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LAYERS OF MANETS

VELLANKI SUMANTH REDDY09B61A05B8

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1 Introduction

What does make routing and communicationin MANET Networks different from routingand communication in usual LANs, WANsetc.? The main peculiarities are the absenceof wires, routers and any predefined infras-tructure. The nodes communicate with eachother over the air and this is a very unreli-able medium. Because of reflection, diffrac-tion, diffusion and other signal propogationproperties the data exchanging by nodes is

frequently lost. Besides the connections be-tween nodes can break because the nodesmove and this changes then the topology ofthe network. Taking into consideration allthese facts, its obvious that the standardapproaches applicable to the usual networkswith pre-existing infrastructure arent suit-able in general for the ad hoc networks. Infollowing Id like to tell a couple of wordsto ISO/OSI layers and explain briefly how

they are realized in MANET networks.Manetis a specification The goal of this report isto present and describe the Dynamic SourceRouting (DSR) OPNET. process model thathas been developed at NIST. In this way itwill be possible for every OPNET user or de-veloper to use this process model in his sim-ulations. Thus the first part is devoted to ageneral overview of the DSR protocol, and ofthe Mobile Ad Hoc Network (MANET) forwhich it has been developed. Then, since

the process model cannot be provided with-out a node model, a presentation of this nodemodel is done in the second part of the re-port. Finally, the third and last part of thereport focuses on the DSR process model;

that is the description of this model com-

paring to its specification and the presenta-tion of its state machine. Detailed techni-cal information relative to the model, such asthe variables, the functions, and the packetformat descriptions, are available in the ap-pendix. It is important to raise this ques-tion since the Dynamic Source Routing pro-tocol was designed especially for this kind ofnetwork. A Mobile Ad Hoc Network, alsocalled a MANET, is an autonomous collec-tion of mobile nodes forming a dynamic wire-

less network. The administration of such anetwork is decentralized, i.e. each node actsboth as host and router and forwards pack-ets for nodes that are not within transmissionrange of each other. A MANET provides apractical way to rapidly build a decentralizedcommunication network in areas where thereis no existing infrastructure or where tempo-rary connectivity is needed, e.g. emergencysituations, disaster relief scenarios, and mili-

tary applications.

2 Application Layer In

Manet

Peer-to-peer (P2P) computing is a network-ing and distributed computing paradigmwhich allows the sharing of computingre-sources and services by direct, symmetric in-

teraction between computers. With the ad-vance in mobile wireless communication tech-nology and the increasing number of mobileusers, peer-to-peer computing, in both aca-demic research and industrial development,

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has recently begun to extend its scope to

address problems relevant to mobile devicesand wireless networks. The mobile ad hocnetwork (MANET) and P2P systems sharekey characteristics including self-organizationand decentralization, and both need to solvethe same fundamental problem: connectiv-ity. Although it seems natural and attrac-tive to deploy P2P systems over MANET duetothis common nature, the special character-istics of mobileen vironments and the diver-sity in wireless networks bring new challenges

for research in P2P computing.

2.1 Application Layer Multi-cast

2.1.1 Introduction

For An increasing number of Peer-to-Peer(P2P) Internet applications rely today ondata dissemination as their cornerstone, e.g.,

audio or video streaming, multi-party games.These applications typically depend on somesupport for multicast communication, wherepeers interested in a given data stream can

join a correspondingmulticast group. As aconsequence, the efficiency, scalability, andreliability guaranteesof these applications aretightly coupled with that of the underly-ing multicastmechanism. At the networklevel, IP Multicast offers quite good efficiencyand scalability but best-effort reliability only.

Moreover, the deployment of IP Multicast re-quires all routers to be appropriately con-figured, which makes it quite impractical inlarge scale or open settings, i.e., where onedoes not have full control over the network-

ing environment. For this reason, several re-

search directions have focused on trying tooffer some form of multicast communicationat a higher level, typically via an application-oriented middleware. Such a higher leveldata dissemination support is often referredto as Application Layer Multicast (ALM). Ofcourse, ALM-based solutions to data dissem-ination usually rely on the lower level net-working mechanism.

2.1.2 Working

At the network level, IP Multicast offers quitegood efficiency and scalability but best-effortreliability only. Moreover, the deployment ofIP Multicast requires all routers to be ap-propriately configured, which makes it quiteimpractical in large scale or open settings,i.e., where one does not have full control overthe networking environment. For this rea-son, several research directions have focused

on trying to offer some form of multicast com-munication at a higher level, typically viaan application-oriented middleware. Such ahigher level data dissemination support is of-ten referred to as Application Layer Multicast(ALM). Of course, ALM-based solutions todata dissemination usually rely on the lowerlevel networking mechanism.namely looselycoupled large-area networks,such as the Inter-net. Indeed, most solutions aim at large sys-tems with hundreds or thousands of nodes. In

these contexts, protocols do not seem to sig-nificantly favor a design for a specific sourceor for multi sources, in which the same over-lay network is reused by any peer willing todisseminate information.While most of the

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protocols surveyed were originally designed

for P2P Internet environments, some couldbe used in MANET settings. Yet, mostof them are not suitable to MANETs. Atfirst glance, this may look surprising due tothe similarities between P2P networks andMANETs. In reality, however, MANET com-ponents are more resource-constrained thenP2P Internet peers. Moreover, some P2Pprotocols rely on assumptions that are notfeasible in MANETs (e.g., the existence ofrendezvous points). With respect to overlay

structure, the large majority of protocols usesphysical node IDs, as opposed to logical IDs.Moreover, by far and large most protocolsbuild tree overlays, and the few ones basedon meshes use it mainly to control informa-tion, not to disseminate data. Disseminatinginformation over a mesh would create redun-dant data paths and waste bandwidth in theabsence of failures

2.1.3 Conclution

Most multicast protocols surveyed focus onminimizing latency and improving scalability.These goals are justified by the nature of theenvironment targeted bytypical application-level multicast protocols, namely loosely cou-pled large-area networks,such as the Internet.Indeed, most solutions aim at large systemswith hundreds or thousands of nodes. Inthese contexts, protocols do not seem to sig-

nificantly favor a design for a specific sourceor for multi sources, in which the same over-lay network is reused by any peer willing todisseminate information.While most of theprotocols surveyed were originally designed

for P2P Internet environments, some could

be used in MANET settings. Yet, mostof them are not suitable to MANETs. Atfirst glance, this may look surprising due tothe similarities between P2P networks andMANETs. In reality, however, MANET com-ponents are more resource-constrained thenP2P Internet peers. Moreover, some P2Pprotocols rely on assumptions that are notfeasible in MANETs (e.g., the existence ofrendezvous points). With respect to over-lay structure, the large majority of protocols

uses physical node IDs, as opposed to logicalIDs. Moreover, by far and large most pro-tocols build tree overlays, and the few onesbased on meshes use it mainly to control in-formation, not to disseminate data. Dissem-inating information over a mesh would cre-ate redundant data paths and waste band-width in the absence of failures. While thiswould provide higher reliability, as we willsee next, protocols tend to resort to differ-

ent mechanisms to handle peer or link fail-ures.It is perhaps less surprising that mostsolutions implement a distributed overlay cre-ation and maintenance, where the responsi-bility is shared among several peers, as op-posed to a centralized approach in which onepeer is responsible for building the overlay.One consequence of the centralized techniqueis that one node must have global knowledgeabout the system. While most multicast pro-tocols surveyed strive to avoid global knowl-

edge, a few adopt a hybrid approach in whichsome nodes must maintain a complete view ofthe system. This is typically the case.

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2.2 Mobile File-Sharing over

P2P NetworksThe current list of application profiles ei-ther published, or in the works are: Peer-to-peer (P2P) computing is a networking anddistributedcomputing paradigm which allowsthe sharing of computing resources and ser-vices by direct, symmetric interaction be-tween computers. With the advance in mo-bile wireless communication technology andthe increasing number of mobile users, peer-

to-peer computing, in both academic researchand industrial development, has recently be-gun to extend its scope to address problemsrelevant to mobile devices and wireless net-works.The mobile ad hoc network (MANET)and P2P systems share key characteristicsincluding self-organization and decentraliza-tion, and both need to solve the same fun-damental problem: connectivity. Although itseems natural and attractive to deploy P2Psystems over MANET due to this commonnature, the special characteristics of mobileenvironments and the diversity in wirelessnetworks bring new challenges for research inP2P computing.

2.2.1 introduction

Currently, most P2P systems work on wiredInternet, which depends on application layerconnections among peers, forming an appli-

cation layer overlay network. In MANET,overlay is also formed dynamically via con-nections among peers, but without requir-ing any wired infrastructure. So the majordifferences between P2P and MANET that

concern us in this article are: P2P is gen-

erally referred to the application layer, butMANET is generally referred to the networklayer, which is a lower layer concerning net-work access issues. Thus, the immediate re-sult of this layer partition reflects the dif-ference of the packet transmission methodsbetween P2P and MANET: the P2P overlayis a unicast network with virtual broadcastconsisting of numerous single unicast packets,while the MANET overlay always performsphysical broadcasting. Peers in P2P overlay

are usually referred to static nodethough nopriori knowledge of arriving and departing isassumed, but peers in MANET are usuallyreferred to mobile node since connections areusually constrained by physical factors likelimited battery energy, bandwidth, comput-ing power, and so forth.

