Concept Of Multiple Interfaces Between Node Systems Computer Science Essay

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In a world of increasing mobility, there is a increasing need for people to communicate and have timely access to information despite of their location information. A phone call placed from a commuter train may close a business deal, remote access to medical records by a paramedic may save a life, or a demand for reconnaissance updates by a soldier with a handheld device may affect the result of a battle. Each of these instances of mobile communications pose an engineering test that can be met only with an efficient, reliable, wireless communication network. The need for wireless communication systems of growing sophistication and ubiquity has led to the demand for a better understanding of fundamental issues in communication theory and electromagnetics and their implications for the design of highly-competent wireless systems.

A wireless ad hoc network is a decentralized wireless network. The network is ad hoc because each node is willing to forward the data to and from other nodes, and the choice of node that acts as a relay must be made dynamically based on the network connectivity. This is in contrast to the wired networks in which routers perform the task of routing. Similarly in the wireless networks a special node known as an access point manages communication among other nodes.

This project deals with a Mobile Adhoc Network Protocol called Adhoc on demand distance vector routing (AODV). AODV is a reactive protocol based on distance vector routing [1]. A wireless network comprises of several wireless network interfaces that are interconnected with each other on a wireless medium over which transmissions and reception of data is carried out. A Wireless Network Interface is the combination of the physical components of a wireless network adapter and the logical component of the Wireless Network Connection linked up with that adapter. It is the entity to which the wireless connectivity and security settings apply.

Communication is vital in sensitive scenarios. If one link among the communicating nodes fails, the nodes must resume communication using other links. It only depends on the availability of other links (i.e interfaces) as well as the support of these multiple interfaces. If a network protocol has the support of multiple interfaces then connectivity or communication can be guaranteed even when one particular link fails. AODV protocol works well for one physical interface. In our study we aim to implement AODV protocol that supports more than one physical interface.

1.1 PURPOSE STATEMENT

Suppose the nodes of a network are available with multiple physical interfaces over which they can communicate separately. If we are transferring the data between two nodes of a network using an interface and the corresponding link fails, there will be a data loss and we will have to retransmit the data using other interface.

B

Link Type 1

A

Link Type 2

Figure 1.1 Concept of Multiple Interfaces between Nodes

In another case, suppose two nodes of a network are connected over a particular interface (link), and second node is connected to a third node over another type of interface. Now suppose first node has to send data to third node via second node, as shown in the figure below.

A

B

C

Link Type 1

Link Type 2

Figure 1.2 Concept of Different type of Interfaces

In this situation, second node must be capable of dealing with multiple physical interfaces while running a single network protocol.

1.2 OBJECTIVES

To provide with guaranteed communication for mission critical applications where connectivity among communicating nodes is required in any case.

To ensure data transfer among communicating nodes of Mobile Ad Hoc Network even if one of physical link fails.

To make a network independent from type of interfaces (links) between the nodes of that network.

1.3 ORGANIZATION OF STUDY

This document comprises of four chapters. Chapter one includes an introduction to manets.

Chapter two includes an overview to mantes routing protocols classifying the generic categories i-e proactive, reactive, hybrid etc.

Chapter three includes complete explanation of adhoc on demand distance vector (AODV) routing protocol describing the route discovery, packet format, traversal of a packet and complete methodology of AODV.

Chapter four contains implementation of AODV in Opnet describing the nodes used in Manets and how to configure the attributes of the specified nodes.

CHAPTER 2

LITERATURE CITED

2. 1 MANET

2. 1. 1 CONCEPT

A mobile ad-hoc network (MANET) is a type of wireless ad-hoc network, that is a self-configurable network consisting of mobile routers and associated hosts that are connected by wireless links. It is an autonomous system in which routers are free to move randomly and organize themselves arbitrarily thus, the network's wireless topology may change rapidly and unpredictably. Such a network may work in a standalone fashion, or may be connected to a bigger network.

Wireless ad-hoc network is a network in which the communication links are wireless. In an ad hoc network each node is willing to forward data for other nodes, so the nodes forwarding data are determined dynamically. This is in contrast to wired network technologies in which designated nodes, such as routers, switches, hubs, and firewalls, perform the task of forwarding the data. It is also in contrast to manage wireless networks, in which a special node known as an access point manages communication between other nodes.

