Ad Hoc Networks 1 (2003) 13–64
`
`www.elsevier.com/locate/adhoc
`
`Mobile ad hoc networking: imperatives and challenges
`
`Imrich Chlamtac a, Marco Conti b,*, Jennifer J.-N. Liu c
`a School of Engineering, University of Texas at Dallas, Dallas, TX, USA
`b Istituto IIT, Consiglio Nazionale delle Ricerche, Pisa, Italy
`c Department of Computer Science, University of Texas at Dallas, Dallas, TX, USA
`
`Abstract
`
`Mobile ad hoc networks (MANETs) represent complex distributed systems that comprise wireless mobile nodes that
`can freely and dynamically self-organize into arbitrary and temporary, ‘‘ad-hoc’’ network topologies, allowing people
`and devices to seamlessly internetwork in areas with no pre-existing communication infrastructure, e.g., disaster re-
`covery environments. Ad hoc networking concept is not a new one, having been around in various forms for over 20
`years. Traditionally, tactical networks have been the only communication networking application that followed the ad
`hoc paradigm. Recently, the introduction of new technologies such as the Bluetooth, IEEE 802.11 and Hyperlan are
`helping enable eventual commercial MANET deployments outside the military domain. These recent evolutions have
`been generating a renewed and growing interest in the research and development of MANET. This paper attempts to
`provide a comprehensive overview of this dynamic field. It first explains the important role that mobile ad hoc networks
`play in the evolution of future wireless technologies. Then, it reviews the latest research activities in these areas, in-
`cluding a summary of MANETÕs characteristics, capabilities, applications, and design constraints. The paper concludes
`by presenting a set of challenges and problems requiring further research in the future.
`Ó 2003 Elsevier B.V. All rights reserved.
`
`Keywords: MAC; Routing; Energy saving; Security; Performance evaluation
`
`1. Introduction
`
`The proliferation of mobile computing and
`communication devices (e.g., cell phones, laptops,
`handheld digital devices, personal digital assis-
`tants, or wearable computers) is driving a revolu-
`tionary change in our information society. We are
`moving from the Personal Computer age (i.e., a
`
`* Corresponding author.
`E-mail addresses: chlamtac@utdallas.edu (I. Chlamtac),
`marco.conti@iit.cnr.it (M. Conti),
`jennifer.liu@sbcglobal.net
`(J.J.-N. Liu).
`
`one computing device per person) to the Ubiqui-
`tous Computing age in which a user utilizes, at the
`same time, several electronic platforms through
`which he can access all the required information
`whenever and wherever needed [268]. The nature
`of ubiquitous devices makes wireless networks the
`easiest solution for their interconnection and, as a
`consequence, the wireless arena has been experi-
`encing exponential growth in the past decade.
`Mobile users can use their cellular phone to check
`e-mail, browse internet; travelers with portable
`computers can surf the internet from airports, rail-
`way stations, Starbucks and other public loca-
`tions; tourists can use Global Positioning System
`
`1570-8705/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
`doi:10.1016/S1570-8705(03)00013-1
`
`
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`(GPS) terminals installed inside rental cars to lo-
`cate driving maps and tourist attractions, re-
`searchers can exchange files and other information
`by connecting portable computers via wireless
`LANs while attending conferences; at home, users
`can synchronize data and transfer files between
`portable devices and desktops.
`Not only are mobile devices getting smaller,
`cheaper, more convenient, and more powerful,
`they also run more applications and network ser-
`vices, commonly fueling the explosive growth of
`mobile computing equipment market. The ex-
`ploding number of Internet and laptop users
`driving this growth further [280]. Projections show
`that in the next two years the number of mobile
`connections and the number of shipments of mo-
`bile and Internet terminals will grow yet by an-
`other 20–50% [280]. With this trend, we can expect
`the total number of mobile Internet users soon to
`exceed that of the fixed-line Internet users.
