Mobile Peer-to-Peer
Computing for Next
Generation Distributed
Environments:
Advancing Conceptual and
Algorithmic Applications
Boon-Chong Seet
Auckland University of Technology, New Zealand
Hershey • New York
Director of Editorial Content: Kristin Klinger Senior Managing Editor: Jamie Snavely Managing Editor: Jeff Ash Assistant Managing Editor: Carole Coulson Typesetter: Chris Hrobak Cover Design: Lisa Tosheff Printed at: Yurchak Printing Inc.
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Library of Congress Cataloging-in-Publication Data
Mobile peer-to-peer computing for next generation distributed environments: advancing conceptual and algorithmic applications / Boon-Chong Seet, editor. p. cm.
Includes bibliographical references and index.
Summary: "This book is dedicated to the coverage of research issues, findings, and approaches to Mobile P2P computing from both conceptual and algorithmic perspectives"--Provided by publisher.
ISBN 978-1-60566-715-7 (hbk.) -- ISBN 978-1-60566-716-4 (ebook) 1. Peer-to-peer architecture (Computer networks) 2. Mobile communication systems. I. Seet, Boon-Chong,
TK5105.525.M63 2009 004.6'52--dc22
2009001030
British Cataloguing in Publication Data
A Cataloguing in Publication record for this book is available from the British Library.
Editorial Advisory Board
Ouri Wolfson, University of Illinois at Chicago, USA
Takahiro Hara, Osaka University, Japan
Jiannong Cao, Hong Kong Polytechnic University, Hong Kong
Hsiao-Hwa Chen, National Sun Yat-Sen University, Taiwan
Aaron Harwood, University of Melbourne, Australia
John F. Buford, Avaya Labs Research, USA
List of Reviewers
Chintada Suresh, Motorola Research Labs, Bangalore, India
Thadpong Pongthawornkamol, University of Illinois at Urbana-Champaign, USA
Kurt Tutschku, University of Vienna, Austria
Thomas Repantis, Akamai Technologies, USA
James Walkerdine, Lancaster University, UK
Wei Wu, National University of Singapore, Singapore
Spyridon Tompros, University of the Aegean, Greece
Dawoud Dawoud, University of KwaZulu-Natal, South Africa
Norihiro Ishikawa, Service and Solution Development Department, NTT Docomo Inc, Japan
Alf Inge Wang, Norwegian University of Science and Technology, Norway
Erkki Harjula, University of Oulu, Finland
Jie Feng, University of Nebraska-Lincoln, USA
Raphael Kummer, Distributed Computing Group, Université de Neuchâtel, Switzerland
Tobias Hossfeld, University of Würzburg, Germany
Fotis Loukos, Aristotle University of Thessaloniki, Greece
Antonio Tadeu Azevedo Gomes, National Laboratory for Scientific Computing (LNCC), Brazil Leonardo B. Oliveira, State University of Campinas (UNICAMP), Brazil
Franca Delmastro, Institute for Informatics and Telematics, National Research Council, Italy
Li Li, Communications Research Centre, Canada
Foreword ... xvi
Preface ...xviii
Acknowledgment ... xxiv
Section I
Information Retrieval and Dissemination
Chapter I
P2P Information Lookup, Collection, and Distribution in Mobile Ad-Hoc Networks ... 1
Raphaël Kummer, University of Neuchâtel, Switzerland Peter Kropf, University of Neuchâtel, Switzerland Pascal Felber, University of Neuchâtel, Switzerland
Chapter II
Data Dissemination and Query Routing in Mobile Peer-to-Peer Networks ... 26
Thomas Repantis, University of California, Riverside, USA Vana Kalogeraki, University of California, Riverside, USA
Section II
Overlay and Mobility Management
Chapter III
Overlay Construction in Mobile Peer-to-Peer Networks ... 51
Jie Feng, University of Nebraska-Lincoln, USA Lisong Xu, University of Nebraska-Lincoln, USA
Chapter IV
Mobility Support in a P2P System for Publish/Subscribe Applications ... 68
Thomas Kunz, System and Computer Engineering, Carleton University, Canada Abdulbaset Gaddah, System and Computer Engineering, Carleton University, Canada Li Li, Communications Research Centre, Canada
Chapter V
P2P over MANETs: Application and Network Layers’ Routing Assessment ... 94 Leonardo B. Oliveira, University of Campinas (UNICAMP), Brazil
Isabela G. Siqueira, Federal University of Minas Gerais (UFMG), Brazil Daniel F. Macedo, Université Pierre et Marie Curie-Paris VI, France José M. Nogueira, Federal University of Minas Gerais (UFMG), Brazil Antonio A. F. Loureiro, Federal University of Minas Gerais (UFMG), Brazil
Section III
Cooperative Mechanisms
Chapter VI
Enabling Cooperation in MANET-Based Peer-to-Peer Systems ... 118
Fotis Loukos, Aristotle University of Thessaloniki, Greece Helen Karatza, Aristotle University of Thessaloniki, Greece
Chapter VII
Cooperation Strategies for P2P Content Distribution in Cellular Mobile Networks:
Considering Selfishness and Heterogeneity ... 132
Tobias Hoßfeld, University of Würzburg, Germany Daniel Schlosser, University of Würzburg, Germany Kurt Tutschku, University of Vienna, Austria
Phuoc Tran-Gia, University of Würzburg, Germany
Chapter VIII
Cooperation Strategies for P2P Content Distribution in Cellular Mobile Networks:
Considering Mobility and Heterogeneity ... 152
Tobias Hoßfeld, University of Würzburg, Germany Michael Duelli, University of Würzburg, Germany Dirk Staehle, University of Würzburg, Germany Phuoc Tran-Gia, University of Würzburg, Germany
Chapter IX
Peer-Based Collaborative Caching and Prefetching in Mobile Broadcast ... 166
Wei Wu, Singapore-MIT Alliance, and School of Computing, National University of Singapore, Singapore
Section IV Resource Management
Chapter X
Wireless Peer-to-Peer Media Streaming: Incentives and Resource Management Issues ... 190
Mark Kai-Ho Yeung, The University of Hong Kong, Hong Kong Yu-Kwong Kwok, Colorado State University, USA
Chapter XI
Incentives for Resource Sharing in Ad Hoc Networks: Going Beyond Rationality ... 218
Panayotis Antoniadis, Université Pierre et Marie Curie, Paris 6, France
Section V Security
Chapter XII
Key Management for Dynamic Peer Groups in Mobile Ad Hoc Networks ... 241
Johann van der Merwe, University of KwaZulu-Natal, South Africa Dawoud Dawoud, University of KwaZulu-Natal, South Africa
Chapter XIII
A Tool Supported Methodology for Developing Secure Mobile P2P Systems ... 283
James Walkerdine, Lancaster University, UK Peter Phillips, Lancaster University, UK Simon Lock, Lancaster University, UK
Section VI Standards and Protocols
Chapter XIV
Integration and Interworking of Fixed and Mobile P2P Systems ... 302
Spyridon L. Tompros, University of the Aegean, Greece
Chapter XV
Peer-to-Peer SIP for Mobile Computing: Challenges and Solutions ... 326
Erkki Harjula, MediaTeam Oulu Group, University of Oulu, Finland Jani Hautakorpi, Ericsson Research Nomadiclab, Jorvas, Finland
Nicklas Beijar, Department of Communications and Networking, TKK, Helsinki University of Technology, Espoo, Finland
Section VII
Architectures and Platforms
Chapter XVI
Mobile P2P in Cellular Mobile Networks: Architecture and Performance ... 349
