vechicular mesh network using mobile milleu

8/2/2019 Vechicular Mesh Network Using Mobile Milleu

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VECHICULAR MESH NETWORK USING MOBILE MILLEU

BY D.MONISHA and K RAJAKUMARI.UNIVERSITY COLLEGE OF ENGINEERING VILLUPURAM

A B S T R A C T:

The first DARPA experiment with wirelessmobile Internet the Packet Radio Networkor PRNET was completely independent ofthe infrastructure. This model was consistentwith DARPA military goals as the PRNETwas designed to support tactical operationsfar away from any wired infrastructure.Beside autonomy, the main challenge wasmobility and radio portability. Scarcity of

spectrum was not an issue, in contrast withthe ARPANET quest to utilize those 50 kbpsTelpak trunks more efficiently. Today, theclosest civilian descendents of the PRNETare vehicular networks and smart phonebased Personal Area Networks. In eithercase, the wired infrastructure turns out toplay a major role. Moreover, spectrumscarcity has now become the most importantchallenge (while, ironically, the wiredInternet has plenty of bandwidth). In this

paper we examine this interplay betweenwired and wireless and extract a message forthe design of a more efficient FutureWireless Internet. We focus on the vehicularnetwork since this field is better establishedand commercially more viable than that ofpersonal, P2P communications amongSmartphones. We are confident however thatmany of our observations will transfer alsoto smart phone/ infrastructure synergy.Specifically, in this paperweidentify the

urban Internet infrastructure role in thesupport of emerging vehicular applicationsand identify the Core Internet servicesmatching the services in the vehicle grid. Asthe vehicular applications range from e-mailand voice over IP to emergency operations(natural disaster, terrorist attack, etc.), thetype of assistance requested from the

infrastructure will vary. A short list includes:(a) addressing (e.g. geoaddressing); (b)directory service, service discovery, mobilitymanagement; (c) resource and congestionmanagement; (d) path redundancy; (e) delaytolerant operations; (f) mobile sensor dataaccess and search from the internet, and; (g)anonymity, privacy and incentives. After thereview of vehicular applications andproperties, we will offer an Internet historyperspective to help understand how the

mobile wireless network field has evolvedfrom the early ARPANET and PRNET days.Thiswill reveal trends that can help predictthe future of the wireless Internet.

1. INTRODUCTION:

Vehicle communications are becomingincreasingly popular, propelled bynavigation safety requirements and by theinvestments of car manufacturers and Public

Transport Authorities. The essential vehiclegrid components (radios, Access Points,spectrum, standards, etc.) are coming intoplace finalizing the concept of VANET(Vehicular Adhoc Network) and paving theway to unlimited opportunities for car-to-carapplications. Safe navigation has nowbecome an important priority for CarManufacturers as well as MunicipalTransportation Authorities. New standardsare emerging (DSRC and more recently

IEEE 802.11p) and several InternationalConsortia and well publicized testbeds wererecently established to promote trajectory ofthese emerging applications. We seek topredict how the VANET will evolve in thefuture and, at the same time, to explain howwe got here as this will help corroborate ourpredictions. Our specific interest is to


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examine the role of the Internetinfrastructure in supporting vehicularapplications. As a difference from typicalMANETs (Mobile Ad hoc Net works), in theVANET the Wired Internet infrastructure is

omnipresent and readilyaccessible via WiFi, DSRC, WiMAX, 3G,LTE, etc. The wired Internet support willvary depending on the vehicular application.During a Katrina type emergency, the wiredinfrastructure is likely to be destroyed andthe VANET cannot count on it it mustoperate autonomously. This is the closest weget to a pure MANET. For content sharing(e.g., advertisements, entertainment)applications, however, the vehicle relies on

Internet access to download files fromInternet Servers. Peer to peer,opportunistic networking among vehicleswill be used to distribute the file only aftersome vehicle has downloaded from theInternet. In fact, in the future, considerablecontent will be played on mobile terminals(vehicle screens or pedestrian phones). It isthus important to understand how the wiredInternet can best accommodate the newrequirements and networking styles (e.g.,P2P dissemination, geo-routing) introducedby the mobile applications at the edge.The business as usual solution of treatingmobile, wireless networks as appendagesattached via edge gateways and to delegateall interface functions and services to theedge is becoming non economical. There arebenefits in extending the services to theInternet backbone itself using meshnetworks, overlays and virtualization. Weenvision that the emerging mobilenetworking will impact the future Internetdesign in the following areas: (a) addressing(e.g. geo-addressing); (b) directory servicesupport and service discovery; (c) resourceand congestion management; (d) pathredundancy and network coding; (e) delaytolerant operations support; (f) mobilesensor data access and search from the

Internet (g) anonymity, privacy andincentives. The following sections reviewrelated work and then describe two researchdirections, namely: (1) emergingapplications and (2) vehicle oriented Internet

services. Representative vehicularapplications have been selected to illustratehow mobile services can be extended intothe Internet core, beyond edge gateways, asa first step towards the design of a fullfledged mobile vehicular architecture. Inparticular, since mobility plays a key role invehicular protocol design and performance,an important effort must go into thedevelopment of realistic motion models.

2. RELATED WORK:

Much of the existing literature on Inter-Vehicle Communications (IVCs) isnavigation safety related. A good surveyof recent physical layer technologies forIVCs can be found in [18]. For scalabledelivery, researchers have proposed geo-routing and further, have focused onexploiting innate characteristics of vehicularnetworks such as high, but restrictedmobility. For example, Urban Multi-hopBroadcast (UMB) [14] features a form ofredundant flood suppression where thefurthest node in the broadcast direction froma sender is selected to forward andacknowledge the packet. In [39], vehiclescollect only the information relative to agiven locality (i.e., a road segment); thepaper further investigates the influence ofbroadcast rate on data propagation takingmobility into account and adapting the rateto traffic conditions. In this field, we haveproposed a scheme by which each vehicleis able to estimate its transmission range andput it to good use to reduce redundanttransmissions. As a result, broadcastingtraffic and delays are reduced thus allowingefficient delivery of, for instance, alertmessages for traffic safety applications.