`Among all the applications and services run by
`mobile devices, network connections and corre-
`sponding data services are without doubt the most
`demanded service by the mobile users. According
`to a study by Cahners In-Stat Group, the number
`of subscribers to wireless data services will grow
`rapidly from 170 million worldwide in 2000 to
`more than 1.3 billion in 2004, and the number of
`wireless messages sent per month will rise dra-
`matically from 3 billion in December 1999 to 244
`billion by December 2004. Currently, most of the
`connections among these wireless devices are
`achieved via fixed infrastructure-based service
`provider, or private networks. For example, con-
`nections between two cell phones are setup by BSC
`and MSC in cellular networks; laptops are con-
`nected to Internet via wireless access points. While
`infrastructure-based networks provide a great way
`for mobile devices to get network services, it takes
`time and potentially high cost
`to set up the
`necessary infrastructure. There are, furthermore,
`situations where user required networking con-
`nections are not available in a given geographic
`area, and providing the needed connectivity and
`network services in these situations becomes a real
`challenge.
`More recently, new alternative ways to deliver
`the services have been emerging. These are focused
`
`around having the mobile devices connect to each
`other in the transmission range through automatic
`configuration, setting up an ad hoc mobile net-
`work that is both flexible and powerful. In this
`way, not only can mobile nodes communicate with
`each other, but can also receive Internet services
`through Internet gateway node, effectively ex-
`tending Internet services to the non-infrastructure
`area. As the wireless network continues to evolve,
`these ad hoc capabilities are expected to become
`more important, the technology solutions used to
`support more critical and significant future re-
`search and development efforts can be expected in
`industry and academy, alike.
`This paper demonstrates the impetus behind
`mobile ad hoc networks, and presents a represen-
`tative collection of technology solutions used at
`the different layers of the network, in particular
`presenting algorithms and protocols unique to the
`operation and dynamic configuration of mobile ad
`hoc networks. Mobile ad hoc network (MANET)
`literature is already too extensive to be covered
`and analyzed in detail in this article. Hereafter, we
`therefore present the main research areas in the
`MANET literature, and inside each, survey the
`main research directions and open issues.
`Inside the ad hoc networking field, wireless
`sensor networks take a special role. A sensor net-
`work is composed of a large number of small
`sensor nodes, which are typically densely (and
`randomly) deployed inside the area in which a
`phenomenon is being monitored. Wireless ad hoc
`networking techniques also constitute the basis for
`sensor networks. However, the special constraints
`imposed by the unique characteristics of sensing
`devices, and by the application requirements,
`make many of the solutions designed for multi-
`hop wireless networks (generally) not suitable for
`sensor networks [12]. This places extensive litera-
`ture dedicated to sensor networks beyond the
`scope of this paper; however, the interested reader
`can find an excellent and comprehensive coverage
`of sensor networks in a recent survey [12].
`The paper is organized as follows. In Section 2,
`we explain why ad hoc networking is an essential
`component of the 4G network architectures. In
`Section 3, we look at mobile ad hoc networks in
`closer detail, covering their specific characteristics,
`
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`15
`
`advantages, as well as design challenges. This is
`followed by an analysis of MANET evolution
`from an historical perspective. Finally, we con-
`clude this section by presenting the design chal-
`lenges facing the MANET research community.
`In Section 4, we examine ad hoc networking
`enabling technologies, by examining Bluetooth,
`and IEEE 802.11 standards in more detail. Ad hoc
`networking research is surveyed in Section 5, in
`which we focus on node location services, for-
`warding and routing, and TCP issues. MANET
`applications and middleware are discussed in
`Section 6. Cross-layer research areas, including,
`energy management, security and cooperation,
`Quality of Service, and performance evaluation
`are analyzed in Section 7. Section 8 concludes the
`paper.
`
`2. 4G and ad hoc networking
`
`A major goal toward the 4G Wireless evolution
`is the providing of pervasive computing environ-
`ments that can seamlessly and ubiquitously sup-
`port users in accomplishing their tasks, in accessing
`information or communicating with other users at
`anytime, anywhere, and from any device [268]. In
`this environment, computers get pushed further
`into background; computing power and network
`connectivity are embedded in virtually every device
`to bring computation to users, no matter where
`they are, or under what circumstances they work.
`These devices personalize themselves in our pres-
`ence to find the information or software we need.
`The new trend is to help users in the tasks of ev-
`eryday life by exploiting technologies and infra-
`structures hidden in the environment, without
`requiring any major change in the usersÕ behavior.
`This new philosophy is the basis of the Ambient
`Intelligence concept [1]. The objective of ambient
`intelligence is the integration of digital devices and
`networks into the everyday environment, rendering
`accessible, through easy and ‘‘natural’’
`interac-
`tions, a multitude of services and applications.
