Intermittently Connected Mobile Ad Hoc Networks: from Routing to Content Distribution PDF
Preview Intermittently Connected Mobile Ad Hoc Networks: from Routing to Content Distribution
SpringerBriefs in Computer Science Forfurthervolumes: http://www.springer.com/series/10028 Abbas Jamalipour • Yaozhou Ma Intermittently Connected Mobile Ad Hoc Networks from routing to content distribution foreword by H. Vincent Poor Abbas Jamalipour Yaozhou Ma The University of Sydney The University of Sydney School of Electrical and School of Electrical and Information Engineering Information Engineering Sydney New South Wales Sydney New South Wales Australia Australia [email protected] [email protected] ISSN2191-5768 e-ISSN2191-5776 ISBN978-1-4614-1571-8 e-ISBN978-1-4614-1572-5 DOI10.1007/978-1-4614-1572-5 Springer New York Dordrecht Heidelberg London Library of Congress Control Number: 2011939060 © The Author(s) 2011 All rights reserved. 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Foreword Wirelessnetworkingisoneofthemostadvancedandrapidlyadvancingtechnolo- giesofourtime.Themodernwirelesserahasproducedanarrayoftechnologiesof tremendous economic and social value and almost ubiquitous market penetration. Many of these technologies, such as mobile phones and WiFi networks, are based onso-calledinfrastructurenetworks,inwhichinformationistransferredwirelessly betweenanend-user’sdeviceandanaccesspointtoabackbonenetworkhavinga hierarchical control structure to manage information flow in the network. A more recentlyemergingnetworkstructureisthatofanadhocnetwork,inwhichend-user terminalscommunicatedirectlywithoneanotherinapeer-to-peerfashionwithout thebenefitofacontrolstructureprovidedbynetworkinfrastructure.Suchnetworks areoftenformedinanadhocfashion(hencetheirname)ascommunicatingdevices appear in somewhat random locations. This type of structure presents new chal- lengesinsupportingefficientinformationflow,asprotocolstypicallymustrelyon information forwarding through multiple intermediate devices, each of which acts autonomously, to deliver messages from source to destination. These challenges become even greater when the devices are moving, as the network topology then becomesdynamic.Evenfurtherchallengesariseduetothefactthatcontinuousend- to-endconnectivitycannotbeguaranteedinsuchnetworks,openinguptheissuesof what types of information content can be practically transferred through such net- worksandhowthiscanbestbeaccomplished.Theselatterissuesarethesubjectof thisexcellentmonograph,whichcollectsforthefirsttimeinbookformtheconsid- erablerecentresearchdedicatedtothisimportantemergingtopic,muchofitbythe authorsthemselves.Applicationsinvolvingsuchintermittentlyconnectedmobilead hocnetworks,orICMANs,arecertaintomultiplyinthecomingyearsasthetech- nicalsophisticationandgeographicalspreadofend-userdevicesincrease,andthus thisworkbytwoleadingcontributorstothefieldshouldbeofconsiderableinterest totheresearchersandengineerslookingtodevelopthenextgenerationsofwireless networkingtechnologies. Princeton,NewJersey,August2011 H.VincentPoor vii Preface MobileAdHocNetworks(MANETs)havechangedtheclassicalcentralizedwire- lessnetworktopologyintoawhole newdomainwithmanypotentialapplications. WhilemilitaryapplicationsoftheMANEThavebeenunderstoodforsometime,re- searchoncivilapplicationsoftheMANETshavebecomeoneofthemostimportant topicsamongtelecomengineersjustinthebeginningofthiscentury. In general, MANETs are the networks that are formed dynamically by an au- tonomoussetofmobilenodesconnectedthroughwirelesslinkswithoutrelyingon anypre-configuredinfrastructureoracentralbasestation.Thesenodesdynamically create the network connectivity through a temporary network topology, allowing them to seamlessly communicate with one another in areas with no pre-existing communicationinfrastructure.Owingtotheself-configurationnatureofMANETs where connectivity between peer end-terminals can be established automatically without any pre-configured infrastructure, data transfer is carried out through the cooperationamongintermediatenodesovermulti-hoproutingpaths.However,one ofthekeyassumptionsforsucharoutingapproach,namelytheexistenceofanend- to-end routing path, becomes untenable in cases where the network experiences intermittentconnectivityduetolimitedtransmissionrange,sporadicnodedensities, power