2.2.2 conclusion

In this article, we studied the peer-to-peersystems over mobile ad hoc networks with acomparison of different settings for the peer-to-peer overlay and underlying mobile ad hocnetwork. We show that the cross-layer ap-proach performs better than separating theoverlay from the access networks in Table 1.

Our results would potentially provide usefulguidelines for mobile operators, value-addedservice providers, and application developersto design and dimensionmobile peer-to-peersystems.

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2.3 Security issues, challenges

solution in MANET2.3.1 abstract

Security has become a primary concern in or-der to provide protected communication be-tween mobile nodes in a hostile environment.Unlike the wireline networks, the uniquecharacteristics of mobile ad hoc networkspose a number of nontrivial challenges to se-curity design, such as open peer-topeer net-work architecture, shared wireless medium,stringentresource constraints, and highly dy-namic network topology. Theprovision of se-curity services in the MANET context facesa set of challenges specific to this new tech-nology. In this paper, we discuss security is-sues, vulnerable nature of the mobile ad hoc-network, security criteria and the main at-tack types that exist in it. Finally we surveythe current security solutions for themobilead hoc network and then conclude this paper

2.3.2 introduction

In recent years mobile ad hoc networks havereceived tremendous attention because oftheir self-configuration and self-maintenancecapabilities. A Mobile Ad hoc network is asystem of wireless mobile nodes that dynami-cally selforganize in arbitrary and temporarynetwork topologies. People and vehicles canthus be internetworked in areas without a

preexisting communication infrastructure orwhen the use of such infrastructure requireswireless extension. In the mobile ad hoc net-work, nodes can directly communicate withall the other nodes within their radio ranges;

whereas nodes that not in the direct com-

munication range use intermediate node(s)to communicate with each other. In thesetwo situations, all the nodes that have partic-ipated in the communication automaticallyform a wireless network, therefore this kind ofwireless network can be viewed as mobile adhoc network. Security has become a primaryconcern to provide protected communicationbetween mobile nodes in a hostile environ-ment. Unlike wire line networks, the uniquecharacteristics ofmobile ad hoc networks pose

a number of non-trivial challengesto the secu-rity design.

2.4 Vulnerabilities of MANET

2.4.1 Unreliability of wireless linksbetween nodes

Because of the limited energy supply for thewireless nodes and the mobility of the nodes,the wireless links between mobile nodes inthe ad hoc network are not consistent for thecommunication participants.

2.4.2 Dynamic topologies

Nodes are free to move arbitrarily; thus,the network topology which is typicallymultihopmay change randomly and rapidlyat unpredictable time. Because the topologyof the ad hoc networks is changing constantly,

it is necessary for each pair of adjacent nodesto incorporate in the routing issue so as toprevent some kind of potential attacks thattry to make use of vulnerabilities in the stat-ically config.d routing protocol.

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2.4.3 Lack of Secure Boundaries

The meaning of this vulnerability is self-evident: there is not such a clear secureboundary in the mobile ad hoc network,which can be compared with the clear lineof defense in the traditional wired network.This vulnerability originates from the natureof the mobile ad hoc network: freedom to

join, leave and move inside the network. Lackof secure boundaries makes the mobile ad hocnetwork susceptible to the attacks. Due to

this mobile ad hoc network suffers from all-weather attacks, which can come from anynode that is in the radio range of any node inthe network, at any time, and target to anyother node in the network. To make mat-ters worse, there are various link attacks thatcan jeopardize the mobile ad hoc network,which make it even harder for the nodes inthe network to resist the attacks. The at-tacks mainly include passive eavesdropping,active interfering, and leakage of secret in-

formation, data tampering, message replay,message contamination, and denial of service.

2.4.4 Threats from Compromisednodes Inside the Network

Since mobile nodes are autonomous unitsthat can join or leave the network with free-dom, it is hard for the nodes themselves towork out some effective policies to prevent

the possible malicious behaviors from all thenodes it communicate with because of the be-havioral diversity of different nodes. Further-more, because of the mobility of the ad hocnetwork, compromised node can frequently

change its attack target and perform mali-

cious behavior to different node in the net-work, thus it is very difficult to track the ma-licious behavior performed by a compromisednode especially in a large scale ad hoc net-work. Therefore, threats from compromisednodes inside the network are far more dan-gerous than the attacks from outside the net-work, and these attacks are much harder todetect because they come from the compro-mised nodes, whichbehave well before theyare compromised.

2.4.5 Lack of Centralized Manage-ment Facility

Ad hoc networks do not have a centralizedpiece of managementmachinery such as aname server, which lead to some vulnera-bleproblems. Due to absence of centralizedmanagement facilityproblems detection of at-tacks, path breakages, transmission impair-

ments and packet dropping, breakage of thecooperativealgorithm take place because de-cision making process isdecentralized.

2.4.6 Restricted Power Supply

Some or all of the nodes in a MANET mayrely on batteries orother exhaustible meansfor their energy. For these nodes, themost im-portant system design criteria for optimiza-tion may be energy conservation. The prob-

lem that may be caused by the restrictedpower supply is denial-of-service attacks .Since the adversary knows that the targetnode is batteryrestricted,either it can contin-uously send additional packetsto the target

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and ask it routing those additional packets,

or it can induce the target to be trapped insome kind of timeconsuming computations.In this way, the battery power of the targetnode will be exhausted by these meaninglesstasks, and thus the target node will be outof service to all the benign service requestssince it has run out of power.

2.4.7 Scalability

Scalability is the problem in the mobile ad

hoc network .Unlike the traditional wired net-work in that its scale is generallypredefinedwhen it is designed and will not change muchduringthe use, the scale of the ad hoc net-work keeps changing allthe time: becauseof the mobility of the nodes in the mobileadhoc network, you can hardly predict howmany nodes there willbe in the network inthe future. As a result, the protocols andser-vices that are applied to the ad hoc networksuch as routingprotocol and key managementservicet should be compatibleto the continu-ously changing scale of the ad hoc network.

2.5 Integration of Application-Layer Scheduling andRouting

2.5.1 Abstract

application-layer ordersfrom a MANETs

leader also control workers mobility and abil-ity to forward messages. Our approach at-tempts to minimize deadline misses and en-ergy consumption by scheduling worker tasksconsidering both applicationand network-

layer needs. Simulations demonstrate per-

formance Natural orman-made disasters canpartition networks while threatening human-lives. Because conventional Mobile Ad-HocNetworks MANETs cannot route messagesacross partitions, they may not adequatelysupport relief efforts. To forward mes-sages across partitions, delay-tolerant net-works (DTNs) exploit in-network storage andmobility. Previous DTN routing protocols ei-ther opportunistically use, but do not mod-ify, nodes mobility, or require dedicated mo-

bile gateways. This paper contributes a new,cross-layer DTN routing approach based onthe observation that benefits of our approachin a variety of scenarios.

2.5.2 Introduction

Mobile ad-hoc networks MANETs are wire-less networks whose hosts are also routers.In addition to processing their own applica-

tions, MANET nodes forward packets des-tined to other nodes. MANETs enable com-munication when network infrastructure doesnot exist e.g., in military tactical communi-cation or has been damaged or compromisede.g., because of a hurricane or terrorist at-tack. This paper considers the problem ofhow to route packets in sparse MANETs witha leader. In such networks, a distinguishednode, the leader, assigns tasks to and receivesreports from other nodes, the workers.This

work was supported in part by the Secure-CITI project, funded by NSF ITR mediumgrant ANI-0325353. We performed this re-search as part of Secure CITI , an interdis-ciplinary project where computer and social

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scientists have joined forces with the Emer-

gency Operations Manager of the county sur-rounding the City of Pittsburgh to designguidelines and software elements for aidingdecision-making during emergencies. Ourmotivating scenario is an emergency, such asa fire, landslide, or flood. We assume thatemergency-response teams use MANETs tocommunicate and each have a leader e.g., afire chief that schedules the tasks of work-ers e.g., firefighters. In many cases, MANETnodes are sparsely distributed or move such

that end-to-end routes may not always exist.However, most MANET routing algorithmsfail to discover a route or drop packets sentwhen there is no end-to-end path betweensender and receiver. Therefore, MANETsare often unsuitable for hard-real-time sys-tems, but may be useful in soft-real-time sit-uations, such as emergency and disaster re-covery, where meeting as many deadlines aspossible is a goal.

2.5.3 Network and application model

This section describes our assumptions aboutthe network, its applications, and perfor-mance metrics. We assume that the net-work has a leader node and n worker nodes.The leader receives reports and responds tothem by sending task assignments to workers.We consider that each task has an expectedprocessing time and a deadline, and signifi-

cant losses result from deadline misses. Forexample, a beach patrol leader may receivereport of a drowning, and respond by as-signing a cardio-pulmonary resuscitation taskto a lifeguard. This task needs to be per-

formed by a deadline, otherwise a life may

be lost. We assume that, after joining a net-work with a leader, a worker moves or per-forms a task only as result of an assignmentfrom the leader. Therefore, the leader alwaysknows approximately where its workers aresupposed to be. We assume that the leaderand workers have a map of the networks area.The map is annotated with landmarks thatleader and workers can identify and report toeach other, so as to convey approximate po-sition information. Alternatively, the map is

annotated with geographic coordinates thatnodes can match to actual GPS measure-ments. We further assume that assignmentsreceived from the leader may cause the net-work to become partitioned. The leader maysend one or more workers to a site that, whenreached, will lack an end-to-end route to theleader. In such a case, the network is splitbetween the main partition, containing theleader, and a subordinate partition, contain-

ing the remote workers. Nodes within eachpartition communicate with each other us-ing conventional multi-hop routing protocols.When the leader needs to communicate witha worker Ws who is in a subordinate parti-tion, the leader sends a courier assignment toa worker Wm within the main partition. Wmphysically moves between partitions so as tobe able to forward task assignments to Wsand receive reports from Ws or other workersand forward them back to the leader.

