wireless ad hoc networking—the art of networking without a network

IntroductionNumerous factors associated with technol-ogy, business, regulation and social behav-ior naturally and logically speak in favor ofwireless ad hoc networking. Mobile wireless

data communication, which is advancingboth in terms of technology and usage/pen-etration, is a driving force, thanks to the In-ternet and the success of second-generationcellular systems. As we look to the horizon,we can finally glimpse a view of truly ubiq-uitous computing and communication. Inthe near future, the role and capabilities ofshort-range data transaction are expected togrow, serving as a complement to traditionallarge-scale communication: most man-machine communication as well as oral com-munication between human beings occursat distances of less than 10 meters; also, asa result of this communication, the twocommunicating parties often have a need toexchange data. As an enabling factor, license-exempted frequency bands invitethe use of developing radio technologies(such as Bluetooth) that admit effortless andinexpensive deployment of wireless com-munication.

In terms of price, portability and usabil-ity and in the context of an ad hoc network,many computing and communication de-vices, such as PDAs and mobile phones, al-ready possess the attributes that are desir-able. As advances in technology continue,these attributes will be enhanced even fur-ther.

Finally, we note that many mobile phonesand other electronic devices already are orwill soon be Bluetooth-enabled. Conse-quently, the ground for building more com-plex ad hoc networks is being laid. In termsof market acceptance, the realization of acritical mass is certainly positive. But per-haps even more positive—as relates to theend-user—is that consumers of Bluetooth-enabled devices obtain a lot of as-yet unrav-elled ad hoc functionality at virtually no cost.

What is an ad hoc network?Perhaps the most widespread notion of a mo-bile ad hoc network is a network formedwithout any central administration whichconsists of mobile nodes that use a wirelessinterface to send packet data. Since the nodesin a network of this kind can serve as routersand hosts, they can forward packets on be-half of other nodes and run user applications.

The roots of ad hoc networking can betraced back as far as 1968, when work on theALOHA network was initiated (the objec-tive of this network was to connect educa-tional facilities in Hawaii).

1Although fixed

stations were employed, the ALOHA pro-tocol lent itself to distributed channel-access management and hence provided a

248 Ericsson Review No. 4, 2000

Wireless ad hoc networking—The art ofnetworking without a networkMagnus Frodigh, Per Johansson and Peter Larsson

Today, many people carry numerous portable devices, such as laptops,mobile phones, PDAs and mp3 players, for use in their professional andprivate lives. For the most part, these devices are used separately—thatis, their applications do not interact. Imagine, however, if they could inter-act directly: participants at a meeting could share documents or presenta-tions; business cards would automatically find their way into the addressregister on a laptop and the number register on a mobile phone; as com-muters exit a train, their laptops could remain online; likewise, incoming e-mail could now be diverted to their PDAs; finally, as they enter the office,all communication could automatically be routed through the wirelesscorporate campus network.

These examples of spontaneous, ad hoc wireless communicationbetween devices might be loosely defined as a scheme, often referred toas ad hoc networking, which allows devices to establish communication,anytime and anywhere without the aid of a central infrastructure. Actually,ad hoc networking as such is not new, but the setting, usage and playersare. In the past, the notion of ad hoc networks was often associated withcommunication on combat fields and at the site of a disaster area; now,as novel technologies such as Bluetooth materialize, the scenario of adhoc networking is likely to change, as is its importance.

In this article, the authors describe the concept of ad hoc networkingby giving its background and presenting some of the technical challengesit poses. The authors also point out some of the applications that can beenvisioned for ad hoc networking.

AODV Ad hoc on-demand distancevector

AP Access pointARQ Automatic repeat requestBGP Border gateway protocolCSMA/CA Carrier sense multiple access with

collision avoidanceDARPA Defense Advanced Research

Projects AgencyDSDV Destination-sequenced distance

vectorDSR Dynamic source routingDSSS Direct-sequence spread

spectrumFA Foreign agentFEC Forward error correctionFHSS Frequency-hopping spread

spectrumFTP File transfer protocolGPRS General packet radio serviceH2 See HiperLAN/2HA Home agentHiperLAN/2 High-performance radio LAN type 2IEEE Institute of Electrical and

Electronic EngineeringIETF Internet Engineering Task Force

IP Internet protocolISM Industrial Scientific Medical band

(2.4 GHz)LAN Local area networkLAP LAN access pointMAC Media access controlMANET Mobile ad hoc networkMIPMANET Mobile IP MANETMT Mobile terminalNC Notebook computerOSPF Open shortest path firstPAN Personal area networkPDA Personal digital assistantPRnet Packet radio networkQoS Quality of serviceRIP Routing information protocolRREP Route replyRREQ Route requestRTS Request to sendSIG Special interest groupTDD Time-division duplexUMTS Universal mobile

telecommunications systemWCDMA Wideband code-division multiple

accessWLAN Wireless LAN

BOX A, ABBREVIATIONS

Ericsson Review No. 4, 2000 249

basis for the subsequent development of dis-tributed channel-access schemes that weresuitable for ad hoc networking. The ALOHAprotocol itself was a single-hop protocol—that is, it did not inherently support rout-ing. Instead every node had to be withinreach of all other participating nodes.

Inspired by the ALOHA network and theearly development of fixed network packetswitching, DARPA began work, in 1973,on the PRnet (packet radio network)—amultihop network.2 In this context, multi-hopping means that nodes cooperated torelay traffic on behalf of one another to reachdistant stations that would otherwise havebeen out of range. PRnet provided mecha-nisms for managing operation centrally aswell as on a distributed basis. As an addi-tional benefit, it was realized that multi-hopping techniques increased network ca-pacity, since the spatial domain could bereused for concurrent but physically sepa-rate multihop sessions.

Although many experimental packet-radio networks were later developed, thesewireless systems did not ever really take offin the consumer segment. When develop-ing IEEE 802.11—a standard for wirelesslocal area networks (WLAN)—the Institute

of Electrical and Electronic Engineering(IEEE) replaced the term packet-radio net-work with ad hoc network. Packet-radio net-works had come to be associated with themultihop networks of large-scale military orrescue operations, and by adopting a newname, the IEEE hoped to indicate an en-tirely new deployment scenario.

Today, our vision of ad hoc networking in-cludes scenarios such as those depicted inFigure 1, where people carry devices that cannetwork on an ad hoc basis. A user’s devicescan both interconnect with one another andconnect to local information points—for ex-ample, to retrieve updates on flight depar-tures, gate changes, and so on. The ad hocdevices can also relay traffic between devicesthat are out of range. The airport scenariothus contains a mixture of single and mul-tiple radio hops.

To put ad hoc networking in its right per-spective, let us make some observationsabout wireless communication, beginningwith present-day cellular systems, whichrely heavily on infrastructure: coverage isprovided by base stations, radio resources aremanaged from a central location, and ser-vices are integrated into the system. Thislead to the good and predictable service of

HiperLAN/2access point

WCDMA indoorbase station

PDA MT

MT

MT

PDA

PDA

NC

NC

Her PAN

His PAN

Bluetooth

His PAN

Figure 1.At an airport, where people can accesslocal- and wide-area networks, ad hocBlutooth connections are used to inter-connect carried devices, such as PDAs,WCDMA mobile phones and notebookcomputers. For instance, a user mightretreive e-mail via a HiperLAN/2 interfaceto a notebook computer in a briefcase,but read messages and reply to them viahis or her PDA.

present-day cellular systems. Figure 2 de-picts this two-dimensional aspect as it re-lates to ad hoc networking.

