iaetsd-wireless ad hoc networks

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“Wireless Ad hoc Networks”

C:LATAH SOUNDARYA M.SREEKAR PRANAV

E-mail:[email protected] E-mail:[email protected]

Wireless Ad-hoc Networks Abst ractDeployed in 1990’s, Mobile Ad-hocnetworks have been widely researchedfor many years. Mobile Ad-hoc

Networks are a collection of two or moredevices equipped with wirelesscommunications and networkingcapability. These devices cancommunication with othernodes thatimmediately within their radio range orone that is outside their radio range. Forthe later, the nodes should deploy anintermediate node to be the router toroute thepacket from the source towardthe destination. The Wireless Ad-hoc

Networks do not have gateway, everynode can act as the gateway. Althoughsince 1990s’, lotsof research has beendone on this particular field, it has oftenbeen questioned as to whether thearchitecture of Mobile Ad-hoc Networksis a fundamental flawedarchitecture.The main reason for the argument isthat Mobile Ad-hoc Networks are almostnever used in practice, almost everywireless network nodes communicate to

base-station and access points insteadofco-operating to forward packets hop-by-hop.We take the position that Mobile

Ad-hoc Networks (MANET) are afundamentally flawed architecture. Asargument, we try to clarify the definition,architecture and the characters ofMANET, as well as the main challenges

of constructing the MANET. Althoughmany works have been done to solvethe problem, we will show in this paperthat it is very difficult to solve theselimitations which made the Mobile Ad-

hoc Networks a flawed architecture. After giving many evidences andanalysis, we could see that the keytechnologies of Wireless Ad-hocNetworks were not implemented as wellas we expect. That is to say, manyproblems are inherently unsolvable.Thus, we could explain why we take theposition that Mobile Ad-hocNetworks areflawed architecture.

IntroductionResearch on Wireless Ad Hoc Networkshas been ongoing for decades. Thehistory of wireless ad hoc networks canbe traced back to the Defense

Advanced Research ProjectAgency(DAPRPA) packet radio networks(PRNet), which evolved into thesurvivable adaptive radio networks(SURAD) program [11]. Ad hoc

networks have play an important role inmilitary applications and relatedresearch efforts, for example, the globalmobile information systems (GloMo)program [12] and the near-term digitalradio (NTDR) program [13]. Recentyears have seen a new spate ofindustrial and commercial applications

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International Conference on Advancements in Engineering Research

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for wireless ad hoc networks, as viablecommunication equipment and portablecomputers become more compact andavailable. Since their emergence in1970’s, wireless networks have become

increasingly popular in thecommunication industry. Thesenetworks provide mobile users withubiquitous computing capability andinformation accessregardless of theusers’ location. There are currently twovariations of mobile wireless networks:infrastructure and infrastructurelessnetworks. The infrastructured networkshave fixed and wired gateways or thefixed Base-Stations which are

connected to other Base-Stationsthrough wires. Each node is withinthe range of a Base-Station. A “Hand-off” occurs as mobile host travels out ofrange of one Base-Station and into therange of another and thus, mobile hostis able tocontinue communicationseamlessly throughout the network.Example applications of this typeinclude wireless local area networks andMobile Phone.The other type of wirelessnetwork, infrastructurelessnetworks,is knows as Mobile Ad-hocNetworks(MANET). These networkshave no fixed routers, every node couldbe router. All nodes are capable ofmovement and can be connecteddynamically in arbitrary manner.The responsibilities for organizing andcontrolling the network are distributedamong the terminals themselves. Theentire network is mobile, and theindividual terminalsare allowed to movefreely. In this type of networks, somepairs of terminals may not be able tocommunicate directly with each otherand have to relay on some terminals sothat the messages are delivered to theirdestinations. Such networks are oftenrefereed to as multi-hop or store

andforwardnetworks. The nodes ofthese networks function as routers,which discover and maintain routes toother nodes in the networks. The nodesmay be located in or on airplanes, ships,

trucks, cars, perhaps even on people orvery small devices. Mobile Ad-hocNetworks are supposed to be used fordisaster recovery, battlefieldcommunications, and rescue operationswhen the wired network is not available.It canprovide a feasible means forground communications andinformation access.2. Characters and FundamentalChallenges of Wireless Ad-hoc

