vehicular telematics over heterogeneous wireless networks: a survey

Our reference: COMCOM 4130 P-authorquery-v7

AUTHOR QUERY FORM

Journal: COMCOM

Article Number: 4130

Please e-mail or fax your responses and any corrections to:

E-mail: [email protected]

Fax: +31 2048 52799

Dear Author,

Any queries or remarks that have arisen during the processing of your manuscript are listed below and highlighted by flags in the proof. Pleasecheck your proof carefully and mark all corrections at the appropriate place in the proof (e.g., by using on-screen annotation in the PDF file) orcompile them in a separate list.

For correction or revision of any artwork, please consult http://www.elsevier.com/artworkinstructions.

Articles in Special Issues: Please ensure that the words ‘this issue’ are added (in the list and text) to any references to other articles in thisSpecial Issue.

Uncited references: References that occur in the reference list but not in the text – please position each reference in the text or delete itfrom the list.

Missing references: References listed below were noted in the text but are missing from the reference list – please make the list completeor remove the references from the text.

Location inarticle

Query / remarkPlease insert your reply or correction at the corresponding line in the proof

Q1 This section comprises references that occur in the reference list but not in the body of the text. Please position each reference in the

text or, alternatively, delete it. Any reference not dealt with will be retained in this section. Thank you.

Q2 Please update Ref. [118] if possible.

Electronic file usageSometimes we are unable to process the electronic file of your article and/or artwork. If this is the case, we have proceeded by:

h Scanning (parts of) your article h Rekeying (parts of) your article h Scanning the artwork

Thank you for your assistance.

mailto:[email protected]

1

2

3

4

56789

10

1 2

1314151617

1819202122

2 3

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

51

52

Computer Communications xxx (2010) xxx–xxx

COMCOM 4130 No. of Pages 20, Model 5G

9 January 2010ARTICLE IN PRESS

Contents lists available at ScienceDirect

Computer Communications

journal homepage: www.elsevier .com/locate /comcom

RO

OFVehicular telematics over heterogeneous wireless networks: A survey

Ekram Hossain a, Garland Chow b, Victor C.M. Leung c,*, Bob McLeod a, Jelena Mišic d, Vincent Wong c,Oliver Yang e

a Department of Electrical and Computer Engineering, University of Manitoba, Winnipeg, Canadab Sauder School of Business, University of British Columbia, Vancouver, Canadac Department of Electrical and Computer Engineering, University of British Columbia, Vancouver, Canadad Department of Computer Science, University of Manitoba, Winnipeg, Canadae School of Information Technology and Engineering, University of Ottawa, Canada

a r t i c l e i n f o a b s t r a c t

2425262728293031

Article history:Received 19 May 2009Received in revised form 16 December 2009Accepted 24 December 2009Available online xxxx

Keywords:Intelligent transportation systemsVehicular telematicsHeterogeneous wireless networks

0140-3664/$ - see front matter � 2010 Published bydoi:10.1016/j.comcom.2009.12.010

* Corresponding author. Address: Department of Eneering, University of British Columbia, Room 4013Mall, Vancouver, BC, Canada V6T 1Z4. Tel.: +1 604 822

E-mail addresses: [email protected] (E. Hosubc.ca (G. Chow), [email protected] (V.C.M. Leun(B. McLeod), [email protected] (J. Mišic), [email protected] (O. Yang).

Please cite this article in press as: E. Hossain edoi:10.1016/j.comcom.2009.12.010

ED

PThis article presents a survey on vehicular telematics over heterogeneous wireless networks. Anadvanced heterogeneous vehicular network (AHVN) architecture is outlined which uses multiple accesstechnologies and multiple radios in a collaborative manner. The challenges in designing the essentialfunctional components of AHVN and the corresponding protocols (for radio link control, routing, conges-tion control, security and privacy, and application development) are discussed and the related work in theliterature are reviewed. The open research challenges and several avenues for future research on vehic-ular telematics over heterogeneous wireless access networks are outlined.

� 2010 Published by Elsevier B.V.

T

32

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

69

70

71

72

UN

CO

RR

EC

1. Introduction

Vehicular telematics and infotainment applications will be keyto developing Intelligent Transportation Systems (ITS) in order toachieve safety and productivity in transportation. Wireless com-munications and networking technologies such as IEEE 802.11(WiFi), IEEE 802.16 (WiMAX), 3G cellular, and satellite technolo-gies will be vital to support data communications for vehicular tel-ematics. The ITS America VII (Vehicle-Infrastructure Integration)framework proposed wireless communications in the 5.9 GHzband for automotive use [1] and the U.S. Department of Transpor-tation proposed a system architecture for development of ITS [2].

ITS applications can be supported through vehicle-to-roadside(V2R) and vehicle-to-vehicle (V2V) communications. V2R commu-nications involve vehicular nodes and road side base stations. IEEE802.11 (WiFi) [3], IEEE 802.16 (WiMAX) [5], and Dedicated ShortRange Communications (DSRC) [6] technologies can be used in thismodel of communication. In particular, with the DSRC standard,onboard units (OBUs) placed at each vehicle can send or receivedata to or from roadside units (RSUs). However, if a vehicle cannot

73

74

75

76

77

78

79

Elsevier B.V.

lectrical and Computer Engi-, Kaiser Building, 2332 Main

6932; fax: +1 604 822 5949.sain), [email protected]), [email protected]@ece.ubc.ca (V. Wong),

t al., Vehicular telematics ove

directly send its data to an RSU, it can relay its data to other vehi-cles until the data reach to the RSU using a multihop transmissionstrategy [7]. It is also possible that OBUs form a group and elect thegroup leader. In this case, all group member OBUs will send theirreports to the leader OBU which will aggregate them and forwardthe resulting message(s) to the RSU. There are several applicationsfor this communication model such as electronic toll collection,infotainment services, safety message dissemination, and webbrowsing. Besides the on-board computer and communicationinterface, OBUs are typically equipped with a Global PositioningSystem (GPS), which provides information on vehicle position inreal-time, and an event data recorder, which stores relevant datathat, in case of an accident, can be used in forensic analysis. RSUsact as base stations or access points, and are connected to applica-tion servers. RSUs and servers can be run by the Department ofTransportation (federal, provincial, or local), Police Department,or third party providers.

V2V communications involve vehicular nodes on a road whichform a vehicular ad hoc network (VANET). This mode of communi-cation is mainly used in safety warning system [2,8], traffic infor-mation system [9], and multimedia streaming [10]. Collisionavoidance, road obstacle warning, intersection collision warning,and lane change assistance are example applications of V2V com-munications. Most of V2V safety applications require low transferlatency since these applications are used in a dynamic and unpre-dictable traffic environment. Most of researches tend to findimprovements of such medium access control (MAC) protocols,

r heterogeneous wireless networks: A survey, Comput. Commun. (2010),

http://dx.doi.org/10.1016/j.comcom.2009.12.010









http://www.sciencedirect.com/science/journal/01403664

http://www.elsevier.com/locate/comcom


T

80

81

82

83

84

85

86

87

88

89

90

91

92

93

94

95

96

97

98

99

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

151

152

153

154

155

156

157

158

159

160

161

162

163

164

165

166

167

168

169

170

171

172

173

174

175

176

177

178

179

180

181

182

183

184

185

186

187

2 E. Hossain et al. / Computer Communications xxx (2010) xxx–xxx



RR

EC

transmission strategies, and wireless technologies in order to re-duce the latency.

By definition, emerging vehicular telematic applications will bewireless. In the past, there has been an emphasis on providingwireless services to individuals, such that they may make alterna-tive route decisions in a more or less independent manner. Theseare essentially first generation applications where the users areautonomous and assumed independent, such as simple directionsystems based on GPS. The conceptual objective of these first-gen-eration applications is to define or identify, and then to reproduceor re-present a measured parameter (e.g., location) back to theuser. Without doubt many have envisioned the day, when at theend of the month a bill will arrive with several GPS/accelerometerdetected infractions, parking, speeding, dangerous driving, non-compliant engine off etc. combined with a micro-bill for eachtransgression. Early vehicular telematic applications were/areuser-centric as well as the latter seemingly coming from a ‘‘bravenew world”.

This article provides a survey on the research issues, challenges,and possible approaches to tackle these challenges for vehiculartelematics over heterogeneous wireless networks. This survey in-cludes the concepts considered and analyzed in existing collectionsof papers obtained as the outcome of some recent and ongoing re-search projects [11–20]. A survey of the related projects carried outin Europe, USA, and Japan can be found in [23]. Based on the pub-licly available information, in this survey, the authors summarizedthe scope and application type of 79 projects that included wirelessvehicle-to-infrastructure and vehicle-to-vehicle communications.It was observed that there are higher number of projects in Europeas compared to USA and Japan. However, there are more overlap-ping projects (i.e., addressing the same issues) in Europe as com-pared to USA and Japan. While the projects in Europe and USAfocus mainly on safety applications, the projects in Japan primarilyfocus on traffic congestion applications. It was also observed thatthe USA and European projects end with a demonstrator or theo-retical results, while the Japanese projects end with a productand deployment.

The outline of the rest of the article is as follows. Section 2 de-scribes different types of vehicular telematic applications and theirrequirements. The advanced heterogeneous vehicular network(AHVN) architecture is presented in Section 3. Sections 4, 5 discussthe challenges and approaches in designing the functional compo-nents and protocols for AHVN. Finally, the open research issues andseveral directions for future research related to vehicular telemat-ics over AHVN are outlined in Section 6.

188

189

190

191

192

193

194

195

196

197

198

199

200

201

202

203

204

205

206

207

208

UN

CO2. Vehicular telematic applications and requirements

Three general types of applications are anticipated to be devel-oped over vehicular networks. Safety applications are the first typeof applications that improve the safety of the passengers on theroads by notifying the vehicles about any dangerous situation intheir neighborhood. Well-known examples are collision warningssuch as notifications about a chain car accident, warnings aboutroad conditions such as slippery road, approaching emergencyvehicle warning, etc. The main concern here is finding low-latency,reliable, and efficient methods for disseminating safety data amongneighboring vehicles. A large number of data dissemination mech-anisms were proposed in the literature. While many of these worksrely on repeaters and (or) access points (APs) for disseminating thesafety data [24,25], some other works suggest that infrastructure-independent fully ad-hoc communications suffice [26,27].

Another type of applications is traffic applications that call forthe deployment of Traffic Information Systems (TISs), which carryout traffic management and provide drivers with the traffic situa-

Please cite this article in press as: E. Hossain et al., Vehicular telematics ovedoi:10.1016/j.comcom.2009.12.010

ED

PR

OO

F

tion and road information. The drivers use this information toavoid congestion and to find the route with minimum delay totheir destinations. In other words, TISs aim at balancing the vehic-ular traffic on streets in order to use the capacity of streets andjunctions efficiently and consequently save the lives and reducethe travel time and waste of energy. One of the seminal TISs isself-organizing traffic information system (SOTIS) [28], in whicheach road is divided into several segments, and vehicles send theaverage velocities of the segments periodically. TrafficView [29]is another TIS which has a mechanism similar to SOTIS, but insteadof the average velocities in the segments, it disseminates the posi-tions and velocities of the individual vehicles periodically. Theauthors of SOTIS expanded the idea of SOTIS to develop a seg-ment-oriented data abstraction and dissemination (SODAD)scheme in their more recent work [30] which has an adaptive ap-proach. All these studies, however, are fully ad-hoc TISs and sufferfrom large delays at far distances and not having a reliable mech-anism to make sure that every vehicle is provided with all the traf-fic information it needs. The coexistence of infrastructure-basedand ad-hoc wireless communications, i.e., a wireless mesh typeof architecture could overcome these problems. One of the sub-stantial challenges that should be addressed in traffic applicationsis the data aggregation algorithm the TIS employs to include asmuch traffic information as possible in the traffic packets vehiclesbroadcast. Different data aggregation algorithms in the literaturewill be described later in this article.

The third type of vehicular applications is non-safety applica-tions also called comfort or entertainment applications. Non-safetyapplications are so varied, ranging from real-time or non real-timemultimedia streaming and interactive communications such as vi-deo-conferencing and interactive games to roadside service appli-cation such as location and price lists of restaurants or gas-stations,weather information or Internet access such as data transfer, webbrowsing, music download and etc. Note that multimedia stream-ing is used for a wide range of applications. Even in traffic or safetyapplications the traffic situation or emergency message can be gen-erated by video sensors already installed along the roadside.

In contrary to the first-generation vehicular telematic applica-tions, the emerging generation of wireless applications capitalizeon the extraction of data from fleets of multiple vehicles. Data min-ing on the extracted data can aid better decision support of diffi-cult-to-predict emergent behavior. The conceptual objective ofthese second-generation applications is to translate or convertmulti-source data, and then to estimate or infer extant conditionsback to the users as well as interested third parties. Examples ofthis include highway safety systems where wireless intra-vehiclerelays can be used to impede or halt oncoming traffic in a freewayaccident scenario (forward collision warning). These are somewhatobvious applications that are built upon layers of sophisticatedtechnology with vehicle safety systems leading the development.

In addition, there is a class of applications that rely on inferencefrom probes or floating cars, with the intent is to capture a statis-tically significant portion of vehicle behavior such that meaningfulinferences can be made and potentially generalized to the entirepopulation of vehicles [31]. Applications include infrastructuremonitoring as well as sampling empirical data input for traffic flowcontrol. In the infrastructure health monitoring application (Fig. 1),fleet of vehicles such as busses would incorporate additional sen-sors to those routinely on-board. An instance may be monitoredsacrificial anodes, accelerometers or strain gauges coupled to GPSetc. that would collect data to provide information on the struc-tural integrity of the vehicle on various routes as well as for variousdrivers. An instance of emission factor estimation (Fig. 2) can beone similar in architecture to the infrastructure health monitoringapplication albeit enhanced through reliance on statistical sam-pling. In some cases, only a very small amount of floating car data



Original text:

Inserted Text

neighbourhood.

Original text:

Inserted Text

neighbouring

OR

REC

TED

PR

OO

F

209

210

211

212

213

214

215

216

217

218

219

220

221

222

223

224

225

226

227

228

229

230

231

232

233

234

235

236

237

238

239

Fig. 1. Infrastructure health monitoring.

Fig. 2. An emission factor statistical estimation architecture.

E. Hossain et al. / Computer Communications xxx (2010) xxx–xxx 3



UN

C

is required to infer significant event such as congestion build-up ordissolution [32]. These newer applications are more cohort-centricas opposed to being individual or user-centric. In these latter casesdata needs to be backhauled (wirelessly) and processed centrally,as it would be impractical to have all probe data processed onboardeach probe vehicle. As such, this type of requirement mandates theuse of data collection management, operating system and applica-tion management systems. Relevant data can then be sent to infor-mation sinks (probes as well as third parties) informing them ofroad or condition hazards, for example. Because not all informationbroadcast would be useful to all recipients, filtering applicationswill have to be developed that provide the operator with usefulinformation. For example, if a statistically significant percentageof probes detect a road hazard after central processing, only vehi-cles in the local (context-specific) area would need to be informed(local area being context specific).


3. Advanced Heterogeneous Vehicular Network (AHVN)architecture for vehicular telematics

Most of the studies in the field of vehicular communicationsand vehicular networks only deal with a single type of applicationin these networks, i.e., none of them addresses all types of safety,traffic and comfort applications, and neither purely infrastruc-ture-based or purely ad-hoc vehicular networks nor even tradi-tional single radio wireless mesh networks meet therequirements of all the applications at the same time. We believethat an advanced heterogeneous vehicular network (AHVN) thatuses multiple radios and multiple access technologies in a collabo-rative manner could be the best candidate for a vehicular network.

A key motivation of considering the AHVN is that DRSC will onlybe effective when it is ubiquitously deployed, but this will not hap-pen until the needed infrastructure is in place, governments legis-



T

240

241

242

243

244

245

246

247

248

249

250

251

252

253

254

255

256

257

258

259

260

261

262

263

264

265

266

267

268

269

270

271

272

273

274

275

276

277

278

279

280

281

282

283

284

285

286

287

288

289

290

291

292

293

294

295

296

297

298

299

300

301

302

303

304

305

306

307

308

309

310

311

312

313

314

315

316




EC

late for DSRC deployment in passenger vehicles, and older non-compliant vehicles have retired. This is not very likely to happenwithin the next 10–20 years. Therefore, in the meantime a hetero-geneous platform is the best way forward. In fact, on the issue ofinfrastructure deployment, the ITS branch of the US DoT is stillexploring different business models, as it is not certain that publicsector can or wish to cover all the costs.

The access technologies that can be employed as well as thearchitecture of AHVN including the functional components andtheir logical relations along with the challenges that should be ad-dressed are discussed in this section.