The traffic types in ad hoc networks are quite different from those in an infrastructure wireless network, including:

1) Peer-to-Peer: In this type of infrastructure communication between two nodes are within one hop. Therefore network traffic (Bps) is usually consistent.

2) Remote-to-Remote: It allows communication between two nodes beyond a single hop while maintaining a stable route between them. It is only possible because of several nodes staying within communication range of each other in a single area or possibly moving as a group.

3) Dynamic Traffic. In this design nodes are dynamic and mobile. Therefore routes must be reconstruct. This results in a poor connectivity and network movement in short bursts.

There are fundamental differences among the architecture of wired networks and wireless networks. The obvious difference is that nodes in ad hoc networks are mobile, there are a number of less obvious but equally significant differences. The bandwidth present is of the order of 1 Mbps, an order of magnitude less than that of wired networks. Secondly, all communication in a wireless network is broadcast, which means that broadcast is no more costly than unicast. And finally, wireless links are much more error prone compare to wired links. Figure shows the examples of both infrastructure and infrastructureless ad hoc wireless networks.

Figure 2.1 Difference between Infrastructure based Network and Ad hoc Network

2. 1. 2 TYPICAL APPLICATIONS OF MANET'S

Minimal configuration and fast deployment make ad hoc networks suitable for emergency situations like natural disasters or military conflicts. The decentralized nature of most wireless ad hoc networks makes them suitable for a variety of applications where central nodes cannot be relied on, and may improve the scalability of wireless ad-hoc networks compared to wireless managed networks. Applications for MANETs are broad ranging and have use in many critical situations:

Figure 2.2 Applications in Military Communications

Rescue Operations

An nonpareil application is for search and rescue operations. These scenarios are characterize by the lack of installed communications infrastructure. This may be because all of the equipment was destroyed, or possibly because the region is too remote. Rescuers must be able to communicate in order to make the most excellent use of their energy, but also to maintain safety. By automatically creating a data network with the communications equipment that the rescuers are already carrying, their job could be made easier.

Scalability

A commercial purpose for MANETs includes ubiquitous computing. By allow computers to forward data for others, data networks may be extended far beyond the usual reach of installed infrastructure. Networks may be made more extensively available and easier to use.

Figure 2.3 Other Applications of MANET's

Reliability

Application of MANETs is sensor networks. This technology is a network based of a very large number of small sensors. These can be used to identify any number of properties of an area. Examples include pressure, temperature toxins, pollutions, etc. The capability of each sensor is very limited, and each must rely on others in order to forward data to a main computer. Individual sensors are limited in their computing capacity and are prone to failure and loss. Mobile ad-hoc sensor networks could be the key to the future homeland security.

More Applications include personal area networking where the mobile nodes may be cell phones, laptops, etc. They also have a great potential in military operations where the nodes may be soldiers, tanks, or airplanes. In addition they could prove to be useful in urban environments as diverse as taxi cab networks, conference rooms, boats and ships, search operations as well as policing and firefighting.

2. 2 MANET ROUTING PROTOCOLS

Mobile Ad hoc network became a hot topic for research especially for notebook and other handheld mobile devices like PDA (Personal Digital Assistant), cell phone etc in the mid to late 90s. Up till now many researchers contributed their efforts in the MANET by proposing their own protocols. Hundreds of protocols have been proposed for MANET that works well under specific network infrastructure and requirements. There is no single protocol that would fit for all the scenarios with different network nodes, node mobility pattern and traffic loads. To overcome this problem we classify the major protocols under various categories as listed below.