NetworksSince Wireless Ad-hoc Networks areinherently differen from the well-knownwired networks, it is an absolutely newarchitecture. Thus some challengesraise from the two key aspects: self-organization and wireless transport ofinformation [4], [5].First of all, since thenodes in a Wireless Ad-hoc Network arefree to move arbitrarily at any time. Sothe networks topology of MANET maychange randomly and rapidly atunpredictable times. This makes routingdifficult because the topology isconstantly changing and nodes cannotbe assumed to have persistent datastorage. In the worst case, we do noteven know whether the node will stillremain next minute, because the nodewill leave the network at any minute.Bandwidth constrained is also a bigchallenge. Wireless links havesignificantly lower capacity than theirhardwired counterparts. Also, due tomultiple access,fading, noise, andinterference conditions etc. the wirelesslinks have low throughput.Energyconstrained operation. Some or all ofthe nodes in a MANET may rely onbatteries. In this scenario, the most



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cluster. This idea is great, by usingcluster, we avoid the floodingprocess when doing routing and faultdiagnoses. And also the self-organization method was explored.

Selforganizationnetworks are improvedMobile Ad-hocnetworks. Theydistinguish themselves from traditionalmobile ad-hoc networks, based on thetraditional internet two level hierarchyrouting architecture, by emphasizingtheir self-organization peculiarities. Self-organized networks can act in anindependent way from any provider.Self-organized networks are alsopotentially very largeand not regularly

distributed. For example, one singlenetwork can cover the entire world. Also, self-organized networks are highlyco-operative, the tasks at any layer aredistributed over the nodes and anyoperation is the results of thecooperation of a group of nodes. Peoplebelieve that MANET will be the mainarchitecture of the future wirelessnetworks where the normal wirelessnetworks are impossible to build,especially in military usage oremergency. They think the mostimportant characteristic which setsWireless Ad-hoc networks apartfrom cellular networks is the fact thatthey do not rely on a fixed infrastructure.They also think Mobile Ad-hoc networksare very attractive for tacticalcommunication inmilitary and lawenforcement. Again, they believe thatWireless Ad hoc Networks will play animportant role not only in military andemergency application, but also canbe applied in civilian forums such asconvention centers, conferences, andelectronic classroom. However, we donot agree with the above statements.Ourpoint of view is that when we talkabout the Mobile Adhoc networks, we

think they are a flawed architecture,because first, until now, we haven’t seenany practice of the Wireless Ad-hocNetworks, are the routing protocols, self-organization, security solutions are all

theories based on simulation. Second,today, almost every wireless networknodes communicate to base-stationsand accesspoints, instead of co-operating to forward packets hop-byhop.In the following section, we will discussin detail the major technical topics aboutthe Wireless Ad-hocnetworks. Theresults show us that even consider forthe basic technical topics, the Wirelessad-hoc networks arefundamentally

flawed architecture.5. Wireless Ad-hoc Networks Issues

Even the most zealot supporters ofMANET have to admit that it is achallenging task to enable fast andreliable communication within such anetwork. The inherent characters ofMANET make it a flawed architecture nomatter what we have done or will do toimprove theperformance of thenetworks. Below are the factors thatprevent the mobile ad hoc networks tobe an in-flawedarchitecture.5.1 Security in Wireless Ad-hocNetworks

Security is an important thing for allkinds of networks including the Wireless

Ad Hoc Networks. It is obviously to seethat the security issues for Wireless AdHocNetworks are difficult than the onesfor fixed networks. This is due to systemconstraints in mobile devices as well asfrequent topology changes in theWireless networks. Here, systemconstraints include low-power, smallmemory and bandwidth, and low batterypower. Mobility of relaying nodes andthe fragility or routes turn Wireless Ad-hoc Network architecture into highlyhazardous architectures. No entity is



