Pervasive Internet Access by Vehicles through Satellite Receive-only Terminals

Pervasive Inerne Access by Vehicles hrough Saellie Receive-only Terminals Baber Aslam, Ping Wang and Cliff C. Zou School of Elecrical Engineering and Compuer Science Universiy of Cenral Florida Orlando, FL, USA {ababer, pwang, czou}@cs.ucf.edu Absrac Ubiquious Inerne conneciviy is very imporan in presen environmen. A lo of research has been done o exend Inerne conneciviy o vehicular ad hoc neworks (VANETs). The bigges challenge o achieve his goal is he requiremen of pervasive fully neworked roadside infrasrucure. This requiremen is difficul o achieve especially during he iniial deploymen phase of vehicular neworks and also in areas wih scarce roadside infrasrucure (such as along highways and in rural areas). This makes soluions ha are solely dependen on roadside infrasrucure impracicable o be implemened. Oher soluions using cellular neworks or symmeric saellie communicaion are eiher expensive or do no provide sufficien bandwidh. Furher saellie communicaion suffers heavy losses in urban area and makes is use difficul in vehicular neworks. We presen a soluion ha complemens he exising ones wihou requiring a fully neworked roadside infrasrucure. The soluion uses saellie receive-only erminals and very few (widely spaced) roadside unis o provide pervasive Inerne conneciviy. The soluion is cos effecive, incremenal and pracical. I can suppor TCP connecion even when he uplink is inerruped for long duraions of ime. We presen several differen design opions wih varying degrees of error handling capabiliies and differen overheads and delays, which can be used according o he given environmen. Keywords VANET; asymmeric saellie; Inerne; low peneraion; iniial deploymen; Land mobile saellie communicaion I. INTRODUCTION Communicaion and especially he conneciviy o he Inerne is he basic requiremen of mos modern producive environmens. We spend a considerable ime raveling from one poin o anoher via vehicles; his ime can be more producive if we are conneced o he Inerne. A lo of research has been done o bring he Inerne o vehicles. To his end, hree main approaches have been adoped: Inerne hrough roadside infrasrucure alone or hrough roadside infrasrucure using vehicle o vehicle (V2V) communicaion [1-5], Inerne hrough cellular nework [1, 6, 7] and Inerne hrough saellie (symmeric/asymmeric) [8, 9]. However, all hree approaches have some challenges o deal wih. The Inerne access hrough roadside infrasrucure requires pervasive roadside unis (RSUs) o achieve conneciviy, since This work was suppored by NSF Cyber Trus Gran CNS-0627318 and Inel Research Fund. he ypical radial range of an RSU is 250m so we need an RSU every 400 o 500m. Furher, hese RSUs mus all be conneced o he Inerne. Also, he insallaion, connecion and mainenance of hese RSUs will be quie expensive, and i may no be possible o achieve he desired conneciviy, especially during he iniial days of VANET deploymen and along highways or in rural areas. The Inerne access hrough cellular neworks, besides having smaller bandwidh, has more cos per bi of daa as compared o oher means. The cellular neworks are designed considering saisical calling properies and hese are quie differen from he Inerne usage paerns. Furher, he cellular neworks are symmeric and do no ake advanage of Inerne raffic s asymmeric propery. Therefore, he cellular neworks may no be able o handle huge volumes of daa especially when he enire vehicle populaion in a cell area ries o access he Inerne. In addiion o hese issues, when a vehicle crosses inernaional boundary, he service providers and heir carrier frequencies will ofen change, which makes user equipmen more expensive and complex. Muliple service providers also mean muliple gaeways and billing/licensing issues. The Inerne access hrough symmeric saellie requires vehicles o be equipped wih saellie ransceiver, which adds o he cos of user equipmen. Saellie channel suffers heavily from losses; hese losses inroduce errors in he communicaion and require some error correcion mechanisms. These losses are much more pronounced in urban areas