Kurt Tutschku, University of Vienna, Austria Andreas Berl, University of Passau, Germany Tobias Hossfeld, University of Würzburg, Germany Hermann de Meer, University of Passau, Germany
Chapter XVII
Peer-to-Peer Networking Platform and Its Applications for Mobile Phones ... 374
Norihiro Ishikawa, NTT DOCOMO, Japan Hiromitsu Sumino, NTT DOCOMO, Japan Takeshi Kato, NTT DOCOMO, Japan Johan Hjelm, Ericsson Research, Japan Shingo Murakami, Ericsson Research, Japan Kazuhiro Kitagawa, Keio University, Japan Nobuo Saito, Komazawa University, Japan
Chapter XVIII
Evaluation Platform for Large Scale P2P Mobile Ad-hoc Networks ... 397
Raphaël Kummer, University of Neuchâtel, Switzerland Peter Kropf, University of Neuchâtel, Switzerland
Jean-Frédéric Wagen, TIC Institute, University of Applied Sciences of Fribourg, Switzerland Timothée Maret, TIC Institute, University of Applied Sciences of Fribourg, Switzerland
Section VIII Applications and Services
Chapter XIX
Mobile Peer-to-Peer Collaborative Framework and Applications ... 415
Alf Inge Wang, Norwegian University of Science and Technology, Norway
Chapter XX
Service Discovery Approaches to Mobile Peer-to-Peer Computing ... 437 Antônio Tadeu A. Gomes, National Laboratory for Scientific Computing (LNCC), Brazil Artur Ziviani, National Laboratory for Scientific Computing (LNCC), Brazil
Chapter XXI
Context-Aware P2P Over Opportunistic Networks ... 460
Marco Conti, IIT Institute – CNR, Pisa, Italy Franca Delmastro, IIT Institute – CNR, Pisa, Italy Andrea Passarella, IIT Institute – CNR, Pisa, Italy
Compilation of References ... 481
About the Contributors ... 518
Foreword ... xvi
Preface ...xviii
Acknowledgment ... xxiv
Section I
Information Retrieval and Dissemination
This section includes two chapters that look at the issue of information retrieval and dissemination, each exploring a different approach to addressing the issue.
Chapter I
P2P Information Lookup, Collection, and Distribution in Mobile Ad-Hoc Networks ... 1
Raphaël Kummer, University of Neuchâtel, Switzerland Peter Kropf, University of Neuchâtel, Switzerland Pascal Felber, University of Neuchâtel, Switzerland
This chapter presents an enhanced Distributed Hash Table (DHT) to facilitate information retrieval (or lookup), and a new multicast tree construction algorithm built on top of the proposed DHT to
con-struct a multicast tree distribution infracon-structure for efficient information dissemination in mobile ad hoc
networks.
Chapter II
Data Dissemination and Query Routing in Mobile Peer-to-Peer Networks ... 26
Thomas Repantis, University of California, Riverside, USA Vana Kalogeraki, University of California, Riverside, USA
This chapter proposes to adaptively disseminate special information called content synopses and
presents a content-driven routing protocol that utilizes this information to efficiently guide the queries
for actual content or information retrieval.
Section II
Overlay and Mobility Management
This section includes three chapters covering overlay construction, mobility support in overlay networks in the context of publish/subscribe systems, and performance study of P2P overlay and MANET routing protocols.
Chapter III
Overlay Construction in Mobile Peer-to-Peer Networks ... 51
Jie Feng, University of Nebraska-Lincoln, USA Lisong Xu, University of Nebraska-Lincoln, USA
Byrav Ramamurthy, University of Nebraska-Lincoln, USA
This chapter reviews P2P overlay construction techniques for mobile networks, including tree- and
mesh-based mobile P2P streaming networks. The authors also discuss advanced design issues, such as session mobility, robustness to high churn, incentive mechanism and content integrity, with relation to managing mobility in P2P overlays.
Chapter IV
Mobility Support in a P2P System for Publish/Subscribe Applications ... 68
Thomas Kunz, System and Computer Engineering, Carleton University, Canada Abdulbaset Gaddah, System and Computer Engineering, Carleton University, Canada Li Li, Communications Research Centre, Canada
This chapter examines the issue of subscriber mobility in publish/subscribe systems and presents a new mobility support solution through proactive context distribution, which is shown to perform better in terms of message loss/duplication, processing overhead and handoff latency than the conventional reactive approach.
Chapter V
P2P over MANETs: Application and Network Layers’ Routing Assessment ... 94 Leonardo B. Oliveira, University of Campinas (UNICAMP), Brazil
Isabela G. Siqueira, Federal University of Minas Gerais (UFMG), Brazil Daniel F. Macedo, Université Pierre et Marie Curie-Paris VI, France José M. Nogueira, Federal University of Minas Gerais (UFMG), Brazil Antonio A. F. Loureiro, Federal University of Minas Gerais (UFMG), Brazil
Section III
Cooperative Mechanisms
This section includes four chapters devoted to discussing the different mechanisms and applications of peer-to-peer cooperation in mobile networks.
Chapter VI
Enabling Cooperation in MANET-Based Peer-to-Peer Systems ... 118
Fotis Loukos, Aristotle University of Thessaloniki, Greece Helen Karatza, Aristotle University of Thessaloniki, Greece
This chapter outlines the current methods for cooperation in standard and MANET-based P2P networks. The authors also describe a number of use cases to illustrate the potential of peer-to-peer cooperation technology for mobile networks, including for such applications as knowledge sharing and social networking.
Chapter VII
Cooperation Strategies for P2P Content Distribution in Cellular Mobile Networks:
Considering Selfishness and Heterogeneity ... 132
Tobias Hoßfeld, University of Würzburg, Germany Daniel Schlosser, University of Würzburg, Germany Kurt Tutschku, University of Vienna, Austria
Phuoc Tran-Gia, University of Würzburg, Germany
This chapter identifies selfish peers as a factor that degrades performance of P2P content distribution
systems in cellular mobile networks and studies several cooperation strategies, including a new strategy
CyPriM proposed by the authors to improve performance in the presence of selfish peers and heteroge
-neous peer resources.
Chapter VIII
Cooperation Strategies for P2P Content Distribution in Cellular Mobile Networks:
Considering Mobility and Heterogeneity ... 152
Tobias Hoßfeld, University of Würzburg, Germany Michael Duelli, University of Würzburg, Germany Dirk Staehle, University of Würzburg, Germany Phuoc Tran-Gia, University of Würzburg, Germany
This chapter extends the discussion in the preceding chapter to consider the impact of mobility and vertical handover in a B3G network. The authors evaluate solutions such as mobile IP in the context of P2P content distribution, and present new strategies to manage mobility and improve utilization of scarce resources in such heterogeneous networks.