2.2.1 Proactive Routing (Table-Driven)

This type of protocols maintains updated lists of destinations and their routes by distributing routing tables throughout the network time to time. Some major protocols of this category are :

WRP

DSDV

2.2.2 Reactive Routing (On-Demand)

This type of protocols finds a route on demand by flooding the network with Route Request packets. This protocol need not to maintain the routes so reduce routing overhead is observed. Three different kinds of messages are circulating among the network [2] i.e. route request (RREQ) to request a new route when one node want to send data, route reply (RREP) after the successful discovery of destination node then the route reply message is forward back to the source node and route error (RERR) is use when an error occurred in the network like link broken etc. Some major protocols of this category are:

DSR

AODV

2.2.3 Hybrid Routing (blend of Reactive and Proactive)

Hybrid Routing, commonly referred to as balanced-hybrid routing, is a combination of distance-vector routing, which works by sharing its knowledge of the entire network with its neighbors and link-state routing which works by having the routers tell every router on the network about its closest neighbors. Some major protocols of this category are :

SSR

ZRP

2.2.4 Hierarchical (Zone/Cluster-Based) Routing Protocols

This type of protocols often group routers together by function into a hierarchy [3]. Its Algorithm is based on link state [4]. The routing is initially established with some proactively prospected routes and then serves the demand from additionally activated nodes through reactive flooding on the lower levels. Some major protocols of this category are:

DDR

GSR

2.2.5 Geographical Routing Protocols (Location based)

Geographic routing is also known as georouting or positionbased routing. Geographic Routing Protocols relies on geographic position information. The main idea is to send the message from source to destination based on geographic location instead of network address. The source node is aware of the location of the destination. So there is no need to discover route and any additional knowledge of network topology. Geographic routing is based on two principal assumptions:

It is assumed that every node knows it own and its network neighbors positions.

The source of a message is assumed to be informed about the position of the destination.

Georouting is very remarkable because it operates without any routing tables. Furthermore, once the location of the destination is know, all operations are rigorously local, that is, every node is required to keep track only of its direct neighbor.

Geographical routing optimizes route calculation mechanism by implying the significance of spatial location with respect to network performance. Usually they use Global Position System (GPS) for routing.

2.2.6 Power-Aware Routing Protocols

Ad hoc nodes are operated by battery and have limited energy assets, because a node in an ad hoc network is normally a laptop, a personal digital assistant or any mobile device, energy supplied by batteries is likely to be a insufficient resource, and in some applications energy is entirely non-renewable [5], make energy efficiency a key concern in the operation of such networks specially during wireless connectivity. Furthermore the lifetime of batteries has not been improved as fast as processing speed of microprocessors. In MANET the node consume more energy as compare to other wireless network because of absence of network infrastructure. Mobile node in MANET must act as a router and join in the process of packets forwarding so packets loads are high. Now we will discuss power management schemes Figure .

Fig 2.4 Provides an overview of the power aware management scheme.

Battery Management: The challenge is not to provide each node with higher battery power but to utilize the available battery power in a very efficient manner.

Transmission Power Management: Find out the minimum power limitation route. Find out the maximum average power route.

System Power Management: Find out the ways to minimize the power consumption during the processing task.

2.2.7 Multicast Routing Protocols

Multicast routing protocols allow a collection of multicast routers to construct distribution trees when a host on a directly attached subnet, usually a LAN, wants to get traffic from a certain multicast group. Some major protocols of this category are:

DVMRP

MOSPF

2.2.8 Adaptive Routing (Situation Aware)

This type of protocols combines the advantages of proactive and of reactive routing. The routing is initially established with some proactively prospected routes and then serves the demand from additionally activated nodes through reactive flooding. [6]

2.3 LOCAL AREA NETWORK (LAN)

Local area networks (LANs) are computer networks ranging in size from a few computers in a single office to hundreds or even thousands of devices spread across several buildings. They function to link computers together and provide shared access to printers, file servers, and other services. LANs in turn may be plugged into larger networks, such as larger LANs or wide area networks (WANs), connecting many computers within an organization to each other and/or to the Internet.[113]

You don't necessarily have only computers on a LAN. You can also connect printers, hard disks, CD-ROMs, Printers, Modems, etc and other devices for use by other computers on the network as if they were their own. For instance, if you connect a printer on a LAN and configure it to be shared among all users on the LAN, print jobs can be sent to that printer from all computers on the LAN. Computers that offer resources are called Servers.

Computers called Workstations can attach the resources (typically hard disks and printers) offered by servers as if they were their own.