where he areas are congesed wih buildings and oher manmade objecs. Therefore Inerne access hrough saellie is paricularly no an economical soluion for urban areas. The Inerne and also some of he possible VANET applicaions exhibi asymmeric naure of raffic, in his downlink raffic is many orders of magniude as compared o he uplink raffic [10]. This asymmery is likely o increase wih ime as more and more conen is becoming mulimedia in naure. Saellie as downlink coupled wih erresrial lowbandwidh reurn channel (such as dial-up) o provide Inerne o home users especially in rural areas has been used successfully for quie someime [11, 12]. Therefore, we use asymmeric saellie communicaion (downlink only). The use of saellie o provide conneciviy in rural areas also seems logical since here will be less losses and hence low errors in rural areas (or along highways). The uplink is via roadside 978-1-4244-4581-3/09/$25.00 2009 IEEE

infrasrucure using vehicle o infrasrucure (V2I) communicaion or V2V in conjuncion wih V2I communicaion. However, he limied number of RSUs makes he radiional asymmeric saellie soluions impracicable. The challenge in VANET is he inermien availabiliy of erresrial reurn channel wih possible long disrupion periods especially during he iniial days of VANET deploymen. In his paper we presen a soluion ha complemens he exising ones and provides Inerne conneciviy during he iniial deploymen phase of he vehicular neworks and also in areas wih very scarce roadside infrasrucure (such as along highways and in rural areas). The soluion uses saellie receive-only erminals and very few (widely spaced) RSUs. The use of saellie receive-only erminals helps in keeping he user cos low. I can suppor TCP connecion even when he uplink is inerruped for long duraions of ime. We presen a number of opions wih varying degrees of error handling capabiliies and recommend heir usage according o he environmen. Laer on when addiional RSUs are insalled hen he soluion improves is performance by making more use of RSUs and also by reducion of iner-rsu disance. The soluion is cos effecive, incremenal and pracical. A lo of research o address challenges of Inerne (especially TCP performance) over delay oleran neworks (DTN)/saellie neworks has been carried ou. In order o avoid he repeiions, we will, in his paper, no focus on lower level deails of wha paricular Inerne proocol o be used; raher, we will idenify he desired characerisics of he proocol and any already defined proocol (or combinaions of hese) can be used for he proposed soluion. The paper is organized in 5 secions. Secion II discusses relaed research work in he field. Secion III explains imporan characerisics of saellie communicaion and mobile saellie communicaion model. Secion IV discusses he proposed sysem design and is various opions along wih he recommended usage. And in he end, secion V presens conclusion and fuure work. II. RELATED WORK The soluions presened so far for provision of Inerne o vehicles can be broadly divided ino hree caegories; firs, he soluions relying on roadside infrasrucure or vehicle o vehicle communicaion, second, he soluions relying in some way on cellular neworks and hird, he soluions making use of saellie links. We will refer some of he imporan research papers in hese caegories. A number of researches such as FleeNe, Drive-hru Inerne, ec exensively rely on road side infrasrucure and/or vehicle o vehicle communicaion o provide Inerne conneciviy o vehicles [1, 2, 4]. The basic requiremen for hese soluions is availabiliy of pervasive roadside infrasrucure and/or a large number of smar vehicles. Boh hese assumpions are no realisic during he iniial deploymen sage, furher use of vehicle o vehicle communicaion has many securiy issues, such as privacy, confidenialiy, denial of service ec. Soluions based on exising WiFi neworks face similar problems [5]. A number of soluions incorporae cellular neworks o provide Inerne o he vehicles [1, 6, 7]. Cellular neworks are mosly used as backbone; a replacemen o roadside infrasrucure. Cellular neworks hough pervasive have several disadvanages, such as, expensive o