3.1. The access technology options

In the AHVN, the vehicles request services with differentrequirements in terms of latency, bandwidth, error rate, area ofcoverage, etc. at any time and any place. Existing access technolo-gies such as wireless LANs (WLAN IEEE 802.11a/b/g/n/p standards),WiMAX (IEEE 802.16 a/e standards), ultra wideband (UWB IEEE802.15.3a standard), third and fourth generation cellular wireless(3G and 4G), satellite communications etc. are designed for a spe-cific service requirement.

� IEEE 802.11-based WLAN which has achieved a great acceptancein the market supports short-range relatively high-speed datatransmission. The maximum achievable data rate in its latestversion 802.11n is about 100 Mbps. Although some studies haveshown its performance reduction due to interference [33], theviability of its deployment for the nodes moving at vehicularspeeds has already been confirmed in several papers [34–37].On the other hand, the short transmission range leads to frequenttransmission interruption particularly when vehicle speed ishigh and consequently many access points have to be deployedalong the road that incurs high deployment cost [38,39].IEEE 802.11p is a new communication standard in the IEEE 802.11family which is based on the IEEE 802.11a. IEEE 802.11p, which isalso referred to as the DSRC standard, is designed for wirelessaccess in the vehicular environment (WAVE) [8,3,6] to supportITS applications. For DSRC, 75 MHz of licensed spectrum at5.9 GHz has been allocated which consists of 7 channels

UN

CO

RR

Fig. 3. Mobile WiMAX applicat


ED

PR

OO

F

(10 MHz each) for supporting safety and non-safety applications.DSRC supports a very high data rate (6–27 Mbps) with a maxi-mum communication range of 1000 m. Presently DSRC is mainlyused in electronic toll collection. Potential applications of DSRCare: emergency warning systems for vehicles, adaptive cruisecontrol, forward collision warning, electronic parking payments,approaching emergency vehicle warning, transit or emergencyvehicle signal priority, and in-vehicle signing. Vehicles equippedwith DSRC can communicate directly with each other, making itpossible to send warning messages to neighboring vehicles. DSRCcan also be used to provide in-vehicle entertainment for driversand passengers.

� IEEE 802.16 standard-based WiMAX (Worldwide Interoperabil-ity for Microwave Access) systems are able to cover a large geo-graphical area, up to 50 km, and to deliver significant bandwidthto end-users up to 72 Mbps theoretically. While IEEE 802.16standard only supports fixed broadband wireless communica-tions, IEEE 802.16e/mobile WiMAX standard supports speedsup to 160 km/h and different classes of quality of service, evenfor non-line-of-sight transmissions. In WLAN, a contention-based channel access mechanism is used which can cause sub-scriber stations distant from the AP to be repeatedly interruptedby closer stations. The key advantage of WiMAX compared toWLAN is that the channel access method in WiMAX uses ascheduling algorithm for which the subscriber station needs tocompete only once for initial entry into the network. After that,it is allocated an access slot by the BS. Fig. 3 shows a list of someapplications envisioned by mobile WiMAX and their QoSrequirements [5].

� For vehicular telematic services, 3G cellular wireless technologycan provide a very broad coverage and support high-mobilityvehicles [40]. Current 3G networks deliver a data rate of 384 kbpsto moving vehicles which goes up to 2 Mbps for fixed nodes. 3Gsystems deliver smoother handoffs compared to WLAN andWiMAX systems, however, due to centralized switching atmobile switching centre (MSC) or serving GPRS support node(SGSN), their latency may become an issue for many applica-tions. Although the data rates of cellular networks are expectedto go higher in 3.5 G high speed downlink packet access (HSDPA)and 4 G, the technology may not be available in near future.

ion and quality of service.



Original text:

Inserted Text

(6-27

Original text:

Inserted Text

meters.

Original text:

Inserted Text

km/hr

Original text:

Inserted Text

3.5G

Original text:

Inserted Text

4G,

317

318

319

320

321

322

323

324

325

326

327

328

329

330

331

332

333

334

335

336

337

338

339

340

341

342

343

344

345

346

347

348

349

350

351

352

353

354

355

356

357

358

359

360

361

362

363

364

365

366

367

368

369

370

371




� Satellite communications provide ubiquitous coverage at anylocation, but incur high cost and large propagation delays. In[41] the key conceptual models and services in a satellite-basedvehicular broadband network as well as the design consider-ations at different levels were discussed.

Designing any heterogeneous network should as much as possi-ble be on the basis of intelligent integration of readily availabletechnologies in order to minimize the deployment cost and tomake the deployment fast. However, the design should also be leftopen to any better substituting or complementing alternatives.

Some studies [7,42–45] proposed the integration of infrastruc-ture into ad-hoc wireless networks, which is commonly referredto as wireless mesh networks (WMNs), for addressing vehicularapplications we mentioned earlier. The deployment of WMNs en-ables vehicles to get access to the APs outside their transmissionrange via multihop communications which improves the networkcoverage, and also enhances the capacity of the network byallowing more parallel transmissions. A WMN architecture thatintegrates IEEE 802.11 access technology with ad-hoc communi-cations was introduced in [44] which is specifically aimed at pro-viding broadband wireless access (BWA) for vehicles. Anothermesh architecture including IEEE 802.16 access technology andad-hoc communications was studied in [7] supporting safetyapplications and Internet access in which the ad-hoc communica-tions among vehicles are via IEEE 802.16 air-interface cards. Theauthors in [45] focused on IEEE 802.16e access technology andintegrated it with ad-hoc communications to introduce a mobilitypattern routing protocol for vehicular networks by equipping the

UN

CO

RR

EC

T

Fig. 4. Architecture


DPR

OO

F

vehicles with both IEEE 802.11 and IEEE 802.16 wireless inter-faces. None of these studies, however, satisfies all the requiredservices and applications outlined earlier. On the other hand, withthe decreasing cost of wireless transceivers, more radios, i.e.,more than one radio, can be used in the OBU of a vehicle whichforms a heterogeneous architecture rather than simple singleradio WMNs. Cooperative use of the multiple radios enhancesthe performance of the network in the sense that the capacityof the network is improved by allowing more parallel transmis-sions in different frequencies.

3.2. The essential functional components and their logical relations

A simplified architecture for the AHVN is shown in Fig. 4 withits functional components, and their interactions.

� The Centralized Management and Control Unit (CMCU) is theentity in the core network that contains all the building blocksdescribed below.

� Inter-operating third party agent [46]: The AHVN is composed ofheterogeneous wireless systems, each with a different serviceprovider. Since direct service level agreements (SLAs) among dif-ferent providers are not feasible, [22] proposed the use of a thirdparty agent and every individual service provider only establishesa direct SLA with the third part agent. The third party agent is com-monly referred to as network inter-operating agent (NIA).

� We propose Mobile IPv6 [47] as the interconnecting protocol forintegrating various access technologies, which ensures a cost-efficient and scalable core backhaul network and keeps the

E

for the AHVN.



T

372

373

374

375

376

377

378

379

380

381

382

383

384

385

386

387

388

389

390

391

392

393

394

395

396

397

398

399

400

401

402

403

404

405

406

407

408

409

410

411

412

413

414

415

416

417

418

419

420

421

422

423

424

425

426

427

428

429

430

431

432

433

434

435

436

437

438

439

440

441

442

443

444

445

446

447

448

449

450

451

452

453

454

455

456

457

458

459

460

461

462

463

464

465

466

467

468

469

470

471

472

473

474




REC

transparency to the underlying access technologies. Moreover,switching from one access network to another could be mappedinto roaming from one wireless network to another and could beeasily addressed considering that a Care-of-Address (CoA) isassigned to each of the vehicles’ radios (i.e., one single IPmulti-homed over different radios). WiMAX, WiFi, DSRC, and3G-LTE technologies are expected to have support for IPv6.

� The system (or network) selection and mobility managementagent (SSMMA): Selecting the most appropriate access network,implementing mobile IP functionalities using home agent (HA)and foreign agent (FA) concepts, and seamless switching amongdifferent networks which is referred to as vertical or intersystemhandoff are among the tasks of SSMMA and can be implementedby employing different mechanisms. In other words, this agentintelligently integrates heterogeneous access networks, each ofwhich is optimized for specific service requirements, in a coop-erative manner to provide ‘‘always best connection (ABC)” to thevehicles.

� Inter-operability gateways (IOGW): In addition to interconnect-ing the access network to the Internet as a lower layer task, italso takes care of higher layer tasks ranging from establishmentof the direct SLA with the NIA to managing interactive conversa-tions with the SSMMA and sharing user profile databases withthe SSMMA. Note that access networks with different serviceproviders use separate gateways even if they are providing thesame access technology.

� The position and status of the vehicles, the neighboring informa-tion, the access radio type that the vehicles are equipped with aswell as all the wireless link states in the communication areaand the characteristics of roads all should be considered for sys-tem selection and mobility management functionalities. Thisinformation could be extracted from the databases of the accessnetworks which have SLAs with the NIA, e.g., HLR in cellular net-work, etc. and should be shared among the entities in the AHVNthat are in charge of radio management and control responsibil-ities. On the core network side, all the information of this typecould be stored in a network database.

� The AHVN also needs to have an authentication, authorization,accounting, and auditing agent (AAAA) which supports securityand billing issues in the network. This functionality could also bedistributed over the different access networks due to the differ-ent billing and authentication methods used the different ser-vice providers.
R 475
476

477

478

479

480

481

482

483

484

485

486

487

488

489

490

491

492

493

UN

CO4. Designing the AHVN architecture: challenges and approaches

4.1. Selection of access network

This functionality could be accomplished by the vehicle, AP orthe CMCU in the core network. In the vehicle-based system selec-tion, the vehicles collect all the data they could obtain in theirneighboring area and select the radio with the lowest cost that alsosatisfies their required QoS. This non-centralized mechanism, how-ever, is sub-optimal due to the vehicles limited access to the globalnetwork status information. The system selection could also becarried out by the APs of the access network the vehicles have reg-istered in as their home agents (HAs) or by the CMCU. As the sys-tem selection responsibility goes towards the core network, thesystem selection procedure becomes more centralized and moreglobally optimal. However, the computing and traffic burden ismostly transferred to the CMCU which in addition to incurring highcosts for service providers as well as vehicles, might not be appro-priate for all applications. For example, the communication thoughthe CMCU instead of direct communication and high traffic load in


PR

OO

F

the CMCU might incur non-tolerable delays in safety applications.Moreover, the vehicles’ system preferences are also not taken intoconsideration. Therefore, we believe that a combination of theabove approaches, i.e., breaking down the SSMMA into severalSSMMAs on the sides of both vehicles and core network, i.e.,SSMMA-V (on the vehicle side) and SSMMA-N (on the networkside) could be a good candidate. SSMMA-V and SSMMA-N have amaster-slave type of interaction in order to finally select the inter-face that in spite of satisfying the service requirements incurs theleast cost and least interference.

In access network selection process, the vehicles’ highest prior-ity is to activate the interface with lowest price that satisfies itsservice requirements. However, the network selection processshould also consider traffic load balancing, the least interferenceto other users and consequently the most efficient resource utiliza-tion in the network which in turn maximize its revenue. Therefore,some compromising mechanism should be employed to keep bothvehicles and service providers satisfied. Some relevant studieswere conducted in [33,48], and [49].

Note that in the network selection procedure, the applicationfor which the interface is being chosen plays an important role.As an example, consider a scenario in which an emergency situa-tion is detected by an 802.16 radio-equipped vehicle. Since notall the vehicles in the neighboring area are equipped with 802.16radios, the AHVN should make other access networks in the areasend notifications as well to ensure that every vehicle in the dangerarea becomes aware of the emergency situation.

ED

4.2. Network selection Vs. link selection Vs. inter-system handoff

Whether to employ the same access technology over all thelinks in an end-to-end route over multiple hops, or to employ themost appropriate access interface in every hop, which might incura considerable cost of inter-system handoff, latency and trafficload, is still an open problem. On the other hand, for some applica-tions it might even be more efficient, in terms of handoff cost andcomplexity to select the access technology only once when the ser-vice is initially admitted to the system, although in this case, anyfailure during the service time initiates the system selection pro-cess again.

In the AHVN, resource management in multiple access net-works should be addressed in order to maximize the resource uti-lization, robustness and stability of the network. Although still anopen problem, some approaches could be the use of efficient sys-tem selection and handoff mechanisms along with dynamic spec-trum sharing through software-defined radios. A game-theoreticapproach was used in [50] for network selection in a heteroge-neous wireless access scenario which ensures fairness among theusers. A utility-based network selection scheme was proposed in[51]. An auction-based resource allocation method for heteroge-neous wireless access was presented in [52]. The problem of seam-less roaming and handoff across cellular networks and WLANs wasaddressed in [53,54].

4.3. Hierarchical design

In order to guarantee the scalability of the AHVN, a hierarchicalstructure could be considered for network components such as theNIA [46], the SSMMA, the network database, etc. in which compo-nents of the regional level, i.e., first-tier components, are integratedto form the second-tire components and the integration processcontinues until the whole network is covered. Determining thenumber of tiers and the number of elements per tier could itselfbe an open problem.



T

PR

OO

F

494

495

496

497

498

499

500

501

502

503

504

505

506

507

508

509

510

511

512

513

514

515

516

517

518

519

520

521

522

523

524

525

526

527

528

529

530

531

532

533

534

535

536

537

538

539

540

541

542

543

544

Fig. 6. A model of direct transmission in V2R networks.




REC

4.4. Operating system and application management

For vehicular telematic applications which are collaborative innature, it is important that the underlying software infrastructuresupports multiple mobile platforms in a ubiquitous manner. Whenapplications are developed or modified, they need to be automati-cally uploaded to the probes, similarly when operating systempatches are required; the update has to be seamless without therequirement of individual operator intervention. Without consid-erable forethought into these issues, the systems being developedextempore will not scale. This issue was investigated and a firstgeneration remotely managed operating system (OS) and applica-tion server was prototyped in [55]. It was observed that these sys-tems are complex enough to warrant high level abstractions andimplementations are identical to those developed under the aus-pices of Services Oriented Architectures (SOA) and web services[56]. In addition, there is a need for an open architecture standardto be developed to relieve the application developers of the detailsof supporting layers in the protocol stack.

5. Designing the AHVN protocols: challenges and approaches

In this section, we discuss the major challenges in protocol de-sign for vehicular networks and the recent research activities cor-responding to these challenges.

5.1. Wireless access strategies

Fig. 5 illustrates the major components of the networking mod-el for vehicular telematics. This model consists of the basic func-tionalities necessary for data communications and the vehiculartelematic applications. The communication model can be designedand optimized to support specific applications.

Transmission strategies determine how data packets are deliv-ered from a vehicular node to an RSU (and vice versa) or from avehicular node to another vehicular node. A direct transmission orsingle hop transmission strategy (e.g., in Fig. 6) can be used wherean RSU or a vehicular node can be reached directly from a vehicularnode (e.g., [40,57,58]). If an RSU or a vehicular node is located faraway from a source node, a multihop transmission strategy canbe employed (e.g., in Fig. 8). In this scenario [42,59], data packetsfrom a vehicular node are relayed by other vehicular nodes until

UN

CO

R

Fig. 5. Wireless access s


EDthey reach the destination (e.g., coordinated external peer commu-

nications (CEPEC) in [7]). Finally, a cluster-based transmission strat-egy forms groups (i.e., clusters) of vehicles, selects a representative(i.e., a cluster head or a gateway) for each group, and transmitsdata through the selected representative (e.g., in Fig. 7). The clusterhead receives data packets from its cluster members and then relaythe packets to the RSU (and vice versa). This strategy is efficient todecrease request/data congestion at the RSUs [60].

In [7], a cluster-based multihop transmission model was pre-sented. Vehicles on a road, which is divided into equal segments,are grouped into several clusters. Which cluster a vehicle will joindepends on its position of the road. For each cluster, a cluster headis chosen based on two criteria: a cluster head must be within asegment border for a segment’s life cycle and it must be the vehicle

trategies in AHVN.



https://www.researchgate.net/publication/4022077_Adaptive_broadcast_for_travel_and_traffic_information_distribution_based_on_inter-vehicle_communication?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==

https://www.researchgate.net/publication/224719558_Efficient_Data_Access_Algorithms_for_ITS-based_Networks_with_Multi-Hop_Wireless_Links?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==

TED

PR

OO

F

545

546

547

548

549

550

551

552

553

554

555

556

557

558

559

560

561

562

563

564

565

566

567

568

569

570

571

572

573

574

575

576

577

578

579

580

581

582

583

584

585

586

587

588

589

590

591

592

593

594

595

596

Fig. 7. A model of cluster-based transmission in V2R networks.Fig. 8. A model of multihop transmission in V2R networks.

Fig. 9. A model of multihop transmission in V2V networks.




UN

CO

RR

EC

which is closest to the centre of its segment. The cluster memberstransfer their data to the corresponding cluster head which acts asa gateway. The data packets are merged into a new packet and thecluster head relays the new data packet to other cluster heads untilthe data reaches the RSU. To guarantee transmission fairness, theRSU assigns an equal amount of bandwidth to each road segment.A multihop V2R communication model and a method based onproxy cache for efficient data access from the Internet were pre-sented in [42].

