i

Modeling and Analytical Performance Evaluation of Route Discovery/Route Maintenance in Reactive and

Proactive Routing Protocols for MANETs and VANETs

By

Mr. Danish Mahmood

Registration Number: CIIT/FA10-REE-010/ISB

MS Thesis

In

Network Engineering

Electrical Engineering Department

COMSATS Institute of Information Technology

Islamabad – Pakistan

Fall, 2011

ii

COMSATS Institute of Information Technology

Modeling and Analytical Performance Evaluation of Route Discovery/Route Maintenance in Reactive and

Proactive Routing Protocols for MANETs and VANETs

A Thesis Presented to

COMSATS Institute of Information Technology, Islamabad

In partial fulfillment

Of the requirement for the degree of

MS (Network Engineering)

By

Mr. Danish Mahmood

CIIT/FA10-REE-010/ISB

Fall, 2011

iii

Modeling and Analytical Performance Evaluation of Route discovery/Route Maintenance in Reactive and Proactive Routing Protocols for MANETs and VANETs

A post Graduate Thesis submitted to Electrical Engineering as partial fulfillment of the requirement for the award of Degree of M.S (Electrical Engineering).

Name Registration Number

Mr. Danish Mahmood CIIT/FA10-REE-010 /ISB

Supervisor

Dr. Nadeem Javaid

Assistant Professor

Department of Electrical Engineering

Islamabad Campus

COMSATS Institute of Information Technology (CIIT)

Islamabad Campus

December, 2011

iv

Final Approval

This thesis titled

Modeling and Analytical Performance Evaluation of Route Discovery/Route Maintenance in Reactive and

Proactive Routing Protocols for MANETs and VANETs By

Mr. Danish Mahmood

CIIT/FA10-REE-010/ISB

Has been approved

For the COMSATS Institute of Information Technology, Islamabad

External Examinar: __________________________________

Supervisor: ________________________

Dr.Nadeem Javaid Department of Electrical Engineering Islamabad Campus

HoD: ________________________

Dr. ShafayatAbrar Department of Electrical Engineering Islamabad Campus

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Declaration

I Mr. Danish Mahmood, CIIT/FA10-REE-010/ISB hereby declare that I have produced the work presented in this thesis, during the scheduled period of study. I also declare that I have not taken any material from any source except referred to wherever due that amount of plagiarism is within acceptable range. If a violation of HEC rules on research has occurred in this thesis, I shall be liable to punishable action under the plagiarism rules of the HEC.

Date: ________________ Signature of the student:

________________ Mr. Danish Mahmood CIIT/FA10-REE-051/ISB

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Certificate

It is certified that Mr. Danish Mahmood CIIT/FA10-REE-051/ISB has carried out all the work related to this thesis under my supervision at the Department of Electrical Engineering COMSATS Institute of Information Technology, Islamabad and the work fulfills the requirements for award of MS degree.

Date: _________________

Supervisor: ____________________

Dr. Nadeem Javaid Department of Electrical Engineering CIIT Islamabad Campus

Head of Department:

_____________________________

Dr.Shafayat Abrar HoD Electrical Engineering

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DEDICATION My work is dedicated to:

To ALLAH Almighty for His guidance and mercy over me,

To my family for their immense love and moral support throughout my master’s program,

To my babies Raaim Mahmood and Nofil Mahmood (Son and Nephew),

Thanks to Almighty that I am blessed with such parents who always backed me up

And

The person who made this work possible, my thesis supervisor, Dr. Nadeem Javaid who acted not only as a supervisor but on every step of my work, he is the one who stood besides and supported everywhere with the help of his knowledge, guidance and any kind of support I needed.

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ACKNOWLEDGMENT

I am grateful to my supervisor, Dr. Nadeem Javaid, whose gradual encouragement, guidance and insightful criticism from the beginning to the final level enabled me have a deep understanding of the thesis. My Thesis Supervisor acted not only as a supervisor but on every step of my work, he is the one who stood besides and supported everywhere with the help of his knowledge, guidance and every kind of support I needed.

Dr. Safdar H. Bouk and Dr. Mustafa Shakir must also be thanked as they, on steps have spared their valuable time for discussing thesis and motivation to work harder.

My Lab Team, must also be acknowledged as it is all due to their cooperation and support that I managed to work.

And

Almighty Allah, who has blessed me with such learned parents, learned supervisor and gave me opportunity to sit besides learned scholars. Without his blessings nothing was possible.

Mr. Danish Mahmood

CIIT/FA10-REE-051/ISB

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ABSTRACT

Ad Hoc networks are the burning issue amongst researchers in current era. The reason is its

challenging environment where a solid mechanism is needed to provide efficient and reliable

communications. Mobility of wireless station which we refer as nodes along with the wireless

communication issues in combination with several other limitations gives a challenging

environment for working on Ah Hoc networks. MANETs or VANETS both are Ad Hoc

networks. In MANETs there may be mobility but not that much as one can imagine in

VANETs. Hence every scenario requires some different attributes to make communication

between nodes possible. Routing protocols play a vital role as they are responsible of

directing information from one sending node to other receiving node. For static and barely

mobile environment, Proactive routing protocols have developed while for highly mobile

environment, reactive protocols are proposed. There are Hybrid protocols as well but, in this

Thesis we confine ourselves to Route discovery and maintenance phases of proactive and

reactive routing protocols which are widely studied and observed now days. We observed

that less mathematical modeling is done with respect to simulations. Hence we contributed a

generalized analytical model for routing overhead of route discovery and maintenance phases

of both proactive and reactive routing protocols. Besides analytical modeling of reactive and

proactive routing protocols, we choose most widely studied reactive routing protocols i.e.

AODV, DSR and DYMO and compare them with each other and most prominent proactive

routing protocols i.e. FSR, DSDV and OLSR. We simulate these six routing protocols under

metrics of throughput, End - End delay and routing over head and discuss results keeping

mobility and scalability factor in emphasis.

