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QUALITY OF SERVICE IN MOBILE AD HOC NETWORK

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QUALITY OF SERVICE IN MOBILE AD HOC NETWORK

SYNOPSIS

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This project represents a literature study on the requirements of Quality of Service in Mobile Ad-Hoc Networks (MANETs) which is universally growing area. A Mobile Ad-hoc Network is a collection of mobile devices which form a communication network with no pre-existing infrastructure. MANETs were initially proposed for use in military and battle field, due to rapid expansion of Multimedia Technology, Mobile Technology, and real time applications has need to strictly support Quality of Service(such as throughput, delay, energy consumption, jitter etc). Due to the dynamic topology and bandwidth constraints, supporting QoS is a challenging task.

This project presents the description about the QoS and the issues of MANETs like Routing, Medium(or channel) Access, Mobility Management, Security and Reliability and Power Consumption and the Routing Protocols and their comparison study and also the current approaches including models and solution strategies.

Keywords:-Mobile Ad-hoc Networks (MANETs), Quality of Service (QoS).

CONTENTS

Chapter – 1 Introduction

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1.1. Overview (Basic Concepts on Mobile Ad hoc Network)1.1.1. Mobile Computing1.1.2. Computer Network

1.1.2.1. Wired Network vs. Mobile Network1.1.2.2. Wireless Network

1.2. Mobile Ad hoc Network (MANET)s1.2.1. Characteristics of MANETs1.2.2. Types of MANETs1.2.3. Some Issues of MANET1.2.4. Applications of MANET

Ch apter – 2 Quality of Service (QoS)

2.1The Need for QoS in MANET2.2 QoS Metrics2.3Types of QoS 2.4 How to maintain QoS in MANET

Chapter – 3 QoS Routing

3.1 Routing3.1.1 Routing Protocol/Algorithm3.1.2 Conventional Routing Protocols

3.1.2.1 Link State3.1.2.2 Distance Vector3.1.2.3 Source Routing3.1.2.4 Flooding

3.2 Classification3.2.1 Proactive vs. Reactive Routing3.2.2 Single Path vs. Multi path3.2.3 Table-driven vs. Source Initiated3.2.4 Source Routing vs. Hop-by-hop Routing3.2.5 Full/Limited/Local Broadcast3.2.6 Periodic vs. Event-driven3.2.7 Flat vs. Hierarchical Structure

3.3Design Issues of Routing Protocols in MANETs3.4QoS Routing3.5List of MANET Routing Protocols

3.5.1 Proactive Routing Protocols3.5.1.1 DSDV

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3.5.1.2 HSR3.5.1.3 WRP

3.5.2 Reactive Routing Protocols3.5.2.1 AODV3.5.2.2 DSR3.5.2.3 TORA

3.5.3 Hybrid Routing Protocols3.5.3.1 ZRP

Chapter – 4 QoS Models

4.1QoS Model4.1.1 IntServ4.1.2 DiffServ4.1.3 FQMM4.1.4 CEQMM

Chapter – 5 Security

5.1 Attacks on MANETs5.2 Security Solutions

Chapter – 6 Protocol Comparison and Simulation

6.1 Comparison6.2 Simulation

6.2.1 Simulation Environment6.2.2 Performance Metrics of Routing Protocols6.2.3 Simulation Results

CHAPTER-1

Introduction

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The people’s future leaving environments are emerging (growing) rapidly, based on the information resource provided by the connections of various communication networks to the users. Out of these networks the mobile wireless networks and devices are becoming increasingly popular as they provide access to information and communication at anytime and anywhere. Usually the conventional wireless mobile communication is supported by a wired fixed infrastructure(like internet). But the class of mobile ad hoc networks (MANET) does not use any fixed infrastructure .Generally there are two distinct approaches of using wireless mobile devices for communicating.

1.Infrastructured (wireless n/w),in which mobile devices communicate with each other through access points.

2. In frastructureless (Ad hoc n/w) ,in which mobile devices communicate with each other without access points.

By the infrastructureless approach, the wireless network is commonly known as a mobile adhoc network(or MANET). A MANET is a collection of autonomous mobile nodes connected by wireless links that can dynamically form a network to exchange information without using any pre-existing fixed network infrastructure . The nodes in MANETs intercommunicate through single-hop and multi-hop paths.The intermediate nodes that are on the communication path are acts as routers. Thus the nodes operate both as hosts and as routers.

The MANETs are useful in many application environments that don’t need any infrastructure support and where the computing and communications are done in smaller areas. Initially these networks are proposed for military applications such as battlefield communications and disaster recovery ,but due to the evalution of the multimedia technology and commercial interest of companies to reach /support the widely civilian applications,it is necessary to provide QoS (Quality of Service)support in MANET like environment. Although much more progress has already been done in QoS for wire-based networks(still there exist some problem),QoS in MANETs is a new concept and much more research work is being done for providing QoS in MANET like enviroment ,as MANETs are facing three new constraints than wired networks.

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1. Bandwidth constraints 2. Dynamic topology

3. Limited processing power 4. Stroing capabilities

Security is a critical aspect in MANETs environment for providing QoS . Due to the above constraints in MANET the conventional security measures can’t be applied so, new security techniques are necessary that can prevent and detect the intrusions/attacks on QoS parameters, authenticate the nodes etc.

Because of the unique charaacteristics of ad hoc environment ,3-models are designed like IntServ and DiffServ as a solution for QoS support in MANETs. These are FQMM,INSIGNIA,SWAN etc.

1.1 OVERVIEW (Basic cocept on mobile adhoc network)

1.1.1 Mobile computing:-

Computing is usually defined as the activity of using and developing computer technology, computer hardware and software.

Mobile means someone /something can move or be moved easily and quickly from place to place.

Mobile computing: - “on-the-go”, e.g., while sitting on a train; possibility of network connections remaining open.

“Mobile computing is a generic term describing one's ability to use technology while moving. Mobile Computing is used to describe technologies that enable people to access network services anyplace, anytime, and anywhere”. It refers to using a computing device while in journey. Mobile computing implies wireless transmission, but wireless transmission does not necessarily mean mobile computing. Fixed wireless applications use satellites, radio systems and lasers to transmit between permanent objects such as buildings and towers. Mobile Computing is done when a (work) process is moved from a normal fixed position to a more dynamic position. Users with portable computers still have network connections while they move is possible due to Mobile Computing .

1.1.2 Computer Network:-

A computer network is a collection of computers and devices connected to each other. The network allows computers to communicate with each other and shared

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information. The first computer network called ARPANET is introduced in the early 1970s. Generally networks are of 2-types:-

Wired Network. Mobile Network. Wireless Network.

1.1.2.1 Wired Network vs Mobile network :-

1.1.2.2Wireless Network:-

Wireless communication does not have the constraint of physical cables.Different radio frequency (RF) spectrum ranges are used in wireless networks.

Types of Wireless Networks

According to the relative mobility of hosts and routers, there are three different types of wireless networks:

1. Fixed Wireless Network 2. Wireless Network with Fixed Access Points3. Mobile Ad hoc Network (MANET)

Fixed Wireless Networks

Fixed hosts and routers use wireless channels to communicate with each other.

Mobile Networks - low bandwidth

- high bandwidth variability- hidden terminal problem - low power machines- low resource machines - need proximity- higher delay - disconnected operation

Wired Networks

- high bandwidth- low bandwidth variability - can listen on wire - high power machines - high resource machines - need physical access(security) - low delay - connected operation

Example:

wireless network formed by fixed network devices using directed antennas, as shown in Figure.

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Wireless Network with Fixed Access Points

** Ad hoc Network **

Ad hoc networks are self-organizing,rapidly deployable,and dynamically reconfigurable networks, which requred no fixed infrastructure. An ad-hoc network is a local area network (LAN) that is built spontaneously as devices connected.Hence an ad hoc network can be regarded as a spontaneous network , that is a network that automatically emerges /created when nodes gather together. Instead of rely on a base station to co-ordinate the flow of messages to each node in the network, the individual network nodes forward packets to and from each other.

Mobile Ad Hoc Network

Mobile Ad Hoc Networks consist of wireless mobile hosts that communicate with each other without the presence of a fixed infrastructure, forming dynamic autonomous networks. Due to its non-

Example:

wireless network formed by fixed network devices using directed antennas, as shown in Figure.

Mobile hosts use wireless channels to communicate with fixed access points.

Example:

Number of mobile laptop users in a

building that access fixed access

points, as illustrated in Figure.

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dependency on a centralized infrastructure, it can be rapidly deployed and can dynamically be reconfigured over time. In detail discussed below.

1.2 Mobile Ad Hoc Network (MANET)

Ad hoc networks in which the nodes are connected by wireless links and can be mobile are referred to as Mobile Ad hoc NETwork (MANET) where all the MN’s function as hosts and routers at the same time .Two MN’s communicate directly if they are within the radio transmission range of each other.Otherwise, they reach eah other via multi-hop route. (In simple, it is a network which consisting of a collection of nodes capable of communicating with each other without the help from a network infrastructure). It is also an autonomous system of mobile routers and associated hosts connected by wireless links forming an arbitrary graph.

In MANET, Routers are free to move randomly and organize themselves arbitrarily hence network topology may change rapidly and unpredictably. It may operate in a stand-alone fashion or may be connected to the Internet. A mobile ad hoc network (MANET), sometimes called a mobile mesh network , that is a self-configuring network of mobile devices connected by wireless links.

Example

vehicle-to-vehicle and ship-to-ship networks that communicate with each other by relying on peer-to-peer routings, as shown in Figure.

1.2.1 Characteristics of MANET

MANET has the following features:1) Autonomous terminal.

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CB

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In MANET, each mobile terminal is an autonomous node (Mobile hosts: MHs) which may function as both a host and a router. The mobile nodes have the basic processing ability as a host and can also perform switching functions as a router. So usually endpoints and switches are indistinguishable in MANET.

