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MOBILE AD HOCNETWORKING
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MOBILE AD HOCNETWORKING
Cutting Edge Directions
Second Edition
Edited by
STEFANO BASAGNIMARCO CONTISILVIA GIORDANOIVAN STOJMENOVIC
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Library of Congress Cataloging-in-Publication Data:
Mobile ad hoc networking : the cutting edge directions / edited by StefanoBasagni, Marco Conti, Silvia Giordano, Ivan Stojmenovic. – Second edition.
pages cm.ISBN 978-1-118-08728-2 (hardback)
1. Ad hoc networks (Computer networks) 2. Wireless LANs. 3. Mobilecomputing. I. Basagni, Stefano, 1965- editor of compilation.
TK5105.78.M63 2012004.6’167–dc23
2012031683
Printed in the United States of America
10 9 8 7 6 5 4 3 2 1
CONTENTS
PREFACE xiii
ACKNOWLEDGMENTS xv
CONTRIBUTORS xvii
PART I GENERAL ISSUES
1 Multihop Ad Hoc Networking: The Evolutionary Path 3Marco Conti and Silvia Giordano
1.1 Introduction, 31.2 MANET Research: Major Achievements and Lessons Learned, 51.3 Multihop Ad Hoc Networks: From Theory to Reality, 161.4 Summary and Conclusions, 25References, 26
2 Enabling Technologies and Standards for Mobile MultihopWireless Networking 34Enzo Mingozzi and Claudio Cicconetti
2.1 Introduction, 352.2 Broadband Wireless Access Technologies, 372.3 Wireless Local Area Networks Technologies, 432.4 Personal Area Networks Technologies, 53
v
vi CONTENTS
2.5 Mobility Support in Heterogeneous Scenarios, 652.6 Conclusions, 67References, 69
3 Application Scenarios 77Ilias Leontiadis, Ettore Ferranti, Cecilia Mascolo, Liam McNamara,Bence Pasztor, Niki Trigoni, and Sonia Waharte
3.1 Introduction, 783.2 Military Applications, 793.3 Network Connectivity, 813.4 Wireless Sensor Networks, 843.5 Search and Rescue, 893.6 Vehicular Networks, 933.7 Personal Content Dissemination, 963.8 Conclusions, 98References, 98
4 Security in Wireless Ad Hoc Networks 106Roberto Di Pietro and Josep Domingo-Ferrer
4.1 Introduction, 1064.2 Wireless Sensor Networks, 1104.3 Unattended WSN, 1254.4 Wireless Mesh Networks, 1304.5 Delay-Tolerant Networks, 1344.6 Vehicular Ad Hoc Networks (VANETs), 1374.7 Conclusions and Open Research Issues, 144References, 144
5 Architectural Solutions for End-User Mobility 154Salvatore Vanini and Anna Forster
5.1 Introduction, 1545.2 Mesh Networks, 1555.3 Wireless Sensor Networks, 1825.4 Conclusion, 188References, 188
6 Experimental Work Versus Simulation in the Studyof Mobile Ad Hoc Networks 191Carlo Vallati, Victor Omwando, and Prasant Mohapatra
6.1 Introduction, 1916.2 Overview of Mobile Ad Hoc Network Simulation Tools
and Experimental Platforms, 1926.3 Gap Between Simulations and Experiments: Issues
and Factors, 199
CONTENTS vii
6.4 Good Simulations: Validation, Verification, andCalibration, 220
6.5 Simulators and Testbeds: Future Prospects, 2266.6 Conclusion, 228References, 228
PART II MESH NETWORKING
7 Resource Optimization in Multiradio MultichannelWireless Mesh Networks 241Antonio Capone, Ilario Filippini, Stefano Gualandi, and Di Yuan
7.1 Introduction, 2427.2 Network and Interference Models, 2447.3 Maximum Link Activation Under the SINR Model, 2457.4 Optimal Link Scheduling, 2477.5 Joint Routing and Scheduling, 2547.6 Dealing with Channel Assignment and Directional
Antennas, 2577.7 Cooperative Networking, 2637.8 Concluding Remarks and Future Issues, 269References, 271
8 Quality of Service in Mesh Networks 275Raffaele Bruno
8.1 Introduction, 2758.2 QoS Definition, 2778.3 A Taxonomy of Existing QoS Routing Approaches, 2788.4 Routing Protocols with Optimization-Based Path
Selection, 2808.5 Routing Metrics for Minimum-Weight Path Selection, 2918.6 Feedback-Based Path Selection, 3078.7 Conclusions, 308References, 308
PART III OPPORTUNISTIC NETWORKING
9 Applications in Delay-Tolerant and Opportunistic Networks 317Teemu Karkkainen, Mikko Pitkanen, and Joerg Ott
9.1 Application Scenarios, 3189.2 Challenges for Applications Over DTN, 3229.3 Critical Mechanisms for DTN Applications, 328
viii CONTENTS