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TABLE OF CONTENTS

1. INTRODUCTION ………………………………………………….………………..1 1.1 Taxonomy of Routing Protocol…...………………………………………………3 1.2 Proactive Routing Protocols………………………………………….…..……….4 1.3 Reactive Routing Protocols……………………………………….……..……......4

1.3.1 Route Discovery Phase…………………………………………………...5 1.3.2 Route Maintenance Phase………………………………………………...5 1.3.3 Route Deletion……………………………………………………………6

2. Routing: Reactive & Proactive…………………………………..........………..7 2.1 Reactive Routing…………………………………………….……………………8 2.2 Ad Hoc On Demand Distance Vector (AODV……………………….……..……8

2.2.1 Route Discovery and Route Maintenance of AODV…………………...10 2.2.2 Binary Exponential Back off Algorithm and AODV…………………...13 2.2.3 BEB Algorithm for AODV……………………………………………...14 2.2.4 Expanding Ring Search Algorithm and AODV………………….……..14 2.2.5 ERS Algorithm for AODV…………………………………….………..15

2.3 Dynamic Source Routing …….....……………………..…................................16 2.3.1 Route Discovery and Route Maintenance of DSR……………………...16 2.3.2 Binary Exponential Back Off Algorithm and DSR……………………..19 2.3.3 Expanding Ring Search Algorithm and DSR………………………..….20

2.4 Dynamic MANET On Demand (DYMO)…………………...…………………..20 2.4.1 Route Discovery and Route Maintenance of DYMO………………...…21 2.4.2 BEB and ERS in DYMO…………………………………………...……23 2.4.3 BEB Algorithm for DYMO…………………………………………...…25

2.5 Comparison: ERS and BEB in AODV, DSR and DYMO……………………….26 2.6 Proactive Routing…………………………………………………………….….27 2.7 Fisheye State Routing…………………………………………………………….27

2.7.1 Fisheye Technique……………………………………………..…………28 2.7.2 FSR working……………………………………………………...………30

2.8 Destination Sequenced Distance Vector (DSDV)…………………………..……31 2.8.1 Route Discovery and Route Maintenance for DSDV………………...…..31

2.9 Optimized Link State Routing (OLSR)………………………………………….34 2.9.1 Multipoint Relay Concept……………………………………………………35 2.9.2 Route Discovery and Route Maintenance of OLSR…………………………36

3. Analytical Modeling: Reactive and Proactive Routing…………………….…….38 3.1 Reactive Modeling……. ………………………………………………….….……...39

3.1.1 Route Discovery…………………………………………………….….……39 3.1.2 Route Maintenance………………………….………………………….……39 3.1.3 Steps involved in RD and RM……………………………………………….40 3.1.4 Routing Overhead for a single Route………………………………………..40

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3.1.5 Overhead due to RREQ Packets……………………………….…………….41 3.1.6 Overhead due to RREP Packets………………………………..……………43 3.1.7 Monitoring Overhead of one Link………………………..…………………44 3.1.8 Routing Overhead for “n” Routes…………………..……………………….45

3.2 Proactive Routing…………………………………………………………………….47 3.2.1 Route failure Impact on routing overhead………………………..………….48 3.2.2 Periodic Message Overhead……………………………………….…………49 3.2.3 Triggered Message Overhead……………………………….……………….49 3.2.4 Routing Overhead of Proactive Routing Protocol…………………….……..51 3.2.5 Calculations and Results……………………………………….…………….53

4. Experiments, Results and Discussions……………...…………………..….………57 4.1 Simulations………………………………………………………………………...…58 4.2 Parameters for Experiments……………………………………………….…………58 4.3 Reactive Experiments………………………………………………….…………….59

4.3.1 Throughput of Reactive Routing…………………………………...………..59 4.3.2 End - End Delay of Reactive Routing…………………………………..….61 4.3.3 Normalized Routing Load of Reactive Routing………………………….…62

4.4 Proactive Experiments……………...…......….……......................................………64 4.4.1 Throughput of Proactive Routing……………………………………..…….64 4.4.2 End - End Delay of Proactive Routing……………………………………..65 4.4.3 Normalized Routing Load of Proactive Routing……………………………67

4.5 Conclusion………………………………….…………...…………………......…….68 5. References…………………………..…..…..………………………………………72

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LIST OF FIGURES

Figure 1.1 Routing protocols………………………..…………………………………….……3

Figure 2.1 Propagation of RREQ packets in AODV…………………………….……………11

Figure 2.2 Propagation of RREP packets in AODV………………………….……………….12

Figure 2.3 Propagation of RREQ packets in DSR…………………………………………….17

Figure 2.4 Propagation of RREP packets in DSR…………………………………………….18

Figure 2.5 Propagation of RREQ packets in DYMO…………………………………………21

Figure 2.6 Propagation of RREP packets in DYMO………………………………………….22

Figure 2.7 Fisheye Routing Protocol………………………………………………………….29

Figure 2.8 Triggered update notification………………………………………………...……32

Figure 2.9 DSDV protocol…………………………………………………………...………..34

Figure 2.10 Functions of MPR in OLSR………………………………………..…………….35

Figure 3.1 RREQ Flooding in Reactive Routing Protocols………………………………..….42

Figure 3.2 RREP and link establishment in Reactive Routing Protocols……………………..43

Figure 3.3 Link Monitoring in reactive Routing Protocol (AODV)…………………….…….45

Figure 3.4 Effect of triggered Messages……………………………………………..………..50

Figure 4.1 Throughput (AODV, DSR, DYMO)…………………………………….………..61

Figure 4.2 End - End Delay (AODV, DSR, DYMO)………………………………..………63

Figure 4.3 Normalized Routing Load (AODV, DSR, DYMO)…………………………..…..64

Figure 4.4 Throughput (FSR. DSDV, OLSR)………………………………………………..66

Figure 4.5 End - End Delay (FSR, DSDV, OLSR)………………………………………….67

Figure 4.6 Normalized Routing Load (FSR, DSDV, OLSR)…………………………..…….68

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LIST OF ABBREVIATIONS:

AODV Ad-hoc On Demand Distance Vector

BEB Binary Exponential Backoff

DSDV Destination Sequenced Distance Vector

DSR Dynamic Source Routing

DV Distance Vector

DYMO Dynamic MANET on Demand

ERS Expanding Ring Search

FSR Fisheye State Routing

IETF Internet Engineering Task Force

LS Link State

MAC Medium Access Control

MANET Mobile Ad Hoc Network

MPR Multi Point Relay

NRL Normalized routing load

OLSR Optimized link State Routing

RD Route Discovery

RERR Route Error

RREQ Route Request

RREP Route Reply

RFC Request for Comments

RM Route Maintenance

TTL Time to Live

VANET Vehicular Ad Hoc Network

WSN Wireless Sensor Network

MANET Mobile Ad Hoc Network

WSN Wireless Sensor Network

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1

Chapter 1

Introduction

2

Communication is being the integral part of every one’s life and so are the challenges

researchers are facing. Last mile communications or infrastructure-less communication is

needed for every one belonging to any aspect of life. Such needs give birth to different kinds

of networks wired or wireless. Wireless communication being the most desired one as no mess

of installations, no worries of cable expiry or hardware constraints, freedom of movement and

more easy to use according to a user prospective.