`Ambient intelligence places the user at the center of
`the information society. This view heavily relies on
`4G wireless and mobile communications. 4G is all
`about an integrated, global network, based on an
`
`open systems approach. Integrating different types
`of wireless networks with wire-line backbone net-
`work seamlessly, and convergence of voice, multi-
`media and data traffic over a single IP-based core
`network are the main foci of 4G. With the avail-
`ability of ultra-high bandwidth of up to 100 Mbps,
`multimedia services can be supported efficiently;
`ubiquitous computing is enabled with enhanced
`system mobility and portability support, and lo-
`cation-based services are all expected. Fig. 1 illus-
`trates the networks and components within 4G
`network architecture.
`Network Integration. 4G networks are touted as
`hybrid broadband networks that integrate different
`network topologies and platforms. In Fig. 1 the
`overlapping of different network boundaries rep-
`resents the integration of different types of net-
`works in 4G. There are two levels of integration.
`First is the integration of heterogeneous wireless
`networks with varying transmission characteristics
`such as Wireless LAN, WAN, PAN, as well as
`mobile ad hoc networks. At the second level we find
`the integration of wireless networks with the fixed
`network backbone infrastructure, the Internet, and
`PSTN. Much work remains to enable a seamless
`integration, for example that can extend IP to
`support mobile network devices.
`All IP Networks. 4G starts with the assumption
`that future networks will be entirely packet-swit-
`ched, using protocols evolved from those in use in
`todayÕs Internet [163]. An all IP-based 4G wireless
`network has intrinsic advantages over its prede-
`cessors. IP is compatible with, and independent of,
`the actual radio access technology, this means that
`the core 4G network can be designed and evolves
`independently from access networks. Using IP-
`based core network also means the immediate
`tapping of the rich protocol suites and services
`already available, for example, voice and data
`convergence, can be supported by using readily
`available VoIP set of protocols such as MEGA-
`COP, MGCP, SIP, H.323, SCTP, etc. Finally the
`converged all-IP wireless core networks will be
`packet based and support packetized voice and
`multimedia on top of data. This evolution is ex-
`pected to greatly simplify the network and to re-
`duce costs for maintaining separate networks, for
`different traffic types.
`
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`Fig. 1. 4G networks.
`
`Lower Cost and Higher Efficiency. 4G IP-based
`systems will be cheaper and more efficient than
`3G. Firstly, equipment costs are expected to be
`four to ten times lower than equivalent circuit-
`switched equipment
`for 2G and 3G wireless
`infrastructures. An open converged IP wireless
`environment further reduces costs for network
`build-out and maintenance. There will be no need
`to purchase extra spectrum as 2G/3G spectrum
`can be reused in 4G, and much of spectrum needed
`by WLAN and WPAN is public and does not re-
`quire a license.
`Ultra-High Speed and Multimedia Applications.
`4G systems aim to provide ultra-high transmission
`speed of up to 100 Mbps, 50 times faster than
`those in 3G networks. This leap in provided
`bandwidth will enable high-bandwidth wireless
`services, allowing users to watch TV, listen to the
`music, browse Internet, access business programs,
`perform real-time video streaming and other
`multimedia-oriented applications,
`like E-Com-
`merce, as if sitting in home or office.
`
`Location Intelligence. To support ubiquitous
`computing requirements, 4G terminals need to be
`more intelligent in terms of userÕs locations and
`service needs,
`including recognizing and being
`adaptive to userÕs changing geographical positions,
`as well as offering location-based services [29].
`Anytime anywhere requires intelligent use of lo-
`cation information, and the embedding of the
`information into various applications. Possible
`Location Based Services include finding nearest
`service providers, such as restaurant or cinema;
`searching for special offers within an areas; warn-
`ing of traffic or weather situations; sending an
`advertisement to a specific area; searching for
`other users; active badge systems, etc. Outdoor,
`wireless applications can use GPS to obtain loca-
`tion information. GPS is a satellite-based system
`that can provide easy, accurate positioning infor-
`mation almost anywhere on earth. Many GPS
`implementations are available, including integrat-
`ing a GPS receiver into a mobile phone (GPS/
`DGPS); or add fixed GPS receivers at regular
`
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`17
`
`intervals to obtain data to complement readings
`on phone (A-GPS); or by using help from fixed
`base stations (E-OTD). These implementations
`provide different fix time and accuracy ranging
`from 50 to 125 m. For indoor applications, since
`GPS signal cannot be received well
`inside the
`buildings, alternative technologies like Infrared,
`Ultrasound or Radio are being considered.