In [40], a one-hop V2V transmission model was used for dissem-inating travel and traffic information in vehicular networks. A vehi-cle acts like a moving wireless station which sends travel and trafficinformation available at its location to other vehicles on the road.Other vehicles can determine whether the received information isup-to-date or not by using the time stamp information.

For V2V communications, multihop broadcast scheme is usedwhen a target vehicle is out of the transmission range of a broad-casting vehicle. In vehicular safety applications, this transmissionstrategy is used to transmit warning messages to other vehicles(e.g., in Fig. 9). However, due to the unpredictable network topol-ogy, interference, packet collisions, and hidden nodes, multihoptransmissions over V2V networks can be very challenging.

A cluster-based communication scheme in V2V environmentwas presented in [60]. If a vehicle can receive a valid invite-to-joint(ITJ) message from a cluster head within a specific time period, itwill become a cluster member; otherwise, it will become a clusterhead by itself. A cluster can be merged with another cluster if thecluster head receives a valid ITJ message from a neighboring clus-ter head which has more members. For intra-cluster communica-tion, cluster members can send data to the cluster head by usinga centralized management scheme, and for inter-cluster communi-cation, data gathered by the cluster head are sent to another headusing contention-based MAC protocol. Furthermore, this proposedscheme uses two transceivers and different channels in order tomake a vehicle be able to simultaneously transmit request/controlmessages, real-time data, and non-real-time data resulting inreduction of time delay for safety messages.


5.2. MAC protocols

For V2R communications, MAC protocols define how the vehic-ular nodes and the RSUs share common radio channels and for V2Vcommunications, MAC protocols define how the vehicular nodesshare channels to transmit data among them. Hidden terminalproblem caused by infrastructures along roadside, frequent hand-offs caused by high mobility of vehicles and high dynamic of topol-ogy, fairness in channel access are challenging issues for efficientMAC design [7,61,62]. The traditional MAC protocols (e.g., ALOHA,CSMA, CSMA/CA, and IEEE 802.11 MAC) may not be suitable forvehicular networks with high node mobility [61]. The new IEEE802.11p (or WAVE) standard enhances the IEEE 802.11 MAC in or-der to support rapid movement of vehicles [6].

The MAC protocols for vehicular networks can be classified intothe following categories:



T

F

597

598

599

600

601

602

603

604

605

606

607

608

609

610

611

612

613

614

615

616

617

618

619

620

621

622

623

624

625

626

627

628

629

630

631

632

633

634

635

636

637

638

639

640

641

642

643

644

645

646

647

648

649

650

651

652

653

654

655

656

657

658

659

660

661

662

663

664

665

666

667

668

669

670

671

672

673

674

675

676

677

678

679

680

681

682

683

684

685

686

687

688

689

690

691

692

693

694

695

696

697

698

699

700

701

Fig. 10. A model of cluster-based transmission in V2V networks.




UN

CO

RR

EC

� Centralized or distributed MAC protocols: With a centralized MACprotocol, the decision of when and how the channels areaccessed is determined by a central controller (e.g., schedulingin [58,60]). With complete node information, a centralizedMAC protocol can be optimally designed at the expense of over-head needed to acquire such information. A distributed MACprotocol, on the other hand, determines how the channels areaccessed based on local information (e.g., contention in[60,61]). Despite decreasing overhead, a distributed MAC proto-col is usually not optimal due to incomplete node information.While centralized MAC protocols would be preferable for V2Rcommunications, distributed MAC protocols would be moresuitable for V2V communications.

� Single or multiple channels: In presence of multiple channels (pos-sibly different technologies), a MAC protocol needs to select chan-nels to satisfy the application requirements. For example, a highdata rate and possibly a high attenuation-sensitive channel (e.g.,in 5.8 GHz) should be used for typical data exchange, while alow data rate (usually more robust) channel (e.g., VHF or UHF)should be used for transmitting control and safety messages [57].

� Single or multiple RSUs: When considering multiple RSUs, theMAC protocol needs to control the handover process when avehicle moves from one roadside base station to another. Forexample, a distributed MAC protocol was designed in [61],which quickly associates and disassociates a vehicular nodewith an RSU.

5.2.1. MAC Protocols for V2R NetworksThe IEEE 802.11-based MAC protocols will not be suitable for

V2R communications due to not short communication range, lowefficiency in multihop transmission, and high degree of movementof vehicles on the road [63]. A new MAC protocol for V2R commu-nications was proposed in [61] which combines the concepts ofboth centralized and decentralized channel access. It provides pri-oritized access to nodes to quickly reassociate or disassociate withthe access points. Also, it aims at minimizing packet delay whileensuring fairness among the nodes.

In a V2R communication scenario, a vehicular node needs to beserved by an RSU within a limited period of time. However, theRSU may not be able to serve requests from all vehicles within alimited time because of fast mobility of vehicles, large amount ofrequests from vehicles, or limited broadcast range. Therefore, ascheduling algorithm would be required at the RSU to make deci-sion on the sequence in which the vehicles will be served. Most ofscheduling algorithms proposed in the literature are based onparameters such as data size, deadline, request arrival time andfrequency etc.

In [58], a scheduling algorithm called Maximum Freedom Last(MFL) scheduling algorithm was presented. The design goal ofMFL algorithm is to minimize the system handoff rate, while theeffective system utilization is maximized. The scheduling algo-rithm uses cell dwell time and remaining transmission time asparameters to make a priority queue. A larger remaining cell dwelltime implies a lower service priority. A larger transmission timeimplies a higher service priority. The MFL scheme minimizes thehandover rate subject to a given delay constraint. Also, the MFLscheduling scheme was shown to perform better when comparedwith the first-come-first-serve (FCFS) and earliest-deadline-first(EDF) scheduling algorithms.

A scheduling algorithm named D � S was proposed in [64] forV2R communications in order to provide efficient data access byconsidering service deadline and data size. There are two mainconcepts in this algorithm. First, given two requests with the samedeadline, the vehicle which requests for a small size data should beserved first. Secondly, given two requests asking for data with


same size, the vehicle with earlier deadline should be served first.The algorithm was shown to outperform other scheduling algo-rithms such as first-come-first-serve, first-deadline-first, andsmallest data size first algorithms.

In an IEEE 802.16/WiMAX-enabled V2R communications sce-nario, the centralized WiMAX MAC can be used to provide broad-band access to vehicles on a motorway scenario [65] whileensuring fairness guarantee in bandwidth usage. Also, the WiMAXMAC can be configured to operate in point-to-multipoint (PMP) ormesh mode depending on the application and availability of infra-structure. In order to increase effective coverage of the wireless ac-cess network, a new system architecture called Wi-FAN (WiMAXfast-moving access network) was presented in [65].

ED

PR

OO5.2.2. MAC protocols for V2V networks

For V2V communications, the latency of medium access shouldbe low enough to achieve the desired application requirement (e.g.,a maximum delay of 100 ms for safety applications as defined bythe Vehicle Safety Communications Consortium). As has alreadybeen mentioned, a distributed MAC scheme is more suitable forV2V communications. IEEE 802.11p standard-based MAC, whichallows a transmission range up to 1000 m, is a candidate MACscheme for distributed V2V communications [2,8,60,66]. With IEEE802.11 MAC, adaptation of the contention window (CW) size andthe physical layer data rate can enhance broadcasting performancein V2V communications [67]. By considering the estimated numberof vehicles in the surroundings, the adaptation of CW size helpsdecreasing the probability of collision and decreasing the transmis-sion delay. Moreover, the data rate selection improves networkcapacity and helps in situations of channel congestion. The combi-nation of both adaptations of CW size and the data rate outper-forms the performance achieved by the traditional IEEE 802.11system.

For a clustered multihop V2V network (Fig. 10), a centralizedmulti-channel MAC protocol was proposed in [60] for intra-clustercommunication. A cluster head uses centralized time-slot basedscheme assignment for the cluster members to transmit real-timedata over a channel and non-real-time requests over another chan-nel. However, each cluster head uses the contention-based IEEE802.11 MAC protocol to deliver real-time and non-real-time dataover two different channels.



T

702

703

704

705

706

707

708

709

710

711

712

713

714

715

716

717

718

719

720

721

722

723

724

725

726

727

728

729

730

731

732

733

734

735

736

737

738

739

740

741

742

743

744

745

746

747

748

749

750

751

752

753

754

755

756

757

758

759

760

761

762

763

764

765

766

767

768

769

770

771

772

773

774

775

776

777

778

779

780

781

782

783

784

785

786

787

788

789

790

791

792

793

794

795

796

797

798

799

800

801

802

803

804

805

806

807

808

809

810

811

812

813

814

815

816

817

818

819

820

821

822

823

824

825

826

827




UN

CO

RR

EC

Based on a survey of the existing MAC protocols, the authors in[4] concluded that more efforts are required to put them into prac-tice. Besides IEEE 802.11, MAC protocol based on UTRA TDD in theunlicensed 2010–2020 MHz band, which is promoted by [21],could be a promising solution for V2V networks.

5.3. Data dissemination protocols

In order to make vehicles run safety applications, many differ-ent data dissemination mechanisms were proposed in the litera-ture. The main purpose of these mechanisms is to deliver thesafety data to the intended recipients of the data in a low-delayreliable manner. Due to unpredictable network topology, interfer-ence, packet collisions, and hidden nodes, data dissemination overvehicular networks can be very challenging.

In [2], a safety data dissemination mechanism for intra-platooncooperative collision avoidance was proposed. A platoon is a groupof vehicles that are connected to each other directly or by multihoptransmissions. In order to reduce the amount of broadcast trafficand to enhance the delivery rate, an implicit acknowledgmentmechanism is used. Unlike other studies, in this paper the impactof the proposed mechanism was evaluated on vehicular crash per-formance, rather than on conventional networking performance.An issue with this mechanism is that since both safety applicationsand traffic applications are using the same frequency channel in adistributed manner, the latency of the packets depend on the over-all traffic and safety applications traffic. Any variation in the overalltraffic may cause the delay to go beyond the tolerable threshold.

The data dissemination mechanism proposed in [24], called ur-ban multihop broadcast (UMB), removes the need for beaconingand it also addresses the problem of data dissemination in theintersections. Unlike flooding-based protocols [2], in UMB eachvehicle forwards the packet only to the node in the furthest seg-ment of its radio transmission range. At the intersections, the pack-ets are broadcast with the help of repeaters. UMB aims ataddressing the broadcast storm, hidden node, and reliability prob-lems. In order to get rid of repeaters and make the mechanisminfrastructure-independent, the authors of UMB proposed an ad-hoc extension of UMB mechanism called ad-hoc multihop broad-cast (AMB) [26], in which within the intersections, the vehicle clos-est to the intersection is responsible for forwarding the broadcastpacket to the other road segments instead of repeaters. However,AMB fails when the message in an intersection leaves the intersec-tion without being disseminated along all the intersecting roadsegments. Therefore, an enhanced intersection mode data dissem-ination mechanism (EIDD) was proposed in [27] that keeps emer-gency messages in the intersection long enough to ensure that themessages are forwarded to all the intersecting road segments.

In the data dissemination mechanism studied in [25], vehiclesuse periodic beacon messages to report their location, directionand velocity to each other. In this mechanism, called data pouring(DP), the broadcast packet is consecutively broadcast along the roadby each forwarding vehicle to the furthest vehicle in its neighbor listin the data dissemination direction. This periodic data pouring, how-ever, results in high data traffic in the network. To reduce the datatraffic and improve the data delivery ratio, another mechanismcalled data pouring with intersection buffering (DP-IB) was pro-posed where instead of periodically pouring the data on the roads,data is only buffered at the intersections and is periodically rebroad-cast to the intersecting secondary road segments by means of simpledevices called relay and broadcast station (IBer).

In [68], a data dissemination mechanism was proposed whichcan cope with extreme traffic situations, such as high traffic orlow traffic. Due to the bi-directional lane mobility model em-ployed, the vehicles in different directions can be considered tobe in different clusters. In this mechanism, if the relaying vehicle


ED

PR

OO

F

is moving in the same direction as the source and has one neighborbehind moving in the same direction, it forwards the packet to thatvehicle. Otherwise, it forwards the packet to one vehicle in theopposite direction. If the relaying vehicle is not connected to anyof the vehicles (in the same or opposite direction), it holds thepacket until it receives a hello packet from any vehicle or untilthe packet expires. To handle the broadcast storm problem [70]in forwarding the packet, the broadcast suppression scheme in[69] was employed.

5.4. Data aggregation protocols

SOTIS [28] and TrafficView [29] (introduced in Section 1) aim atproviding vehicles with traffic information within the 50–100 kmradius. However, due to limited system capacity, each vehicle is onlyallowed to disseminate a small packet in every beaconing period. Toinclude as much traffic information as possible in the traffic packetsthat the vehicles broadcast, every traffic information system (TIS)employs a data aggregation algorithm. In TrafficView, the aggrega-tion algorithm considers the vehicles in close relative distances tominimize the error resulting from aggregation, and the timestampof an aggregate is the minimum generation time of the consideredrecords. In order to improve efficiency and reliability, [71] proposeda hierarchical data aggregation algorithm, called quad-tree aggrega-tion algorithm, which allows the generation of traffic informationaggregates for areas of variable geographic extensions.

In the quad-tree aggregation algorithm, the map is divided intonon-overlapping areas by an overlay grid of a hierarchical quad-tree architecture instead of road segments. The raw atomic infor-mation units, which are the number of free parking spots countedand periodically broadcast by the RSUs, constitute the aggregatesof the lowest hierarchical level, and four aggregates of a lower levelare integrated into a higher level aggregate, and the timestamps ofthe aggregates are the average generation times of the atomicunits. To deal with the limited system capacity, only a fixed num-ber of aggregates of each hierarchical level are broadcast by anyvehicle. The aggregates are prioritized based on their relevancewhich is computed by taking their age and distance into consider-ation. In SOTIS, TrafficView, and quad-tree aggregation algorithm,when several aggregates with different but overlapping knowledgefor the same segment or the same area are received, the one withthe newest timestamp is taken into account and the rest aredropped. However, the timestamps are the generation times ofthe aggregates or the minimum or average generation times ofthe atomic units and this makes direct comparison of the aggre-gates rather inaccurate and unreliable in terms of their complete-ness and up-to-dateness of the contained data. To overcome thisproblem, [72] proposed another hierarchical data aggregation algo-rithm in which multiple aggregates for the same area can bemerged and none of them is dropped. Instead of having all the datafor generating the aggregates first, the data is incorporated intoaggregates on-the-fly while they are being passed around. In thisalgorithm, the distinct traffic values, e.g., the velocity or positionof the vehicles or the number of parking spots, are mapped intoprobabilistic data structures called Flajolet–Martin sketches [33].The sketches are merged by a simple bitwise OR guaranteeing thatadding already present elements again does not change the results.In order to remove old observations, a time-to-live counter is as-signed to each bit of the sketches that counts down one unit beforeeach broadcast, if not yet zero, or it can be refreshed by a newerobservation.

5.5. Routing protocols

The employment of a routing protocol is inevitable in manyvehicular applications. These include, for example, a scenario in



Original text:

Inserted Text

neighbour

Original text:

Inserted Text

50-100

Original text:

Inserted Text

Flajolet-Martin

T

828

829

830

831

832

833

834

835

836

837

838

839

840

841

842

843

844

845

846

847

848

849

850

851

852

853

854

855

856

857

858

859

860

861

862

863

864

865

866

867

868

869

870

871

872

873

874

875

876

877

878

879

880

881

882

883

884

885

886

887

888

889

890

891

892

893

894

895

896

897

898

899

900

901

902

903

904

905

906

907

908

909

910

911

912

913

914

915

916

917

918

919

920

921

922

923

924

925

926

927

928

929

930

931

932

933

934

935

936

937

938

939

940

941

942

943

944

945

946

947

948

949

950

951

952

953

954

955

956

957




UN

CO

RR

EC

which a vehicle inquires information about traffic condition oravailable facilities on a road segment or a scenario where a pieceof information on the Internet is required, or applications in whichtwo vehicles need to have a peer-to-peer communication. Broad-cast routing, which disseminates information to a set of vehicularnodes far from each other, will be a supporting mechanism formany ITS applications. Many routing protocols for the vehicularad-hoc networks were proposed in the literature [73]. In [73],the authors observed that only a few of the existing routing proto-cols for inter-vehicle networks are able to handle the requirementsof safety applications. This is primarily due to the large overheadincurred for route discovery and route maintenance for highly mo-bile uncoordinated vehicles. An important group of routing proto-cols for ad-hoc networks is topology-based routing protocolswhich needs an establishment of an end-to-end path betweensource and destination before sending any data packet. Due to fastchanges in the network topology and highly varying communica-tion channel conditions, the end-to-end paths determined by reg-ular ad-hoc topology-based routing protocols are easily broken.Therefore, modifications of regular topology-based routing proto-cols were proposed to make them applicable to VANETs [74,75],and completely new topology-based routing protocols were pro-posed as well [76–78].