2) Distributed operation. Since there is no background network for the central control of the network operations, the control and management of the network is distributed among the terminals and hence no central authority and all are free. So the functions like routing and security are implemented collaborately among the nodes.

3) Multihop routing. Generally ad hoc routing algorithms can be single-hop or multihop, based on different link layer attributes and routing protocols. Single-hop MANET is simpler than multihop in terms of structure and implementation, with the cost of lesser functionality and applicability. When delivering data packets from a source to its destination out of the direct wireless transmission range, the packets should be forwarded via one or more intermediate nodes is called multihop routing.

4) Dynamic network topology. Since the nodes are mobile, they are free to move arbitrarily with different speeds, thus the network topology may change rapidly and unpredictably and the connectivity among the terminals may vary with time. The mobile nodes dynamically establish the route among themselves as they move and forming their own network on the fly.

5) Fluctuating link capacity.The wireless channel over which the terminals communicate are subject to noise, fading, and interference conditions etc due to multiple access(One end-to-end path can be shared by several sessions.), and has less bandwidth than a wired network. In some scenarios, the path between any pair of users can traverse multiple wireless links and the link themselves can be heterogeneous.

6) Light-weight terminals. The MANET nodes are mobile devices with less CPU processing capability, small memory size, and low power storage. Such devices need optimized algorithms and mechanisms that implement the computing and communicating functions with less overhead.

1.2.2 Types of MANET

The MANETs are of two types depending upon the no of nodes it contains.These are: -

1. Small-scale MANET –less than 30 nodes.

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2. Large –scale MANET- at least about 100 nodes.

Like MANET other ad hoc networks are

Vehicular Ad Hoc Networks (VANETs) are used for communication among vehicles and between vehicles and roadside equipment.

Intelligent vehicular ad hoc networks (InVANETs) are a kind of artificial intelligence that helps vehicles to behave in intelligent manners during vehicle-to-vehicle collisions, accidents, drunken driving etc.

Internet Based Mobile Ad-hoc Networks (iMANET) are ad-hoc networks that link mobile nodes and fixed Internet-gateway nodes. In such type of networks normal ad-hoc routing algorithms don't apply directly.

1.2.3 Some Issues of MANETs

There are several issues and challenges for relization of benefits from Ad-hoc networking. These challenges include:

Routing Medium (or channel) Access Mobility Management Security and Reliability Power Management Quality of Service (QoS) issues

Routing: Due to frequent changes in topology between any pair of nodes, routing of packets between these nodes becomes a challenging task. The routes among different nodes may potentially contain multiple hops, increasing the complexity of communication in comparison to single hop.

Medium (or Channel) access: The basic use of MAC is to manage the channel access among multiple nodes to achieve high channel utilization. In other words, the coordination of channel access should minimize or eliminate the incidence of collisions and maximize spatial reuse at the same time.

Mobility Management: The nodes move freely from one place to another place. The location of the nodes must be identified before the data is transferred from one node to another node and a connection needs to be established. Mobility management deals with storage, maintenance, and retrieval of the mobile host location information.

Security and Reliability: Security problems arise due to dynamic topologies and membership, vulnerable wireless links, roaming in dangerous environment.

Power Consumption: Wireless devices usually rely on portable power sources such as batteries to provide the necessary power; power management in wireless networks has become a crucial issue. It has been observed that energy is not always consumed

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by active communication in Ad hoc networks. Energy consumed by wireless devices in the idle state is comparatively less than that in the transmitting or receiving states.

Transmit mode: The mode at a node when transmitting a packet. Receive mode: The mode at a node when receiving a packet. Idle mode: The mode generally used at a node with the node is neither

transmitting nor receiving a packet. This mode consumes power because the node has to listen to the wireless medium continuously in order to detect a packet that it should receive, so that the node can then switch into receive mode.

Sleep mode: Sleep mode has very low power consumption. The network interface at a node in sleep mode can neither transmit nor receive packets; the network interface must be woken up to idle mode first by an explicit instruction from the node. From the above it can be seen that power consumption is lower when the node is in sleep mode.

Quality of Service (QoS): Due to resource constraint and dynamic topology of MANETs, supporting QoS in MANETs is a challenging task. QoS is needed in MANETs, as different applications have different service requirements. The objective to achieve the QoS is that the information carried by the network can be successfully delivered and resources can be better utilized.

1.2.4 Applications of MANETs

Application

Tactical Networks

Emergency Services

Possible Secnarios/Services

Military communications and operations Automated Battlefield

Search and rescue operations Disaster Recovery Replacement of fixed infrastructure in case of

environmental disasters. Policing and fire fighting. Supporting Doctors and nurse in hospitals.

E-commerce: electronic payments anytime and

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CHAPTER-2

Quality of Service(QoS)

According to CCITT (Consultative Committee for Internatinal Telegraphy and Telephony), the QoS is defined as “The collective effect of service performance which determines the degree of satisfaction of a user of the service”. Quality of service is a set of service requirements provided to certain traffic by the network to meet the satisfaction

Application

Tactical Networks

Emergency Services

Possible Secnarios/Services

Military communications and operations Automated Battlefield

Search and rescue operations Disaster Recovery Replacement of fixed infrastructure in case of

environmental disasters. Policing and fire fighting. Supporting Doctors and nurse in hospitals.

E-commerce: electronic payments anytime and

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of the user of that traffic. Also QoS is the network’s ability to provide the level(s) of service promised to the users and/or applications.

The objective of QoS is that, the information carried by the network can be successfully delivered and resources can be better utilized. For obtaining QoS in MANETs, it may not be sufficient to provide basic routing functionalities, other QoS parameters may also be taken into consideration such as bandwidth constraint due to shared media, dynamic topology as MNs are mobile, and power consumption due to limited battery power.

The capability to control traffic-handling mechanisms in the network such that the network meets the service needs of certain applications and users subject to network policies.

Quality of Service (QoS) involves adding mechanisms to control the network activity such as transmission and error rates, to assure certain level of service parameters. After accepting a service request from the user, the network must ensure to provide a set of service guarantees while transporting a flow.

Example to show Why QoS is important

2.1 The Need For QoS in MANETs

The ad-hoc networks, by definition, lack of four essential QoS ingredients which leads the need for QoS in MANETs. These are:

1. The lack of processing power and storage capacity that can be employed to monitor, track, and store information about specific flows, or node mobility.

Video frame without QoS Video frame with QoS Support

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2. The limited capabilities of mobile nodes batteries, which leads to a tight use of resource to reserve power. For example the nodes having low battery power needs to route high priority traffic first and then the low priority traffics.

3. The lack of central authority and human intervention that is needed to manage, to monitor, and to engineer the network resources as MANETs provide distributed operation.

4. The dynamic mobile nature, which leads to possible network partitioning or merger, and make it difficult to maintain resources over a period of time which needs robust, self-recovering routing operation, which is important.

2.2 QoS Metrics

Quality of Service (QoS) routing protocols search for routes with sufficient resources in order to satisfy the QoS requirements of a flow. The QoS routing protocol should find the path that consume minimum resources. Depending on the application involved, the QoS constraints could be available bandwidth, cost, end-to-end delay, delay variation (jitter), energy, probability of packet loss, and so on. The QoS metrics can be classified as additive metrics, concave metrics and multiplicative metrics.

Let m(u,v) be the performance metric for the link (u,v) connecting node u to node v, and path (u,u1,u2…uk,v) a sequence of links for the path from u to v.

A constraint is additive if m(u,v) = m(u,u1) + m(u1,u2) +...+ m(uk,v).For example, the end-to-end delay (u,v) is an additive constraint because it consists of the summation of delays for each link along the path.

A constraint is concave if m(u,v)=min{m(u,u1), m(u1,u2),…., m(uk,v)}. The bandwidth bw(u,v) requirement for a path between node u and v is concave. This is due to the fact that it consists of the minimum bandwidth between the links along the path.

A constraint is multiplicative if m(u,v) = m(u,u1) x m(u1,u2) x ... x m(uk,v). The probability of a packet prob (u,v), sent from a node u to reach a node v, is multiplicative, because it is the product of individual probabilities along the path. Bandwidth and energy are concave metric, where as cost, delay and jitters are additive metrics. The reliability or availability of a link based on some criteria such as link break probability is a multiplicative metric .

QoS is usually defined as a set of service requirements that needs to be meet by the network while transporting a packet stream from a source to its destination. The network is expected to guarantee a set of measurable pre-specified services attributes to the users in terms of end-to-end performance such as delay, bandwidth, probability of packet loss, delay variance(jitter) etc. Power consumption and service coverage area are two other

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QoS service attributes that are more specific to MANETs. The QoS metrics could be concave or additive. Bandwidth is concave in the sense that end-to-end bandwidth is the minimum of all the links along the links along the path. Delay and delay jitter are additive. The end-to-end delay is accumulation of all delays (jitters) of the links along the path. Furthermore, the QoS metrics could be defined in terms of one of the parameters or a set of parameters in varied proportions. The multi-constraint QoS aim at optimizing multiple QoS metrics while provisioning network resources, and is an admittedly complex problem.

2.3 Types of QoS

Due to node mobilityy and scarcity of resources such as enegy of nodes and bandwidth of wireless links, it is much more difficult to provide QoS guarantee in MANETs than in the Internet. In fact, guaranteeing QoS in such a network may be imposssible if the nodes are too mobile. There are two types of QoS services depending upon the service requirements of particular applications. These are :

Hard-QoS: - In a hard QoS protocol based on the well-known IntServ model is proposed in MANETs, which searches multiple paths in parallel in order to find the most qualified one. In ,the location information in QoS routing decisions,and concider connection time (estimated lifetime of a link)as a QoS constraint

Soft-QoS: - In a soft-QoS protocol based on the well-known Differentiated Services model is proposed in MANETs. It extends the Dynamic Source Routing (DSR) protocol to embed the QoS constraints in the discovery, maintenance of routes, and the traffic management. In highly dynamic MANETs, soft-QoS protocols may have better overall performance than hard –QoS protocols due to the highly unpredictable topological change of the MAENTs.