`ex-
`Non-infrastructure-based MANET are
`pected to become an important part of the 4G
`architecture. An ad hoc mobile network is a
`transient network formed dynamically by a col-
`lection of
`(arbitrarily located) wireless mobile
`nodes without the use of existing network infra-
`structure, or centralized administration. Ad hoc
`networks are created, for example, when a group
`of people come together, and use wireless com-
`munications for some computer-based collabora-
`tive activities; this is also referred to as spontaneous
`networking [93].
`In a MANET, the usersÕ mobile devices are the
`network, and they must cooperatively provide the
`functionality usually provided by the network in-
`frastructure (e.g., routers, switches, servers). In a
`MANET, no infrastructure is required to enable
`information exchange among usersÕ mobile de-
`vices. We can envisage these devices as an evolu-
`tion of current mobile phones, and emerging
`PDAÕs equipped with wireless interfaces. The only
`external resource needed for their successful op-
`eration is the bandwidth, often the (unlicensed)
`ISM band. Nearby terminals can communicate
`directly by exploiting, for example, wireless LAN
`technologies. Devices that are not directly con-
`nected, communicate by forwarding their traffic
`via a sequence of intermediate devices.
`MANETs are gaining momentum because they
`help realizing network services for mobile users in
`areas with no pre-existing communications infra-
`structure, or when the use of such infrastructure
`requires wireless extension [67,102]. Ad hoc nodes
`can also be connected to a fixed backbone network
`through a dedicated gateway device enabling IP
`networking services in the areas where Internet
`services are not available due to a lack of pre-
`installed infrastructure. All these advantages make
`ad hoc networking an attractive option in future
`wireless networks.
`
`3. Mobile ad hoc networks
`
`As concluded in Section 2, ad hoc networking
`capabilities can become essential
`in delivering
`overall next generation wireless network func-
`tionalities. Next, we will look at mobile ad hoc
`network applications from an historical perspec-
`tive, and then we will focus on challenges in the
`MANET research activities.
`
`3.1. MANET evolution
`
`Historically, mobile ad hoc networks have pri-
`marily been used for tactical network related ap-
`plications to improve battlefield communications/
`survivability. The dynamic nature of military op-
`erations means that military cannot rely on access
`to a fixed pre-placed communication infrastructure
`in battlefield. Pure wireless communication also
`has limitation in that radio signals are subject to
`interference and radio frequency higher than 100
`MHz rarely propagate beyond line of sight (LOS)
`[97]. Mobile ad hoc network creates a suitable
`framework to address these issues by providing a
`multi-hop wireless network without pre-placed
`infrastructure and connectivity beyond LOS.
`Early ad hoc networking applications can be
`traced back to the DARPA Packet Radio Network
`(PRNet) project in 1972 [97], which was primarily
`inspired by the efficiency of the packet switching
`technology, such as bandwidth sharing and store-
`and-forward routing, and its possible application
`in mobile wireless environment. PRNet features a
`distributed architecture consisting of network of
`broadcast radios with minimal central control; a
`combination of Aloha and CSMA channel access
`protocols are used to support the dynamic sharing
`of the broadcast radio channel. In addition, by
`using multi-hop store-and-forward routing tech-
`niques, the radio coverage limitation is removed,
`which effectively enables multi-user communica-
`tion within a very large geographic area.
`Survivable Radio Networks (SURAN) were
`developed by DARPA in 1983 to address main
`issues in PRNet, in the areas of network scalabil-
`ity, security, processing capability and energy
`management. The main objectives were to develop
`network algorithms to support a network that can
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`scale to tens of thousands of nodes and withstand
`security attacks, as well as use small, low-cost,
`low-power radios that could support sophisticated
`packet radio protocols [97]. This effort results in
`the design of Low-cost Packet Radio (LPR) tech-
`nology in 1987 [94], which features a digitally
`controlled DS spread-spectrum radio with an in-
`tegrated Intel 8086 microprocessor-based packet
`switch. In addition, a family of advanced network
`management protocols was developed, and hier-
`archical network topology based on dynamic
`clustering is used to support network scalability.