buil/mainain, higher cos per bi of daa, low daa raes (especially a vehicular speed), heerogeneous echnologies (WAP, GPRS, EDGE, HSDPA, ec [13]), billing/licensing issues among differen service providers, higher roaming raes, large and variable laency, cenral swiching/resource managemen, difficul o scale, occasional blackous, ec [3, 4, 14-16]. Use of saellie channel for provision of Inerne o erresrial (saic) and mobile users has been an ineresing opic of research. Mos of he researches in his area are relaed o performance-sudies or enhancemens of Inerne proocols over symmeric/asymmeric saellie channels wih saionary nodes [11, 12, 17, 18]. There are also quie a few researches dealing wih he mobile nodes bu mos of hese sudy Inerne proocol performance/enhancemens [8, 9]. Furher hese consider symmeric saellie channel i.e., boh uplink and downlink communicaion akes place via saellie. Symmeric communicaion requires expensive ransceiver a he mobile nodes and i does no ake advanage of he asymmeric naure of Inerne communicaion. In his paper we are using saellie downlink communicaion only and he nodes are mobile nodes. Our work comes closer o [19], where asymmeric saellie communicaion has been used for provision of Inerne o he mobile nodes. In [19] he saellie is only used for downlink and uplink is via cellular nework. The sysem design requires he mobile node o be equipped wih boh he saellie and cellular inerfaces. The design suffers from he disadvanages of using cellular nework (described above). Also, he design does no incorporae any roadside infrasrucure, which when available could provide much higher daa raes a lower coss. Furher his also implies ha he design will no be very successful in urban areas since saellie communicaion is no very reliable in urban areas (connecion/fade raio can be 33.3/66.6 in higher densiy ciies like New York [20]). Our sysem design differs in a number of ways from he researches presened above. Firs, we use saellie communicaion for downlink only hus reducing complexiy of user erminals and operaing coss. We use roadside infrasrucure for uplink communicaion and do no need any cellular ransceivers or saellie ransmiers a nodes. This eases compaibiliy wih oher vehicular nework archiecures. The design works wih very small number of RSUs and is especially suied for iniial deploymen sages. We presen a number of opions wih varying degrees of error handling capabiliies and recommend heir suiabiliy for differen environmens. III. SATELLITE CHANNEL A. Channel Characerisics The saellie channel is characerized by long delays, high fading/aenuaion o signal, one way, high bandwidh and inorder packe delivery. As he signal ravels from saellie o an earh saion (or a mobile node) i undergoes a variey of

impairmens or losses. I can be safely assumed ha he exising saellie link akes care of all such losses, excep amospheric aenuaion (due o rain, ice, ec) and mobile channel losses (mulipah fading and signal shadowing). These are closely relaed o he environmen of he recipien [21, 27]. B. Channel Model The mos commonly used land mobile saellie channel (LMSC) model is a wo-sae Markov chain based channel model, which has been represened by a digial wo-sae Gilber-Ellio model [21]. In his paper we will use his wosae channel model. I is a wo-sae ON/OFF model. In ON (1) sae he communicaion is error free afer applying exising saellie communicaion channel coding; he sae mainly covers line of sigh (LOS) region. In OFF (0) sae communicaion errors are beyond he exising channel correcion capabiliy and reliable communicaion is no possible, he sae mainly covers non line of sigh (NLOS)/shadowed/deep-fade regions [22]. Transiion probabiliies of his model depend on he environmen (mean duraion of ON/OFF sae), vehicle speed and ransmission (bi) rae [22]. The model excludes fading evens wih shor duraions, so he sae ransiions can be assumed o ake place a cell boundaries, where a cell corresponds o a daa segmen. The average sojourn ime in each sae mainly depends on he environmen in which he vehicle/node is moving. C. Saellie Communicaion The saellie downlink communicaion makes use of exising