2.4 How to Maintain QoS in MANETs

QoS in MANETs can be achieved in following ways with:

1. Routing.2. Model.3. Security.

The primary function of routing is to find a route to destination, not to find the best/optimal/shortest-path route. But to support multimedia real-time communications like video-on-demand, news-on-demand, web browsing, traveler information system etc, we need that our routing protocol should be designed to support some of the QoS parameters like bandwidth, delay, jitter, packet loss, throughput etc.

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For obtaining QoS in MANETs, it may not be sufficient to provide basic routing functionalities, but we need to provide some sort of architecture for providing some kind of services in the network, called QoS model, that should consider the challenges of MANETs e.g. dynamic topology and time-varying link capacity etc.

As the wireless media is more exposed to attacks, thus security is a critical aspect of QoS provisioning in the MANET environment. Without protection from a security mechanism, attacks on QoS signaling system could result in QoS routing malfunction, interference of resource reservation, or even failure of QoS provision. Due to the characteristics of the MANETs, such as rapid topology change and limited communication and computation capacity, the conventional security measures cannot be applied and new security techniques are necessary.

These three issues for providing QoS in MANETs are discussed in further chapters and are analysed theoratically.

CHAPTER-3

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QoS Routing

3.1 Routing

Routing is the process of selecting paths in a network along which to send network traffic. The process of finding a route or path along which the data or control packets can be delivered between nodes in the network is also known as routing. Again routing is process of creating or updating the table, called routing table, which contains the information that a router needs to route packets, that helps in forwarding (the way a packet is delivered to the next station). The information may include the network address, the cost, the address of next hop and so on. The routing tables are of two types:

a) Static routing table: - The informations contained in this routing table are entered/altered manually by the administrator. It cannot update automatically when there is a change in the network.

b) Dynamic routing table: - This routing table is updated periodically, when there is a change in topology, by using one of the dynamic conventional routing protocols.

3.1.1 Routing Protocol/Algorithm

Because of the fact that, it is necessary to find several hops (multi-hop) before a packet reaches the destination, a routing protocol is needed. Routing aprotocol is that part of the network layer software responsible for deciding on which output line an incoming packet should be transmitted. The Routing protocols are used to continuously to update the routing tables to keep up-to-date route information that is needed for forwarding of data packets along an appropriate route. The routing protocol has two main functions:

Selection of routes for various source-destination pais and The delivery of messages to their correct destination.

The routing algorithm can be grouped into two major classes:

Nonadaptive Algorithm: - This algorithm does not base their routing decisions on measurement or estimates of the current traffic and topology. Here the routes are computed in advance, off-line, and are downloaded to the routers when the network is booted. This procedure sometimes called static routing.

Adaptive Algorithm: - In this algorithm, the routing decisions are changed to reflect the changes in the network topology. This procedure is also called dynamic routing.

In MANETs, only adaptive algorithms are used ,as the nodes are mobile and the network topology is contineously changing in this type of network.

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3.1.2 Coventional Routing Protocols

3.1.2.1 Link State

In Link state routing, each node maintains a view of the complete topology with a cost for each link. To keep these costs consistent; each node periodically broadcasts the link costs of its outgoing links to all other nodes. As each node receives this information, it updates its view of the network and applies a shortest path algorithm to choose the next hop for destination.

3.1.2.2 Distance Vector

It is known also as Distributed Bellman-Ford or RIP (Routing Information Protocol) . In distance vector, each node only monitors the cost of its outgoing links, Each node maintains a table of minimum distances to every nodes, that stores the information about the all available destinations, the next node to reach to destination, and the number of hops to reach the destination (minimum distance). Instead of broadcasting the routing table inforamation to all nodes, it broadcasts to each of its immediate neighbors periodically and when there is a change. The receiving nodes then use this information to recalculate their routing tables, by using a shortest path algorithm.

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B

DG

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link costs

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Compared to link-state, distance vector is more computation efficient, easier to implement and requires much less storage space. However, the distance vector can cause the formation of both short-lived routing loops and also it has count-to-infinity problem. The primary cause for this is that the nodes choose their next-hops in a completely distributed manner based on information that can be stale.

3.1.2.3 Source Routing

Source routing is a routing technique in which the sender of a packet determines the complete sequence of nodes through which the packet has to pass. The sender explicitly lists this route in the packet’s header, that identify each forwarding “hop” by the address of the next node to which to transmit the packet on its way to the destination host. Here the routing decision is therefore made at the source. The advantage of this approach is that it is easy to avoid routing loops. The disadvantage is that each packet requires a slight overhead.

3.1.2.4 Flooding

Many routing protocols uses broadcast to distribute/send control information from an origin node to all other nodes. A widely used form of broadcasting is flooding. In flooding, the origin node sends its information to its neighbors (i.e all nodes that are within transmission range). The neighbors relay it to their neighbors and so on, until the packet has reached all nodes in the network. A node will only relay a packet once and to erase this some sort of sequence number can be used. This sequence number is increased for each new packet a node sends.

3.2 Classification

There are different criteria for designing and classifying routing protocols for wireless ad hoc networks. For example, what routing information is exchanged; when and how the routing information is exchanged, when and how routes are computed and so on. I will discuss these criteria in this section.

3.2.1 Proactive vs. Reactive Routing

Proactive Schemes determine the routes to various nodes in the network in advance, so that the route is already present whenever needed. Route Discovery overheads are large in such schemes as one has to discover all the routes. They consume bandwidth to keep routes up-to-date. Packet forwarding is faster in these schemes as the route is already present. Examples of such schemes are the conventional routing schemes, Destination Sequenced Distance Vector (DSDV).

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Reactive Schemes determine the route when needed. Therefore they have smaller Route Discovery overheads. They employ a flooding (global search) mecanism. A node trying to transmit a packet may have to wait for route discovery. Examples of such schemes are Dynamic Source Routing, Ad-Hoc On Demand Distance Vector Routing (AODV) etc.

Apart form proactive and reactive there is another mechanism called Flooding. In flooding no route is computed or discovered. A packet is broadcasted to all the nodes in the network. Flooding is the easiest routing method, however it generates heavy traffic. Different proactive, reactive and even hybrid (reactive as well as proactive) schemes e.g. Zone Routing Protocol, have been proposed for Wireless Ad-Hoc networks

3.2.2 Single path vs. multiple path

There are several criteria for comparing single-path routing and multi-path routing in ad hoc networks. First, the overhead of route discovery in multi-path routing is much more than that of single-path routing. On the other hand, the frequency of route discovery is much less in a network which uses multi-path routing, since the system can still operate even if one or a few of the multiple paths between a source and a destination fail. Second, it is commonly believed that using multipath routing results in a higher throughput. The reason is that all nodes are assumed to have (and limited) capacity (bandwidth and processing power). Since multi-path routing distributes the load better, the overall throughput would be higher.

3.2.3 Table driven vs. Source Initiated

In Table Driven Routing protocols, up-to-date routing information from each node to every other node in the network is maintained on each node of the network. The changes in network topology are then propagated in the entire network by means of updates. Destination Sequenced Distance Vector Routing (DSDV) and Wireless Routing Protocol (WRP) are two schemes classified under the table driven routing protocols head.

The routing protocols classified under Source Initiated On-Demand Routing, create routes only when desired by the source node. When a node requires a route to a certain destination, it initiates the route discovery process. This process basically comprises of packets with a description of the destination (address information of the destination etc.) being forwarded from one hop to the next. Any node receiving such a request looks into its available routing table to find if it has a route to the described destination. If a route to the destination is present, the node returns this route to the source and the process ends else the request packet is forwarded to its neighbors continuing the route search process. Once a route is found, it is temporarily maintained in the routing table and then subsequently removed after either a timeout, or if the destination node leaves the network etc. Some of the schemes classified under this head are Ad-Hoc On Demand Distance Vector Routing (AODV), Dynamic Source Routing (DSR), Temporally Ordered Routing Algorithm (TORA) etc.

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3.2.5 Source routing vs. hop by hop routing

A few routing protocols utilize source routing. This means, forwarding depends on the source of the message. Commonly, the source puts all the routing information into the header of a packet. Forwarding nodes utilize this information. In some cases, the forwarding nodes may alter the routing information in the packet to be forwarded. They are just a few protocols using source routing: CBRP, DSR. In hop by hop routing, the route to a destination is distributed in the “next hop” of the nodes along the route. The problem is that all nodes need to maintain routing information and there may be a possibility of forming a routing loop.

3.2.6 Full/Limited/Local Broadcast

There is a full network broadcast, which means, a message is intended for every node in the network, and needs to be retransmitted by intermediate nodes. On the other hand, there is a local broadcast, which is intended for any node within the senders reach, but which is not retransmitted at all. In limited broadcasts, the maximum hop count (time to live) is limited as desired and the packet is to forwarded to next hops uop count reach, after that the packet is discarded. There is no routing protocol, that always issues full broadcasts, but there are some, that may use full broadcasts: CEDAR, DSDV, and DSR. Many protocols prefer a limited broadcast: AODV, HSR, and ZRP. And also there are protocols, which use only local broadcasts: TORA and WRP.

3.2.7 Periodic vs. Event Driven

Periodical update protocols broadcast routing information periodically. Periodical updates will simplify protocols and maintain network stability and most importantly enable nodes (new) to learn about the topology and the state of the network. However if the period between updates is large, the protocol may not keep the information up-to-date. On the other hand, if the period is small, too many routing packets will be distributed which consumes a large amount of valuable bandwidth of the wireless network.