2.5.4 Courier scheduling algorithms

Algorithms that we compare in our simula-tions. The leader uses one of these algorithms

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when the leader needs to communicate with

a node in a subordinate partition. The al-gorithms differ in how the leader selects thecourier Wm: random courier This is thebaseline algorithm. It picks Wm randomlyfrom among the workers in the main parti-tion. The main advantage of this algorithmis that it requires only time and does not needinformation about node locations, speeds, orcurrent assignments. dedicated courier Thisalgorithm sets aside ncnodes from the mainpartition for use as couriers. Similarly to

dedicated mobile gateways used in previousworks, such as, dedicated couriers perform noapplication-layer tasks, and only dedicatedcouriers perform courier assignments. Theleader selects the dedicated courier that isclosest to any worker in the destinations par-tition or, in case of a tie, the dedicated courierwith the lowest identifier. If there are O(ns)nodes in the destination partition, selectionof the closest edicated courier by exhaustive

search takes O(ncns) time. closest courierThis algorithm picks as courier the workerWm in the main partition that happens tobe the closest to any worker in the destina-tion partition. If there are O(nm) workers.

2.5.5 Evaluation Model

We implemented the four courier schedulingalgorithms described in the previous sectionin the ns-2 simulator. In this section, we de-

scribe our implementation and report simu-lation results. We describe in this subsectionour implementations data structures, mes-sages, timers, and node behavior in responseto message reception and timeouts. In the

description, we interchangeably use message

for bundle and work order for task assign-ment. The leader uses a graph data struc-ture, Graph, to keep track of network con-nectivity. Each worker reports its position tothe leader every reportPositionInterval. Theleader maintains a list of dispatched couri-ers dispatchedNodes, where a node is insertedwhen it is selected to courier a message andremoved when it returns to its home positionin the main partition. The leader also has alist of dedicated couriers dedicatedCouriers.A

work order is queued at the leader if its as-signed node has been dispatched to couriera message, or there are no reachable couriersto deliver the work order to its destination.The leader maintains a queue pendingOrder-sQueue to hold these pending work orders.PendingOrdersQueue is large enough that itdoesnot overflow. On the other hand, eachcourier nodemaintains a list remoteWorkO-rders of work orders that it has been assigned

to deliver. Workers receive workOrder mes-sages from the leader. Each workOrder mes-sage has a destination node workDestinationas well as a task description, including dead-line and processing time. Upon reception ofa workOrder, a node sends an Ack messageto the sender, which can be the leader or an-other node forwarding the message. Then, itchecks if it is the workDestination. If so, itensures that it has not received the workO-rder message before and that the work order

has not expired. It immediately starts exe-cuting the new task and drops the task beingexecuted. If the node is not the destination ofthe workOrder message, it forwards the mes-sage toward the ultimate workDesti.

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2.5.6 Conclusions

Natural or man-made disasters can disrupt

communications, making rescue and recov-ery missions moredifficult. MANETs havegreat potential for providing connectivity insuch situations, but ordinarily cannot routepackets across network partitions, which arecommon in emergencies. Previous DTNrouting protocols can overcome this limita-tion under certain conditions, such as fa-vorable node mobility patterns or availabil-ity of dedicated mobile gateways.We pro-

pose a new, crosslayer DTN routing approachfor MANETs with leader, such as typicalemergency-response teams. In our approach,the leader schedules workers tasks consid-ering both application- and network-layerneeds. Thus, a worker may be assigned notonly application-layer tasks, but also couriertasks, whose primary purpose is to provideforwarding needed for the networks opera-tion. Our simulations show that cross-layerDTN routing can result in fewer missed dead-

lines and less distance traveled (and conse-quently, greater network uptime) than DTNrouting algorithms that allocate or schedulemobile gateways in disregard of application-layer load.

2.6 Multimedia Applications

for MANETs over Homo-geneous and HeterogeneouMobile Devices

2.6.1 Introduction

Mobile Ad Hoc Networks are considered a vi-tal part in beyond third generation wirelessnetworks Nicopolitidis et al., 2003. In thematter of fact, they present a new wirelessnetworking paradigm. Any sort of fixed in-

frastructure is not used byMANETs. Theyare important sorts of WLANs, therefore,in a distributed and a cooperative envi-ronment, MANETs do efficiently function. MANETs are networks of self-creatingsince there is a lack of routers, configura-tion prior to the network setup, Access Points(APs) and predetermined topology (Wu etal., 2007). MANETs are as well networks ofself-administering and self-organizing. This

is because in the network creation process,there is no application for central control. OnMANETs, it is extremely hard to apply anyof the central administration types, for in-stance, congestion control due to the dynamicnature of the network topology inMANETs,authentication or central routing. In short,several important applications benefited fromMANETs, for example, in military, ubiqui-tous, emergency and collaboration comput-ing. In this chapter, describe the necessary

background for the MANETs over homoge-neous and heterogeneous mobile devices. Theresearcher begin this chapter to introducethe related background and main conceptsof the Mobile Ad Hoc Network (MANETs)

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in Section, and explained briefly about the

existing wireless mobile network approaches,wireless ad hoc networks, wireless mobile ap-proaches in Section. The characteristic ofMANETs are in Section. The types of Mo-bile Ad hoc network in Section. The traf-fic types in ad hoc networks which includethe Infrastructure wireless LAN and ad hocwireless LAN are presented in Section. InSection highlight the relevant details aboutthe ad hoc network routing protocol perfor-mance issues. The types of ad hoc protocols

such as (Table-driven, On-demand and Hy-brid) and Compare between Proactive versusReactive and Clustering versus Hierarchicalrespectively. The existing ad hoc protocolsare presented in Section . The four impor-tant issues significant in MANET are Mobil-ity, QoS Provisioning, Multicasting and Secu-rity is presented in Section Furthermore, thepractical application and the MANET layersare shown in Section.

2.6.2 Overview of MANETs

The main concept of Wireless Local AreaNetworks (WLANs) refers to MANETs whichare also called either infrastructure-basedwireless networks or a single hop networkInside a WLAN, the transmission is gov-erned by at least one fixed Access Point (AP)between different mobile nodes. An exist-ing network backbone and the stations con-

tain a bridge as AP functions (Basagni etal., 2004). Both QoS and security issuesare efficiently controlled by the AP withina particular network. Inside the network ofWLAN, there is no need for different mo-

bile nodes since the AP is the source that

does communication through a single hopmanner. Wireless network standards are in-cluded by the WLAN implementations anddeveloped by Institute of Electrical and Elec-tronics Engineers (IEEE) 802 project (IEEE802.11, IEEE 802.11b, IEEE 802.11g, IEEE802.11a, and IEEE 802.11n) and High Per-formance Radio Local Area Network Type2 (HiperLAN2). In addition, the EuropeanTelecommunications Standardization Insti-tute (ETSI) Broadband Radio Access Net-

works (BRAN) project (ETSI, 1999) devel-oped the European version of IEEE 802.11a.A frequency of 2.4GHz runs for these stan-dards. However, 5GHz runs for the IEEE802.11a. For these standards, the transmis-sion rates (bandwidths) are 2 Mbps where asfor IEEE 802.11a and IEEE 802.11g, 54 Mbpsis run. For IEEE 802.11b, 11 Mbps is run andfor IEEE 802.11n, 100 Mbps is run. Note thata single hop WLAN with one WLAN.

2.7 Probabilistic, ApplicationLayer Service Discoveryfor MANETs and Hybrid

Wired-Wireless Networks

2.7.1 Abstract

Over the past years, Mobile ad-hoc networks(MANETs) have attracted a considerable de-

gree of research attention, with service dis-covery, selection and invocation being amongthe topics of interest of previous efforts. Inthis paper we introduce ADDER, a proba-bilistic, hybrid, directory-less service discov-

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ery mechanism. It has been designed for

military IPv6-based MANETs but will workin any hybrid wiredwireless deployment. Itachieves very low service acquisition timethrough the exchange of a very small num-ber of short messages. Propagation of servicedescriptions is based on a distance vector al-gorithm, achieving loop and starvation free-dom through a feasibility condition, whichhas been adopted from established and well-tested routing protocols. This paper alsopresents evaluation results, obtained by ac-

tual execution of the ADDER daemon ontwo different test beds. The experiments aimto demonstrate that the mechanism achievesgood scalability with increasing number ofservices and network size.