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ensured to be present at every time andit is then impossible to rely on acentralized architecture that couldrealize network structure or evenauthentication. The people who consider

the Mobile Ad hoc Networks are not aflawed architecture, while we cannot seeit used in practice is only because mostof its applications are in military aretotally wrong. Itis true that Mobile Adhoc Networks come from the military.But perhaps those persons forgot one ofthe most important things: the Security!Everybody knows that the corerequirement for military applicationsdealing with trust and security! That is to

say,security is the most important issuefor ad hoc networks, especially for thosesecurity sensitive applications. As wehave mentioned before, in Mobile Ad-hoc Networks, security is difficult toimplement because of the networksconstrains and the rapidly topologychanges.After investigation, we foundthat there are two kinds of securityrelated problems in the Mobile Ad-hocNetworks. One is the attacks based onthe networks which are justsimilar to theInternet, the other is Fault Diagnoses.Fault Diagnoses algorithm is used topick out the faultynodes and at the sametime remove the node from the wholenetworks. This process should be real-time as to guarantee the performance ofthe whole networks. In order to solve thefault diagnoses problem, many faultdiagnoses algorithms [6] were bring out.

After carefully surveying the existingalgorithm today, we found that theycannotcorrectly diagnose faulty nodewith the presence of the changing of thenetwork topology during the process ofdiagnosis, and these algorithms areanalyzed with repetitious diagnosis forall the mobile hosts and cause the greatsystem overhead due to the

transmission of diagnosis messages bymeans of flooding throughout the wholenetworks. While the topology of Mobile

Ad-hoc Networks changes from time totime, then we cannot use this kind of

Fault Diagnoses Algorithm to solve thequestions.Therefore, we can see thatthe current fault diagnosis algorithmscannot solve the fault diagnosisproblem. As for the networks attacks,there are several factors ofsecurity thatwe should consider. First, Availabilityensures the survivability of networkservices despitedenial of serviceattacks. Confidentiality ensures thatcertain information is never disclosed to

unauthorized entities. Integrityguarantees that a message beingtransferred is never corrupted. Authentication enables anode to ensurethe identity of the peer node it iscommunicating with. Yet, active attacksmight allow the adversary to deletemassages, to modify messages, and toimpersonate a node, thus violatingavailability, integrity, authentication, andnon-repudiation. Although that manysecurity-related researches have beendone to this problem[7], [8], we couldsee that Mobile Ad hoc networks areinherently vulnerable to security attacks.While, on the other hand, it is said thatthe main applications of MANETare inmilitary and emergency, all theseapplications are security-sensitive.MENAT can not satisfy the securityrequirement of the applications, so thismakes that MANET is a flawedarchitecture.5.2 Routing Protocol in Ad-hocNetworks

Wireless Ad-hoc Networks operateswithout a fixed infrastructure. Multi-hop,mobility, large network size combinedwith device heterogeneity andbandwidth and battery power



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limitations, all these factors make thedesign of routing protocols a majorchallenge. Lots of researchers didtremendous work on the Wireless Ad-hoc Routing Protocols.

Two main kinds of Routing Protocols areexisted today: one is called table-drivenprotocols (including distance vector andlink state), another is on-demandprotocols.In table driven routingprotocols, the protocols consistent andup-to-date routing information to allnodes is maintained at each nodewhereas in on-demand routing theroutes are created only when desired bythe sourcehost. While for the on

demand Routing protocols, “on demand”means that it builds routes betweennodes only as desiredby source nodes.It maintains these routes as long as theyare needed by the sources.If we look upthe key words “Wireless Ad hocNetworks Routing Protocols” in Google,we could find tons of millions of all kindsof routing protocols, as LAR (Location-