limitations, and so on. To administer information tracking and data deliv- erycapabilityinfosteringserviceimprovementintheemergencyresponseandthe eHealthsector,aswellaspervasivecomputinginruralareas,itisnecessarytode- velopasupplementaldatadisseminationframeworkbasedonopportunisticdelivery probability.Infact,ifthedeliverydelaycanbetolerated,thennodemobilitycanbe exploitedtodeliverselectedmessagestothedestination.Obviously,theseso-called store-carry-forward (SCF) techniques incur considerable signaling overhead to in- cludemessagesummariesandmeetingprobabilities,resultinginthedegradationof networkefficiency. Based on the above concept, a new subset of MANETs, called Intermittently Connected Mobile Ad Hoc Networks (ICMANs) could be created. By consider- ingthenatureofintermittentconnectivityinmostrealworldmobileenvironments withoutanyrestrictionsplacedonusers’behavior,ICMANsareeventuallyformed withoutanyassumptionabouttheexistenceofanend-to-endpathbetweenanypair ix x Preface of nodes who are wishing to communicate. It is different from the conventional MANETs, which have been implicitly viewed as a connected graph with estab- lishedcompletepathsbetweeneverypairofnodes.FortheconventionalMANETs, mobilityofnodesisconsideredasachallengeandneedstobehandledproperlyto enableseamlesscommunicationbetweennodes.However,toovercomeintermittent connectivityintheICMANscontext,mobilityisrecognizedasacriticalcomponent fordatacommunicationsbetweenthenodesthatmayneverbepartofthesamecon- nectedportionofthenetwork.Thiscomesatthecostofadditionalandconsiderable delayindataforwarding,sincedataareoftenstoredandcarriedbytheintermediate nodeswaitingforthemobilitytogeneratethenextforwardingopportunitythatcan probably take the data packet close to the destination. Such incurred large delays primarilylimitICMANstotheapplications,whichmusttoleratedelaysbeyondtra- ditionalforwardingdelays.ICMANsbelongtothefamilyofdelaytolerantnetworks (DTNs).However,theiruniquecharacteristics(e.g.,self-organizing,randommobil- ityandadhocbasedconnection)derivedfromMANETsdistinguishICMANsfrom othertypicalDTNssuchasinterplanetarynetwork(IPN)withinfrastructure-based architecture. By allowing mobile nodes to connect and disconnect based on their behaviors and wills, ICMANs enable a number of novel applications to become possible in thefieldofMANETs.Forexample,thereisagrowingdemandforefficientarchitec- turesfor deployingopportunisticcontent distributionsystemsoverICMANs.This isbecausealargenumberofsmarthandhelddeviceswithpowerfulfunctionsenable mobile users to utilize low cost wireless connectivity such as Bluetooth and IEEE 802.11forsharingandexchangingthemultimediacontentsanytimeanywhere.Note thatsuchphenomenalgrowthofcontent-richserviceshaspromotedanewkindof networkingwherethecontentisdeliveredfromitssource(referredtoaspublisher) towardsinterestedusers(referredtoassubscribers)ratherthantowardspre-specified destinations. Comparing to the extensive research activities relating to the routing andforwardingissuesinMANETsandevenDTNs,opportunisticcontentdistribu- tionbasedonICMANisjustinitsearlystageandhasnotbeenwidelyaddressed. Thisbookcoverstheresultsofresearchcarriedoutbytheauthorsonthetopicof ICMAN.Thisbookprovidesanin-depthdiscussiononthelatestresearcheffortsfor opportunistic content distribution over ICMANs. The discussion begins by intro- ducingICMANs,DTNs,andthemostnotableforwardingandroutingtechnologies (e.g., epidemic routing and its variations, cluster-based routings and super-node- based routings). Chapter 1 also briefly discusses the mobility impact on routing performance; an important factor used in enabling packet routing in the network. Chapter 2 explains various forms of opportunistic content distributions over IC- MANs. It gives details about some proposed optimizing solutions by considering the mobility characteristics of the nodes. The idea of cooperation is further em- ployedtoallowtheencounteringnodestoworktogetherforcarryingoutthecoop- erativedecision-makingstrategieswhenthenetworkresourcesbecomeconstrained. Apartfromdesigningforwardingstrategiestodeliverthecontentfromitspublisher to their interested subscribers, content search or content lookup is another funda- mental problem that determines the architecture and performance of opportunistic
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