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DTIC ADA461597: Poll-before-Data Multiple Access PDF

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Poll-before-Data Multiple Access AsimakisTzamaloukasand J.J.Garcia-Luna-Aceves ComputerEngineeringDepartment BaskinSchoolofEngineering UniversityofCalifornia,SantaCruz,California95064 jamal,jj @cse.ucsc.edu f g Abstract—Weintroduceanewmediumaccesscontrol(MAC)protocolnamed Wepresentanewreceiver-initiatedMACprotocolthateliminates PDMA(Poll-before-Data Multiple Access). Mostprior MACprotocols aimedat the performance limitations of MACA-BI, which we call the Poll- avoidingcollisionsofdatapacketsinnetworkswithhiddenterminalsaresender- before-DataMultipleAccess(PDMA)protocol.PDMAturnstheRTT initiated,inthatthesendertransmitsashortrequesttosend(RTS)askingthere- usedinMACA-BIintoadual-usecontrolpacketcalledRT2(ReadyTo ceiverforpermissiontotransmit.Incontrast,inPDMA,whenadatapacketarrives ReceiveandTransmit). Whenanodehasdatatosendtoanintended atthereceiver,thereceiversendsaready-to-receive-and-transmit(RT2)packetstat- ingtheidentifiersofaspecificsenderandreceiver.AnodereceivinganRT2packet receiver, itsends anRT2using carriersensing, which weassume to addressedtoitasasenderisenabledtosendadatapacket,ifithasone;otherwise, benon-persistentinthispaper. TheRT2specifiestwoneighbors: (a) ifthesenderspecifiedintheRT2isquiet,thereceiverspecifiedintheRT2sends anintendedsourceofdata,whichischosenusinganypollingscheme aclear-to-send(CTS)packet,enablingthesenderoftheRT2tosenditsowndata (e.g.,roundrobin),and(b)anintendedreceiverofthedatathenode packetfreeofcollisions. PDMAisshowntoavoidthecollisionofdatapacketswith hasfortransmission. TheRT2leadstoasuccessful transmissionof anytypeofpacket.AnanalyticalmodelisusedtoshowthatPDMAachieveshigher dataifeitherthepolledsourcehasdataforthesenderoftheRT2,orthe throughputthanpriorcollision-avoidanceprotocolsforwirelessnetworks,namely MACA-BI,FAMA-NCS,andMACA.AveragedelaysinPDMAarealsoshowntobe intendedreceiversendsaclear-to-send(CTS)tothenodeifthepolled shorterthanthoseinCSMA. sourceremainsquiet. SectionIIdescribesPDMAindetail,andSec- tionIIIshowsthatPDMAcorrectlyavoidscollisionsofdatapackets withanyotherpacketsintheabsenceoftransmissionerrorsandfad- I. INTRODUCTION ing.SectionIVshowstheimprovementinthroughputoverMACA-BI Therehasbeenasignificantamountofresearchondesigningeffi- andevenFAMA-NCSresultingfromthemodifiedcollision-avoidance cientMAC(mediumaccesscontrol)protocolsforwirelessnetworks. dialogueofPDMAusingananalyticalmodel. ThefirstattemptwasCSMA(carriersensemultipleaccess),whichis basedonsensingthechannelbeforeattemptingtotransmitapacket. II. PDMA KleinrockandTobagi[7]studiedCSMA’sbehaviorandidentifiedthe Acriticaldesignissueinanyreceiver-initiatedMACprotocolisde- hidden-terminalproblemofCSMA,whichmakesCSMAperformas cidingonthefrequencywithwhichareceivermustpollitsneighbors poorly as the ALOHAprotocol when the senders of packets cannot forpackets. A polling ratethat istoo small renders lowthroughput hear one another and the vulnerability period of packets becomes andlongaveragedelays,becauseeachsenderwithapackettosendis twicea packet length. TheBTMA (busytone multipleaccess) pro- sloweddownbythepollingrateofthereceiver. Conversely,apolling tocolwasafirstattempttosolvethehiddenterminalproblembyin- ratethatistoohighalsorenderspoorperformance,becausethepolling