In [76] a topology-based routing protocol called MURU was pro-posed which assumes that an end-to-end path can be obtained byselecting the most robust paths with lowest breakage probabilitiesusing mobility information. Regarding the number of nodes whichmight lead to network partitioning, and highly varying communi-cation channel through the coverage area of the network, thisassumption, i.e., the existence of an end-to-end path, may not al-ways be valid.

In [78], a path selection scheme called receive on most stablegroup-path (ROMSGP) was proposed. Vehicles are grouped to-gether according to their velocity vectors which include positions,directions, speeds and digital mapping of the roads and the vehi-cles belonging to the same group are given priority in formingthe end-to-end routes to ensure the establishment of more stableroutes. In other words, the selection of the stable path is basedon the set of available paths which have the highest link expirationtime (LET) value. Simulation results showed that ROMSGP can re-duce the number of path breakage and control overhead.

Another group of routing protocols for ad-hoc networks is posi-tion-based or geographic routing protocols which are known to bemore scalable since the forwarding decisions are based on the cur-rent neighbors of the forwarding node and the next forwardingnodes are not initially determined. However, these protocols failin a considerable number of scenarios because they do not considerinformation on the roadmaps or vehicles’ mobility patterns in theirdecision-making procedure. To overcome this problem, spatiallyaware routing (SAR) was proposed in [79] where the routes arecompared by Dijkstra’s algorithm on the basis of roadmap informa-tion. The protocol fails when the packets are forwarded over a dis-connected route including links with no vehicles, i.e., with noconnectivity. Anchor-based street and traffic aware routing (A-STAR) was then proposed in [80] which employs the informationon city bus routes to identify an anchor path with high connectivityfor packet delivery and takes advantage of a new recovery strategyfor packets routed to improve the performance of the protocol.Although in this protocol the chance that more connected routesare selected increases, there is still the possibility that the packetsare forwarded over disconnected routes for some periods. Further-more, pushing all the data traffic towards main roads increases thechance of data traffic congestions over those roads. To overcomethis problem, the authors in [81] proposed a vehicle-assisted datadelivery protocol. In [81], both the traffic pattern and road layoutare used by a forwarding vehicle to find the next road to forward


ED

PR

OO

F

the packet with the purpose of minimizing the end-to-end datadelivery delay by using carry and forward strategy.

Although many studies showed that in vehicular communica-tions position-based routing protocols outperform topology-basedrouting protocols, in [82], a position-based routing protocol calledconnectivity-aware routing (CAR) was proposed which uses anend-to-end route discovery process, i.e., a topology-based ap-proach to locate the destination. However, the discovered routecontains a set of anchor points formed by the velocity vectors ofthe relaying vehicles along the path. In other words, CAR is indeedan integration of position-based and topology-based routing proto-cols which combines finding the location of the destination as wellas determining the connected path between the source and thedestination. It also includes a path maintenance mechanism calledguard to keep track of the current position of the destination.

In [83], empirical vehicle traffic data (measured on I-80 freewayin California) was used to develop a comprehensive analyticalframework to study the disconnected network phenomenon andits network characteristics. It was shown that depending on thesparsity of the vehicles, the VANET can be disconnected from afew seconds to several minutes. This suggests that for many appli-cations new ad-hoc routing protocols are needed as the regular ad-hoc protocols will not work with such long disconnection periods.

In [84], a scenario was considered where some vehicles areequipped with both WLAN and WWAN communication capabili-ties and other vehicles only have WLAN communication capability.Those vehicles which have the dual capabilities can serve as themobile gateways for other vehicles to access the Internet. In addi-tion, a prediction-based routing (PBR) protocol was proposed todetermine the path between a given source vehicle with only theWLAN capability and the destination vehicle which has the dualcapabilities. With the location and velocity information, the life-time of the path can be predicted. A new path can be created beforethe old one breaks. Thus, it can reduce the chance of route failures.

All the routing protocols we discussed were proposed for inter-vehicle communications or VANETs. In [85], an on-demand differ-entiated reliable routing (DRR) protocol was proposed for hybridVANETs. In hybrid VANETs, vehicles can also communicate withthe stationary RSUs. The DRR protocol can find a number of link-disjoint paths for each application in order to guarantee its reliabil-ity requirement, and utilize the RSUs to reduce the overhead andimprove the probability of successful connection setup. In [45], amobility pattern aware routing was proposed for a network com-posed of WMAN and VANET technology which is different fromthe routing protocols used in MANETs or VANETs. With the WMANinfrastructure support, the mobility pattern aware routing protocolcan exploit information of the vehicular network and unique char-acteristics of vehicle mobility to establish a reliable route path inhighly dynamic vehicular networks. Overall, the routing problemfor VANETs is a challenging problem which requires innovativesolutions.

5.6. Congestion control protocols

Provisioning of various ITS services mentioned earlier alsointroduces the problem of data traffic congestion in vehicular net-works. Service providers are usually allotted with fixed bandwidthto provide their service. Congestion arises when there is a demandfor more bandwidth then the available capacity. One way to ad-dress this problem is to increase the bandwidth but this is usuallynot cost-effective because quite often congestion arises due to theinappropriate allocation/utilization of resources. Another approachis to fairly share the available bandwidth among the users withoutcausing congestion, i.e., congestion avoidance with efficient band-width management. For example, MAC queues were manipulatedto deal with channel congestion in a contention-based channel ac-



Original text:

Inserted Text

spplications.

T

958

959

960

961

962

963

964

965

966

967

968

969

970

971

972

973

974

975

976

977

978

979

980

981

982

983

984

985

986

987

988

989

990

991

992

993

994

995

996

997

998

999

1000

1001

1002

1003

1004

1005

1006

1007

1008

1009

1010

1011

1012

1013

1014

1015

1016

1017

1018

1019

1020

1021

1022

1023

1024

1025

1026

1027

1028

1029

1030

1031

1032

1033

1034

1035

1036

1037

1038

1039

1040

1041

1042

1043

1044

1045

1046

1047

1048

1049

1050

1051

1052

1053

1054

1055

1056

1057

1058

1059

1060

1061

1062

1063

1064

1065

1066

1067

1068

1069

1070

1071

1072

1073

1074

1075

1076

1077

1078

1079

1080

1081

1082

1083

1084

1085

1086

1087




UN

CO

RR

EC

cess scheme [90]. This MAC protocol has application to the perfor-mance of Emergency Electronic Brake Light with Forwarding(EEBL-F) application in congested scenarios [90] which addressesthe safety and traffic information issues mentioned in Section 2.

Streaming traffic (e.g., streaming video) is another importantapplication in the future AHVN architecture that would require asteady supply of bandwidth to provide un-interrupted service.Since many of the applications in wired networks are alreadyTCP (Transmission Control Protocol)-based, it is natural to extendTCP to wireless networks. However, it has been observed thatTCP performs less efficiently in wireless networks compared towired networks (e.g., [86]). In a wired network, TCP intercepts dataloss as the main reason for congestion [88]. This assumption holdswell in reliable wired networks. In wireless networks packet lossmay be observed due to link failure, high bit error rate, handoveror any other reason [87]. When packet loss is observed due to suchan event, triggering the congestion control algorithm may result inun-necessary reduction in source sending rate. Therefore, consid-ering packet drops as the major cause for congestion is not efficientin wireless networks especially for streaming multimedia trans-mission [93].

In order to address the problem of data traffic congestion in VA-NET, we need an algorithm that can regulate all types of modernInternet traffic (like streaming multimedia) while considering var-ious congestion factors in wireless networks. Below is the classifi-cation of two types of existing congestion control algorithms.Discussion of some potential candidates is also provided.

5.6.1. Window-based congestion control algorithmsThe dominant window-based congestion control algorithm is

TCP, which plays an important role in order to address the problemof congestion [91]. TCP interprets packet loss as the major reasonfor congestion. It relies on AIMD (Additive Increase MultiplicativeDecrease) [88,92] technique to address the congestion problem.However, such a practice is not efficient for streaming multimediatransmission [93].

In order to improve the performance of TCP, new features wereadded to the exiting protocol. The well-known TCP variants are Ta-hoe, Reno, and NewReno. TCP Tahoe [88,94] includes slow startand congestion avoidance techniques. TCP Reno [95] was devel-oped by adding two additional features to TCP Tahoe – fast retrans-mit and fast recovery. This technique, at times, detects packet lossand performs error recovery before the transmission timer expires.TCP New Reno [96–98] is an improved version of TCP Reno. TCPNew Reno provides better thresholds for fast recovery and im-proves retransmissions. TCP New Reno is the most commonlyimplemented algorithm. For all the TCP variants discussed so far,the TCP window size exhibits a saw-tooth behavior resulting insource sending rate fluctuations. Furthermore, TCP along with itsvariants assumes packet loss as the main reason for congestionwhich is not appropriate for wireless networks.

TCP and its variants discussed above are source-based tech-niques. AQM (Active Queue Management) is a router-based con-gestion avoidance mechanism to improve the performance of TCPcongestion control. A well-known example of AQM is RED (Ran-dom Early Detection) [99]. Traditional tail-drop techniques bufferpackets until the buffer is full. Once full, the node drops any newpackets leading to congestion. As a result, there is an unfair distri-bution of buffer among traffic flows. Buffering may also lead to anincrease in RTT (Round-Trip Time), thus degrading the quality ofservice. RED addresses these problems by dropping packets witha probability and maintaining the average queue size betweenthe configured minimum and maximum thresholds. When thequeue is empty, all incoming packets that cannot be servicedimmediately will be queued. As the queue grows, RED will startdropping packets with a probability that increases with the queue


ED

PR

OO

F

length. It has been observed that the throughput of RED is sensitiveto traffic load and decreases when the queue size is greater thanthe configured maximum threshold [100,101]. Furthermore, REDdoes not perform well in wireless ad-hoc networks. NRED was pro-posed to deal with the problems of RED in wireless ad-hoc net-works [102]. BLUE [103] and FRED [104] schemes improve REDby adjusting the packet drop probability. AVQ (Adaptive VirtualQueue) [106] makes use of token bucket algorithm to provideAQM. Most of these protocols are based on heuristics withoutstrong theoretical backing.

Like the TCP variants above, the general observation is that win-dow-based protocols (e,g, RED, BLUE) exhibit a saw-tooth behaviorwhich leads to sending rate fluctuations, and are not suitable forstreaming multimedia transmission.

5.6.2. Rate-based congestion control algorithmsRate-based congestion controllers adjust the source transmis-

sion rate by controlling the size of the TCP window at the source.Source transmission rate is directly proportional to the TCP win-dow and inversely proportional to the RTT. As a result, the size ofTCP window can be derived from the source transmission rate.Rate-based controllers are well-suited for streaming multimediaapplications [93]. TFRC (TCP Friendly Rate Control) [108] is arate-based controller at the source for unicast traffic. As in the tra-ditional AIMD, TFRC does not halve the sending rate in response tocongestion notification. This makes TFRC a candidate protocol forstreaming multimedia transmission in wired network. TFRC re-sides at the source and provides an equation-based congestioncontrol mechanism for unicast traffic. The proposed equation is afunction of packet loss observed during the transmission. Unfortu-nately, considering only packet loss is not reasonable for wirelessnetworks.

Rate-based controllers can also use AQM at the intermediatenodes to participate in congestion management [109]. The algo-rithm residing at the intermediate node calculates the source send-ing rate based on congestion and converts it to TCP window tomanage traffic. The TCP rate control improves the TCP performanceby controlling the source sending rate. The sending rate of the TCPsource is derived from window size, round-trip time, and the rateof acknowledgements. TCP rate control maintains states per TCPflow and provides protection against misbehaving TCP sources.The window size can be calculated as a function of input-outputrate mismatch in order to match the servicing capability or band-width of a node. In another approach, the network layer conveysavailable bandwidth and propagation delay measurements to TCPsources, which computes the source window using bandwidth de-lay product. The EXACT (Explicit rate based flow control) [110] pre-sents an end-to-end flow control scheme where the intermediatenode conveys the source rate to the end host in the control headerof each packet. It relies on MAC and transport layers to address theproblem of congestion. The source sending rate is calculated basedon current measured bandwidth of the outgoing links and the cur-rent rate of information flow going through the router.

The Adaptive Proportional Integral (PI) Rate Controller [111] is arate-based controller that supports best-effort traffic in the Inter-net. It employs control theory and AQM in order to deal with con-gestion. The controller calculates the source sending rate based oninstantaneous queue length of the intermediate router and adver-tises it to the sources using the acknowledgement message. Theadaptive feature of the controller allows it to self-tune only whenthere is a dramatic change in the network traffic. The adaptive PIrate controller does not interpret packet loss as the reason for con-gestion. The controller is capable of providing a steady throughputat the source which is well suitable for multimedia streaming.

The utility-based control can be a variation of rate-based con-trol method. The source node adjusts its transmission rate based



Original text:

Inserted Text

well known

T

1088

1089

1090

1091

1092

1093

1094

1095

1096

1097

1098

1099

1100

1101

1102

1103

1104

1105

1106

1107

1108

1109

1110

1111

1112

1113

1114

1115

1116

1117

1118

1119

1120

1121

1122

1123

1124

1125

1126

1127

1128

1129

1130

1131

1132

1133

1134

1135

1136

1137

1138

1139

1140

1141

1142

1143

1144

1145

1146

1147

1148

1149

1150

1151

1152

1153

1154

1155

1156

1157

1158

1159

1160

1161

1162

1163

1164

1165

1166

1167

1168

1169

1170

1171

1172

1173

1174

1175

1176

1177

1178

1179

1180

1181

1182

1183

1184

1185

1186

1187

1188

1189

1190

1191

1192

1193

1194

1195

1196

1197

1198

1199

1200

1201

1202

1203

1204

1205

1206

1207

1208

1209

1210

1211

1212

1213

1214




UN

CO

RR

EC

on feedback network congestion information and utility function.The UBPFCC (Utility-Based Packet Forwarding and Congestion Con-trol) algorithm [112] assumes broadcast to be the dominant formof communication in VANET and addresses congestion caused bybroadcast applications. This is a significant setback of this ap-proach as transaction-based applications can also exist in VANETsand either of these applications can be the reason for congestion.The algorithm utilizes a utility function and encodes the utilityinformation in each data packet. The average utility value is thencalculated for each individual node and based on this the availabledata rate is shared.

5.7. Cross-layer protocol design in vehicular networks

Traditional layered approach relies on adapting the communi-cation layers independently from other layers. The arguments thatsupport layered approaches consider that designing independentprotocols for each communication layer will create long-term solu-tions. However, this type of implementation has been long criti-cized as being rigid and incapable of having proactive change toshort term changes in network environment, and the excessiveoverhead from layer to layer represent degradation in throughput.

As a different approach, cross-layer design makes use of feed-back information from lower layers to help the transport layer per-form better under network congestion [113]. This is dealt with thedetection, control and corresponding reaction to particular net-work conditions such as channel errors, link contention and routefailures. By exploiting this information, the network itself will beable to determine the current load situation and protect itself fromcongestion [113]. There can be different combination of layers in-volved in this approach such as application and network layers,and transport and link layers. In fact, the TCP suit has not beenstrictly a layered protocol to start with. Non-linear design can beused to study the tradeoff of the power control in the physical layerand the transport layer congestion in a multihop network such as aVANET [114].

In the area of MAC protocols for VANETs, some starting pointsfor proposals dealing with novel concepts like cross-layer exploita-tion of IEEE 802.11-based MAC mechanisms and dynamic cluster-ing for efficiency and realiability of V2V multihop broadcast,multichannel MACs, and practical performance issues in differentscenarios can be found in [115–117]. In particular, [115] illustratedthe design and analysis of a fast multi-hop forwarding MAC andclustering scheme for VANETs which is compliant with IEEE802.11 DCF systems. A multichannel MAC protocol was proposedin [116] for high density VANETs using directional antennas. Theproposed scheme was observed to provide a high spatial reuseand high probability of reliable transmission. A simulation-basedcross-layer (MAC and routing) performance study was presentedin [117] for IEEE 802.11 MAC (i.e., CSMA/CA), and ADHOC-MACwhich is based on reliable reservation (RR)-ALOHA used in CalTALKand FleetNet projects [21,22]. Efficient design of cross-layer proto-cols for VANETs remains as an open problem.