`Other improvements in radio adaptability, secu-
`rity, and increased capacity are achieved through
`management of spreading keys [253].
`Towards late 1980s and early 1990s, the growth
`of the Internet infrastructure and the microcom-
`puter revolution made the initial packet radio
`network ideas more applicable and feasible [97].
`To leverage the global information infrastructure
`into the mobile wireless environment, DoD initi-
`ated DARPA Global Mobile (GloMo) Informa-
`tion Systems program in 1994 [171], which aimed
`to support Ethernet-type multimedia connectivity
`any time, anywhere among wireless devices. Sev-
`eral networking designs were explored; for exam-
`ple Wireless Internet Gateways (WINGs) at UCSC
`deploys a flat peer-to-peer network architecture,
`while Multimedia Mobile Wireless Network
`(MMWN) project from GTE Internetworking uses
`a hierarchical network architecture that is based
`on clustering techniques.
`Tactical Internet (TI) implemented by US Army
`at 1997 is by far the largest-scale implementation
`of mobile wireless multi-hop packet radio network
`[97]. Direct-sequence spread-spectrum, time divi-
`sion multiple access radio is used with data rates in
`the tens of kilobits per second ranges, while
`modified commercial Internet protocols are used
`for networking among nodes. It reinforces the
`perception that commercial wireline protocols
`were not good at coping with topology changes, as
`well as low data rate, and high bit error rate
`wireless links [254].
`In 1999, Extending the Littoral Battle-space
`Advanced Concept Technology Demonstration
`(ELB ACTD) was another MANET deployment
`exploration to demonstrate the feasibility of Ma-
`
`rine Corps war fighting concepts that require over-
`the-horizon (OTH) communications from ships at
`sea to Marines on land via an aerial relay. Ap-
`proximately 20 nodes were configured for the
`network, LucentÕs WaveLAN and VRC-99A were
`used to build the access and backbone network
`connections. The ELB ACTD was successful in
`demonstrating the use of aerial relays for con-
`necting users beyond LOS. In the middle of 1990,
`with the definition of standards (e.g., IEEE 802.11
`[131]), commercial radio technologies have begun
`to appear on the market, and the wireless research
`community became aware of the great commercial
`potential and advantages of mobile ad hoc net-
`working outside the military domain. Most of the
`existing ad hoc networks outside the military arena
`have been developed in the academic environment,
`but recently commercially oriented solutions star-
`ted to appear (see, e.g., MeshNetworks 1 and
`SPANworks 2).
`
`3.2. Ad hoc networking issues
`
`In general, mobile ad hoc networks are formed
`dynamically by an autonomous system of mobile
`nodes that are connected via wireless links without
`using the existing network infrastructure or cen-
`tralized administration. The nodes are free to
`move randomly and organize themselves arbi-
`trarily; thus, the networkÕs wireless topology may
`change rapidly and unpredictably. Such a network
`may operate in a standalone fashion, or may be
`connected to the larger Internet. Mobile ad hoc
`networks are infrastructure-less networks since
`they do not require any fixed infrastructure, such
`as a base station, for their operation. In general,
`routes between nodes in an ad hoc network may
`include multiple hops, and hence it is appropriate
`to call such networks as ‘‘multi-hop wireless ad hoc
`networks’’. Each node will be able to communicate
`directly with any other node that resides within its
`transmission range. For communicating with
`nodes that reside beyond this range, the node
`
`1 http://www.meshnetworks.com
`2 http://www.spanworks.com
`
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`19
`
`needs to use intermediate nodes to relay the mes-
`sages hop by hop.
`The ad hoc networks flexibility and convenience
`do come at a price. Ad hoc wireless networks in-
`herit the traditional problems of wireless commu-
`nications and wireless networking [132]:
`
`• the wireless medium has neither absolute, nor
`readily observable boundaries outside of which
`stations are known to be unable to receive net-
`work frames;
`• the channel is unprotected from outside signals;
`• the wireless medium is significantly less reliable
`than wired media;
`• the channel has time-varying and asymmetric
`propagation properties;
`• hidden-terminal and exposed-terminal phenom-
`ena may occur.
