $  $8%0 0` !!`   7.` ProperDefinitionofConnectionTypeServices!D!H!P.|bC` !` !!12$8%S%݌ "# Ќ  $  $E&0 0` !!`   8.` "TalkSpurt"VoiceCircuitCapacityEnhancement!D!H!P.\E` !` !!12$E&`&݌ o#`$ Ќ  $  $T'0 0` !!`   9.0` ` !` !PollingMethodofAccessControl!D!H!P.6` !` !!13$T'o'݌ G$8% Ќ  $  $\(0 0` !!`   10.` IncreasedRiskofEarlyObsolescencefromUseofDistributedLogic!D!H!P.lX` !` !!13$\(w(݌ % & Ќ  $  $)0 0` !!`   11.0` ` !` !SusceptibilitytoMaliciousJammingandImpoliteAccess!D!H!P.XM` !` !!14$))݌ % ' Ќ  $  $*0 0` !!`   12.0` ` !` !DeficienciesofOmission!D!H!P.`.` !` !!14$**݌ &!( Ќ  #  #+0   CONCLUSIONS!D!H!P.  !!!15#++݌ (p#* Ќ  aAdditionalReferencesD!H!P. 15 /* %, AttachmentARelativeRawCapacityofDFWMACandSAMACin2.4GHzISMBandD!H!P.X16  +&.     3X\X%3%\6 x` @  # EVALUATIONOFTHEDFWMACd R  1        @VV/ @@ ,&3%\%X3X\  PartIPROLOGUE .     MOTIONADOPTINGDFWMAC /   TheMACsubcommitteeof802.11onNovember11voted35,30,7tobringtheDFWMACproposalasa"foundation"plantotheplenaryforacceptance.Theplenaryactedonthemotionbelowvotinge%;%%3%\Ԁ43, $  14,4(75.44,24.56%)topassby75%#3%\%%e%;0#.   I8fD8($hxv `I !!                  !!Thisprotocolwaspossiblyaccepted,whenuncertainmembersacceptedtheadviceofsomerespectedcommitteemembersthatthemarketwindowandthepatienceoftheExecutiveCommitteewerepassing.Becauseanumberofcompetent802.11membersbelievethattheprinciplesoftheDFWMACarecorrect,thispaperundertakesdescriptionoftheinadequaciesandconsequencesofthischoicetomotivatenecessarymajorchanges.  Nonresponsiveto802.11FunctionalRequirements '4  j[ T8ghDA1-x| P `T !!                        !!Theemphasizedstatementisaccurate.Thisplancannotprovideitsrequiredservicesoveralarge % " percentage(99.9%required)oftheserviceareaprovidedbythecontentionservice.Evenwiththe1525 &!# channelsthattheFHPHYmightprovideforseparationofcoverages,thiswouldonlybeenoughtoreducethemalfunctionstoaminorproportionoftransactions.Ifintheiruncoordinatedwaytheuserclustersassociatedwiththeseseparatechannelsshouldfailtodistributethemselvesuniformlyoverthearea,theconditionintheboxabovewouldbeviolatedwithincreasedlossofcapacity.  O*@%'   Consequences 9   MovingtheproposedDFWMACinitspresentformtothebasisforastandardwillprobablyhavethefollowingresults:1.07 Theamountoftimeandefforttodocumentthisprotocolinstandardsformismuchlargerthanis L= eithernecessaryorappropriatewhencomparedwithaMAClevelmultiplex. !! 2.07 Usingpresenttechnicalmethods,theresultingsystemwillbeinadequatetounserviceablefor:a R!! 0 a.0` !!connectiontypeservicesbecauseof:1)undefinedexcessamountsofsetupandtransfer  z delay,and2)interferenceormediumcontentionfromcontiguoususerclusterswithinthesamesystem;andfor ` !` !  b.0` connectionlessservicesrequiringequivalence(withinanorderofmagnitude)to802defined |  accuracyandtransferratewiththepresentlyproposedPHYlayers;andfor ` !` !  c.0` sustainableuserdensityandcapacitydemandlevelslimitedtoadecadeormoreinferiorto   infrastructurebasedandinterferencelimitedalternativesystemdesigns. ` !` ! 3.07 Withlargescaleuse,onlythecontentionmodewillhavepracticalusefulness,andtheremaining   timeboundedandcontentionfreeserviceswillbeunfulfilledpromises.. !! 4.07 Ifthesystemimplementsdistributedadaptivepowercontrolandreceiverthresholdtogether,the  systemwilldegenerateintoanAlohaprotocolundermediumtohighloadconditionsmakingredundantmostofthedetailmeasurestoprioritizeandtominimizeinternalinterference.. !! 5.07 Usercostwillbehigherthanexpectedbecauseofearlyinadequacyoffunctionandconsequentshort  usefulproductlife. !!   RemedialPossibilities A   Todefinenotonlyaworkingsystem,butoneinwhichthestandardsdocumentcanbedraftedwithachievabletimeandeffort,the802.11committeeshouldnowtakeatleastoneofthefollowingsteps:1.07  ForthosewhobelievethatthecapabilityoftheCSMAportionisadequate,aremaining  alternativeistodeletetimeboundedandcontentionfreeservicesfromthisMACPHYcarryingitforwardasaninterimplanfor2.4GHzonly. !! 2.07 Undertaketoconvertthepresentplantoausableplanprovidingtrueconnectiontypeservicesand %  baseduponwellknownprinciplesofhighcapacityradiosystemdesign. !! Furthersummaryisgiveninthe"CONCLUSIONS"ofthisdocument.8 Itisveryimportantthatthosewhosupportthisprotocolshouldexaminetheargumentsgiven.Sometheminvolveextremenarrowingoftheconditionsunderwhichadequateandpredictableperformancecanbeobtained.Othersleadtosuchdrasticlimitationsoncapacityandtoexposuretolongsetupandtransferdelaysthatmarketabilitycanbequestioned.Theinevitableappearanceofothermorecompetentcompetitivesystemsshouldbeconsidered.Thecapacityandspectrumutilization"gap"isatleastadecadeandprobablymuchmoreitisnotten'sofpercent.    * %$ @ {   PartIIDFWMACOPERATINGCONCEPTS G   ThechoicesmadeonsomeofthefundamentalmattersbelowfortheDFWMACpreventtherealizationofacompetentsystemplan:1.07 Selectionofthedistributedcontrolfunctions(DCF)optimizedforpeertopeeroperationasthe L= primarymode.Thepointcontrolfunction(PCF)isthenusedonlyforfunctionsthatcannotbedistributedratherthanallofthoseforwhichitisadvantageous. !! 