Mobile Ad Hoc networks give such flexibility to a user and are becoming popular in market

for the said reasons. Apart from user view, it is a complex mechanism to provide

communication fulfilling such conditions. Besides many wireless communication issues, one

major issue is this that these wireless nodes/ transceivers are not always in range of each other

in accordance with their mobility. In such a scenario, there was a mechanism established that

makes each node/ transceiver a router. Hence whenever, one node wants to communicate with

a node that is out of communication range, some intermediate node between originator node

and the destined node will act as a router and make the communication between main

originator node and destined node possible.

A Mobile Ad Hoc network basically is a decentralized autonomous wireless system that has

mobility based or infrastructure-less nodes. These nodes are devices that contain transceivers

and processing capability. There are many versions of Mobile Ad Hoc network (MANET) i.e.

Vehicular Ad Hoc Networks (VANET) and Wireless Sensor Networks (WSN) are being the

most prominent ones. (IETF) Internet Engineering Task Force has defined a working group

namely MANET working group that explicitly works on routing protocols and define

standards for use within the IP suite. [1]

Several protocols have been developed on lower layers but in accordance with them, the

protocols of network layer or routing protocols play a vital role. [2]These routing protocols are

3

the main source to create, maintain and provide synchronization amongst the nodes of network

with the help of routing tables at each node of the network. Routing protocols not only have to

do the said job but they also have to cope with the ever changing positions of nodes with

different speeds, scalabilities, Transmission rates, bandwidth consumptions and many more.

Specifically, a routing protocol is said to provide efficient and quality routing.

1.1 Taxonomy of routing protocols

A routing protocol is basically a governing authority that how two communication devices

communicate with each other. More over it defines the procedures in creating/ establishing

and maintaining a route along with the data communication procedures. It is also responsible

of recovering a route in case of route failure. Numerous studies have been done and we have

categorized Mobile Ad Hoc routing protocols into major three class’s i.e.

1. Proactive Routing Protocols

2. Reactive Routing Protocols

Though now some other categories are under consideration which are geography based and

hybrid i.e. combination of reactive and proactive routing protocols for specified networks. But

still now, Reactive and Proactive routing is the prominent ones which are being studied in this

work.

ROUTING PROTOCOLS

ProactiveReactive

1. FSR2. DSDV3. OLSR

1. AODV2. DSR3. DYMO

Fig 1.1: Protocols discussed in this work

4

1.2 Proactive Routing Protocols:

These protocols are Table driven routing protocols and are meant amongst dense networks. In

such protocols, Routing information of next hop is preserved on the initialization of network

regardless of Communication Requests. As the network initializes, periodic Control packets

are flooded among nodes to uphold the paths or link states. In this way, they form a table on

each node describing the paths to/from each node. In other words, when a network initiates,

these protocols starts discovering the routes within all the nodes of network regardless of use

of that route. Such procedure may cause network over burden for a specific time but later on,

there would be no delay when a route is required within the network. in scalable and highly

dense networks that offer mobility as well, the routing information (information exchange to

keep the routing table up to date) results in huge network resources consumption. That was the

reason that reactive than hybrid and other kinds of protocols are developed. [3], [4], [5].

Features of Proactive Routing:

1. No route discovery time delay as every node has full topology routing table stored.

(Hence they provide lower latency rates for real time app.)

2. Maintaining unused or unwanted routes occupies major portion of bandwidth /

network resources, especially in highly mobile environments.

1.3 Reactive Routing Protocols:

These Routing protocols are also known as On Demand Routing protocols and their specialty

is to deal with high mobility. In such protocols, a node request for a route to its destination

only when it is needed. At nodes, routing table maintains only those routes which are in use.

5

Such routing protocols basically have a route discovery process where packets are flooded into

network in search of desired destined node. Path repairing and monitoring are being other

phases of such networks.

In both categories of routing protocols, following phases are undertaken for efficient and

quality routing.

1. Route discovery Phase

2. Route Maintenance Phase

3. Route Deletion Phase/ in reactive routing

1.3.1 Route Discovery Phase:

In a network of unknown nodes, where there is aspect of mobility is also under consideration

along with network resources usage, a protocol must be able to accomplish the route

establishment. For this purpose the initial step is to find the destined node which we want to

send data. It is also the fact that we are intended to provide two way communications not

unidirectional. For this purpose we have also to measure the route from destined node to the

source node. This process of route establishment in terms of MANET technology is known as

route discovery process.

1.3.2 Route Maintenance Process:

Once a route is established between two nodes, and data is being transferred, considering

mobility and other unpredictable aspects of Ad Hoc networks in mind, it is necessary to

continuously monitor the links using some technique. And if a link is found broken, the

protocol has to run such algorithms that can again establish the route so that the data which is

to be transmitted must be sent. This process of link monitoring and than if in case of broken

link, link repairing is termed as Route maintenance in Ad hoc Terminology.

6

1.3.3 Route Deletion:

When a route is used and data has been sent, now there is no need to store its routing

information. Routing protocol also has to delete the stale or broken or used routes to save

network resources. This process is known as route deletion process.

In our work, we focused our study to the route discovery and route maintenance phases of

reactive and proactive routing protocols for MANETs and VANETs

7

Chapter 2

Routing:

Reactive (AODV, DSR, DYMO)

&

Proactive (FSR, DSDV, OLSR)

8

2.1 Reactive Routing:

As stated earlier, route discovery initiates only when a route is required. There are numerous

protocols that are proposed and developed under this category and works well for desired

scenarios. The most widely studied, and used protocols are: Ad Hoc on Demand Distance

Vector (AODV) [16], Dynamic Source Routing (DSR) [14] and Dynamic MANET on

Demand (DYMO) [14]. We in this work are concerned only with the route discovery and

route maintenance phases of routing protocols.