5.8. Security protocols

Security is among the most important aspects of vehicular net-works. All messages exchanged between OBUs and RSUs must havethe standard properties of authentication and non-repudiation, i.e.,that the source of each message can be authenticated, and also thatthe originator of the message can’t subsequently deny sending themessage. Contents of the message must be checked for integrity ifnecessary. All safety-related messages must be delivered withbounded delay. Senders of safety messages must have the rightto preserve their privacy so that their identity can be revealed ifnecessary only to legal authorities. In this context, wireless loca-


ED

PR

OO

F

tion privacy protection [118] and secure location verification[119] are two important issues in vehicular ad hoc networks. Fur-thermore, some of the messages that are encrypted may need to beexamined later for forensic evidence. On the other hand, all partic-ipants in a vehicular network may have incentives for misbehavior,which may easily result in some kind of security attacks.

There has been a significant research activity in listing and ana-lyzing potential security attacks in vehicular networks [120–123,4,124–129]. Several possible security threats in VANETs wereidentified in [124]. For example,

� Drivers might attempt to modify speed and position informationto avoid liability for the accidents.

� Drivers could also modify congestion information in order to getfaster to the destinations.

� Bogus RSUs may be placed along the road to transmit false infor-mation about traffic congestion, thus causing the drivers tomake wrong decisions, or perhaps to prevent transmission ofsafety messages which amounts to a Denial of Service (DoS)attack.

� An attacker may cause channel jamming or inject dummy mes-sages to bring down the network (DoS attack).

� An attacker may pretend to be another vehicle by using falseidentities (Masquerading).

� Industrial vendors and service providers that manufacture and/or operate RSUs and servers may collect and sell informationabout the vehicles’ driving patterns, traffic parameters, andaccidents.

� Police officers might abuse their authority using their network-ing privileges.

All these security attacks indicate that attacks should comemostly from ‘insiders,’ and that no participant – be it an OBU,RSU, or even a network server – should not be fully trusted. Thereis also a possibility of attacks by outsiders who can attempt to dis-turb traffic safety by replaying old messages, or even launch a DoSattack by flooding the area with bogus messages. The obvious con-clusion is that appropriate security mechanisms must be deployedin order to raise security assurance of a VANET. Of course, the secu-rity mechanisms must comply with the AHVN communicationarchitecture described before.

In [124], it was concluded that, given the nature of the VANETs,the existing security solutions cannot be readily applied to thesenetworks. The requirements for a security system for safety mes-saging in a VANET are as follows [124]: authentication, verificationof data consistency, availability of a robust communication chan-nel, tamper evidence mechanisms at the vehicular nodes and RSUs,non-repudiation, privacy, and real-time constraints. To addressthese security requirements, a number of proposals for a securityarchitecture have been published in recent years. Most of the pro-posals use some form of public key infrastructure (PKI), possiblymodified to cater to the characteristics of a vehicular network,where the certification authority (CA) is placed on informationservers, while RSUs and OBUs obtain certificates with public/pri-vate key pairs. However, some approaches use a hybrid of PKIand symmetric key architecture, based on pre-established secretkeys between components of infrastructure. Symmetric keys thusshared are subsequently used to generate message authenticationcode (MAC), using keyed hash function HMAC (Hash MutualAuthentication Code) technique. The main motivation for thedevelopment of the hybrid security architecture is to decreasethe computational overhead of generating and verifying digital sig-natures in PKI architectures.

It was pointed out in [125] that the overall security in a vehic-ular network can be enhanced by doing local plausibility checks invehicles (e.g., internal sensors) and the RSUs. These checks can in-



https://www.researchgate.net/publication/4206522_Congestion_control_in_vehicular_ad_hoc_networks?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==

1215

1216

1217

1218

1219

1220

1221

1222

1223

1224

1225

1226

1227

1228

1229

1230

1231

1232

1233

1234

1235

1236

1237

1238

1239

1240

1241

1242

1243

1244

1245

1246

1247

1248

1249

1250

1251

1252

1253

1254

1255

1256

1257

1258

1259

1260

1261

1262

1263

1264

1265

1266

1267

1268

1269

1270

1271

1272

1273

1274

1275

1276

1277

1278

1279

1280

1281

1282

1283

1284

1285

1286

1287

1288




clude, for example, comparison of received information to sensordata and evaluation of messages from different sources about asingle event.

We list the main categories of security architectures below, themain difference among them being the level of trust built intoOBUs, RSUs, and application servers, as well as the level of IDand location privacy offered to the drivers. Note that privacy isconditional, since in the case of dispute legal authorities have theright to reveal the IDs of OBUs and RSUs involved in accident. Allapproaches assume that vehicle has tamper proof hardware(TPH) to store certificates or/and elements of shared secret.

T

1289

1290

1291

1292

1293

1294

1295

1296

1297

1298

1299

1300

1301

1302

1303

1304

1305

1306

1307

1308

1309

1310

1311

1312

1313

1314

1315

1316

1317

1318

1319

1320

1321

1322

1323

1324

1325

1326

1327

1328

1329

1330

1331

1332

1333

1334

1335

1336

UN

CO

RR

EC

5.8.1. PKI-based architecturesOne of the pioneering proposals in this area is [130] where

Drive Ad Hoc Networking Infrastructure (DAHNI) was proposedincluding PKI infrastructure for managing public/private key pairs.Authentication and integrity is achieved using RSA encryption fordigital signatures.

In [131], the authors presented a PKI infrastructure within theSecCar project. It is based on a cluster communication model,where cluster heads sign the messages and transmit them to indi-vidual recipients.

The next step was done in [120], where a vehicular public keyinfrastructure was proposed, including a Certificationing Authority(CA) which issues public/private key pairs to vehicles. Authors as-sume that vehicles contain electronic identity in the form of elec-tronic licence plate (ELP) issued by the government and/orelectronic chassis number (ECN) issued by the vehicle vendor. Topreserve privacy and prevent location tracking, each vehicle is gi-ven a large set of short-lived anonymous key certificates whichdo not contain the vehicle ID. To prevent location tracking, pub-lic/private key pairs have to be periodically changed. The authorsevaluated the computational complexity and size of signaturesfor three Public Key Cryptosystems (PKCS). Proposed digital signa-ture is based on ECDSA (Elliptic Curve Digital Signature Algorithm),which helps to reduce the packet size.

A slightly more secure architecture was proposed in [132]where vehicle certificates are blindly signed by the CA, so thatinsiders cannot easily establish the link between the vehicle IDand issued certificate(s). This link is escrowed [133] by multipleauthorities.

In [123,134], the PKI infrastructure is enhanced with two cryp-tographic techniques that improve drivers’ privacy. Namely, for thecommunication scenario in which a group of OBUs communicateswith the RSU, group signature is used to secure the communica-tions among OBUs in the communication group. Messages are se-curely and anonymously signed by the OBUs so that neither RSUnor any other eavesdropper is able to resolve the actual identityof the signer. Identities of the signers can be recovered by theauthorities though. Messages sent by the RSU to the OBUs areauthenticated by digital signature, using ID-based cryptography.

Work reported in [135] is an extension of [120] in the sense thatanonymous public key certificates are associated with OBU’spseudonyms which are not issued by the same authority (CA) asproposed in [136]. As a result, linking messages under differentpseudonyms becomes increasingly hard over time and space. Thiswork also defines the rules for changing the pseudonym, i.e., thepublic key. These rules require changing MAC address and IP ad-dress of the OBU in order to prevent tracking.

1337

1338

1339

1340

1341

1342

5.8.2. Hybrid security architectures for vehicular networksThe security architecture proposed in [137] is based on shared,

long-lived vehicle pseudonyms. They are pre-installed on RSUs andOBUs. The link between the vehicle pseudonym and its real iden-tity is kept in trusted servers. Long-lived pseudonyms are used to


ED

PR

OO

F

derive session keys which are used to provide packet authentica-tion code using HMAC technique [133].

A modification of hybrid PKI security architecture was dis-cussed in [138]. In this proposal, a trusted third party (TTP) whichplays the role of the CA, allocates a number of pseudonym certifi-cates to each vehicle. Pseudonym certificates are preloaded in theTPH, together with the root certificate of the CA. After the certifi-cate exchange, the two neighbors can securely exchange a secretsymmetric key.

In [139], a security architecture for application services in avehicular network was proposed based on Kerberos. The architec-ture supports authentication, authorization, and accounting. Theuser submits a request for service to the Kerberos Server at the ser-vice provider (SP) site. If the request is successful, the SP issues aTicket Granting Ticket (TGT) which contains authorization forinformation services. The user then submits the TGT to the Kerber-os proxy residing at the RSU in order to receive an IP address fromDHCP server and public key certificate. The public key is used after-wards for the generation of symmetric keys between OBUs, for thepurpose of mutual authentication.

A hybrid architecture in which the OBU does not trust public serv-ers was proposed in [140]. This architecture is characterized withgroup-based anonymous authentication protocol in which an OBUobtains the RSU’s certificate, and then uses the RSU’s public key toencrypt and submit group session key and other authenticationparameters to the RSU. An extension of this approach was proposedin [141], where each vehicle is assigned a symmetric key pool.

The framework from [120] was combined with the TESLA broad-cast authentication protocol [142] to develop the TESLA based Se-cure Vehicular Communication protocol (TSVC) [143]. In thisarchitecture, an OBU is allocated a large number of short-livedanonymous certificates, like in [120], but during the lifetime of eachcertificate messages are authenticated using a hash chain [144]. Thehash chain for each certificate is initiated using a random seed S.Each hash value is used as a secret key to generate the HMAC for anumber of packets, and released with a delay of d so that HMACcan be verified. Therefore, a digital signature with anonymous keysis needed only for the first packet in the chain sequence, and thecomputational burden of verifying packet integrity is decreased.

5.8.3. Enhancing security by data aggregation, validation, andcorrection

The overhead incurred in implementing a security mechanismcan be reduced (and hence the channel efficiency can be improved)through data/message aggregation in a group communicationenvironment [126]. Data aggregation can also contribute to betterdata correctness and hence to a higher level of security. In [126],the authors proposed three aggregation techniques for the relayingvehicles (i.e., group leaders). These are based on combining signa-tures from a group of vehicles reporting the same event, using over-lapping groups with each geographically-predefined group havingits own symmetric key, and dynamic group key creation. With se-cure aggregation mechanisms, the effects of vehicle density andspeed on the bandwidth consumption and delay were observedby simulations.

The problem of validating aggregated data in V2V networks wasaddressed in [127]. The authors proposed a solution to this prob-lem based on PKI-based authentication the main idea of which isto use random checks to catch the attacker probabilistically, anddiscouraging the attackers by imposing a high penalty. After anaggregated message has been sent, to validate the message, theaggregator is asked to provide a randomly-chosen original signedmessage. The overhead of the proposed approach is small in termsof communication costs.

A general sensor-driven approach to detect and correct mali-ciously introduced errors in VANET data was proposed in [129].



1343

1344

1345

1346

1347

1348

1349

1350

1351

1352

1353

1354

1355

1356

1357

1358

1359

1360

1361

1362

1363

1364

1365

1366

1367

1368

1369

1370

1371

1372

1373

1374

1375

1376

13781378

1379

1380

1381

1382

1383

1384

1385

1386

1387

1388

1389

1390

1391

1392

1393

1394

1395

1396

1397

1398

1399

1400

1401

1402

1403

1404

14061406

1407

1408

1409

1410

1411

1412

1413

1414

1415

1416

1417

1418




In this approach, each node maintains a model of the VANET con-taining its knowledge on the network, and it tests the validity ofdata received from other nodes against this model. The sensor datacollected by the nodes are shared with immediate neighbors andpropagated to a neighboring region.

A distributed method to detect forged of position information inVANETs was proposed in [128]. The main idea is to calculate a trustvalue for the other nodes based on the observations over time onthe different network parameters such as maximum transmissionrange, maximum speed, maximum node density. Although the pro-posed method does not entirely prevent the malicious nodes toforge the position information, it however significantly reducesthe possibilities for attackers using falsified position information.

The problem of design, analysis, and implementation of efficientdata aggregation, validation and correction in VANETs still remainsas an open problem.

T

1419

1420

1421

1422

1423

1424

1425

1426

1427

1428

1429

1430

1431

1432

1433

1434

1435

1436

1437

1438

1439

1440

1441

1442

1443

1444

1445

1446

1447

1448

1449

1450

1451

1452

1453

1454

1455

1456

1457

1458

1459

1460

1461

1462

1463

1464

UN

CO

RR

EC

5.9. Privacy protocols

As has been mentioned before, drivers have the incentive to ‘tryto bend the rules’ and avoid liability for violating traffic rules, bymodifying the information about their speed, position, accelera-tion/deceleration, and other relevant variables in the safety mes-sages, in order to avoid liability. On the other hand, as noted in[121], the majority of drivers is honest and would not feel comfort-able tinkering with their OBUs. Such drivers will gladly contributesafety messages but under the condition that these messages willnot reveal their ID, name, location and driving patterns to unautho-rized third party. However, drivers’ privacy in a VANET is condi-tional, since in case of a dispute it can be revealed by legalauthorities. This issue has launched significant research activityand basically all aforementioned VANET security architectures dif-fer in their view and implementation of driver’s privacy.

Driver’s privacy is generally achieved using pseudonyms [136],which can be time- or geographically based.

Time-based pseudonyms were defined in [145] as:

PXðtÞ ¼ HMACK�XðIDX ; tÞ

where IDX is the real identity of the OBU (and, by extension, thevehicle) X; PXðtÞ is the vehicle pseudonym calculated at time t,HMAC is the keyed hash function, and K�X is the secret key. Similarapproach was used in [146] where pseudonyms change over time.Mapping between pseudonyms and real identities is performed bythe trusted authority which stores the real identities and can, thus,easily perform the translation in either direction.

Geographically based pseudonyms were proposed in[120,132,135,143]. These pseudonyms can be implemented as alarge set (probably 43800 certificates per OBU) of anonymous cer-tificates with public keys, which the OBU changes after some tra-versed distance. Legal authorities maintain the link between theset of anonymous certificates and the ID of the OBU which is equalto electronic licence plate. An interesting technique, called Cara-van, for changing geo-based pseudonyms was proposed in [147].This approach is based on a navigation group of vehicles sharingthe same geographical zone. All vehicles within the group deploya random silent interval before changing the pseudonyms. Afterthe silent period, the vehicle designated as Group Leader transmitsthe updates of pseudonyms to the members of the navigationgroup. In this manner, mapping of new pseudonyms to vehicleIDs by an unauthorized third party is prevented.

Similar approach to anonymity was proposed in [121], whereanonymizer servers are placed at RSUs. When vehicle V wants tochange its pseudonym and its public/private key pair KV ; K�1

V , itwill interact with the RSU/anonymizer R in the following way:


ED

PR

OO

F

R! V : N

V ! R : KV ; fNgK�1V

R! V : fK 0V ;K0�1V ; T; fK 0V ; TgK�1

RgKV

where N is a random nonce, T is the timestamp, and pair K 0V ; K 0�1V is

the new set of keys. The problem with this approach is that the RSUhas to be properly authenticated by the vehicle. Moreover, there isthe problem of tracking the identity of a vehicle through the set ofRSUs, if it has liability issues. Therefore, it would be appropriate ifthe vehicle submits its real identity to the anonymization server,as indicated by the authors in [121].

The work in [135] has the potential to achieve a high degree ofuntraceability. However, it assumes existence of a pseudonymityresolution authority (PRA), the implementation of which is cur-rently vague. If the role of the PRA is played by the CA, this frame-work is virtually identical to the one described in [120];furthermore, about the same level of location privacy can beachieved using the proposal in [143]. However, the price of privacyfor these techniques is that since the number of certificates per OBUis large, detecting an OBU which has sent false message requiressearching the table of certificates which has an enormous numberof entries (43,800 times the number of cars in the province/country).

Yet another privacy preserving technique was presented in[138] where each new member in the vehicle group submits itsown certificate together with x other (dummy) certificates. In thismanner, the attacker will not be able to trace the vehicle identity.However, all existing neighbors would have to encrypt all theirmessages with all public keys (or all symmetric keys in hybrid var-iant), which makes this approach costly and not scalable.

Finally, the GSIS scheme [134], which offers a high degree ofprivacy using group signature technique, has high computationaland communication cost.

6. Open issues and research directions

The objective of the AHVN architecture is to integrate the di-verse wireless access technology so as to provide an ‘‘always bestconnected (ABC)” communication capability that is secure, reliableand cost-effective. Such a communication platform is not currentlyavailable but is highly desirable to advance the capabilities of fu-ture ITS applications. Efficient protocol solutions (e.g., for mediumaccess control, radio resource management, radio link control,Internetworking between DSRC, 3G cellular, and WiMAX networks,and end-to-end transmission control) will be essential for cost-effective deployment of AHVN. The protocol solutions should con-sider the dynamics of a highly mobile and potentially sparsely con-nected network of vehicles. Addressing (and hence routing) is adifficult problem as vehicular clusters change compositionsdynamically and communities of interests are formed and dis-solved rapidly. When multiple wireless access capabilities exist,it can complicate the problem of finding and addressing these dy-namic network nodes. Sophisticated solutions can be developedthat leverage the different capabilities of diverse networks forthe AHVN. Security and privacy continue to be a serious concernto users of wireless communications, particularly in the unlicensedbands. Efficient methods to transport multimedia data, especiallyvideo, over the AHVN will also need to be developed as vehicles be-come mobile nodes in the global network.