2.07 Noprovisionforinterferencelimitedsystemdesignevenforthenoncontentioncapacitypartitions.N ?!! 3.07 Separateaccessmethodsforeachofthethreeservicetypesafterphysicalmedium v g multiplex/demultiplex.Twooftheseincludepollinginthedistributedlogictimespaceforaccesstothereservationtypespace. !! Afterincorporatingtheseconceptualpoints,anumberofspecificfunctionaldifficultiesappearwhicharemorespecificallydescribedinthefollowingsections.Theconversionofthisplantoonewhichisworkablerequiresreversalofthesephilosophiesandcorrectionofthestatedmajorproblems.Ifthisneedisnotaccepted,theremainingminorimprovementsthatarepossibleanddesirablewillstillnotyieldanadequateplan.  SELECTIONOFPEERTOPEEROPERATIONASPRIMARYMODE  M   Peertopeer,asusedintheDFWMAC,isanarchitecturewithmaximizeddistributedlogicitisnotadescriptionofanecessaryuserservice.ThemaindifficultyofDFWMACisdefiningpeertopeerarchitecturefortheprimaryoperatingmode,andthenattemptingtoprovidenoncontentionservicesbyextension.Infact,thesubframetimedescribedas"contentionfree"forbothconnectionlessandconnection  typeservicecannotcomplywiththatdescriptioninalargescalesystem.Evenwithinthelimitationsdescribed,onlythedegreeofinterference/contentionisabated.ThemaindifficultycomesfromtheaddonPCF(pointcoordinationfunction)whichdoesnotprovidealloftheessentialinfrastructurefunctionsthoughretainingmostofthesamedisadvantages.Neglectingcostandcomplication,theattempttodistributemanyoftheinherentPCFfunctionstoallstationsresultsincreatingmanymoreopportunitiesforfailureandincreasesaccessdelay.N8jkD;+'x p  `N !!                        !!  AutonomousAdHocGroups S  *|%& Ithasbeenagreedthatautonomousadhocgroupswillbepermitted.Anyalternativemusthavethisprovision.Thepotentialdisagreementisaboutwhethertheproportionoftrafficcarriedinthismodeis:a)thepreponderance,orb)asmallpart. -~() Theextensionofadhocgroupsupporttomeanthatanystationcantransmitwheneveritbelievesthechanneltobevacant,isunworkableandunnecessaryinanyareawhereaninfrastructureexists.Stationscanonlytransmitwhengrantedpermissionfromthatinfrastructure.Ifthereisnoinfrastructurenearenoughtoexperienceinterferenceandtomanageorderlyaccess,thenCSMAorLBTaccessmaybeused.Thepracticalmeaningisthatifbothformsareproperlysupportedinthestandard,thepartitioningwillbeadaptivelyproportioned.Theuserwilldecideproportioningbyhowthestationsandenvironmentareconfigured.  MarketNeedforPeertopeerServices |W    Theneedfordirectpeertopeerisadifferentquestionthanautonomousadhocgroupsthoughsuchgroupsmayworkinthatmode.Evenwithinfrastructure,directpeertopeermaybesupportedwhenstationsarewithinnecessaryradiorange.Therewillbesomesavinginchanneltimefromavoidinganaccesspointrepeat.Themarketinformationthat802.11hasgatheredhasnotshownthatpeertopeerisneededasafunction.Peertopeerseemstobearallyingsloganforthosewhofindanyformofcommonequipment   abhorrentregardlessofeconomicorfunctionalbenefits.   Inlate1991,largeeffortsweremadetodetermineuserrequirements.OneofthesewasaCommittee  approvedQuestionnairetypeusersurveyimplementedbyNCRamongsomeofitscustomers.l R  2      ׀Whenthe   datawasanalyzed, norespondentreportedaneedforpeertopeeroperation. Therewasconsiderableuse  ofdepartmentalcommunicationbetweenstationsandserversandbetweenstationsandexternalnetworksorhostcomputers.Thisresultisnotrecalledtoshowzeroneedforpeertopeer,buttoassertthatthe s dominantcommunicationincompaniesmakeslittleuseofthispatternoftrafficflow. o` L8mnD9)%x 0  `L !!                    !!  AdvantagesofMakingClientServerPathPreeminent b_    Anaccesspointrelatedtoaserverclusterisanarchitecturalconfigurationthatcorrespondstoalargeproportionoflargescalebusinessinstallations.Considerableadvantagecanbetakenoftheinevitabletrafficconcentrationattheserverports.Oneofthemostimportantistheuseofanadvantagedlocationfortheaccesspointantenna.Ashasbeendescribed,theradiosystemperformanceisfarbetterifallcommunicationisto/fromaserverevenwithoutanadvantagedantenna.TheDFWMACacquiresnearlyallofthedisadvantagesofaninfrastructurewhenitputsinplacethe"beacon"withPCFfunctionfortheasserted"contentionfree"serviceswithoutobtainingthemajoradvantagesthenavailable.Itishardtoimaginethatthebeaconfunctionissimplerthananaccesspoint. +%'   INTERFERENCELIMITEDRADIOSYSTEMDESIGNNOTIMPLEMENTED c   TheDFWMACdoesnotrecognizetheneedforandlimitationsofinterferencelimitedradiosystemdesign. 7( Aninterferencelimitedsystemdesign(e.g.,cellular)isonethatmaximallycrowdstogetherstationsandaccesspointsusingandreusingagivenchannel.Thetransmissioncriterionisthatthedesiredsignalissufficientlygreaterthantheaggregateinterferencetoallowsuccessfulcommunication.Thiscriteriais  absolutelyrequiredtocomewithinoctavesofmaximizingthecapacityobtainedfromagivenamountofradiospectrum.   A4stephandshakeisastartintherightdirection,sinceitincludesatestofreceivabilityatthedestinationaddress,butmuchmoremustbedone.ItisreasonablyefficientappliedtoStationoriginatetraffic,andunnecessaryandredundantifappliedtoStationterminatetraffic.Timeseparationbetweenthestepsofthehandshakeisharmfultoperformance.TheseconsiderationswererecognizedanddescribedbyDiepstratenasshowninthefollowingbox..L8opD9)%x 0  `L !!                                !!Thestatementsmadearegenerallyaccurate.Ifthislevelofknowledgeweregeneralandacceptedin802.11,alargestepwouldbetakentowardreachingagreementonaworkablesolution.However,hisassertionthatpowercontrolandadaptivethresholdsareanimplementationofinterferencelimitedsystemdesignareinerror.Inlaterpartsofthesamereference,Diepstratenintroduces20dBofobstaclelossbetweencochanneluses.Theobviousresultisevengreaterisolationandindependence.Thisuserecognizesthevalueandneedforisolationbetweenclusters,andmoreparticularlyclusterswithlimitedfunctionPCFaspreviouslydescribed.Properconsiderationofthesefactorsforaninterferencelimitedsystemdesignprovidesmanyoctavesofimprovementinsystemcapacity,withmuchmoreeffectthandifferencesbetweenthenumberofstepsinahandshakeforeachtransfer.  PHYLAYERMULTIPLEXINGOFINTEGRATEDSERVICES n  )$& Whenacommonsystemisusedforpacketandconnectiontypeservices(integratedservices=IS),thefirstdecisionisaboutthedegreeofcommonalitybetweenthem.Thelayertwoandhigherprotocolstacksareinevitablyseparate,andthesharingofthephysicalmediumisinherentinthedefinition.WhatcanbechoseniswhetherthemultiplexingofthetwoserviceswillbejustthePHYlayerorbothPHYandMAClayer.  -(* APHYlayermultiplexisgenerallybasedonafixedlengthframetimedividedintosubframesforoverheadandmanagement,connectiontypeandpackettypeservices.ThepacketsaremappedintotheavailableslotsasapayloadforthePHYlayerframe.Theinternalboundariescanbeadaptive.AcurrentexampleofanISPHYlayermuxistheIEEE802.9standard.TheapparentmodelfortheDFWMACisshownbelow.Itshouldbenoticedthatthereisarecursiveaspectwheretheinformationdecodedinthereceivedmessagesmaychangethedimensionsoftheframestructure. @%5THEMACSERVICEMODEL  ; , uLETdTPr| ,`',#,#3333g@u !!                                                  !!ThedifferentMACsmustinteractwitheachother.Afundamentalproblemistheinterlockingofallocationeventsbetweenthemultipleservices.Useoftheacronym"timebounded"providesthebenefitofavoidingresponsibilityforlimitationsonsetupandtransferdelayandonlostsegmentsthatmightbeimposedifcompatibilitywithwellknowntelecomstandardswerenecessary.InaMAClevelmultiplexedprotocol,thePHYandMACarecommonabovewhichisaMAClevelmultiplexerthatassembles/splitsthepacketandconnectiontypeservices.ThediagramfortheMAClevelmuxisshownin802.119413.TheimplementationofaMAClevelmuxgenerallymeansthatthereisapacketmediumandanaccessmanagerthatcanprioritizepacketsandreservefuturecapacity(nottimeslots)inresponsetoservicedemands.Thisfunctioncannotbedistributed,anditcannotbeefficientunlesssupportofthesefunctionsisanintegralpartoftheMACdesign.  - (* @%  PartIIIPROBLEMS ;{   MostofthefollowingdescribedproblemsarisefromstartingwiththepeertopeerformofCSMA,andthendoingaddonstoexpandthefunctiontoincludenoncontentionandreservationservices.Underthe $ nextheading,threeconsiderationsareshown,eachofwhichtakenbyitselfisconsidereddisqualifying.  Earlyinitslife802.11adoptedasetofFunctionalRequirementsthatincludeddelay,mobilityandservicesfactors.TheDFWprotocolandconcurrentPHYscannotmeettheseandotherkeyparametersintheserequirements.Theoperationallimitationsthatresultfromdisregardingtheserequirementsis   addressedratherthanthelegalisticargumentaroundnoncompliance.     DISQUALIFYINGPROBLEMS ~    ThePHYcontextisa1Mbpstransferrate.Adjustmentsmaybemadefornecessarychannelcodinglossesora2Mbpsphysicaltransferrategain.  1.07 AbsenceofFrequencyReusePlanNeedforECF(ExtendedareaCoordinationFunction) p RC !! Themereassertionthatadditionalchannelswillbeusedtocreatedistancebetweenthereferenceuserclusterandtheinterferersisoflittlevalueunlessassociatedwiththeeffectontotalcapacity.Theimmediateconclusionisthatthecapacitywillbereducedbyafactorequaltothenumberofchannelsrequired(notused).UsingdatafromtheDiepstratenanalysis, thisfactorisgreaterthan25 forDirectSequencespread A2 spectrummodulationwiththebenefitsofchannelcodingdiscriminationanddiversityalreadyconsidered 3$ andwhicharenotpresentintheFHPHY.Regardlessofthenumberofchannelsusedbutconsideringthe   divisionofspectrumfor100%areacoverage,thecapacityperclusterislessthan4%ofwhatthatclusterwouldhaveinisolationusingallofthespectrumavailable.  