MMTP - Multimedia Multiplexing Transport Protocol - CiteSeerX

10 downloads 1768 Views 136KB Size Report
Laptops commonly come with built in ..... tolerance for delay, while applications using store d media ..... connection to an HP NetBeamIR using an Actisys 2000.
MMTP Multimedia MultiplexingTransportProtocol LuizMagalhaesandRobinKravets DepartmentofComputerScience UniversityoIllinois, f Urbana-Champaign 1304WSpringfieldAvenue Urbana,IL61801

{magalhae,rhk}@cs.uiuc.edu

ABSTRACT Multimediadatahasspecialrequirementsthatareh onmobilehostsduetopotentiallylowbandwidthan duetohostmobility.Suchlimitedcommunicationca mobilehostscanbeoffsetbythesimultaneoususe link layer technologies.MMTPim as ember of sauit thatsharethenovelcharacteristicoaggregating f multiplelink-layerchannels. Theuseofmultiple transportuserdataprovidesfivekeybenefits:(1) afastfeedbackpath,(3)theretransmissionofsel messages,withoutdelayingtheplayoutofthedata sensitivitytominorbandwidthfluctuationsonany channel,and(5)smoothverticalhandoffsfor activ

ardtobemet d isruptions pabilitiesof ofmultiple oeprotocols f bandwidthfrom channelsto faatterpipe,(2) ectedlost stream,(4)less oneindividual deata streams.

MMTPisarate-basedprotocoldesignedfortransfer ring multimediadataonmobilesystems,andmakessimult aneoususe ofeverycommunicationchannelavailabletosendda taatthe requiredrate.TransmissioninMMTPisgovernedby two mechanisms.Thefirstisasetofratecontrolprot ocolsassociated witheachoutgoingchannel.Thesecondisaschedu ling algorithmthatplacesincomingpacketsontheappro priate channel.MMTPislink-layerawareprotocolthatuse bs andwidth estimationforcongestioncontrol,andrelaystoth eapplication informationneededforrateadaptation.Inthispap er,weshow thatthequalityodata f transmissioncanbiemprov edthroughthe useofMMTPthroughexperimentalcomparisonswithd ata transmittedviaUDP.Wealsodemonstratetheeconom yof bandwidth:MMTPonlysendspacketsthatitestimate w s illarrive withinthepacketdeadline,thusdecreasingthenum beroflate packetsthatwillbe discardedathe t receiver.

Keywords Wirelesscommunication,multimediatransportprotoc bandwidthlink.

ols,low

1. INTRODUCTION Asmobiledevicesbecomemoreprevalent,thedemand

for

anytime/anywhereconnectivityforthosedevicesinc reases,and therequirementsonthatconnectivitybecomemores tringent. Connectivity for mobile devices is governed by the communicationtechnologyonthedeviceandthecove rageareaof thattechnology. Toaddversatility tothemobile devices,they are normallybuiltwithmultiplecommunicationtechnolo giesandthe capacityforexpansion. Laptopscommonlycomewith builtin infraredandwithmultiplePCMCIAslots,allowingf ormultiple communicationcards. Withthegrowingdemandform obility support,coverageareasforwirelessconnectivitya regrowingand overlapping.Duetodifferentadministrativeautho ritiesand different underlying link layer technologies, the current infrastructures only support coordination and coope ration betweenhomogenoussupportstations(“horizontalha ndoffs”). In ordertosupportbetterhandoffs,communicationqua lityandcost optimization,themobilenode’soperatingsystemca ncoordinate thesimultaneoususeomultiple f diverse communicat ionchannels, providingseamlessconnectivityasthemobilenode migrates [1]Ift.hemobile betweencoverageareas(“verticalhandoffs”) nodehasaccesstomultiplecommunicationchannels, the applicationcanbeguidedastowhichchanneliscu rrentlythe . supportislimitedtotheuseoof ne mostappropriate [2]Such communicationchannelper applicationdata stream. Thegoalofourresearchistoaggregatethebandwi frommultiplechannelstocreateavirtualchannel bandwidththaneachchannelalone. Giventhatthe mostwirelesscommunicationisthelasthoptothe theadditionofbandwidthatthislasthopwillall theresourcesconstraintsonthemobilenode. Our exposeslink-layerconnectivityandresourceinform transportlayer,allowingthetransportprotocolto changesinavailablebandwidthoneachchanneland availabilityofchannels.Oursolutionpreservese semantics,transparentlyprovidingtheapplication simultaneoususe omultiple f channels.