2.2 Ad Hoc on Demand Distance Vector (AODV):

AODV is abbreviated by Ad Hoc On-Demand Distance vector and is reared up by classical

DSDV algorithm as described in [16]. Actually it is another flavor of distance vector routing

algorithms [1, 4], we can also conclude that it is a combination of DSDV (a proactive routing

protocol) [14] and DSR [14] algorithms. Form DSR it lends on demand features i.e. discover

paths when required, While from DSDV, it receives, loop free routes along with repairing of

link breakages. We can say that it is a modification of old DSDV algorithm that was

previously defined. Major modification is the minimization of number of unwanted broadcasts

by establishing paths/ routes on requirement basis rather than managing and maintaining full

topology routing table. The developers/ authors of AODV call it a pure on demand route

acquisition as the nodes which are not source or destination or in between the source to

destination route, are free and don’t maintain any routing table [16].

According to RFC3561 [29] AODV is designed to be used by mobile nodes of an Ad Hoc

network offering qualities of rapid adaptation of mobility of nodes, less processing and lower

memory over head. It establishes unicast paths to the destined node within the network. To

9

ensure loop freedom, a unique destination sequence number is utilized to avoid counting to

infinity or other such problems rose in previous distance vector routing protocols.

AODV, use three types of messages i.e. one for requesting a route, route request message, one

for replying a route request, route reply message and finally if a broken route is detected, route

error message (RREQ, RREP, and RERR respectively.) [4] [9] RREQ message as the name

indicates is specified for requesting a route from one node to another. When some node wants

to transmit some data to another node within the network, route is to be established first. This

RREQ message is propagated within whole network in search of a new route. Route is thought

to be determined when route request message reaches the destined node or it reaches the node

that has a fresh enough route up to the destined node. If route request message reaches the

destined node, a route replies packet is issued that follow the reverse path to the main

originating node of route request. If a route request packet reaches a node that has a fresh

enough route to destined node, than that intermediate node will generate a Gratuitous route

reply packet also termed as grat. RREP.

A route is said to be established when a RREP or grat. RREP is reached at the main

originating node of RREQ. When a route is established, link monitoring starts. At this stage,

AODV, use periodic messages (hello messages). These periodic HELLO messages are used

only by the active nodes of the route not by every node of the network; hence a great amount

of bandwidth and network usage is saved. In a route there would be numerous intermediate

nodes. During a route active time, these intermediate nodes will emit periodically hello

message to sense the topological changes occurring within the route. If a link is found broken

than after a small interval of time, a route error message is propagated from the node where

broken link is found. This RERR message shows that destined node is not reachable. This

10

reporting mechanism is based upon the concept of “precursor lists” [29]. These lists actually

store the address for all of the neighbors that can be used as next hop to destination.

2.2.1 Route Discovery and Route Maintenance of AODV:

In a network whenever a node intend to send some data to some other node, it needs to know

where actually the destination lies and if there is a valid route to its destination. For the said

purpose, route discovery process initiates.

Whenever a source node want to send its data to some destination node, it disseminates a

RREQ if, node needs a route to its destination. It happens when source node doesn’t have the

proper route of destination, or the route node knows is invalid or expired. In RREQ packet, a

Destination Sequence Number field also exists that presents the last known destined node’s

sequence number. This node’s own sequence number is incremented on every node the RREQ

packet passes. The Route Request identification field is incremented from the previous hop.

Before transmitting RREQ packet, the source node safeguards the route request ID and

address of source node for PATH_DISCOVERY_TIME. This is done so that when the node

receives back the RREQ packet which has already processed by it, it will not process it again

but just forward it.

After broadcasting the RREQ packet, a node has to wait for a RREP packet from destined

node. If the route destination is not found within “NET_TRAVERSEAL_TIME

(milliseconds)”, than the source node has to resent/ broadcast the RREQ packet until the

maximum of REQ_RETRIES times at maximum TTL value. At each try, the RREQ_ID is

incremented and updated.

11

The figure shows the propagation of RREQ packet across the network. To ensure loop free

and most recent path information, AODV use destination sequence number for all the routes

reaching destination from source. Sequence number and broadcast ID is maintained at each

node and on propagation of RREQ packet, each node increments its broadcast ID in the RREQ

(Route Request) packet. This incremented broadcast ID and node’s IP address combines to

identify uniquely every RREQ packet. Intermediate nodes can reply this route request packet

only and only if destination is in their neighborhood or have established route to the

destination.

During this RREQ forwarding process each intermediate node saves the address of neighbor

from where this route request packet is received in its routing table hence it automatically

establish a reverse path to the source. If one node received multiple copies of RREQ packet,

than it will take and forward the first copy and discards all the others.

When the route request packet reaches its destination, or reaches an intermediate node from

where a fresh route is available towards destination, than that intermediate node or destination

12

node responds by uni-casting RREP to its one hop neighbor from where it received RREQ

packet.

Normally it is expected that there is a bidirectional communications between originator and

destined nodes i.e. not only source should know the route to its destination but also the

destination to know the route to source. For this purpose, a RREP packet is generated. Only

that node can generate RREP message that itself is destination, or that has a valid route to the

destination.

If the route is discovered and RREQ packet has reached at a node which has fresh route to

destination or destined node itself than, an RREP packet is generated. Via reverse path, RREP

packet is routed back while the nodes on this route establish the forward path entries in their

routing tables pointing the neighbor from where RREP has arrived. These entries than finally

provide an active forward route to the destination from source. To avoid stale routes there is a

route timer associated with each route/ path entry. Whenever the timer expires, the route is

deleted. [8] [16]

When a route is established and link is properly periodically monitored. If during this link

sensing, routing protocol finds a broken link due to topology change or any other reason, it

13

will generate an RERR message back to main originating node of RREQ. When the

originating node receives this RERR message, it starts a new route discovery deleting the

previously stored route.

During route discovery time, i.e. when an RREQ is broadcasted the data which actually is to

be transferred from source to destination is buffered until it receives an RREP packet. If RREP

packet is received than it is transmitted on the discovered route else, it will wait for the

RREQ_RETRIES times at Maximum TTL. If even after that time, no RREP is received than

data packets are dropped.

2.2.2 Binary Exponential Back off Algorithm and AODV

Considering all the traffic on network for route discovery process, it is almost congested.

Repeated attempts by an originator node for a single destination makes the network traffic

jam. [16][13] To avoid collisions and loss of packet transmissions, binary exponential is

utilized in AODV.

Binary exponential back off is an algorithm used to space out repeated retransmissions for the

same block of data, normally used to avoid network congestion.