As we decrease, or move away from, cen-tral management, we find ourselves movingin the direction of pure ad hoc operation,which can also be classified in terms of sin-gle or multiple hops.

Without having fully relinquished con-trol, but given the direct mode of commu-nication in HiperLAN/2, adjacent terminalscan communicate directly with one anoth-er. Thus, the transport of traffic is not en-tirely dependent on the coverage providedby access points.

Dependency on centrally administeredcoverage is further reduced when end-userterminals relay traffic in a multihop fashionbetween other terminals and the base sta-tion (cellular multihop).3 A similar ap-proach applies to commercial or residentialwireless local loop (WLL) multihop accesssystems, primarily conceived for Internet ac-cess (Figure 2, bottom left and middle).

Fully decentralized radio, access, androuting technologies—enabled by Blue-tooth, IEEE 802.11 ad hoc mode, PRnet sta-tionless mode, mobile ad hoc network(MANET), and concepts such as the per-sonal area network (PAN) or PAN-to-PANcommunication—fit more or less entirelyinto the ad hoc domain. The MANET ini-tiative by the Internet Engineering TaskForce (IETF) also aims to provide servicesvia fixed infrastructure connected to the In-

ternet.4 Recent development and character-istics within this genre are the focus of thisarticle (Figure 2, bottom right).

Typical applicationsMobile ad hoc networks have been the focusof many recent research and development ef-forts. So far, ad hoc packet-radio networkshave mainly been considered for military ap-plications, where a decentralized networkconfiguration is an operative advantage oreven a necessity.

In the commercial sector, equipment forwireless, mobile computing has not beenavailable at a price attractive to large mar-kets. However, as the capacity of mobilecomputers increases steadily, the need forunlimited networking is also expected torise. Commercial ad hoc networks could beused in situations where no infrastructure(fixed or cellular) is available. Examples in-clude rescue operations in remote areas, orwhen local coverage must be deployedquickly at a remote construction site. Ad hocnetworking could also serve as wireless pub-lic access in urban areas, providing quick de-ployment and extended coverage. The accesspoints in networks of this kind could serveas stationary radio relay stations that per-form ad hoc routing among themselves andbetween user nodes. Some of the accesspoints would also provide gateways viawhich users might connect to a fixed back-bone network.5

At the local level, ad hoc networks thatlink notebook or palmtop computers couldbe used to spread and share informationamong participants at a conference. Theymight also be appropriate for application inhome networks where devices can commu-nicate directly to exchange information,such as audio/video, alarms, and configura-tion updates. Perhaps the most far-reachingapplications in this context are more or lessautonomous networks of interconnectedhome robots that clean, do dishes, mow thelawn, perform security surveillance, and soon. Some people have even proposed ad hocmultihop networks (denoted sensor net-works)—for example, for environmentalmonitoring, where the networks could beused to forecast water pollution or to pro-vide early warning of an approaching tsuna-mi.6

Short-range ad hoc networks can simplifyintercommunication between various mo-bile devices (such as a cellular phone and aPDA) by forming a PAN, and thereby elim-inate the tedious need for cables. This could


GSMIEEE 802.11*

IEEE 802.11**

* Infrastructure mode ** Ad hoc mode

Cellular

Cellular multihop

MANET

PAN PAN

Piconet Bluetooth scatternet

PAN

Coverage of BSControl of BSService of BS

PRnet

Residential (WLL) Internet

UMTS WCDMA HIPERLAN/2

direct mode

Mul

tihop

Sing

le-h

op

Figure 2Various wireless networks mapped to two independent aspects of ad hoc networking: thelevel of centralized control (horizontal), and the use of radio multihopping (vertical).


also extend the mobility provided by thefixed network (that is, mobile IP) to nodesfurther out in an ad hoc network domain. TheBluetooth system is perhaps the mostpromising technology in the context of per-sonal area networking.

PAN—a network extensionSeen from the viewpoint of the traditionalmobile network, a Bluetooth-based PANopens up a new way of extending mobile net-works into the user domain. Someone on atrip who has access to a Bluetooth PANcould use the GPRS/UMTS mobile phoneas a gateway to the Internet or to a corpo-rate IP network. In terms of traffic load inthe network, the aggregate traffic of thePAN would typically exceed that of the mo-bile phone. In addition, if Bluetooth PANscould be interconnected with scatternets,this capacity would be increased. Figure 3shows a scenario in which four BluetoothPANs are used. The PANs are intercon-nected via laptop computers with Bluetoothlinks. In addition, two of the PANs are con-nected to an IP backbone network, one viaa LAN access point and the other via a sin-gle GPRS/UMTS phone.

A PAN can also encompass several differ-ent access technologies—distributedamong its member devices—which exploitthe ad hoc functionality in the PAN. For in-stance, a notebook computer could have awireless LAN (WLAN) interface (such asIEEE 802.11 or HiperLAN/2) that providesnetwork access when the computer is usedindoors. Thus, the PAN would benefit fromthe total aggregate of all access technologiesresiding in the PAN devices. As the PANconcept matures, it will allow new devicesand new access technologies to be incorpo-rated into the PAN framework. It shouldalso eliminate the need to create hybrid de-vices, such as a PDA-mobile phone combi-nation, because the PAN network will in-stead allow for wireless integration. In otherwords, it will not be necessary to trade offform for function.

In all the scenarios discussed above, itshould be emphasized that close-range radiotechnology, such as Bluetooth, is a key en-abler for introducing the flexibility repre-sented by the PAN concept.

Characteristics andrequirementsIn contrast to traditional wireline or wire-less networks, an ad hoc network could be

expected to operate in a network environ-ment in which some or all the nodes are mo-bile. In this dynamic environment, the net-work functions must run in a distributedfashion, since nodes might suddenly disap-pear from, or show up in, the network. Ingeneral, however, the same basic user re-quirements for connectivity and traffic de-livery that apply to traditional networks willapply to ad hoc networks.

Below, we discuss some typical opera-tional characteristics and how they affect therequirements for related networking func-tions. To limit the scope of the discussion,we will examine the case of a PAN-oriented ad hoc network that involves a mixof notebook computers, cellular phones, andPDAs. • Distributed operation: a node in an ad hoc

network cannot rely on a network in thebackground to support security and rout-ing functions. Instead these functionsmust be designed so that they can oper-ate efficiently under distributed condi-tions.

• Dynamic network topology: in general,the nodes will be mobile, which sooner orlater will result in a varying networktopology. Nonetheless, connectivity in

Internet or corporate IP network

LAN

GPRS

Router

Router

Figure 3PAN scenario with four interconnected PANs, two of which have an Internet connectionvia a Bluetooth LAN access point and a GPRS/UMTS phone.

the network should be maintained toallow applications and services to operateundisrupted. In particular, this will in-fluence the design of routing protocols.Moreover, a user in the ad hoc network willalso require access to a fixed network (suchas the Internet) even if nodes are moving around. This calls for mobility-management functions that allow net-work access for devices located severalradio hops away from a network accesspoint.