In this section, we outline some of the open issues and direc-tions for future research to realize AHVN architecture and imple-ment the corresponding protocols for vehicular telematics overheterogeneous wireless networks.

� Enhanced multi-channel MAC protocols for DSRC: Although theMAC for DSRC (i.e., IEEE 802.11p) follows the original IEEE



Original text:

Inserted Text

(43800

https://www.researchgate.net/publication/37420754_Secure_and_Privacy-Preserving_Communication_in_Hybrid_Ad_Hoc_Networks?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==

T

1465

1466

1467

1468

1469

1470

1471

1472

1473

1474

1475

1476

1477

1478

1479

1480

1481

1482

1483

1484

1485

1486

1487

1488

1489

1490

1491

1492

1493

1494

1495

1496

1497

1498

1499

1500

1501

1502

1503

1504

1505

1506

1507

1508

1509

1510

1511

1512

1513

1514

1515

1516

1517

1518

1519

1520

1521

1522

1523

1524

1525

1526

1527

1528

1529

1530

1531

1532

1533

1534

1535

1536

1537

1538

1539

1540

1541

1542

1543

1544

1545

1546

1547

1548

1549

1550

1551

1552

1553

1554

1555

1556

1557

1558

1559

1560

1561

1562

1563

1564

1565

1566

1567

1568

1569

1570

1571

1572

1573

1574

1575

1576

1577

1578

1579

1580

1581

1582

1583

1584

1585

1586

1587

1588

1589

1590

1591

1592

1593

1594

1595

1596




UN

CO

RR

EC

802.11 MAC and its extensions (e.g., IEEE 802.11e), the problemof multi-channel coordination/access in the DSRC MAC is open.This problem also needs to be addressed for a multihop V2Vcommunication scenario. Efficient distributed multi-channelMAC protocols for DSRC can be developed based on the ‘‘cogni-tive radio” concept. A DSRC radio transceiver may use intelligentalgorithms (e.g., reinforcement learning) to learn the surround-ing environment and then to exploit the knowledge thusobtained to adaptively select the transmission channel and thetransmission parameters (e.g., transmission power) to achievethe target system performance.

� Dynamic spectrum sharing between DSRC and WiMAX radio: ForV2R communications through WiMAX base stations, dynamicspectrum sharing between DSRC radio and the WiMAX radiocan potentially improve the communication efficiency as wellas the spectrum utilization (and hence the service providers’revenue). This would be particularly true when the density ofthe vehicles (i.e., traffic load) increases, and therefore, the DSRCspectrum becomes congested. This dynamic spectrum sharingcan be implemented through software-defined radio. Sincedynamic spectrum access by multiple DSRC radio gives rise toa competitive scenario, game-theoretic models will be suitableto analyze this problem and the system dynamics.

� Heterogeneous wireless access for vehicular telematics: Efficientintegration of different wireless access technologies (e.g., WiFi,WiMAX, 3G cellular) and optimal radio resource managementfor vehicular networks is an open problem. In the AHVN, resourcemanagement in multiple access networks should be addressed inorder to maximize the resource utilization, robustness and stabil-ity of the network. Although still an open problem, someapproaches could be the use of efficient system selection andhandoff mechanisms along with dynamic spectrum sharingthrough software-defined radios. A related issue here is pricingof radio resources in the different access networks. A pricingmodel characterizes the service fee (i.e., price) for utilizingresources in a radio access network. To access the radio resources,a vehicular node has to pay to the radio resource owner which istypically the service provider. The decision on price setting hasto be optimally made by a service provider (or radio resourceowner) in a vehicular network to maximize network utility.

� Multimedia transmission and QoS support over vehicular networks:Multimedia (e.g., video) transmission in wireless environmentsis still a challenging task calling for high-compression efficiencyas well as a network friendly design. Parameters in video coding,such as frame rate, quantization parameters, and frame drop-ping, can be controlled to give different bitrates (and hence dif-ferent decoded video quality). There are challenges in adjustingthese parameters in order to transmit multiple compressedvideo programs over wireless networks in real-time subject tochannel fading, co-channel interference (CCI), and limited band-width and power [148]. Other factors are caused by mobility,network partitions and route failures, change in channel qualityand data rate, and network load. Some of these have to beaddressed by data congestion control at the same time.We needto understand its design limits due to its extreme bandwidthdemands on real-time, and to provide adequate networkresources from the limited bandwidth of the wireless networkto support and differentiate the QoS requirements (e.g., reliabil-ity and latency) from different real-time streams. Previous wire-less architecture and infrastructure are pretty much set up foreither voice or data, which is not fit for transportation of videostream.

� Data congestion in vehicular networks: There is much work toextend its capability to wireless network especially if one wantsto stay within the TCP realm in light of earlier discussion. Thedifficulties are the results of 1) dramatic changes in the BDP


ED

PR

OO

F

(Bandwidth-Delay Product) contributed by RTT (Round TripTime) fluctuations, node mobility, and traffic load change at amobile node, and 2) multihop communication characteristicsin terms of path asymmetry, channel conditions from errors,medium contention, as well as hidden and exposed stations.To combat these problems several modifications to the transportlayer were proposed in the literature. However, usefulness ofthese modifications needs to be investigated in a realistic V2Rand V2V communications scenario considering lower layer pro-tocol intricacies. Achieving a steady supply of bandwidth forstreaming traffic in presence of congestion is a challenging task.

� Cross-layer approaches: Although the cross-layer approachesprovide better performance, they are more complex to imple-ment and design. Since implementation requires modificationof multiple communication layers, joint optimization amongall the layers can be challenging. Most of the works on thecross-layer optimization are derived from heuristics and simula-tion. A mathematical framework to characterize the interactionamong the layers would be desirable. This would allow reliablealgorithms to be developed for real-time applications which arebecoming increasingly important for ITS applications over vehic-ular wireless networks.

� Implementation of security primitives with a good tradeoffbetween authentication, privacy, computational complexity,communication complexity and scalability in vehicular net-works is a big research challenge. Some variation of the PKI sys-tem with careful trust analysis of OBU, RSU and authenticationservers will eventually need to be adopted. Security primitivesmust be computationally lightweight for OBUs and should prob-ably be derived from some suitable form of identity based cryp-tography, similar to one developed in [149,150]. RSUs shouldhave tamper-free hardware as well (this is necessary for OBUs)and they should be connected using an IPSec tunnel [133] tothe authentication server. Furthermore, all parties in the archi-tecture should be able to authenticate each other.It is necessaryto develop full protocols for transmission safety messages aswell as protocols for transmission of liability messages duringand after the accidents. These protocols should be developedfor the scenarios where the infrastructure (RSUs and servers)is fully present, but also for the situations when only OBUs arepresent while the infrastructure is missing. Protocols for valueadded services (infotainment) and billing for all VANET servicesshould be developed as well.

� Neither of the privacy proposals described before (with theexception of [135]) even mentions that OBU can be traced usingits MAC address. An OBU can also be traced using its IP address,but since it is periodically changed via DHCP, the IP addresstraceability is more complex than MAC address traceability.Therefore, it is necessary to remove the source MAC addressfrom the header of the MAC frame, and use some generic MACaddress similarly to generic 0.0.0.0 IP address used in DHCP.

� At the application layer, there are challenges in developing ser-vices and applications for most effective use of ITS and data theycollect. In particular, the implementation and software develop-ment has to resemble and mirror that of similar complex infra-structures. The applications have to be as low level protocolagnostic as applications being developed for the web, capitaliz-ing on the efficiencies of layered architectures and modern soft-ware engineering. Also, it is essential that applications scale upof any vehicular technology employed across a large numberof vehicles that are intended to have more functionality thansimple monitoring. Applications developed for next generationvehicular telematics will require an ITS-SOA similar to that infound in the business and electronic commerce sector. Thenew breed of ITS application developer will also need a healthydegree of statistical processing in his or her toolbox.



https://www.researchgate.net/publication/4272175_Architecture_for_Secure_and_Private_Vehicular_Communications?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==

T

15971598

1599

1600

1601

1602

1603

1604

1605

1606

1607

160816091610161116121613161416151616161716181619162016211622162316241625162616271628162916301631163216331634163516361637163816391640164116421643164416451646164716481649165016511652165316541655165616571658165916601661166216631664166516661667166816691670167116721673

16741675167616771678167916801681168216831684168516861687168816891690169116921693169416951696169716981699170017011702170317041705170617071708170917101711171217131714171517161717171817191720172117221723172417251726172717281729173017311732173317341735173617371738173917401741174217431744174517461747174817491750175117521753175417551756175717581759

Q1




UN

CO

RR

EC

7. Uncited references

[89,105,107].

Acknowledgments

This work was supported by the AUTO21 NCE research grant forthe project F303-FVT. The authors would like to thank KhajonpongAkkarajitsakul, Subir Biswas, Man Hon Cheung, Mahbubul Haque,Kelly He, Yang Hong, Seyed Ali Hosseininezhad, Jinwoo Lee, BrijechK. Mohandas, Kaveh Shafiee, Joo-Han Song, and Daxin Tian for theircontributions towards this article.

References

[1] W. Chen, S. Cai, Ad hoc peer-to-peer network architecture for vehicle safetycommunications, IEEE Communications Magazine 43 (4) (2005) 100–107.April.

[2] S. Biswas, R. Tatchikou, F. Dion, Vehicle-to-vehicle wireless communicationprotocols for enhancing highway traffic safety, IEEE CommunicationsMagazine 44 (1) (2006) 74–82. January.

[3] M. Wellens, B. Westphal, P. Mahonen, Performance evaluation of IEEE 802.11-based WLANs in vehicular scenarios, in: Proceedings of IEEE VehicularTechnology Conference (VTC) Spring, April 2007, pp. 1167–1171.

[4] J. Luo, J.-P. Hubaux, A survey of inter-vehicle communication, EPFL TechnicalReport IC/2004/24, March 2004.

[5] D. Gray (Ed.), Mobile WiMAX Part I: A Technical Overview and PerformanceEvaluation v2.8, Apr 2006, http://www.wimaxforum.org/techno-Logy/downloads/Mobile_WiMAX_Part1_Overview_and_Performance.pdf, lastaccess by July, 2007.

[6] D. Jiang, L. Delgrossi, IEEE 802.11p: towards an international standard forwireless access in vehicular environments, in: Proceedings of IEEE VehicularTechnology Conference (VTC) Spring, May 2008, pp. 2036–2040.

[7] K. Yang, S. Ou, H.-H. Chen, J. He, A multihop peer-communication protocolwith fairness guarantee for IEEE 802.16-based vehicular networks, IEEETransactions on Vehicular Technology 56 (6) (2007) 3358–3370. Part 1,November.

[8] H. Menouar, F. Filali, M. Lenardi, A survey and qualitative analysis of MACprotocols for vehicular ad hoc networks, IEEE Wireless Communications 13(5) (2006) 30–35. October.

[9] M. Khabazian, M. Ali, A performance modeling of connectivity in vehicular adhoc networks, IEEE Transactions on Vehicular Technology 57 (4) (2008)2440–2450. July.

[10] F. Xie, K.A. Hua, W. Wang, Y.H. Ho, Performance study of live video streamingover highway vehicular ad hoc networks, in: Proceedings of IEEE VehicularTechnology Conference (VTC) Spring 2007, September–October 2007, pp.2121–2125.

[11] <http://www.cvisproject.org/>.[12] <http://www.sevecom.org/>.[13] <http://www.preciosa-project.org/>.[14] <http://evita-project.org/>.[15] <http://www.com2react-project.org/>.[16] <http://www.ertico.com>.[17] <http://wiki.fot-net.eu/index.php?title=SIM-TD>.[18] <http://www.safespot-eu.org/>.[19] <http://www.comesafety.org/>.[20] <http://www.geonet-project.eu/>.[21] CarTalk2000, <http://www.cartalk2000.net>.[22] FleetNet Program, 2001. <http://www.fleetnet.de>.[23] L. Stranden, E. Uhlemann, E.G. Strom, State of the art survey of wireless

vehicular communication projects, in: Proceedings of 15th World Congresson Intelligent Transport Systems (ITS), New York City, NY, November 2008.

[24] G. Korkmaz, E. Ekici, F. Ozguner, Urban multihop broadcast protocols forinter-vehicle communication systems, in: Proceedings of First ACMWorkshop on Vehicular Ad-hoc Networks (VANET’04), October 2004, pp.76–85.

[25] J. Zhao, Y. Zhang, G. Cao, Data pouring and buffering on the road: a new datadissemination paradigm for vehicular ad hoc networks, IEEE Transactions onVehicular Technology 56 (6) (2007) 3266–3277. November.

[26] G. Kokmaz, E. Ekici, F. Ozguner, Black-burst-based multihop broadcastprotocols for vehicular networks, IEEE Transactions on VehicularTechnology 56 (5) (2007) 3159–3167. September.

[27] K. Shafiee, V.C.M. Leung, A reliable robust fully ad hoc data disseminationmechanism for vehicular network, International Journal of Advanced Scienceand Technology 2 (2009) 53–62. January.

[28] L. Wischhof, A. Ebner, H. Rohling, M. Lott, R. Halfmann, SOTIS: a self-organizing traffic information system, in: Proceedings of IEEE VehicularTechnology Conference, April 2003, pp. 2442–2446.

[29] T. Nadeem, S. Dashtinezhad, C. Liao, L. Iftode, TrafficView: traffic datadissemination using car-to-car communication, ACM SIGMOBILE MobileComputing and Communications Review 8 (3) (2004) 6–19. July.


ED

PR

OO

F

[30] L. Wischhof, A. Ebner, H. Rohling, Information dissemination in self-organizing intervehicle networks, IEEE Transactions on IntelligentTransportation Systems 6 (1) (2005) 90–101. March.

[31] B.S. Kerner, C. Demir, R.G. Herrtwich, S.L. Klenov, H. Rehborn, M. Aleksic, A.Haug, Traffic state detection with floating car data in road networks, in:Proceedings of the 8th International IEEE Conference on IntelligentTransportation Systems, September 2005, pp. 44–49.

[32] G. Halbritter, T. Fleischer, C. Kupsch, J. Kloas, U. Voigt, NationaleInnovationsstrategien fr neue Techniken und Dienste zur Erreichung einernachhaltigen Entwicklung im Verkehr, DIW Berlin, Report FZKA 7157,Forschungszentrum Karlsruhe GmbH, Karlsruhe, 2005.

[33] A. Brzezinski, G. Zussman, Enabling distributed throughput maximization inwireless mesh networks – a partitioning approach, in: Proceedings of ACMMOBICOM’06, September 2006, pp. 26–37.

[34] V. Bychkovsky, B. Hull, A. Miu, H. Balakrishnan, S. Madden, A measurementstudy of vehicular Internet access using unplanned 802.11 networks, in:Proceedings of ACM MOBICOM’06, September 2006.

[35] J. Ott, D. Kutscher, Drive-thru Internet: IEEE 802.11b for automobile users, in:Proceedings of IEEE INFOCOM, March 2004.

[36] R. Gass, J. Scott, C. Diot, Measurements of in-motion 802.11 networking, in:Proceedings of IEEE Workshop on Mobile Computing Systems andApplications, August 2005, pp. 69–74.

[37] M.L. Sim, M. Nekovee, Y.F. Ko, Throughput analysis of Wi–Fi based broadbandaccess for mobile users on the highway, in: Proceedings of Joint IEEE MalaysiaInternational Conference on Communications and IEEE InternationalConference on Network (MICC & ICON), p. 6, November 2005.

[38] S.R. Dickey, C.-L. Huang, X. Guan, Field measurements of vehicle to roadsidecommunication performance, in: Proceedings of IEEE Vehicular TechnologyConference (VTC) Fall, September–October 2007, pp. 2179–2183.

[39] H. Cai, Y. Lin, Design of a roadside seamless wireless communication systemfor intelligent highway, in: Proceedings of IEEE Networking, Sensing andControl, March 2005, pp. 342–347.

[40] L. Wischhof, A. Ebner, H. Rohling, M. Lott, R. Halfmann, Adaptive broadcast fortravel and traffic information distribution based on inter-vehiclecommunication, in: Proceedings of IEEE Intelligent Vehicles Symposium,June 2003, pp. 6–11.

[41] D.G. Oh, P. Kim, Y.J. Song, S.I. Jeon, H.J. Lee, Design considerations of satellite-based vehicular broadband networks, IEEE Communications Magazine 12 (5)(2005) 91–97. October.

[42] S. Pack, H. Rutagemwa, X. Shen, J. Mark, K. Park, Efficient data accessalgorithms for ITS-based networks with multihop wireless links, in:Proceedings of IEEE International Conference on Communications (ICC)2007, June 2007, pp. 4785–4790.