9.4 DTN Applications (Case Studies), 3369.5 Conclusion: Rethinking Applications for DTNs, 357References, 358
10 Mobility Models in Opportunistic Networks 360Kyunghan Lee, Pan Hui, and Song Chong
10.1 Introduction, 36010.2 Contact-Based Measurement, Analysis, and Modeling, 36110.3 Trajectory Models, 37610.4 Implications for Network Protocol Design, 39910.5 New Paradigm: Delay-Resource Tradeoffs, 406References, 414
11 Opportunistic Routing 419Thrasyvoulos Spyropoulos and Andreea Picu
11.1 Introduction, 42011.2 Cornerstones of Opportunistic Networks, 42211.3 Dealing with Uncertainty: Redundancy-Based Routing, 42811.4 Capitalizing on Structure: Utility-Based Forwarding, 43511.5 Hybrid Solutions: Combining Redundancy and Utility, 44411.6 Conclusion, 447References, 448
12 Data Dissemination in Opportunistic Networks 453Chiara Boldrini and Andrea Passarella
12.1 Introduction, 45412.2 Initial Ideas: PodNet, 45612.3 Social-Aware Schemes, 46012.4 Publish/Subscribe Schemes, 46412.5 Global Optimization, 46912.6 Infrastructure-Based Approaches, 47412.7 Approaches Inspired by Unstructured p2p Systems, 47812.8 Further Readings, 482References, 486
13 Task Farming in Crowd Computing 491Derek G. Murray, Karthik Nilakant, J. Crowcroft, and E. Yoneki
13.1 Introduction, 49113.2 Ideal Parallelism Model, 49413.3 Task Farming, 49813.4 Socially Aware Task Farming, 500
CONTENTS ix
13.5 Related Work, 51013.6 Conclusions and Future Work, 510References, 512
PART IV VANET
14 A Taxonomy of Data Communication Protocols for VehicularAd Hoc Networks 517Yousef-Awwad Daraghmi, Ivan Stojmenovic, and Chih-Wei Yi
14.1 Introduction, 51714.2 Taxonomy of VANET Communication Protocols, 52014.3 Reliability-Oriented Geocasting Protocols, 52514.4 Time-Critical Geocasting Protocols, 52714.5 Small-Scale Routing Protocols, 52914.6 Large-Scale Routing, 53414.7 Summary, 53914.8 Conclusion and Future Work, 539References, 542
15 Mobility Models, Topology, and Simulations in VANET 545Francisco J. Ros, Juan A. Martinez, and Pedro M. Ruiz
15.1 Introduction and Motivation, 54515.2 Mobility Models, 54715.3 Mobility Simulators, 55115.4 Integrated Simulators, 55715.5 Modeling Vehicular Communications, 56015.6 Analysis of Connectivity in Highways, 56515.7 Conclusion and Future Work, 572References, 573
16 Experimental Work on VANET 577Minglu Li and Hongzi Zhu
16.1 Introduction, 57716.2 MIT CarTel, 57916.3 UMass DieselNet, 58116.4 SJTU ShanghaiGrid, 58416.5 NCTU VANET Testbed, 58716.6 UCLA CVeT, 58916.7 GM DSRC Fleet, 59016.8 FleetNet Project, 59116.9 Network on Wheels (NOW) Project, 592
x CONTENTS
16.10 Advanced Safety Vehicles (ASVs), 59316.11 Japan Automobile Research Institute (JARI), 594References, 595
17 MAC Protocols for VANET 599Mohammad S. Almalag, Michele C. Weigle, and Stephan Olariu
17.1 Introduction, 59917.2 MAC Metrics, 60217.3 IEEE Standards for MAC Protocols for VANETs, 60217.4 Alternate MAC Protocols for VANET, 60617.5 Conclusion, 616References, 617
18 Cognitive Radio Vehicular Ad Hoc Networks: Design,Implementation, and Future Challenges 619Marco Di Felice, Kaushik Roy Chowdhury, and Luciano Bononi
18.1 Introduction, 62018.2 Characteristics of Cognitive Radio Vehicular Networks, 62218.3 Applications of Cognitive Radio Vehicular Networks, 62818.4 CRV Network Architecture, 62918.5 Classification and Description of Existing Works on
CRV Networks, 63018.6 Research Issues in CRVs, 63618.7 Conclusion, 640References, 640
19 The Next Paradigm Shift: From Vehicular Networks toVehicular Clouds 645Stephan Olariu, Tihomir Hristov, and Gongjun Yan
19.1 By Way of Motivation, 64619.2 The Vehicular Model, 64719.3 Vehicular Networks, 64919.4 Cloud Computing, 65019.5 Vehicular Clouds, 65219.6 How are Vehicular Clouds Different?, 65419.7 Feasible Instances of Vehicular Clouds, 65719.8 More Application Scenarios, 66019.9 Security and Privacy in Vehicular Clouds, 66619.10 Key Management, 67719.11 Research Challenges, 68019.12 Architectures for Vehicular Clouds, 68119.13 Resource Aggregation in Vehicular Clouds, 68319.14 A Simulation Study of VC, 690