• Fluctuating link capacity: the effects ofhigh bit-error rates might be more pro-found in a multihop ad hoc network, sincethe aggregate of all link errors is what af-fects a multihop path. In addition, morethan one end-to-end path can use a givenlink, which if the link were to break, coulddisrupt several sessions during periods ofhigh bit-error transmission rates. Here,too, the routing function is affected, butefficient functions for link layer protection(such as forward error correction, FEC, andautomatic repeat request, ARQ) can sub-stantially improve the link quality.

• Low-power devices: in many cases, thenetwork nodes will be battery-driven,which will make the power budget tightfor all the power-consuming componentsin a device. This will affect, for instance,CPU processing, memory size/usage, sig-nal processing, and transceiveroutput/input power. The communica-tion-related functions (basically the entireprotocol stack below the applications) di-rectly burden the application and servicesrunning in the device. Thus, the algo-rithms and mechanisms that implementthe networking functions should be opti-mized for lean power consumption, so asto save capacity for the applications whilestill providing good communication per-formance. Besides achieving reasonablenetwork connectivity, the introduction ofmultiple radio hops might also improveoverall performance, given a constrained

power budget. Today, however, this canonly be realized at the price of more com-plex routing.

Given the operating conditions listed above,what can the user expect from an ad hoc PANnetwork? The support of multimedia ser-vices will most likely be required within andthroughout the ad hoc PAN. As an example,the following four quality-of-service (QoS)classes would facilitate the use of multi-media applications including• conversational (voice);• streaming (video/audio);• interactive (Web); and• background (FTP, etc.).These service classes have been identified forQoS support in the UMTS network andshould also be supported in the PAN envi-ronment. However, the inherent stochasticcommunications quality in a wireless ad hocnetwork, as discussed above, makes it diffi-cult to offer fixed guarantees on the servicesoffered to a device. In networks of this kind,fixed guarantees would result in require-ments for how nodes move, as well as re-quirements for node density, which wouldinherently inhibit the notion of ad hoc oper-ation. Nevertheless, when communicationconditions are stable, the PAN infrastruc-ture should provide the same QoS as has beendefined for the access network. To furtherimprove user perception of the service, userapplications that run over an ad hoc networkcould be made to adapt to sudden changesin transmission quality.

QoS support in an ad hoc network will af-fect most of the networking functions dis-cussed above, especially routing and mobil-ity. In addition, local buffer managementand priority mechanisms must be deployedin the devices in order to handle differenti-ated traffic streams.

In the following section we elaborate moreon three of the functions briefly mentionedabove, namely, security, routing, and mo-bility. We believe that these functions aregood points of departure for a discussion ofthe implications that ad hoc operation willhave on network functionality.

Typical ad hoc networkfunctions

SecurityObviously, security is a concern in an ad hocnetwork, in particular if multiple hops areemployed. How can a user be certain thatno one is eavesdropping on traffic via a for-


BA

G1

G2

G3

C

D

E

F

G H

Figure 4This ad hoc network has three separatetrust groups: G1, G2 and G3. At thisstage, a secure exchange of data cannotoccur between the nodes—except withnode C, which belongs to G1 and G2.

G1

G2

G3

BA

C

D

E

F

G H

D, E, F OK!

Figure 5Node C sends the signed public keys itreceived from nodes D, E and F to servernode A. In addition, node A establishes anew trust relationship to node G.


warding node? Is the user at the other endreally the person he claims to be? From apurely cryptographic point of view, ad hocservices do not imply many “new” problems.The requirements regarding authentica-tion, confidentiality, and integrity or non-repudiation are the same as for many otherpublic communication networks. However,in a wireless ad hoc network, trust is a cen-tral problem. Since we cannot trust themedium, our only choice is to use cryptog-raphy, which forces us to rely on the cryp-tographic keys used. Thus, the basic chal-lenge is to create trusted relationships be-tween keys without the aid of a trustedthird-party certification.

Since ad hoc networks are created sponta-neously between entities that happen to beat the same physical location, there is noguarantee that every node holds the trustedpublic keys to other nodes or that they canpresent certificates that will be trusted byother parties. However, if we allow trust tobe delegated between nodes, nodes that al-ready have established trusted relationshipscan extend this privilege to other membersof the group.

The method described below can be usedfor distributing relationships of trust to anentire ad hoc network. The method is basedon a public key approach and is exemplifiedby a small ad hoc network (Figures 4-7). Weassume that connectivity exists between allthe nodes in the network, and that it can bemaintained by, say, a reactive ad hoc routingprotocol.• Initially, node A takes on the role of serv-

er node in the procedure of delegatingtrust. A triggers the procedure by flood-ing a start message into the network. Eachnode that receives this message floods thead hoc network with a message containingthe set of trusted public keys. A can thenestablish a “map” of trusted relations andidentify them in the ad hoc network. Inthe example shown (Figure 4), three dif-ferent groups (G1, G2, and G3) share achain of trust.

• All the nodes in G2 share an indirecttrusted relationship to A (through nodeC). Node A can thus collect the signedkeys it received from G2 via C (as illus-trated in Figure 5). By contrast, the nodesin G3 do not have a trusted relationshipto A. However, a trusted relationship be-tween, say, node G in G3 and A can becreated by manually exchanging trustedkeys.

• Node A can now collect signed keys re-

ceived from G3 via G (Figure 6). A canthen flood the ad hoc network with all col-lected signed keys. This procedure createstrusted relationships between every nodein G1, G2 and G3, and forms a new trustgroup, G1’ (Figure 7).

This example can be generalized into a pro-tocol that handles the distribution of trustin an arbitrary ad hoc network.7

Routing in ad hoc networksFor mobile ad hoc networks, the issue of rout-ing packets between any pair of nodes be-comes a challenging task because the nodescan move randomly within the network. Apath that was considered optimal at a givenpoint in time might not work at all a fewmoments later. Moreover, the stochasticproperties of the wireless channels add to theuncertainty of path quality. The operatingenvironment as such might also cause prob-lems for indoor scenarios—the closing of adoor might cause a path to be disrupted.

Traditional routing protocols are proac-tive in that they maintain routes to all nodes,including nodes to which no packets arebeing sent. They react to any change in thetopology even if no traffic is affected by thechange, and they require periodic controlmessages to maintain routes to every nodein the network. The rate at which these con-trol messages are sent must reflect the dy-namics of the network in order to maintainvalid routes. Thus, scarce resources such aspower and link bandwidth will be used morefrequently for control traffic as node mobil-ity increases.

An alternative approach involves estab-lishing reactive routes, which dictates thatroutes between nodes are determined solelywhen they are explicitly needed to routepackets. This prevents the nodes from up-dating every possible route in the network,and instead allows them to focus either onroutes that are being used, or on routes thatare in the process of being set up.