Thissituationcanbeimprovedbyadaptivepowercontrolandreceiverthreshold,q R  3      ׀howeveritwillbefound " thatthesetwofactorsareatbestanimprovement,notacure.Tothedegreethatunnoticedinterferers(becauseofhighthresholdsetting)causeinterference,thesystemisoperatingin"Aloha"mode.Ifthesystemusesasinglechannel,thentheremustbeaplanforthatfrequencytobereused.Withmultipledistributeduserclusters,thecapacityofoneclustermustbeshared10to25waysminimum.Withthecurrent802.11frequencyhoppingPHYitispossibletohave1525conditionallyorthogonal 9* channelswhichpotentiallycouldmakepossible100%areacoverage.However,theDFWMACwouldusethesechannelsasseparateunrelatedanduncoordinatedsystems,probablyeachwithitsownbeacon.ThereisnomethodofferedtocoordinatetheseNchannelsintooneplan.ItispossiblethateachaccesspointwithitsownbridgetoacommonbackboneLANisconsideredaplan,butthisfunctionisimpossiblewithoutintelligenceanddatabasecommontoalltheaccesspointsinadditiontothatwhichisforeachaccesspoint.Onecasualconsequenceisthatexternalnetworksmustuseadifferentstationroutingaddressforeach $  hoppingpattern.StationsmovingfromoneBSStoanotherwillrequireupdatingofexternalroutingtables. &!" Withoutafrequency/channelreusestrategy,thereisnopossibilityofacceptablereliabilityandspectrumutilizationwithnear100%areacoverageonalargescale.Thereusestrategymustbeimplementedina (#$ ECFmanagingthatwhichiscommontomanyaccesspointsordependsuponstatusincontiguousBSAs. )$% ThisdeficiencyappliestoCSMALANintheuncontainedmediumwheretheconsequencesarediminishedcapacityandunreliableaccesstostationsmovingbetween(basic)coverageareas.Italsoappliesto +&' connectiontypeserviceswheretheassignmentofanexclusiveslotwithinonecoveragemaybeeffective,buthasnoinfluenceontheinterferencefromsurroundingcoverageswithinonesystem. AttachmentA (lastpage)isaTableaboutthecapacityconsequencesof not consideringfrequencyreuse. $ Itisnotaboutaprotocolcomparison.Itisnormalizedforcommondataratesandmodulationtechnology.ThisTableisveryoptimisticaboutthecapacityofanFHsysteminallowingsimultaneoususe   ofmostoftheavailablehoppingpatternswithoutconsideringintermodulationlimits.TheTablecomparesrawcapacity(beforeprotocoloverheadandtrafficadvantagesfromqueuingofrequests)oftheDFWMACwiththeFHandDSPHYandusingthesameorderivativePHYsforDSwiththeSequentialAsynchronousMACaproposalusinginterferencelimiteddesignandfullyexploitingtheadvantagesofinfrastructureandextendedareacoordination.Thepeaktransferrateatastationisthemediumtransferratepercell.CapacityissustainedaverageaggregatecapacityavailabletoallstationsbeforeconsideringoverheadfromMACfunctions.ThischartisexceedinglyoptimisticaboutthechannelizationcapabilitiesofthefrequencyhoppingPHYrelativetoDS.Likesignalcochannelinterferenceismuchmoredegradingtonarrowthanwidebandmodulations.Theapparentadvantagesofthenarrowbandmodulationisalsoreducedbyintermodulationandotherconsequencesofcrowdingmanyradiosinasmallspace.Nonetheless,thedifferencesareverylarge,andwillhavecompetitiveimplicationsinthemarket.  2.07 UseofNegativeInformation ` !! 8 TheCSMAaccessmethodandthecontentionfreepropertyofthenoncontentionframe  subdivisionsdependsuponeachandeverypeerstationusing absenceofsignals  (ordinary,priorityandDCFspacecontentofRTSandCTSforNAV) asavalidlogic  statetoenabletransmission.Theteachingofmanydecadesofradiosystemdesignisthat  actioncanonlybeinitiateduponpositivepresenceofinformationasanenablingsignal.  Thenomenclatureof"hiddenstationproblem"isasymptomofapossiblefailuretounderstandtheproblem.Thereversecaseistheproblemwhereastationisheardandpresumedtobecapableofcausinginterference,butwouldnot.Thetermforsustainedlossofchanneltimeinthiswayis"busylockout."Whatmaybelessobviousisthatwhilethefrequencyofinvalidbusyindicationsmaybereducedinmanyways,itcannotbemadesosmallthatasystemisefficient.ThisisaninherentlimitationoftheCSMA/CAaccessmethodinthecontentionperiod.L8stD9)%x 0  `L !!                  !!TheCSMA/CApriorityschemeiswhollydependentonabsenceofsignalapartfromthosedefinedandexpectedforitsoperation.Itrequiresanearflawlesschannelstatusassessmentfunctionforittowork.Iftherearecontiguoussystemscontributingbackgroundsignalpresentindications,thefunctionwilllockoutandbeincapableofrenderingthepriorityaccessfunctions.SincethePCFfunctionsbeginintheDCFspace,thereservationtypeservicesareexposedtothistypeoffailure,delayorloss.  -(*   3.7 UnacceptableTransferDelayforConnectiontypeServices    Transferdelaysofuptotwosuperframeperiodsareinherentinthisplanfortheconnectionorientedservice.Theprimarycauseisthatreceivedoctetsmustbeaccumulatedforatleastonesuperframeperiodbeforetheburstisavailablefortransmission.Ontopofthisdelayisthedelaybeforetheycanbetransferredaftertheoctersareavailable.Thisismanytimesthevalueswhichwereunderstoodas802.11objectivesattheculminationofconsiderableeffortin1991andofwhatisactuallyrequired.   SuperframeStructuralDelay     Usingthestatedsuperframeperiodof2030milliseconds,itispossibletoestimatetheworstcasetransferdelayassumingthatthereisnodelayorlossfrominterferenceandcontention(anisolatedandbelow (  capacityloadedsystem).Theframeperiodassumedforestimatesis12and24milliseconds.Zerodelay   forspeechcodingisassumedthoughthisonlytrueforminimalcompression.ForoneDFWconnection,theremightbeatbestonetransferpersuperframe.Thequantizingdelay(thedelaynecessarytoaccumulatethereceivedoctetsintoabundlefortransmission)isatbestequaltooneframeperiod.Aftertheburstisready,theworstcaseaccessdelayisoneframeperiod.Whilethisdelaymayaveragehalftheworstcasevalue,longdelayswillbecommon.Oncethetransferdelayisestablishedbyslotallotmentatsetup,itwillremainapproximatelythesamethereafter.Theworstcasetransferdelayforconnectionsisthenuptotwicetheframeperiodorabout24or48millisecondsindependentoftransferrateexceptasitinfluencesframeperiod.Toimprovethisvalueinthepresentstructure,onestepistodiminishthesuperframelength.Afurtherstepwouldbetobetterinterleavetransfersforvoiceanddata.ThismightbeabenefitofusingthesameMACforconnectionsandpacketsabolishingthesuperframeanditsassociateddelaysentirely.Iftheactualoperation,allowssuccessivetransmissionsforaparticularconnectiontobespacedmorethanoneframe,theproblemdescribedbecomesevenmoreacute.  