A computer can be both a Server and Workstations at the same time, in which case it is called a Peer. Networks without dedicated servers are called peer-to-peer networks. Networks with one or more dedicated servers are called server based networks even though they may also have peers on them.

Because the technologies used to build LANs are extremely diverse, it is impossible to describe them except in the most general way. Universal components consist of the physical media that connect devices, interfaces on the individual devices that connect to the media, protocols that transmit data across the network, and software that negotiates, interprets, and administers the network and its services. Many LANs also include signal repeaters and bridges or routers, especially if they are large or connect to other networks.

The following characteristics differentiate one LAN from another:

Topology : The geometric arrangement of devices on the network. For example, devices can be arranged in a star, ring or in a straight line.

Figure 2.5 Star Network Topology and Bus Topology

Protocols : The rules and encoding specifications for sending data. The protocols also determine whether the network uses a peer-to-peer or client/server architecture.

Figure 2 Peer to Peer Architecture and Clint Server Architecture

Figure 2.6 Peer to Peer and Client Server Architecture

Media : Devices can be connected by twisted-pair wire, coaxial cables, or fiber optic cables. Some networks do without connecting media altogether, communicating instead via radio waves.

LANs are capable of transmitting data at very fast rates, much faster than data can be transmitted over a telephone line; but the distances are limited, and there is also a limit on the number of computers that can be attached to a single LAN.

2.4 WIRELESS LOCAL AREA NETWORK

A wireless local area network (WLAN) is a local area network (LAN) that doesn't rely on wired Ethernet connections. A WLAN can be either an extension to a current wired network or an alternative to it. Use of a WLAN adds flexibility to networking. A WLAN allows users to move around while keeping their computers connected.

Figure 2.7 Wireless Local Area Network

WLANs have data transfer speeds ranging from 1 to 54Mbps, with some manufacturers offering proprietary 108Mbps solutions. The 802.11n standard can reach 300 to 600Mbps.

Because the wireless signal is broadcast so everybody nearby can share it, several security precautions are necessary to ensure only authorized users can access your WLAN.

A WLAN signal can be broadcast to cover an area ranging in size from a small office to a large campus. Most commonly, a WLAN access point provides access within a radius of 65 to 300 feet.

IEEE 802.11 is a set of standards for wireless local area network (WLAN) computer communication, developed by the IEEE LAN/MAN Standards Committee (IEEE 802) in the 5 GHz and 2.4 GHz public spectrum bands.

Figure 2.8 Wireless Local Area Network Ad Hoc Mode (No Access point)

2.4. 1 802.11 Standards

The 802.11 family includes several hardware standards. The most popular are those defined by the 802.11b and 802.11g protocols, and are amendments to the original standard. 802.11a was the first wireless networking standard, but 802.11b was the first widely accepted one, followed by 802.11g and 802.11n. The 802.11a, b, and g standards are the most common for home wireless access points and large business wireless systems.

Security was originally purposefully weak due to export requirements of some governments. The security standard WEP (Wired Equivalent Privacy) was introduced. It encrypts data traffic between the wireless access point and the client computer, but doesn't actually secure either end of the transmission. Also, WEP's encryption level was relatively weak (only 40 to 128 bits). After WEP another security scheme was introduced known as WPA(Wi-Fi Protected Access). This scheme implemented higher security and addresses the flaws in WEP, but is intended to be only an intermediate measure until further 802.11i security measures were developed. It was later enhanced via the 802.11i amendment after governmental and legislative changes. 802.11n is a new multi-streaming modulation technique that is still under draft development, but products based on its proprietary pre-draft versions are being sold. Other standards in the family (c-f, h, j) are service amendments and extensions or corrections to previous specifications.

802.11b and 802.11g use the 2.4 GHz ISM band. Because of this choice of frequency band, 802.11b and g equipment may occasionally suffer interference from microwave ovens and cordless telephones. Bluetooth devices, while operating in the same band, in theory do not interfere with 802.11b/g because they use a frequency hopping spread spectrum signaling method (FHSS) while 802.11b/g uses a direct sequence spread spectrum signaling method (DSSS). 802.11a uses the 5 GHz U-NII band, which offers 8 non-overlapping channels rather than the 3 offered in the 2.4GHz ISM frequency band.