error correcion echniques on each ransmied segmen. I is assumed ha he exising error correcion echniques applied are sufficien o provide error free communicaion in he absence of deep fading and shadowing [22]. To furher reduce he effecs of segmen loss due o deep fading and shadowing, ime diversiy is applied [23]. I can be achieved by iner-user or inra-user segmen inerleaving or boh (Fig. 1). This helps in spreading he error among differen users or differen sessions, and by employing error correcion echniques a higher layer he chances of recovery are improved. The inerleaving removes he impac of consecuive losses and herefore we can assume ha consecuive daa segmens of a session/user are independen of each oher. In he res of he paper (especially in figures) he segmens considered/shown adjacen o each oher are consecuive segmens of a session and are no necessarily ransmied consecuively unless described/shown oherwise. IV. PROPOSED ARCHITECTURE In his paper our focus is on provision/exension of Inerne o vehicular neworks in rural areas and along he highways especially during he iniial deploymen sages. The working environmen is characerized by a very small number of RSUs ha are widely inerspaced. These RSUs may be co-locaed wih isolaed populaed areas along he highways and are conneced o he Inerne. The environmen does no exhibi high shadow losses. A. Assumpions Our sysem design is based on a few simple assumpions. Firs, vehicles are equipped wih GPS, can record heir locaion a precise ime and can provide direcion of ravel informaion o he RSU. Second, vehicles can receive he saellie broadcas. And hird, RSUs have he digial map of he area and are aware of he locaions of adjacen RSUs. B. Basic Idea A vehicle connecs o a nearby RSU and requess some Inerne daa. The reques will include locaion, speed and direcion of ravel of he vehicle. This informaion will help an RSU o calculae possible connecion ime lef and possible nex RSU. If sufficien connecion ime is lef hen he reques may be serviced hrough he same RSU. When he vehicle exis he coverage of curren RSU, furher responses o he vehicle s earlier reques will be sen o he nex RSU in he direcion of ravel. If he wo RSUs are locaed a a reasonable disance, which is likely in urban environmen, he nex RSU will coninue o deliver he conen o he vehicle when he vehicle comes wihin is coverage area (RSU-based region in Fig. 2). If he nex RSU is no wihin a reasonable disance (especially in rural environmen where he RSUs will be widely spaced) hen saellie downlink channel will be used for delivery of conen (saellie downlink-only region in Fig. 2). We will mosly address he saellie downlink opion in his paper. Consecuive segmens of one User (U 1, F 1, P 1 ) Acual segmen ransmission sequence in ime (U 1, F 1, P 1 ) (U 1, F 1, P 2 ) (U 1, F 1, P n ) (U 1, F 2, P 1 ) (U 1, F 2, P n ) (U 1, F n, P n ) (U 2, F 1, P 1 ) (U n, F 1, P 1 ) (U 1, F 1, P 2 ) Where (U a, F b, P c ) is segmen # c of session # b for user 'a (U n, F 1, P n ) (U n, F n, P n ) Figure 1. Iner and Inra user segmen inerleaving o achieve ime diversiy. While a vehicle ravels beween wo RSUs in he saellie downlink-only region, i canno send acknowledgemens. In order o keep TCP connecion alive and avoid unnecessary reransmissions, adapive TCP imeou and delayed ACK will be used [25, 26]. TCP imeous will be calculaed/prediced depending on he locaion of he nex RSU and will be used accordingly. The downlink has large delays so in order o avoid unnecessary reransmissions selecive acknowledgemen will be used. Modified TCP is only employed beween he proxy and mobile hos so no modificaions are required in proocols running on exising Inerne. The use of UDP is much simpler han TCP and will no require any modificaions. The flow of raffic beween differen eniies is oulined below (refer o Fig. 2): The mobile node auhenicaes wih he proxy hrough an RSU and is issued wih an IP address; his IP address will uniquely idenify he mobile node as long as i remains wihin he boundary of he proxy. The mobile node sends a reques o he RSU. The RSU acs as a rouer and forwards he reques o he proxy. The proxy esablishes a connecion o Server on behalf