Aided Routing), DSDV (Destination-Sequenced Distance-Vector Routing),

AODV (Ad-hocOn-Demand DistanceVector Routing), and DSR (DynamicSource Routing Protocol)…… However,after survey various types of routingstrategies proposed for wireless ad-hocnetworks, we find the truth is all theserouting protocols are all have inherentdrawbacks and cannot be considered asgood routing protocols for Wireless adhoc Networks. Just like Windowsoperatingsystems need patch at all thetime, the Wireless Ad hoc networksrouting protocol are all needs patchestoo. The main problems about therouting protocols are asfollowing: First of all, consider the rapid passingpattern. Wedefine the rapid passingpattern to be one node passing through

the whole network very quickly. Such arapid passing node will generate thefollowing affects to the whole network.First, the topology of the networkchanged rapidly, which will lead to the

lost of packets. Second, we have tomodify every node’s routing table thatwithin the communication distance ofthe rapid-passing node, that will greatlyimprove the consumption of thebandwidth and the overhead of thenetworks. Third, obviously there will betremendous delay of the datasending to the rapid-moving node. Transmission between two hosts overa wireless network does not necessarily

work equally well in both directions.Thus, some routes determined by somerouting protocols may not work in someenvironments. Many routing protocols may createredundant routes, which will greatlyincrease the routing updates as well asincrease the whole networks overhead. Periodically sending routing tables willwaste network bandwidth. When thetopology changes slowly, sendingrouting messages will greatly waste thebandwidth of Wireless Ad-hoc Networks.This will add additional burdens to thelimited bandwidthof the Ad-hocNetworks. Periodically sending routing tablesalso waste the battery power. Energyconsumption is also a critical factorwhich prevents Wireless Ad-hocNetworks to be a non-flowedarchitecture. We will discuss this in 5.3.We all understand that a stable networkrouting protocols is essential for anykinds of networks. However, for theWireless ad hoc Networks, we could notfind a stable routing protocol even afterwe have done research on it more than10 years. Needless to say that it is the



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Wireless Ad hoc Networks itself isflawed.5.3 Energy Consumption of Wireless Ad-hocNetworks Energy consumption is also

one of the most importantperformancemetrics for wireless ad hoc networks, itdirectly relates to the operational lifetimeof the networks. Mobile elements haveto rely on finite source of energy.Whilebattery technology is improving overtime, the need for power consumptionwill not diminish. This point will have aharmful effect on the operation time as itwill haveon the connection quality andbandwidth.In the Wireless Ad-hoc

Networks, battery replacement may notbe possible. So as far as energyconsumption concerned, we should tryto preserve energy while maintaininghigh connectivity. Each node dependson small low-capacity batteries asenergy sources, and cannot expectreplacement when operating in hostileand remote regions. For Wireless AdhocNetworks, energy depletion andreduction is the primary factor inconnectivity degradation and length ofoperational lifetime. Overallperformance becomes highly

dependent on the energy efficiency ofthe algorithm. Energy consumption isone of the most important performancemetrics for wireless ad hoc networksbecauseit directly relates to theoperational lifetime of the network. Mostresearch efforts are focused onperformance comparisons and trade-offstudies between various lowenergyrouting and self-organization protocols,whilekeeping other system parametersfixed. As a result, very little has beenrevealed about the relationship betweenthe aggregate energy consumption andnon-protocol parameters such as nodedensity, network coverage area,and

transceiver power characteristics. Weemphasis energy consumption not onlybecause that it is the key problem in theresearch of Wireless Ad-hoc Networks,but also, we find that Energy

consumption problem also affects therouting protocols and the QoS of thewhole networks. Let’s assume that eachsource randomly selects one of thepossible routes and asks theintermediate nodes on the route to relaytraffic. Sinceenergy is a valuableresource, intermediate nodes may notwish to consume their energy to carrythe source’s traffic. This is called“Selfish” of the node. However, if every

node behaves ‘Selfish’ and refuse tocooperate, networkthroughput may bedrastically reduced.Also, there are manyworks have done to solve the energyconsumption problem. However,unfortunately, little practical informationis available about theenergyconsumption behavior of wirelessad hoc network interfaces and devicespecifications do not provide informationin a form that is helpful to protocoldevelopersThis, again, prove that theWireless Ad Hoc Networks cannot beput into practice. Further, we can holdour position that the Wireless Ad HocNetworks are a fundamentally flawedarchitecture.6. Conclus ion