2.4.2 WLAN types

The private home or small business WLAN

Commonly, a home or business WLAN employs one or two access points to broadcast a signal around a 100- to 200-foot radius. With few exceptions, hardware in this category subscribes to the 802.11a, b, or g standards (also known as Wi-Fi). Home and office WLANs adhering to the new 802.11n standard are appearing.

The enterprise class WLAN

This type employs a large number of individual access points to broadcast the signal to a wide area. The access points have more features than equipment for home or small office WLANs, such as better security, authentication, remote management, and tools to help integrate with existing networks. These access points have a larger coverage area than home or small office equipment, and are designed to work together to cover a much larger area. Such equipment adheres to the 802.11a, b, g, or n standard.

Wireless WAN (wide area network)

Although a WAN by definition is the exact opposite of a LAN, wireless WANs (WWANs) deserve brief mention here, especially because the distinction is becoming less and less obvious to end users. WANs used to exist in order to connect LANs in different geographical areas.

CHAPTER 3

3 ADHOC ON DEMAND DISTANCE VECTOR (AODV) ROUTING PROTOCOL

AODV (Ad-hoc On-demand Distance Vector Routing) is a loop-free routing protocol for Ad hoc networks. It is designed to be self-starting in an environment of mobile nodes, defying a variety of network doingses such as node mobility, link failures and packet losses. It is a reactive routing protocol, meaning that it establishes a route to a destination only when required. The most common routing protocols of the Internet are proactive, meaning they find routing paths independently of the utilization of the paths.

AODV maintains a routing table at each node. The routing table entry for a destination contains following essential fields:

• Destination IP Address

• Prefix Size

• Destination Sequence Number

• Next Hop IP Address

• Lifetime (expiration or deletion time of the route)

• Hop Count (number of hops to reach the destination)

• Network Interface

• State and routing flags (e.g. valid, invalid)

All packets designated to the destination are sent to the next hop node. The sequence number acts as a form of time-stamping, and is a measure of the freshness of a route. The hop count interprets the current distance to the destination node.

3.1 ROUTE DISCOVERY IN AODV

In AODV, nodes detect routes in request-response cycles. A node requests a route to a destination by broadcasting an RREQ (Route Request) message to all its neighbors. When a node receives an RREQ message but does not have a route to the called for destination, it in turn broadcasts the RREQ message. Also, it retrieves a reverse-route to the requesting node which can be used to forward subsequent reactions to this RREQ.

This process repeats until the RREQ reaches a node that has a valid route to the destination. This node (which can be the destination itself) responds with an RREP (Route Reply) message. This RREP is unicast along the reverse routes of the intermediate nodes until it reaches the requesting node. Thus, at the end of this request-response cycle a bidirectional route is accomplished between the requesting node and the destination.

When a node loses connectivity to its next hop, the node invalidates its route by sending an RERR (Route Error) to all nodes that have potentially received its RREP.

On receipt of the AODV messages: RREQ, RREP and RERR, the nodes update the next hop, sequence number and the hop counts of their routes.

3.1.1 Flow of Events in AODV

Following is a flow chart which shows the activities of nodes in the network and the sequence of those activities when they receive AODV messages.

Figure 3.1 Flow Chart describing responses of Nodes on receiving different AODV messages

3.1.2 EXAMPLE

An example is presented over here to understand the route discovery in AODV.Suppose S would like to communicate with D.

Figure 3.2 AODV Route Development step 1

The node broadcasts a RREQ to find a route to the destination. S generates a Route Request with destination address, Sequence number and Broadcast ID and sent it to his neighbor nodes.

Figure 3.3 AODV Route Development step 2

Each node receiving the route request sends a route back (Forward Path) to the node.

Figure 3.4 AODV Route Development step 3

A route can be determined when the RREQ reaches a node that offers accessibility to the destination, e.g., the destination itself).

Figure 3.5 AODV Route Development step 4

The route is made available by unicasting a RREP back to D and is written in the routing table from S. After receiving the route reply each node has to update its routing table if the sequence number is more recent.