.. Saellie Nework VANET INTERNET of he mobile node and ges/caches all he conen (based on iniial reques of he mobile node). The proxy esablishes a connecion wih he mobile node on behalf of Server and sends he conen via an RSU. When he mobile node moves ou of he range of an RSU and he direc connecion wih RSU imes ou (Fig. 2, saellie downlink-only region); he RSU informs he proxy abou expeced ime of nex ACK from he mobile node. The ime period depends on he speed and locaion of he nex RSU along he ravel direcion of he mobile node. The proxy sars sending furher conen via saellie. I keeps on sending wihou waiing for ACK from he node ill he ime period expires. The mobile node keeps on receiving daa via saellie ill i reaches he nex RSU (Fig. 2, end of saellie downlink-only region). The mobile node sends ACK for he received daa or NACK for segmens los due o errors. The proxy updaes he mobile node s new posiion and acs according o ACK/NACK. The process is repeaed ill all he requesed conen is delivered o he mobile node. SERVER Wireless Wired INTERNET PROXY RSU-based region SATELLITE GATEWAY UPLINK Saellie downlink-only region Figure 2. Proposed design in conex of higher level vehicular nework archiecure. 1) Baseline Archiecure: A vehicle sends a reques o is nearby RSU (Fig. 3, R 1 ), which in urn forwards he reques o he proxy server. The proxy server ges he response/daa from he server and forwards i o he saellie gaeway. The proxy server splis he end-o-end connecion beween he vehicle and server [24]. I mainains wo separae connecions, one wih he server on behalf of he vehicle and he oher wih he vehicle. The session wih vehicle will be asymmeric, ha is, he down link will be hrough saellie and reurn will be hrough RSUs. No modificaions are required on he server side nor on he saellie downlink. 20 19 2 1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 NAK (4, 5, 13, 14, 15) Zone 1 Zone 2 R 1 R 2 Figure 3. Baseline archiecure, delivery of conen akes place hrough saellie while he mobile node is raveling beween R 1 and R 2. The mobile node sends NAK for he los segmens when reaching R 2, where R 2 akes charge and resends hese los segmens o he mobile node. The connecion beween he proxy and he vehicle will employ TCP enhancemens/modificaions such as Adapive imeou, delayed ACK, and selecive ACK/NAK [25, 26]. The adapive imeou caers for he ime during which he vehicle canno send ACKs, ha is while raveling beween he RSUs (Fig. 3, beween R 1 and R 2 ). When a reques is received by he proxy, i forwards he reques o he original server in a separae connecion. I also calculaes he imeous and delays (for delayed ACK) expeced based on he disance beween adjacen RSUs (Fig. 3, beween R 1 and R 2 ), he vehicle speed and is direcion of ravel. The proxy server receives all he daa, which maybe a large file, from he server and also keeps he connecion alive for furher requess from he vehicle (his will be necessary if he ransacion has o be compleed afer receiving some response from he vehicle during is connecion wih he nex RSU). The proxy server hen forwards he daa o he vehicle hrough he saellie gaeway and wais for he ACK/NAK. Because of high bandwidh-delay produc (he delay of he saellie communicaion and also beween sending he daa and receiving ACK due o separaion of RSUs), i may be necessary ha all daa segmens are sen before waiing for an ACK/NAK from he vehicle. If some of he received frames have been los (Fig. 3, segmens 4, 5, 13, 14 and 15) hen he vehicle sends selecive ACK/NAK on is nex conac wih roadside infrasrucure (Fig. 3, R 2 ). These ACK/NAK segmens are forwarded o he proxy server, which reransmis he los segmens hrough saellie/rsu. 2) Repeaed Transmissions: A mehod o address segmen losses is by repeaing he complee ransmission in cyclic manner for a fixed number of imes. This opion adds maximum daa redundancy. Alhough his is no an efficien uilizaion of he bandwidh available and we will have low informaion per bi ransmied, his approach can miigae he effecs of channel impairmens. Especially during he iniial VANET deploymen sages when no many of smar vehicles will be on roads, a given saellie channel will be shared by a limied number of vehicles and each vehicle will have sufficien share of saellie bandwidh, which can be used for repeaed ransmissions. Also, during he iniial sages here will be fewer number of RSUs which means larger disances