In an event-driven update protocol, when events occur, (such as when a link fails or a new link appears), an update packet will be broadcast and the up-to-date status can be distributed over the network soon. The problem might be that if the topology of networks changes rapidly, a lot of update packets will be generated and distributed over the network which will use a lot of valuable bandwidth, and furthermore, may cause too much fluctuation of routes.

3.2.8 Flat vs. Hierarchical Structure

In a flat structure, all nodes in a network are at the same level and have the same routing functionality. Flat routing is simple and efficient for small networks. The problem

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is that when a network becomes large, the volume of routing information will be large and it will take a long time for routing information to arrive at remote nodes.

For large networks, hierarchical (cluster-based) routing is used to solve the above problems. In hierarchical routing, the nodes in the network are dynamically organized into partitions called clusters, and then the clusters are aggregated again into larger partitions called superclusters and so on. Organizing a network into clusters helps maintain a relatively stable network topology. The high dynamics of membership and network topology is limited within clusters. Only stable and high level information such as the cluster level or the supercluster level will be propagated across a long distance, thus the control traffic (or routing overhead) may be largely reduced.

3.3 Design Issues of Routing Protocols/Desirable properties in MANETs

The primary function of routing is to find a route to destination, not to find the best/optimal/shortest-path route. Hence the routing protocols in MANETs should consider some special characteristics such as mobility, limited energy, power consumption, limited bandwidth, high bit error rates etc of MANETs. It should be:

If the conventional routing protocols do not meet our demand, we need a new routing protocol. These are some properties of routing protocols that are desirable in MANETs:

Distributed Operation

The protocol should be distributed. It should not be dependent on a centralized controlling node.

Loop Free

To improve the overall performance, we want the routing protocol to guarantee the routes supplied are loop-free. This avoids any waste of bandwidth or CPU consumption.

Demand based Operation

To minimize the control overhead in the network and thus not wasting network resources more than necessary, the protocol should be reactive. The protocol should react only when there is a change in the network and that protocol should not periodicaly broadcast control information.

Security

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The radio environment is exposed to impersonation (imitation ) attacks, so ensure the wanted behavior from the routing protocol, we need some sort of preventive security measures.

Power Consumption

The nodes in an ad-hoc network can be laptops, PDAs that are very limited in battery power and therefore uses some stand-by mode to save power. It is therefore important that the routing protocol should support for these sleep-modes.

Multiple routes

To reduce the number of reaction to topological changes and congestion, multiple routes could be used. If one route has become invalid, it is possible that another stored route could still be valid and thus saving the routing protocol from initiating another route discovery procedure.

Quality of Service Support

The QoS support is probably necessary to incorporate into the routing protocol to support real-time traffic in the network.

None of the proposed protocols for MANETs have all these properties, but a protocol is used, if it support one or more of these above these properties. All the protocols are still under development and are probably extended with more functiona-lities.

3.4 QoS Routing

QoS routing is “a routing process that guarantees to support a set of QoS parameters during establishing a route”.

The QoS routing in MANETs is needed only to support the multimedia real-time communications like video-on-demand, news-on-demand, web browsing, traveler information system etc. These application requires a QoS guarantee not only over a single hop, but also over the entire wireless multi-hop.The QoS routing supports QoS-Driven selection and QoS reporting and provides path QoS information at each router.

The goal for QoS routing is 2-fold:-

First, the QoS routing schemes can help admission control. That is, routing protocol not only provides route to destination, but also computes the QoS, that is supportable on a route during the process of route computation. It accepts a new

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connection request, if it finds a suitable loop-free path from the source to destination having necessary resources (bandwidth) available to meet the QoS requirements of desired service, otherwise the connection request is rejected.

Secondly, QoS routing scheme that consider multiple constraints provide better load balance by allocating traffic on different paths subject to the QoS requirements of different traffics.

3.5 List of MANET Routing Protocols

Many routing protocols have been developed which support establishing and maintaining multi-hop routes between nodes in MANETs. These routing protocols in MANETs may be classified into basic 3-groups:

Pro-active (table-driven) routing Reactive (on-demand) routing

Hybrid (both pro-active and reactive) routing

3.5.1 Proactive (table-driven) routing Protocols (PRP)

These routing protocols are similar to and come as a natural extension of the protocols used for the wired networks. In proactive routing, each node advertises their presence by sending an advertisement message on the Ad hoc network side and has one or more tables that contain the latest or fresh lists of destinations and the information of the routes to any node in the network. Each row in the table contains the next hop for

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reaching to a node/subnet and the cost of that route. There are two kind of table updating process in proactive protocols. These are: -

a) Periodic Update: - Each node periodically broadcasts its table in the network and each node in the network receives that table.

b) Triggered Update: - As soon as a node detects a change in its neighborhood, it broadcasts entries in its routing table that are changed recently.

Examples:

Various table-driven protocols differ in the way the information about change in topology is propagated through all nodes in the network.The examples of this class of ad hoc routing protocols are:

DSDV (Highly Dynamic Destination-Sequenced Distance Vector routing protocol HSR (Hierarchical State Routing protocol) WRP (Wireless Routing Protocol) etc.

Advantages:

1. Establish routes in advance.2. Good Connectivity: Always maintain routes from a node to every other node.3. Low or no delay (via frequent broadcasts of current AGs) for route determination.

Disadvantages:

1. Bandwidth and power get wasted in the network because of the need to broadcast the routing tables/updates.

2. Slow reaction on restructuring and failures. 3. As the number of nodes in the MANETs increases, the size of table increases that

results high control message overhead.4. Maintain the routes which may never be used.

Summary: Proactive protocols give the QoS guarantees related to connection set-up, latency, or other real-time requirements. But in this scheme there are overheads in lightly loaded networks.

3.1.2.5 Destination-Sequenced Distance Vector routing

Destination-Sequenced Distance-Vector Routing (DSDV) is a table-driven routing scheme for ad hoc mobile networks based on the Bellman-Ford algorithm. It was developed by C. Perkins and P. Bhagwat in 1994. The main contribution of the algorithm was to solve the Routing Loop problem.

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Packets are transmitted between the stations of the network by using routing tables which are stored at each station of the network. Each routing table, lists all available destination, and the number of hops to each. Each route table entry is tagged with a sequence number, which is originated by the destination and the emitter needs to send out the next update with this number. To maintain the consistency of routing tables in a dynamic network, each station periodically transmits updates, and transmits updates immediately when significant new information is available. Thus, no nodes maintain any sort of synchronization.

Routing information is distributed between nodes by sending two types of packets, called full dumps and incremental. The full dumps carry all the available routing information and the other type will carry only the information changed since the last full dump send. The full dumps can be transmitted infrequently and smaller incremental updates more frequently.

For example the routing table of Node A in this network is

Destination Next Hop Number of Hops Sequence Number Install Time

A A 0 A 46 001000

B B 1 B 36 001200

C B 2 B 28 001500

Naturally the table contains description of all possible paths reachable by node A, along with the next hop, number of hops and sequence number.

Selection of Route:

When a Mobile Host receives new routing information (usually in an incremental packet), that information is compared to the previous information that already present in the routing table. Any route with a more recent sequence number is used. Routes with older sequence numbers are discarded. A route with a sequence number equal to an existing route is chosen if it has a “better” metric, and the existing route discarded, or

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stored as less preferable. The metrics for routes chosen from the newly received broadcast information are each incremented by one hop. Newly recorded routes are scheduled for immediate advertisement to the current Mobile Host’s neighbors.

Route Maintenance:

Mobile Hosts cause broken links as they move from place to place, The broken link may be detected by the MAC layer protocol, or it may instead be inferred if no broadcasts have been received for a while from a former neighbor. A broken link is described by a metric of ∞ (i.e., any value greater than the maximum allowed metric). When a link to a next hop has broken, any route through that next hop is immediately assigned a ∞ metric and assigned an updated sequence number. Since this qualifies as a substantial route change, such modified routes are immediately disclosed in a broadcast routing information packet. Sequence numbers defined by the originating Mobile Hosts are defined to be even numbers, and sequence numbers generated to indicate ∞ metrics are odd numbers. When a node receives an ∞ metric, and it has a later sequence number with a finite metric, it triggers a route update broadcast to disseminate the important news

Advantages:• Routes available to all destinations: Less latency in route set up

• DSDV was one of the early algorithms available. It is quite suitable for creating ad hoc networks with small number of nodes. Since no formal specification of this algorithm is present there is no commercial implementation of this algorithm. Many improved forms of this algorithm have been suggested.

Disadvantages:

1. DSDV requires a regular update of its routing tables, which uses up battery power and a small amount of bandwidth even when the network is idle.

2. Whenever the topology of the network changes, a new sequence number is necessary before the network re-converges; thus, DSDV is not suitable for highly dynamic networks.

3. It leads to count-to-infinity problem.

Influence:

While DSDV itself does not appear to be much used, today other protocols have used similar techniques. The best-known sequenced distance vector protocol is AODV, which is a reactive protocol, can use simpler sequencing heuristics.

3.5.1.2 Hierarchical state routing

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It is a multilevel clustering-based LS routing protocol. HSR maintains a hierarchical topology. The nodes in HSR are of three kinds called clusterheads, gateways, and internal nodes. As it is multilevel, new cluster heads are elected at each level and become members of the higher-level cluster. The elected clusterheads at the lowest level become members of the next higher level. On the higher level, superclusters are formed, and so on. HSR uses hierarchical addresses. Nodes which want to communicate to a node outside of their cluster ask their clusterhead to forward their packet to the next level, until a clusterhead of the other node is in the same cluster. The packet then travels down to the destination node.

Furthermore, HSR proposes to cluster nodes in a logical way instead of in a geological way: members of the same company or in the same battle group are clustered together, assuming they will communicate much within the logical cluster. HSR does not specify how a cluster is to be formed.