troducing aseparate busytonechannel [11]. Thesameauthorspro- packetsaremorelikelytocollidewitheachotherandnosourcegets posed SRMA [12], which attempts to avoid collisions by introduc- polled. The basicsolution advocated inPDMAconsistsof twoele- ing a collision-avoidance handshake between the sender and the re- ments: (a)making thedatarateatthesourcesdeterminethepolling ceiver.Anodewithadatapackettosendsendsfirstarequest-to-send rateat thereceivers, and (b)eliminating wastedpolling packets. To (RTS)packettotheintendedreceiver, whorespondswithaclear-to- achievethedesiredclockingeffectofdatapacketsoverpollingpack- send(CTS)ifitreceivestheRTScorrectly. Thesendertransmitsthe ets,anodesendsanRT2(readytoreceiveandtransmit)packetwhen datapacketafterreceivingtheRTSsuccessfully. ALOHAorCSMA ithasdatatosenditself. Toavoidwastefulpollingpackets, theRT2 canbeusedbythesenderstotransmitRTSs. servestwopurposes: it pollsaspecific neighbor asking for packets, Several variations of the basic SRMA scheme to avoid collisions anditaskspermissionfromanotherspecificneighbortosendpackets ofdatapacketshavebeendeveloped;MACA[6],MACAW[1],IEEE ifthepolledsourceremainsquiet. 802.11[5],andFAMA[2],[4]arejustafewexamples. Allofthese InPDMA,everynodestartsoperationintheSTARTstate,inwhich MACprotocols,andmostprotocolsbasedoncollision-avoidanceex- the node waits twice the maximum channel propagation delay, plus changestodate,aresender-initiated,inthatthenodewantingtosend the hardware transmit-to-receive transition time ( ), before sending adatapacketfirsttransmitsashortcontrolpacketaskingpermission anythingoverthechannel. Thisenablesthenode(cid:15)tofindoutifthere fromthereceiver.Incontrast,intheMACAbyinvitation(MACA-BI) are any ongoing transmissions. After a node is properly initialized, protocol[9],[10],thecollision-avoidancehandshakebetweensender ittransitionstothePASSIVEstate. Inallstates,beforetransmitting andreceiverisreversedandismadereceiverinitiated. InMACA-BI, anything to the channel, a node must listen tothe channel for a pe- a node with a packet to send must wait for the intended receiver to riodoftimethatissufficientforthenodetostartreceivingpacketsin sendapollingpacket,calledRTR(readytoreceive),addressedtothe transit.Ifanode isinthePASSIVEstateandsensescarrier,ittransi- node,beforeitcantransmitanything. Thisisaninterestingapproach; tionstotheREMxOTEstatetodefertoongoingtransmissions.Anode however, as we show in Section IV-B, it renders a low throughput, inREMOTEstatemustallowenoughtimeforacompletesuccessful unless the average rate of packets is high, because many RTRs go handshaketotakeplace,beforeattemptingtotransitionfromremote unanswered. state. Figure 1 illustrates the basic handshakes that occur in PDMA. If ThisworkwassupportedbytheDefenseAdvancedResearchProjectsAgency(DARPA)underGrant No.F30602-97-2-0338andbyagrantfromRaytheon. node isinPASSIVEstate and obtains an outgoing packet tosend x Report Documentation Page Form Approved OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE 3. DATES COVERED 1999 2. REPORT TYPE 00-00-1999 to 00-00-1999 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER Poll-before-Data Multiple Access 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION University of California at Santa Cruz,Department of Computer REPORT NUMBER Engineering,Santa Cruz,CA,95064 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR’S