dthavailable withmore bottleneckfor basestation, eviatesomeof approach ationtothe adapttoboth changesin nd-to-end withthe

Wearecurrentlydesigningaframeworkfortheaggr egationof multiplecommunicationchannels,enablingtranspare ntusefor multipleandindividualdatastreams. Amaincompo nentofthis frameworkiprotocol as suitethatprovidesdiverse transportlayer protocols able to operate in the context of multipl e communicationchannels. Inthispaper,wepresent aprotocol fromthissuite,MMTP,MultimediaMultiplexingTran sport Protocol,whichsupportsthetransmissionoftimes ensitiveratebaseddatastreams(e.g.audio,video) thatmaybegeneratedlive orfromstoreddata. MMTPisarate-basedprotocol thatuses bandwidthanddelay estimationfor bothdetermining the available

bandwidthandforcongestioncontrol.Maintenance ofthese estimationsprovidesnaturalsupportfor adaptivemultimedia applications.Giventhecharacteristicsofthemul timediadata stream intermsoframe f rate andbandwidthrequire ments,MMTP usesanyavailablecommunicationchannelstotransm itthedata. Astheavailablechannelresourceschange,MMTPada pts, changingthefractionofflowthatisbeingsenton eachchannel andadding oremoving r channelsasnecessary. MMTP providesa besteffortservice. Iftheaggregationofavailab lechannelsdoes notprovideenoughbandwidthfortheapplicationst ream,MMTP willdroppacketsthatitestimatescannotarriveo ntimeand inform the applicationothe f lack onecessary f res ources. TheuseoMMTP f providesfivekeybenefits. First thereisthebenefitoaffatterpipe,whichenable multimediatraffic.Second,MMTPprovidesfast a fe Althoughthedelayfordatatransmissionwilldepen channelwiththelongestpropagationdelay,control bereturnedonthechannelwiththeshortestpropag Third,extrabandwidthonanyofthechannelsmaye retransmissionofselectlostmessages,withoutdel playoutofthedatastream. Forth,duetotheuse channels,MMTPislesssensitivetominorbandwidth onanyoneindividualchannel. Finally,smoothver foractivedatastreamsareanaturalbenefitofus channelsandohiding f link-layer connectivity. Thispaperisorganizedintofiveadditionalsectio presentsrelevantresearchassociatedwiththecurr communicationsupportformobilecomputing.Areal ofmultimediainmobileenvironmentsisinvestigate MMTP 3. ispresentedonSection4where , wexplor behavior,flowandcongestioncontrol.InSection5 experimentalresultsarepresented,andSection6c conclusionsandfuture researchdirections.

andforemost, sbetterquality edbackpath. donthe feedbackcan ationdelay. nablethe ayingthe ofmultiple fluctuations ticalhandoffs ingmultiple ns.Section2 entworkin life scenario dinSection ietsstartup ,the ontains

2. BACKGROUND AND RELATED RESEARCH ThecurrentInternetinfrastructurewasnotdesigne dwiththe needsof multimediatrafficinmind.Thepervadingbesteffo rt deliveryprotocolthatformsthebaseoall f Intern ettraffic,IP,has nobuiltinmechanism for reservationobandwidth f or for periodic traffic.Theprotocolsthatweredevelopedlaterto allowtheuseof theIPinfrastructureformultimediatrafficdonot consider mobility. Adaptingthesolutionsusedonwiredhos tstomobile systemsisnotstraightforward,becausethecharact eristicsof wirelesscommunicationchannelsareevenlessagree ableto multimediatraffic.Inaddition,normalreservation schemes [3] usedforwiredhostswillnotworkomay r becomeve ryexpensive duetochangesinthelocationom af obilehost.Ho wever,varying thequalityothe f sourcestreamtomatchtheavail ablebandwidth andlossratehasbeensuccessfullyadaptedtothe mobile environment,althoughitfallstotheapplicationt okeeptrackof theavailablebandwidthandotherparametersnecess aryforthe adaptation. Duetheperiodicnatureofmultimediatraffic,iti acceptedthatthebestprotocolsforsuchdatastre basedmechanisms.Moreover,thelossynatureofwir communicationchannelsmakeschannellossesapoor indicator. Inresponse,bandwidthestimationinco congestionavoidancehasbeensuggestedforusewit