`
`To these problems and complexities, the multi-
`hop nature, and the lack of fixed infrastructure
`add a number of characteristics, complexities, and
`design constraints that are specific to ad hoc net-
`working [67,70]:
`Autonomous and infrastructure-less. MANET
`does not depend on any established infrastructure
`or centralized administration. Each node operates
`in distributed peer-to-peer mode, acts as an inde-
`pendent router and generates independent data.
`Network management has to be distributed across
`different nodes, which brings added difficulty in
`fault detection and management.
`Multi-hop routing. No default router available,
`every node acts as a router and forwards each
`othersÕ packets to enable information sharing be-
`tween mobile hosts.
`Dynamically changing network topologies. In
`mobile ad hoc networks, because nodes can
`move arbitrarily, the network topology, which is
`typically multi-hop, can change frequently and
`unpredictably, resulting in route changes,
`fre-
`quent network partitions, and possibly packet
`losses.
`Variation in link and node capabilities. Each
`node may be equipped with one or more radio
`interfaces that have varying transmission/receiving
`capabilities and operate across different frequency
`bands [63,64]. This heterogeneity in node radio
`
`capabilities can result in possibly asymmetric links.
`In addition, each mobile node might have a dif-
`ferent software/hardware configuration, resulting
`in variability in processing capabilities. Designing
`network protocols and algorithms for this heter-
`ogeneous network can be complex, requiring dy-
`namic adaptation to the changing conditions
`(power and channel conditions, traffic load/distri-
`bution variations, congestion, etc.).
`Energy constrained operation. Because batteries
`carried by each mobile node have limited power
`supply, processing power is limited, which in turn
`limits services and applications that can be sup-
`ported by each node. This becomes a bigger issue
`in mobile ad hoc networks because, as each node is
`acting as both an end system and a router at the
`same time, additional energy is required to for-
`ward packets from other nodes.
`Network scalability. Currently, popular net-
`work management algorithms were mostly de-
`signed to work on fixed or relatively small wireless
`networks. Many mobile ad hoc network applica-
`tions involve large networks with tens of thou-
`sands of nodes, as found for example, in sensor
`networks and tactical networks [97]. Scalability is
`critical to the successful deployment of these net-
`works. The steps toward a large network consist-
`ing of nodes with limited resources are not
`straightforward, and present many challenges that
`are still to be solved in areas such as: addressing,
`routing,
`location management,
`configuration
`management,
`interoperability,
`security, high-
`capacity wireless technologies, etc.
`
`3.3. Ad hoc networking research
`
`The specific MANET issues and constraints
`described above pose significant challenges in ad
`hoc network design. A large body of research has
`been accumulated to address these specific issues,
`and constraints. In this paper, we describe the
`ongoing research activities and the challenges in
`some of the main research areas within the mobile
`ad hoc network domain. To present the huge
`amount of research activities on ad hoc net-
`works in a systematic/organic way, we will use, as
`a reference, the simplified architecture shown in
`Fig. 2.
`
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`
`
`
`
` Security and Cooperation
`Energy Conservation
`
`Simulation
`
`Quality of Service
`
`Cross Layers
`issues
`
`Applications
`&
`Middleware
`
`Networking
`
`application 1
`
`application 2
`
`application k
`
`middleware
`Services Location, Group Communications shared memory
`
`transport and network layer protocols
`
`TCP, IP routing, Addressing, Location,
`Multicasting, Interconnection
`
`Enabling
`Technologies
`
`802.11
`
`Bluetooth
`
`......
`
`HiperLAN
`
`Medium Access Control, Antennas, Power Control
`
`Fig. 2. A simple MANET architecture.
`
`As shown in the figure, the research activities
`will be grouped, according to a layered approach
`into three main areas:
`
`• Enabling technologies;
`• Networking;
`• Middleware and applications.
`
`In addition, as shown in the figure, several is-
`sues (energy management, security and coopera-
`tion, quality of service, network simulation) span
`all areas, and we discuss them separately.
`
`4. Enabling technologies
`
`As shown in Fig. 3, we can classify ad hoc
`networks, depending on their coverage area, into
`several classes: Body (BAN), Personal (PAN),
`
`Local (LAN), Metropolitan (MAN) and Wide
`(WAN) area networks.