[43] S. Yousefi, M.S. Mousavi, M. Fathy, Integrated architecture for messagedissemination in vehicular ad hoc networks, in: Proceedings of 6thInternational Conference on ITS Telecommunications, June 2006, pp. 57–60.

[44] Y.F. Ko, M.L. Sim, M. Nekovee, Wi–Fi based broadband wireless access forusers on the road, BT Technology Journal 24 (2) (2006) 123–129. April.

[45] C.C. Hung, H. Chan, E.H.K. Wu, Mobility pattern aware routing forheterogeneous vehicular networks, in: Proceedings of IEEE WirelessCommunications and Networking Conference (WCNC), March–April 2008,pp. 2200–2205.

[46] I.F. Akyildiz, S. Mohanty, J. Xie, A ubiquitous mobile communicationarchitecture for next-generation heterogeneous wireless systems, IEEECommunications Magazine 43 (6) (2005) S29–S36. June.

[47] D. Johnson, C. Perkins, J. Arkko, RFC 3775: Mobility support in IPv6, IETF, June2004.

[48] F. Bari, V.C.M. Leung, Automated network selection in a heterogeneouswireless network environment, IEEE Network 21 (1) (2007) 34–40. January.

[49] J. Xie, I.F. Akyildiz, A hybrid control resource allocation scheme for policy-enabled handoff in wireless heterogeneous overlay networks, 2004.

[50] D. Niyato, E. Hossain, Dynamics of network selection in heterogeneouswireless networks: an evolutionary game approach, IEEE Transactions onVehicular Technology 58 (4) (2009) 2008–2017. May.

[51] O. Ormond, J. Murphy, G.-M. Muntean, Utility-based intelligent networkselection in beyond 3G systems, in: Proceedings of IEEE InternationalConference on Communications (ICC), vol. 4, June 2006, pp. 1831–1836.

[52] O. Sallent, J. Perez-Romero, R. Agusti, L. Giupponi, C. Kloeck, I. Martoyo, S.Klett, J. Luo, Resource auctioning mechanisms in heterogeneous wirelessaccess networks, in: Proceedings of IEEE Vehicular Technology Conference(VTC) Spring, vol. 1, May 2006, pp. 52–56.

[53] N. Shenoy, R. Montalvo, A framework for seamless roaming across cellularand wireless local area networks, IEEE Wireless Communications 12 (3)(2005) 50–57. June.

[54] V. Gazis, N. Alonistioti, L. Merakos, Toward a generic always best connectedcapability in integrated WLAN/UMTS cellular mobile networks (and beyond),IEEE Wireless Communications 12 (3) (2005) 20–29. June.

[55] D. Sanders, M. Laskowski, R.D. McLeod, A framework for mobile wirelessapplications, Presented at WIN-ITS, Vancouver, August 2007.

[56] Reference Model for Service Oriented Architecture 1.0 OASIS Standard,<http://docs.oasis-open.org/soa-rm/v1.0/>, October 2006 (accessed October2008).

[57] O. Maeshima, S. Cai, T. Honda, H. Urayama, A roadside-to-vehiclecommunication system for vehicle safety using dual frequency channels, in:Proceedings of IEEE Intelligent Transportation Systems Conference (ITSC)2007, September–October 2007, pp. 349–354.


http://www.wimaxforum.org/techno-Logy/downloads/Mobile_WiMAX_Part1_Overview_and_Performance.pdf

http://www.wimaxforum.org/techno-Logy/downloads/Mobile_WiMAX_Part1_Overview_and_Performance.pdf

http://www.cvisproject.org/

http://www.sevecom.org/

http://www.preciosa-project.org/

http://evita-project.org/

http://www.com2react-project.org/

http://www.ertico.com

http://wiki.fot-net.eu/index.php?title=SIM-TD

http://www.safespot-eu.org/

http://www.comesafety.org/

http://www.geonet-project.eu/

http://www.cartalk2000.net

http://www.fleetnet.de

http://docs.oasis-open.org/soa-rm/v1.0/


https://www.researchgate.net/publication/224647084_Measurements_of_In-Motion_80211_Networking?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==

https://www.researchgate.net/publication/224647084_Measurements_of_In-Motion_80211_Networking?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==

https://www.researchgate.net/publication/3198846_A_ubiquitous_communication_architecture_for_next-generation_heterogeneous_wireless_systems?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==






https://www.researchgate.net/publication/4153939_Design_of_a_roadside_seamless_wireless_communication_system_for_intelligent_highway?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==




https://www.researchgate.net/publication/224760960_Integrated_Architecture_for_Message_Dissemination_in_Vehicular_Ad_Hoc_Networks?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==










https://www.researchgate.net/publication/4102788_Drive-thru_Internet_IEEE_80211b_for_Automobile_Users?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==




https://www.researchgate.net/publication/3427913_Information_dissemination_in_self-organizing_intervehicle_networks_IEEE_Trans_Intell_Transp_Syst_690-101?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==




https://www.researchgate.net/publication/224675855_Utility-based_Intelligent_Network_Selection_in_Beyond_3G_Systems?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==








https://www.researchgate.net/publication/220926356_Enabling_distributed_throughput_maximization_in_wireless_mesh_networks_-_A_partitioning_approach?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==






https://www.researchgate.net/publication/250797655_Wi-Fi_based_broadband_wireless_access_for_users_on_the_road?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==




https://www.researchgate.net/publication/224327442_Dynamics_of_Network_Selection_in_Heterogeneous_Wireless_Networks_An_Evolutionary_Game_Approach?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==




https://www.researchgate.net/publication/4244189_Throughput_analysis_of_Wi-Fi_based_broadband_access_for_mobile_users_on_the_highway?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==




https://www.researchgate.net/publication/3283090_Leung_VCM_Automated_Network_Selection_in_a_Heterogeneous_Wireless_Network_Environment_IEEE_Network_21_34-40?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==




https://www.researchgate.net/publication/224310339_Mobility_Pattern_Aware_Routing_for_Heterogeneous_Vehicular_Networks?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==




https://www.researchgate.net/publication/3436056_Design_considerations_of_satellite-based_vehicular_broadband_networks?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==






https://www.researchgate.net/publication/224290778_Field_Measurements_of_Vehicle_to_Roadside_Communication_Performance?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==




T

17601761176217631764176517661767176817691770177117721773177417751776177717781779178017811782178317841785178617871788178917901791179217931794179517961797179817991800180118021803180418051806180718081809181018111812181318141815181618171818181918201821182218231824182518261827182818291830183118321833183418351836183718381839184018411842184318441845

18461847184818491850185118521853185418551856185718581859186018611862186318641865186618671868186918701871187218731874187518761877187818791880188118821883188418851886188718881889189018911892189318941895189618971898189919001901190219031904190519061907190819091910191119121913191419151916191719181919192019211922192319241925192619271928192919301931




UN

CO

RR

EC

[58] C.-J. Chang, R.-G. Cheng, H.-T. Shih, Y.-S. Chen, Maximum freedom lastscheduling algorithm for downlinks of DSRC networks, IEEE Transactions onIntelligent Transportation Systems 8 (2) (2007) 223–232. June.

[59] Y. Yang, M. Marina, R. Bagrodia, Evaluation of multihop relaying for robustvehicular Internet access, in: Proceedings of IEEE 2007 Mobile Networking forVehicular Environments, May 2007, pp. 19–24.

[60] H. Su, X. Zhang, Clustering-based multichannel MAC protocols for QoSprovisionings over vehicular ad hoc networks, IEEE Transactions on VehicularTechnology 56 (6) (2007) 3309–3323. November.

[61] B. Sikdar, Design and analysis of a MAC protocol for vehicle to roadsidenetworks, in: Proceedings of IEEE Wireless Communications and NetworkingConference (WCNC), March–April 2008, pp. 1691–1696.

[62] J. Zhang, Q. Zhang, W. Jia, A novel MAC protocol for cooperative downloadingin vehicular networks, in: Proceedings of IEEE Global TelecommunicationsConference (GLOBECOM’07), November 2007, pp. 4974–4978.

[63] J. Zhu, S. Roy, MAC for dedicated short range communications in intelligenttransport system, IEEE Communications Magazine 41 (12) (2003) 60–67.December.

[64] Y. Zhang, J. Zhao, G. Cao, On scheduling vehicle-roadside data access, in:Proceedings of the fourth ACM international workshop on Vehicular ad hocnetworks, September 2007, pp. 9–18.

[65] W. Xing, X.H. Nguyen, Y. Li, WiMAX fast-moving access network, in:Proceedings of IEEE Wireless Communications and Networking Conference,March–April 2008, pp. 2663–2668.

[66] D. Jiang, V. Taliwal, A. Meier, W. Holfelder, R. Herrtwich, Design of 5.9 GHzDSRC-based vehicular safety communication, IEEE Wireless Communications13 (5) (2006) 36–43. October.

[67] Y. Mertens, M. Wellens, P. Mahonen, Simulation-based performanceevaluation of enhanced broadcast schemes for IEEE 802.11-based vehicularnetworks, in: Proceedings of IEEE Vehicular Technology Conference (VTC)Spring, May 2008, pp. 3042–3046.

[68] O.K. Tonguz, N. Wisitpongphan , F. Bai, P. Mudalige, V. Sadekar, Broadcastingin VANET, in: Proceedings of IEEE INFOCOM MOVE Workshop 2007, May2007, pp. 7–12.

[69] N. Wisitpongphan, O.K. Tonguz, J.S. Parikh, P. Mudalige, F. Bai, V. Sadekar,Broadcast storm mitigation techniques in vehicular ad hoc wirelessnetworks, IEEE Wireless Communication Magazine 14 (6) (2007) 84–94.December.

[70] S. Ni, Y. Tseng, Y. Chen, J. Sheu, The broadcast storm problem in a mobile adhoc network, in: Proceedings of ACM Mobicom, 1999, pp. 151–162.

[71] M. Caliskan, D. Graupner, M. Mauve, Decentralized discovery of free parkingplaces, in: Proceedings of the 3rd ACM International Workshop on VehicularAd Hoc Networks, September 2006, pp. 30–39.

[72] C. Lochert, B. Scheuermann, M. Mauve, Probabilistic aggregation for datadissemination in VANETs, in: Proceedings of ACM VANET, September 2007,pp. 1–8.

[73] J. Chennikara-Varghese, W. Chen, O. Altintas, S. Cai, Survey of routingprotocols for inter-vehicle communications, in: Proceedings of 3rd AnnualInternational Conference on Mobile and Ubiquitous Systems – Workshops,pp. 1–5, 17–21 July 2006, San Jose, CA, USA, Digital Object Identifier 10.1109/MOBIQW.2006.361764.

[74] O. Abedi, M. Fathy, J. Taghiloo, Enhancing AODV routing protocol usingmobility parameters in VANET, in: Proceedings of IEEE/ACS InternationalConference on Computer Systems and Applications (AICCSA 2008), March–April 2008, pp. 229–235.

[75] V. Naumov, R. Baumann, T. Gross, An evaluation of inter-vehicle ad hocnetworks based on realistic vehicular traces, in: Proceedings of ACMMobiHoc, May 2006, pp. 108–119.

[76] Z. Mo, H. Zhu, K. Makki, N. Pissinou, MURU: a multihop routing protocol forurban vehicular ad hoc networks, in: Proceedings of the 3rd AnnualInternational Conference on Mobile and Ubiquitous Systems: Networks andServices (MOBIQUITOUS), July 2006, pp. 1–8.

[77] H.F. Wedde, S. Lehnhoff, B.V. Bonn, Highly dynamic and scalable VANETrouting for avoiding traffic congestions, in: Proceedings of the Fourth ACMInternational Workshop on Vehicular Ad hoc Networks, September 2007, pp.81–82.

[78] T. Taleb, E. Sakhaee, A. Jamalipour, K. Hashimoto, N. Kato, Y. Nemoto, A stablerouting protocol to support ITS services in VANET networks, IEEE Transactionon Vehicular Technology 56 (6) (2007) 3337–3347. November.

[79] J. Tian, L. Han, K. Rothermel, C. Cseh, Spatially aware packet routing formobile ad hoc inter-vehicle radio networks, in: Proceedings of ITS’03, October2003, pp. 1546–1551.

[80] B. Seet, G. Liu, B. Lee, C. Foh, K. Wong, K. Lee, A-STAR: a mobile ad hoc routingstrategy for metropolis vehicular communications, Lecture Notes inComputer Science 3042 (0302-9743) (2004) 989–999. January.

[81] J. Zhao, G. Cao, VADD: vehicle-assisted data delivery in vehicular ad hocnetworks, in: Proceedings of IEEE INFOCOM’06, April 2006, pp. 1–12.

[82] V. Naumov, T.R. Gross, Connectivity-aware routing (CAR) in vehicular adhoc networks, in: Proceedings of IEEE INFOCOM’07, May 2007, pp. 1919–1927.

[83] N. Wisitpongphan, F. Bai, P. Mudalige, V. Sadekar, O. Tonguz, Routing insparse vehicular ad hoc wireless networks, IEEE Journal on Selected Areas inCommunications 25 (8) (2007) 1538–1556. October.

[84] V. Namboordiri, L. Gao, Prediction-based routing for vehicular ad hocnetworks, IEEE Transaction on Vehicular Technology 56 (4) (2007) 2332–2345. July.


ED

PR

OO

F

[85] R. He, H. Rutagemwa, X. Shen, Differentiated reliable routing in hybridvehicular ad-hoc networks, in: Proceedings of IEEE ICC’08, May 2008, pp.2353–2358.

[86] H. Balakrishnan, V.N. Padmanabhan, S. Seshan, R.H. Katz, A comparison ofmechanisms for improving TCP performance over wireless links, IEEE/ACMTransactions on Networking 5 (6) (1997) 756–769. December.

[87] Z. Fu, H. Luo, P. Zerfos, S. Lu, L. Zhang, M. Gerla, The impact of multihopwireless channel on TCP performance, IEEE Transactions on MobileComputing 4 (2) (2005) 209–221. March–April.

[88] V. Jacobson, M.J. Karels, Congestion avoidance and control, in: Proceedings ofACM SIGCOMM ’88 Workshop, 1988, pp. 314–329.

[89] Y. Yi, S. Shakkottai, Hop-by-hop congestion control over a wireless multihopnetwork, in: Proceedings of INFOCOM’04, vol. 4, March 2004, pp. 2548–2558.

[90] Y. Zang, L. Stibor, X. Cheng, H. Reumerman, A. Paruzel, A. Barros, Congestioncontrol in wireless networks for vehicular safety applications, in: Proceedingsof 13th European Wireless Conference, April 2007.

[91] J. Mo, J. Walrand, Fair end-to-end window-based congestion control, IEEE/ACM Transactions on Networking 8 (5) (2000) 556–567. October.

[92] L. Zhao, Y. Jing, G.M. Dimirovski, Improvement of AIMD algorithm consideringmultimedia transfer over Internet, in: Proceedings of the 6th InternationalConference on Telecommunications in Modern Satellite, Cable andBroadcasting Service, October 2003, pp. 392–394.

[93] C. Huang, L. Xu, SRC: Stable rate control for streaming media, in: Proceedingsof IEEE Globecom, December 2003, pp. 4016–4021.

[94] W.R. Stevens, TCP slow start, congestion avoidance, fast retransmit and fastrecovery algorithms, IETF RFC 2001, September 1997.

[95] G. Hasegawa, M. Murata, H. Miyahara, Fairness and stability of congestioncontrol mechanisms of TCP, in: Proceedings of INFOCOM’99, March 1999, pp.1329–1336.

[96] S. Floyd, T. Henderson, The NewReno modification to TCP’s fast recoveryalgorithm, IETF RFC 2582, April 1999.

[97] S. Kim, S. Choi, C. Kim, Instantaneous variant of TCP NewReno, ElectronicsLetters, October 1999, pp. 1818–1820.

[98] N. Parvez, A. Mahanti, C. Williamson, TCP NewReno: slow-but-steady orimpatient?, in: Proceedings of IEEE International Conference onCommunications (ICC’06), June 2006, pp. 716–722.

[99] S. Floyd, V. Jacobson, Random early detection gateways for congestionavoidance, IEEE/ACM Transactions on Networking 1 (4) (1993) 397–413.August.

[100] M. May, J. Bolot, C. Diot, B. Lyles, Reasons not to deploy RED, in: Proceedingsof the 7th International Workshop on Quality of Service, IWQoS, June 1999,pp. 260–262.

[101] S. Floyd, R. Gummadi, S. Shenker, Adaptive RED: an algorithm for increasingthe robustness of RED, UC Berkeley ICIR Technical Report, August 2001,<http://www.icir.org/floyd/papers/adaptiveRed.pdf>.

[102] K. Xu, M. Gerla, L. Qi, Y. Shu, Enhancing TCP fairness in ad-hoc wirelessnetworks using neighborhood RED, in: Proceedings of ACM 9th AnnualInternational Conference on Mobile Computing and Networking (Mobicom2003), September 2003, pp. 16–28.