2.7.2 Introduction

In this paper we introduce ADDER, a novel,lightweight and efficient service discovery

(SD) mechanism. It is the outcome of aproject on military ad-hoc networks. Thosenetworks are composed of nodes with highvariance in mobility as well as power sup-ply. For example, foot soldier carry equip-ment with limited power supply, while it canbe assumed that ground vehicles and aircrafthave an on-board energy source which canbe used to power communication equipment.However, vehicles and aircraft are highly mo-bile and often follow unpredictable movement

patterns. With that in mind, we have de-signed ADDER to be energy efficient by lim-iting the size and number of messages ex-changed between nodes. in order to copewith high speeds and mobility, the mecha-

nism has low service acquisition time. Mil-

itary deployments often span across multi-ple ad-hoc partitions (e.g. foot squads) in-terconnected over a wired infrastructure net-work. The resulting diversity in underlyingtechnologies (routing protocols, layer 2 mech-anisms) makes cross-layer approaches unsuit-able. In order to cope with this diversity,ADDER has been designed as an applica-tion layer service. Lastly, ADDER adoptsa loop-free, starvation free forwarding algo-rithm in order to propagate service informa-

tion throughout the network.Additionally, inorder to cope with high speeds and mobil-ity, the mechanism has low service acquisi-tion time. Military deployments often spanacross multiple ad-hoc partitions (e.g. footsquads) interconnected over a wired infras-tructure network. The resulting diversityin underlying technologies (routing protocols,layer 2 mechanisms) makes cross-layer ap-proaches unsuitable. In order to cope with

this diversity, ADDER has been designed asan application layer service. Lastly, ADDERadopts a loop-free, starvation free forwardingalgorithm in order to propagate service infor-mation throughout the network.

2.7.3 Conclusion

We are planning to extend our evaluation ina larger scale wireless test bed. Additionally,comparisons with other approaches are going

to be conducted in a simulated environment,where we can also evaluate ADDER in verylarge scale deployments and validate its be-haviour in mobile scenarios ADDER is cur-rently hybrid; it always operates in reactive

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mode, while proactive mode can be turned on

optionally on all or part of the nodes. As partof our future work, we are planning to makeit adaptive. Proactive mode will be turned onand off automatically at runtime, dependingon node speed, mobility and energy. For ex-ample, on fixed nodes with unlimited supplyof energy, proactive mode will be automati-cally enabled. On the other hand, low poweror high mobility nodes will be able to auto-matically switch off proactive mode withoutuser intervention. Lastly, we are currently in-

vestigating various alternative algorithms forthe adaptation of p over time on a per-servicebasis and evaluating their impact on ADDERsperformance.

3 Mac Layer In Manet

A diversity of possible communication as-sumptions complicates the study of algo-

rithms and lower bounds for radio networks.We address this problem by defining an Ab-stract MAC Layer. This service provides re-liable local broadcast communication, withtiming guarantees stated in terms of a col-lection of abstract delay functions applied tothe relevant contention. Algorithm designerscan analyze their algorithms in terms of thesefunctions, independently of specific channelbehavior. Concrete implementations of theAbstract MAC Layer over basic radio net-

work models generate concrete definitions forthese delay functions, automatically adapt-ing bounds proven for the abstract service tobounds for the specific radio network underconsideration. To illustrate this approach, we

use the Abstract MAC Layer to study the

new problem of Multi-Message Broadcast,a generalization of standard single-messagebroadcast, in which any number of messagesarrive at any processes at any times. Wepresent and analyze two algorithms for Multi-Message Broadcast in static networks: a sim-ple greedy algorithm and one that uses re-gional leaders. We then indicate how theseresults can be extended to mobile networks.

3.1 Selective Bit-error Check-ing at the MAC Layer forVoice Over Mobile Ad HocNetworks

3.1.1 Abstract

Mobile ad hoc networks (MANET) have moresevere operating conditions than traditionalwireless networks. The MAC protocol of

IEEE 802.11 mitigates collisions and ensureserror-free packet transmissions at the costof limiting capacity and increasing latency.For voice transmission over MANETs thiscost should be minimized.We propose andexamine selective error checking (SEC) atthe MAC layer of 802.11 that takes advan-tage of the fact that many of the speechbits can tolerate errors while other bits mustbe protected for effective reconstruction ofthe speech. Simulation results demonstrate

that the network performance and the speechquality are substantially improved by modi-fying the MAC layer with SEC to suit a par-ticular GSM speech compression standard,the Narrow-Band Adaptive MultiRate (NB-

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AMR) coder operating at a rate of 7.95 kbps.

3.1.2 Introduction

A mobile ad hoc network (MANET) is a wire-less LAN (WLAN) wherein mobile nodes cancommunicate with one other without rely-ing on any pre-existing infrastructure. In a

MANET, all the mobile nodes have equalcapabilities and operate not only as hostsbut also as network routers. Communica-tion links might be broken and a dynamicrouting protocol is needed. Dynamic rout-ing requires a nontrivial amount of overheadtraffic on the network to discover changes inthe available paths or to identify on demanda specific route when needed. The efficiencyof the routing protocol and other higher layer

protocols such as IP can indirectly depend onthe underlying medium access control (MAC)protocol. The IEEE 802.11 [1], includes aMAC protocol and a physical (PHY) layerprotocol. The MAC protocol mitigates colli-sions and ensures error-free packet transmis-sions at the cost of limiting capacity and in-creasing latency. Many research efforts haveconcentrated on improving the performanceand capacity of the 802.11 MAC protocolfor data. Also, some studies have focused

on modifying the IEEE 802.11 MAC proto-col to support real-time traffic, such as voice,in MANETs. In general, the performance ofreal-time communication in MANETs can beimproved by reserving bandwidth.

3.1.3 Voice Transmission Over Ad

Hoc Networks

A simple MANET with three colinear nodesis shown in fig. Nodes A and C are outof range for either direction of transmission(e.g., they cannot hear each other, while Aand B and also B and C can hear eachother). For voice communication betweennodes A and C, an intermediate nodeIII.VOICE TRANSMISSION OVER AD HOCNETWORKS A simple MANET with three

colinear nodes is shown in Fig. 1. NodesA and C are out of range for either direc-tion of transmission (e.g., they cannot heareach other, while A and B and also B andC can hear each other). For voice communi-cation between nodes A and C, an interme-diate node is needed to forward the packetand B serves this role here. Let A be thesource node where the speech signal is gen-erated, compressed and packetized with the

UDP/IP protocol stack. The MAC frame inthis case consists of the voice data, the UDPheader, the IP header and the MAC headeras shown in We assume for simplicity herethat the nodes have a fixed location for theduration of a voice call, so they are not cur-rently mobile. However, since the nodes arecapable of mobility, a routing protocol, an es-sential part of any MANET, operates at nodeA to discover node B as the desired nextn-ode. Each successive packet is transmitted

over the wireless medium by the 802.11 physi-cal layer. At node B, the routing protocol andthe 802.11 protocol are involved to identify Cas the next-node (and final destination) anddeliver the packet to C. At the destination

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node C, the received packets are buffered,

reordered as needed, unpacketized, and thevoice data is uncompressed and speech is re-constructed.

3.1.4 Simulation and Results

A network scenario shown in Fig. 2 is ex-amined by NS- 2 simulator [15] in this re-search. The distances between thenodes arechosen so that the nodes are at a hearing dis-tancefrom each other and share the medium.

The data rate of IEEE 802.11 was configuredto be 2 Mbps. In our simulation model, thenodes have no mobility. This is primarily be-cause our interest in this paper is to focus onthe effectiveness of SEC at the MAC layer.Hence, we assume that the network is fixedfor the duration of the voice transmission, yetthe normal overhead traffic due to dynamicrouting protocol is present. Specifically, weuse the destination sequenced distance vec-

tor (DSDV) routing protocol. To evaluatethe effectiveness of the new MAC protocolfor multihop transmission, one voice trans-mission is separately simulated from node 1to A, 1 to B, 1 to C, and 1 to 2. To evalu-ate the effectiveness of the new MAC protocolfor multiple traffic transmission, 1, 2, 3, and 4voice transmissions from node 1 to node B areseparately simulated. The Elliott-Gilbert twostate Markov model [17], [18], shown in fig, isused to model the wireless channel. The bit

errors generated by this model are introducedto MAC frames. In this model, each staterepresents a binary symmetric channel. Biterrors occur with low probability pG in thegood state (G), and bit errors happen with

high probability pB in the bad state (B). pGB

and pBG represent the probability of switch-ing from the good state to the bad state andvice versa. An average link proposed in [19]is used in our simulation where pG = 0, pB= 0.33, pGB = 0.01 and pBG = 0.14. Basedon the Elliott-Gilbert model, this results inan average error probability for this link of0.022. Voice TransmissionFor our simulation,we use 25 seconds of speech, consisting of 4male sentences and 4 female sentences mod-eled as a constant bit rate traffic source with

20 ms of speech for each packet. After thespeech is compressed by the NB-AMR coderat 7.95 kbps, there are 159 bits (20 bytes) fora 20 ms.

3.1.5 Conclusions

In this paper, we proposed the SEC mecha-nism at the IEEE 802.11 MAC layer for voiceover MANETs. We have shown that SECimproves the network performance and en-hances the speech quality. While further re-search is needed to make voice over MANETspractical, it is evident that SEC can be com-bined with many other schemes for voice overMANETs, such as reservation schemes or

high priority schemes, header compression,error concealment and silence compression.SEC is simple to implement and it is effec-tive in conserving bandwidth and reducinglatency for voice communication over manets.