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Geo-routing has been extensivelyinvestigated. A critical issue is the relaxingof beacon message requirements toeliminate the associated overhead. Fler etal has proposed Contention-Based

Forwarding (CBF). This scheme does notrequire proactive transmission of beaconmessages for current locationadvertisements; instead, data packets arebroadcast to all direct neighbors and theneighbors themselves decide if they shouldforward the packet based on a distributedtimer-based contention process. A similarapproach has been proposed by Zorzi inGeRAF exploiting staggered MAC inter-segment intervals. In, the authors have

proposed a set of knowledge-basedopportunistic forwarding protocols that usegeographic information such as motionvectors. Zhao and Cao propose to reducethe delay to a known destination throughmobility prediction. Geocasting serviceshave been proposed to disseminate messagesto all nodes within a target region. MDDVaims to support geocast by forwarding apacket along a predefined trajectorygeographically. It works even withintermittent connection; intermediatevehicles must buffer and forward messagesopportunistically, exploiting mobility.Abiding Geocast features a lifetimeconstraint; namely, it restricts the delivery ofmessages to all the nodes that are in thegeocast region sometime during thegeocast lifetime. At the applications level,several cooperative peer to peer typeschemes have been proposed. TrafficViewdisseminates (through flooding) and gathersinformation about the vehicles on the road,thus providing real-time road trafficinformation to drivers. To alleviatebroadcast storms, this work has focused ondata aggregation based on distance from thesource. EZCab is a cab booking applicationthat discovers and books free cabs through

vehicle multi-hopping. Free cabs arediscovered with probabilistic flood search(static or decreasing probability as hop countincreases). After discovery, georouting isused to negotiate the fare etc. has proposed

an opportunistic resource discovery protocolwith a finite-buffer space model. Theresource is a spatio-temporal resource, e.g.,the availability of parking in a parking lot. Avehicle either senses the resources orobtains new resources from passingvehicles. Nodes exchange local databasesand each keeps a fixed number (the size ofbuffer) of relevant resources. In PeopleNet ,a wireless virtual social network is used tosupport searching for spatio-temporal

information, exchanging resources byrandom swapping. 458 M. Gerla, L.Kleinrock / Computer Networks 55 (2011)457469 Vehicular Information TransferProtocol (VITP) provides on-demand,location-based, traffic-oriented services todrivers using information retrieved fromvehicular sensors. A user location-awarequery is forwarded to the target locationwhere virtual ad hoc servers (VAHS), i.e.,collection of private vehicles, resolve thequery. Content sharing in MANETs as wellas VANET mainly involves cross-layeroptimization of Internet-based protocols.Most protocols have been designed toovercome the discrepancy between a logicaloverlay and a physical topology of mobilenodes. XL-Gnutellamaps the logical overlayneighbors to physical neighbors. The UCLAgroup has proposed CarTorrent, a BitTorrentstyle content sharing protocol in wirelessnetworks. It uses a proximity-driven pieceselection strategy that has proven better thanthe rarest first piece selection.We havedesigned CodeTorrent to provide aBitTorrent style content distribution withnetwork coding .To stimulate cooperationamong selfish nodes in mobile ad hocnetworks, incentives have been proposed.Yet, abuse and forgery must be prevented.


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For example, with the assumption oftamper-proof hardware on board, eachrelaying node earns some virtual credit thatis protected by the tamper-proof hardware.Other secure incentive approaches make

use of reputation-based schemes.Uncooperative nodes are detected andisolated. Researchers have investigated suchnon-cooperative communication scenarioswithin a game theory framework. Bymanipulating the parameters (e.g. theamount of gain per forwarding, thedesignation of charging subject, etc.), thoseschemes encourage cooperative behavioramong selfish nodes. However, as pointedout in , if poorly implemented in practice,

these incentive schemes themselves have thepotential to backfire by offering an incentiveto cheat the system in order to gain furtherbenefits. The advantages of using theinfrastructure to enhance the per nodethroughput capacity of an ad hoc networkare well documented in. The asymptoticcapacity is found to be H(pNlogN)-foldbetter than in a flat ad hoc network, mainlydue to the fact that relaying over APseffectively reduces the mean number of hopsfrom source to destination. Most proposedhybrid (infrastructure + ad hoc) networksare to provide extended coverage of existingservices, e.g., wireless LAN and 3G. Re-routing AODV packets over theinfrastructure has been proposed. However,flooding of RREQ packets over APs doesnot scale as the number of mobile nodes andAPs increases. To overcome this problem,an Overlay Location Service (OLS) can beused, which maintains geographic locationsof APs and mobile nodes, and allows mobilenodes to efficiently utilize geo-routing notonly over the vehicular grid but also overthe Internet. In addition, OLS provides aglobal view of AP congestion levels, thusleveraging efficient use of communicationresources. A wide range of emerging urbanmonitoring applications are clear proof of

growing interest in the field. Intel ResearchIrisNet provides large-scale monitoringbased on Internet-connected PCs equippedwith off-the-shelf cameras and microphones.IrisNet also supports urban monitoring

through a group of agents that collect andprocess raw data to answer queries relevantof the application: for instance, camera datais processed to track available parking in ametropolitan area. CarTel is a distributedmobile sensor computing system. It iscomposed of intermittently connecteddatabase (ICEDB) and carry-and-forwardnetwork (CafNet). ICEDB is installed inboth clients (mobile user side) and a server(portal), allowing users to send queries.

Queries are then sent to mobile users viaCafNet. Clients then resolve the query andreturn the results to the server. ICEDBextends SQL queries to support user friendlyinterface to a portal and provide efficientmanagement of sensing devices. Our Teamhas proposed MobEyes a distributedproactive urban monitoring solution.Vehicles sense events, process sensed dataand opportunistically diffuse meta-data byexploiting vehicles mobility. As wementioned earlier, safe navigation andintelligent transport have now becomeimportant priorities for Car Manufacturersas well as Municipal TransportationAuthorities. VANET research is moving outof academia and is now carried out in manynational and international projects that bringtogether government, industry, andacademia. These projects have broad reachand go beyond fundamental research toaddress also development, standardization,field trials and commercialization. Amongthe on going programs that address safe andefficient driving we mention the eSafetyframework of the European Union, theIntellidrive initiative in the US, Smartway,DSSS (Driving Safety Support System) andASV (Advanced Safety Vehicle) in Japan,simTD in Germany and SCOREF in France.