Chapter IX
Peer-Based Collaborative Caching and Prefetching in Mobile Broadcast ... 166
Wei Wu, Singapore-MIT Alliance, and School of Computing, National University of Singapore, Singapore
This chapter reviews the problem of cooperative cache management in mobile environments that support data broadcast, and presents two peer-to-peer based schemes: CPIX and ACP for caching and pre-fetching information, respectively, to improve the data availability and access latency in mobile environments.
Section IV Resource Management
This section includes two chapters on methods to foster resource sharing among peers: one in the context of P2P media streaming in hybrid wireless networks; the other on general resource sharing in ad-hoc networks.
Chapter X
Wireless Peer-to-Peer Media Streaming: Incentives and Resource Management Issues ... 190
Mark Kai-Ho Yeung, The University of Hong Kong, Hong Kong Yu-Kwong Kwok, Colorado State University, USA
This chapter focuses on energy cost sharing in wireless P2P media streaming, and presents two energy
efficient protocols based on game-theoretic concepts to improve collaboration and streaming performance
of peers in hybrid wireless networks.
Chapter XI
Incentives for Resource Sharing in Ad Hoc Networks: Going Beyond Rationality ... 218
Panayotis Antoniadis, Université Pierre et Marie Curie, Paris 6, France
This chapter presents the case for social incentives to be used to foster resource sharing in ad hoc net-works, and proposes a new cross-layer concept that considers both social and economic solutions in application layer and network layer, respectively, in the design of incentive mechanisms.
Section V Security
This section includes two chapters that concern security: one relates to the design of group key management schemes for mobile ad hoc networks; the other looks at the development of secure mobile P2P applications.
Chapter XII
Key Management for Dynamic Peer Groups in Mobile Ad Hoc Networks ... 241
This chapter provides a comprehensive coverage of conventional group key management schemes for dynamic peer groups, and discusses their design challenges and potential for MANET through an analysis of their communication and computation costs.
Chapter XIII
A Tool Supported Methodology for Developing Secure Mobile P2P Systems ... 283
James Walkerdine, Lancaster University, UK Peter Phillips, Lancaster University, UK Simon Lock, Lancaster University, UK
This chapter presents a development tool that considers the user’s security, mobility, and P2P technology
requirements, and proposes a suitable system architecture and sub-system designs for developing secure
mobile P2P applications.
Section VI Standards and Protocols
This section includes two chapters that cover current standards and protocols of interest to the research and development of mobile P2P systems.
Chapter XIV
Integration and Interworking of Fixed and Mobile P2P Systems ... 302
Spyridon L. Tompros, University of the Aegean, Greece
This chapter discusses the relevance of ITU standard architecture for next generation networks, and
presents an overlay architecture for integrating P2P systems in interoperable fixed-mobile environments based
on the IP Multimedia Sub-system (IMS) technology.
Chapter XV
Peer-to-Peer SIP for Mobile Computing: Challenges and Solutions ... 326
Erkki Harjula, MediaTeam Oulu Group, University of Oulu, Finland Jani Hautakorpi, Ericsson Research Nomadiclab, Jorvas, Finland
Nicklas Beijar, Department of Communications and Networking, TKK, Helsinki University of Technology, Espoo, Finland
Mika Ylianttila, MediaTeam Oulu Group, University of Oulu, Finland
Section VII
Architectures and Platforms
This section includes three chapters on new architectures and platforms, including a new content-distribution architecture for cellular networks, a P2P networking platform for mobile phones, and a platform for emulation of P2P algorithms for MANET.
Chapter XVI
Mobile P2P in Cellular Mobile Networks: Architecture and Performance ... 349
Kurt Tutschku, University of Vienna, Austria Andreas Berl, University of Passau, Germany Tobias Hossfeld, University of Würzburg, Germany Hermann de Meer, University of Passau, Germany
This chapter first discusses the current incompatibilities between cellular mobile and P2P networks,
and then presents a new P2P architecture for cellular mobile networks using content-distribution as an example application. The authors also investigate extensively the proposed architecture using analytical and simulation-based evaluation.
Chapter XVII
Peer-to-Peer Networking Platform and Its Applications for Mobile Phones ... 374
Norihiro Ishikawa, NTT DOCOMO, Japan Hiromitsu Sumino, NTT DOCOMO, Japan Takeshi Kato, NTT DOCOMO, Japan Johan Hjelm, Ericsson Research, Japan Shingo Murakami, Ericsson Research, Japan Kazuhiro Kitagawa, Keio University, Japan Nobuo Saito, Komazawa University, Japan
This chapter describes the architecture and protocols of a new P2P networking platform for mobile phones, and discusses the experimentation of the platform using three classes of mobile phone ap-plications namely, multimedia content search, instant messaging over Bluetooth, and remote access to networked home appliances.
Chapter XVIII
Evaluation Platform for Large Scale P2P Mobile Ad-hoc Networks ... 397
Raphaël Kummer, University of Neuchâtel, Switzerland Peter Kropf, University of Neuchâtel, Switzerland
Jean-Frédéric Wagen, TIC Institute, University of Applied Sciences of Fribourg, Switzerland Timothée Maret, TIC Institute, University of Applied Sciences of Fribourg, Switzerland
Section VIII Applications and Services
This section includes three chapters that look at the development of collaborative applications, service discovery, and context-awareness in mobile P2P services.
Chapter XIX
Mobile Peer-to-Peer Collaborative Framework and Applications ... 415
Alf Inge Wang, Norwegian University of Science and Technology, Norway
This chapter describes the Peer2Me software framework for developing P2P applications that support collaboration on mobile phones with JavaME and Bluetooth. The authors also illustrate the potential use of the framework through a portfolio of developed applications that demonstrate a wide spectrum of collaborative functions.
Chapter XX
Service Discovery Approaches to Mobile Peer-to-Peer Computing ... 437 Antônio Tadeu A. Gomes, National Laboratory for Scientific Computing (LNCC), Brazil Artur Ziviani, National Laboratory for Scientific Computing (LNCC), Brazil
Luciana S. Lima, National Laboratory for Scientific Computing (LNCC), Brazil Markus Endler, Pontifical Catholic University of Rio de Janeiro (PUC-Rio), Brazil
This chapter presents a comprehensive coverage and comparative analysis of the current service dis-covery approaches in P2P systems for a variety of mobile networks, including infrastructured wireless networks, single-hop and multi-hop ad hoc networks.
Chapter XXI
Context-Aware P2P Over Opportunistic Networks ... 460
Marco Conti, IIT Institute – CNR, Pisa, Italy Franca Delmastro, IIT Institute – CNR, Pisa, Italy Andrea Passarella, IIT Institute – CNR, Pisa, Italy
This chapter discusses the use of context to enhance distributed services in opportunistic networks, and
describes two context management architectures and their use in a context-aware opportunistic file
sharing application that considers not only the social context of user, but also the utility of data objects for the context the user is in.