`Wide- and Metropolitan-area ad hoc networks
`are mobile multi-hop wireless networks that pre-
`sent many challenges that are still to be solved
`(e.g., addressing, routing, location management,
`security, etc.), and their availability is not on im-
`mediate horizon. On the other hand, mobile ad
`hoc networks with smaller coverage can be ex-
`pected to appear soon. Specifically, ad-hoc single-
`hop BAN, PAN and LAN wireless technologies
`are already common on the market [48], these
`technologies constituting the building blocks for
`constructing small, multi-hop, ad hoc networks
`that extend their range over multiple radio hops
`[67]. For these reasons, BAN, PAN and LAN
`technologies constitute the Enabling technologies
`for ad hoc networking. A detailed discussion of
`Body, Personal, and Local Ad hoc Wireless Net-
`
`BAN PAN
`
`LAN
`
`MAN
`
`WAN
`
`~1m ~10m
`
`~500m
`
`20 - 50 Km
`
`Range
`
`Fig. 3. Ad hoc networks taxonomy.
`
`
`
`8
`
`

`

`I. Chlamtac et al. / Ad Hoc Networks 1 (2003) 13–64
`
`21
`
`works can be found in [48]. Hereafter, the char-
`acteristics of these networks, and the technologies
`available to implement them, are summarized.
`A body area network is strongly correlated with
`wearable computers. A wearable computer dis-
`tributes on the body its components (e.g., head-
`mounted displays, microphones, earphones, etc.),
`and the BAN provides the connectivity among
`these devices. The communicating range of a BAN
`corresponds to the human body range, i.e., 1–2 m.
`As wiring a body is generally cumbersome, wire-
`less technologies constitute the best solution for
`interconnecting wearable devices.
`Personal area networks connect mobile devices
`carried by users to other mobile and stationary
`devices. While a BAN is devoted to the intercon-
`nection of one-person wearable devices, a PAN is
`a network in the environment around the persons.
`A PAN communicating range is typically up to 10 m,
`thus enabling the interconnection of the BANs
`of persons close to each other, and the intercon-
`nection of a BAN with the environment around it.
`The most promising radios for widespread PAN
`deployment are in the 2.4 GHz ISM band. Spread
`spectrum is typically employed to reduce interfer-
`ence and bandwidth re-use.
`Wireless LANs (WLANs) have a communica-
`tion range typical of a single building, or a cluster
`of buildings, i.e., 100–500 m. A WLAN should
`satisfy the same requirements typical of any LAN,
`including high capacity, full connectivity among
`attached stations,
`and broadcast
`capability.
`However, to meet these objectives, WLANs need
`to be designed to face some issues specific to the
`wireless environment,
`like security on the air,
`power consumption, mobility, and bandwidth
`limitation of the air interface [235].
`Two different approaches can be followed in the
`implementation of a WLAN: an infrastructure-
`based approach, or an ad hoc networking one [235].
`An infrastructure-based architecture imposes the
`existence of a centralized controller for each cell,
`often referred to as Access Point. The Access Point
`(AP) is normally connected to the wired network,
`thus providing the Internet access to mobile de-
`vices. In contrast, an ad hoc network is a peer-
`to-peer network formed by a set of stations within
`the range of each other, which dynamically con-
`
`figure themselves to set up a temporary network.
`In the ad hoc configuration, no fixed controller is
`required, but a controller may be dynamically
`elected among the stations participating in the
`communication.
`The success of a network technology is con-
`nected to the development of networking products
`at a competitive price. A major factor in achieving
`this goal
`is the availability of appropriate net-
`working standards. Currently, two main standards
`are emerging for ad hoc wireless networks: the
`IEEE 802.11 standard for WLANs [133], and the
`Bluetooth specifications 3
`[39]
`for
`short-range
`wireless communications [15,40,179].
`Due to its extreme simplicity, the IEEE 802.11
`standard is a good platform to implement a single-
`hop WLAN ad hoc network. Furthermore, multi-
`hop networks covering areas of several square
`kilometers can potentially be built by exploiting
`the IEEE 802.11 technology. On a smaller scale,
`technologies such as Bluetooth can be used to
`build ad hoc wireless Body, and Personal Area
`Networks, i.e., networks that connect devices on
`the person, or placed around him inside a circle
`with radius of 10 m.
`I