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Standardization is well under way with theactivities worldwide in ISO TC204 andIEEE (802.11p and 1609.x), SAE J2735 inthe US, ETSI TC ITS and CEN WG278 inEurope and ARIB T-75 in Japan.

The European Union recently has been veryactive in this field, sponsoring severalprojects that deal with the vehicularenvironment, like CVIS (for the vehicularnetwork architecture definition), Coopers(for the cooperative systems potential forroad safety), Geo-Net (for geoaddressingand routing), PRE-DRIVE C2X (for theapplications support and V2V and V2I proofof concept as core technologies for fieldoperating tests), iTETRIS (for the modeling

and simulation), Sevecom and Preciosa(about security architecture and privacy),EVITA (about the invehicle tamper-proofnetwork architecture modules) just tomention a few of the most recent (and stillongoing) projects touching the themes ofthis paper.

3. VEHICULAR APPLICATIONS ANDINTERNET REQUIREMENTS:

Vehicles in a grid are only a few hops awayfrom the infrastructure (WiFi, cellular,satellite, etc.). Protocol and applicationdesign must account for easy access to theInternet during normal operation. At thesame time, the vehicles are among the fewcommunications nodes that can continue tooperate when the Internet goes away, duringurban emergency, with enough reservepower to establish a vehicle basedemergency network. To this end we examineinnovative peer to peer content sharingapplications that can still operate withintermittent connectivity and sporadicvehicular traffic and connectivity. Peer toM. Gerla, L. Kleinrock / ComputerNetworks 55 (2011) 457469 459 peerapplications have so far been confined to thefixed Internet (e.g., BitTorrent, etc.). The

storage and processing capacity of modernvehicles make such applications feasiblealso on mobile platforms. In these dynamicscenarios we must understand the role of theInternet in facilitating the smooth transition

from full Internet connectivity to fullautonomy. This is a radical concept in adhoc networks traditionally designed forexclusively autonomous operation and thusunable to exploit the interconnection andresource sharing of the wired Internet. In thesequel, we consider a number of emergingVANET applications and study theirinterdependence with the Internet.

3.1.CONTENT DOWNLOADING:

Probably the application that best illustratesthe interaction between wired Internet andvehicle grid is peer to peer contentdistribution. Beyond conventional filedownloads from the Internet (i.e., movies,IPTV), the drivers in the vehicular grid areinterested in access to location dependentand aware content. This includes not onlydelay-sensitive content (e.g., emergency-related video streaming), but also delay-tolerant content, namely proximityadvertising and marketing segments (e.g.,movie clips from the nearby theaters.Roadside access points (e.g., at gasolinestations), or digital billboards are used forthis purpose. Limited availability of accesspoints and/or limited AP capacity encouragethe mobile users to cooperatively assemblethe file through BitTorrent-style, P2P filesharing (Fig. 1). A file is divided into piecesand missing pieces are pulled whenavailable from the neighborhood (say up toK hop deep). The car then selects the bestpeer for download. Simulation experimentsin show that the best strategy combinescloseness and rarity of the piece (whileBitTorrent generally selects the rarestpiece). This however involves quite a bit ofoverhead, namely, peer selection (from


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several responses) is followed by TCPtransfer of the pieces (typically, with severalretransmissions).An architectural feature that canconsiderably enhance P2P content sharing is

network coding. One immediate advantageis the relaxation of the piece selection (i.e.coupon collection) problem, a criticalissue at the end of the download. Accesspoints generate/distribute coded pieces thatare random linear combinations of theoriginal pieces, and the intermediate nodesfurther mix coded pieces in their buffers.Assuming that each piece is exactly onepacket long, a prefix in the packet tells theweights of the linear combination. If the

receiver does not have enough packets toinvert the matrix and recover the file(e.g., some packets may have been lost), itsimply requests more random combinationsfrom neighbors, as opposed to requestingspecific packets. The network codingscheme offers several advantages. Itdrastically reduces the number of messagerequests (seeking a specific piece) and thusthe overhead. No TCP is required, just UDP.In fact, TCP will not work with multiplesimultaneous sources. Simulation results inconfirm that routing overhead in highlymobile/dense network like VANET, isprohibitive, and thus, UDP-based single-hop pulling outperforms TCP-basedmulti-hop pulling. Network coding forP2P sharing has been proposed also for thewired network (e.g. Avalanche file sharingby Microsoft). The role of the Internetbecomes clear if one considers that, whenvehicles download real time streams, theymay download from several different APs.Each AP must provide a coded streamconsistent with the others. To this end, thetorrent coordinator in the Internet mustanticipate which APs must be served andwith what generations. Another enhancerof vehicu- Fig. 1. Car Torrent. 460 M. Gerla,L. Kleinrock / Computer Networks 55

(2011) 457469 lar content sharing isparallel downloading. Suppose vehicles onthe freeway can download with GPRS, attop speed = 100 kbps. This gives very poorvideo quality. However, if users team up,

and the Internet server uses multiresolutioncodes, vehicles in a neighborhood canexchange packets and combine the multiplestreams with quasi linear performanceimprovement with respect to a single stream.These are all examples of architecturalchoices (Network Coding andMultiresolution Codes) that tie togethervehicles and infrastructure.