CONTENTS xi
19.15 Future Work, 69119.16 Where to From Here?, 693References, 694
PART V SENSOR NETWORKING
20 Wireless Sensor Networks with Energy Harvesting 703Stefano Basagni, M. Yousof Naderi, Chiara Petrioli, and Dora Spenza
20.1 Introduction, 70320.2 Node Platforms, 70420.3 Techniques of Energy Harvesting, 70920.4 Prediction Models, 71320.5 Protocols for EHWSNs, 717References, 728
21 Robot-Assisted Wireless Sensor Networks: Recent Applicationsand Future Challenges 737Rafael Falcon, Amiya Nayak, and Ivan Stojmenovic
21.1 Introduction, 73721.2 Robot-Assisted Sensor Placement, 74021.3 Robot-Assisted Sensor Relocation, 75121.4 Robot-Assisted Sensor Maintenance, 76221.5 Future Challenges, 763References, 765
22 Underwater Networks with Limited Mobility: Algorithms,Systems, and Experiments 769Carrick Detweiler, Elizabeth Basha, Marek Doniec, and Daniela Rus
22.1 Introduction, 77022.2 Related Work, 77222.3 Decentralized Control Algorithm, 77522.4 General System Architecture and Design, 77922.5 Application-Specific Architecture and Design, 78622.6 Experiments and Results, 78922.7 Conclusions, 799References, 800
23 Advances in Underwater Acoustic Networking 804Tommaso Melodia, Hovannes Kulhandjian, Li-Chung Kuo, andEmrecan Demirors
23.1 Introduction, 80523.2 Communication Architecture, 806
xii CONTENTS
23.3 Basics of Underwater Communications, 80723.4 Physical Layer, 81423.5 Medium Access Control Layer, 82223.6 Network Layer, 82923.7 Cross-Layer Design, 83323.8 Experimental Platforms, 83423.9 UW-Buffalo: An Underwater Acoustic Testbed at the
University at Buffalo, 84223.10 Conclusions, 842References, 843
Index 853
PREFACE
The mobile multihop ad hoc networking paradigm was born with the idea of extendingInternet services to groups of mobile users. In these networks, often referred to asMANETs (Mobile Ad hoc NETworks), the wireless network nodes (e.g., the users’mobile devices) communicate with each other to perform data transfer without thesupport of any network infrastructure: Nearby users can communicate directly byexploiting the wireless technologies of their devices in ad hoc mode. For this reason,in a MANET the users’ devices must cooperatively provide the Internet servicesusually provided by the network infrastructure (e.g., routers, switches, and servers).
At the time we published our first book, “Mobile Ad Hoc Networking” (IEEE-Wiley, 2004), mobile ad hoc networking was seen as one of the most innovative andchallenging areas of wireless networking, and was poised to become one of the maintechnologies of the increasingly pervasive world of telecommunications. In that spirit,our first book presented a comprehensive view of MANETs, with topics ranging fromthe physical up to the application layer.
After about a decade, we observe that the promise of ad hoc networking never fullyrealized, and that MANET solutions are not used in people’s life. What happened,and why?
We start from these questions to write this second book. Our main interests hereare
• to highlight the reasons of MANET’s failure;• to illustrate how the mobile ad hoc networking paradigm gave birth to several
cutting-edge research directions;• to present the emerging technologies that derived from MANET, their chal-
lenges, and their current development;
xiii
xiv PREFACE
• to show that these new technologies successfully penetrated the marked andexist in everybody’s life.
We initially analyze the reasons of the lack of success of the generic ad hoc technology,and show how the derived new technologies did not repeat the same mistakes:
• The multihop ad hoc networking paradigm is extended to include some infras-tructure to provide a cost-effective wireless broadband extension of the Internet.Mesh networks constitute the most relevant example of this approach.
• Node mobility is not considered as a problem to face, but as a feature to exploit,allowing the design of a completely new networking paradigm. Opportunisticnetworks constitute one of the most relevant examples in this sense.