WLANRequirementsofJanuary1992 9  2# The"WirelessLocalAreaNetworkRequirementsu R  4      "documentshowsforallsurveyedapplicationsanominal ZK transferdelaymedianrequirementof20milliseconds(Figure3.3).Thestatisticsusedinthisanalysisaremisleading.Theaveragingandsummingofdifferentkindsofcriticalanduncriticaluserswith10:1ormorespreadisconfusingparticularlyforstandarddeviation.Theimportanceoftimecriticalusersisdilutedout.Thefollowingtableselectsvaluesfromthisreferencetoinferwhat50%oftheapplicationsmightfindadequateandtheperformancetheeditorthoughtadequate.@ hec  TableISelectedResultsfromTables3.53.8inP802.11/9220 cԈ ## *j]D6v ddd Xdd Xdd Xj,g  ,  , , , +  " K$< " @  Parameter  Timedelaysinmilliseconds 1'!A%2 !   1A  Asynchronous #i$Z"  #  Synchronous 1'i$Z#    1 @  @  _%P #   Median }%n $    Stddev }%n %    Median }%n &  1  StdDev * }%n '   *R @z @oNominalTransferDelay: 5+ &!(  $@10$@510 VL)&!)  $@10 $@ d@164d@V164 VL*&!* d@164 d@  >@30>@V30 TJ)&!+  >@30 >@  0T0 B8.&!,  0   B« @ @TargetNominalXferDelay: 4* '"-  @2@42 SI('".  @2 @  @5@S5 TJ('"/  @5 @  $@10$@T10 TJ)'"0  $@10 $@  ?1?T1 @ @>42'"1  ?1   ? > @~V (#1 Thedesiresofasynchronoususersarecertainlyfasterthanforthesynchronoususers,howeverpoorperformancecanbehiddenunderthelargesuggestedstandarddeviationwhichwouldbeacceptabletoonlyafractionofusers.Forsynchronoususers,thereisnosuchflexibilityinthetolerance. Thosein802.11whoworkedtoactuallymeetthesetargetvalueswere misled ifmuchlongerdelayswere  actuallypermissible.Thiscriticcannotclaimtohavebeenmisled,becausehethoughtandstillbelievesthe   targetvaluesarenearwhatisnecessarytomeetthepreponderanceofmarketneed.     SERIOUSPROBLEMS Ʋ    Thereareseverallesserproblemswhichdonotpreventoperationbutwhichifcorrectedincreasecapacity,reliabilityandclarityoffunction.MostofthemaretheresultofaminimalPCFwhichmissesmanyofthebenefitsofawellstructuredPCF.  4.07 NAV(networkaccessvector)FunctionalityinContentionSpace[revised]   B3 !! TheNAV(networkaccessvector)ismaintainedatallstationsusingthe DCFtimespace toprovidealocal j[  estimateoftheamountoftimethechannelwillremaininusebyobservingRTSandCTSmessagesreceived.Thepresenceofthisfunctionrecognizesthatsomethingmaybegainedifstationtransmitisconditionedbyknowledgeofcommittedchanneluse.Thisfunctionasimplementedwillcauseasmuchtroubleasbenefit.TheeffectoftheNAVfunctionistoinhibitstationtransmitattemptswithintheintervalthatthechanneliscommittedtouseforthecasewhereastationhearsonlyoneofthetwopartiestothetransfer.Theconceptisimmediatelylimitedbytheneedtoreceiveinordertodefer(nottransmit).UnsuccessfulreceiptoftheRTSorCTSinformationenablestransmit(useofnegativeinformation).Thisconceptcouldworkforoneclusterwithoutinterferencefromanyotherlikecluster.UndoubtedlydependenceisplacedonthechannelizationpropertyofFHtoenableindependenceofuncoordinatedgroups.Thereareotherdifficultieswiththatassumption,mostparticularlythattherewillnointerferencefromlike  patternhoppers.WithasinglechannelPHYorwhentheindependencecapacityoftheFHPHYisexhausted,therewillbemanyRTSandCTSsignalsfromunrelatedsystemstobedealtwith.ThenadecisionmustbemadeastowhethertheinhibitpropertyoftheNAVappliestoallsignalsheardorjusttotherelatedgroup.Neitherchoiceissatisfactory.IftheNAVconsidersonlyRTSandCTSfromitsowngroup,thenmanyofthemessageswillinevitablybelostfrominterference.Thisfunctionrequiresdecodeofthegroupidentifieraswellasthemessagefacts.Itisnotclearwhetherthisfunctioncanbeperformedquicklyenoughtofilteronlytherelevantsignalinformationfromallsignalsheard.IftheNAVconsidersallRTSandCTSreceived,itwillthenbefalselydelayedwithconsiderablelossofchannelaccesswhenthechannelcouldbeused.Sincetheinterferencerangeismanytimestheservicerange,messagesareunlikelytoreachallofthestationsincontiguoussystemscapableofinterferenceduringtheprotectedintervals.TheassertionoftheprotectionfunctionoftheNAVdependsuponreliablereceiptoftheNAVinformation  ("# intheRTSandCTSmessagesbyallotherstations,becauseactionisenabledbytheirabsenceandinhibited (#$ bytheirdecodedcontent.Given100%(theoretical)areacoverage,thenumberofreadablestationsismanytimesthenumberinvolvedinoneautonomousgroup.IfinformationneededforNAVisalwaystransmittedfromanaccesspoint,thesuccessprobabilityismuchhigher.Thisistheonlywaychannelstatusandavailabilitycanorshouldbemadeknowntostations. -()   5.07 WaitstateinContentionfreePacketTransfers[revised]  !! Fortheclassofpacketdatatransferdescribedas"noncontending"witha PCF(pointcoordination 7( function) ,theaccessprocedureissimilartothatforconnections.Sincetherequestw R  