Figure 3.6 AODV Route Development step 5

Now node S can communicate with node D.

Figure 3.7 AODV Route Development step 6

When a link break in an active route is discovered, the broken link is invalid and a RERR message is sent to other nodes. If the nodes have a route in their routing table with this link, the route will be wiped off. Node S sends once again a route request to his neighbor nodes, or a node on the path to the destination can try to find a route to D. This mechanism is called: Local Route Repair.

Figure 3.8 Generation of Route Error on link break

3.3 ADVANTAGES AND DISADVANTAGES

The main advantage of this protocol is that routes are established on demand and destination sequence numbers are utilized to find the most latest route to the destination. The connection setup delay is minor. One of the disadvantages of this protocol is that intermediate nodes can result in 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 holding stale entries. Also multiple Route Reply packets in response to a single Route Request packet can lead to heavy control overhead. Another disadvantage of AODV is that the periodic beaconing results in unnecessary bandwidth consumption.

3.4 RECEVING RREQ (Route Request)

When a node receives RREQ, it checks whether it has an entry for the originator of RREQ in its routing table or not. If an entry is not present, it saves the route to the originator with sequence number present in RREQ message. If an entry is already present in its routing table for the originator, then it compares the existing sequence number in routing table with the received one. If the received sequence number is greater than the existing one it updates the route entry for originator and then processes this RREQ. If the received sequence number is smaller or equal to the existing one it does not update the route entry for originator and then processes this RREQ.

The receiving node then compares its route RREQ ID with the RREQ ID's of RREQ's which it has already received (seek list). If RREQ ID matches, it discards RREQ and does not forward it.

If RREQ ID does not match with any entry of the list of RREQ ID's, then Further the receiving node of RREQ checks whether it is the destination of that RREQ or not. If it is the target destination, it generates RREP (Route Reply) in response and unicasts it to the originator. if it is not the target destination of that RREQ, it checks its routing table to see whether it contains the route to the target destination or not. Also this route is fresh or not (by comparing sequencing number). If it finds a fresh route to destination in its routing table then in response it generates RREP and unicasts it to the originator of RREQ. If it does not contain a fresh route to the target destination then it broadcasts this RREQ on its all interfaces.

In case of multiple physical interfaces, every node deals with RREQ received on a particular interface independently and separately. It means, when a node receives RREQ on interface 1, it will process it as mentioned above but when it will receive the same RREQ (with same RREQ ID) through other interface, the node will discard this request after saving reverse route to originator through this path.

While this node will send RREP of this RREQ it will unicast it on both interfaces.

3.5 RECEVING RREP (Route Reply)

When a node receives a RREP message, it first updates its forward route to the immediate sender of RREP. Then it checks whether this RREP is the response of a RREQ generated by itself or not. If the received RREP is of its own RREQ, the process of route discovery is completed here. Now it starts sending data to the desired destination. If this RREP is not of its RREQ then it unicasts RREP to the next hop towards destination.

In case of multiple physical interfaces, when a node receives RREP on an interface, it updates its forward route corresponding to that interface and unicasts RREP to next hop on the interface over which it previously received corresponding RREQ.

RECEVING RERR (Route Error)

When a node receives RERR message, it removes corresponding affected routes. If the receiving node is the next hop of any other node towards the destination with affected link break, then it forwards RERR to its next hops so that they can also remove their affected routes; else it discards RERR.

In case of multiple physical interfaces, RERR will be generated and forwarded only when all links to a node fail because it can be a case that one link to a node may fail but other may work fine.

3.7 EXAMPLE

An example is presented over here to understand the node based AODV routing. This example covers traversing and processing of Route Request, Route Reply and Route error messages. In this example a scenario is shown in which four nodes are connected as shown:

Supposition:

Suppose a network of four Nodes as shown in diagram below.

Node 1 has one interface IF-1 and its neighbor is Node 2.

Node 2 and Node 3 are neighbors on both interfaces IF-1 and IF-2.