Mobile Ad hoc Networks are an idealtechnology to establish in an instantcommunication infrastructurelessfor military application or a flawedarchitecture has been bought out in thisposition paper. As we have provedusing the three main technical topics ofthe Wireless AdhocNetworks, We holdthe position that the Wireless Ad hocNetworks are a flawed architecture forthe following technical reasons:



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The most important thing for thenetworks is security. It is even importantfor Wireless Ad hoc Networks becauseits applications are in military. TheMANET can not appropriately solve the

problem of the security. Routing is also a big problem. All therouting protocols for Wireless Ad hocNetworks are need patches. No suitableand stable routing protocols until now. Energy consumption problem stillcannot be solved even much of effortshave been done to it. All these provethat the Wireless Ad hoc Networks is aflawed architecture. Not only because itis almost never used in practice but also

because there are severaltechnical difficulty that cannot beconquered.Besides, all the Wireless Ad-hoc Networks are expected to be self-configuration. Self-configuration arereferring to two aspects, one is duringthe first construction of thenetwork, theself-configuration network is supposedto be forming the network itself. Theother problem is when one host movesin or moves out the Wireless Ad-hocnetworks,the network should have the ability to re-configuration the topology of the wholenetworks. Again we could see thatalthough many works have been doneon this topic, but unlucky, all thediscussions do not give us a satisfiedanswer to the self-configurationquestion. The question is never tackledin systematic way. That again prove outargument that the Wireless Ad-hocNetworks is a fundamental flawedarchitecture, or else we should find theappropriated answer to the problems.However as the wireless and embeddedcomputing technologies continue toadvance, I do hope later, one day, wecould build our wireless networks rely on

some kinds of the Wireless Ad hocNetworks.References:[1] IEEE Std 802.11 – 1999: WirelessMedium Access Control (MAC) and

Physical Layer (PHY) specifications,Inst. Elec. Electron. Eng., New York,USA, 1999.ISBN 0-7381-1658-0[2] IPN Progress Report, August 15,2002, Analysis of Energy Consumptionfor Ad Hoc Wireless Sensor NetworksUsing a Bit-Meter-Per-Joule Metric,J.L.Gao[3] A Distributed Light-Weight

Authentication Model for Ad-hocNetworks

[4] M. Satyanarayanan. Fundamentalchallenges in mobilecomputing.submitted paper .[5] M. Haardt W. Mohr R. Becher, M.Dillinger. Broadband wireless accessand futurecommunicationnetworks.Proceedings of the IEEE,89(1), 2001.[6] S.Chessa, P.Santi, “ComparisonBased System-Level Fault Diagnosis in

Ad-Hoc Networks”, Proc. IEEE20thSymp. on Reliable Distributed Systems(SRDS), New Orleans, pp. 257-266,October 2001[7] Erik Skow, Jiejun Kong, ThomasPhan, Fred Cheng, Richard Guy,RajiveBagrodia, Mario Gerla, andSongwu Lu, “A Security Architecture for

Application Session Handoff”[8] Lidong Zhou, Zygmunt J. Haas,“Securing Ad Hoc Networks”[9] David B. Johnson, “Routing in AdHoc Networks of Mobile Hosts”,Proceedings of the IEEE Workshop onMobile Computing Systems and

Applications, December 1994.[10] LjubicaBlazevic, LeventeButtyan,SrdanCapkun, Silvia Giordano, Jean-Pierre, Hubaux and Jean-Yves LeBoudec, “Self-Organization in Mobile



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