Compilation of References ... 481
About the Contributors ... 518
xvi
Foreword
We are witnessing an explosive growth in the number of mobile computing devices, including smart phones, personal assistant devices, and sensors, and in wireless communication technologies and capa-bilities. Despite such growth, systems in which the devices collaborate directly to process information, namely mobile P2P systems, are in their infancy.
This does not mean that research on the subject has not been done, but that the problem is very
difficult. An example of an MP2P application that has been worked on for more than twenty years is routing, which is important in the digital battlefield, vehicular networks, and others. The problem is to
route messages between a sender and a receiver that are out of each other’s transmission range, using the mobile devices as intermediaries. Despite the extensive amount of work on this problem, it is not solved yet.
Furthermore, not all reasons for the slow start on mobile P2P systems are technological. For example, data broadcasting is a well understood mechanism that is technologically easy to implement and can facilitate mobile P2P systems development and deployment. Some of the chapters in this book discuss broadcasting. Yet it is not implemented by existing cellular service providers.
Nevertheless, technology is a major stumbling block. The technological challenges include resource constraints on the mobile device, security and privacy, variable and/or disconnected network topology,
and heterogeneity of devices. More specifically, it is hard to build systems when energy, memory, CPU
power, and bandwidth resources are constrained on each one of the devices participating in the P2P system. Furthermore, the wireless medium is easier to tap into, and the devices are harder to protect physically. Thus, serious security and privacy concerns arise. Additionally, many mobile P2P systems cannot rely on an infrastructure for wireless communication among the devices. For example, an infrastructure
of-ten does not exist in a battlefield. Thus, such systems depend on direct collaboration among the mobile devices via short-range wireless networks, which is difficult when mobility and failures continuously
change the set of neighbors with which a node can directly communicate.
This book addresses the technological challenges. It describes the problems, some existing solutions,
and proposes new ones. The first section deals with the problem of finding information in a network
lacking an infrastructure. Observe that this is different than the routing problem. It is harder in the sense that even the identity of the receiver, that is the location of information, is unknown; but easier in the sense that the information may be replicated and therefore routing to a single receiver is often not strictly
necessary. The proposed solutions combine query and information dissemination in an intelligent way. P2P methods have been quite successful in the fixed world, and the second section explores adaptation
xvii
deal with the resource constraints, and it discusses incentives and mechanisms for cooperation. Section V discusses the critical topic of security, and sections VI, VII, and VIII discuss strategies that facilitate the development of mobile P2P systems. These strategies include standards, software tools, platforms, programming paradigms, service provision and discovery, and protocols.
Overall, the book is an invaluable resource for both researchers and practitioners. It addresses the most important issues in mobile P2P systems, it is well organized, very readable, comprehensive, and presented at the right level of depth. It strikes a good balance between presentation of novel ideas, and survey of the state of the art.
Ouri Wolfson
University of Illinois, USA
Ouri Wolfson’s main research interests are in database systems, distributed systems, and mobile/pervasive computing. He received his PhD degree in Computer Science from Courant Institute of Mathematical Sciences, New York University. He is currently the Richard and Loan Hill professor of Computer Science at the University of Illinois at Chicago, where he directs
the Mobile Information Systems Research Center. He is also an affiliate professor in the Department of Computer Science at
xviii
Preface
Computing systems are playing an essential role as an indispensable nervous system of modern society.
The ubiquitous use of computing systems for the operation of our society, such as in our banking, public
transportation, and healthcare systems, and in our daily lives for meeting our personal learning, entertain-ment and productivity needs, has resulted in them being of fundaentertain-mental importance to keeping our modern
society alive and thriving. The subsequent trend of integrating computing systems with communication
networks such as the Internet further extended the reach of computing systems beyond geographical boundaries, ushering in an era of networked computing systems.
Computer-mediated communication for distant human-to-human interaction, that is computer tele-phony systems, has become a cost-effective alternative to traditional telephone networks (Yarberry, 2002).
Distant human-to-machine interaction has also benefited from the advent of networked computing, such
as by enabling remote access to computing resources such as shared printers and databases. More recently, machine-to-machine (M2M) interaction has been a subject of interest in networked computing where ma-chines leverage on their network (wired or wireless) connectivity to directly interact with each other and in some cases make their own decisions without human intervention (Lawton, 2004).
Networked computing systems have traditionally been based on the client-server model (Goodyear et al., 1999). In this architecture, the network consists of a server, typically a high-performance com-puter, and a group of clients. The server is the only provider of resources or services in the network,
while the clients only request for resources or the execution of services from the server. It is apparent
that each addition of a new client to the network is a new load added to the server. As the number of clients grows, the server capacity must increase to avoid becoming a bottleneck in the system. It is also apparent that in this model, the server represents a single point of failure in the network, and thus can be a major cause of downtime and a vulnerable target for security attacks.
In recent years, the development of networked computing has evolved from the centralized and hier-archical model of client-server computing to encompass a more decentralized and distributed model
of peer-to-peer (P2P) computing (Subramanian & Goodman, 2005). Using the widely-accepted definition
by Schollmeier (2001), P2P is a network where the participants share a part of their own resources, which can be hardware resources such as processing power, storage capacity, network link capacity, printers,
and so forth, or software resources such as media content, (e.g., pictures, videos and music files, and other
xix
Due to its promising potential to resolve the above issues of scalability and fault-tolerance in
client-server computing, this radical and contrasting approach to computing has gained significant attention
from both industry and academic research communities, and is suited for applications that have a mass of users in complex open distributed environments such as the Internet. Today, P2P technologies have
been widely embraced by Internet users, and are best exemplified by popular file sharing systems such as
eMule or BitTorrent, and Voice-over-P2P (VoP2P) applications such as Skype. Other emerging applications based on P2P that are gaining popularity include live or on-demand media (TV and video) streaming
ap-plications, for example, Joost, Zattoo, and PPLive (Krieger & Schwessinger, 2008; Mushtaq, & Ahmed,
2008; Akkanen, Karonen, & Porio, 2008), and large-scale distributed online storage systems such as Wuala (Caleido AG, 2008), which provides its users with free online storage service for private or shared data by exploiting the unused disk space of participating computers on the Internet.
In a parallel development with Internet P2P computing from late 1990s, the landscape of telecom-munications also experienced profound changes with the rapid proliferation of a plethora of wireless technologies ranging from technologies for wide area networks (e.g., UMTS, HSDPA, HSPA+), metro-politan area networks (e.g., Mobile WiMAX [802.16e], Mobile-Fi [802.20]), local area networks (e.g., 802.11a/g/n/p/s), personal area networks (e.g., Bluetooth, ZigBee, WiMedia), to more recently regional area networks based on emerging cognitive radios (802.22). Today, wireless-enabled laptops and PDAs, and cellular handsets with Internet access have become widely available and increasingly affordable. It
is also not uncommon to find multi-mode terminals where computing devices or handsets have multiple
modes of wireless connectivity such as 3G UMTS, WiFi (802.11) and Bluetooth. These technological advances are believed to have fueled the uptake of a mobile lifestyle where the daily lives of people are increasingly empowered by and dependent on wireless technologies. For instance, the increasing need of people to stay connected to the Internet at anytime from anywhere for work or for play. This brings forth a
prediction that a significant portion of future users of P2P systems will be mobile, which calls for a need
to investigate the suitability of developed P2P technologies for mobile and wireless networks, such as mobile cellular networks, infrastructured wireless local area networks (WLAN), and the infrastructure-less mobile ad hoc networks (MANET).