• The multihop ad hoc networking paradigm is applied to specialized fields wherethe self-organizing nature of this paradigm and the absence of a pre-deployedinfrastructure are a plus, and not a limitation. Notable examples of this approachare application-driven networks such as vehicular networks and sensor networks.
In order to create a common background for understanding the challenges and theresults in the field of the emerging networking technologies illustrated in this book,we give general descriptions of their enabling technologies and standards, applica-tion scenarios, the need for securing their communications, and their architecturalsolutions for mobility.
We then present the new challenges and the most advanced research results in meshnetworks, opportunistic networks, vehicular networks, and sensor networks.
This book is intended for developers, researchers, and graduate students incomputer science and electrical engineering, researchers and developers in thetelecommunication industry, and researchers and developers in all the fields that makeuse of mobile networking, which can potentially benefit from innovative solutions.We believe that this book is innovative in the topics covered, relies on the expertise oftop researchers, and presents a balanced selection of chapters that provides current hottopics and cutting-edge research directions in the field of mobile ad hoc networking.
We take this opportunity to express our sincere appreciation to all the authors, whocontributed high-quality chapters, and to all invited reviewers for their invaluable workand responsiveness under tight deadlines. A special thank goes to the Associate Editorof Wiley-IEEE Press, Mary Hatcher, who has been truly outstanding in supportingus through all the book construction phases, and to the teams at Wiley and ThomsonDigital.
Enjoy your reading!
Stefano Basagni
Marco Conti
Silvia Giordano
Ivan Stojmenovic
ACKNOWLEDGMENTS
Stefano Basagni was supported in part by the NSF funded project “GENIUS: GreenSensor Networks for Air Quality Support” (NSF CNS 1143681).
Marco Conti wishes to thank his wife, Laura, for her invaluable support, encour-agement, and understanding throughout this book project.
Silvia Giodrano wishes to personally thank her husband Piergiorgio, and her kidsVirginia and Lorenzo for their support and encouragement in creating this book.
Ivan Stojmenovic was supported in part by NSERC Discovery grant.
xv
CONTRIBUTORS
Mohammad S. Almalag, Department of Computer Science, Old DominionUniversity Norfolk, Virginia, USA
Stefano Basagni, Department of Electrical and Computer Engineering, NortheasternUniversity, Boston, Massachusetts
Elizabeth Basha, University of the Pacific, Stockton, California; and MassachusettsInstitute of Technology, Cambridge, Massachusetts
Chiara Boldrini, Institute of Informatics and Telematics (IIT), Italian NationalResearch Council (CNR), Pisa, Italy
Luciano Bononi, Department of Computer Science, University of Bologna,Bologna, Italy
Raffaele Bruno, Institute of Informatics and Telematics (IIT), Italian NationalResearch Council (CNR), Pisa, Italy
Antonio Capone, Dipartimento di Elettronica e Informazione Politecnico di Milano,Milano, Italy
Song Chong, Department of Electrical Engineering, Korea Advanced Institute ofScience and Technology, Daejon, Korea
Kaushik Roy Chowdhury, Department of Electrical and Computer Engineering,Northeastern University, Boston, Massachusetts
Claudio Cicconetti, Telecommunications Business Unit, Intecs S.p.A., Pisa, Italy
xvii
xviii CONTRIBUTORS
Marco Conti, Institute of Informatics and Telematics (IIT), Italian National ResearchCouncil (CNR), Pisa, Italy
J. Crowcroft, Computer Laboratory, University of Cambridge, Cambridge, UnitedKingdom
Yousef-Awwad Daraghmi, Department of Computer Science, National Chiao TungUniversity, Hsinchu City, Taiwan
Carrick Detweiler, University of Nebraska—Lincoln, Lincoln, Nebraska; andMassachusetts Institute of Technology, Cambridge, Massachusetts
Emrecan Demirors, Department of Electrical Engineering, State University of NewYork at Buffalo, Buffalo, NY, USA
Marco Di Felice, Department of Computer Science, University of Bologna, Bologna,Italy
Roberto Di Pietro, Department of Mathematics, Università di Roma Tre, Rome,Italy
Josep Domingo-Ferrer, Department of Computer Engineering and Mathematics,Universitat Rovira i Virgili, Tarragona, Catalonia, Spain
Marek Doniec, Massachusetts Institute of Technology, Cambridge, Massachusetts
Rafael Falcon, Electrical Engineering and Computer Science, University of Ottawa,Ottawa, Canada
Ettore Ferranti, ABB Corporate Research, Zurich, Switzerland
Ilario Filippini, Dipartimento di Elettronica e Informazione, Politecnico di Milano,Milano, Italy
Anna Foster, Networking Laboratory, University of Applied Technology of SouthernSwitzerland (SUPSI), Lugano, Switzerland
Silvia Giordano, Institute of Systems for Informatics and Networking (ISIN),University of Applied Technology of Southern Switzerland (SUPSI), Lugano,Switzerland
Stefano Gualandi, Dipartimento di Matematica, Università di Pavia, Pavia, Italy
Tihomir Hristov, Old Dominion University, Norfolk, Virginia