G1

G2

G3

BA

C

D

E

F

G H

H OK!

Figure 6Node G sends the signed public key itreceived from node H to node A.

G1'

BA

C

D

E

F

G H

All OK!

Figure 7Node A floods the ad hoc network with allthe signed keys. A new chain of trust isthus created in a new, secure trust group,G1', which comprises all the nodes in thenetwork.

In a simulation study, SwitchLab8

(Ericsson Research) compared two reactiverouting algorithms (ad hoc on-demand dis-tance vector, AODV9, and dynamic sourcerouting, DSR10) and one proactive routingalgorithm (destination-sequenced distancevector, DSDV11) (Box B). In every case test-ed, the reactive algorithms outperformedthe proactive algorithm in terms of through-put and delay. Moreover, the reactive pro-tocols behaved similarly in most of the sim-ulated cases. The main conclusion drawnfrom this study is that a reactive approachmight well be necessary in a mobile envi-ronment with limited bandwidth capacity.The proactive approach depletes too manyresources updating paths (if the route-up-date periods are to match the mobility of thenodes). If the update interval is too long, the

network will simply contain a large amountof stale routes in the nodes, which results ina significant loss of packets.

Mobility functionsIn present-day cellular networks, node anduser mobility are handled mainly by meansof forwarding. Thus, when a user circulatesoutside his home network any calls direct-ed to him will be forwarded to the visitingnetwork via his home network. This sameforwarding principle applies to mobile IP.12, 13 A user, or actually the node with theIP interface, can also continue to use an IPaddress outside the subnetwork to which itbelongs. A roaming node that enters a for-eign network is associated with a c/o addressprovided by a foreign agent (FA). In thehome network, a home agent (HA) estab-lishes an IP tunnel to the FA using the c/oaddress. Any packet sent to the roamingnode’s address is first sent to the home agent,which forwards it to the FA via the c/o ad-dress (tunneling). The FA then decapsulatesthe packet and sends it to the roaming nodeusing the original (home) IP address. Theactual routing in the fixed network is not af-fected by this tunneling method and can usetraditional routing protocols such as openshortest path first (OSPF), the routing in-formation protocol (RIP), and the bordergateway protocol (BGP). This forwardingapproach is appropriate in cases where onlythe nodes (terminals) at the very edges of(fixed) networks are moving.

However, in an ad hoc network, this is notthe case, since the nodes at the center of thenetwork can also move—or rather, thewhole network is based on the idea of de-vices that serve both as routers and hosts atthe same time. Hence, in an ad hoc network,mobility is handled directly by the routingalgorithm. If a node moves, forcing trafficanother way, the routing protocol takes careof the changes in the node’s routing table.

In many cases, interworking can be ex-pected between ad hoc and fixed networks.Interworking would make it possible for auser on a trip who takes part in a laptop con-ference but wants mobility, to be reachablevia the fixed IP network. Moreover, sincethe user wants to be reachable from the fixednetwork, mobile IP would be a convenientway of making him reachable through thefixed IP network. If the user is located sev-eral radio hops away from the access point,mobile IP and the ad hoc network routingprotocol must interwork to provide connec-tivity between the travelling user and his


Destination-sequenced distance vector DSDV is a proactive hop-by-hop distance vec-tor routing protocol. Each network node main-tains a routing table that contains the next hopto any reachable destination as well as the num-ber of hops that will be required. Periodicalbroadcasts of routing updates are used to keepthe routing table completely updated at alltimes. To guarantee loop-freedom, DSDV usesa concept that is based on sequence numbersto indicate how new, or fresh, a given route is.Route R, for example, will be considered morefavorable than R' if R has a higher sequencenumber; whereas if the routes have the samesequence number, R will have the lower, or morerecent, hop-count.

Note: in a distance vector (or Bellman-Ford)algorithm, the network nodes exchange rout-ing information with their neighbors. The rout-ing table in a node contains the next hop forevery destination in the network, and is asso-ciated with a “distance” metric—for example,the number of hops. Based on the distanceinformation in the neighbor’s routing tables, itis possible to compute the shortest-path (orminimum-cost) routes to every destination in afinite time for a network with no topologychanges.

Ad hoc on-demand distance vectorLike DSDV, AODV is a distance vector routingprotocol, but it is reactive. This means thatAODV solely requests a route when it needs one,and does not require that the nodes shouldmaintain routes to destinations that are notcommunicating. AODV uses sequence num-bers in a way similar to DSDV to avoid routingloops and to indicate the freshness of a route. Whenever a node needs to find a route to anoth-er node, it broadcasts a route request (RREQ)message to all its neighbors. The RREQ mes-sage is flooded through the network until it

reaches the destination or a node that has afresh route to the destination. On its way throughthe network, the RREQ message initiates thecreation of temporary route table entries for thereverse route in the nodes it passes. If the des-tination—or a route to it—is found, its availabil-ity will be indicated by a route reply (RREP) mes-sage that is unicast back to the source alongthe temporary reverse path of the receivedRREQ message. On its way back to the source,the RREP message initiates, in the intermediatenodes, routing table entries for the destination.Routing table entries expire after a certain time-out period.

Dynamic source routingDynamic source routing is a reactive routingprotocol that uses source routing to deliver datapackets. The headers of the data packets carrythe addresses of the nodes through which thepacket must pass. This means that intermedi-ate nodes need only keep track of their imme-diate neighbors in order to forward data pack-ets. The source, on the other hand, must knowthe complete hop sequence to the destination. As in AODV, the route acquisition procedure inDSR requests a route by flooding the systemwith an RREQ packet. A node that receives anRREQ packet searches its route cache, whereall its known routes are stored, for a route to therequested destination. If no route is found, it for-wards the RREQ packet after first having addedits own address to the hop sequence stored inthe packet. The packet propagates through thenetwork until it reaches either the destination,or a node with a route to the destination. If aroute is found, an RREP packet containing theproper hop sequence for reaching the destina-tion is unicast back to the source node. Anoth-er feature of the DSR protocol is that it can learnroutes from the source routes in packets itreceives.

BOX B, THREE MOBILE AD HOC NETWORK-ROUTING PROTOCOLS


unit’s peer node, which is located in the fixednetwork or in another ad hoc network.

MIPMANET

Mobile IP for mobile ad hoc networks (MIP-MANET)14 is designed to give nodes in adhoc networks • access to the Internet; and • the services of mobile IP.The solution uses mobile IP foreign agentsas access points to the Internet to keep trackof the ad hoc network in which any givennode is located, and to direct packets to theedge of that ad hoc network.

The ad hoc routing protocol is used to de-liver packets between the foreign agent andthe visiting node. A layered approach thatemploys tunneling is applied to the outwarddata flow, to separate the mobile IP func-tionality from the ad hoc routing protocol—Figure 8 illustrates how mobile IP and ad hoc routing functionality are layered. Thismakes it possible for MIPMANET to pro-vide Internet access by enabling nodes to se-lect multiple access points and to performseamless switching between them. In short,MIPMANET works as follows:• Nodes in an ad hoc network that want In-

ternet access use their home IP addressesfor all communication, and register witha foreign agent.