ACRONYM(S) 11. SPONSOR/MONITOR’S REPORT NUMBER(S) 12. DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release; distribution unlimited 13. SUPPLEMENTARY NOTES 14. ABSTRACT 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 18. NUMBER 19a. NAME OF ABSTRACT OF PAGES RESPONSIBLE PERSON a. REPORT b. ABSTRACT c. THIS PAGE 5 unclassified unclassified unclassified Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18 toneighbor ,ittransitionstotheRT2state. IntheRT2state,node packetcollideswithotherpackets,hastobelargerthanthemaximum uses non-pyersistent carrier sensing to transmit an RT2. If node propagationdelaybetweenanytwoneighbors. xdetectscarrierwhenitattemptstosendtheRT2,ittransitionstothxe Toreduce theprobability that thesame nodes would compete re- BACKOFF state, which makes the node back off immediately for a peatedlyforthesamereceiveratthetimeofthenextRT2,leadingto sufficient amount of time to allow a complete handshake between a successivecollisionsofRT2s,theRT2specifiesabackoff-periodunit sender-receiverpairtooccur;otherwise, sendsitsRT2. forcontention. ThenodesthatmustentertheBACKOFFstatecom- The RT2 specifies two addresses: thxe address of a neighbor , putearandomtimethatisamultipleofthebackoff-periodunitadver- which is the intended source being polled and can be chosen usinzg tisedintheRT2. Thesimplestcaseconsistsofcomputingarandom anyneighborpollingschedule(e.g.,roundrobin,setting equalto ), numberofbackoff-periodunitsusingauniformlydistributedrandom andtheaddressof astheintendedreceiver. z y variablefrom1to , where isthemaximum number ofneighbors If receivestheyRT2correctlyandhasdatafor ,itimmediately forareceiver. Thedsimplestbdackoff-periodunitisthetimeittakesto transiztions totheXMIT state, where ittransmitsaxdata packet to ; sendasmalldatapacketsuccessfully. otherwise, transitionstotheBACKOFFstatetoremainquiet forxa timeperiodzthatislongenoughtoallowthedesignatedreceiver start III. FLOORASSIGNMENTINPDMA sendingaCTS,enabling tosendadatapacket. y Theorem1belowshowsthatPDMAensuresthatanypacketissent If receivestheRT2cxorrectlyanddoesnothearanytransmission toitsdestinationwithinafinitetimeafteritbecomesreadyfortrans- fromy foraperiodoftimeequaltoamaximumround-tripdelaywith mission,andthattherearenocollisionsbetweendatapacketsandany anynezighbor,ittransitionstotheCTSstateandsendsaCTSaddressed othertransmissions,underthefollowingassumptions([4]): to ifnocarrierisdetectedinthechannel. A0) AstationtransmitsanRT2thatdoesnotcollidewithanyother xAnynodeinPASSIVEstatethatdetectsnoiseinthechannelmust transmissionswithanon-zeroprobability. transitiontotheBACKOFFstate.Anynodeotherthan and receiv- A1) Themaximumend-to-endpropagationtimeinthechannelis inganRT2transitionstotheBACKOFFstate. Anynodyeothezrthan . receivingtheCTSfor transitionstotheBACKOFFstate. x A2)(cid:28) <Ap1acketsentoverthechannelthatdoesnotcollidewithother Whennode receivxestheCTSfrom ,ittransitionstotheXMIT transmissionsisdeliverederrorfreewithanon-zeroprobability. stateandtransmxitsadatapacketto . y A3) AllnodesexecutePDMAcorrectly. Therefore, PDMA can have twoy types of successful exchanges, A4) The transmission time of an RT2 and a CTS is , the max- whichareillustratedinFig.1(a)and(b).Thepollednode mayhave imum transmission time of a data packet is , an(cid:13)d the hard- data tosend to (Fig.1(a)) or isidleand theintendedzreceiver