Binary exponential back off in AODV works in a simpler manner. For the first attempt of a

source node to search its route to destination, source node simply will wait

NET_TRAVERSAL_TIME milliseconds for RREP packet. IF Route Reply packet (RREP) is

not received during NET_TRAVERSAL_TIME milliseconds, it broadcasts a new RREQ

packet with this time it will wait for 2 * NET_TRAVERSAL_TIME milliseconds to receive a

RREP packet. For each additional broadcast of new RREQ packet, the time to wait for source

node will be multiplied by 2 from previously calculated time. This is how, binary exponential

back off algorithm works in AODV routing protocol.

14

2.2.3 BEB Algorithm for AODV RREQ is broadcasted Source node waits for NET_TRAVERSAL_TIME milliseconds= (a) If RREP reaches within NET_TRAVERSAL_TIME milliseconds= (a) Data Packets transmission initializes Else New RREQ is broadcasted Source node waits for 2 * NET_TRAVERSAL_TIME milliseconds= (b) If RREP reaches within 2 * NET_TRAVERSAL_TIME milliseconds= (b) Data Packets transmission initializes Else New RREQ is broadcasted Source node waits for 2 * (b) If RREP reaches within 2 *(b) Data packets transmission initializes

2.2.4 Expanding Ring Search Algorithm and AODV

The binary exponential back off algorithm in AODV has limited the generation of timely route

requests and congestion of an AODV network. A simple approach for broadcasting RREQ in

AODV can be of blind flooding technique that is each node has to rebroadcast the packet

whenever it receives it for the first time.[16] This is an easy way of broadcasting but this way

can cause BROADCAST STORM PROBLEM by generating redundant transmissions. To

avoid this broadcast storm problem, there are many optimization techniques and one of which

is expanding ring search algorithm. In this mechanism, the flooding is controlled via TTL

value though ERS also uses blind flooding for broadcasting.

15

In ERS, initially on broadcasting of source node,[16] TTL value is set as 1. If RREP is not

received during a specified time, than RREQ packet is again broadcasted by incrementing

TTL value by 1 and waiting time is doubled from the previously calculated waiting time. This

process continues till the destination is discovered or it reaches the last limit of expanding ring

search broadcast. The figure produced by [16] very clearly explain the expanding ring search

algorithm.

2.2.5 ERS Algorithm for AODV

According to AODV RFC 3561, ERS is used under following parameters

Originator node initially uses TTL= TTL_START in RREQ packet IP header RREP Time out= (RING_TRAVERSAL_TIME=2 * NODE_TRAVERSAL_TIME *(TTL_VALUE + TIMEOUT_BUFFER)) If RREQ times out and no RREP is received, the source node broadcast the RREQ again while TTL= TTL_INCREMENT. The same process continues unless, RREP is received by source node or TTL value reaches TTL_THRESHOLD Beyond TTL_THRESHOLD, TTL= NET_DIAMETER is used for each attempt.

16

When TTL=NET_DIAMETER, the timeout for waiting RREP is set to NET_TRAVERSAL_TIME(NET_TRAVERSAL_TIME= 2 * NODE_TRAVERSAL_TIME * NET_DIAMETER) 2.3 Dynamic Source Routing (DSR):

DSR abbreviated by dynamic source routing protocol [14] is basically on demand routing

algorithm designed upon the concept of source routing. Each node in the network carries a

cache that saves the source routes. The updates in these caches are continues as new routes are

known. DSR is also stated as first on- demand source routing based protocol [5, 6]. Source

routing basically allow the sender of a packet to partially or completely specify the route by

which the packet is traversed through the network. The path is based upon destination of the

packet.

2.3.1 Route Discovery and Route Maintenance of DSR:

In DSR, some extra route discovery features are adopted i.e. caching Overhead routing

information, replying to route requests using cached routes and route request hop limits. [14]

DSR specifies that any node which is forwarding or just hearing any packet should store all

the routing information from that packet which can be useful in its own cache. RFC4728

termed it as CACHING OVERHEAD ROUTING INFORMATION. RFC4728 also specifies

that any node that receives a RREQ where this node is not the destined node, it will searches

its own routing cache for the route towards destined node of the RREQ. If a route to destined

node is found in the route cache, this node will not forward this RREQ message further,

instead it will generate route reply back to the main source node. Such route reply is termed as

“grat. RREP”. DSR also adds a HOP LIMIT field in the header of RREQ message. This hop

limit field can be used to limit the number of hops up to which, route request has to be

flooded. It is an easier way to implement expanding ring search algorithm. This hop limit

17

implements in accordance with the “Time To Live” TTL field in the header of RREQ message.

As this message is propagated, hop limit decrements, and route request packet is expired when

hop limit reaches zero value provided if destination is not found.

DSR uses Source routing in which packet has ordered list of nodes in its header by which this

packet has traversed. [7] In this way, source node or sender selects and take control of the

routes used by and for its own messages.

When some node wants to transmit data to a destination in the network, initially, it queries

whether the route exists from source node to destination node in cache/ buffer or not. If there

is some route stored from source to destination in buffer/ cache, than it sends data else route

discovery process is initiated.

If no route is found in the cache, the source node floods RREQ packet in the network. When

an intermediate node receives a RREQ packet, it checks if this packet has reached again or

not. If node found repetition, it will discard that RREQ packet else it will attach its address to

the route record in the head part of packet. After that, intermediate node will forward it to all

of its adjacent nodes.

18

When destination node receives the RREQ packet, it reverses the route records in route

request packet and returns back a RREP packet on the same reversed route. Source node when

receive the RREP packet it immediately saves the route information in its cache for future use.

When a route is established between source node and the destined node, than link monitoring

activates. In DSR, advanced maintenance concepts are introduced as packet salvaging; queued

packets destined over a broken link, automatic route shortening and increased spreading of

route error messages [14].

The concept of packet salvaging specifies that when a node which is taking part in forwarding

packets during data transmission session detects via periodic acknowledgements that next link

is broken. If node have an alternate route saved in its cache, than it will not discard the packet

rather salvage it. Packet salvaging actually refers the replacement of original routing data in

the packet than alternate data which was saved in the cache of node as alternate. The packets

will then be stored within the node. Besides packet salvaging, when an active node (node

participating in a link) detects the nest link is broken, it will intend to salvage the packet. If

19

there is no alternate route saved in the route cache, than the packets are to be buffered at

node’s network interface queue and maintenance buffer [14].