• To send a packet to a host on the Inter-net, the node in the ad hoc network tun-nels the packet to the foreign agent.

• To receive packets from hosts on the In-ternet, packets are routed to the foreignagent by ordinary mobile IP mechanisms.The foreign agent then delivers the pack-ets to the node in the ad hoc network.

• Nodes that do not require Internet accessinteract with the ad hoc network as thoughit were a stand-alone network—that is,they do not require data regarding routesto destinations outside the ad hoc network.

• If a node cannot determine from the IPaddress whether or not the destination islocated within the ad hoc network, it willfirst search for the visiting node withinthe ad hoc network before tunneling thepacket.

By using tunneling, MIPMANET can in-corporate the default route concept into on-demand ad hoc routing protocols, such asAODV and DSR, without requiring anymajor modifications. Packets addressed todestinations that are not found within thead hoc network are tunneled to foreignagents. In MIPMANET, only registered vis-iting nodes are given Internet access, thus

the only traffic that will enter the ad hoc net-work from the Internet is traffic that is tun-neled to the foreign agent from a registerednode’s home agent. Likewise, traffic thatleaves the ad hoc network is tunneled to theforeign agent from a registered node. Thisresults in a separation between, and therebythe capacity to control, traffic that is localin the ad hoc network and traffic that entersthe ad hoc network.

Radio layer implications

Why multiple hops?In dealing with an unreliable wirelessbroadcast medium, special “radio” consid-erations should be addressed in the com-munication system of an ad hoc network, toensure reliable and efficient operation. Oneway of doing this is to employ multihop-ping, which facilitates the reuse of re-sources in both the spatial and temporal do-mains, provided that the nodes which par-ticipate in the network are reasonably welldistributed in space.15 In contrast, single-hop networks mainly share the channel re-sources in the temporal domain. Figure 9shows a schematic depiction of the spatialinterference in multihopping and single-hopping scenarios. Each case considers anidentical situation with respect to node dis-tribution, sources, and destinations. In themultihopping scenario, packets are routed

Home agent

Correspondent nodes

IP

IP network

Visiting nodes

Foreign agent

Ad hoc network

Mobile IP

Transport

Figure 8An overview of the MIPMANET architecture.

over intermediate relays. However, the sin-gle-hop network sends the data directlyfrom the source to destination. The circlesin the figure indicate a power-controlledrange of the transmitting nodes. The fig-ure also depicts inactive nodes—thesenodes are not involved as sources, destina-tions, or intermediate relays. From this fig-ure, we get the feeling that the multihopscenario provides greater spectral efficien-cy (bit/s/Hz/m2).

Comparison of multiple hops and single hops

Whether multihopping is necessary, suit-able or even possible depends on factors suchas the number and distribution of terminalsin the network, relative traffic density, radiochannel characteristics, practical communi-cation limitations, and reasons for optimiz-ing certain parameters. Under some cir-cumstances, a multihop network might ac-tually degenerate into a single-hop network.One obvious reason for employing multi-hopping is to provide connectivity, sincesome terminals might be out of range of eachother, and cannot therefore form a single-hop network.

Multihop characteristics—forwarding

In a multihop scenario, it makes sense notto waste more energy than what each hop

requires. In essence, the key to conservingenergy is to control the transmit power, inorder to compensate for path losses thatoccur when a message is sent between adja-cent nodes.

In a network scenario with little data traf-fic, the overall power consumption can bereduced by approximately a factor of Nα-1,where N is the number of equidistant hopsbetween the source and the destination, andα is the propagation constant. In theory, αis equal to 2 for free space propagation. Butfor realistic environments, it is often as-signed a value of 3 or 4. To derive the rela-tionship Nα-1, we first describe propagationloss (L) in terms of its relationship to dis-tance (R):

For correct reception at a given level of re-ceiver noise, a minimum receiving powerPRX_min is required. Accordingly, thetransmit power for one hop over distance Ris (stated somewhat simplistically):

If the distance (R) is divided into N hops,then each individual hop requires

This is a factor Nα less than a long single

PTX_N=PRX_min ⋅ Const ⋅ (R/N)α

PTX_1=PRX_min ⋅ Const ⋅ Rα

L=Const ⋅ Rα


Multihop

Example of power- controlled transmit range

Source Destination Relay Other node

Single-hop

Figure 9Comparison of multihop networking withsingle-hop networking. Both exampleshave an identical distribution of networknodes.


hop. Thus, the overall end-to-end reductionin transmit power is

In this analysis, we have excluded manydetrimental factors, such as unequal hopranges, retransmissions, and the character-istics of fading channels. Moreover, we haveassumed a very simple model of propagationloss. Notwithstanding, the results hint atpotential power savings. For example, com-pared to the single-hop case, given α=3.5and N=16, the overall theoretical end-to-end transmit power per packet is reduced by1000 times, or 30 dB. The bad news is thatin a mobile ad hoc network • connectivity usually needs to be main-

tained between neighbors; and • routing information needs to be distrib-

uted.Thus, in highly mobile situations, the con-trol traffic required in a multihop networkmight consume a noticeable amount of en-ergy, even in the absence of data traffic.

A direct benefit of controlling power overshort-range transmissions is that it can re-duce the total interference level in a homo-geneous multihop network with multiplecommunicating nodes and fixed traffic. In afirst approximation—without consideringthe specific interference location—the aver-age level of interference is reduced by thesame amount as the transmit power; that is,by Nα−1 . Furthermore, less interference im-plies greater link capacity. Given a some-what crude application of Shannon’s bandwidth-limited channel capacity rela-tion, and by assuming that the interferenceis well modeled with complex Gaussiannoise, the individual link capacity increasesfor large N: lg(N). This is shown below,where B is the bandwidth and SIR1 is thesignal-to-interference ratio for a link in a ref-erence single-hop system that has been re-placed with a multihop system:

The end-to-end delay depends on the levelat which latency is measured and the appliedforwarding principle. A message of reason-able size which is to be forwarded in thestore-and-forward manner will experiencedelay that is proportional to the number ofhops. Nonetheless, this delay is compensat-ed for in part by an increase in the link datarate.

The segmenting of large messages intomultiple packets also affects the end-to-end

Cl i n k=B.lg2(1+SIR1.Nα–1) ≈Const1.lg2(N)+Const2

Nα =Nα−1

N

delay. By segmenting the message, severalpackets can be transferred concurrently overconsecutive hops. Under those assumptions,the delay imposed by multiple hops is smallin comparison to the delay resulting fromthe link rate and message size. In fact, end-to-end delay might actually benefit frommultiple hops. Because traffic can be rout-ed concurrently over multiple links in a“multihop chain,” the challenge is to alle-viate the associated interference.

Obviously, when transmit power is lim-ited, it might not be possible to reach thedesired station without multiple hops. Onthe other hand, because the maximum sizeof messages is fixed, too many hops will in-crease delay. This implies that a given num-ber of hops, N, can provide a minimum delayunder transmit power constraints and agiven message size.

In summary, multihopping is beneficial,since it • conserves tranmit energy resources;• reduces interference; and• increases overall network throughput. Multihopping might also be a necessity, toprovide any kind of connectivity betweenvery distant terminals.