Car Torrent

3.2. P2P LOCATION SIGNIFICANTADVERTISING:

Another application that benefits frommultiple neighbors downloading is AdTorrent. Say, a driver needs to downloadpreviews of movies are playing in aparticular neighborhood. And, the samedriver wants to dine at an Italian restaurantafter the movie. Videoclips, menus,restaurant reviews and addresses must beacquired within tight latency constraints.Driving up to an access point each time istoo time consuming and traffic congestionprone. Multihop downloading from a remoteaccess point or from LTE is not practical dueto wireless TCP limitations. It may alsocreate excessive data traffic overload on thesystem. As an alternative, in Ad Torrent theaccess point feeds passing cars withrandomly selected ad segments. Next,


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each car probabilistically disseminates thepieces using an epidemic (gossip) scheme(we later review the effectiveness ofepidemic dissemination in the vehicularcontext). As a result the neighborhood

becomes populated with ads. Again, thereare different neighbor download strategies.One method is to query the neighborhoodand selectively download pages that satisfymulti-value queries using Bloom Filters.Another approach is to solicit networkcoding downloads from neighbors ofwhatever pieces, they have, that are useful tothe driver. The main difference from CarTorrent is that Ad Torrent epidemicallydisseminates segments (to increase the hit

ratio of even not so popular files); also, itdownloads from 3rd party peers who arenot trying to assemble the informationthemselves. This may have impact on tit-for-tat incentives bookkeeping. Again, theInternet plays an important role; forexample, the APs will deliver the Ads thatare most popular in the area. The learningmust be coordinated in the Internet serverssince the individual vehicle interests areephemeral.

a. P2P (DRIVER TO DRIVER)INTERACTION:

There is also content that is generated andconsumed entirely in the vehicle grid. Agood example is content and messagesrelated to navigation safety. Suppose that acritical traffic/safety situation occurs on ahighway, e.g., major traffic congestion,weather condition, natural or manmadedisaster or even hostile attack. In such cases,multimedia content, say, video, could bestreamed from one or more lead cars to thevehicles following several miles behind tovisually inform them of the problem.This will allow them to make a betterinformed decision (say, whether they shouldturn around) than if they simply got an alarmtext message. Conventional ad hoc broadcast

(e.g., via ODMRP or MAODV) mayintroduce excessive loss in intermittentconnectivity and severely impair videoreception. In the intermittent situationnetwork coding can greatly enhance stream

reliability. Ad hoc Network Codedbroadcast, CodeCast, improves deliveryratio as compared to ODMRP reducing atthe same time the overhead.vehicular communications and demonstratetheir feasibility and effectiveness. In thispaper, we look at the likely

Network Coding

Vehicular networks are emerging as

important sensor platforms, for example forproactive urban monitoring and for sharingand disseminating data of common interest.Each vehicle can sense one or more events(e.g., imaging from streets and detectingtoxic chemicals), process sensed data (e.g.,recognizing license plates), and routemessages to other vehicles (e.g., diffusingrelevant notification to drivers or policeagents). Vehicles can generate much largervolumes of data than traditional sensor

networks.They can also store the data, instead ofperiodically reporting it to sinks. Buildingupon previously proposed techniques forepidemic information dissemination inmobile ad hoc networks with pedestrianmobility, a lightweight strategy for proactiveurban monitoring is proposed in MobEyes.


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The basic idea is to exploit vehicle mobilityand wireless broadcast to opportunisticallydiffuse concise summaries (meta-data) of thedata stored in cars. The data can beharvested by agents for forensic

investigation. It is discarded after timeout.The use of MobEyes is not limited tovehicular sensors. It can be adapted toembrace sensors embedded in theenvironments (e.g., fixed video and roadsensors, etc.), or in the human body (e.g.,pedestrians with medical sensors).Interestingly, these types of sensors areassociated with the infrastructure. Forinstance, video cameras installed in theintersections are connected to Police

Headquarters via private wire connections.Medical sensors, e.g., ECG probes, requireinteraction with the attending physician incase of emergency and exchange messagesvia the cellular network through the smartphone. An emerging area of research is theseamless integration of heterogeneoussensing environments. This integration mustaddress issues such as applicationconstraints (e.g., latency, coherency ofobservations, etc.), infrastructure support(deployment of fixed sensors, Internetconnectivity), mobility patterns (e.g., groupmobility or individual mobility),compatibility of different radio technologies(e.g., WiFi, ZigBee, Bluetooth), etc. Inaddition, alternative indexing schemes mustbe explored between the two extremes ofmetadata uploading to the Internet Server orepidemic dissemination. We envisionhierarchical schemes that combineepidemically generated indexes with higherlevel structured indices (e.g., GHT [36] andDHT [57]), some of which will be stored inthe Internet infrastructure (Fig. 3).

4. NETWORK AND INTERNETSERVICES:

4.1 ROUTABLE ADDRESSES ANDPOSITION BASED ADDRESSING:

Addressing is a major challenge in themanagement of vehicular network mobility

and an important enabler of interconnectionto and through the Internet. First, we mustdistinguish between Unique Identifier (e.g.,license plate#; Vehicle-ID#), and; RoutableAddress (geo-coordinates, or; unique ID(typically IP address) for conventionalrouting, e.g. AODV). It is becomingapparent that the dominant form of routingin the vehicle grid will be position basedrouting (e.g., geo-routing). This is becauseof the emergence of location aware

communications, i.e., the need to establishconnections and route packets to entities andresources characterized by location ratherthan a specific ID. More traditional MANETrouting schemes, e.g. AODV and OLSR,will also be used in the vehicle grid. Theseschemes currently use IP address as theroutable address to set up/maintain theroutes. The IP address is an extremelyeffective routable address in the static,hierarchical Inter-

Urban Sensing

net structure (enabling, for example, prefixrouting etc.). It is not very helpful in finding(hierarchical) routes in a constantly


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changing network like the vehicle gridunless it is combined with the Mobile IPconstruct, with provides the desiredredirection. Mobile IP is fine for movablenodes (like laptops), but it does not scale

well in very dynamic population likevehicles. Still, IP is widely used as identifierin AODV routing and it is required by mostInternet upper layer protocols like forinstance TCP. For these reasons, it isimportant to maintain in the vehicle grid aunique IP address for cars, to avoidcollisions in TCP connections and routingmishaps in AODV. There have been manyproposals for enforcing unique IP addressesin MANETs. A prominent example is the IP

address auto-configuration of nodes.However, auto-configuration of IPaddresses, such that the assignment isunique, requires some extra work in thevehicle grid scenario. ConventionalMANET solutions cannot be directlyapplied due to the high density of nodes;high absolute speed (2080 mph) (but, lowrelative speed with respect to other carstraveling in the same direction (320 mph));and practically unbounded network diameter(hundreds of thousands of cars). Onepossible solution is to implement a leaderbased approach. Leader approachesgenerally use a hierarchical structure toconfigure nodes and perform the DAD(Duplicate Address Detection) procedureonly within a cluster. A recent solution thatis more directly inspired to vehicular trafficenvisions leaders proactively organized in achain (in the same direction of traffic alonga highway, say) and operating like DHCPservers to assign (and manage) unique IPaddresses to vehicles within their range.Moreover, they maintain uniqueness notonly in their cluster but also in the entirechain, exploiting the low relative speed andlong contact time of vehicles in the samechain moving in the same direction. Thisguarantees higher longevity than traditional

leader schemes. After solving the unique IPaddress issue, one must focus on routableaddress selection. The goal is efficientpacket delivery between cars in thevehicular grid as well as between Internet