Early investigations along this direction (such as Klemm, Lindemann, & Waldhorst, 2004; Ding & Bhargava, 2004) for MANET, and (such as Eberspächer, Schollmeier, Zöls, Kunzmann, & Für, 2004)
for a heterogeneous mobile and fixed environment, have shown that contemporary P2P technologies performed neither well nor efficiently as they were designed for a relatively stable and resource-rich
environment where hosts are stationary, well-endowed (i.e., in terms of processing power, memory, and energy) and connected by high bandwidth links. Thus, research is needed to innovate new approaches
to P2P computing in a mobile environment. Specifically, the design of the mobile P2P systems should
address the new challenges of dynamic changes in connectivity and resource availability, the new con-straints in mobile devices as well as wireless capacity, and respond to these concon-straints and changes in an intelligent, timely, and adaptive manner. However, the research possibilities of Mobile P2P computing
are not limited to extending conventional P2P systems to perform effectively and efficiently under mobile conditions, but include, for instance, turning the new constraints into strengths by finding new usages of unique characteristics of mobile P2P, or creating new patterns of collaboration and sharing that can
potentially move mobile applications and services into a new dimension for next generation distributed environments.
This book is dedicated to the coverage of research issues, findings, and approaches to mobile P2P
xx
experts in the field, and guided by an Editorial Advisory Board of prominent international researchers, the overall aim of this book is to serve as a valuable resource that captures the present state of the field, and to
inspire ideas for future challenges through presenting the latest insights and thoughts of expert researchers on major topics of this emerging discipline.
The key contribution of this book is in providing a much needed body of knowledge on mobile P2P computing in a single reference source, which to the best of our knowledge, is still largely missing from currently available book titles. Through a careful selection of topics that address some of the most
important and essential issues in the field, including topics of both theoretical (e.g., models, algorithms, architectures) and practical interests (e.g., tools, platforms, applications), this book seeks to fill the gap
in available titles with its dedicated and comprehensive coverage on mobile P2P computing. Readers
would also benefit from the scholarly value of the book through its balanced and quality coverage of
theoretical ideas and practical research. This book therefore comes as a timely contribution to the growing
and flourishing research community in mobile P2P computing.
The book is intended to provide an up-to-date advanced reading of important topics for academic researchers, graduate students, and senior undergraduate students in computer science, electrical and electronic engineering, and telecommunications, to enhance their research or studies. It is also intended for industry professionals such as R&D engineers, application developers, and technology business
managers who wish to keep abreast of the recent developments in the field, and who are interested or
involved in the research, use, design, development, and deployment of mobile P2P technologies. This book is organized into eight sections comprising a total of 21 chapters. Each section addresses
a specific topic area or relates to works of a specific nature. Under each section, the chapters are gener
-ally self-contained, thus readers are not required to read in the order in which they are listed, but could
focus directly on those chapters that interest them. The following is a summary of contents covered in each section, including a brief description of each chapter listed under the section.
Section I: Information Retrieval and Dissemination
This section includes two chapters that look at the issue of information retrieval and dissemination, each exploring a different approach to addressing the issue.
Chapter I presents an enhanced Distributed Hash Table (DHT) to facilitate information retrieval (or lookup), and a new multicast tree construction algorithm built on top of the proposed DHT to
construct a multicast tree distribution infrastructure for efficient information dissemination in mobile
ad hoc networks.
Chapter II proposes to adaptively disseminate special information called content synopses and
presents a content-driven routing protocol that utilizes this information to efficiently guide the queries
for actual content or information retrieval.
Section II: Overlay and Mobility Management
This section includes three chapters covering overlay construction, mobility support in overlay net-works in the context of publish/subscribe systems, and performance study of P2P overlay and MANET
routing protocols. Specifically:
Chapter III reviews P2P overlay construction techniques for mobile networks, including tree- and
xxi
Chapter IV examines the issue of subscriber mobility in publish/subscribe systems and presents a new mobility support solution through proactive context distribution, which is shown to perform better in terms of message loss/duplication, processing overhead and handoff latency than the conventional reactive approach.
Chapter V investigates the performance of three MANET routing protocols: AODV, DSR, and DSDV under a Gnutella P2P network, and two P2P overlay protocols: Gnutella and Chord, over MANET with AODV as the underlying routing protocol through extensive computer simulations.
Section III: Cooperative Mechanisms
This section includes four chapters devoted to discussing the different mechanisms and applications of peer-to-peer cooperation in mobile networks.
Chapter VI outlines the current methods for cooperation in standard and MANET-based P2P networks. The authors also describe a number of use cases to illustrate the potential of peer-to-peer cooperation technol-ogy for mobile networks, including for such applications as knowledge sharing and social networking.
Chapter VII identifies selfish peers as a factor that degrades performance of P2P content distribution
systems in cellular mobile networks and studies several cooperation strategies, including a new strategy
CyPriM proposed by the authors to improve performance in the presence of selfish peers and heteroge
-neous peer resources.
Chapter VIII extends the discussion in the preceding chapter to consider the impact of mobility and vertical handover in a B3G network. The authors evaluate solutions such as mobile IP in the context of P2P content distribution, and present new strategies to manage mobility and improve utilization of scarce resources in such heterogeneous networks.
Chapter IX reviews the problem of cooperative cache management in mobile environments that support data broadcast, and presents two peer-to-peer based schemes: CPIX and ACP for caching and pre-fetching information, respectively, to improve the data availability and access latency in mobile environments.
Section IV: Resource Management
This section includes two chapters on methods to foster resource sharing among peers: one in the con-text of P2P media streaming in hybrid wireless networks; the other on general resource sharing in ad-hoc networks.
Chapter X focuses on energy cost sharing in wireless P2P media streaming, and presents two energy
efficient protocols based on game-theoretic concepts to improve collaboration and streaming performance
of peers in hybrid wireless networks.
Chapter XI present the case for social incentives to be used to foster resource sharing in ad hoc networks, and proposes a new cross-layer concept that considers both social and economic solutions in application layer and network layer, respectively, in the design of incentive mechanisms.
Section V: Security
This section includes two chapters that concern security: one relates to the design of group key man-agement schemes for mobile ad hoc networks; the other looks at the development of secure mobile P2P applications.
xxii
Chapter XIII presents a development tool that considers the user’s security, mobility, and P2P
tech-nology requirements, and proposes a suitable system architecture and sub-system designs for developing
secure mobile P2P applications.