waretransmit-to-receivetransitiontimeis (cid:14) . furthermore, sendsaCTSsucxcessfully(Fig.1z(b)). y . (cid:28) (cid:20) (cid:15) A5)2(cid:28)T<her(cid:13)e(cid:20)isn(cid:14)o<ca1ptureorfadinginthechannel. Theorem1: PDMAprovidescorrectflooracquisitioninthepres- (a) enceofhiddenterminals. Proof: The topology depicted in Figure 2 includes all the possible RTR RTR situations of hidden terminals withrespect tosource and receiver x RRTTRR z x data z . Node representsalltheneighborsof thatcanbSehiddenfrom RTR RandtheLreforewecanhaveinterferenceatS .Node representsall y Rtheneighborsof hiddenfrom thatcancSauseinteKrferenceat so that won’tbeaLbletofollowthSepacketexchangebetween anLd . (b) LikeLwise,node isaneighbor of thatishiddenfrom S,causiRng interferenceat X;andnode isanReighborof thatishiSddenfrom RTR RTR data data ,preventing RfromunderYstandingthedialogXuebetween and . x RTR y x CTS y x data y R X S R RTR RTR data data X S K (c) Y R L RTR RTR x RRTTRR y x BACKOFFy Fig.2. PDMAfloorassignment RTR RTR Theproofneedstoshowthat,ifnode sendsadatapacketto , noothertransmissioncancollidewithit,SindependentlyofthestatRus Fig.1. PDMAillustrated ofallaforementionednodes. Node cansendadatapacketto onlyafterreceivingasuccessful WhenmultipleRT2saretransmittedwithinaone-waypropagation RT2fromS . WithoutlossofgenerRality,wecanassumethat,attime delayacollisiontakesplaceandthenodesinvolvedhavetotransition ,node RsendsanRT2to . Becausethechannelhasaminimum totheBACKOFFstateandtryagainatalatertimechosenatrandom, pt0ropagatiRondelaylargerthanS0,alltheneighborsof startreceiving asshowninFig.1(c). ’sRT2atsometime . Node eitherreceivRestheRT2from Node determinesthatitsRT2wasnotreceivedcorrectlybyeither Rintheclearattime t1 >t0 Xorithearsnoiseandmustback X or aftxeratimeperiodequaltothemaximumround-tripdelaytoits Roffuntil t2 (cid:20)t0+(cid:13)+(cid:28). X zneighyborsplusturn-aroundtimesandprocessingdelaysatthenodes. If ret2cei>vest0+’s2R(cid:13)T+2w(cid:14)i+th5e(cid:28)rr+ors(cid:15)orifacollisionhappenswitha ThelengthofRT2sandCTSsisthesameand,toensurethatnodata transmSissionfromRanodethatishiddenfrom (e.g., ),then does R L S notsendadatapacket;inthiscase, backsoffuntil A. PDMA S seconds. Otherwise, Sreceives a cleart2RT>2ta0t+tim2e(cid:13)+ Thefollowingtheoremprovidesthroughputasafunctionofoffered a(cid:14)n+ds5e(cid:28)nd+sa(cid:15)datapacketafterwaitinSgfor seconds.However,thiscatn1 loadforPDMA. happenonlyafter hastransitionedtoal(cid:28)isteningmode,whichoccurs Theorem2: ThethroughputofPDMAisgivenby attime S . S At titm2e(cid:20)t0+(cid:13)+(cid:15)+(cid:28) node has S (2) receivedthet3da=tatp2ac+ket(cid:14).+Be(cid:28)ca(cid:20)uset0 +is(cid:13)in+th(cid:14)e+BA2C(cid:28)K+O(cid:15)FFstateRuntil (cid:14) time X ,thXerearenopacketssentfromnode S = (cid:14)+(cid:28) + (cid:21)1 +((cid:13)+3(cid:28))(cid:1)e(cid:0)N(cid:21)(cid:13)2 +((cid:13)+2(cid:28))(cid:1)e(cid:21)(cid:28) totn2od>et0;+th2e(cid:13)re+fo(cid:14)re+, t4h(cid:28)e+da(cid:15)ta packet sent from to , must be Proof: To analyze the throughput of PDMA as a function of the rXeceivedfroRm intheclear. S R rate of data packet arrivals at nodes, we assume that all nodes have InthecasetRhat receivesanRT2intheclearbutdoesnothaveany thesamerateofpacketarrivalsandthatanodechoosestherecipient datapacketstosenSdto , waitsfor ,untiltime S ofadatapacketwithequalprobability. Therefore,thearrivalofdata .If sensesthattRheSchannelisid2l(cid:28)eatthatmomte3nt=,ittt0ra+nsm(cid:13)i+ts packetsatagivennodeforaspecificreceiveris . Becausenodes (cid:15)a+CT3S(cid:28).NoSdes and receivetheCTSattime .If (cid:21) S sendRT2swhentheyobtaindatapacketstosend,Nth2earrivalofRT2s triestotransmiRtapackLetatthesametime,acollits4io<nhta3p+pe(cid:13)ns+an(cid:28)dboKth isalsoaPoissonwitharateof RT2spersecond. stationsbackoff;otherwise, receivesaclearCTSandmustbackoff (cid:21) WithPDMAwheneveranRTN2istransmittedsuccessfullyapacket for seconds,Kwhile waits tosendanydatapacket willalwaysfollow,eitherfromthesenderorthereceiver. Therefore, that(cid:13)it+m(cid:14)ay+ha4v(cid:28)e.+N(cid:15)ode alwaysrecSeivesacRlearCTSfrom asnode theprobabilityofsuccess ,isequaltotheprobabilitywithwhichan isintheBACKOFFRstate,untiltime X S . RT2istransmittedsuccesPsfSully. Becauseallnodesareconnected,an FXinally,thedatapacketsentfromnode t2to>tw0i+lla2ls(cid:13)o+be(cid:14)in+th5e(cid:28)c+lea(cid:15)r RT2fromnode issuccessfuliftherearenootherRT2stransmitted as receivesthedatapacketattime SR S and within secondws from thestart of the RT2. After thisvulnerability iSsintheCTSstateuntilatleasttimte3 <t0+2(cid:13)+(cid:14)+4(cid:28).+(cid:15) period (cid:28)of seconds, all the nodes detect the carrier signal and act L In the special case that we have a ste0ri+es2o(cid:13)f+RT(cid:14)2+sc4o(cid:28)lli+din(cid:15)g inthe appropriate(cid:28)ly.Accordingly, channel,let bethetimewhenagivennode receivesthefirstRT2 packetofthet0series.Inorderforthistohappenw,allthecollidingRT2s (cid:0)(cid:21)(cid:28) (3) mustbetransmittednolaterthan ;otherwise wouldbeable PS =e todetecttheexistenceofanothertR0T+2a(cid:28)lreadyinthewchannel. Ifsuch According to the PDMA specification, a successful transmission a collision occurs, node should be able to detect it no later than occursintwocases: (a)whenthepolledsenderhasadatapacketto . w send, or (b) when the sender has nothing to send and the intended t0+2(cid:28) 2 receiversendsaCTSsuccessfully. Theprobability, ,withwhich IV. APPROXIMATETHROUGHPUTANALYSIS thefirstcasehappensisequaltotheprobabilitythataPnSR1T2issentin theclear,timestheprobabilitythatthereisatleastonepacketarrival WeanalyzethethroughputofPDMAandMACA-BI([9],[10])us- atthepollednodedestinedtothepollingnodeduring seconds,that ingthemodelfirstintroducedbyKleinrockandTobagi[7]forCSMA is: (cid:13) protocolsandusedsubsequentlytoanalyzeMACA[6]andFAMA[4]. APDccMorAdianngdtoMtAhiCsAm-oBdIe:lthefollowingassumptionsaremadeforboth The timethat it takPeSs1to=trea(cid:0)n(cid:21)sm(cid:28)(i1t a(cid:0)seu(cid:0)ccN(cid:21)e(cid:13)s2s)ful packet in this ca(4se) 1. Thenetworkisfullyconnectedandhas nodes. is equal to the transmission time for a successful RT2 and the data 2. AsingleunslottedchannelisusedforalNlpackets,andthechan- packet,plusthepropagationtimeassociatedwitheach;thatis: nelintroducesnoerrors. 3. Allnodescandetectcollisionsperfectly. (5) 4. Eachnodehasanindependent Poissonsourceofdatapackets, TS1=(cid:13)+(cid:14)+2(cid:28) The second case of a successful busy period happens when the withameanrateof datapacketspersecond. (cid:21) 5. EachnodehasatmoNstonedatapackettosendatanygiventime. polled sender does not have a packet to send and therefore it sends aCTSpacketbacktothesenderoftheRT2enablingthenodetosend 6. Thesizeforadatapacketis secondsandthesizeofanRTR, RT2andanCTSis seconds.