Servers and mobile vehicles. The routableaddress clearly goes hand in hand with therouting strategy. Geo-routing fits the bill.With adequate architecture support, geo-routing takes a packet all the way to theneighborhood of the target destination.From that point, the receiver uniqueidentifies (e.g. IP address) carried in thepacket header will enable correct delivery.To accomplish the delivery to theneighborhood, the source must know

with a reasonable accuracy the location ofthe destination. A critical component of thegeo-routing address structure is the GeoLocation Service (GLS) - a distributedservice that maps a vehicle name to the setof most recent geo locations. If the VANETmust be capable to operate autonomously inemergency mode, there must be seamlesstransition from infrastructure supportedmode to autonomous mode. A possiblesolution is to implement two parallelversions of GLS, namely: OLS (OverlayLocation Service) and VLS (Vehicle GridLocation Service). OLS is maintained withinthe Internet infrastructure with overlaytechnology; VLS is maintained entirely inthe vehicle grid, possibly using Geo HashTable (GHT) technology. The two servicesare synchronized, but are independentlymaintained to provide tolerance to totalinfrastructure failures.Let us illustrate a possible OLSimplementation. An overlay structure isestablished in the urban Internet. Each car,whenever it passes by an AP, registers its ID(license#, IP address(es), time, owner name,owner IP address billing address, etc.) andthe current geo-location. OLS maintains anindex of IDs mapped to geo coordinates.The index is managed via DHT (Distributed


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Hash Tables). Suppose now Host A (fixed ormobile) wants to establish a TCP connectionto mobile Host B. Host A first queries OLSwith the unique car ID, say:[email protected] starting from the

nearest server of the OLS overlay. Afterproper authentication of the query by OLSand verification that this request isauthorized by the receiver, Host A gets backthe mostrecent geo-locations, the IP address, etc. ofVehicle B. It then extrapolates from pastlocations the future location of B and theaccess point AP nearest to B. Host A sendsthe TCP connection set up message to AP.The message is encapsulated in an IPv6

network envelope that contains the geo-address in the extended header. Routing inthe Overlay is based on geo-addresses.Namely, the geo address defines the AP atthe end of the Internet path. At thedestination, the AP geo-routes the packetthrough the ad hoc net; vehicle B respondswith its own IP address and directs theresponse (encapsulated in the overlayenvelope) to the sender IP. Theencapsulation in the geo routed envelope isidentical regardless whether the sendingHost A is fixed or mobile. Should the urbanInternet infrastructure (or wireless access toit) fail, one must maintain also a VLS totallysupported in the Urban Grid. A considerableamount of research has gone into VLSdesign. The goal is to minimize registrationoverhead while at the same time minimizingthe index search two conflictingrequirements. A possible solution is basedon a hierarchal design. At the lowest level,there is a unique (mobile) server e.g., aCalTran truckthat roams in a cell (1 km _ 1km), periodically advertising its coordinates.Vehicles register locally with the truck. Atthe higher level each vehicle has apermanent Home Agent, say. As the vehiclemoves from one cell to another in the UrbanGrid, it must update the pointer in its home

agent. During normal operations, when theinfrastructure is up, home agent updating isdone through the Internet overlay, at thesame time when the OLS updating takesplace. In disconnected operations, the

Location Service is supported by the cellulartrucks (Fig. 4)

4.2. ROUTING IN THE VEHICULARGRID:In general, the vehicle grid will supportmany routing options simultaneously, theselection depending on the name/addressmap scheme. The prominent scheme,especially to remote destinations, will begeo-routing. Yet geo-routing in vehicular

grids poses research challenges. The firstissue is vulnerability to dead end traps.Vehicle grids are full of such traps. OnceGPSR falls in a trap, the recovery must bedone with time consuming graphplanarization followed by perimeterrouting. One open research issue is toinvestigate schemes that prevent/recoverfrom traps more efficiently thanplanarization.

Routing in the overlayOne option is to use landmark assisted geo-routing (Geo- Lanmar). We can detect if


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geo-routing leads to a trap by comparing theEuclidian distance/direction (i.e., thedirection as the crow flies) with theGeoLanmar advertised distance/direction . Ifthe GeoLanmar distance is substantially

higher, there is a good probability of a deadend and the landmark path is chosen. Thisscheme however carries the overhead ofperiodic GeoLanmar advertising. An optionwithout planarization nor advertisingoverhead is Geo-Cross, where planarizationis NOT performed before perimeter routing.Rather, loops are allowed to occur, and areefficiently detected a posteriori during therouting process.The above protocols forward packets

efficiently when the underlying network isfully connected. However, the dynamicnature of vehicular network, such as vehicledensity, traffic pattern, and radio obstaclescan create temporary disconnections andnetworks partitions. To overcome theseproblems, disruption and delay tolerantgeographic routing solutions such asGeoDTN+Nav must be used. As the nameindicates, GeoDTN+Nav is a delay tolerantextension of geographic routing that exploitsthe on-board navigator. GeoDTN+Nav firstdetermines when the network has becomepartitioned (this is inferred when geo-routing has switched from greedy toperimeter mode and the packet has travelledan unusually large number of hops). With apartitioned network, packet routing isprocessed in DTN mode (i.e., carry andforward). Delivery latency is improved inGeoDTN+Nav by using passing vehiclesVirtual Navigation Information (e.g.,intended destination, direction, trace of theroute covered so far, future route plan, etc.)to select the most appropriate vehicle forpassing the packet to. Moreover, theinformation obtained by neighbor vehiclescarries a certain confidence level. As shownin Fig. 5, the path declared by a public bushas 100% confidence, while the path