Section VI: Standards and Protocols
This section includes two chapters that cover current standards and protocols of interest to the research
and development of mobile P2P systems. Specifically:
Chapter XIV discusses the relevance of ITU standard architecture for next generation networks, and
presents an overlay architecture for integrating P2P systems in interoperable fixed-mobile environments
based on the IP Multimedia Sub-system (IMS) technology.
Chapter XV reviews the current IETF standard for P2P-SIP (Session Initiation Protocol), which is designed to serve as a lightweight P2P based protocol for communication, session management, and service provisioning in infrastructured mobile networks such as wireless LAN and 3G cellular networks.
Section VII: Architectures and Platforms
This section includes three chapters on new architectures and platforms, including a new content-distri-bution architecture for cellular networks, a P2P networking platform for mobile phones, and a platform for emulation of P2P algorithms for MANET.
Chapter XVI first discusses the current incompatibilities between cellular mobile and P2P networks,
and then presents a new P2P architecture for cellular mobile networks using content-distribution as an example application. The authors also investigate extensively the proposed architecture using analytical and simulation-based evaluation.
Chapter XVII describes the architecture and protocols of a new P2P networking platform for mobile phones, and discusses the experimentation of the platform using three classes of mobile phone applications namely, multimedia content search, instant messaging over Bluetooth, and remote access to networked home appliances.
Chapter XVIII presents Freemote, a Java-based emulation platform that could integrate emulated and real nodes such as the Berkeley motes to enable large-scale emulation of P2P algorithms for MA-NET with a high level of realism.
Section VIII: Applications and Services
This section includes three chapters that look at the development of collaborative applications, service
dis-covery, and context-awareness in mobile P2P services. Specifically:
Chapter XIX describes the Peer2Me software framework for developing P2P applications that sup-port collaboration on mobile phones with JavaME and Bluetooth. The authors also illustrate the potential use of the framework through a portfolio of developed applications that demonstrate a wide spectrum of collaborative functions.
Chapter XX presents a comprehensive coverage and comparative analysis of the current service discovery approaches in P2P systems for a variety of mobile networks, including infrastructured wire-less networks, single-hop and multi-hop ad hoc networks.
Chapter XXI discusses the use of context to enhance distributed services in opportunistic networks,
and describes two context management architectures and their use in a context-aware opportunistic file
xxiii
REFERENCES
Akkanen, J., Karonen, O., & Porio, J. (2008). Peer-to-peer video streaming on mobile phones, In Pro-ceedings of the IEEE Consumer Communications and Networking Conference.
Caleido AG (2008). Wuala – The social online storage, Retrieved December 28, 2008, from http://
wuala.com/en/
Ding, G., & Bhargava, B. (2004). Peer-to-peer file-sharing over mobile ad hoc networks. In Proceedings of the Second IEEE Annual Conference on Pervasive Computing and Communications Workshops. Eberspächer, J., Schollmeier, R., Zöls, S., Kunzmann, G., & Für, L. (2004). Structured P2P networks in
mobile and fixed environments, In Proceedings of the International Working Conference on Performance
Modeling and Evaluation of Heterogeneous Networks.
Goodyear, M. et al., (1999).Netcentric and client/server computing: A practical guide. USA: Auerbach Publications.
Klemm, A., Lindemann, C., & Waldhorst, O. P. (2004). Peer-to-peer computing in mobile ad hoc networks. In Proceedings of the 11th IEEE/ACM International Symposium on Modeling, Analysis and Simulation of Computer and Telecommunication Systems.
Krieger, U. R., & Schwessinger, R. (2008). Analysis and quality assessment of peer-to-peer IPTV systems. In Proceedings of the IEEE International Symposium on Consumer Electronics (ISCE).
Lawton, G. (2004). Machine-to-machine technology gears up for growth. Computer,37(9), 12-15. Mushtaq, M., & Ahmed, T. (2008). P2P-based mobile IPTV: Challenges and opportunities. In Proceed-ings of the IEEE/ACS International Conference on Computer Systems and Applications.
Schollmeier, R. (2001). A definition of peer-to-peer networking for the classification of peer-to-peer
architecture and applications. In Proceedings of the First International Conference on Peer-to-Peer Computing.
Subramanian, R., & Goodman, B. D. (Eds.). (2005). Peer-to-peer computing: The evolution of a disruptive technology. Hershey, PA: Idea Group Publishing.
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The editor would like to express his sincere appreciation and gratitude to all who have rendered sup-port in one way or another to this year-long book project, without which this book could not have been
satisfactorily completed. The editor would like to first thank members of the Editorial Advisory Board
for their support and help in this project, despite their demanding work schedules and commitments. The editor would also like to thank all who are involved in the review process of the book, which includes most of the chapter authors in this book who also served as referees for chapters written by other authors. Special thanks must also go to a number of individuals who volunteered their time to serve as external referees and offered some of the most comprehensive, critical, and constructive comments in their reviews. They are: Thadpong Pongthawornkamol of University of Illinois at Urbana-Champaign; Chintada Suresh of Motorola Research Labs; Dr. Aaron Harwood of University of Melbourne; and Dr. John Buford, a Research Scientist at Avaya Labs Research.
Grateful acknowledgement must also be given to the publishing team at IGI Global for its
contribu-tions throughout the whole process from setting up a website for my initial call for chapters to the final
publication of the book. In particular, the editor is most grateful to Julia Mosemann for her assistance
throughout the development process of the book and her consistently quick responses to my many questions and requests via e-mail.
I am also grateful to professor Wen-Jing Hsu, whose encouragement and kind words motivated me to initially accept the challenge of taking on this project. Last but not least, I would also like to thank my parents for their moral support and encouragement over the years, which have been instrumental in getting me to where I am today.
In closing, I sincerely wish to thank all of the authors for sharing their research insights, ideas, and experiences through their excellent chapter contributions to this book.
Boon-Chong Seet Editor, PhD
Auckland, New Zealand December 2008
Section I
1
Chapter I
P2P Information Lookup,
Collection, and Distribution in
Mobile Ad-Hoc Networks
Raphaël Kummer
University of Neuchâtel, Switzerland
Peter Kropf
University of Neuchâtel, Switzerland
Pascal Felber
University of Neuchâtel, Switzerland
Copyright © 2009, IGI Global, distributing in print or electronic forms without written permission of IGI Global is prohibited.
ABSTRACT
2
P2P Information Lookup, Collection, and Distribution in Mobile Ad-Hoc Networks
INTRODUCTION
Wireless technologies have become ubiquitous,
providing improved connectivity in urban areas and also allowing outlying areas to connect to information networks. Now almost everyone makes use of wireless technologies to surf the web using portable phones or computers. The well-known applications they rely on are spread over wide areas and the number of service access points has increased exponentially.
In addition to phone calls and web surfing,
many other applications are available on wireless enabled devices. They may take the form of
ad-hoc networks requiring no specific infrastructures
such as access points, and where these devices produce a self-organized mesh network in which each node able to communicate directly with its closest physical neighbors.