5      ׀ismadeinthe ) "contentionspace,"theabsenceofcontentionfromstationswithinthesamecoverageareaisobtainedonlyaftertherequesthasbeenhonored.Theconceptisdefinedasonewheretheuseofcontentionfreespaceiscoupledwithindeterminateaccessdelay.Thefirstconceptualflawisthatthereisnoboundonthenecessaryaccessdelay.Thealternativeistosaythatthetrafficcapacityofthesystemisdefinedbythelevelatwhichdelayisbeyondlimits.Withoutthisrestraint,thereisnomotivationfortimeandprotocolefficiency.Thedetailimplementationflawisthefrequentpossibilityofcarryoverofonetransactionfromonesuperframetothenextintroducingavoidablewaitstates.ThemostobviousoftheseisthewaitstatebetweenRTSandCTSwhichcanbeasmuchasonesuperframeperiod.Thisisnotconsistentwithminimizedtransferdelay.AfurtherimportantdifficultyoccursifandwhenARQmustbeinvoked.FailuretoreceiveACKmustcauseresendasacontinuationofthecurrenttransfer,inparticularavoidingdeferraluntilthesamesubframecomesupinafollowing"superframe.x R  6      "Sincetheremainingtimewithintheframemayhavebeenusedby  theinitialtransfer,theextensionofthecurrentsubframemaynotbeallowedcausingtheresendtobeputovertothenextframe.Thisdelayisafurtherpossiblewaitstatewhichisincreasinglyprobablethelongerthepermittedpacketlengthandwhichiscertainwithhigherlayererrorrecovery.Ifaphysicalmediumisused(FHnarrowband)whichdoesnothavestrongmeasurestomitigateradiotransmissionerrors,alargeproportionoftransferswillfailinvokingARQ.  6.07 SegmentationandMaximumPacketLength  !! Whileordinaryconnectionswillbeintrinsicallylimitedtotransfersof64octetsorlessbyacceptablequantizingdelay,thereisnosuchlimitfor802packets.Themaximumspermittedby802.3areabout1500octets.Proprietarynetwareoftenusestransfersizesof512and1024octets.Theadvantageofalongermaximumisthedilutionofaccessoverheadforgreaterutilizationofthemedium;andthedisadvantageisincreasedaccessdelayandprobabilityoftransmissionerror.TheremustbeaMAClevelsegmentationplanforbothconnectionandpackettypeserviceslimitingtransferlength.Thisisanacuterequirementforsystemswithdelaylimitedservicesanddesirableforpureconnectionlesssystemstominimizeflawedpackettransfers.Assoonassegmentationisunderstoodtobeessential,alargerproportionofchanneltimeisinoverhead,butalsoproblemsinDFWMACwithwastetimespacefromfragmentationofunusedtime,deferralsandtruncationarediminished. $    7.7 ProperDefinitionofConnectionTypeServices    ThePCFproposaldoesnotaddressconnectiontypeservicesappropriately.DFWMACassumesthatoctetbundlesdeliveredperiodicallymeetthatneedprovidedeachbundleisdeliveredattheexpectedinstantwithinatolerancespecifiedbya"jitter"parameter.TheDFWMACrequiresthePCFtoallottimewhenitshouldbereservingcapacity.Failuretopracticethisphilosophyisacauseoffragmentedidlechanneltime.TheessentialpropertyofadigitalconnectionisavirtualcircuitwhichtotheuserisorcouldbeindistinguishablefromthedigitalstreamusedinorprovidedbyaPCMchannelbank.Suchbankstransferoneoctetofachannelatprecisely125secondintervals.Inthiscontext,itisnecessarytointroducequantizingdelaywhileoctetbundlesareaccumulatedfor2to8milliseconds(largervalueslimituseinpublicnetworkconnections).Thisquantizingdelayisinevitable,butitssizeisatradeoff.AtthereceivingendtherewillbeaFIFOorUARTfunctiontodecouplethelevelofsynchronizationwiththesignalsource.Theessentialfunctionattheoutputofthisdeviceistoreconstructtheoriginalserialbit  streamoftheconnectionsourceexceptdelayedintimebytheminimumachievableamount.Thedifferencebetweensourceanddestinationmustandcanbesmall,butitdoesnothavetobeabsolutelyidentical.InPCMchannelbanks,unmatchedclockswhichaccumulatebitofmismatch,causethelossoradditionofabitintheregeneratedstream.Theremaystillbeaneedtotransmitnetworkclockacrosstheradiopathtothewirelessstation,butitneednotbeinstantaneous.ItisabsolutelyrequiredthattheMACenablesanewbundlebedeliveredtothereceiveFIFOorUARTinputbeforeitisneeded.Thereisnouseforajitterspecification,butthereisforaworstcaseaccessdelay  whichifexceededwillcausethebundleofoctetstoarrivetolateforthecurrentoutputdumpfromtheFIFOorUART.Theessentialpropertiesofaconnectiontypeservicearequiteunrelatedtothosenecessarytotransmit  arecognizablevoice.CopyingcircuitdefinitionsfromDECT,GSMordigitalcellularisnotausableguide  becausethesenetworksthedigitaltransmissionpathsaredifferentfromthoseinthepublicnetwork.TheprecedentsarebettertakenfromISDNorfromIEEE802.9.Thereisguidancein802.6onIntegratedServicesusinga48octetcellpayloadandintegrated802/E.164addressing.Theproperrolefor802.11istoprovideatleastone64KbpsclearBchannelandaparallelDchannelwhichmaybetransferredinthepacketmode.Compressionofvoiceisneitheran802.11responsibilityorafunctionalneed,thoughhavingaconnectiontypeserviceat16or32Kbpswouldbeuseful.Theuseof ADPCM(adaptivedifferentialpulsecodemodulation) speechinestimatingtransfercapacity !v invoicechannelsisnotproper.Theeconomyofhalfbandwidthisnottherebecauseofincreasedoverheadpertransferorelsequantizingdelayisdoubled.Theadvantageofcompressionisnotavailablewhenthelimitfortransferdelayisalreadyinvoked.Theminimumrelevanttransferrateformultimediaapplicationsisone64KbpsBchannelclearandanunimpaired..  