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3.2 AN ENHANCED MAC

PROTOCOL STACK FORMANETs

3.2.1 ABSTRACT

This paper deals with design goals to provideseamless connection to the Internet when mo-bile hosts roam between MANETs and toachieve load-balancing routing when mobilehosts have multiple gateways available. Weaddress three issues in this paper namely

IP address resolution, mobility managementunder NAT structure, and load-balancingrouting. Mobile IP and NAT traversal areadopted to provide seamless roaming capa-bility in private networks. A load-balancingrouting protocol was implemented to relievethe bottleneck problem. A prototype is im-plemented on Windows platform to verify ourarchitecture and test results do show the ben-efit of load-balancing routing.

INTRODUCTION

Due to its flexibility, Mobile Ad Hoc Net-work (MANET) has attracted a lot of atten-tion recently. Most existing works, however,limit a MANET as a stand-alone network. Inthis paper, we propose a multi-tier MANETby extending the connectivity of the MANETto the Internet and voice-networks. Somehosts in the MANET are equipped with cellu-lar interfaces and are called gateways, whichcan provide Internet connections. Such ex-

tension would greatly improve the connec-tivity of MANET. With the advance of em-bedded computing technologies, portable de-vices, such as laptops, Personal Digital As-sistants (PDAs), and cellular phones, have

been widely used. A portable device usu-

ally has several wireless interfaces, such asIEEE 802.11 Wireless LAN (WLAN), Gen-eral Packet Radio Service (GPRS), PersonalHandy-phone System (PHS), and/or Blue-tooth. Wireless communications are typicallysupported in two models: infrastructure andad hoc. Of these two options, forming a mo-bile ad hoc network(MANET) is more flexi-ble since it is independent of the availabilityof base stations. Hence, intensiveresearch hasbeen dedicated to MANET [1, 2]. A MANET

is typically considered as a stand-alone net-work. However, it is important to enable itsInternet accessibility. On one hand, usersin a MANET can enjoy the tremendous re-sources in the Internet. On the other hand,the connectivity between multiple MANETsmay be greatly improved. For such connec-tivity, several works [4, 5, 6, 7] have proposedpossible architectures by deploying gatewaysto help mobile hosts route packets to the In-

ternet. Among these approaches, some takesa proactive approach by modifying DSDV ,some takes a reactive approach by modify-ing AODV, while some takes a hybrid ap-proach. In this paper, we propose a multi-tier MANET architecture in which broad-band WLANs (such as IEEE 802.11 a/b/g)are equipped in all mobile stations to formthe low-tier network, and cellular interfaces(such as GPRS/PHS/3G) are equipped insome stations to form the high-tier network.

Stations with high-tier interfaces are calledgateways and can connect to the Internet.Depending on its service range, each gate-way together with the stations whose Inter-net connections are supported by the gateway

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constitutes a sub-MANET. The MANET un-

der our scope is a collection of multiple sub-MANETs. In this paper, we address severalimportant design issues in MANET architec-ture.

3.2.2 NETWORK ARCHITECTURE

We consider a set of mobile hosts form-ing a MANETs. Each host is equippedwith an IEEE 802.11 WLANcard, andthese interfaces form the low-tier network.

The Destination-Sequenced Distance Vector(DSDV) routing protocol [3], which adopts aproactive approach, is used on the low-tiernetwork. A number of hosts are designatedas gateways. Each gateway host is equippedwith an extra cellular interface, such as PHSor GPRS, which enables the host to accessinfrastructure networks (and thus the Inter-net). Cellular interfaces with Internet accesscapability form the high-tier network. Note

that these interfaces can be heterogeneous.The MANET can be physically connected(through the low- or high-tier network) ordisconnected. Each gateway together withthe stations whose Internet connections aresupported by it is called a sub-MANET. Aset of stations that forms a connected com-ponent but does not have a gateway inside isdisconnected from the MANET and is not al-lowed to connect to the Internet. When thenetwork topology changes or then gateways

change their points of attachment, handoffprocedure may be taken. To support seam-less roaming, we adopt Mobile IP with the co-located address mode [8]. Hosts rely on theirhome agents to maintain their connections

while roaming. Note that the high-tier inter-

faces may also use private IP addresses, mak-ing traditional Mobile IP unusable. Severalsolutions [9, 10, 11] have been proposed tosupport IP mobility under private networks.We apply the NAT traversal mechanism [9] toachieveseamless roaming in private networks.

3.2.3 PROTOCOL DESIGN

Our design goal is to provide seamless con-nection to the Internet when mobile hosts

roam between MANETs and to achieve load-balancing routing when mobile hosts havemultiple gateways available. Weaddress threeissues: IP address resolution, mobility man-agement under NAT structure, and load-balancing routing. However, the full treat-ment of each of these issues is beyond thescope of this paper.

A DHCP server is installed in each gate-way. Before communicating with other hosts,

a mobile host needs to retrieve an IP addressfrom a gateway. To avoid confusion, we as-sign an exclusive section of IP addresses toeach DHCP server. Note that we also allowa host to use its old IP address after roaminginto a new sub-MANET. When a new mobilehost n joins the MANET, it first broadcastsa DHCPdiscover.

3.2.4 CONCLUSION

In the literature, most works consider aMANET as a stand-alone network. In thispaper, we design a multitier MANET, con-sidering gateways as bridges to the Inter-net. This greatly improves the connectivity

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of MANET because cellular networks nowa-

days are almost globally available. How-ever, Internet connectivity does cause sev-eral problems: address configuration, connec-tion maintenance when roaming, and traf-fic bottleneck on gateways. In this paper,we show how to configure a MANET as aprivate network and modify DHCP to avoidpossible broadcast storms. Mobile IP andNAT traversal are adopted to provide seam-less roaming capability in private networks.A load-balancing routing protocol was imple-

mented to relieve the bottleneck problem. Aprototype is implemented on Windows plat-form to verify our architecture and testingresults do show the benefit of load-balancingrouting

3.3 A novel efficient power-saving MAC protocol for

multi-hop MANETs

3.3.1 INTRODUCTION

Following recent improvements in the per-formance of wireless communication sys-tems, mobile ad hoc networks (MANETs) [1]have become increasingly important in in-creasingly wide range of applications, suchas battlefields and other military environ-ments, disaster areas, and outdoor activities.AMANET is a multi-hop wireless networkthat is formed dynamically from an accu-

mulation of mobile nodes without the assis-tance of a centralized coordinator. As theradio propagation range is limited, each mo-bile node has only limited information, suchas its own ID and the Medium Access Con-

trol (MAC) address of its one-hop neigh-

bors. Therefore, if two nodes are not withinthe radio propagation range, a multi-hop,via one or more intermediate nodes, is re-quired to forward packets. The forward func-tion of each intermediate node consumes timeand resources, such as power and bandwidth.However, a mobile node has limited power.This study addresses the maximization ofthe lifetime of mobile nodes through variousmechanisms. The power consumption of abattery in a mobile node must be minimized

to maximize its lifetime [2, 3]; otherwise, thebattery may quickly run out of power, mak-ing the mobile node useless. The operatingstates of a network interface can be catego-rized into transmit, receive, idle, and sleepstates, and the estimated power consumptionof each state is as presented in Table I. Aninterface in the sleep state can neither trans-mit nor receive any packets, and thus thisstate consumes the lowest power. To be able

to transmit and receive packets, an interfacemust be woken up. A mobile node that isawake, but neither transmitting nor receiv-ing data, is said to be idle. A node consumesthe most power when it is in the awake state.Therefore, the proposed power-efficient pro-tocol depends on mobile nodes staying in thesleep state most of the time, unless data haveto be transmitted. The reduction of powerconsumption by MANETs has been studiedwidely. Existing powersaving MAC proto-

cols can be classified into two categoriessyn-chronous wake up approaches [48] and asyn-chronous wake up approaches [1015]. In syn-chronous wake up approaches, all nodes mustexecute a clock synchronization mechanism

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[4, 1620]. Asynchronous wake up approaches

require no such synchronization mechanism.However, the neighbor discovery time is themost important issue in asynchronous wakeup approaches. They must adjust the over-lap of a nodes wake up time with that of itsneighbors, resulting in increased power con-sumption and long transmission delay. Thus,this study focuses on the synchronous wakeup approach.