For example: Think of identifying a soldier in the army: <division #, battalion #, company #, platoon #, squad #, name>

Advantages:

1. It works for a large no of nodes. 2. Due to hierarchy, the traffic leads to suboptimal path.

Disadvantages:

1. Maintaining clusters or hierarchy of clusters causes additional overhead.

3.5.1.3 Wireless Routing Protocol (WRP)

Clusterheads

Gateway

Internal nodes

Links

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Wireless Routing Protocol (WRP) is a proactive unicast routing protocol for mobile ad-hoc networks (MANETs). WRP uses an enhanced version of the distance-vector routing protocol, which uses the Bellman-Ford algorithm to calculate paths. Because of the mobile nature of the nodes within the MANET, the protocol introduces mechanisms which reduce route loops and ensure reliable message exchange.

The wireless routing protocol (WRP), similar to DSDV, inherits the properties of the distributed Bellman-Ford algorithm. To counter the count-to-infinity problem and to enable faster convergence, it employs a unique method of maintaining information regarding the shortest distance to every destination node in the network. Since WRP, like DSDV, maintains an up-to-date view of the network, every node has a readily available route to every destination node in the network.

Difference between DSDV & WRP

It differs from DSDV in table maintenance and in the update procedures. While DSDV maintains only one topology table, WRP uses a set of tables to maintain more accurate information. The tables that are maintained by a node are the following:

Distance table (DT): - The DT contains the network view of the neighbors of a node. It contains a matrix where each element contains the distance and the predecessor node reported by a neighbor for a particular destination.

Routing table (RT): - The RT contains the up-to-date view of the network for all known destinations. It keeps the shortest distance, the predecessor node (penultimate node), the successor node (the next node to reach the destination), and a flag indicating the status of the path. The path status may be a simple path (correct), or a loop (error), or the destination node not marked (null).

Link cost table (LCT): - The LCT contains the cost (e.g., the number of hops to reach the destination) of relaying messages through each link. The cost of a broken link is infinity. It also contains the number of update periods (intervals between two successive periodic updates) passed since the last successful update was received from that link. This is done to detect links breaks.

Message retransmission list (MRL): - The MRL contains an entry for every update message that is to be retransmitted and maintains a counter for each entry. This counter is decremented after every retransmission of an update message. Each update message contains a list of updates. A node also marks each node in the RT that has to acknowledge the update message it transmitted. Once the counter reaches zero, the entries in the update message for which no acknowledgments have been received are to be retransmitted and the update message is deleted. Thus, a node detects a link break by the number of update periods missed since the last successful transmission. After receiving an update message, a node not only updates the distance for transmission

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neighbors but also checks the other neighbors’ distance, hence convergence is much faster than DSDV.

Method:

Each node implementing WRP keeps a table of routes, distances, and link costs. It also maintains a 'message retransmission list' (MRL).

Routing table entries contain distance to a destination node, the previous and next nodes along the route, and are tagged to identify the route's state: whether it is a simple path, loop or invalid route. (Storing the previous and successive nodes assists in detecting loops and avoiding the counting-to-infinity problem - a shortcoming of Distance Vector Routing.)

The link cost table maintains the cost of the link to its nearest neighbors (nodes within direct transmission range), and the number of timeouts since successfully receiving a message from the neighbor.

Nodes periodically exchange routing tables with their neighbors via update messages, or whenever the link state table changes. The MRL maintains a list of which neighbors are yet to acknowledge an update message, so they can be retransmitted if necessary. When there is no change in the routing table, a node is required to transmit a 'hello' message to affirm its connectivity.

When an update message is received, a node updates its distance table and keeps the best route paths. It also carries out a consistency check with its neighbors, to help eliminate loops and speed up convergence.

Advantages:

1. WRP has the same advantage as that of DSDV. 2. In addition, it has faster convergence and involves fewer table updates.

Disadvantages:

1. Due to the complexity of maintenance of multiple tables, it demands a larger memory and greater processing power from nodes in the ad hoc wireless network.

2. At high mobility, the control overhead involved in updating table entries is almost the same as that of DSDV and hence is not suitable for highly dynamic and also for a very large ad hoc wireless network.

Summary:

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WRP has faster convergence and involves fewer table updates and requires large memory storage and resources in maintaining its tables. The protocol is not suitable for large mobile ad hoc networks as it suffers from limited scalability.

3.1.2.6 Reactive (on-demand) routing Protocols (RRP)

These routing protocols take a lazy approach to routing. In this approach the nodes do not maintain or constantly update their route tables with the latest route topology. Instead, when a source node wants to transmits a message (packet), the routes are discovered between a source and a destination by flooding a query into the network. The discovery packet is called the Route Request (RREQ) and the mechanism is called Route Discovery. By receiving the request, destination replies with a Route Reply (RREP) packet. As a result of which, the source dynamically finds the route to destination. Then the actual communication takes place. The discovered route is maintained (in the cache) until the destination becomes inaccessible or until the route is no longer desired.

Advantages:

1. It achieves low routing overhead (control message) of communication and scalability since routes are determined on demand.

Disadvantages:

1. It increases route discovery delay or latency time in route finding.2. Excessive flooding can lead to network congestion.

Examples of reactive algorithms:

The protocols in this class differ in handling cache routes and in the way route discoveries and route replies are handled.

AODV (Ad-hoc On-demand Distance Vector). DSR (Dynamic Source Routing). TORA (Temporarily Ordered Routing Algorithm).

3.1.2.7 Ad hoc On-Demand Distance Vector Routing

Ad hoc On-Demand Distance Vector (AODV) Routing is a routing protocol for mobile ad hoc networks (MANETs) and other wireless ad-hoc networks. It is jointly developed in Nokia Research Center of University of California, Santa Barbara and University of Cincinnati by C. Perkins and S. Das. AODV is capable of both unicast and

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multicast routing. It is a reactive routing protocol, meaning that it establishes a route to a destination only on demand. In contrast, the most common routing protocols of the Internet are proactive, meaning they find routing paths independently of the usage of the paths. AODV is one of the distance-vector routing protocol. AODV avoids the counting-to-infinity problem of other distance-vector protocols by using sequence numbers on route updates, a technique like DSDV.

Workings:

In AODV, the network is silent until a connection is needed. At that point the network node that needs a connection, broadcasts a request for connection. Other AODV nodes forward this message, and record the node that they heard it from, creating an explosion of temporary routes back to the needy node. When a node receives such a message and already has a route to the desired node, it sends a message backwards through a temporary route to the requesting node. The needy node then begins using the route that has the least number of hops through other nodes. Unused entries in the routing tables are recycled after a time.

When a link fails, a routing error is passed back to a transmitting node, and the process repeats.

Much of the complexity of the protocol is to lower the number of messages to conserve the capacity of the network. For example, each request for a route has a sequence number. Nodes use this sequence number so that they do not repeat route requests that they have already passed on. Another such feature is that the route requests have a "time to live" number that limits how many times they can be retransmitted. Another such feature is that if a route request fails, another route request may not be sent until twice as much time has passed as the timeout of the previous route request.

The advantage of AODV is that it creates no extra traffic for communication along existing links. Also, distance vector routing is simple, and doesn't require much memory or calculation. However AODV requires more time to establish a connection, and the initial communication to establish a route is heavier than some other approaches.

Technical Description:

The AODV Routing protocol uses an on-demand approach for finding routes, that is, a route is established only when it is required by a source node for transmitting data packets. It employs destination sequence numbers to identify the most recent path. The major difference between AODV and Dynamic Source Routing (DSR) stems out from the fact that DSR uses source routing in which a data packet carries the complete path to be traversed. However, in AODV, the source node and the intermediate nodes store the next-hop information corresponding to each flow for data packet transmission. In an on-

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demand routing protocol, the source node floods the RouteRequest packet in the network when a route is not available for the desired destination. It may obtain multiple routes to different destinations from a single RouteRequest. The major difference between AODV and other on-demand routing protocols is that it uses a destination sequence number (DestSeqNum) to determine an up-to-date path to the destination. A node updates its path information only if the DestSeqNum of the current packet received is greater than the last DestSeqNum stored at the node.

A RouteRequest carries the source identifier (SrcID), the destination identifier (DestID), the source sequence number (SrcSeqNum), the destination sequence number (DesSeqNum), the broadcast identifier (BcastID), and the time to live (TTL) field. DestSeqNum indicates the freshness of the route that is accepted by the source. When an intermediate node receives a RouteRequest, it either forwards it or prepares a RouteReply if it has a valid route to the destination. The validity of a route at the intermediate node is determined by comparing the sequence number at the intermediate node with the destination sequence number in the RouteRequest packet. If a RouteRequest is received multiple times, which is indicated by the BcastID-SrcID pair, the duplicate copies are discarded. All intermediate nodes having valid routes to the destination, or the destination node itself, are allowed to send RouteReply packets to the source. Every intermediate node, while forwarding a RouteRequest, enters the previous node address and its BcastID. A timer is used to delete this entry in case a RouteReply is not received before the timer expires. This helps in storing an active path at the intermediate node as AODV does not employ source routing of data packets. When a node receives a RouteReply packet, information about the previous node from which the packet was received is also stored in order to forward the data packet to this next node as the next hop toward the destination.

Advantages:

1. The main advantage of this protocol is that routes are established on demand and destination sequence numbers are used to find the latest route to the destination.

2. The connection setup delay is lower.

Disadvantages:

1. One of the disadvantages of this protocol is that intermediate nodes can lead to inconsistent routes if the source sequence number is very old and the intermediate nodes have a higher but not the latest destination sequence number, thereby having old entries.

2. Multiple RouteReply packets in response to a single RouteRequest packet can lead to heavy control overhead.

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3. Another disadvantage of AODV is that the periodic beaconing leads to unnecessary bandwidth consumption.