(cid:14) adatapacket. Theprobability thatthisscenario happens isequal to 7. Theturn-aroundtim(cid:13)e is0. theprobabilitythatanRT2issentintheclear, timestheprobability 8. Thepropagationdelay(cid:15)ofthechannelbetweenanytwonodesis thatthepolledsenderexperiencesnoarrivalsofdatapacketsdestined forthepollingnodein seconds;thatis: seconds. (cid:13) As(cid:28)wehaveshownintheprevioussection,PDMAensuresthatno datapacketscollidewithothersundertheaboveassumptions,andthe PS2=e(cid:0)(cid:21)(cid:28)e(cid:0)N(cid:21)(cid:13)2 (6) sameisalsotrueforMACA-BI. Thetimeforasuccessfuldatapacketinthiscase, isequalto Theaveragechannelutilizationis: thetransmissiontimeforasuccessfulRT2,CTSanddaTtSa2packet,plus the waiting timeof needed for the polled sender, plus the corre- (1) spondingpropagation2(cid:28)delays;thatis: . U S= AbusyperiodalwaysconsistsofatTlSea2s=tan2(cid:13)RT+2(cid:14)an+d5th(cid:28)eassociated B+I propagationdelay, i.e. . IftheRT2fails,thebusyperiodlasts where is the expected duration of a busy period, defined to be a , where (cid:13)is+the(cid:28)time between the start of the first and periodBoftimeduringwhichthechannelisbeingutilized; istheex- t(cid:13)he+la(cid:28)st+RTY2s of theYbusy period and is the same as in CSMA [11]. pecteddurationofanidleperiod,definedasthetimeintervIalbetween Accordingly,afailedbusyperiodlasts two consecutive busy periods; and is the average length of time duringabusyperiodthatthechannelUisusedfortransmittinguserdata successfully. 1(cid:0)e(cid:0)(cid:21)(cid:28) (7) TF =(cid:13)+2(cid:28) (cid:0) (cid:21) Ifabusyperiodissuccessfulbecausethepolledsourcehasapacket Therefore,thelengthoftheaveragebusyperiodisgivenby tosend, thebusyperiodlasts ,whichcorresponds tothe durationoftheRT2,thedatap(cid:13)ac+ket(cid:14)a+nd2t(cid:28)heirpropagationdelays.Al- (cid:0)(cid:21)(cid:28) ternatively,ifthebusyperiodissuccessfulwhenthepolledsourceis B=(cid:13)+2(cid:28) (cid:0) 1(cid:0)e silent,itlasts ,whichcorrespondstoanRTR,aCTS,adata (cid:21) packet,theirp2r(cid:13)o+pa(cid:14)g+ati5o(cid:28)ndelays,and waittimebeforetheCTSis +e(cid:0)(cid:21)(cid:28) (cid:1)(1(cid:0)e(cid:0)N(cid:21)(cid:13)2)(cid:1)((cid:14)+(cid:28))+e(cid:0)(cid:21)(cid:28) (cid:1)e(cid:0)N(cid:21)(cid:13)2 (cid:1)(2(cid:28)) speenrito.dFirsomgivtehnebabyove,itfollowsthatth2e(cid:28)durationoftheaveragebusy =(cid:13)+2(cid:28) (cid:0) 1 +e(cid:0)(cid:21)(cid:28) (cid:1) (cid:14)+(cid:28)+ 1 +((cid:28)(cid:0)(cid:14))(cid:1)e(cid:0)N(cid:21)(cid:13)2 (13) (cid:21) h (cid:21) i Thelengthoftheaverageidleperiodis asinPDMA,andthelength (cid:0)(cid:21)(cid:28) 1 1(cid:0)e oftheaverageutilizationperiodis (cid:21) B=(cid:13)+2(cid:28)(cid:0) (cid:21) +e(cid:0)(cid:21)(cid:28) (cid:1)h(1(cid:0)e(cid:0)N(cid:21)(cid:13)2)(cid:1)((cid:14)+(cid:28))+e(cid:0)N(cid:21)(cid:13)2 (cid:1)((cid:13)+(cid:14)+4(cid:28))i U =(cid:14)(cid:1)PS =(cid:14)(cid:1)e(cid:0)(cid:21)(cid:28) (cid:1)(1(cid:0)e(cid:0)N(cid:21)(cid:13)2) (14) =(cid:13)+2(cid:28)(cid:0) 1 +e(cid:0)(cid:21)(cid:28) (cid:1) (cid:14)+(cid:28) + 1 +e(cid:0)N(cid:21)(cid:13)2 (cid:1)((cid:13)+3(cid:28)) (8) Thetheoremfollowsbysubstitutingthevaluesoftheaverageidle, (cid:21) h (cid:21) i busyandutilizationperiodsinEq.