3.3.2 PRELIMINARIES

Various power-saving protocols for IEEE802.11 wireless local area network have re-cently been proposed. This section brieflyreviews several power-saving protocols [415]and discusses some of the problems asso-ciated with MANETs, as the synchronouspower-saving approaches, which require aneffective time synchronization mechanism, isconsidered. Section 2.2 also reviews nu-

merous time synchronization mechanisms [4,1620].reviews of power-saving protocols Syn-chronous wake up approaches. The mostwell-known synchronous wake up powersav-ing protocol is the IEEE 802.11 standard [4],which was originally designed for single-hopad hoc networks. As shown in Figure 1, timeis divided into beacon intervals. In the PSMof the IEEE 802.11 standard, all nodes aresynchronized by transmitting beacon framesto one-hop neighbors at the beginning of the

beacon interval. After the beacon frame hasbeen sent, the node sends an ad hoc Traf-fic Indication Map (ATIM) frame to informother nodes that it has packets that are wait-ing to be transmitted during the ATIM win-

dow. Upon receiving an ATIM-ACK frame

from the destination node, a node obtainsthe right of transmission and begins to trans-mit data immediately after the ATIM win-dow ends. Both sender and destination nodesare awake during the transmission period.Otherwise, at the end of ATIM window, anode enters the power-saving state. IEEE802.11 PSM has been extended to multi-hopMANETs [5], to activate paths, minimize de-lay, and conserve energy. However, the pro-posed synchronization strategy, routing strat-

egy, and power management capability de-pend on extra support from MAC layer. Ad-ditionally, the potential problem of networkpartitioning has not been addressed. Span[6] is based on the notion of a dominating setand extends the sleep time of mobile hoststo reduce power consumption. Span adap-tively elects coordinators to generate a con-nected domination set; they are kept awakeat all times to perform low-latency multi-hop

routing. Other noncoordinators go throughperiodic cycles of sleep and wakefulness andperiodically check whether they should wakeup and become coordinators. Although Spanguarantees efficient energy consumption andlow delay latency in dense networks, it hastwo limitations. One is that coordinatorsmust remain active at all times, broadcastingHELLO messages to maintain the backbone,increasing the overhead. The other is itssynchronization overhead. Special-purpose

methods for reducing power consumption ofMANETs have been proposed [7, 8]. A nodecan power down during its natural silent pe-riods [7]: when a node does not expect totransmit, receive, or relay packets, it can

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power off its network interface. Traffic aware

PSM (TA-PSM) [8] also achieves good per-formance with a light traffic load. TA-PSMallows the node directly to enter the dozestate when it does not need to transmit orreceive packets, even if a beacon or ATIMframe has to be sent. Instead of entering theidle state of IEEE 802.11 PSM, the node en-ters a doze state to save more power. How-ever, such approaches depend on the mon-itoring of traffic at each node to guaranteetransmission throughput and low transmis-

sion latency. Hence, these approaches maybe not suitable for heavy traffic scenarios.

3.3.3 CONCLUSIONS AND FU-TURE WORK

Power conservation is very important toprolong the battery life of important de-

vices. This work proposed a novel effi-cient power-saving MAC protocol for multi-hop MANETs, called p-MANET. p-MANETconsists of three mechanismsthe hibernationmechanism to prevent the consumption ofpower for unnecessary tasks, the beacon inhi-bition mechanism solves beacon storm prob-lem, and the low-latency next hop selectionmechanism offers heuristic strategies to se-lect efficiently the next-hop node for packetforwarding. To confirm the effectiveness of p-

MANET, we present the theoretical analysisrelated to p-MANET concerning the averageawake time and average delay time. And ex-tensive simulations were performed, and theresults revealed a power saving of over 70

3.4 MAC Improvements for

MANET

3.4.1 ABSTRACT

Broadcasting is one of the essential commu-nication models of MANETs. Many MANETmulticast routing protocols rely heavily uponMAC layers broadcast support. However,

the broadcast mechanism of the standardIEEE 802.11 cannot provide reliable broad-casting service. In this paper, we improvethe IEEE 802.11 broadcast mechanisms reli-ability by introducing the new layer of MACcalled Dual MAC. Multihop ad-hoc wire-less networks offer great challenges for pro-tocol designers. Stations in such networksare constrained by factors like low power,limited bandwidth, link errors, and colli-

sions. Changes are needed at various levels ofthe protocol stack, most importantly at themedium access layer (MAC). The mediumaccess mechanism in multihop wireless net-works should minimize collisions, and takecare of the hidden and exposed node prob-lems. The IEEE 802.11 MAC with Dis-tributed Coordination Function (DCF) doesnot scale well in such networks. We intro-duce Point Coordination Function (PCF) inthe region of high traffic areas, and discuss its

effect on network performance. To improvenetwork scalability and throughput, we pro-pose the design of a new MAC called DualMAC. This work discusses architecture andworking of the dual MAC in detail.

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3.4.2 INTRODUCTION

In recent times, the wireless networks havebecome very popular.Wireless LANs are be-ing deployed on airports, conferences, etc.People have started using portable laptopsto access Internet and other resources us-ing wireless networks while moving. Anotherarea which has generated a lot of interest re-cently, is wireless adhoc networks. An ad-hoc network is formed when two or more sta-tions come together form an independent net-

work. Ad-hoc networks are also termed asinfrastructure-less networks since as they donot require any prior infrastructure. Two sta-tions that are within transmission range ofeach other are called one hop neighbors. Mul-tihop ad-hoc networks are ones in which thestations can talk to stations more than onehop away via intermediate stations. Cooper-ative ad-hoc networks are formed by severalhomogeneous wireless stations. All the sta-

tions cooperate with each other, i.e., the traf-fic for the stations that are more than one hopaway is routed by the intermediate stations.The intermediate stations are called relayingstations If the channel is still idle at the endof the CONTENTION period the node trans-mits its packet otherwise it repeats the pro-cess defined in 3 above until it gets a freechannel. Key: D = DCF Inter Frame Space(DIFS) S = Short Inter Frame Space (SIFS)CW = Contention Window MPDU = MAC

Protocol Data Unit A = Ack 802 11 also of-fers a polling mode (known as PCF - PointCoordination Function) which is fairly classicpolling scheme e.g. 3270 bi-sync!! As with allpolling protocols a single master (Base Sta-

tion) is required.

3.4.3 ORIGINAL MAC

The basic 802.11 MAC layer uses the Dis-tributed Coordination Function (DCF) toshare the medium between multiple sta-tions. DCF relies on CSMA/CA and optional

802.11 RTS/CTS to share the medium be-tween stations. This has several limitations:If many stations communicate at the sametime, many collisions will occur, which willlower the available bandwidth (just like inEthernet, which uses CSMA/CD)The origi-nal 802.11 MAC defines another coordinationfunction called the Point Coordination Func-tion (PCF): this is available only in infras-tructure mode, where stations are connected

to the network through an Access Point (AP).This mode is optional, and only very fewAPs or Wi-Fi adapters actually implementit. APs send beacon frames at regular in-tervals (usually every 0.1 second). Betweenthese beacon frames, PCF defines two peri-ods: the Contention Free Period (CFP) andthe Contention Period (CP). In CP, the DCFis simply used. In CFP, the AP sends Con-tention Free-Poll (CF-Poll) packets to eachstation, one at a time, to give them the right

to send a packet. The AP is the coordina-tor. This allows for a better management ofthe QoS. Unfortunately, the PCF has limitedsupport and a number of limitations (for ex-ample, it does not define classes of traffic).

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4.1 A Novel security frame-

work for protecting Net-work Layer operations

Mobile ad hoc network (MANET) is a typeof wireless ad hoc network, and is a self-configuring network of mobile devices con-nected by any number of wireless links. Everydevice in a MANET is also a router becauseit is required to forward traffic unrelated toits own use. Each MANET device is free tomove independently, in any arbitrary direc-

tion, and thus each device will potentiallychange its links to other devices on a regu-lar basis. Such networks extend the limitedwireless transmission range of each node by-multihop packet forwarding. Security is onecrucial requirement for these mission-criticalapplications. In particular, in MANET, anynode may compromise the routing protocolfunctionality by disrupting the route discov-ery process.

4.1.1 Abstract

The important security issue in mobile ad hocnetworks is to protect the routing layer frommalicious attacks. A unified security solutionfor such networks is applied to protect bothrouting and data forwarding operations in therouting layer. In this paper the proposedmodel does not apply he cryptographic prim-itives on the routing messages This model

protects the network by detecting and iso-lating the malicious nodes. In this proposedmodel, every node is monitoring other near-est neighboring nodes. A novel recognitionstrategy is applied to decrease its overhead

as time evolves. In the proposed model infor-

mation cross-validation is used to protect thenetwork in a self-organized manner. Throughboth analysis and simulation results, the ef-fectiveness of proposed model in a MANETenvironment is demonstrated.

4.1.2 INTRODUCTION

Mobile ad hoc network (MANET) is a typeof wireless ad hoc network, and is a self-configuring network of mobile devices con-

nected by any number of wireless links. Everydevice in a MANET is also a router becauseit is required to forward traffic unrelated toits own use. Each MANET device is freeto move independently, in any arbitrary di-rection, and thus each device will potentiallychange its links to other devices on a regularbasis. Such networks extend the limited wire-less transmission range of each node bymulti-hop packet forwarding. Security is one crucial

requirement for these mission-critical appli-cations. In particular, in MANET, any nodemay compromise the routing protocol func-tionality by disrupting the route discoveryprocess. In this paper, an important securityissue is tackled in ad hoc networks, namelythe protection of their network-layer opera-tions from malicious attacks. Without ap-propriate protection, the malicious nodes canreadily function as routers and prevent thenetwork from correctly delivering the pack-

ets. For example, the malicious nodes canannounce incorrect routing updates which arethen propagated in the network, or drop allthe packets passing through them. A pro-posed model is used to protect both routing

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and packet forwarding together. The research

directions towards security in MANETs arestill at their infancy. Security issues arise inmany different areas including physical secu-rity, key management, routing and intrusiondetection, many of which are vital to a func-tional MANET. Due to their particular ar-chitecture, ad-hoc networks are more easilyattacked than wired network. There are twokinds of attacks: the passive attacks and theactive attacks. A passive attack does not dis-rupt the operation of the protocol, but tries

to discover valuable information by listeningto traffic. Instead, an active attack injectsarbitrary packets and tries to disrupt the op-eration of the protocol in order to limit avail-ability, gain authentication, or attract pack-ets destined to other nodes. The routing pro-tocols in MANET are quite insecure becauseattackers can easily obtain information aboutnetwork topology. Indeed in AODV and DSRprotocols, the route discovery packets are car-

ried in clear text. So a malicious node can dis-cover the network structure just by analyzingthis kind of packets and may be able to de-termine the role of each node in the network.With all these information more serious at-tacks can be performed in order to disturbthe network operation by isolate importantnodes, etc. The attacks in modification andimpersonation are: One of the simplest waysfor a malicious node to disturb the good op-eration of an ad-hoc network is to announce

better routes (to reach other nodes or just aspecific one) than the other nodes.