Automatic Route Shortening is also done in DSR in the same way as in [14]. The concept

behind is this that there may exist some unnecessary intermediate nodes that can be bypassed

without effecting the route. As in DSR, a node hears and saves useful information from the

packets passing through neighboring nodes, and it get to know that some of any one of the

intermediate node can be bypassed than, it simply deflects the route, shortening it. Nodes need

to be in promiscuous mode for such operations.

Taking an very simple example of link monitoring and link breaking, suppose that there are 3

intermediate nodes “x”, “y” and “z” in between the source and destination nodes “a” and

“b” respectively. Hence the links of the route are a-x, x-y, y-z and z-b. Now according to [14]

“a” node is responsible for the link (a-x). Hence node “a” require periodic acknowledgments

from node “x” in response of the acknowledgement requests from node “a”. If during a

specified interval of time or specified number of acknowledgement request attempts, no

acknowledgements are received, the link is considered as broken. On discovery of broken link,

a RERR message is generated. The broken route is deleted from memory and route error

message is than transmitted to main source node via reverse path.

2.3.2 Binary exponential Back OFF and DSR:

If a node retires many times to search a route for a single destination and in the same way

some other nodes at the same time are requesting for routes to their destinations, there would

be large number of unproductive route request packets that almost congest the network.

[14]To avoid such jumble up of route request messages, binary exponential back off algorithm

20

is used just as in AODV. For every failure, it simply doubles the time to resend or rebroadcast

the same route request.

2.3.3 Expanding ring search Algorithm and DSR:

RREQ packet in DSR also contains a hop count field that represents number of hops of any

described route. If hop limit field is set to 1 than only its neighbors will receive the packet and

they will not further broadcast it as the hop limit was 1 and it has been full filled. If no route

reply packet is received by the source node at the hop limit of 1, it will increment the hope

limit and rebroadcast the packet. [14] This hop limit is implemented using TTL field in the IP

header of the packet carrying the route request. As this request passes from node, its TTL field

is decremented and the route request packet is dropped when that TTL field reaches at zero

before finding its target.

ERS approach could increase the average latency of the route discovery as multiple discovery

attempts and timeouts may be needed before discovering a route i.e. from source to

destination.

2.4 Dynamic MANET on Demand (DYMO):

DYMO stands for Dynamic MANET on Demand is another proposed reactive routing

protocol and is meant for highly mobile nodes in multi hop networks. It is forecasted that such

mobile networks are future networks. In 2005 DYMO draft was submitted [11] [29] it attained

lots of attention and this is the reason that draft has been modified many times. In some

manner we can say that DYMO base upon reactive routing protocols like AODV and DSR.

Main features of DYMO routing protocol is path discovery and path management. This is the

cause that DYMO is not so simple and easy to implement but on the other hand this protocol

21

is flexible, scalable and bears other enhancements in capability and expansion [12] [14].

Moreover, DYMO routing protocol can work either on IPV4 or IPV6 hence we can

interconnect network with internet as well.

Just like AODV, this protocol also works on RREQ and RREP packets for path discovery

process. A RERR packet is also used in this routing protocol which is responsible of error

notification within some established route.

2.4.1 Route Discovery and Maintenance of DYMO:

The source node, in DYMO routing protocol, like AODV, broadcast RREQ packet in the

entire network to reach destination node [15].

Once a node requires discovering a route, it initiates dissemination of RREQ message through

the entire network. During this hop-hop process, each intermediate node keeps the record of

route to the main originator node of RREQ. When a destined node receives a RREQ, like the

procedure of reactive routing protocols, it sends a reply message RREP to confirm and

establish a route. During the hop – hop dissemination of RREP message, again this time the

22

intermediate nodes saves the route to destined node in their routing tables. When the main

originator of RREQ message receives the route reply message, the route is said to be

established [29].

Route maintenance in DYMO is divided into two operations. In order to preserve active

routes, DYMO extends the route life time if a packet is successfully transferred via that route.

And 2ndly, each route is monitored and if in case one link of a route breaks, than as in he

basic theme of reactive routing protocols, route error message is initiated. When the main

originator node of RREQ receives an RERR message, it initially deletes the route and then

new route discovery process is initiated.

Accuracy and security is maintained by digital signatures and hash functions are also used in

this routing protocol. For the discovery of new route, the originator DYMO node broadcast

RREQ message in the network to find its destination. [10]During this hop by hop searching

procedure, each intermediate node saves the route of source or originator node.

When the destination node receives RREQ packet, it issues an RREP message/ packet that is

sent to originator or source node hop by hop. Each intermediate node at this time as well

23

records the route to destination. When the RREP packet is received by the source node, route

is established between originator and destination in both directions.

During this broadcasting each intermediate node saves a route to the source node. When the

destination node gets the RREQ packet, it than responds to the RREP packet, unicasting it

towards the source node by using reversal of saved paths. On each iteration, the intermediate

nodes save the route to the destination till the RREP packet reaches source node.

2.4.2 BEB and ERS in DYMO

Like AODV, when a node is required to search a route, it broadcast a route request packet

RREQ to find a valid route to some destination. The source node than waits for a unit time to

get the route reply but if reply is not obtained than it again rebroadcast the RREQ packet. To

avoid the repeated attempt that makes a network congested, a binary exponential back off

algorithm is used. The data packets which are waiting for a valid route to be transmitted are

kept in a buffer of fixed size. If route discovery is attempted at its maximum times and yet no

destination is found than, data packets for that undiscovered destination are discarded or

dropped from buffer and an ICMP, un reachable destination packet is delivered. If route was

discovered but link has broken than a route error message is issued.

Binary exponential back off functionality in DYMO can be expressed with the following

procedures.

2.4.3 BEB Algorithm for DYMO:

RREQ packet is broadcasted

Source node waits RREQ_WAIT_TIME for a route to destination

If route not found within RREQ_WAIT_TIME send another route request packet.

Source then has to wait for 2* RREQ_WAIT_TIME.

24

If even than route not found

Rebroadcast RREQ and wait for 2*(2* RREQ_WAIT_TIME)

This procedure continues and at every rebroadcast the source node has to wait for route twice the previous time

If route is not discovered until DISCOVARY_ATTEMPTS_MAX limit reaches.

AT this level, route discovery process is assumed as failed

Data packets at source node waiting to be transmitted are buffered.

BUFFER_SIZE_PACKETS or BUFFER_SIZE_BYTES stores a fixed and limited size of data to be buffered.

This buffer act as FIFO (first in fist out). The packet that is buffered earlier will be removed earlier.

Buffer setting BUFFER_DURING_DISCOVERY should be manually or intelligently controlled as it is configurable.