Bluetooth networkingWorldwide, the industry has shown atremendous interest in techniques that pro-vide short-range wireless connectivity. Inthis context, Bluetooth technology is seenas the key component.16-18 However, Blue-tooth technology must be able to operate inad hoc networks that can be stand-alone, orpart of the “IP-networked” world, or a com-bination of the two.

The main purpose of Bluetooth is to re-place cables between electronic devices, suchas telephones, PDAs, laptop computers,digital cameras, printers, and fax machines,by using a low-cost radio chip. Short-rangeconnectivity also fits nicely into the wide-area context, in that it can extend IP net-working into the personal-area network do-main, as discussed earlier.

Bluetooth must be able to carry IP effi-ciently in a PAN, since PANs will be con-nected to the Internet via UMTS or corpo-rate LANs, and will contain IP-enabledhosts. Generally speaking, a good capacityfor carrying IP would give Bluetooth net-works a wider and more open interface,which would most certainly boost the de-velopment of new applications for Blue-tooth.

Bluetooth basicsBluetooth is a wireless communication tech-nology that uses a frequency-hoppingscheme in the unlicensed Industrial-Scientific-Medical (ISM) band at 2.4 GHz.Two or more Bluetooth units that share thesame channel form a piconet (Figure 10).Within a piconet, a Bluetooth unit can playeither of two roles: master or slave. Each pi-conet may only contain one master (andthere must always be one) and up to sevenactive slaves. Any Bluetooth unit can be-come a master in a piconet.

Furthermore, two or more piconets can beinterconnected, forming what is called ascatternet (Figure 11). The connection point

between two piconets consists of a Bluetoothunit that is a member of both piconets. ABluetooth unit can simultaneously be a slavemember of multiple piconets, but only amaster in one. Moreover, because a Blue-tooth unit can only transmit and receive datain one piconet at a time, its participation inmultiple piconets has to be on a time-division multiplex basis.

The Bluetooth system provides duplextransmission based on slotted time-divisionduplex (TDD), where the duration of each slotis 0.625 ms. There is no direct transmissionbetween slaves in a Bluetooth piconet, onlyfrom master to slave and vice versa.

Communication in a piconet is organizedso that the master polls each slave accordingto a polling scheme. A slave is only allowedto transmit after having been polled by themaster. The slave will start its transmissionin the slave-to-master timeslot immediate-ly after it has received a packet from the mas-ter. The master may or may not include datain the packet used to poll a slave. However,it is possible to send packets that cover mul-tiple slots. These multislot packets may beeither three or five slots long.

Scatternet-based PANsBluetooth networks will most likely be usedto interconnect devices such as cellularphones, PDAs, and notebook computers—in other words, via a PAN. The PAN itselfcan be a Bluetooth-based IP network—in alllikelihood it will be based on a single piconettopology. However, when a PAN user wantsto connect to one or more other PANs, Blue-tooth scatternet capability will serve as thefoundation for the IP network. Similarly, ifone or more PANs connect to an Internet ac-cess point on a LAN (LAN access point, LAP)a scatternet will provide the underlyingBluetooth infrastructure (Figure 12).

We can expect to see a combination ofPAN interconnection and Internet access.In addition, Internet access to one PAN orseveral interconnected PANs can be pro-vided by using a cellular phone (for exam-ple, via GPRS/UMTS) as a bridge/routergateway (Figure 13).19

Scatternets can also be rearranged to givebetter overall performance. For instance, iftwo slave nodes need to communicate, itmight be wiser to create a new piconet thatsolely contains these two nodes. The nodescan still be part of their original piconets iftraffic flows to or from them, or if they needto receive control information. Since the frequency-hopping spread-spectrum (FHSS)


Piconet 1

Piconet 2

Piconet 3

Bluetooth unit (master)

Bluetooth unit (slave)Figure 10Examples of Bluetooth piconets.

Piconet 1

Piconet 4

Piconet 5

Piconet 6

Piconet 7

Piconet 9

Piconet 10

Piconet 12

Piconet 11

Piconet 8Piconet 2

Piconet 3

Bluetooth unit, master Bluetooth unit, slave Bluetooth unit—master in one piconet, slave in another Bluetooth unit—slave in two piconets

Bluetooth unit—master in one piconet, slave in two Bluetooth unit—slave in three piconets

Figure 11A Bluetooth scatternet.


system makes Bluetooth very robust againstinterference, new piconets gain substantial-ly more capacity than they lose as a result ofincreased interference between them.

Scatternet functionalityThe concept of scatternets offers a flexibleway of creating Bluetooth networks and in-troduces a number of Bluetooth-specificfunctions. Ideally, these functions should bekept in the background to keep them frombothering the user of the Bluetooth networkand to facilitate applications development.The Bluetooth networking functions fallinto three main areas:

• scatternet forming and maintenance; • scatternet-wide packet forwarding; and• intra- and interpiconet scheduling.

Scatternet forming

To have an efficient infrastructure for IP net-working on Bluetooth, piconets and scatter-nets must be able to adapt to the connec-tivity, traffic distribution, and node mobil-ity in the network. This is mainly achievedby setting up new piconets or terminatingothers, in order to attain the optimal scat-ternet topology. In this context, optimalrefers to a scatternet that, for instance, yieldsminimum delay or maximum throughput.

LAN

IP backbone

Bluetooth LAN access point

M

S

M

MS

S

S

S

PAN 1

PAN 2

Figure 12A scatternet with three interconnectedpiconets, in which two are PANs and oneis used to provide network access to thetwo PANs via a Bluetooth LAN accesspoint. In this scenario, the letters M and Sindicate the distribution of master andslave units.

IP backboneGPRS

M

SM

M

S

S

S

S

PAN 1

PAN 2

Figure 13A scatternet with three interconnected piconets. Via a GPRS/UMTS cellular phone, onepiconet provides IP network access to the other two piconets.

But it could also mean minimizing energyconsumption in network nodes. To ensuread hoc operation, the function for formingand maintaining scatternets must be dis-tributed.

Packet forwarding in the scatternet

Forwarding—or routing—becomes neces-sary when packets must traverse multiplehops between the source and destinationnodes. Given that IP will be commonplacein scatternet contexts, one might concludethat routing over the scatternet should behandled within the IP layer (Figure 14).However, there are good arguments for tak-ing another course.• The current IP dynamic host configuration

protocols20 (DHCP) and emerging zero-configuration methods21, 22 (IETF Zero Con-figuration Networking Working Group,zeroconfig) rely on link layer connectivity.These protocols are typically used to attaina dynamic IP address for an IP host or to se-lect a random IP address. Generally, theprotocols will not work beyond an IP router,which means that they will not reach nodeslocated more than one Bluetooth hop awayin an IP-routed scatternet. A scatternet thatprovides broadcast segment-like connec-tivity would enable these protocols to workfor Bluetooth-based IP hosts that are sepa-rated by multiple hops.