announced by a private car is treated with55% confidence. GeoDTN+Nav is anexample of hybrid routing algorithm. It canswitch from conventional greedy geo-routing to delay tolerant routing and back

depending on road density conditions. Thepresence of the infrastructure has again animportant impact on urban routing. In mostcases, one must find a route to the closestAccess Point, to connect to the Internet, orto remote vehicles. In a city with advancedwireless infrastructure deployment, it willtake only a few hops to reach the nearest AP,in day traffic conditions. Routing overthe infrastructure instead of the VehicularGrid to reach remote vehicles will be the

norm. In the previous sections, we haveargued that most vehicularapplications/services must be supported by aroadside infrastructure with robust Internetconnectivity. Navigator based intelligenttransport and content distribution (viaCarTorrent, say) are representativeexamples. Offering an infrastructure that isinstantly available to support vehicles isitself a challenge. Roadside Access Pointsmust be placed in special locations, in clearview of the moving traffic, in contrast toAccess Points designed for smart phoneaccess in shopping centers, pedestrianmalls, bus/train stations, industrialCampuses etc. Ideal AP installations forvehicles are traffic lights, light poles,overpasses and other public structures.Traffic lights in particular are perfectlypositioned to act as traffic routers.

GeoDTN+NAV Selecting the carrier using the

Virtual Navigation Interface (VNI).


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They already form a traffic grid; are locatedwhere traffic is most intense, and; areequipped with power and directlymaintained by local municipalities. Not allthe roadside APs will have direct access to

the Internet, due to cost and physicallimitations. Some APs have not evenelectric power and must be supplied bysolar. This calls for wireless meshconnectivity at the periphery of the fixedinfrastructure. In the sequel we introduceMobiMESH, a mesh architecture thatinterconnects vehicular ad hoc segmentswith the infrastructure to support extendedvehicular applications and services. TheMobiMESH architecture consists of three

main building blocks as shown in Fig. 6.(1) Mesh Backbone: a network ofMobiMESH routers providing routing,mobility management and Internetconnection.(2) Ad hoc network extension, exportingMobiMESH functionalities to mobile nodes.(3) Access network featuring standard WiFiconnectivity.The Mesh Backbone and the ad hocextension operate in ad hoc mode, routing isbased on OLSR with modifications toaccount for multiple radios and link qualitymetrics. The access network operates in theinfrastructure mode and can be accessed bystandard clients with no specific software asif it were an off the shelf WLAN.

MobiMESH network architecture

The routers are the main building block ofMobiMESH. They are responsible for

creating the broadband backhaul, and forproviding access to mobile clients. They areequipped with 2 to 4 radio interfaces to beused interchangeably as backbone or localaccess interfaces. Any radio interface can be

tuned to any available channel in thefrequency bands 2.4 GHz, 5.7 GHz and 5.9GHz (via DSRC). In access routers, one ofthe interfaces is dedicated to WiFi clients.4.3. EMERGENCY ROUTING WHENTHE GRID HAS FAILED:Consider the aftermath of a majorearthquake in Southern California or thedestruction of a Katrina class hurricane inthe Gulf Coast. Power lines are down andelectric service is spotty and intermittent.

The Communications infrastructure (wiredand wireless) is either out of power orheavily congested. Traffic lights do not workand the major traffic arteries have sustainedstructural damage.Emergency medical services cannot becontacted or otherwise cannot reach the siteswith the most essential means. Fire breaksout in several places because of damagedgas pipelines, and firefighters cannot reachthose spots quickly in order to repairdamage and prevent further loss of life. Thisis when the VANET steps in as the ultimateEmergency Network. The VANET continuesto run in spite of natural disasters, and isable to configure itself and route informationusing the available resources. Queries aresent out to the VANET by EmergencyManagement Agencies to gather informationabout vehicle traffic in the city and alsoabout road conditions. The queries are highpriority and are instantly relayed byintermediate vehicles to the entire city.Within seconds, detailed congestion mapsare created and optimal routes are plannedand forwarded to the emergency vehiclesalready on route. If necessary, evacuationroutes are configured to lead unfortunatemotorists to safety.


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The vehicular network also allowsparamedics to inform hospital staff inadvance about injuries and vital signs ofincoming victims. At the same time, hospitalbed availability is relayed to ambulances to

facilitate patient distribution to facilities.Instant, efficient communications are key toa prompt recovery. The VANET plays apivotal role in the recovery as it is alwayson the ready. VANET routing protocolsare designed to work well even withoutinfrastructure. No extra protocols must bebootstrapped for P2P operation.5. HISTORICAL PERSPECTIVES ANDFUTURE TRENDS:At the beginning, in the early 70s, the

Internet (then called ARPANET) and thewireless packet switching counterpart (thePacket Radio NET or PRNET) started ondifferent journeys, with different missions.ARPANET was targeting better trunk lineefficiency and resource sharing of expensivecomputer resources. Over the years, this wasachieved by building an increasinglypowerful backbone with gigabit/s fiber linksand terabit/s routers and ground trunks.PRNET was targeting mobility, portabilityand light weight. The major customer of thePRNET concept was, and still is, theMilitary. Over the years, the tacticalMANETs have become the building block ofthe Network Centric Battlefield, withincreasingly sophisticated radios (SDR andCog Radios); more intelligent, selfconfiguring, robust network architectures,and; total independence from the wiredInternet.In the mid 80s the cellular phone wasinvented and in the late 90s the WirelessLAN was established. These have been themost important commercial successes ofwireless communications since the PRNET.However, architecturally, they are still awireless, one hop extension of the wiredinfrastructure. Peer to peer networking withsmart phones and WiFi laptops has been

limited to research lab experiments. Duringthe past five years, the vehicular network(VANET) has emerged as the truecommercial heir of the PRNET. Peer to peer,ad hoc communications are made possible in