Pan Hui, Deutsche Telekom Laboratories, Berlin, Germany
Teemu Karkkainen, Comnet, Aalto University, Espoo, Finland
Hovannes Kulhandjian, Department of Electrical Engineering, State University ofNew York at Buffalo, Buffalo, NY, USA
Li-Chung Kuo, Department of Electrical Engineering, State University of New Yorkat Buffalo, Buffalo, NY, USA
CONTRIBUTORS xix
Kyunghan Lee, School of Electrical and Computer Engineering, Ulsan NationalInstitute of Science and Technology, Ulsan, Korea
Ilias Leontiadis, Computer Laboratory, University of Cambridge, Cambridge,United Kingdom
Minglu Li, Department of Computer Science and Technology, Shanghai Jiao TongUniversity, Shanghai, China
Juan A. Martinez, Department of Information and Communications Engineering,University of Murcia, Murcia, Spain
Cecilia Mascolo, Computer Laboratory, University of Cambridge, Cambridge,United Kingdom
Liam McNamara, Department of Information Technology, Uppsala University,Uppsala, Sweden
Tommaso Melodia, Department of Electrical Engineering, State University of NewYork at Buffalo, Buffalo, New York
Enzo Mingozzi, Dipartimento di Ingegneria dell’Informazione, University of Pisa,Pisa, Italy
Prasant Mohapatra, Department of Computer Science, University of California atDavis, Davis, California
Derek G. Murray, Computer Laboratory, University of Cambridge, Cambridge,United Kingdom
M. Yousof Naderi, Department of Electrical and Computer Engineering, Northeast-ern University, Boston, Massachusetts
Amiya Nayak, Electrical Engineering and Computer Science, University of Ottawa,Ottawa, Canada
Karthik Nilakant, Computer Laboratory, University of Cambridge, Cambridge,United Kingdom
Stephan Olariu, Department of Computer Science, Old Dominion University,Norfolk, Virginia
Victor Omwando, Department of Computer Science, University of California atDavis, Davis, California
Joerg Ott, Comnet, Aalto University, Espoo, Finalnd
Andrea Passarella, Institute of Informatics and Telematics (IIT), Italian NationalResearch Council (CNR), Milan, Italy
Bence Pasztor, Computer Laboratory, University of Cambridge, Cambridge, UnitedKingdom
xx CONTRIBUTORS
Chiara Petrioli, Dipartimento di Informatica, Università di Roma “La Sapienza,”Roma, Italy
Andreea Picu, Communication System Group, ETH Zürich, Zürich, Switzerland
Mikko Pitkanen, Comnet, Aalto University, Espoo, Finland
Francisco J. Ros, Department of Information and Communications Engineering,University of Murcia, Murcia, Spain
Pedro M. Ruiz, Department of Information and Communications Engineering,University of Murcia, Murcia, Spain
Daniela Rus, Department of Electrical Engineering and Computer Science,Massachusetts Institute of Technology, Cambridge, Massachusetts
Dora Spenza, Dipartimento di Informatica, Università di Roma “La Sapienza,”Roma, Italy
Thrasyvoulos Spyropoulos, Mobile Communications Department, EURECOM,Sophie Antipolis, France
Ivan Stojmenovic, Electrical Engineering and Computer Science, University ofOttawa, Ottawa, Canada
Niki Trigoni, Department of Computer Science, University of Oxford, Oxford,United Kingdom
Carlo Vallati, Dipartimento di Ingegneria dell’Informazione, University of Pisa,Pisa, Italy
Salvatore Vanini, Networking Laboratory, University of Applied Technology ofSouthern Switzerland (SUPSI), Lugano, Switzerland
Sonia, Waharte, Department of Computer Science and Technology, University ofBedfordshire, Luton, United Kingdom
Michele C. Weigle, Department of Computer Science, Old Dominion UniversityNorfolk, Virginia, USA
Gongjun Yan, School of Science, Indiana University, Kokomo, Indiana
Chih-Wei Yi, Department of Computer Science, National Chiao Tung University,Hsinchu City, Taiwan
E. Yoneki, Computer Laboratory, University of Cambridge, Cambridge, UnitedKingdom
Di Yuan, Department of Science and Technology, Linköping University, Linköping,Sweden
Hongzi Zhu, Department of Computer Science and Technology, Shanghai Jiao TongUniversity, Shanghai, China
PART I
GENERAL ISSUES
1MULTIHOP AD HOC NETWORKING:THE EVOLUTIONARY PATH
Marco Conti and Silvia Giordano
ABSTRACT
In this chapter we discuss the evolution of the mobile/multihop ad hoc networkingparadigm. This paradigm has often been identified with the technologies developedinside the MANET IETF working group. For this reason we first review the failuresand the success stories in the MANET research. Specifically, we analyze the reasonswhy the MANET paradigm does not have a major impact on computer communi-cations. Then, starting from the lessons learned from the MANET research activi-ties, we discuss how the multihop ad hoc networking paradigm has evolved towarda set of pragmatic networking approaches that are currently penetrating the massmarket. Specifically, in this chapter we discuss four successful networking paradigmsthat emerged from the evolution of the multihop ad hoc networking concept: mesh,opportunistic, vehicular, and sensor networks. In these cases the multihop ad hocparadigm is applied in a pragmatic way to extend the Internet and/or to support well-defined application requirements, thus providing a set of technologies that have amajor impact on the wireless-networking field.