8.7 "TalkSpurt"VoiceCircuitCapacityEnhancement   f&W!" Thevoicechannelcapacitygivenassumesthatthevoicechannelactivityfactoris0.4,howevernothingissaidabouttheprobabilitythatallchannelswillbesimultaneouslyactivewithoutpeakcapacitytocarrythatload.SuchtechniqueswerecalledTASI(timeassignmentspeechinterpolation)whenusedontransoceaniccables,andtherearesincemanyfurtherapplications.Alloftheseapplicationshaveincommontrunkgroupsoftheorderof30ormorechannels,andthattheyexperiencepeakclippingdistortionordelayedcutthroughwhenfullyloaded.Noneofthemclaimadvantageabove0.5with48channeltrunkgroups.Becauseofpeakdemandprobabilities,thistechniqueisnotbeneficialwithonly4to8fulltimechannelsintheavailabletrunkgroup.Inacellularalternative,achannelholdingrateof1/8thwasconsiderednecessaryduringsilence.  .(* Theconceptisinapplicabletoan802.11LAN.Thesavingsfromtalkspurt,ifavailable,areanapplicationlevelfunctionstrictlylimitedtospeech,andafataldegradationforanyotherservice.Thetrafficestimatesshouldbeforclearduplex64Kbpsdigitalchannels,orfractionsthereof,andassociatedwithadefinedquantizingandaccessdelay.Theintroductionofspeechcompressionatlevels1and2(intheMAC)maybeaviolationofthedefinitionofaconnectiontypeservice.BecauseofthetalkspurtandADPCMassumptions,theestimatesofcapacityshownin"6.1.4Estimates   oftimeboundedcapacity"areconsideredtobeirrelevantand 4:1overstated .     9.07 PollingMethodofAccessControl   !! IntheDFWMAC,arequestinthecontentionintervalwillputastationonthepollinglistforaccesstothecontentionfreespace.Morespecifically,itisdescribedasatokenpassingschemeinwhichthetokenisalwaysreturnedfromthestationtothePCF,howeveritisalsodescribedthatthestationhastheoptionofnotansweringifithasnotraffic.Theperiodofonestation'spollanduseofthechannelisgivenasanintegernumberof"superframes."Ifthatnumberistwoandthelengthofasuperframeis24milliseconds,thesetupcouldaddatransferdelayof96    millisecondsbyextensionoftheestimateinDisqualifyingProblem3unlessthestartoftheconnectionistruncated.Delaysarealreadyoverlimitsbeforeintroducingthisfurtherdegradation.  Pollsofalleligiblestationswillthentakeplaceevery1toNsuperframesandshouldbesodiagrammed.Apollevery24millisecondsforeachstationata1or2Mbpswilluseaconsiderablepartoftheframetime.Itiswellthata shortaddress waschosenforidentificationofstationsafteraccessingthecontentionfree  function.ThisisusefulsteptowardsthevirtualcircuitandpathidentifiersintheATMcellheaders.  Theperiodforconnectionburstsisthenone"superiorsuperframe."Iftheperiodwiththesuperframeisbasedonatimer/counterpositionfromabeaconreference,itfollowsthenthattheperiodofasuperframecanbesynchronizedtoanintegermultipleofaprecise125secondsobtainedfromaconnectednetwork.Otherwisethecorrecttimepositionforthetransferwilldriftovertimerelativetotheinformationsourceorthenetworkconnectioneventuallyslippingaheadaframeorlosingaburst.Astationcouldreserveconnectiontypespace,possiblyuseitforawhile,butlosepowerduringorafterthelastconnection.ThereisnoexplanationofhowthePCFremovesadisappearedstationfromthepolling  listordiscoversthatitneedstoconsideringthataresponseisnotrequired.  Pollinginandofitselfisnotgoodorbad.Thetechniquemustbeassociatedwithnecessaryfunctionsandproportionedtohavealowdutycycleuseofthechannel.Afrequentpollhasenergyconsequencesnotonly ! foronestationbutfortheaggregateofallstationsinawidearea.Itiseasytoignorethisconsideration " forsmall"oneup"systemsbutnotfornationwidestandards.AdifferentlyproportionedpollingfunctionforadifferentpurposeisanecessarychangeintheDFWMAC.  10.IncreasedRiskofEarlyObsolescencefromUseofDistributedLogic  % ! Asomewhatmoresubtlematteristheimportanceofsimplicityinthestationanditsrelationtotheprobabilityorearlyobsolescence.Ifthealgorithmsforpartitioningtimebetweentwoorthreemediumaccessmethodsandofreactingtoapparentperpetualbusychannelconditionareinthestation,itiscertainthatstationlogicwillhavetobeiteratedafteroperatingexperienceisobtained.Thecost,speedandaddedprotocolcomplexityofanticipatingthisneedbyprovidingdownloadablesoftwareforstationswouldbeaconsiderablenegative.Yetmoresubtleistheconsequenceofplacingfunctionsinthestationthatdependuponsystemfactsnotreadilyknowntoindividualstations.Because,thestationhasinferiorradiocoveragecomparedwithafixed -() accesspoint,theobservationofactivityofotherstationsandaccesspointsisnecessarilyincomplete.Perhapslessthan10%oftherelevantactivityisreadableatastation.Thecostandcomplexityofrelayingnecessarydecisionfactstoeverystationthroughabackbonecommontoseveralaccesspointswouldbeunbearableintransmissiondelayandcomplexity.Theadjustmenttonewknowledgeontheseconsiderationswillrequirerevisionofstationlogic,possiblymorethanonce.Thisisanunnecessaryconsequenceofdistributedlogic.Thealternativeisplacingsystemalgorithmsininfrastructurehubswheremodificationandadaptationarefeasible,anduniformlyaffectallstations.ThenecessaryinformationmustbekeptindatabasesconvenienttowheretheyaregatheredpointandExtendedareacoordinationfunctionswithintheinfrastructure.MattersofjudgementontimingandtheprobabilityofinterferencewithadjoininguserclustersisbetterlefttopointandExtendedareaCoordinationFunctionswithintheinfrastructure.Itisthenpossibleanddesirableto limitstationfunctiontothe   protocolofsendingandreceivingmessagesfromashortlistoftypes.    