scommonly amsuserateeless congestion njunctionwith hwireless

rate-basedprotocols. Oneotfheearliestexamples ofareliable rate-basedprotocolisNETBLT [4],whichwasdesignedforthe transportobf ulkdataandisnotsuitableformult imediatraffic. Recentexamplesoother f reliablerate-basedprotoc olsareWTCP andRAP.WTCP [5]isareliablesplitconnectionprotocolthat hasgoodperformanceoverlossylowbandwidthlinks thathave highlatency.RAP [6]isaTCP-friendlyrate-basedprotocolfor realtime streams. Theaggregationofthebandwidthfromtwomodemsha sbeen implementedinbothLinuxandWindows. Inbothsys tems,the characteristicsofbothchannelsmustbethesamea nd onlya simple load-balancing algorithm is used for schedul ing transmission. Theaggregationomany f lower bandwi dthchannels inalargerpipeicsalled“reversemultiplexing”i nATM [7],and isnowpartoftheATMspecification,asiallows t m a ultiplicity of ratesandflexibilityinallocatingbandwidthforc ommercial services.Someworkhasalsobeendoneintheaggre gationof bandwidth [8]inwirelesslinksbyusingthefacilitiesofPP P (multiheaderextensions [9].ThemechanismsinMMTParemore general,workingwithheterogeneousinterfaces. By uncoupling thetransportprotocolfromthenetworkprotocol,t ransitionsfrom onenetworktoanotherareverynaturalinMMTP,an drequireno switching.The Barwanprojectpresentedtheconceptof“vertical handoffs”[1],transitionsfromonelinklayertoan other.WTCP uses similar a model,whenthe mobile transitionsf rom one area of coveragetoanother,thereihandoff as andtheold erconnectionis relinquished.InMMTP,ifanareaisconnectivityr ichand multiplewaystoaccesstheinfrastructureareavai lable,the activationofanewinterfacedoesnotcauseanothe rtobe dropped.The new interface iadded s tothe existing pool. Adapting thebandwidthrequirementsoafmultimediastreamt o theavailablebandwidthothe f channelhasbeenpro posedin [10]. Becausethisrequiresacloseinteractionbetweent hetransport protocolandthecodingapplication,therearemany proposalsfor integratingsourcecodingandthetransportprotoco l. [11] proposesatranscodingthesourceintoanon-priori tizedpacket streamtoensuregracefuldegradationinthepresen ceofpacket loss,anddescribesaTCP-friendlyratebasedproto colandthe frameworkfortheinteractionothe f protocolandt ranscoder. [12] proposesmodificationstotheTPCprotocol,aresil ientencoder andaratecontrolalgorithmforthesameobjective While . wedo notdelveintosource coding,MMTPexposesratechangestothe application,enabling adaptation. MMTPcanbveiewedatswoone-wayprotocols,onefr omsender toreceivercarryingdata,andanotherfromtherec eivertothe sender,carryingcontrolinformation.RTP [13]usesdifferent streamsfordataandcontrolinformation,whileMMT Pcarries controlinformationinsidethedatapackets,allowi ngforchanges intherateforpresentationbecommunicatedtothe application simultaneously withthe receiptof data. BecauseMMTPdoesnotback-offonlostpackets,mec hanisms suchasRED [14]willnotaffectthesendingrate.Althoughwe believethatourcongestioncontrolmethodresults infairresource utilization,theworkpresentedon [15]onthedifferentiating multimediatrafficonroutertoavoidcongestionca nbeusedto police MMTPtraffic. Anewapproachtomobilityistomakemobilityvisi endpoint.WhileMobileIPtriestohidehostmobili proxies,mobilitycanalsobeachievedbylettingt

bletothe tybyusing ransport

protocolstakecareothe f switch.Thisrequiresth ue ncouplingof thenetworkaddressfromtheconnectionidentifier, andscheme a forlocation.TCPandDNSweremodifiedtoaccompli shthatin [16].Thesameend-to-endargumentsapplytoMMTP, but MMTPreliesonaproxyforlocation. MMTPhasthe additional advantageinthecaseofmultimediatrafficbecause itgenerally doesnotneednor acceptsthe addedoverheadoTCP f reliability.