1.1 INTRODUCTION
At the end of the 1990s, the proliferation of mobile computing and communica-tion devices (e.g., cell phones, laptops, handheld digital devices, personal digital
Mobile Ad Hoc Networking: Cutting Edge Directions, Second Edition. Edited by Stefano Basagni,Marco Conti, Silvia Giordano, and Ivan Stojmenovic.© 2013 by The Institute of Electrical and Electronics Engineers, Inc. Published 2013 by John Wiley & Sons, Inc.
3
4 MULTIHOP AD HOC NETWORKING: THE EVOLUTIONARY PATH
assistants, or wearable computers) fueled the explosive growth of the mobile comput-ing market and cellular networks, and WiFi hot spots quickly replaced wired accessnetworks. While infrastructure-based networks offer a great way for mobile devicesto get network services, it takes time and potentially high cost to set up the necessaryinfrastructure everywhere. These costs and delays may not be acceptable for dynamicenvironments where people and/or vehicles need to be temporarily interconnectedin areas without a preexisting communication infrastructure (e.g., intervehicular anddisaster networks), or where the infrastructure cost is not justified (e.g., in-buildingnetworks, residential communities networks, etc.). In these cases, infrastructurelessnetworks, often referred to as ad hoc networks or self-organizing networks, providea more efficient solution [1,2]. Single-hop ad hoc networks are the simplest formof self-organizing networks obtained by interconnecting devices that are within thesame transmission range. Several wireless-network standards support the single-hopad hoc network paradigm: IEEE 802.15.4 for short-range low data rate (< 250 kbps)networks (also known as Zigbee), Bluetooth (IEEE 802.15.1) for personal area net-works, and the 802.11 standards’ family for high-speed LAN ad hoc networks (seeChapter 2 in this book). Nearby nodes can thus communicate directly by exploitingwireless-network technologies in ad hoc mode. In a multihop network, often re-ferred to as Mobile Ad hoc Networks (MANETs), the network nodes (e.g., the users’mobile devices) must cooperatively provide the functionalities usually provided by thenetwork infrastructure (e.g., routers, switches, servers). In a MANET, users’ deviceswith wireless interface(s) (typically 802.11 in ad hoc mode) activate communicationsessions with the other mobile devices to perform data transfer operations without theneed of any network infrastructure. The potentialities of this networking paradigmmade ad hoc networking an attractive option for building 4G wireless networks,and hence MANET immediately gained momentum and this produced tremendousresearch efforts in the mobile-network community (see, for example, references 1and 2). However, in spite of the enormous research efforts, after more than 15 yearsof intense research activities, the MANET technology has only a marginal role inthe wireless networking field: It is applied only in very specialized scenarios. Indeed,as pointed out in reference 3, while from an academic standpoint MANET has beena very productive research area, the impact of this networking paradigm on civil-ian computer communications has been negligible. More precisely, while MANETresearch produced an extensive literature that highly influenced the development ofthe next generation of multihop ad hoc networks, from a usage standpoint MANETresearch has been a failure. This is mainly due to a lack of realism in the researchapproach/objectives that produced tons of scientific papers but only a very limitednumber of real deployments, with limited involvement of real users and no killerapplication. However, by exploiting the lessons learned in the MANET research,along with the scientific results produced, the scientific community has been able toturn the multihop ad hoc networking paradigm in a successful networking paradigmby applying it in several classes of networks that are currently penetrating the massmarket. As discussed in this chapter, relevant examples of these technologies includemesh, opportunistic, vehicular, and sensor networks.