8 Keepthemorenumerousstationssimple,andabsorbcomplexityintoinfrastructureequipmentcommontomanystations.TheefforttoavoidnaturalPointandExtendedareaCoordinationFunctionsininfrastructureisuneconomicforanythingbutthesimplestofnetworks.    11.0SusceptibilitytoMaliciousJammingandImpoliteAccess 1 !! TheeasewithwhichtheLBT/CSMAaccesslogiccanbejammedisobvious;andifitcanbedone,itwillhappen.Thepossibilitiesaresimilarfor"channelgrabbers.z R  7      "Ifthemeasureofchannelactivityis  decodabilityorclockacquisition,therewouldbeanimprovement;however,thiswouldforeclosethepossibilityofmixedsystemtypes(ortheFCC/WINTechetiquette).Withsomeimplementations,the"listen"functioncanbeforcedintoan"alwaysidle"indicationatapointbetweenradioandlogic.Soonerorlaterastationwillbemodifiedtoblockthebusyindicationsothatstationcanalwaysaccess.Thegoodwillandsenseofcommunityoftheuserscannolongerbereliedupontoprotecttheessentialbusinesstoolswhichcomputershavebecome.Anytechnologywhichreducessusceptibilitytotransmissionerrorsalsocanbebeneficialinreducingthescopeandeffectofsimplerjammingandgrabbingtechniques.  12.0DeficienciesofOmission   !! ThereareanumberofnecessarybutomittedfunctionsmanyofwhicharerelatedtoimplementingaPCFfunctionthatiscompetentfor100%areacoveragewithinterferencelimitedradiosystemdesignandforintegrationofpacketandconnectionserviceswhicharecontentionfree.ManyoftheseareexplainedinanassociatedpaperIEEE802.1194/13'"Morphing"theDFWMAC...'  % !   CONCLUSIONS    TheDFWMACisneitheranadequateorafunctionallyresponsivechoicefor802.11Standardsrecognitionbecauseofflawedprimarypremises.Thefunctionalneedsmotivatingitspreferencebymanymemberscanbemetinotherwayswithoutmakingautonomouspeertopeertheprimaryoperatingmode.Thisemphasishasresultedinchoicesfortheothermodeswhicharegrosslyinadequate.Whencoupledwithanequallypoorchoiceoffrequencyhopping2.4GHzPHY,theresultwillbeofsmallvaluetomostusers.8 ThisdeliberatelypermitteddeficiencyinareacoverageforreservationtypeservicesgivestheappearancethatthesupportersoftheDFWMACdonottakeeither"contentionfree"or"timebounded"servicesasacommerciallysignificantrequirement.  8 Itisimportanttorecognizethesefunctionalshortfalls,andmoreimportantlythemechanismswhichcausethem;andthentogetonwithcorrectionsorevolvingabetterchoice.Failuretodothiswillresultinwastedeffortandfinancialresourcesandpoorservicetothepublicthatdependsuponourstandardsprocess.  Whenthefullimplicationsofthesemattersareunderstood,itshouldbeunderstoodthatthebenefitsofproceedingwiththeDFWMACwillbeshortlived.ThereisincentivetoconsideranddevelopthearchitecturalandlogicalchangesproposedinIEEE802.1194/13"'Morphing'theDFWMAC..." @AdditionalReferences (unlessotherwisenotedcontributionnumbersareIEEE802.11...) . ondetailtechnicalconsiderationsandontheSequentialAsynchronousMAC. @86*)pd8  93/105"HiddenTerminalProblemsinWirelessLANs,"R.Allen,Apple,Jul93  ThispaperincludesdiscussionananalysisofthevariousLBTprotocolsofferedto802.11.Seetheinset  paragraphonpage1.  91950T"SequentiallyusedCommonChannelAccessMethod,"C.Rypinski,Sep'91!! Thiscontributionupdatesthe9119presentationofthesequentialasynchronousMAC.  93/1630"ComparisonandCommonalitiesofAsynchronousSequentialAccessandAdaptivelyPartitioned  PeriodicFrameMACProposals,"C.Rypinski,Sept93 !! Comparessequentialasynchronousagainstaclasscomposedofregularframetimeslottedproposalsof  whichthe,IBMproposalisaparticularlycompetentrepresentative.   93/1510"NecessaryConditionsforSupportofConnectionTypeandConnectionlessServices...,"C. ! Rypinski,Sept93 !! Assertsthatacommoncontrollerisessentialtoprovidereservationcapabilityagainstfuturecapacity #  withoutwhichaconnectiontypeserviceisunreliable.93/101"DataCapacityofRadioSpectrum,"C.Rypinski,Jul93 % " EstimatesspectrumcapacityinMbps/hectareforseveralproposed802.11PHYmethods.Acentralpoint &!# isthatthiscapacityisaseparatematterfromitsutilization.(expandedandrevisedversioninpreparation)(TheseandotherreferencesonthissubjectcanbesuppliedbytheAuthor)  *u%' @  AttachmentARelativeRawCapacityofDFWMACandSAMAC6in2.4GHzISMBand   (pg8)  *^D6_ ddg      ]D6v,=dd",dd",dd",dd",dd"+   " PARAMETER %w %DFWMAC %w" %DFWMAC %w" %SAMAC %w" %SAMAC w" PHY   1MbpsFH   2MbpsDS    2MbpsDS    6MbpsDS    Reachmeters: 6, ^ O  Y@100Y@6100 VL*^ O  Y@100 Y@  I@50I@V50 UK)^ O  I@50 I@  I@50I@U50 UK)^ O  I@50 I@  A@35A@U35 5+)^ O  A@35 A@ 5APIllumination:    Omni    Omni    Omni    Corner    Cellaream2: 8. 6 ' @20000@820000 ZP,6 ' @20000 @ @5000@Z5000 YO+6 ' @5000 @ @5000@Y5000 XN+6 ' @5000 @ @625@X625 6,*6 ' @625 @ 6Reusefactor:    36(19channels)    16(3channels)    9(3channels)    4(1channel)    Rawcapacity/cell:    1Mbps   ! 2Mbps