Despite the various types of devices and communication standards on which they are based, networking infrastructures and devices are all subject to the same limitations. The main concerns are limited resources and energy, and also practicality, such as movement and deploy-ment almost anywhere. Most often the devices are small, simple and battery powered, and make use of limited resources (i.e., memory and CPU). Related to these, communications generate non-negligible costs leading to an overall reduction in network lifetimes. At this time, communication
between remote nodes requires multiple hops via
relay nodes, because nodes can only communi-cate directly with their physical neighbors (i.e., the nodes located in its communication range), although they may listen to all the messages transiting within its physical neighborhood.
As new devices with ad-hoc networking ca-pacities and enhanced resources become devel-oped their use is extended well beyond original functions related to wide-area monitoring. New developments now allow information lookup
and multicasting, requiring novel and efficient
solutions.
The focus in this chapter is lookup and
multi-casting mechanisms able to efficiently locate and
distribute information in mobile ad-hoc networks (MANETs). The basic concept applied to achieve these objectives involves peer-to-peer (P2P)
para-digms, which can be roughly classified as either
structured or unstructured.
Unstructured approaches such as Gnutella or KaZaA (Kirk, 2003; KaZaA, 2008) typically
have neither control over topology nor file place -ment, meaning they often rely on locating data by
simply flooding the network and thus overloading
it. Unstructured approaches such as these have not been adapted for MANETs because locating the desired content involves too many transmissions and too much energy. Moreover, scaling them can
prove difficult (Oliveira et al., 2005).
Structured solutions on the other hand consist of specialized placement algorithms designed to
assign the responsibility for each content unit (file) to a specific node and then efficiently locate the files using directed search protocols, requiring
only limited communication. They are mostly based on distributed hash tables (DHTs) that locate
each item and node by means of a unique key
identity, producing a logical space. The nodes are thus arranged according to their logical key and are only responsible for an item located at the small-est logical distance from them. Another feature is
provided so that a node responsible for a specific key can be located without flooding and without
producing false negatives (i.e., a search fails only
if no matching file exists in the system).
3 P2P Information Lookup, Collection, and Distribution in Mobile Ad-Hoc Networks
logical neighborhood through expensive multiple hop paths, thus making simple mapping from a DHT design to ad-hoc networks unrealistic.
Similarly, solutions based on flooding will not
attain acceptable performance levels when dis-tributing content to a subset of interested nodes. Indeed in the MANET approach, all nodes are forced to participate, even when not interested in the distributed content. This leads to ineffective solutions and poor performance, with the network
quickly becoming overloaded and consuming
a lot of energy and bandwidth. Flooding might also be used to build a shortest-path spanning
tree, except that while flooding is reduced, inef
-ficient use of already limited resources results, given that many nodes are not interested in the
content. Furthermore, some flooding is still re
-quired to build the tree, and no efficient solution
for locating the multicast group is available to the content provider. Scribe (Rowstron, Kermarrec, Castro, & Druschel, 2001) for example, superim-poses a structured overlay substrate on top of the physical network and is able to construct more
efficient multicast trees. Here multicast trees are rooted in “rendezvous” nodes managed by an underlying Pastry DHT. The nodes interested in joining a multicast group route a request via
Pastry towards the source and connect to the first
member reached on their way to the rendezvous point. While it is perhaps an effective strategy in wired networks, it cannot be easily transposed to mobile ad-hoc networks where communication is multi-hop and physical proximity is an essential consideration.
In this chapter, we thus present a DHT lookup
algorithm specifically designed for MANETs. It
combines a minimalist overlay structure with an
adaptive routing mechanism that is able to quickly
locate the content. As in well-known wired ap-proaches such as Chord or Pastry, the nodes are organized in a logical ring. Yet, no long-range links are created for the logical shortcuts, given
the prohibitive maintenance costs involved. Al-ternatively, the physical neighborhood of the
nodes traversed by requests provides low-cost shortcuts that are able to quickly converge at
their destination within the logical space. We also propose extensions that consider an extra level of visibility in the physical neighborhood (neighbors of neighbors) and memorizing
previ-ous requests to dynamically identify and exploit
possible shortcuts.
We then present an algorithm for building multicast trees in mobile ad-hoc networks using this specialized lightweight DHT overlay. A tree is created by the source (i.e. the multicast group),
which can be efficiently located by searching the DHT. Several techniques of connecting adjacent
nodes to a physically close member are proposed, along with extensions able to reduce the number of relay nodes involved in message distribution.
We conducted simulations on both lookup and multicast algorithms to evaluate their per-formance in various scenarios. We did not take
churns (nodes frequently joining and leaving the
system) into account because we were primarily
interested in evaluating their lookup efficiency
and the structural properties of the multicast trees produced. Our results indicate that the DHT algorithm performs very well in MANETs and that the multicast tree-building algorithm produces well-structured trees, comprising of only a limited number of relay nodes. Moreover, both algorithms scale well to large networks.
The remainder of this chapter is organized as follows. The Background section discusses
related approaches. The DistributedHashTable for Mobile Ad-hoc Networks section presents
the ad-hoc DHT algorithm in detail, including evaluation results. The Building Multicast Trees in Mobile Ad-hoc Networks section describes and
4
P2P Information Lookup, Collection, and Distribution in Mobile Ad-Hoc Networks
BACKGROUND
In this section, we provide an overview of various approaches related to the algorithms presented. We begin with the DHT paradigms and then explore the various methods of multicasting in mobile ad-hoc networks.
Existing Distributed Hash Tables
for MANETs
Peer-to-peer overlays have emerged from file
sharing applications placed on top of the Internet, leveraged by the IP protocol routing infrastruc-ture and its intrinsic peer-to-peer properties. In MANETs the situation is different since the path between nodes may traverse many relay nodes not being part of the overlay. Furthermore, two nodes are directly connected only if they are physical neighbors (i.e., within communication range of each other). As discussed in the introduction, the DHT paradigm, including its regular topology
(often a ring) and shortcuts (fingers) introduced
at the overlay layer make direct mapping to
ad-hoc networks particularly difficult. Found in
literature are various approaches to carrying out these mappings.
Although GRACE (Global Replication And Consistency) (Bosneag & Brockmeyer, 2005) was
not specifically designed with ad-hoc networks in
mind, it does enable mobile collaboration through combining DHT properties with layered architec-ture. GRACE also supports mobility in wide-area networks and different layers or consistency levels are interconnected through “consistency neighbors” logically located in close proximity
to each other. Requests are routed along these
neighbors and the system’s lookup algorithm is based on Pastry (Rowstron & Druschel, 2001). This approach still relies on the standard Internet infrastructure.
(Pucha et al., 2004b) implement Pastry on top of the routing protocol DSR (Dynamic Source Routing) used by MANETs (Johnson & Maltz,
1996). Three modifications are suggested and can
be compared to implementation on the Internet:
(1) the node joining procedure is modified by
expanding the ring search in order to locate dis-tinguished bootstrap nodes in charge of arrivals; (2) to reduce network load the Pastry ping metric is replaced by a distance metric; and (3) the DSR
protocol is modified to inquire about the proximity
used in the adapted Pastry routing.