MANET RESEARCH: MAJOR ACHIEVEMENTS AND LESSONS LEARNED 5
In this chapter we discuss the evolution of the multihop ad hoc networkingparadigm. Specifically, Section 1.2 is devoted to analyze and discuss the MANETresearch by first presenting the main scientific achievements in this research area(with a special attention to the highly innovative cross-layering concept) and thendiscussing the lessons learned from MANET “failure.” Then, in Section 1.3 we reviewthe most successful networking paradigms based on the multihop ad hoc network-ing, by discussing the results already achieved and the open challenges. Section 1.4concludes the chapter.
1.2 MANET RESEARCH: MAJOR ACHIEVEMENTSAND LESSONS LEARNED
In this section we review the scientific results in MANET research and then wediscuss the reasons why this paradigm does not have a major impact on the wireless-networking field, and we conclude with a set of lesson learned from MANET research.
1.2.1 Major Achievements in MANET Research
The MANET research focused on what we call pure general-purpose MANET, wherepure indicates that no infrastructure is assumed to implement the network functionsand no authority is in charge of managing and controling the network. General-purpose denotes that these networks are not designed with any specific application inmind, but rather to support any legacy TCP/IP application. Specifically, the researchersconcentrated their efforts to design and evaluate algorithms and protocols to imple-ment efficient communications in a scenario like the one shown in Figure 1.1. Here,users’ devices cooperatively provide the functionalities that are usually provided bythe network infrastructure (e.g., routers, switches, servers). In this way, mobile nodes
Figure 1.1 MANET topology.
6 MULTIHOP AD HOC NETWORKING: THE EVOLUTIONARY PATH
Middleware and Applications
TCP UDPTransport Layer
Network Layer
802.11 BluetoothZigBee
IP protocol
Enabling Technologies
Figure 1.2 MANET layered stack.
not only can communicate with each other, but also can access Internet by exploitingthe services offered by MANET gateway nodes, thus effectively extending Internetservices to the non-infrastructure area (e.g., see references 4 and 5).
Pure general-purpose MANET represents a major departure from the traditionalcomputer-network paradigms calling for a complete redesign of the network archi-tecture and protocols. This has generated intense research activities. An in-depthoverview of MANET research activities can be found in reference 2, while refer-ence 1 summarizes the main results and challenges in MANET research.
The MANET IETF working group has been the reference point for the researchactivities on pure general-purpose MANET. The MANET IETF WG adopted anIP-centric view of a MANET (see Figure 1.2) that inherited the TCP/IP protocols stacklayering with the aim of redesigning the network protocol stack to respond to the newcharacteristics, complexities, and design constraints of MANET [6]. All layers of theprotocol stack were the subjects of intensive research activities. Hereafter, accordingto a layered view of the protocol stack (see Figure 1.2), we will briefly summarize themain research directions/results, from the enabling technologies up to middlewareand applications.
1.2.1.1 Enabling Technologies. Enabling technologies are the basic block ofMANET that guarantees direct single-hop communications between users’ devices.Therefore, intense research activities focused on investigating the suitability ofexisting wireless-network standards to support multihop ad hoc networks with specialattention to the IEEE 802.11 family (e.g., see references 7–10), to Bluetooth (e.g.,see references 7, 11, and 12), and, more recently, to ZigBee (e.g., see references 13and 14). Typically, these wireless network standards have not been designed for sup-porting multihop ad hoc networks; hence several enhancements, both at the MACand physical layer have been proposed and evaluated for improving these technolo-gies when operating in ad hoc mode. Enhancements at the physical layer includethe use of directional antennas and power control [15], the use of OFDM, improvedsignal processing schemes, software defined radio, and MIMO technologies; while
MANET RESEARCH: MAJOR ACHIEVEMENTS AND LESSONS LEARNED 7
at the MAC layer there have been several proposals for controlling the collisions andinterferences among nodes still guaranteeing an efficient energy consumption [1].An updated analysis of the enabling technologies for multihop ad hoc networks ispresented in Chapter 2 of this book.