4.1.3 SIMULATION RESULTS AND

ANALYSISIn this section, the performance of proposedmodel is evaluated through extensive simula-tions. The simulation methodology is startedand performance metrics is evaluated. Theresults show that proposed model is effec-tive in protecting the network layer of ad hocnetworks even in a highly mobile and hostileenvironment. The proposed model is imple-mented in the ns-2 simulator. Performance

evaluations are based on the simulations of100 wireless nodes that form an ad hoc net-work over a rectangular (3000 m 600 m) flatspace in 1500 s of simulation time. Thephysical layer at each networking interfaceis chosen to approximate the Lucent WaveLAN wireless card. The MAC layer protocoland the routing protocol are 802.11 DCF andmodified AODV protocol, respectively. Animproved version of random waypoint model,which is recently proposed as the mobility

model. Set the minimum speed for each nodeas 2 m/s except for the static network case,and vary the maximum speed to evaluate theimpact of node mobility on proposed modelperformance. The pause time is set to 0 tosimulate an ad hoc network in which nodesare constantly roaming. Before the simula-tion runs, randomly select a certain fraction,ranging from 0

4.1.4 CONCLUSION

One fundamental challenge for security de-sign in mobile ad hoc networks is the absenceof any preexisting infrastructure support.

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This work explores a novel self-organized ap-

proach to securing such networks. To thisend, we have presented a proposed model, anetwork-layer security solution that protectsrouting and forwarding operations in a uni-fied framework. This model exploits local-ized collaboration to detect and react to se-curity threats. All nodes in a local neigh-borhood collaboratively monitor each otherand sustain each other, and no single nodeis superior to the others. The proposed de-sign is self-organized, distributed, and fully

localized. Both analysis and simulations re-sults have confirmed the effectiveness and ef-ficiency of the proposed framework in pro-tecting the network layer in mobile ad hocnetworks.

4.2 Network Layer Attacks andDefense Mechanisms

4.2.1 ABSTRACT

The foremost concerned security issue in mo-bile ad hoc networks is to protect the net-work layer from malicious attacks, therebyidentifying and preventing malicious nodes.A unified security solution is in very muchneed for such networks to protect both routeand data forwarding operations in the net-work layer. Without any appropriate securitysolution, the malicious nodes in the networkcan readily act to function as routers. This

will solely disturb the network operation fromcorrect delivering of the packets, like the ma-licious nodes can give stale routing updates ordrop all the packets passing through them. Inthis paper a study that will through light on

such attacks in MANETS is presented The

paper also focuses on different security as-pects of network layer and discusses the ef-fect of the attacks in detail through a surveyof approaches used for security purpose.

4.2.2 INTRODUCTION

Mobile ad hoc network (MANET) is a typeof wireless ad hoc network, and is a self-configuring network of mobile devices con-nected by any number of wireless links. Each

device in a MANET is free to move inde-pendently in any direction, and will there-fore change its links to other devices fre-quently. Each must forward traffic unre-lated to its own use, and therefore be arouter. The primary challenge in buildinga MANET is equipping each device to con-tinuously maintain the information requiredto properly route traffic. Such networks mayoperate by themselves or may be connected

to the larger Internet. Many academic pa-pers evaluate protocols and abilities assumingvarying degrees of mobility within a boundedspace, usually with all nodes within a fewhops of each other and usually with nodessending data at a constant rate, packet droprate, the overhead introduced by the rout-ing protocol, and other measures. Security isan essential service for wireless network com-munications. However, the characteristicsof MANETS pose both challenges and op-

portunities in achieving security goals, suchas confidentiality, authentication, integrity,availability, access control, and nonrepudia-tion [1]. The countermeasures can be con-sidered as features or functions that reduce

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or eliminate security vulnerabilities and at-

tacks. First, in this paper an overview of net-work layer attacks is given, and then the secu-rity counter measures. Since in MANETS thenodes dynamically set up paths among them-selves to transmit the packets, it is referredas infrastructure less network. The nodes inMANET can communicate directly if theyare in within each others wireless transmis-sion ranges otherwise they have to rely onsome other nodes to transmit messages ifthe nodes are outside each others transmis-

sion range [2]. Thus, several intermediatehosts relay the packets which are sent by thesource host before they reach the destinationhost, which in turn leads to a multi-hop sce-nario I.e. each node, will act as a router.The nodes cooperation is very much impor-tant for a successful communication. Thus,a MANET has several salient characteristics[3]: dynamic topologies, resource constraints,limited physical security, and no infrastruc-

ture. Possible applications of MANET in-clude: Soldiers relaying information for sit-uational awareness on the battlefield, busi-ness associates sharing information during ameeting; attendees using laptop computersto participate in an interactive conference;and emergency disaster relief personnel co-ordinating efforts after a fire, hurricane, orearthquake [1]. The other possible applica-tions [2] include personal area and home net-working, location-based services, and sensor

networks. There are a wide variety of at-tacks that target the weakness of MANETS.For example, routing messages are an impor-tant component of mobile network communi-cations, as each packet needs to be passed

quickly through intermediate nodes, which

the packet must traverse from a source to thedestination. Malicious routing attacks cantarget the routing discovery or maintenancephase by not following the specifications ofthe routing protocols. There are also attacksthat target some particular routing protocols,such as DSR, or AODV [4] [5]. More sophis-ticated and subtle routing attacks have beenidentified in recent published papers, such asthe black hole (or sinkhole) [6], Byzantine [7],and wormhole [8] [9] attacks. Currently rout-

ing security is one of the hottest research ar-eas in MANET, so only the research initiativeis taken for a specific layer like network layerin OSI model [1]. This paper is organized asfollows. In Section 2, description about thenetwork layer attacks is given. In Section 3,proposed solutions for the different networklayer attacks are discussed, including multi-layer attacks. In section 4, a discussion onopen challenges and future directions is given.

4.2.3 NETWORK SECURITY AT-TACKS

The connectivity of mobile nodes over a wire-less link in MANETS which is multihop in na-ture strongly relies on the fact that ensurescooperation among the nodes in the network.Since network layer protocols forms connec-tivity from one hop neighbors to all othernodes in MANET, the assurance of cooper-

ation among nodes is required. Recently va-riety of network layer targeted attacks havebeen identified and heavily studied in re-search papers. As a consequence of attackingnetwork layer routing protocols, adversaries

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can easily disturb and absorb network traffic,

inject themselves into the selected data Thepackets in the network traffic could be for-warded to a suboptimal path or to a not ex-isting path, which introduces significant de-lay and packet losses in the network. Theadversaries send some fictitious routing up-dates to create routing loops or to introducesevere congestion in some portions of the net-work or to make some parts of the networkinaccessible. The main effect of the presenceof malicious nodes in the network is exces-

sive network control traffic which intensifiesthe network congestion and as a result theperformance of the network degrades. Theprinciple idea behind this paper is to evalu-ate what security measures have been consid-ered till date for identification of maliciousnodes and preventing them in the network.Through a relative study, it can be revealedthe research work carried using different cryp-tographic techniques considered for the se-

curity purposes to avoid malicious nodes inMANETS. Finally it can be concluded witha note that what precautions can be appliedto ensure confidentiality and integrity in thenetwork to upgrade the network performance.

4.2.4 Network Layer Attacks Descrip-tion

Black hole Attack: In routing mechanism ofad hoc networks three layers namely physi-

cal, MAC and network layers plays a majorrole. As MANETs are more vulnerable tovarious attacks, all these three layers sufferfrom such attacks and cause routing disor-ders. The variety of attacks in the network

layer differs such as not forwarding the pack-

ets or adding and modifying some parametersof routing messages; such as sequence num-ber and hop count. The most basic attackexecuted by the nodes in the network layeris that an adversary can stop forwarding thedata packets. The consequence caused bythis is that, whenever the adversary is se-lected as an intermediate node in the selectedroute, it denies the communication to takeplace. Most of the times the black hole at-tack is launched by the adversaries, whenever

AODV is used as the data forwarding proto-col. Consider a malicious node which keepswaiting for its neighbors to initiate a RREQpacket. node receives the RREQ packet, itwill immediately send a false RREP packetwith a modified higher sequence number. So,that the source node assumes that node ishaving the fresh route towards the destina-tion. The source node ignores the RREPpacket received from other nodes and be-

gins to send the data packets over maliciousnode. A malicious node takes all the routestowards itself. It does not allow forwardingany packet anywhere. This attack is called ablack hole as it swallows all the data packets[13] [14]. Gray hole Attack: A variation ofblack hole attack s is the gray hole attack, inwhich nodes either drop packets selectively(e.g. dropping all UDP packets while for-warding TCP packets) or drop packets in astatistical manner (e.g. dropping 50

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4.2.5 DEFENSE AGAINST NET-

WORKLAYER ATTACKS

The previous section reveals the possibilityof various attacks on the network layer andnow the focus is on the several security mea-sures taken to overcome these attacks. Asit is a known fact, cryptography is one ofthe most common and reliable means to en-sure security in MANETS. The main no-tions for cryptography are confidentiality, in-tegrity, authentication and non-repudiation.