NODE 1

IF-1

IF-1

NODE 4

IF-1

IF-1

IF-2

IF-2

NODE 2

NODE 3

IF-1

IF-1

IF-2

IF-2

IF-1

IF-1

IF-2

IF-2

Similarly Node 3 and Node 4 are neighbors on both interfaces IF-1 and IF-2.

Figure 3.9 Example Wireless Ad hoc Network of four Nodes

Sequence of Events in Route Discovery of Node 4 from Node 1:

Types of messages used to develop AODV routing:

RREQ: Route Request

RREP: Route Reply

RERR: Route Error

3.7.1 Traversing of RREQ:

Processing of Node 1

Node 1 will generate a RREQ with a sequence number and broad cast this RREQ on its interface IF-1. Node 1 is only listenable by Node 2 and only on IF-1.

Processing of Node 2

Node 2 will receive RREQ on its interface IF-1.

Node 2 will set reverse route for Node 1 on interface IF-1 if the sequence number of received RREQ is greater than the existing one.

Node 2 will check if it is the target destination or not.

If Node 2 is the destination node, it will update its sequence number for Node 1 (if necessary), generate RREP and will unicast it to Node 1 on interface 1.

If Node 2 is not the destination then it will check whether it has any route to destination or not.

If it already has the route to the destination on its both interfaces or any interface, it will compare the existing sequence number and that in the RREQ. If the existing sequence number is equal or greater than the received one, Node 2 will generate and unicast RREP to Node 1 on its interface 1.

If the existing sequence number is less than the received one, Node 2 will broadcast this RREQ on its both interfaces IF-1 and IF-2. Before broad casting the RREQ on either interface, Node 2 will set the correct interface index in RREQ.

In this example, since Node 2 will not have route to Node 4, so it will broad cast received RREQ.

Processing of Node 3

Node 3 will receive RREQ on its both interfaces IF-1 and IF-2.

Suppose Node 3 will receive RREQ on interface IF-1 first.

Node 3 will set reverse route for Node 1 on interface IF-1 if the sequence number of received RREQ is greater than the existing one.

Node 3 will check if it is the target destination or not.

If Node 3 is the destination node, it will update its sequence number for Node 1 (if necessary), generate RREP and will unicast it to Node 2 on interface 1.

If Node 3 is not the destination then it will check whether it has any route to destination or not.

If it already has the route to the destination on its both interfaces or any interface, it will compare the existing sequence number and that in the RREQ. If the existing sequence number is equal or greater than the received one, Node 3 will generate and unicast RREP to Node 2 on its interface 1.

If the existing sequence number is less than the received one, Node 3 will broadcast this RREQ on its both interfaces IF-1 and IF-2. (Does not have fresh enough route). Before broad casting the RREQ on either interface, Node 3 will set the correct interface index in RREQ.

Node 3 will also receive this RREQ on interface IF-2 again. If Node 3 has already flooded this RREQ received on interface 1, it will discard this RREQ, but later it will also send RREP to Node 2 on this Interface 2. Also Node 3 will set reverse route for Node 1 on interface IF-2.

In this example, since Node 3 will not have route to Node 4, so it will broad cast received RREQ on its both interfaces 1 and 2.

Node 3 is only listenable by Node 4 on its both interfaces IF-1 and IF-2.

Processing of Node 4

Same steps will be repeated by Node 4 as by Node 3.

In this example Node 4 will generate RREP.

Traversing of RREP:

Processing of Node 4

Suppose Node 4 receives RREQ on interface 1 first.

First Node 4 will set reverse route to Node 3 on interface 1. Then it will update its own sequence number by comparing its sequence number with the sequence number of destination in received RREQ.

Then it will generate and unicast RREP to Node 3 on interface 1.

When Node 4 will again receive same RREQ through other interface, it will set its reverse route to Node 3 through this interface and will discard it.

Processing of Node 3

Suppose Node 3 will receive RREP on interface 1 first.

When Node 3 will receive RREP message, it will set its forward route to Node 4 on interface 1.

Then Node 3 will check if it is the originator of corresponding RREQ or not.

If it is the originator of corresponding RREQ, it will start sending the data packets queued to the node from which it recently received RREP.

If it is not the originator of corresponding RREQ of received RREP then it will unicast (forward) this RREP to next hop through the interfaces over which it received corresponding RREQ.