After DISCOVERY_ATTEMPTS_MAX, without receiving the route, destination unreachable ICMP packet is issued and data packets in buffer for the said destination are dropped.

During all this process, to control the RREQ propagation network wide and to reduce the over

head, DYMO may use expanding ring search algorithm. In DYMO routing protocol, ERS

algorithm can be implemented at MsgHdr.Hoplimit in RREQ packet along with all the

procedures, AODV routing protocol adopted.

There is a very small difference in the route discovery process of AODV and DYMO. AODV,

only generate routes for the destination whereas, DYMO, at each intermediate node towards

the destination store routes in its routing table.

25

2.5 Comparison: ERS and BEB in AODV, DSR, and DYMO:

Flooding is an essential part of AdHoc networks especially in the process of route discovery.

On the other hand, this is the major cause of network overflow. The route discovery messages

can generate a broadcast storm problem in such networks. To avoid or to control this problem

several techniques and algorithms are presented and implemented. Binary exponential back

off, expanding ring search, Directed flooding and Query localization are the algorithms that

are used in AODV, DSR, DYMO and TORA routing protocols.

In AODV, DSR and DYME, ERS is used to avoid or solve broadcast problem in any network

while BEB is utilized to avoid collisions and loss of data traffic along with being part of

network congestion control mechanism. The Mechanism of Expanding ring search Algorithm

in AODV and DYMO are same as DYMO adopted the same procedure as that of AODV.

AODV , DYMO and DSR use Both of these techniques in simultaneously but with a little

difference in parameters and achieve the said goals of these mechanisms. In all these routing

protocols, expanding rings circles algorithm is utilized with the help of TTL field in header of

the packet but with a little difference.

In AODV and DYMO, the TTL field is based upon time factor, while in DRS, TTL field is

based upon hop count factor.

The rings made in AODV are incrementing that unit time which normally is set as

RING_TRAVERSAL_TIME milliseconds and each time, when route request packet fails to

reach its destination in the ring and no route reply packet is received by source node in given

time period, that RING_TRAVERSAL _TIME milliseconds is incremented and new route

request packet is broadcasted with extending ring via more time for the route request packet to

find its destination.

26

In DRS, the mechanism though is implemented via TTL field as well but in procedure it is a

bit simpler than that of AODV adopted. In DRS, the TTL field is dependent of hop limit field.

If hop limit field is set to 1 it means that the route request packet will be dropped or discarded

when the one hop search is done. In this way, the hop limit field can be modified and new

route request packet can be sent to find the destination with in that hop limit. Suppose that

hope limit set is 10 than at each hop, the hop limit value is decremented and when hop limit

reaches its value at 0, the packet is discarded.

In AODV, the processing for TTL value is much greater than that of DRS.

If we consider DYMO, it also works almost similar than that of AODV. Its binary back off

exponential time is same as that of AODV and DSR i.e. multiple of 2 on each iteration and it

copies exactly the same algorithm for expanding ring search as used in AODV. The only

difference between AODV and DYMO is this that AODV, only generate routes for the

destination whereas, DYMO, at each intermediate node towards the destination store routes in

its routing table.

In DYMO routing protocol, the information of routes is recorded at intermediate nodes with

the help of RREQ and RREP packets while in DSR, the routes are stored in the header of

packet.

These three routing protocols use ERS and BEB for controlling the broadcast storm problem

but if we consider another routing protocol like TORA, it doesn’t use these algorithms.

Besides it uses the concept of directed flooding and query localization. Directed flooding is

made possible with the help of Directed Acyclic Graph which limit the broadcasting in one

direction i.e. upstream to downstream, form source to destination while query localization

technique works well with the topological changes and partitioning of network.

27

2.6 Proactive Routing:

As discussed in previous chapter, whenever a network with proactive routing protocols

initiates, the route discovery for every possible destination also initiates. Proactive routing

protocols don’t wait for the data to be transmitted and then search only required route as in

reactive routing protocols. They initialize and maintain the routing table at each node. That is

the reason that latency rate is much lower in proactive routing protocols than that of reactive

routing protocols. But on other hand, proactive routing protocols raise the issue of network

resources due to flooding nature. Widely studied and practiced proactive routing protocols are

Fisheye State Routing (FSR), Destination Sequenced Distance Vector (DSDV) and Optimized

Link State Routing (OLSR) protocols.

2.7 Fisheye State Routing (FSR)

In proactive routing protocols, there is a huge problem of initial flooding of packets for

topology and routing information. This process may choke the network or use maximum of its

resources. To solve this problem, Fisheye state routing algorithms defined the phrase “Multi

level scope” that is able to reduce the routing overhead in dense networks. Fisheye state

routing floods the periodic control messages of a destined node with respect to its neighbors

with a frequency that is dependent on the hop distance to that destined node. As the

correspondent of these control or status update messages moves away from the destination, the

information propagated gradually declines to lower frequencies. From such status updates or

control messages, every node in the network built and maintains a routing table. This routing

table is precise for the nodes nearby but as the hop distance increases; the routing information

in the same proportion fades or gets imprecise. Hence the route on which a packet travels may

seems to be faded but as it gets closer to the destination, route becomes more precise and

accurate. FSR follows the link state algorithms as it issue periodical updates of link state, but

28

instead of flooding these periodic updates to whole of the network, it floods in step wise

manner. In this way, FSR results in huge savings of routing overhead which was caused in

maintaining the topology details of every node in the routing table of every node. Fisheye state

routing is briefly discussed and implemented by [20].

Fish eye state routing [1, 2] is a routing protocol providing a tree like structure. It updates the

link state information in different frequencies that depends upon fish eye scope distance. That

is frequencies are higher for nearer nodes and lower for far away nodes. Within scalable and

dynamic environment, a packet as reaches near the destination, the routing gets more accurate

regardless of mobility and scalability. FSR basically provide, simplicity of routing, gives

updated shortest routes , provide robustness in mobile and scalable environments and one of

the major benefits is the reduction of routing overhead [19].

2.7.1 Fisheye Scope Technique:

FSR use fisheye technique given by [18]. According to a fish eye structure, it can capture the

details of nearby things but fades for far away things. [17] In routing the same approach is

utilized that within neighbors of a node, precise information is gathered but as the hop

distance increases, the details get fader.