3.1.2.8 Dynamic Source Routing (DSR)

Dynamic Source Routing (DSR) is an on-demand routing protocol that is based on the concept of source routing. Mobile nodes are required to maintain route caches that contain the routes to the destinations that the node is aware of. Entries in the route cache are continually updated as new routes are learned.

There are two significant stages in working of DSR:1. Route Discovery & 2. Route Maintenance.

Route Discovery

When a mobile node has a packet to send to some destination, it first consults its route cache to determine whether it already has a route to the destination. If it has an unexpired route to the destination, it will use this route to send the packet. On the other hand, if the node does not have such a route, it initiates route discovery by broadcasting a route request packet. This route request contains the address of the destination, along with the source node's address and a unique identification number. Each node receiving the packet checks whether it knows of a route to the destination. If it does not, it adds its own address to the route record of the packet and then forwards the packet along its outgoing links. To limit the number of route requests propagated on the outgoing links of a node, a mobile only forwards the route request if the request has not yet been seen by the mobile and if the mobile's address does not already appear in the route record.

A route reply is generated when either the route request reaches the destination itself, or when it reaches an intermediate node which contains in its route caches an unexpired route to the destination. By the time the packet reaches either the destination or such an intermediate node, it contains a route record yielding the sequence of hops taken. Above figure (a) illustrates the formation of the route record as the route request propagates through the network. If the node generating the route reply is the destination, it places the route record contained in the route request into the route reply. If the responding node is an intermediate node, it will append its cached route to the route record and then generate the route reply. To return the route reply, the responding node

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have a route to the initiator. If it has a route to the initiator in its route cache, it may use that route. Otherwise, if symmetric links are supported, the node may reverse the route in the route record. If symmetric links are not supported, the node may initiate its own route discovery and piggyback the route reply on the new route request. Above figure (b) shows the transmission of the route reply with its associated route record back to the source node.

Route maintenance

Route maintenance is accomplished through the use of route error packets and acknowledgments. When the Route Maintenance Phase detects a problem with a route in use, a Route Error packet is generated at a node which detects the failure and send back to source node. When a route error packet is received, the hop in error is removed from the node's route cache and all routes containing that hop are truncated at that point. Again, the Route Discovery Phase is initiated to determine the most viable route to destination.

Example

Consider a source node that does not have a route to the destination. When it has data packets to be sent to that destination, it initiates a RouteRequest packet. If an intermediate node receiving a RouteRequest has a route to the destination node in its route cache, then it replies to the source node by sending a RouteReply with the entire route information from the source node to the destination node. Otherwise this RouteRequest is flooded throughout the network. Each node, upon receiving a RouteRequest packet, rebroadcasts the packet to its neighbors if it has not forwarded it already, provided that the node is not the destination node and that the packet’s time to live (TTL) counter has not been exceeded. Each RouteRequest carries a sequence number generated by the source node and the path it has traversed. A node, upon receiving a RouteRequest packet, checks the sequence number of the packet before forwarding it. The packet is forwarded only if it is not a duplicate RouteRequest. The sequence number

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on the packet is used to prevent loop formations and to avoid multiple transmissions of the same RouteRequest by an intermediate node that receives it through multiple paths. Thus, all nodes except the destination forward a RouteRequest packet during the route construction phase. A destination node, after receiving the first RouteRequest packet, replies to the source node through the reverse path the RouteRequest packet had traversed. The route to destination is stored in the cache. This route cache is also used during the route construction phase.

Advantages:

This protocol uses a reactive approach which eliminates the need to periodically flood the network with table update messages.

As the cache can store multiple paths to a destination. The intermediate nodes also utilize the route cache information efficiently to reduce the control overhead.

Disadvantages:

In DSR the routed packets contain the address of each device the packet will traverse. This may result in high overhead for long paths or large addresses, like IPv6(Address field is large i.e. 128 bits). This routing overhead is directly proportional to the path length.

The connection setup delay is higher. Even though the protocol performs well in static and low-mobility environments,

the performance degrades rapidly with increasing mobility.

3.5.2.3 Temporally-ordered routing algorithm (TORA)

The Temporally-Ordered Routing Algorithm (TORA) is an algorithm for routing data across Wireless Mesh Networks or Mobile ad-hoc networks. It was developed by Vincent Park at the University of Maryland and the Naval Research Laboratory.

The TORA is a distributed routing protocol that attempts to achieve a high degree of scalability using a "flat", non-hierarchical link reversal routing algorithm. It is designed to minimize the reaction to topological changes. The algorithm attempts to suppress, the generation of far-reaching control message propagation by localizing the propagation of control messages to a very small set of nodes. It guarantees that all routes are loop-free (temporary loops may form) and provides multiple routes for any source/destination pair.

TORA does not use a shortest path solution; an approach which is unusual for routing algorithms of this type. TORA builds and maintains a Directed Acyclic Graph (DAG) rooted at a destination.

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Operation:

The operation of TORA can be separated into three basic functions:

1. Route creation,2. Route maintenance, 3. Route erasure.

Route creation:

During route creation TORA basically assigns directions to links in an undirected network or portion of the network, building a Directed Acyclic Graph (DAG) rooted at the destination. TORA uses a height metric and associates a height with each node in the network. No tree nodes may have the same height. All information in the network may flow from nodes with higher heights to nodes with lower heights. Information can therefore be thought of as a fluid that may only flow downhill. Routes are discovered by using QueRY (QRY) and UPaDate (UPD) packets. When a node with no downstream links needs to send a packet (a route) to destination, it will broadcast a QRY packet.

This QRY packet will propagate through the network until it reaches a node that has a route to destination or the destination itself. Such a node will then broadcast a UPD packet that contains the node’s height. Each node receiving this UPD packet will then broadcast a UPD packet that contains the node height. Every node receiving this UPD packet will set its own height to a larger height that specified in the UPD message. The node will then broadcast its own UPD packet. This will result in a number of directed links from the source to destination. This process can result in multiple routes, and the source node chooses the best route among them to send its data packets. By maintaining a set of totally-ordered heights at all times, TORA achieves loop-free multipath routing, as information cannot 'flow uphill' and so cross back on itself.

Figure: Route creation (showing link direction assignment)

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Route maintenance:

During the times of mobility, if the DAG is broken then the route maintenance unit comes into picture to reestablish a DAG routed at the destination. All nodes react to topological changes in the network to re-establish a route to the destination in a finite time.

Figure: Route Maintenance (showing link reversal phenomenon) in TORA.

Route Erasure:

TORA's route erasure phase is essentially involving flooding a broadcast clear (CLR) packet throughout the network to erase invalid routes by marking the invalid links as undirected.

Advantages:

Limits control packets to a small region when topology changes: less overhead. It provides loop free paths at all instants and multiple routes so that if one path is

not available, other is readily available

Disadvantage:

Local reconfiguration of paths could lead to non-optimal route to the destination. It exhibits instability behavior similar to "count-to-infinity" problem.

3.1.3 Hybrid Routing Protocols (HRP)

This type of protocols combines the advantages of purely proactive and of reactive routing. As the number of nodes increases, hybrid protocols are used to achieve higher

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performance. The key idea is to use a reactive routing procedure at the global network level while employing a proactive routing procedure in a node’s local neighborhood.

Disadvantage:

The main disadvantages of such algorithms are: Advantage depends on amount/number of nodes activated.

Hybrid Routing is a third classification of routing algorithm. Hybrid routing protocols use distance-vectors for more accurate metrics to determine the best paths to destination networks, and report routing information only when there is a change in the topology of the network. Hybrid routing allows for rapid convergence but requires less processing power and memory as compared to link-state routing.

Examples of hybrid algorithms are

ZRP (Zone Routing Protocol).

3.1.4 Zone Routing Protocol (ZRP)

ZRP can be classified as a hybrid reactive/proactive routing protocol. It aims to address the problems of both proactive and reactive by combining the best properties of both approaches. It divides the network into several routing zones.

Routing Zone:

In ZRP, a routing zone of a node is defined as a set nodes, within a specific minimum distance (in number of hops) away from that node. The distance is reffered to as the zone radius. Every node has a zone around itself. A node may belongs to more than one routing zone. All nodes at hop distance exactly zone radius are said to be peripheral nodes of the node’s routing zone.

ZRP specifies two totally detached protocols that operate inside and between the routing zones. These protocols are:

a) IntrA-zone Routing Protocol (IARP): - This protocol operates inside the routing zone and proactively maintains routes to all nodes within the source node’s own routing zone. The protocol is not defined and can include any number of proactive

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protocols. Different zone can operate with different protocol but the protocols are restricted to those zones.

b) IntEr-zone Routing Protocol (IERP): - This protocol is reactive and is used to find routes between different routing zones. This protocol uses a Bordercast Resolution Protocol (BRP) when the destination is outside the source node’s zone. This protocol bordercasts (Bordercasting is the process of sending IP datagram from one node to all its peripheral nodes) a Route REQuest (RREQ) to all boarder/peripheral nodes within the routing zone, which in turn forwards the request if the destination isn’t found within their routing zone. The procedure is repeated until the requested node is found and a route reply is send back to the source node indicating the route.

Consider the network in following figure. Let R=2 is the zone radius. Node S wants to send a packet to node D.

Figure : Network Using ZRP, The dashed squares show the routing zone for node S and D

Since node D isn’t in the routing zone of S, a route request with source node’s ID and request number is send to the peripheral nodes B and C. Each border node checks whether D is in their routing zone. Neither B nor C finds D in their zone , thus forwards the request to respective border/peripheral nodes. C sends the request to S, B, F, and H while B sends the request to S, C, E, and G. Now the requested node is found within the range of both F and G. Thus the Route REPly is send back to the source node S by node F and G. From them the source node chooses the best path and sends the packet along that path.