In this example, Node 3 will unicast this RREP to Node 2 on interfaces 1.

Processing of Node 2

Suppose Node 2 will receive RREP on interface 1 first.

When Node 2 will receive RREP message, it will set its forward route to Node 3 on interface 1.

Then Node 2 will check if it is the originator of corresponding RREQ or not.

If it is the originator of corresponding RREQ, it will start sending the data packets queued to the node from which it recently received RREP.

If it is not the originator of corresponding RREQ of received RREP, then it will unicast (forward) this RREP to next hop (Node 1) through interface 1 only.

In this example Node 2 will unicast this RREP to Node 1 on interface 1.

Processing of Node 1

When Node 1 will receive RREP message, it will set its forward route to Node 2 on interface 1.

Then Node 1 will check if it is the originator of corresponding RREQ or not.

If it is the originator of corresponding RREQ, it will start sending the data packets queued to the node from which it recently received RREP.

In this example, since Node 1 is the originator of RREQ so it will now start sending data to Node 2 destined for Node 4.

Hence the Route Discovery process completes.

In this example the routing table of Node 1 will look like:

Destination node

Next node

Hop Count

My Interface index

Next node IP

Destination Sequence Number

1

1

1

1

IP-1

X

3

3

1

1

IP-1

X

4

3

2

1

IP-1

X

The routing table of Node 2 will look like:

Destination node

Next node

Hop Count

My Interface index

Next node IP

Destination Sequence Number

2

2

1

1

IP-1

X

3

2

2

1

IP-1

X

4

2

3

1

IP-1

X

Flags, states and timers are not shown in the table.

Data type of node and interface index is 8 bit integer.

CHAPTER4

4.1 IMPLEMENTATION

We have chosen Opnet environment in order to implement our task. Opnet provides a complete environment for developing communication networks.Opnet modeling task falls into three phases of i-e data collection, simulation and analysis. The package consists of a number of tools, each one focusing on particular aspects of the modeling task. These tools fall into three major categories that correspond to the three phases of modeling and simulation projects: Specification, Data Collection and Simulation and Analysis. These phases are inevitably performed in series. They generally form a cycle, with a return to Specification following Analysis. Specification is in fact divided into two parts: initial specification and re-specification.

Figure 4.1 Simulation Project Cycle of OPNET

4. 1. 1 Manets Node Model

Figure 4.2 Nodes of MANET's

Wireless LAN workstations and servers

Node models can be used to make application traffic such as Email, VOIP, HTTP , TCP over IP and can also be configured to run AODV as the routing protocol.

MANET stations

These node models can be used to generate raw packets over IP over WLAN. They can configure as a traffic source or destination and can be configured to run AODV as the routing protocol.

Profile Config

Profiles config describes the activities of a user or group of users in terms of the applications used over a interval of time. Different profiles can be created that can represent different user groups.

Application Config

A profile is created using different application definitions; for every application definition, you can specify handling parameters such as start time, duration and repeatability.

Rxgroup Config

Rxgroup Config is used to calculate set of possible receiver that a node can communicate with, this utility node can significantly speed up a simulation by eliminating receivers that do not match.

Task Config

Task confrigration nodes are used to configure custom Applications

Mobility Config

These nodes are used to define mobility profile. Movement of the object (node)Is controlled by this node based on configure parameters.

4. 1.2 AODV CONFIGURATION in OPNET

AODV can be configured by editing the attributes of a node.

Figure 4.3 Attribute of a Node

4. 1.3 AODV network modeled in Opnet

The network with five Wireless LAN nodes is deployed. All the nodes in the network are configured to work under ad hoc mode. Among the five nodes as shown in figure four nodes are fixed ad hoc nodes while one node (mobile_node) is mobile. The mobile_node starts moving after 200 seconds along the path specified during the simulation period.

Figure 4.4 Configured five node campus network for TCP traffic

After deploying the nodes they are to be configured and the following configuration is to be done:

Task Configuration, Application Configuration, Profile Configuration, Mobile node

Once you are done with the configuration results are analyzed by running discrete event simulation.

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