: : beween RSUs and more ime o service a given reques. This available ime can be uilized for he redundancy. This scheme suffers from long delays because in wors case a vehicle migh have o wai for a complee cycle of reransmission o recover he los daa segmen. I has high delay bu is a suiable scheme when we are experiencing high error rae ha canno be correced by oher schemes. Fig. 4 shows a vehicle driving beween wo widely spaced RSUs. The daa is being sen hrough saellie which comprises of segmens numbered 1 o 8. The vehicle fails o receive segmens 4 and 5 during he firs ransmission cycle since i was passing hrough error zone 1 during heir ransmissions. The vehicle recovers he los segmens from he second ransmission cycle and is successful in receiving all eigh segmens before reaching he nex RSU, where i acknowledges he receip of all he segmens. 8 2 1 8 2 1 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 ACK (8) R 1 Zone 1 Zone 2 R 2 fac ha he speed of vehicles has generally less variaions in highway environmen also helps in minimizing he esimaion error. However, an error margin can be added on boh sides of probable error locaion o caer for variaions in driving speeds. The RSU wih which he vehicle was las auhenicaed/associaed (Fig. 5, R 1 ) lisens for he segmens which were sen during he error zone period and sends NAK o he proxy for reransmission of hese segmens. Take Fig. 5 as an example. A vehicle sends a reques o RSU R 1, which forwards he reques o he proxy server and daa is sen o he vehicle via saellie. The RSU R 1 calculaes approximae imes ({ 0-1 } and { 2-3 }) when he vehicle will be passing hrough error zones. I hen moniors he saellie ransmissions desined o his vehicle. I records he segmen numbers sen by saellie when he vehicle passes hrough hese error zones (segmens {4, 5}, {11, 12, 13}) and sends NAK o he proxy server for hese segmens (segmens NAK {4, 5}, NAK {11, 12, 13}). When receiving hese NAKs, The proxy server reransmis he los segmens hrough saellie. When he vehicle reaches he nex RSU, i sends NAK if i sill could no receive all he segmens. These NAK locaions are hen used by previous RSU o modify is error zone informaion. I is imporan o noe ha here is no way for he iniial RSU o know if an earlier repored error zone has disappeared or no. There may be a siuaion (e.g. heavy rain) when mos of he locaions are marked as error zones. To address his possible siuaion i is necessary from ime o ime o rese he error zones o zero. Figure 4. Repeaed ransmission, whole daa se is repeaed several imes. Daa segmen(s) los can be recovered from laer repeaed ransmissions. 3) Locaion Predicion and Avoidance: The saellie mobile channel suffers mosly from shadowing and fading. These errors are srongly correlaed o he environmen. Vehicles raveling along a paricular highway are expeced o experience channel impairmens a approximaely he same locaions (refered as error zones ). If he locaion of hese error zones can be regisered and he segmens ha were sen o a vehicle while i was passing hrough hese error zones can be deermined, hen hese segmens may be reransmied o he vehicle wihou waiing for an ACK/NAK from he vehicle. This will improve he performance since he vehicle does no need o wai for he nex RSU, which may be quie far off, o recover from he error. The locaion of error zones can be deermined if a vehicle also includes locaion informaion wih NAK, which is he locaion where segmen loss was experienced. This locaion informaion is used o predic he possible locaion of segmen losses for fuure vehicles raveling along he same pah. For example in Fig. 3 he vehicle experiences loss of segmens 4 and 5 in error zone 1 and can repor {NAK (4,5), Zone 1} o RSU-R 2. (Also loss of segmens 13, 14 and 15 in error zone 2 can be repored as {NAK (13,14,15), Zone 2}). The ime period during