[103] W. Feng, K. Shin, D. Kandlur, D. Saha, The blue: active queue managementalgorithms, IEEE/ACM Transactions on Networking 10 (4) (2002) 513–528.August.

[104] D. Lin, R. Morris, Dynamics of random early detection, in: Proceedings ofConference on Applications, Technologies, Architectures, and Protocols forComputer Communication, 1997, pp. 127–137.

[105] S. Athuraliya, V.H. Li, S.H. low, Q. Yin, REM: active queue management, IEEENetwork 15 (3) (2001) 48–53. May–June.

[106] S. Kunniyur, R. Srikant, An adaptive virtual queue (AVQ) algorithms for activequeue management, IEEE/ACM Transactions on Networking 12 (2) (2004)286–299. April.

[107] K.J. Astrom, G.C. Goodwin, P.R. Kumar, Adaptive control, filtering and signalprocessing, The IMA Volumes in Mathematics and its Applications, vol. 74,April 1995.

[108] M. Hanley, S. Floyd, J. Padhye, J. Widmer, TCP Friendly Rate Control (TFRC):Protocol Specification, IETF RFC 3448, January 2003.

[109] D. Katabi, M. Handley, C. Rohrs, Congestion control for high bandwidth delayproduct networks, in: Proceedings of ACM SIGCOMM’02, October 2002, pp.89–102.

[110] K. Chen, K. Nahrstedt, and N. Vaidya, The utility of explicit rate-based flowcontrol in mobile ad-hoc networks, in: Proceedings of IEEE WirelessCommunication and Networking Conference, vol. 3, March 2004, pp. 1921–1926.

[111] Y. Hong, O.W.W. Yang, Design of adaptive PI rate controller for best-efforttraffic in the Internet based on phase margin, IEEE Transactions on Paralleland Distributed Systems 18 (4) (2007) 550–561. April.

[112] L. Wischhof, H. Rohling, Congestion control in vehicular ad hoc networks, in:Proceedings of IEEE International Conference on Vehicular Electronics andSafety 2005 (ICVES 2005), October 2005, pp. 58–63.

[113] S. Shakkottai, T.S. Rappaport, P.C. Karlsson, Cross-layer design for wirelessnetworks, IEEE Communications Magazine 41 (10) (2003) 74–80. October.

[114] M. Chiang, To layer or not to layer: balancing transport and physical layers inwireless multihop networks, in: Proceedings of IEEE INFOCOM’04, April 2004,pp. 2525–2536.

[115] L. Bononi, M. Di Felice, A cross layered MAC and clustering scheme forefficient broadcast in VANETs, in: Proceedings of 1st IEEE InternationalWorkshop on Mobile Vehicular Networks (MoVeNet), 2007.


http://www.icir.org/floyd/papers/adaptiveRed.pdf


https://www.researchgate.net/publication/3436419_The_impact_of_multihop_wireless_channel_on_TCP_performance?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==




https://www.researchgate.net/publication/3334841_The_BLUE_active_queue_management_algorithms?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==




https://www.researchgate.net/publication/3436144_Design_of_59_GHz_DSRC-based_vehicular_safety_communication?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==














https://www.researchgate.net/publication/221164606_Congestion_control_for_high_bandwidth-delay_product_networks?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==






https://www.researchgate.net/publication/3790123_Fairness_and_stability_of_congestion_control_mechanisms_of_TCP?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==






https://www.researchgate.net/publication/3334716_Fair_End-to-End_Window-based_Congestion_Control?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==

https://www.researchgate.net/publication/3334716_Fair_End-to-End_Window-based_Congestion_Control?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==

https://www.researchgate.net/publication/220926411_Enhancing_TCP_fairness_in_ad_hoc_wireless_networks_using_neighborhood_RED?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==




https://www.researchgate.net/publication/4102885_To_layer_or_not_to_layer_Balancing_transport_and_physical_layers_in_wireless_multihop_networks?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==






https://www.researchgate.net/publication/3334975_An_Adaptive_Virtual_Queue_AVQ_algorithm_for_Active_Queue_Management?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==




https://www.researchgate.net/publication/224675689_TCP_NewReno_Slow-but-Steady_or_Impatient?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==




https://www.researchgate.net/publication/4310517_A_cross-layered_MAC_and_clustering_scheme_for_efficient_broadcast_in_VANETs?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==




https://www.researchgate.net/publication/234780531_Congestion_avoidance_and_control?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==

https://www.researchgate.net/publication/234780531_Congestion_avoidance_and_control?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==



https://www.researchgate.net/publication/4044112_Improvement_of_AIMD_algorithm_considering_multimedia_transfer_over_Internet?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==




https://www.researchgate.net/publication/4080681_The_utility_of_explicit_rate-based_flow_control_in_mobile_ad_hoc_networks?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==




https://www.researchgate.net/publication/3199050_Cross-layer_design_for_wireless_networks?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==




https://www.researchgate.net/publication/224315777_Differentiated_Reliable_Routing_in_Hybrid_Vehicular_Ad-Hoc_Networks?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==






https://www.researchgate.net/publication/245188348_Adaptive_RED_An_algorithm_for_increasing_the_robustness_of_RED?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==

https://www.researchgate.net/publication/245188348_Adaptive_RED_An_algorithm_for_increasing_the_robustness_of_RED?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==

https://www.researchgate.net/publication/3801454_Reasons_not_to_deploy_RED?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==






https://www.researchgate.net/publication/239535308_TCP_Slow_Start_Congestion_Avoidance_Fast_Retransmit_and_Fast_Recovery_Algorithms?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==




https://www.researchgate.net/publication/3382824_Instantaneous_variant_of_TCP_NewReno?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==

https://www.researchgate.net/publication/3382824_Instantaneous_variant_of_TCP_NewReno?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==

https://www.researchgate.net/publication/4051908_SRC_Stable_rate_control_for_streaming_media?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==




https://www.researchgate.net/publication/2591533_Dynamics_of_Random_Early_Detection?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==

https://www.researchgate.net/publication/2591533_Dynamics_of_Random_Early_Detection?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==

https://www.researchgate.net/publication/2780357_RFC_2582_The_NewReno_modification_to_TCP's_fast_recovery_algorithm?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==




https://www.researchgate.net/publication/4102886_Hop-by-hop_congestion_control_over_a_wireless_multi-hop_network?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==




https://www.researchgate.net/publication/3282808_REM_Active_queue_management?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==

https://www.researchgate.net/publication/3282808_REM_Active_queue_management?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==

https://www.researchgate.net/publication/242505628_Random_Early_Detection_Gateways_for_Congestion_AIvoidance?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==




https://www.researchgate.net/publication/288520114_Congestion_control_in_wireless_networks_for_vehicular_safety_applications?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==






https://www.researchgate.net/publication/262371151_Comparison_of_mechanisms_for_improving_TCP_performance_over_wireless_links?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==






T

19321933193419351936193719381939194019411942194319441945194619471948194919501951195219531954195519561957195819591960196119621963196419651966196719681969197019711972197319741975197619771978197919801981198219831984

198519861987198819891990199119921993199419951996199719981999200020012002200320042005200620072008200920102011201220132014201520162017201820192020202120222023202420252026202720282029203020312032203320342035

2036

Q2




EC

[116] X. Xie, F. Wang, H. Wang, K. Li, Adaptive multi-channel MAC protocol fordense VANET using directional antennas, in: Proceedings of SecondInternational Conference on Future Generation Communication andNetworking, vol. 2, 2008, pp. 398–401.

[117] C. Cuyu, X. Yong, S. Meilin, L. Liang, Performance observations on MACprotocols of VANETs in intelligent transportation system, in: Proceedings ofInternational Conference on Communications and Mobile Computing, vol. 2,2009, pp. 373–379.

[118] J.-H. Song, V.W.S. Wong, V.C.M. Leung, Wireless location privacy protection invehicular ad-hoc networks, ACM/Springer Mobile Networks and Applications(MONET), submitted for publication.

[119] J.-H. Song, V.W.S. Wong, V.C.M. Leung, Secure location verification forvehicular ad-hoc networks, in: Proceedings of IEEE Global CommunicationsConference (Globecom), New Orleans, LA, November/December 2008.

[120] M. Raya, J.-P. Hubaux, The security of vehicular ad hoc networks, in:Proceedings of 3rd ACM Workshop on Security of Ad Hoc and SensorNetworks 2005, 2005, pp. 11–21.

[121] B. Parno, A. Perrig, Challenges in securing vehicular networks, in: Proceedingsof Workshop on Hot Topics in Networks (HotNets-IV), 2005.

[122] E. Coronado, S. Cherkaoui, An AAA study for service provisioning in vehicularnetworks, in: Proceedings of 32nd IEEE Conference on Local ComputerNetworks 2007, October 2007, pp. 669–676.

[123] X. Sun, X. Lin, P.H. Ho, Secure vehicular communications based on groupsignature and id-based signature scheme, in: Proceedings of InternationalConference on Communications 2007 (ICC’07), June 2007, pp. 1539–1545.

[124] M. Raya, J.-P. Hubaux, Securing vehicular ad hoc networks, Journal ofComputer Security 15 (2007) 39–68. IOS Press.

[125] A. Aijaz, B. Bochow, F. Doetzer, A. Festag, M. Gerlach, R. Kroh, T. Leimueller,Attacks on inter vehicle communication systems – an analysis, in:Proceedings of 3rd International Workshop on Intelligent Transportation(WIT 2006), 14–15 March, 2006.

[126] M. Raya, A. Aziz, J.-P. Hubaux, Efficient secure aggregation in VANETs, in:Proceedings of 3rd International Workshop on Vehicular Ad hoc Networks,Los Angeles, CA, USA, 2006, pp. 67–75.

[127] F. Picconi, N. Ravi, M. Gruteser, L. Iftode, Probabilistic validation of aggregateddata in vehicular ad-hoc networks, in: Proceedings of 3rd InternationalWorkshop on Vehicular Ad hoc Networks, Los Angeles, CA, USA, 2006, pp. 76–85.

[128] T. Leinmueller, C. Maihoefer, E. Schoch, F. Kargl, Improved security ingeographic ad-hoc routing through autonomous position verification, in:Proceedings of 3rd International Workshop on Vehicular Ad hoc Networks,Los Angeles, CA, USA, 2006, pp. 57–66.

[129] P. Golle, D. Greene, J. Staddon, Detecting and correcting malicious data inVANETs, in: Proceedings of 1st ACM international Workshop on Vehicular Adhoc Networks, Philadelphia, PA, USA, 2004, pp. 29–37.

[130] M. El Zarki, S. Mehrotra, N. Tsudik, N. Venkatasubramanian, Security issues infuture vehicular network, in: Proceedings of European Wireless Conference2002, 2002.

[131] J. Blum, A. Eskandarian, The threat of intelligent collisions, IEEE ITProfessional Magazine, January–February 2004, pp. 24–29.

[132] Vehicle Safety Communications Project – Final report, U.S. Department ofTransportation, National Highway Safety Administration, 2006, <http://www-nrd.nhtsa.dot.gov/pdf/nrd-12/060419-0843/PDFTOC.htm>.

UN

CO

RR


ED

PR

OO

F

[133] M. Bishop, Computer Security: Art and Science, Pearson Education, Inc.,Boston, MA 02116, 1st edition, 2003.

[134] X. Lin, X. Sun, P. Ho, X. Shen, GSIS: a secure and privacy-preserving protocolfor vehicular communications, IEEE Transactions on Vehicular Technology 56(6) (2007) 3442–3456. November.

[135] L. Buttyan, J.-P. Hubaux, F. Kargl, M. Raya, Architecture for secure and privatevehicular communications, in: Proceedings of ITST 2007, June 2007.

[136] D. Chaum, Security without identification: transactions to make big brotherobsolete, Communication of the ACM 28 (10) (1985) 1030–1044.

[137] J. Choi, M. Jakobsson, S.Wetzel, Balancing auditability and privacy invehicular networks, in: Proceedings of Q2SWinet 2005, 2005, pp. 79–87.

[138] K. Plossl, T. Nowey, C. Mletzko, Towards a security architecture for vehicularad hoc networks, in: Proceedings of the First International Conference onAvailability, Reliability and Security ARES 2006, April 2006, p. 8.

[139] H. Moustafa, G. Bourddon, Y. Gourhant, Providing authentication and accesscontrol on vehicular environments, in: Proceedings of IFIP 2006, 2006, pp.62–73.

[140] K. Sha, Y. Xi, W. Shi, L. Schwiebert, T. Zhang, Adaptive privacy-preservingauthentication in vehicular networks, in: Proceedings of First InternationalConference on Communications and Networking in China, October 2006, pp.1–8.

[141] Y. Xi, K. Sha, W. Shi, L. Schwiebert, T. Zhang, Enforcing privacy usingsymmetric random key-set in vehicular networks, in: Proceedings of EighthInternational Symposium on Autonomous Decentralized Systems (ISADS’07),March 2007, pp. 344–351.

[142] A. Perrig, R. Canneti, D. Tygar, D. Song, The tesla broadcast authenticationprotocol, RSA Cryptobytes 5 (2) (2002) 2–13.

[143] X. Lin, C. Zhang, X. Sun, P.-H. Ho, X. Shen, Performance enhancement forsecure vehicular communications, in: Proceedings of IEEE GlobalCommunications Conference (GLOBECOM’07), Washington, DC, USA, Nov.26–30, 2007.

[144] L. Lamport, Password authentication with insecure communication,Communication of the ACM 24 (11) (1981) 770–772.

[145] S. Capkun, J.-P. Hubaux, M. Jakobsson, Secure and privacy preservingcommunications in hybrid ad hoc networks, Technical Report EPFL-IC, EPFL,2004.

[146] F. Dotzer, Privacy issues in VANET, in: Proceedings of Workshop on PrivacyEnhancing Technologies, 2005.

[147] K. Sampigethaya, L. Huang, M. Li, R. Poovendran, K. Matsura, K. Sezaki,Caravan: Providing location privacy for VANET, in: Proceedings of Workshopon Embedded Security in Cars, 2005.

[148] G.-M. Su, Z. Man, M. Wu, K.J.R. Liu, Multiuser cross-layer resource allocationfor video transmission over wireless networks, IEEE Network 20 (2) (2006)21–27. March–April.

[149] K. Ren, W. Lou, K. Kim, R. Deng, A novel privacy preserving authentication andaccess control scheme for pervasive computing environments, IEEETransactions on Vehicular Technology 55 (4) (2006) 1373–1384. July.

[150] S. Wang, Anonymous wireless authentication on a portable cellular mobilesystem, IEEE Transactions on Computers 53 (10) (2004) 1317–1329.October.


http://www-nrd.nhtsa.dot.gov/pdf/nrd-12/060419-0843/PDFTOC.htm

http://www-nrd.nhtsa.dot.gov/pdf/nrd-12/060419-0843/PDFTOC.htm


https://www.researchgate.net/publication/221439888_Enforcing_Privacy_Using_Symmetric_Random_Key-Set_in_Vehicular_Networks?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==




https://www.researchgate.net/publication/4302740_Performance_Enhancement_for_Secure_Vehicular_Communications?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==




https://www.researchgate.net/publication/3283042_Multiuser_cross-layer_resource_allocation_for_video_transmission_over_wireless_networks?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==




https://www.researchgate.net/publication/2910704_The_TESLA_broadcast_authentication_protocol?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==




https://www.researchgate.net/publication/242481468_Computer_Security_Art_and_Science_M?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==

https://www.researchgate.net/publication/242481468_Computer_Security_Art_and_Science_M?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==

https://www.researchgate.net/publication/215439657_Security_without_identification_Transaction_systems_to_make_big_brother_obsolete?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==

https://www.researchgate.net/publication/215439657_Security_without_identification_Transaction_systems_to_make_big_brother_obsolete?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==







https://www.researchgate.net/publication/221454076_Balancing_auditability_and_privacy_in_vehicular_networks?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==






https://www.researchgate.net/publication/3156607_GSIS_A_Secure_and_Privacy-Preserving_Protocol_for_Vehicular_Communications?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==








https://www.researchgate.net/publication/284776272_Password_authenticated_with_insecure_communication?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==

https://www.researchgate.net/publication/284776272_Password_authenticated_with_insecure_communication?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==

https://www.researchgate.net/publication/291780625_Anonymous_wireless_authentication_on_a_portable_cellular_mobile_system?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==




https://www.researchgate.net/publication/220722455_Providing_Authentication_and_Access_Control_in_Vehicular_Network_Environment?el=1_x_8&enrichId=rgreq-459223c1-8e6c-4ab3-89d8-f53b36b8e133&enrichSource=Y292ZXJQYWdlOzIyMzkxNzkxOTtBUzoxNjc0NDQ2MTAwMzU3MTJAMTQxNjkzMzMxNDM0Ng==






vehicular telematics over heterogeneous wireless networks: a survey

Documents