(1). When PDMA is used, the channel is only idle for a time period 2 equaltotheinterarrivalrateofRT2s,and 1.Theaverageutiliza- C. PerformanceComparison tiontimeatnode istheproportionoftiIm=ein(cid:21)whichusefuldataare sent,consequentlyw, (cid:0)(cid:21)(cid:28). TocomparePDMAwithotherwidelyknownMACprotocols, we Equation (2) follUow=sf(cid:14)ro(cid:1)mPSsu=bs(cid:14)tit(cid:1)ueting , andEq. (8) intoEq. introducethefollowingvariables: (1). I U 2 (normalizedpropagationdelay) (cid:28) B. MACA-BI a= (cid:14) (normalizedcontrolpackets) MACA-BIisverysimilartoPDMA,withtheexceptionthat,when- (cid:13) b= everthesenderpolledbyanRTRhasnopackettosendtothepolling (cid:14) (normalizedtransmittoreceiveturnaroundtime) " node,nospecialactionistaken.TheperformanceanalysisforMACA- c= BIaspresentedin[9]doesnottakeintoaccounttheprobabilitythat (cid:14) (OfferedLoad,normalizedtodatapackets) G=(cid:21)(cid:2)(cid:14) an RTRsent intheclear may not result inadatapacket being sent. Withthe above notation, we calculate the normalized throughput Accordingly,theperformanceresultsshownforMACA-BIby[9]cor- forPDMA,MACA-BI[9],non-persistentCSMA[7],MACA[6],and respondtothecaseinwhichthereceiverknowsexactlywhenaneigh- FAMA-NCS[4]asshownintableI. borhaspacketforit,andisthereforeanunattainableupperboundon performance. Inourcomparison,weassumeafully-connectednetworktopology Our analysis of MACA-BI makes the same assumptions used for withapropagationdelayof ; 500 and1000 bytedatapackets; a PDMA,assumesthatanRTRhasthesamelengthasanRT2,andthat length of 20 bytes for RTRs1,(cid:22)RsT2s and CTSs for PDMA; CTSs of anodesendsanRTRtoaneighborwhenthenodehasdatatosend. length forFAMA-NCS;achanneldatarateof1Mb/s;andzero Theorem3: The throughput for the MACA-BI protocol, is given preamb(cid:13)le+an(cid:28)dprocessingoverheadforconvenience. by The performance demonstrated by PDMA is much better than MACAandMACA-BI. Theupper bound fornon-persistent CSMA, (cid:14)(cid:1)(1(cid:0)e(cid:0)N(cid:21)(cid:13)2) (9) which assumes an ideal channel over which acknowledgments to S = (cid:14)+(cid:28) + (cid:21)1 +((cid:28) (cid:0)(cid:14))(cid:1)e(cid:0)N(cid:21)(cid:13)2 +((cid:13)+2(cid:28))(cid:1)e(cid:21)(cid:28) pPaDcMkeAtscaoremisnegntshinorzteoronlytimwehe[n7]t,hheaosffaerseidmilloaardthisrobuegtwhpeuetnc1u0r0veanads Proof: The probability that a successful transmission occurs is 2000forafully-connectedtopology. Thenumberofnodesinthenet- equaltotheprobabilitythatanRT2istransmittedsuccessfullytimes workdoesnotaffectthethroughputachievedbyCSMA,FAMA-NCS theprobabilitythatthereisatleastonedatapacketarrivalatthesender andPDMAprotocols. forthereceiverwithin seconds,thatis, As we can see in Figures 3 and 4, for a fully-connected network (cid:13) with500and1000bytesdatapacketsPDMAandFAMA-NCSshow PS =e(cid:0)(cid:21)(cid:28) (cid:1)(1(cid:0)e(cid:0)N(cid:21)(cid:13)2) (10) vinerFyAsMimAil-aNrCthSroisugalhwpauytscluersvsetshainnaolrleeqxupaelritmoethnets.onTehaechtihervoeudghwpiutht Inthiscasethedurationofthebusyperiodis . PDMA. InMACA-BI,afailedbusyperiodcanoccurin(cid:13)t+wo(cid:14)c+as2es(cid:28):(a)when thereisacollisionbetweenRTRs,and(b)whenanRTRissentinthe V. CONCLUSIONS clearbutthepolledsenderdoesnothaveadatapackettosend. The Wehavespecifiedandanalyzedthereceiver-initiatedmultipleac- firstcaseoccurswithprobability: cess (PDMA) protocol. We compared PDMA with non-persistent (cid:0)(cid:21)(cid:28) (11) CSMA, MACA, MACA-BI and FAMA-NCS, and showed that the PF1=1(cid:0)e throughputinPDMAismuchhigherthanMACA,alwaysbetterthan ThedurationofsuchafailedbusyperiodisthesameasEq. 