1.2.1.2 Networking Layer. MANET research efforts mainly focused on the net-working layer, with a special attention to routing and forwarding, because these arethe basic networking services for constructing a multihop ad hoc network. Routingis the function of identifying the path between the sender and the receiver, and for-warding, the subsequent function of delivering the packets along this path. Thesefunctions are strongly coupled with the characteristic of the network topology. Dueto the unpredictable and dynamic nature of MANET topology, legacy routing pro-tocols developed for wired networks are not suitable for multihop ad hoc networks,and this stimulated an intense research activity that produced an impressive (andcontinuously increasing) number of routing protocol proposals (see reference 16 foran updated list). Routing and forwarding protocols can be classified according to thecast property—that is, whether they use a Unicast, Geocast, Multicast, or Broad-cast forwarding. Broadcast is the basic mode of operation over a wireless channel;each message transmitted on a wireless channel is generally received by all neigh-bours located within one hop from the sender. The simplest implementation of thebroadcast operation to all network nodes is by flooding, but this may cause the broad-cast storm problem due to redundant re-broadcast [17]. Schemes have been proposedto alleviate this problem by reducing redundant broadcasting. A discussion on effi-cient broadcasting schemes is presented in reference 18. Multicast routing protocolscome into play when a node needs to send the same message, or stream of data, toa subset of the network-node destinations. Geocast forwarding is a special case ofmulticast that is used to deliver data packets to a group of nodes situated inside a spec-ified geographical area. From an implementation standpoint, geocasting is a form of“restricted” broadcasting: Messages are delivered to all the nodes that are inside agiven region. This can be achieved by routing the packets from the source to a nodeinside the geocasting region and then applying a broadcast transmission inside theregion. Position-based or location-aware routing algorithms, by providing an efficientsolution for forwarding packets toward a geographical position, constitute the basisfor constructing geocasting delivery services [19]. Location-aware routing protocolsuse the nodes’ position (i.e., geographical coordinates) for data forwarding. A nodeselects the next hop for packets’ forwarding by using the physical position of itsneighbors, along with the physical position of the destination node: Packets are senttoward the known geographical coordinates of the destination node [20].
Unicast forwarding means a one-to-one communication; that is, one source trans-mits data packets to a single destination. It is the basic forwarding mechanism incomputer networks; for this reason, unicast routing protocols comprise the largestclass of MANET routing protocols. According to the MANET WG, unicast rout-ing protocols are classified into two main categories: proactive routing protocolsand reactive (on-demand) routing protocols. Proactive routing protocols are de-rived from legacy Internet distance-vector and link-state protocols. They attempt to
8 MULTIHOP AD HOC NETWORKING: THE EVOLUTIONARY PATH
maintain consistent and updated routing information for every pair of network nodesby propagating, proactively, route updates at fixed time intervals. Conversely, reactiverouting protocols establish the route to a destination only when requested (the sourcenode usually initiates the route discovery process by sending a route request mes-sage). Once a route has been established, it is maintained until either the destinationbecomes inaccessible or until the route is no longer used. In particular, three mainrouting protocols emerged from the MANET field and constitute a reference for othermultihop ad hoc networks: two reactive routing protocols, AODV (and its successorDYMO) and DSR, and one proactive protocol, OLSR. A survey on MANET rout-ing protocols is presented in reference 21, while reference 1 summarizes the mainresearch directions in this area.
In addition to proactive and reactive protocols, other classes of protocols have beenidentified to improve the network performance at least in specific scenarios. Hybridprotocols combine both proactive and reactive approaches, thus trying to bring to-gether the advantages of both. Energy-aware routing protocols take into considerationthe energy available in the network nodes to select the path(s) for data forwarding.This may imply either (a) to minimize the energy consumed to forward a packet fromthe source to the destination or (b) to maximize the network lifetime by preservingas much as possible the network connectivity. Hierarchical routing aims at reducingthe overhead by structuring the network on more levels and allowing the multihopcommunications among only few nodes, representing a group of nodes at a lowerlevel. Cluster-based routing is a relevant example of hierarchical routing. The basicidea behind clustering is to group the network nodes into a number of overlappingclusters. Paths are recorded only between clusters (instead of between nodes); thisenables the aggregation of the routing information and consequently increases therouting algorithms scalability. In its original definition, inside the cluster, one node isin charge of coordinating the cluster activities (clusterhead). Beyond the clusterhead,inside the cluster, we have ordinary nodes that have direct access only to their clus-terhead and gateways—that is, nodes that can hear two or more clusterheads and thatrelay the traffic among different clusters. Cluster-based routing has been extensivelyadopted in multihop ad hoc networks, and consequently the definition of a cluster andcluster-based routing has significantly evolved.
1.2.1.3 Higher Layers. On top of the networking protocols, MANET generallyassumes the Internet transport protocols. Unfortunately, the Transmission ControlProtocol (TCP) does not work properly in this scenario, as extensively discussedin the literature (see, e.g., reference 1). To improve the performance of the TCPprotocol in a MANET, several proposals have been presented. Most of these proposalsare modified versions of the legacy TCP protocol used in the Internet. However,TCP-based solutions might not be the best approach when operating in MANETenvironments, and hence several authors have proposed novel transport protocolstailored on the MANET features (e.g., see reference 22 and references therein).
Middleware and applications constitute the less investigated area in the MANETfield. Indeed, general-purpose MANETs have been designed to support legacy TCP/IPapplications without a clear understanding of the applications for which multihop ad