Zone for C

A

Zone for S

B

A

S

C A

Zone for D

F

E

H

G

D

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To prevent the request from going back to previously queried routing zone, a Processed Request List is used that stores the previously processed request and drops the request, if it already has processed.

Route Maintenance:

If the intermediate nodes detects a broken link in the path then it sends a path update message to the sender to inform it about the link failure. The sender then chooses an alternative path to send the packets.

Advantage:

It combines the best features of proactive and reactive routing schemes. By this it reduces:

o The control traffic produced by periodic flooding of routing information packets (proactive scheme).

o The wastage of bandwidth and control overhead compared to reactive schemes.

Disadvantage:

As the proactive IARP protocol is not specified. The use of different IARP would mean that the nodes would have to support several different routing protocols. It is better to use same IARP in the entire network.

Large overlapping of routing zones is also another problem. When there are overlaps in the nodes’ routing zones, there may be redundant RouteRequests sent out. These need to be suppressed.

Choosing zone radius is quite tricky.

CHAPTER-4

QoS Models

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The QoS Model specifies the architecture which will enable us to offer services that operate better than the current "best effort" model that exists in MANETs. The QoS model also specifies the architecture for providing some kind of services in the network. A QoS model for MANETs should consider the challenges of MANETs e.g. dynamic topology and time-varying link capacity etc. There are a few QoS models specifically developed for MANETs. In addition, the potential commercial applications of MANETs require connection to the Internet. Thus the QoS model for MANETs should also consider the existing QoS models in the Internet. 4.1 QoS Model Classification

The QoS models are generally classified into the following major groups:

Integrated Services (IntServ) where framework provides explicit end-to-end reservation.

Differentiated Services (DiffServ) architecture which offers hop-by-hop differentiated treatment of packets.

Flexible QoS model for MANETs (FQMM). Complete and Efficient QoS Model for MANETs (CEQMM).

4.1.1 Integrated Services (IntServ) on Wired Networks

The basic idea of Integrated Services (IntServ) model is that the routers have to reserve resources to provide special QoS for specific user packet streams i.e. the flow-specific states are kept in every IntServ-enabled router. A flow is an applicati-on session between a pair of end users. The flow-specific state should include the information about bandwidth requirement, delay bound, jitter, cost etc of the flow.

IntServ proposes two service classes in addition to Best Effort Service:

a) Guaranteed Service: - The Guaranteed Service is provided for applications requiring fixed delay bound.

b) Controlled Load Service: - The Controlled Load Service is for applications requiring reliable and enhanced best effort service.

The implementation of IntServ relies on four components:

The Signaling Protocol: - The Resource ReSerVation Protocol (RSVP) is used as signaling protocol to reserve resources in IntServ before transmission.

The Admission Control Routine: - This routine is used to decide whether to accept the resource requirement. It is invoked at each router to make a local accept/reject decision when a host makes a request for real-time service along some paths through the Internet. This routine notifies the application through RSVP if the QoS requirement is granted or not as the application can transmit its data packets only after the QoS requirement is accepted.

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The Classifier: - When a router receives a data packet, the classifier performs a Multi-Field (MF) classification. It classifies a packet based on these multiple fields such as source and destination addresses, source and destination port number, Type Of Service (TOS) bits and protocol ID in the IP header. These classified packets are then put in a queue according to classification results.

The Packet Scheduler: - The packets in the output queue are reordered by the scheduler to meet different QoS requirements.

It also relies on other components like Routing Agent and Management Agent mechanisms provided by the router in advance and can be kept unchanged.

The IntServ/RSVP model is not suitable for MANETs due to the resource limitation in MANETs:

1. Keeping flow state information in each node implies huge storage and processing overheads depending upon the number and duration of flows.

2. The RSVP signaling packets will consumes a substantial percentage of bandwidth in MANETs. Signaling overhead also increases as the network becomes more dynamic.

3. Every mobile host must perform the processing of admission control, classification, and scheduling. This place a heavy burden for the resource-limited mobile hosts.

In spite of all these constraints, the main idea of the IntServ approach can be taken and modified to be supported in MANETs.

4.1.2 Differentiated Service (DiffServ) on Wired Network

Differentiated Service (DiffServ) is designed to overcome the difficulty of implementing and deploying IntServ and RSVP in the Internet backbone. DiffServ deals with bulk flows of data rather than single flows and resource reservations. While IntServ provides per-flow guarantees, DiffServ follow the philosophy of mapping multiple flows into a few service levels.

DiffServ architecture avoids the problem of scalability by defining the layout of the Type Of Service (TOS) bits in the IP header, called the DS (Differentiated Services) field, and a base set of packet forwarding rules, called Per-Hop-Behavior (PHB). At the boundary of the network, the boundary routers control the traffic entering to the network with classification, marking, policing and shaping mechanisms.

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A “DiffServ cloud” is a collection of DiffServ-enabled routers. When a data packet enters a DiffServ-enabled domain, a boundary router marks the packet’s DS field in the IP packet header and the interior routes along the forwarding path forward the packet according to the PHB associated with the DS field.

Many services are supported in DiffServ model:

1. Premium Service: - is supposed to provide low loss, low delay, low jitter, and end-to-end assured bandwidth service.

2. Assured Service: - is for applications requiring better reliability than Best Effort Service. It provides guaranteed or at least expected throughput for applications. It is more qualitative-oriented than quantitative-oriented and thus easy to implement.

3. Olympic Service: - provides 3- tiers of services: Gold, Silver, Bronze with decreasing quality.

Supporting premium service is almost impossible in MANETs because the strict requirement of Premium Service is not suitable in the dynamic MANETs environment.

DiffServ may be a possible solution to MANET QoS model because it is lightweight in interior routers and it provides Assured Service which is a feasible service in MANETs. However, we still face some challenges to implement DiffServ in MANETs as it is designed for fixed wire network.

1. It is difficult to define boundary routers. Naturally the source nodes play the role of boundary router and the node along the forwarding path from source to destination are interior nodes. Thus every node must function as both boundary and interior nodes because the source nodes cannot be predefined. This raises a heavy storage cost in every host.

2. The concept of Service Level Agreement (SLA, is a contract between a customer and its ISP that specifies the forwarding services the customer should receive) in the Internet does not exist MANETs which is necessary for functioning of DiffServ because it includes the whole or partial traffic conditioning rules.

4.1.3 Flexible QoS Model for MANET (FQMM)

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Flexible QoS Model for MANETs (FQMM) is the first QoS Model for Mobile Adhoc Networks. It considers the characteristics of MANETs and tries to take t he advantage of both the per-flow service granularity in IntServ and the service differentiation in DiffServ. The applications with high priority, per-flow QoS guarantees of IntServ are provided and for the applications with lower priorities are given per-class differentiation of DiffServ. This model is based on the assumption that not all packets in the network are actually seeking highest priority, as this made this model resembles with the IntServ model. Therefore FQMM uses a hybrid of IntServ and DiffServ approaches.

The FQMM hybrid model defines three types of nodes:

a) Ingress: - An Ingress node is a node that sends data.b) Interior: - Interior nodes are the nodes that forward data to other nodes. c) Egress: - An egress node is a destination node.

Each node may have multiple nodes depending on its position and the network traffic.

FQMM tries to preserve the per-flow granularity for a small portion of traffic, given that a large amount of traffic belongs to per aggregate of flows i.e. per-class granularity. A traffic conditioner is placed at each ingress nodes where the traffic originates. This conditioner marks, discards and shapes the packets according to the traffic profile, which describes the temporal properties of traffic stream such as rate and burst size.

The advantage of FQMM is that it is relatively simple and it borrows for the existing QoS models of traditional wired IP network. However some problems are there as the size of network increases:

a) Without an explicit control on the number of services with per-flow granularity the scalability problem still exists.

b) The traffic conditioning algorithm may also increase the complexity of the wireless nodes in a MANET.

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c) It is difficult to code the PHB in the DS field of IP, if the PHB includes per-flow granularity considering the DS field is at most 8 bits without extension, as in DiffServ, the interior nodes forward the packets according to PHB defined in DS field.

d) To make a dynamically negotiated traffic profile is a very difficult problem.

4.1.4 Complete and Efficient QoS Model for MANETs (CEQMM)

This model is similar to FQMM, which too combines the IntServ and DiffServ models for provisioning of QoS in MANETs. In contrast to FQMM which does not define the use of any particular QoS routing protocol, CEQMM specifies the QoS Optimized Link State Routing (QOLSR) protocol. Multi-metric routing are supported using IntServ for highest priority flows, and DiffServ for the remaining flows. Since CEQMM is based on QOLSR, it spends a lot of battery power and network resources for exchanging routing data, which is a limitation for small battery-constrained wireless devices.

CHAPTER-5

Security

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With the increase in number of applications, more cocerns arise for security issues in MANETs. Security is a critical aspect of QoS provisioning in the MANET environment, as security threats and attacks on routing operations can severely disrupt network operations, degrade network performance, and adversely affect the QoS (quality of service) provisioning in MANETs. Without protection from a security mechanism, attacks on QoS signaling system could result in QoS routing malfunction, interference of resource reservation, or even failure of QoS provision. Due to the characteristics of the MANETs, such as rapid topology change and limited communication and computation capacity, the conventional security measures cannot be applied and new security techniques are necessary. However, little research has been done on this topic. In this dissertation, the security issues will be addressed for MANET QoS systems. The major contributions of this research are: (a) design of an authentication mechanism for ad hoc networks; (b) design of a security mechanism to prevent and detect attacks on the QoS signaling system; (c) design of an intrusion detection mechanism for bandwidth reservation to detect QoS attacks and Denial of Service (DoS) attacks.

Providing Security is one of the major issues in MANETs due to the challenges in ad hoc networks. These challenges include:

Shared radio channel and insecure environment: - The wireless network is more susceptible to attacks ranging passive eavesdropping to active interfering.