The cryptography is discussed in detailedin. MANETS have certain challenges in keymanagement due to lack of infrastructure, ab-sence of dedicated routers and mobility ofnodes, limited processing power and limita-tion of battery power, bandwidth and mem-ory. The main requirement to ensure securityin MANETS is to have a secure routing pro-tocol which should have properties to detectmalicious nodes, guarantee of exact route dis-

covery process, maintaining confidential net-work topological information and to be self-stable against attacks. SAR (Secure-AwareAd Hoc Routing protocol), which defines alevel of trust as a metric for routing and asan attribute for security for routing. SARusing AODV uses encryption and decryptionprocess using a common key. The main draw-back with SAR protocol is whenever the lev-els of security rise; it needs different keys fordifferent levels, thereby increasing the num-

ber of keys . SEAD (Secure Efficient Ad HocDistance Vector Routing protocol) is mainlydesigned for DSDV (Destination-SequencedDistance Vector). This protocol can over-come DoS, all types of routing attacks and

resource consumption attacks. It uses one-

way hash function without the usage of asym-metric cryptographic mechanism. The mech-anism uses authentication to differentiate be-tween malicious and non-malicious nodes,which in turn reduces resource consumptionattacks launched by malicious nodes. SEADavoids routing loops, but the drawback lieswhenever the attacker uses the same metricand sequence number used for authenticationwere same by the recent update message andupdates with new update message. The re-

search update message from this mechanismis that it can also be used for other distancevector routing protocols.

4.3 A Robust Approach to De-tect and Prevent Network

Layer Attacks in MANETS

4.3.1 Abstract

A dynamic wireless network that is formedwithout any pre-existing infrastructure, inwhich every node can act as a router is calleda mobile ad hoc network (MANET). SinceMANETS has not got clear cut security pro-visions, it is accessible to any of the au-thorized network users and malicious attack-ers. The greatest challenge for the MANETSis to come with a robust security solutioneven in the presence of malicious nodes, sothat MANET can be protected from var-

ious routing attacks. Several countermea-sures have been proposed for theseroutingattacks in MANETS using various crypto-graphic techniques. But most of these mech-anisms are not considerably suitable for the

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resource constraints, i.e., bandwidth limita-

tion and battery power, since they results inheavy traffic load for exchanging and verifi-cation of keys. In this paper, a new semanticsecurity solution is provided, which suits forthe different MANET constraints and also isrobust in nature, since it is able to identifyand prevent four routing attacks parallelly.The experimental analysis shows the identifi-cation and prevention of the four attacks par-allelly I.e., packet dropping, message tamper-ing, black hole attack and gray hole attack.

4.3.2 INTRODUCTION

A MANET has got some of the importantproperties like self organized and rapid de-ployable capability; which makes it widelyused in various applications like emergency

operations, battlefield communications, re-lief scenarios, law enforcement, public meet-ing, virtual class rooms and other security-sensitive computing environments. Thereare several issues in MANETS which ad-dresses the areas such as IP addressing, ra-dio interference, routing protocols, powerConstraints, security, mobility management,bandwidth constraints, QOS, etc;. As ofnow some hot issues in MANETS can be re-lated to the routing protocols, routing at-

tacks, power and bandwidth constraints, andsecurity, which have raised lot of interest inresearchers. Even though in this paper weonly focus on the routing attacks and secu-rity issue in MANETS.

4.3.3 A Distributed Security Scheme

Reliable network connectivity in wireless net-works is achieved if some counter measuresare taken to avoid data packet forwardingagainst malicious attacks. A lot of researchhas taken place to avoid malicious attackerslike, a Survey on MANET Intrusion Detec-tion, Advanced Detection of Selfish or Mali-cious Nodes in Ad hoc Networks , DetectingNetwork Intrusions via Sampling : A GameTheoretic Approach , Collaborative security

architecture for black hole attack preventionin mobile ad hoc networks , A DistributedSecurity Scheme for Ad Hoc Networks [6],Wormhole attacks detection in wireless adhoc networks: a statistical analysis approach[12], Enhanced Intrusion Detection Systemfor Discovering Malicious Nodes in MobileAd Hoc Networks Detection and Accusationof Packet Forwarding Misbehavior in MobileAd- Hoc networks WAP: Wormhole Attack

Prevention Algorithm in Mobile Ad Hoc Net-works A Reliable and Secure Fra1mework forDetection and Isolation of Malicious Nodes inMANET Secure Routing Protocol with Mali-cious Nodes Detection for Ad Hoc Networks(ARIADNE) A Cooperative Black hole NodeDetection Mechanism for ADHOC NetworksMalicious node detection in Ad Hoc networksusing timed automata Addressing Collabora-tive Attacks and Defense in Ad Hoc WirelessNetworks dpraodv: a dynamic learning sys-

tem against black hole attack in aodv basedmanet and Performance Evaluation of theImpact of Attacks on Mobile Ad hoc Net-works . All these research work reveals thata single or to a maximum of two or three

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attacks identification and prevention using

some approach is considered. Our solutionto this research gap is to provide a semanticsecurity scheme that considers a minimum of4 attacks identification and prevention par-allelly using a simple acknowledgement ap-proach. The above related study justifiesthat, the proposed scheme is not consideredanywhere and is a new security solution fornetwork layer attacks. The reason to con-centrate on network layer attacks because; aswe know a MANETS network connectivity is

mainly through the link-layer protocols andnetwork-layer protocols. The Link-layer pro-tocols are used to ensure one-hop connectiv-ity while network-layer protocols extend thisconnectivity to multiple hops [2]. So only toincorporate MANETS security we can con-sider two possible counter measures namely,link-layer security and network-layer security.Link-layer security is to protect the one-hopconnectivity between two adjacent nodes that

are within each others communication rangethrough secure protocols, such like the IEEE802.11 WEP protocol [3] or the more re-cently proposed 802.11i/WPA protocol . Thenetwork-layer security mainly considers fordelivering the packets between mobile nodesin a secure manner through multihop ad hocforwarding. This ensures that the routingmessage exchange within the packets betweennodes is consistent with the protocol specifi-cation. Even the packet forwarding of every

node is consistent with its routing states. Ac-cordingly, the protocols are broadly classifiedin to two categories: secure ad hoc routingprotocols and secure packet forwarding pro-tocols. The paper mainly discusses about the

network-layer security.

4.3.4 PROPOSED APPROACH

The routing attacks like black hole, grayhole, worm hole, rushing attack, DOS at-tack, flooding etc; can become hazardous tothe network-layer protocol which needs to beprotected. Further the malicious nodes maydeny forwarding packets properly even theyhave found to be genuine during the routingdiscovery phase. A malicious node can pre-

tend to join the routing correctly but latergoes on ignoring all the packets that passthrough it rather than forwarding them. Thisattack is called black hole, or selective for-ward of some packets is known as grey holeattack. The basic solution needed to resolvethese types of problems is to make sure thatevery node in a network forwards packetsto its destination properly. To ensure thiskind of security to network layer in MANETS

a new secure approach which uses a simpleacknowledgement approach and principle offlow conservation is proposed here. As a partof this research work we have tried the same.

4.3.5 CONCLUSION AND FUTUREWORK

In mobile ad hoc networks, protecting thenetwork layer from attacks is an importantresearch topic in wireless security. This pa-

per describes a robust scheme for network-layer security solution in ad hoc networks,which protects both, routing and packet for-warding functionalities without the contextof any data forwarding protocol. This ap-

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proach tackles the issue in an efficient manner

since four attacks have been identified paral-lelly. The overall idea of this algorithm isto detect malicious nodes launching attacksand misbehaving links to prevent them fromcommunication network. This work exploresa robust and a very simple idea, which can beimplemented and tested in future for morenumber of attacks, by increasing the num-ber of nodes in the network. To this end,we have presented an approach, a network-layer security solution against attacks that

protects routing and forwarding operations inthe network. As a potential direction for fu-ture work, we are considering measurement ofmore number of network parameters, to ana-lyze the performance of such a network usingthe proposed approach.

4.4 Network Layer Attacksand Defense Mechanisms inMANETS- A Survey

4.4.1 ABSTRACT

The foremost concerned security issue in mo-bile ad hoc networks is to protect the networklayer from malicious attacks, thereby identi-fying and preventing malicious nodes. A uni-fied security solution is in very much need forsuch networks to protect both route and dataforwarding operations in the network layer.Without any appropriate security solution,

the malicious nodes in the network can read-ily act to function as routers. This will solelydisturb the network operation from correctdelivering of the packets, like the maliciousnodes can give stale routing updates or drop

all the packets passing through them. In this

paper a study that will through light on suchattacks in MANETS is presented. The pa-per also focuses on different security aspectsof network layer and discusses the effect ofthe attacks in detail through a survey of ap-proaches used for security purpose.

4.4.2 INTRODUCTION