which he vehicle was raveling hrough a regisered error zone can be esimaed from he vehicle s speed and is iniial ime-locaion informaion. The 0 1 2 3 1 : NAK (4, 5) 1 2 3 4 5 6 4 5 7 8 9 10 11 12 13 14 11 12 13 15 3 : NAK (11, 12, 13) ACK (15) R 1 Zone 1 Zone 2 R 2 Figure 5. locaion predicion and avoidance. The sysem predics he segmens which may have been los on he bases of previous daa and proacively reransmis hese segmens. C. Comparison of Opions The opions presened in preceding secions offer differen levels of error olerance a he cos of overheads and delays. One mus balance he performance (error olerance) vs. cos (overheads and delays) in selecing a paricular soluion; also, some opions may be more suied o a paricular environmen han he oher environmens. The baseline archiecure uses simple ACK/NAK for flow conrol and error correcion. This scheme has no overhead bu successful compleion of communicaion may be delayed ill he vehicle reaches he nex RSU. This archiecure is suiable where RSUs are no very widely dispersed. locaion predicion and avoidance uses proacive reransmission of prediced los segmens. This scheme has low overheads and low delays. This scheme is especially useful where saellie mobile channel losses are reasonably localized in cerain areas. Repeaed Transmission is he mos robus scheme, i is especially useful where longer

duraions of Bad sae is experienced, bu a he cos of having high overhead and medium delays. A summary of he opions wih recommended usage is also presened in Table I. TABLE I. RECOMMENDED USAGE OF DIFFERENT OPTIONS Opion Overhead Delay Recommended Usage Baseline None High Where RSUs are no very widely spaced Repeaed Transmission High Medium Where Bad sae duraion is longer han FEC can olerae Locaion Low Low Where Bad sae Predicion and Avoidance environmens are relaively sable over a relaively long period of ime V. CONCLUSION AND FUTURE WORK We have presened a viable soluion for provision of he Inerne access o he vehicular neworks, especially during he iniial deploymen phase of vehicular neworks and also in areas wih very scarce roadside infrasrucure (such as along highways and in rural areas). The soluion is pracical and economical since i only uses saellie receive-only erminals and very few (widely spaced) RSUs. We have also presened a number of error handling opions which can be employed according o he operaing environmens. The efficiency of he soluion can be furher enhanced by using V2V communicaion in a variey of ways. For example, caching and laer relaying he daa for oher vehicles (ha migh no have been able o receive i due o error zone), relaying NAK o previous RSU (via vehicles raveling in opposie direcion), using V2V communicaion as he reverse channel o send all he selecive ACKs and NAKs, ec. The soluion is bes suied for reques-response ype of applicaions, where a small reques is followed by a large response daa (such as file ransfer, mulimedia download, ec). The soluion does no provide coninuous conneciviy so ineracive or coninuous conneciviy demanding applicaions, such as IP elephony canno be suppored. Also, he soluion is no inended o suppor securiy based applicaions ha are ime criical and require large daa flow from vehicles; however, non-ime criical or broadcas naure of securiy applicaions are suppored, for example, disseminaion of cerificae revocaion liss (or oher securiy alers) hrough saellies. REFERENCES [1] M Bechler, WJ Franz, and L Wolf, Mobile inerne access in FleeNe, 13h Fachagung Kommunikaion in vereilen Sysemen, Leipzig, April 2003. [2] Franz, W. and Harensein, H. and Bochow, B., Inerne on he road via iner-vehicle communicaions, in GI/OCG Annual Conference: Workshop on Mobile Communicaions over Wireless LAN: Research and Applicaions, Vienna, Sep 2001. [3] J. O, and D. Kuscher, Drive-hru Inerne: IEEE 802.11b for auomobile users, in IEEE Infocom Conf., 2004. [4] Y. Yang, M. Marina, and R. Bagrodia, Evaluaion of mulihop relaying for robus vehicular Inerne zccess, in MObile Neworking for Vehicular Environmens (MOVE), 2007. [5] V. Bychkovsky, B. Hull, A. Miu, H. 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