7. The FAMA-NCSandMACA-BI,andbetterthannon-persistentCSMAat probabilityofthesecondbusyperiodscenariooccurringisgivenby highloads. Wealsoarguedthattheaveragepacketdelayexperienced withPDMAislessthanthatwithCSMA.AssuchPDMAisthefirst PF2 =e(cid:0)(cid:21)(cid:28) (cid:1)e(cid:0)N(cid:21)(cid:13)2 (12) MACprotocolbasedonareceiver-initiatedcollisionavoidancemech- and the duration of such a busy period is , corresponding to anism that outperforms MAC protocols for wirelessnetworks based the RTR, the propagation delay, and the ti(cid:13)me+n3o(cid:28)des must wait after onsender-initiatedcollisionavoidance.Ourworkcontinuestoextend receivingtheRTRintheclear. theanalysisofPDMAforthecaseofamultihopnetwork. Protocol Unslottedversion np-CSMA[7] Ge(cid:0)aG G(1+2a)+e(cid:0)aG MACA[6] 1 e(2b+a)G(b+a+G1+F0)+ebG[b+a2+P0(a(cid:0)F0)]+1+32a+F0+P0(a(cid:0)F0) where 0 ebG(cid:0)1(cid:0)bG and 0 e(cid:0)bG(cid:0)e(cid:0)G(a+b) F = bG(1(cid:0)e(cid:0)bG) P = 1(cid:0)e(cid:0)G(a+b) FAMA-NCS 1 b+4a+1+G1+eaG(b+4(cid:3)a) (cid:0)bG MACA-BI 1(cid:0)e N2 (cid:0)bG 1+G1(cid:0)e N2+(b+2a)eaG PDMA 1 (cid:0)bG 1+a+G1+(b+3a)(cid:1)e N2+(b+2a)(cid:1)eaG TABLEI THROUGHPUTOFSENDER-INITIATEDANDRECEIVER-INITIATEDMACPROTOCOLS a = 0.00025; b = 0.04; c = 0.005 a = 0.00025; b = 0.04; c = 0.005 1 1 NP−CSMA PDMA NP−CSMA FAMA−NCS PDMA 0.9 FAMA−NCS 0.9 0.8 0.8 0.7 0.7 MACA−BI MACA−BI S (Throughput)000...456 S (Throughput)000...456 MACA MACA 0.3 0.3 0.2 0.2 0.1 0.1 0 0 10−3 10−2 10−1 100 101 102 103 104 105 10−3 10−2 10−1 100 101 102 103 104 105 Offered Load: G Offered Load: G Fig.3. 500Bytedatapackets;1Mbit/secnetworkspeed Fig.4. 1000Bytedatapackets;1Mbit/secnetworkspeed REFERENCES riersensemultiple-accessmodesandtheirthroughput-delaycharacteristics,”IEEE Trans.Commun.,vol.COM-23,no.12,pp.1400–1416,1975. [1] V. Bharghavan, A.Demers, S.Shenkerand L.Zhang,“MACAW:AMediaAccess [7] R. Rom and M. Sidi, “Multiple Access Protocols Performance and Analysis,” ProtocolforWirelessLAN’s”Proc.ACMSIGCOMM94,London,UK,Aug.31- Springer-Verlag,1990. Sep.2,1994. [8] F.Talucci,M.GerlaandL.Fratta“MACA-BI:AReveiverOrientedAccessProtocol [2] C.L.FullmerandJ.J.Garcia-Luna-Aceves,“FloorAcquisitionMultipleAccessfor forWirelessMultihopNetworks,”Proc.ofIEEEPIMRC,1997. Packet-RadioNetworks,”Proc.ACMSIGCOMM95,Cambridge,MA,August30- [9] F.TalucciandM.Gerla“MACA-BI(MACAbyinvitation).AWirelessMACProto- September1,1995. colforHighSpeedAdhocNetworking,”Proc.ofIEEEICUPC,1997. [3] C.L.FullmerandJ.J.Garcia-Luna-Aceves,“SolutionstoHiddenTerminalProblems [10] F.A.TobagiandL.Kleinrock,“Packetswitchinginradiochannels: PartII-the inWirelessNetworks,”Proc.ACMSIGCOMM97,Cannes,France,September14- hiddenterminalproblemincarriersensemultiple-accessmodesandthebusy-tone 18,1997. solution,”IEEETrans.Commun.,vol.COM-23,no.12,pp.1417–1433,1975. [4] P802.11–Unapproved Draft: Wireless LAN Medium AccessControl (MAC) and [11] F.A.TobagiandL.Kleinrock,“Packetswitchinginradiochannels:PartIII-polling PhysicalSpecifications,IEEE,January1996. and(dynamic)split-channelreservationmultipleaccess,”IEEETrans.Commun., [5] P.Karn,“MACA-anewchannelaccessmethodforpacketradio,”inARRL/CRRL vol.COM-24,no.8,pp.832–845,1976. AmateurRadio9thComputerNetworkingConference,pp.134–40,ARRL,1990. [6] L.KleinrockandF.A.Tobagi,“Packetswitchinginradiochannels: PartI-car-

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