• To operate efficiently, the routing func-tion should be joined with the functionfor forming scatternets. A routing func-

tion on the IP layer would thus need tobe adapted to, or interact very closelywith, the underlying Bluetooth layer,which violates the idea of keeping the IPlayer independent of the link layer tech-nology.

• IP routing is typically performed betweennetworks with different link layer tech-nologies or to separate different networkdomains. Scatternets use only one tech-nology—Bluetooth—and typically be-long to only one network domain.

In summary, the best way of providing net-working in a Bluetooth scatternet is to per-form the routing on a network layer resid-ing below IP (Figure 15). This layer will • be able to interact closely with the Blue-

tooth baseband functions during the es-tablishment or tear-down of a Bluetooth-specific piconet; and

• provide a broadcast segment-like inter-face to IP.

Intra- and interpiconet scheduling

The master unit of a piconet controls thetraffic within the piconet by means ofpolling. A polling algorithm determineshow bandwidth capacity is to be distributedamong the slave units. The polling algo-rithm assesses the capacity needs of the unitsin the scatternet and ensures that capacityis shared fairly, or according to a weightedcapacity-sharing policy.

In a scatternet, at least one Bluetooth unitis member of more than one piconet. These


IP hosts and routers

Slave 2

Slave 1 Slave 3

Slave 4Slave 5

MasterMaster

Bluetooth link and baseband layer

Figure 14A Bluetooth scatternet where the net-working functionality is handled within theIP layer (that is, by IP routing).


interpiconet nodes might have a slave rolein numerous piconets but can have the mas-ter role in only one of them. The main chal-lenge is to schedule the presence of the in-terpiconet node in its different piconets, inorder to facilitate the traffic flow both with-in and between piconets. Given that the in-terpiconet node is a single transceiver unit,only one of its entities (master or slaves) canbe active at a time.

To manage scatternet traffic efficiently,the intrapiconet scheduler must considerthe interpiconet scheduler when it polls theslaves of a piconet. For instance, the in-trapiconet scheduler in a master unit mightnot schedule an interpiconet node when thelatter is active in another piconet. Howev-er, the interpiconet scheduler might sched-ule this node more often, after it is once againactive in the piconet.

The Bluetooth SIGThe Bluetooth Special Interest Group (SIG),comprised of leaders in the telecommunica-tions, computing, and network industries,drives the development of Bluetooth tech-nology and its exposure in the market. TheBluetooth SIG includes promoter compa-nies (3Com, Ericsson, IBM, Intel, Lucent,Microsoft, Motorola, Nokia and Toshiba)and more than 2000 other companies thathave adopted Bluetooth.

The work of specifying the next step inthe development of Bluetooth technologyhas been delegated to a set of working

groups. Among them, the Personal AreaNetworking Working Group (PAN WG) isresponsible for developing functions andprotocols that will allow IP-based applica-tions to be implemented in Bluetooth de-vices. The current support provided for IPin the Bluetooth specification needs to beenhanced to facilitate future IP applica-tions—in order to facilitate improved per-formance and functionality.

Other ad hoc technologiesIEEE 802.11The IEEE 802.11 specification23 is a wirelessLAN standard that specifies a wireless inter-face between a client and a base station or ac-cess point, as well as between wireless clients.

IEEE 802.11 defines two physical char-acteristics for radio-based wireless local areanetworks: direct-sequence spread spectrum(DSSS), and frequency-hopping spread spec-trum (FHSS), both of which operate on the2.4 GHz ISM band.

Two network architecture modes havebeen defined in the IEEE 802.11 standard,namely the point coordination function(PCF) mode and the distributed coordina-tion function (DCF) mode. The former usesa centralized approach in which a networkaccess point controls all traffic in the net-work, including local traffic between wire-less clients in the network. The DCF modesupports direct communication betweenwireless clients.

Bluetooth networking layer

IP hosts

Bluetooth link and baseband layer

Slave 2

Slave 1 Slave 3

Slave 4Slave 5

MasterMaster

Figure 15A Bluetooth scatternet where networkingis handled within a Bluetooth networkinglayer, which provides a broadcast seg-ment to the IP hosts.

The media access control (MAC) layer usesthe carrier-sense multiple-access-with-collision-avoidance (CSMA/CA) algorithm.A terminal operating in DCF mode thatwants to send data: listens to make certainthe channel is free and then waits for a ran-domly drawn period (backoff). If no otherstation attempts to gain access after this pe-riod of waiting, the terminal can gain accessaccording to one of two modes:• Four-way handshake—the sending node

sends a request-to-send (RTS) packet tothe receiving terminal. If the receiver ac-cepts the request, it replies with a clear-to-send (CTS) packet. If no collisions haveoccurred, the sender then begins trans-mitting its data.

• The sender immediately begins sendingits data. This mode is used when the datapacket is short.

In either mode, the receiver responds withan acknowledgement (ACK) packet if thepacket was successfully received. TheCSMA/CA mechanism is also active for thePCF mode. However, because the accesspoint has greater priority than terminals, ithas total control of the channel.

The IEEE 802.11 standard does not spec-ify a method for multihop ad hoc network-ing. However, in several experimental net-works, MANET-based IP routing has beenused. Nonetheless, the experiments did notemploy automated host configuring—thatis, static IP addresses were assumed.

HiperLAN/2As a rule, a HiperLAN/2 (H2) network hasa centralized mode (CM) in which mobileterminals communicate with access points(AP) over the air interface as defined by theHiperLAN/2 standard. The user of a mobileterminal can move around freely in theHiperLAN/2 network, which ensures thatthe terminal, and hence, the user, gets thebest possible transmission performance.

The development of a high-speed trans-mission environment with controlled QoShas been the main focus regarding the de-sign choices for the H2 network. The rateof the H2 network will give up to 54 Mbit/son layer 3 and it will operate in the 5 GHzfrequency band.

The connection-oriented nature of H2makes it easy to implement support for QoS.Each connection can be assigned a specificQoS, for instance in terms of bandwidth,delay, and bit error rate. It is also possibleto use a more simple approach, in which eachconnection can be assigned a priority level

relative to other connections. This type ofQoS support combined with high transmis-sion rate will facilitate simultaneous trans-mission of many different types of datastream, such as video and voice.

H2 also provides a direct mode (DM) ofcommunication between mobile terminals,which means that it has some of the prop-erties that fit into the ad hoc network cate-gory. However, the AP needs to controlcommunication between mobile terminalseven though the radio link is direct betweenthe nodes. Thus, any two given H2 mobileterminals cannot communicate on an ad hocbasis without having an access point with-in reach. This differs from the IEEE 802.11way of managing ad hoc communication.Nevertheless, the ad hoc mode of operationof H2 is still in its early phase of develop-ment and the final design might deviatefrom this description.24

ConclusionIn this article we have tried to survey ad hocnetworking mainly from a technical pointof view. We have also made an attempt toclarify what an ad hoc network actually is andfound that the definitions vary. However,by proceeding from familiar wireless net-work architectures, we have allowed thelevel of independent operation of the net-work nodes to define the notion of ad hocnetworking. Typically, these networks op-erate with distributed functions and allowtraffic to pass over multiple radio hops be-tween source and destination.