ShortRange Radio

In-Building Infrared

3. MULTIMEDIA IN MOBILE ENVIRONMENTS

Cellular Network

Multimediatrafficivs erysensitivetodelay,jitt erandbandwidth restrictions.Introducingwirelesslinksintothe pathofa multimediadatastreamnotonlyincreasesthepoten tialforsuch problems,butalsobringswithitproblemsfromhan doffs. Inan efforttooffsetthesenegativeeffects,amobileh ostmayhave accesstomultiplecommunicationtechnologies.Wit hthe growingpervasivenessofthewirelessinfrastructur e,inmany placestherewillbeanoverlapofcoverage.Thisp resentsan opportunitytotapadditionalresourcestohelpthe transmissionof multimediatraffic.Athesametime,mobility-awar eprotocols mayaccountforcommunicationartifactscreatedby movement, suchasvariationsinbandwidthandchangesinchan nel availability. Considerthefollowingscenario:auseriw s aiting wantstowatchthe news.The trainstationterminal rangeradioandinfraredconnectivity. Theuserha modeminadditiontotheinfraredandshort-ranger onthepalmtop.Currently,theuserwouldhavetoc interfacetousetoaccesshis/herfavoritenewsso userchosetheinterfacewiththebestqualities,a servicecharacteristicswoulddirectlyimpactrecep userboardsthetrain,thelocalconnectivity(shor infrared)becomesunavailable.Iftheuserhadchos localconnections,therewouldbgap ae inthetran connection wasbeinghandedofftothecellularmodem. The solutionspresentedinthispaperimprovethisscen ways:better channelquality andseamlesshandoffs.

Cellular Network

foratrainand hasbothshortsacellular atiointerfaces hoosewhich urce.Evenithe f nyfluctuationsin tion.Whenthe t-rangeradioand enanyotfhe smissionatshe ariointwo

Theimprovementoqf ualitycomeswiththeuseoaf l al vailable channels.Thisnotonlyaggregatesbandwidth,permi ttingbetter a qualityinthemultimediadatastream,butalsosmo othesout variationsinsingle a channelthatwouldimpactda tapresentation byspreadingconsecutivepacketsindifferentmedia We . enable thesimultaneoususeofmultiplechannelsbyexposi ngthe underlyinglinklayertothetransportprotocol.By creatinga transportprotocolthatismobility-aware,andknow tsheexistence ofmultipleinterfaces,wecanoffertheillusiono safingle“fatter” pipewithbettertransmissionqualitiestothemult imedia application.Thisaggregatedchannelhasinteresti ngqualities. Althoughtheindividualchannelwithlongestpropag ationdelay dominatesthepropagationdelayfordata,aswillb sehowninthe nextsection,thecontroldatamaytakeadvantageo tfhechannel withlowestpropagationdelay,helping adaptation.

Figure 1.WirelessMobility Theuseofoverlappingcommunicationchannelsallow smoothhandoffsasthemobilenodemigratesbetween areas. Iftheusermovesslowlyoutfromanareac certaincommunicationmeans,thedegradationinqua perceivedbytheprotocol,andthechannelisslowl withnointerruptions. Whenenteringanareacover linklayer,theprotocoladdsthenewchanneltoit withthe entailing gainsinquality.