VANETs by the ample supply of power onboard of the vehicle. Moreover, VANETapplications like content distribution andcrash avoidance require P2P exchanges.However, as we have amply illustrated inthis paper, the VANET is not a stand alonenetwork. Rather, it is intimatelydependent on the wired infrastructure for itsapplications (e.g. content) and its services(e.g. security, mobility management, routingamong remote vehicles, etc.). Let us take

another look at the applications we havestudied in this paper:(a) navigation safety applications (e.g., crashprevention, road problem warnings,conditions of the driver, etc.);(b) navigation efficiency (e.g., IntelligentTransport Sys, road congestion avoidance,personalized navigator, pollutionmitigation);(c) entertainment: download multimedia;multiuser games (some also educational);(d) vehicle monitoring (OBD, low Carbonemission, green hybrid vehiclemanagement);(e) urban sensing (congestion, pollution,forensic); also participatory sensing,involving P2P exchanges with other vehicles(e.g., monitoring the density of roadsegments);(f) social networking; proximity andcorrelated motion driven acquisition offriends/peers; blog uploading (e.g., placeswe have seen recently);(g) emergency (e.g., evacuation for Katrinatype disasters);The diligent reader will note that all theabove applications involve a P2P componentside by side with an infrastructure supportcomponent. This interaction betweenwireless P2P communications and wired


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Internet access in VANETs and moregenerally in all mobile networked platformswill be the most important trend to watch forin the Future Wireless Internet. This trendwill be in part influenced by the new

applications that will emerge in future years(a short list is presented above; but, asInternet History has taught us, applicationsare the most difficult thing to predict in thisfield). P2P penetration will also depend onour ability to solve the privacy and securityrisks intrinsic in P2P sharing. There are twomore important factors that will influencethis trend:(1) Spectrum shortage: according to theObama Administration we need 500 Mhz

more to satisfy the emerging wireless dataneeds (experts say we actually need close to800 Mhz more bandwidth)(2) Emergence of Cognitive Radios andFCC white spectrum ruling: new technologyand regulations will give an enormousimpulse to the creation of new wirelessprotocols and architectures (some will beP2P) to reclaim the unused bandwidth.These two factors go hand in hand.Cognitive radios help create moreavailable bandwidth. Some of the solutionsare P2P. For example, in a future urbanscenario we will have LTE (Long TermEvolution) cellular service, with very highbandwidth and broad range, and; WiFi APand Femtocells for high bandwidth withinshorter range. Possibly, WiMAX will also bepresent. In addition, plenty of TV bandwidthwill be available to scavenge when notused.The Cognitive radios will allow the user tobe best connected all the time. Forinstance, in a shopping mall or in an airportlounge LTE will become congested. Theuser cognitive radio will disconnect fromLTE and will rehome to APs or femtocells.If necessary, it will invade unused TVspectrum. Eventually, when all theseresources will become exhausted, Cognitive

radios will seek better spectrum reuse viaP2P, ad hoc, multihop solutions. Instead ofscavenging unused licensed spectrum, theywill reuse unlicensed spectrum moreefficiently, exploiting the presence of

multiple channels (say, 11 channels inIEEE802.b). Recent studies on Cognitive AdHoc Networking in urban environmentshave shown that the efficient reuse ofresidential WiFi spectrum in ad hoc meshnetworks (URBAN X) and ad hoc multicast(CoCAST) has led to significant spectrumsavings.There is one more theme that will contributeto shape the wireless mobile trend: privacy(of location and motion patterns) and

security (mainly, confidentiality andprotection from DDoS attacks). We did notdwell on the privacy/security topic in thispaper because wechose to focus onconventional network layer aspects (saysingle hop to Internet vs P2P multihop).However, two trends are clear. The need ofa Certificate Authority (CA) will requireefficient connection to Internet Servers. Atthe same time, to handle protection frombogus attacks in situationswhenthey aredisconnected from the Internet, or it issimply too time consuming to consult theInternet CA, the mobile users must organizein P2P communities and use majority rulesand/or elect proxy mobile CAs to resolvesecurity issues.In summary, the journey of ad hoc networksstarted on the pure ad hoc, no infrastructurepath in the early 70s. Vehicular networkshave reaffirmed the importance of theinfrastructure. But, emerging need for betterspectrum efficiency and stronger securitymake P2P ad hoc networking very desirable,with the help of advanced Cognitive RadioTechnology.

6. CONCLUSIONS:


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This paper has addressed advanced wirelessnetwork architectures and applicationsfocused on vehicle networks. The legacy forthese designs comes from the early ARPAstudies of Packet Radio networks in the

1970s when many of the core multi-accesstechnologies were developed, namely,ALOHA, CSMA, and related extensions.That early focus was on analytical models aswell as testbed implementations andexperiments that led to ALOHANET,PRNET, etc. Among the lessons learnedfrom those early studies is that multi-hopwireless networks are extremely inefficientdue to collisions, lost packets, long paths,ephemeral connections, hidden terminals,

etc. Moreover, the technology of the 1970sproduced large, heavy and power-hungryradios. In the 1990s, DARPA revisited thepacket radio design issues since, by then, thetechnology permitted smaller, lighter, andpower-efficient radios. This surge of interest,around the time when the mobile cellularrevolution was taking place, has led tosignificantly renewed research anddevelopment in MANET systems. Thegrowth and development of peer-to-peersystems provided the technology andexperience to extend P2P to the cartorrentnetworks described in this paper. Today theP2P paradigm is playing an increasinglyimportant role in efficient spectrum reuseand in robust operation during intermittentconnectivity episodes. In this paper, we haveidentified the need for routing and topologymaintenance as being critical for thesevehicle networks. The introduction ofadvanced digital and networking technologyinto automobiles is expanding dramaticallyand is in the process of enabling the kinds ofapplications we have discussed; this is asignificant direction of expansion for theautomobile industry.A representative example is the use ofparked automobiles as stationary, yet

ephemeral, content stores and providers.Basically these stationary vehicles have theability to form a MANET without mobilityin which routing is far more easily enabled,although updates to network routing are