Furthermore, we have discussed some ofthe typical properties of ad hoc networks,such as routing algorithms and the impli-cations of radio layers. The inherent unpre-dictability in a network whose nodes moveposes a challenge to routing and mobilityfunctions if they are to deliver data consis-tently between the network nodes.Nonetheless, multihop radio systems alsomake it possible to save battery capacitywhile retaining, or even improving, perfor-mance. In any case, the most attractive prop-erty of an ad hoc networking model is per-haps its independence from centralized con-trol and, thus, the increased freedom andflexibility it gives the user.

Ad hoc networks have mostly been used inthe military sector, where being able to es-tablish ad hoc communication is often a ne-cessity. On the other hand, in the commer-cial sector, successful examples of ad hocradio networks are few so far, if any. How-



ever, instead of looking at large-scale net-works we turned to the small-scale person-al area networks that are emerging in re-sponse to the introduction of short-rangeradio technologies, such as Bluetooth. Here,ease of use and flexibility are fueling the de-mand for ad hoc operation. In addition, a cen-tralized network architecture would have se-rious problems trying to control all PANdevices. In particular, ad hoc Bluetooth net-works—scatternets—will give rise to awhole new set of business and consumer ap-plications for small, battery-driven user de-vices, such as mobile phones, PDAs, andnotebook computers. The combination ofwide-area IP connectivity via UMTS (mo-bile phone) access, and personal area con-nectivity in the PAN presents new oppor-tunities for the user on the go. End-to-endIP networking is a key component in thisrespect, providing the basis on which to de-velop applications for PAN products. Thus,

the current development of IP support inBluetooth networks is crucial.

Due to its inherent flexibility, ad hoc net-working is easy to deploy and would fit nice-ly into, say, an office setting, where userscould set up ad hoc networking groups usingfewer LAN access points and potentially lesstransmitting power. However, the productsthat apply the concepts of ad hoc network-ing will most likely see its light in the short,personal area range. These products willmainly focus on facilitating communicationbetween a user’s personal devices—eitherfor local traffic or as gateways to the Inter-net. The ad hoc network functionality willalso enable the interconnection of differentusers’ devices—for instance, to facilitatelarger ad hoc working groups. The intrinsicability to create generic, small-scale, ad hocnetworks in portable devices represents anentirely new area for future ad hoc-based ap-plications.

1 N. Abramsson “The ALOHA system—another alternative for computer communi-cations” in AFIPS Conf. Proc., vol 37, FJCC,1970, pp. 695-702.

2 J.Jubin and J.D.Tornow, “The DARPApacket radio network protocol,” Proc. Ofthe IEEE, vol 75, No.1, Jan 1987, pp.21-32.

3 Y.D.Lin and Y.C.Hsu, “Multihop Cellular: Anew architecture for wireless communica-tions” in IEEE INFOCOM 2000, pp. 1273-1282.

4 Mobile Ad hoc Networks (MANET). URL:http://www.ietf.org/html.charters/manet-charter.html. (2000-05-28). Work inprogress.

5 “What’s Behind Ricochet: A NetworkOverview,” http://www.ricochet.net/rico-chet_advantage/tech_overview.

6 D.C.Steere et. al., “Research challenges inenvironmental observation and forecastingsystems,” MOBICOM 2000, pp. 292-299.

7 Christian Gehrmann, Pekka Nikander,“Securing ad hoc services, a Jini view,”MobiHoc ‘00, August 2000.

8 Per Johansson, Tony Larsson, NicklasHedman, Bartosz Mielczarek, and Mikael Degermark. Scenario-based Performance Analysis of Routing Proto-cols for Mobile Ad hoc Networks. In Proceedings of the Fifth Annual International Conference on MobileComputing and Networking, August1999.

9 Charles E. Perkins, “Ad Hoc On DemandDistance Vector (AODV) Routing.” Internet

draft, draft-ietf-manet-aodv-02.txt,November 1998. Work in progress.

10 Josh Broch, David B. Johnsson, David A.Maltz, “The Dynamic Source Routing Pro-tocol for Mobile Ad hoc networks.” InternetDraft, draft-ietf-manet-dsr-00.txt, March1998. Work in progress.

11 Charles E. Perkins and Pravin Bhagwat,“Highly dynamic Destination-SequencedDistance-Vector routing (DSDV) for mobilecomputers.” In Proceedings of the SIG-COM '94 Conference on CommunicationsArchitecture, protocols and Applications,pages 234-244, August 1994. A revisedversion of the paper is available fromhttp://www.cs.umd.edu/projects/mcml/papers/Sigcomm94.ps. (1998-11-29)

12 Charles E. Perkins. RFC 2002: IP Mobili-ty Support, October 1996. Updated byRFC2290. Status: PROPOSED STAN-DARD.

13 Charles E. Perkins. Mobile IP. IEEE Commu-nications Magazine, pages 84–99, May1997.

14 Ulf Jönsson, Fredrik Alriksson, Tony Lars-son, Per Johansson, Gerald Q. Maguire Jr.,“MIPMANET - Mobile IP for Mobile Ad hocNetworks,” MobiHoc ‘00, August 2000.

15 L.Kleinrock, and J.Silvester, “Spatial reusein multihop packet radio nework” Proc. Ofthe IEEE, vol 75, No.1. pp. 156-166, Jan 87.

16 Haartsen, J.: Bluetooth - The universalradio interface for ad hoc, wireless connec-tivity. Ericsson Review Vol. 75(1998):3, pp. 110-117.

17 J. Hartsen, M. Naghshineh, J. Inouye, O.J. Joeressen and W. Allen, “Bluetooth:Visions, goals, and architecture,” ACM Mobile Computing and Communi-cations Review, pp. 38-45, No. 2, Vol. 4,1998.

18 Bluetooth Specification, Baseband Speci-fication,http://www.bluetooth.com/link/spec/bluetooth_b.pdf

19 Per Johansson et al. Short-Range Radio-Based Ad hoc Networking: Performanceand Properties ICC’99, Vancouver, 1999

20 R. Droms, “RFC 2131: Dynamic Host Con-figuration Protocol,” March 1997, availablefrom http://www.ietf.org/rfc/rfc2131.txt

21 IETF, Charter of the Zero ConfigurationNetworking (zeroconf) WG, Available fromhttp://www.ietf.org/html.charters/zero-conf-charter.html.

22 S. Cheshire, “Dynamic Configuration ofIPv4 link-local addresses,” Internet Draft,8th October 2000, Available fromhttp://www.ietf.org/internet-drafts/draft-ietf-zeroconf-ipv4-linklocal-00.txt

23 IEEE Computer Society LAN MAN Stan-dards Committee, “Wireless LAN MediumAccess Control (MAC) and Physical Layer(PHY) Specifications,” IEEE Std 802.11-1997. The Institute of Electrical and Elec-tronics Engineers, New York.

24 Khun-Jush, J., Malmgren, G., Schramm, P.and Torsner, J.: HIPERLAN type 2 forbroadband wireless communication. Ericsson Review Vol. 77(2000):2, pp.108-119.

REFERENCES

wireless ad hoc networking—the art of networking without a network

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