Ekta (Pucha, Das, & Hu, 2004a) and MAD-Pastry (Zahn & Schiller, 2005) integrate the DHT paradigm with ad-hoc network routing. Both approaches introduce the functions needed at the network routing layer. The principal idea of Ekta is to move the DHT protocol from the overlay level to the MANET network layer, applying one-to-one mapping between IP addresses and logical (DHT) node IDs. MADPastry is then built on top of the AODV protocol (Ad-hoc On-demand Vector Routing) (Perkins & Belding-Royer, 1999). The purpose of this protocol is to avoid full broadcasts as much as possible, because in ad-hoc networks this becomes too costly when the entire network is targeted. MADPastry creates clusters composed of physically close nodes that also share a
com-mon overlay prefix. Given physical and logical
closeness of that the nodes in a cluster, routing is based on the logical overlay node IDs.
The disadvantage of all the aforementioned approaches is the size of their routing table and the complexity involved when setting up and managing connections with all the nodes con-tained in them.
(Cramer et al., 2005) suggest the chord-based Proximity Neighbor Selection strategy (PNS-CHORD), in which nodes are connected to their logical successors on the ring and through logical shortcuts to further nodes, the way Chord usu-ally does. These logical long-range neighbors are chosen according to their physical proximity in the ad-hoc network and are located either one or two steps away.
5 P2P Information Lookup, Collection, and Distribution in Mobile Ad-Hoc Networks
cal path pursued by a request traverses the same
node several times. This can only be prevented
when nodes keep track of the requests that pass them and that subsequently adjust their routing tables in the event that the same request passes
twice, but on different logical shortcuts.
Cell Hash Routing (CHR) (Araujo, Rodrigues, Kaiser, Liu, & Mitidieri, 2005) is a specialized ad-hoc form of DHT. To construct a DHT, CHR uses position information clusters instead of organizing individual nodes in the overlay. This approach groups nodes according to their physi-cal location, and the routing between clusters is done by position-based routing using the GPSR (Karp & Kung, 2000) routing algorithm. A major limitation of this approach is that nodes are ad-dressed in clusters and not individually.
Finally, (Caesar, Castro, Nightingale, O’Shea, & Rowstron, 2006) suggest Virtual Ring Routing
(VRR), a DHT solution for MANETs that is quite
similar to that presented in this chapter and which also targets combining ad-hoc routing and logical DHT-like addressing. However, their algorithm differs from ours in several ways. First, in their approach, they build and proactively maintain bidirectional routes between nodes, while we
always try to find the best route at each node and then send the request along the selected path,
making the most of local situations. Second, VRR also maintains existing routes in a proactive way. While our solution does not maintain existing routes, previous routing decisions are kept in a cache and can thus be reactivated when appro-priate. Finally in an effort to improve routing, VRR nodes make use of information about the physical paths traversing the nodes. Based on our experiments however any improvement achieved is only minimal. In fact, these cached entries are
only effective when a request’s path goes through
the node that recorded them. In the DHT shown, the nodes also capture communications from any nodes in the physical neighborhood. The
infor-mation acquired thus implicitly includes routing
decisions and therefore allows paths to avoid
tra-versing the same physical area twice. It should be noted that no communication overhead is needed to capture this information, given the nature of that wireless networks (i.e. radio transmissions) allow it to be captured for free.
Related MANET Multicasting
Solutions
Several P2P approaches to multicasting have been suggested for ad-hoc networks, with some using a logical overlay substrate for locating sources and
others relying on flooding. Here we only discuss a
selection of approaches available in the literature that closely resemble the presented algorithm (see (Chen & Wu, 2003) for a good survey).
In ad-hoc networks there are various logical structures used to facilitate appropriate tree con-struction. To build a multicast tree, MZR (Devara-palli & Sidhu, 2001) relies on the Zone Routing
Protocol (Haas, 1997). The nodes in ZRP define
the area around them and proactively maintain routes to all nodes within that zone. When the destination is outside the sender’s zone, a reac-tive route discovery protocol is used, and when a source has data to multicast, it advertises this to all the nodes in its zone, and then extends the tree to nodes located at the border of other zones. An interested node simply answers the source and then a branch is created when the message reaches a multicast group member. Although the zone
structure contains the flooding needed to build the tree, it still floods the entire network zone by zone. Not only does this results in significant
bandwidth and energy consumption, the protocol provides no generic lookup facilities as used in our algorithm by the DHT.
6
P2P Information Lookup, Collection, and Distribution in Mobile Ad-Hoc Networks
bandwidth. XScribe exploits the DHT’s routing ca-pacities to distribute multicast messages, wherein each source has to know all group members and then multicast messages directly to them using a unicast method. This approach thus does not scale well, nor does it make any attempt to optimize resource consumption (minimizing the number of relay nodes or the number of transmissions
required).
Georendezvous relies on CHR (Araujo et al., 2005), a specialized ad-hoc DHT that groups nodes in clusters according to their physical location.
The DHT is used to efficiently locate the cell
responsible for a group, and the cell’s nodes can manage group membership and forward the mul-ticast messages to all the members. Membership management is centralized in a cell containing multiple nodes, which are also responsible for distributing multicast messages. The disadvan-tage of this approach lies in its high bandwidth
and energy requirements, thus resulting in poor
scalability.
Other than flooding, many solutions have been proposed to efficiently look up a key (data)
in MANETs. No mention is made of transpos-ing existtranspos-ing direct search algorithms to ad-hoc networks, since when creating the logical overlay no attention was given to the physical proximity of nodes. Other approaches adapted for ad-hoc networks unfortunately involve large routing tables or pathological situations, wherein a
re-quest passes repeatedly through the same node
or network area.
As in the DHT algorithms, flooding is not a
suitable solution to distributing content to a set of multicast group members. A large number of nodes do in fact have to participate without being interested in the distributed content, a problem that also appears in certain approaches adapted for MANETs. Given that communication is fairly expensive, it is important that the number of relays be minimized. Other solutions also suffer from
centralized membership management, a technique
requiring extensive memory resources and also
leading to network congestion during multicast distribution.
The following section describes DHT and multicast tree-building algorithms that target
efficient information lookup and distribution in
MANETs.
DISTRIBUTED HASH TABLE FOR
MOBILE AD-HOC NETWORKS
In a DHT system, each node and key has a
spe-cific position within a logical identifier space,
thus creating a logical overlay superimposed on the physical network. The keys are mapped to nodes according to proximity metrics in the logical space, thus allowing any node to use this DHT substrate to determine the current live node responsible for a given key. Chord (Stoica et al., 2001) for example connects each node to its closest neighbors (successor and predecessor)
in the identifier space, thus organizing nodes into
a logical ring. This neighborhood always allows traversing the entire ring, albeit at a very high cost. These connections are necessary however
and sufficient to ensure the system’s safety and
reliability. Additionally, each node has a number
of long-range neighbors called fingers, used to maintain liveliness properties and efficient look -ups. They are located at exponentially increasing distances within the logical space, and with these
links, a node can quickly reach remote locations:
the expected path length of a lookup is expressed by O(logN) hops, where N is the number of nodes in the system.