sfor coverage overedbya lityis yphasedout, edbyanew sprocessing,

4. MMTP MMTPsupportsthetransmissionotime f sensitivera te-baseddata streamsthatmaybgeeneratedliveofrom r storedd ata.Giventhe characteristicsofthedatastreamsintermsoffra merateand bandwidth requirements, MMTP uses any available communicationchannelstotransmitthedata. Asth eavailable channelresourceschange,MMTPadapts,addingorre moving channelsans ecessary. MMTPprovidesabesteffort service. If theaggregationofavailablechannelsdoesnotprov ideenough bandwidthfortheapplicationstream,MMTPwilldro ppackets thatitestimatescannotarriveontimeandinform theapplication of the lack onecessary f resources. MMTPisarate-basedprotocolthatmultiplexesdata acrossmultiplecommunicationchannels.Themaint MMTPisthedecisionatsowhichchanneltousefor thecurrentpacket. Thisdecisionisbasedonesti bandwidthanddelaycharacteristicsofeachchannel startup,twocontrolmechanismsare usedtoadaptt tothechannelbandwidth:ratedecreasemessagesan probe. Inthissection,wepresenttheprotocolpa describe the operationoMMTP. f

packets askof transmitting mationsotfhe .After he sending rate dchannel rametersand

4.1 CommunicationFramework MMTPwasdesignedinthecontextofacommunication frameworkthatprovidessupportforthesimultaneou suseof multiplelink-layercommunicationtechnologies. Re levanttothis protocol,theframeworkprovidesthefollowingfunc tionality. First, the framework monitors for the availability of communicationchannelsforeachcommunicationinter faceonthe mobilecomputer. Dynamicprobingtechniquesareus edtofind newchannelsandmaintaininformationaboutexistin gchannels. Second,theframeworkprobesidleavailablechannel sfor information about channel parameters such as available

bandwidthandpropagationdelay. Informationabout active channelsiscollectedfromtheprotocolsusingthem The . framework continues monitoring dynamically, providi ng informationaboutavailableandactiveinterfacest ointerested protocolsuchasMMTP. Thiscommunicationframewor kis currentlybeingdesignedinconjunctionwiththepr otocolsthat willbeusingit. Thedetailsoftheframeworkare beyondthe scope othis f paper.

4.2 Data Characteristics Multimediadatastreamscanbge eneratedonthefly attherateat whichtheyneedtobeplayedoutorretrievedfors torage. Applicationsusingon-the-flystreamsoftenhaveve rylittle tolerancefordelay,whileapplicationsusingstore dmediamaybe moretolerant.Inaddition,fortheformer,frames areonly accessiblefortransmissionastheyaregenerated, whileinthe later,allframeareaccessibleatthesametime.F ramesfrom multimediadatastreamsoftenexceedthemaximumtr ansmission sizeandmustbefragmentedintomultiplepackets. Intelligent fragmentationcanbedonethatenablesthereceptio nand processingopieces f of the frame,evenithe f enti re frame doesnot arrive,supportingtheconceptoaf pplicationlevel framing [17]. Intherestofthispaper,wediscussMMTPinthec ontextofonthe-fly data withone packetper frame.

t andframe1attime +1/frameRate t InF.igure1tahe firstframe wassentonthechannelwithlongestpropagationde lay,so playoutcanstartasoonasframe0isreceived,s inceweknow thatframe1willhavearrivedattheendofframe 0playperiod. Ifpropagationdelaysotfhetwochannelsarevery different,itis possiblethatframe1willarrivebeforeframe0. Inthissituation, webufferframe1andstillbeginplayoutuponrece iptofframe0. InFigure1b,frame0arrivesfirst,butplayoutmu stbedelayed untilwearewithinoneplayperiodofthereceipt offrame1or , elsetheremaybeagapattheendoftheplayouto frame0. BecauseMMTPusesestimationforboth available bandwidth and propagationdelay i,tisdifficulttoimplementoption2,since initialdelay dependsdirectlyontheestimatedvaluefor propagationdelay inbothchannels.Sendingthefirstpacketon thechannelwithlongestpropagationdelayallowst heplayoutto be self-clocked

Time

t0 Frame rate

sender

4.3 StartupBehavior

receiver

Onstartup,theapplicationdefinestherequested framerate The . protocolqueriesthecommunicationframeworktolea rnthe numberofavailablechannels,andanestimateoth f e propagation delayand packetrate foreach.Toseeitfherequired framerate canbemet,theprotocolcalculatestheavailablea ggregated channelrate.There are twocases: 1.

Frame rate > o

2.



Prop delay 1

packetrate(i)

theapplicationisnotifiedthatpackets willbedropped.Theapplicationmay decidetoabortthetransmission,to change the frame rate or justcontinue.

Frame rate