required when the parked automobiles leavetheir parking spaces. Another extension is toexploit the use of public buses as reliableroving servers on a known route.On a broader scope, we anticipate that thefuture of vehicular networks will beintertwined with that of smart phones andwireless sensor networks. For example,vehicular networks will interoperate withsmart phones and possibly airborne sensorsto map the environment. In the vehicle itself,

body area sensor networks will monitor thedrivers vital signs and will cooperate withVANET alert mechanisms to avoid accidentsin case of driver collapse. Vehicle networkswill leverage the broad gamut of servicesavailable on modern smart phones to supportgeo-location aware applications and socialnetworking. Naturally, the type of data thatcan be fed to a pedestrian is quite differentfrom what can be fed to a driver since onemust not distract the driver! In summary,plenty new applications are emerging in thevehicular arena and anyone is betting on oneor the other. Unfortunately, Internet historyhas taught us that it is absolutely impossible(and useless) to predict the KillerApplication. One thing is sure: vehicles willneed to use the Internet infrastructure moreand more for advancedservices. And, the infrastructure must beenhanced and expanded to support mobileusers more efficiently.REFERENCES:[1] M. Conti, E. Gregori, G. Turi, A cross-layer optimization of gnutella for mobile adhoc networks, in: ACM MobiHoc, Urbana-Champaign, IL, USA, 2005.[2] A. Capone, M. Cesana, S. Napoli, A.Pollastro, MobiMESH: a complete solution


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for wireless mesh networking, in: IEEEMASS07, Pisa, Italy, October 2007.[3] Pei-Chun Cheng, Jui-Ting Weng, Lung-Chih Tung, Kevin C. Lee, Mario Gerla,Jerome Haerri, GeoDTN+Nav: a hybrid

geographic and DTN routing withnavigation assistance in urban vehicularnetworks, in: MobiQuitous/ISVCS 2008,Trinity College Dublin, Ireland, July 2008.[4] M. Dikaiakos, S. Iqbal, T. Nadeem, L.Iftode, VITP: an information transferprotocol vehicular computing, in: ACMWorkshop on Vehicular Ad Hoc Networks(VANET05), Cologne, Germany, August2005.[5] M. Fazio, C.E. Palazzi, S. Das, M. Gerla,

Automatic IP Address Configuration inVANETs, in: Proceedings of the Third ACMInternational Workshop on Vehicular AdHoc Networks (VANET 2006), MOBICOM2006, Marina del Rey, Los Angeles, CA,USA, September 2006.[6] M. Fazio, C.E. Palazzi, S. Das, M. Gerla,Vehicular address configuration, in:Proceedings of the First IEEE Workshop onAutomotive Networking and Applications(AutoNet), GLOBECOM 2006, SanFrancisco, CA, USA, December 2006.[7] M. Fazio, C.E. Palazzi, S. Das, M. Gerla,Facilitating real-time applications inVANETs through fast address auto-configuration, in: Proceedings of the ThirdIEEE CCNC International Workshop onNetworking Issues in MultimediaEntertainment (CCNC/NIME 2007), LasVegas, NV, USA, January, IEEECommunications Society, 2007.[8] H. Fler, J. Widmer, M. Ksemann, M.Mauve, H. Hartenstein, Contention-basedforwarding for mobile ad-hoc networks,Elseviers Ad Hoc Networks 1 (4) (2003)351369.[9] Phillip B. Gibbons, Brad Karp, Yan Ke,Suman Nath, Srinivasan Seshan, IrisNet: anarchitecture for a world-wide sensor web,IEEE Pervasive Computing 2 (4) (2003).

[10] C. Gkantsidis, P. Rodriguez, Networkcoding for large scale content distribution,in: IEEE INFOCOM, Miami, March 2005.[11] C. Gkantsidis, J. Miller, P. Rodriguez,Anatomy of a P2P content distribution

system with network coding, in:International Workshop on Peer-to-PeerSystems (IPTPS06), Santa Barbara, CA,February 2006.[12] B. Hull, V. Bychkovsky, K. Chen, M.Goraczko, A. Miu, E. Shih, Y. Zhang, H.Balakrishnan, S. Madden, CarTel: adistributed mobile sensor computing system,in: Proceedings of ACM SenSys, 2006.[13] X. Hong, D. Huang, M. Gerla, ZhenCao, SAT: building new trust architecture

for vehicular networks, in: ACMSIGCOMM Workshop on Mobility in theEvolving Internet Architecture (MobiArch),Seattle, WA, August 2008.[14] G. Korkmaz, E. Ekici, F. Ozguner, U.Ozguner, Urban multi-hop broadcastprotocols for inter-vehicle communicationsystems, in: ACM Workshop on VehicularAd Hoc Networks (VANET04),Philadelphia, PA, USA, October 2004.[15] W. Kim, A. Kassler, M. Felice, M.Gerla, Urban-X: towards distributed channelassignment in cognitive multi-radio meshnetworks, in: Wireless Days Conference,Venice, Italy, October 2010.[16] W. Kim, S.Y. Oh, M. Gerla, J.-S. Park,CoCast: multicast mobile ad hoc networksusing cognitive radio, in: IEEE MilitaryCommunications Conferences (MILCOM2009), Boston, MA, October 2009.[17] J. LeBrun, C-N. Chuah, D. Ghosal,Knowledge-based opportunistic forwardingin vehicular wireless ad hoc networks, in:IEEE Vehicular Technology Conference,May/June 2005.[18] J. Luo, J.-P. Hubaux, A survey of inter-vehicle communication, Technical ReportIC/2004/24, School of Computer andCommunication Sciences, EPFL, 2004.


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[19] Kevin C. Lee, Michael Le, JeromeHaerri, Mario Gerla, LOUVRE: landmarkoverlays for urban vehicular routingenvironments, WiVeC 2008, Calgary,Canada, March 2008.

[20] A. Laouiti, P. Muhlethaler, A. Najid, E.Plakoo, Simulation results of the OLSRrouting protocol for wireless network, in:First Mediterranean Ad-Hoc NetworksWorkshop (Med-Hoc-Net),

Sardegna, Italy, 2002.

vechicular mesh network using mobile milleu

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