Lack of central authority: - The lack of an online CA or Trusted Third Party adds the difficulty to deploy security mechanisms.

Limited resources: - Mobile devices tend to have limited power consumption and computation capabilities which makes it more vulnerable to Denial of Service attacks and incapable to execute computation heavy algorithms like public-key algorithms

Lack of permanent association: - The node mobility enforces frequent networking reconfiguration which creates more chances for attacks, for example, it is difficult to distinguish between stale routing information and faked routing information.

Physical vulnerability: - There are more probabilities for trusted node being compromised and then being used by adversary/challenger to lunch attacks on networks, in other words, we need to consider both insider attacks and outsider attacks in MANETs, in which insider attacks are more difficult to deal with.

There are six main security services for MANETs:

Authentication: - It means that correct identity is known to communicating partner.

Confidentiality: - It means the ability to protect confidential information from unauthorized user.

Integrity: - It means the message is unaltered during the communication. It Guarantee that a message being transferred is not corrupted.

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Non-repudiation: - It means the origin of a message cannot deny having sent the message. This attribute ensures that a node having sent a message cannot deny it.

Availability: - It means MANET should be able to survive Denial of service attacks (DoS).

Privacy (location, data, identity, existence): - It means having the power to control information about you. The person must exercise that control consistent with his or her interests and values.

Attacks on MANETs

There are two kinds of possible attacks in ad hoc networks:a) Passive attacks b) Active attacks

- Passive attacks: A passive attack does not disrupt the operation of the protocol, but tries to discover valuable information by listening to traffic.

- Active attacks: An active attack injects arbitrary packets and tries to disrupt the operation of the protocol in order to limit availability

Active Attacks

Attacks using Modification Attacks using impersonation Attacks using fabrication

Attacks using Modification

Based on the modification of the metric value for a route or altering control message fields (DoS Attacks)

A malicious node hacker could keep track from reaching node D by consistently advertising to node B a shorter route to node D than the route to D that C is advertising.

There are three types attacks Redirection by changing route request number Redirection with modified hop count DoS Attacks with modified source routes

Node B

Node C

Node D

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Attacks using Impersonation

These attacks are called spoofing since the malicious node hides its real IP address or MAC address and uses another one.

To do this, the hacker just has to take IP address of other node in the network and use them to announce new route to others nodes.

By doing this, a hacker can easily modify the network topology as he wants and disturb traffic.

Attacks using Fabrication

These attacks can be distinguished as follows:

Falsifying route error messages Corrupting route state: Route cache poisoning Routing table overflow Relay attack: An attacker sends old advertisements to a node causing it to

update its routing table with stale routes. Black hole: An attacker advertises a zero metric for all destinations causing

all nodes around it to route packets towards it

Security Solutions

Security in MANETs is a Cross-layer/Multi-layer issue, rather it is not a single layer issue. Thus a five layered security architecture for mobile ad hoc networks is proposed. This architecture can provide the advantages such as modularity, simplicity, flexibility, and standardization of protocols.

SL5

SL4 SL3 SL2 SL1

Hacker

Node A

Node D

End-to-end SecurityNetwork SecurityRouting/Protocol SecurityCommunication SecurityTrust Infrastructure

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The functions of each layer is given below:

End-to-end Security Layer

This refers to end system security, such as SSL (Secure Sockets Layer (SSL), is a cryptographic protocol for application layer that provide security and data integrity for communications over networks such as the Internet.) , SSH (Secure Shell or SSH is a network protocol that allows data to be exchanged using a secure channel between two networked devices.), and any application-specific security protocol.

Network Security Layer

This layer achives the security services like entity authentication, confidentiality, and integrity as IPSec provides.

Routing/Protocol Security Layer

This refers to security mechanisms applied to routing protocols. The conventional routing protocol attacks are: redirect traffic, packet forwarding to wrong destination, create routing loops, network congestion and channel contention in certain area, multiple colluding attackers may partition the network. This layer provides solution to these attacks by involving two aspects:

Secure Routing. Secure data forwarding.

Protocol Security (Using Secure Protocols)

The requirements for secure protocols are:

Detection of malicious nodes. Guarantee of correct route discovery. Confidentiality of network topology. Stability against attacks.

Examples:

The examples of some secure routing protocols are: ARIADNE (Extension of DSR), SLSP (Secure Link State Routing Protocol), ARAN (Authenticated Routing for Ad Hoc Networks), SAODV (Extension of AODV) (Secure Ad Hoc On Demand Distance Vector), SRP (Secure Routing Protocol), SAR (Security-aware Ad Hoc Routing Protocol), SEAD (Secure Efficient Ad Hoc Distance Vector Routing Protocol).

Communication Security

Secure Protocols

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This refers to the security mechanisms applied in transmitting data frames in a node-to-node manner. It deployes Authentication and Key Management schemes to keep data frame from eavesdropping, interception, alteration, or dropping from unauthorized party along the route from source to destination.

Authentication and Key Management Schemes

In this scheme,

CHAPTER – 5

PROTOCOL COMPARISION AND SIMULATION

6.1 ComparisonThe performance comparison between the proactive, reactive, and hybrid routing

protocols discussed in chapter-3 is done by discussing different criteria of these protocols. The qualitative analysis/comparison is as follows:

Properties DSDV HSR AODV DSR TORA ZRP WRPRouting Philosophy

Proactive Proactive Reactive Reactive Reactive Hybrid(Proactive/Reactive)

Proactive

Loop Free Yes Yes Yes Yes Yes YesRoutes Single Single Multiple Multiple Multiple Multiple SingleRoute Computation

Distributed Heir addr.

Broad-cast

Broad-cast

Broad-cast

Boader-cast Distributed

Route Selection

Distance Vector

Link State

Shortest Path

Source Routing

Link State

DistanceVector, Link State

Shortest Path

Method Broadcast Multicast Broadcast Mutlicast Broadcast Muticast BroadcastUpdate Destination

Neighbor Nodes in Cluster

Source Source Neighbor Neighbor Neighbor

Update

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Broadcast Method

Full Limited Full Limited Local Local, Limited

Local

Update Information

Distance Vector

Virtual Link state

Route Error

Route Error

Nodes Height

Distance vector

Storage Complexity

O(x) O(M*H) O(E) O(E) O(Dd*A) O(L) O(X*A)

Time Complexity

O(d) O(D+r) O(2d) O(2d) O(2d) O(h)

Computational complexity

O(N) O(N+Y) O(2N) O(2N) O(2N) O(N)

DSDV will probably be good enough in the networks, which allows the protocol to converge in reasonable time where mobility cannot be too high. Hence AODV is designed, which is a reactive version of DSDV. It includes multicast capabilities, which will enhance the performance significantly when one node communication with several nodes. The proactive approach in AODV is similar to DSR. They both have route discovery mode that uses request messages to find new routes. The difference is that DSR uses source routing and will learn more routes than AODV. DSR has also one drawback as the source routes that must be carried in each packet. This can be quite costly, especially when QoS is going to be used.

ZRP is very interesting protocol that divides the network into several routing zones. This approach is a very good solution for large networks. Within the zone this has a proactive scheme and between the zones this has a reactive scheme.

6.2 Simulation

The main interest of the project was to test the ability of different routing protocols to react on network topology changes. Furthermore the focus was set on different network sizes, varying number of nodes and area sizes. I have taken 3 routing protocols, one from each type, in account, AODV, DSDV and ZRP. The main aim of taking these 3 protocols was that I wanted to include different kinds of protocols in this comparison, as I have on-demand vs. hybrid routing (ZRP), hop-by-hop vs. source routing. These three protocols cover almost all categories of protocols.

6.2.1 Simulation Environment

The simulations were performed using the QualNet Simulator v3.6 from Scalable Network Technologies, which is a commercial GloMoSim based product. The simulator is fully implemented in C++ while the graphical toolkit is implemented in Java. In this project, only the simulator part was used in order to speed up the simulations. The experiments were executed using the batch mode and the according configuration files.

6.2.2 Performance Metrics of Routing Protocols

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The major four metrics used for evaluation of the relative performance of ad hoc routing algorithms are as follows:

Packet delivery ratio: This can be calculated as the total number of packets received at their intended destination divided by the total number of generated messages at the application layer of the source. It specifies the packet loss rate, which limits the maximum throughput of the network. The better the delivery ratio, the more complete and correct is the routing protocol.

Routing overhead: This can be measured in terms of number of control packets for route discovery and route maintenance or as the ratio of the number of control bytes and the total number of bytes transmitted by the network. It is an important measure for the scalability of a protocol. It for instance determines, if a protocol will function in congested or low-bandwidth situations, or how much node battery power it consumes. If a protocol requires sending many routing packets, it will most likely cause congestion, collision and data delay in larger networks.

Hop count: This can be also referred as path optimization, the average number of hops that successful messages did travel to reach their final destination.

End-to-end delay: End-to-end delay indicates how long it took for a packet to travel from the source to the application layer of the destination. It represents the average delay time of all successfully delivered packets that an application or a user experiences when transmitting data.

6.2.3 Simulation Results

We experimented with different network sizes from 50 up to 1000 nodes. The performance of AODV was very good in all network sizes Almost all protocols perform relatively well in small networks (i.e. 50 nodes), when only few hops need to be taken to reach the destination node. Nevertheless, ZRP already at this point fails to deliver a greater percentage of the originated data packets - it only reaches a delivery ratio of 66%. As the network size grows, AODV always manages to deliver the packets with reliability greater than 90%. At a first glance, it can easily be stated that DSR and ZRP completely fail in larger networks: in a network of 200 nodes, the packet delivery drops below 30 percent

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Figure: Packet delivery ratio introduced by routing protocols with no of nodes

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Figure: Variation of Routing overhead with no of nodes

Figure: Average hop count variation with no of nodes

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Figure: Average End To End delay introduced by routing protocols with no of nodes