Fisheye scope technique basically permits exchanging routing information at different

intervals for the nodes existing at different fish eye scope or fish eye distances. This gives a

vital effect on routing overhead by reducing the size of the message. According to [19], 37

Fisheye state routing broadcasts the topology messages only to the neighboring nodes. With

such optimizations FSR proves to handle scalable and dense networks.

Fisheye state routing, routes every packet In accordance with local computing, i.e. each packet

is routed with respect to the routing table of the node it is passing through. The routing table of

29

the node by which packet is passing through is handling the most up to date routing

information and as the basic theme of FSR, as the packet gets nearer to destination, the routing

becomes more precise. 37 For inner scope of fisheye, the routing is accurate due to short

intervals but for outer scope the routing information may be outdated due to longer intervals.

If we consider a dynamic and highly mobile environment, the accuracy of outer fisheye scopes

will be more blur and inaccurate but on the other side, when the packet reaches a node that has

destination in its inner fisheye scope; the routing information again gets precise.

Fisheye scope routing don’t use any trigger [19] for repairing a link or when a link is found

broken, it simple will not include this link in its next fisheye scope control message exchange.

Whereas FSR use sequence numbers along with table refreshment to remain updated with loop

free routing table.

Maximum accuracy in scope 1

Minimum accuracy in Last

Scope

SCOPE 1

SCOPE 3 SCOPE 2

Fig 2.7:

According to [19] the fisheye scope is represented as the nodes that are accessible within some

limited number of hops. Fisheye scope can be better understandable by the above illustration.

30

2.7.2 FSR WORKING:

In a network, where Fisheye state routing is operating, each node will maintain the following

tables. On the basis of these tables routing is made possible.

Topology Table:

This table maintains the information contained by periodic link state messages. Routing table

is made on the basis of this table that contains the LS information and destination sequence

number. Each topology table includes

1. Destination address field

2. Destination sequence number field

3. Lint state list

Neighbor link state table:

On receiving a LS message, link state information of the sender node is saved in neighbor link

state list. If a node didn’t get any LS message from some neighbor for a

NEIGHBOR_TIMEOUT period, that neighbor will be deleted from node’s neighbor link state

table.

Routing Table:

Routing table comprises of following fields

1. Destination Address

2. Next hop Address

3. Distance

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Link Breakage:

Ad Hoc networks are known for mobility and mobility causes link breakages. In Fisheye state

routing each node uses soft state to find a broken link. i.e. as according to neighbor link state

table, a node will delete all the routing information from that neighbor if it appears not in

contact for a NEIGHBOR_TIMEOUT time value.

2.8 Destination Sequenced Distance Vector (DSDV)

DSDV is one of the parent Ad Hoc networks routing protocols. Basically it is derieved from

Bellman Ford algorithm [21] [22]. Bellman ford Algorithm basically provides solutions for

shortest path between source node and destined node [6]. DSDV in addition of classical

Bellman Ford Algorithm introduces a new feature i.e. sequence number for each routing table

entry of whole of the network. In DSDV, Routing Table on each node make lists of all the

possible destined nodes within the underlying network along with their number of hops and a

sequence number to prioritize the routes. This routing information is broadcasted or multi

casted to the neighbors. Not only periodically the change in topology is also transmitted in

form of triggered updates whenever a change in topology due to mobility or any other reason

occurs. C Perkins presented this protocol in 1994[6]. There is some detailed description of

protocol provided in [6] Till to-date, numerous comparisons have been made between DSDV

and other routing protocols both reactive and proactive in nature.

2.8.1 Route Discovery and Route Maintenance of DSDV:

DSDV transmits control packets periodically for updating of topological changes or when a

link breaks it issue a trigger message. This aptitude of protocol makes the network suffer with

delay in updating of routing information when the environment is highly mobile or dynamic.

There are two types of updates considering DSDV.

32

1. Incremental Updates

2. Routing table updates.

The new feature” sequence numbers” are utilized to ensure loop freedom and attaining

information about shortest possible route to destination. Any route that has the highest

sequence number is prioritized among other routes and if the sequence number for two routes

having same source and destined nodes are equal than decision is to be made on lower metrics.

The one route that has lower value of metrics must be used. According to [22], [6] the routes

which are broken normally use even numbered sequence numbers. This assumption also helps

in loop freedom.

DSDV use two types of routing tables.

1. Forwarding Table:

i. The forwarding table contains the information addresses of all nodes

within the underlying network

2. Broadcast table:

i. The broadcast table calculated the time for periodic updates or

broadcasts advertisements

33

All the routing information, routing info or periodic updates uses these two tables. Routing

table of a node mainly comprises of

a) Nodes address,

b) Next hop address

c) Routing metrics

d) Destined node sequence number

As the basic theme of proactive routing, all nodes with underlying DSDV protocol maintain a

routing table for the interconnectivity of different nodes. These routing tables are maintained

for all the available destinations and number of intermediate hops to the destination. Each

destination route in the routing table is distinguished with a unique sequence number. To

remain interactive and gather latest routing information, periodic control messages are

transmitted. And with the help of these periodic control messages, the routing tables of every

node are updated. According to [6] each node that broadcasts the data, will contain its new

sequence number along with the

a) Destined node address

b) Hop count to reach destined node

c) Destined node sequence number

The routing tables that are shared also have the hardware address of mobile node forwarding

them. They will also contain sequence number of source node. The latest destination sequence

number is prioritized on making packet forwarding decisions. When every a new sequence

number is generated, it is updated to all nodes of the network. This new sequence number is

used in maintaining and updating the routing table entries of source node. When route

information is received by a node, it simply advertises this information among all the

corresponding nodes. In case a broken link is found than the protocol don’t wait for the next

34

periodic control message to flood this broken link information but issue a trigger message on

the vary time.

Though DSDV provides many benefits like loop freedom, infinity count problems, and

avoiding extra traffic using incremental updates etc but in contrast to these plus points, DSDV

also make the underlying network suffer with the bandwidth wastage due to unwanted routing

advertisement, not supporting multipath routing and not efficient in larger/ dense networks.

2.9 Optimized Link State Routing (OLSR):

Optimized link state routing protocol is a proactive routing protocol for MANETs [24], [25]. It

follows the basic concept of link state routing along with the Multipoint relay concept. Each

node in OLSR routing protocol selects a set of multipoint relay nodes which are its neighbors.

Only MPRs forward the control packets in such a way that information should reach whole of

the network [24]. These selected MPR nodes are held responsible for declaring LS

information in entire network. Multipoint relays are also used in route calculations from a

source node to destined node. An MPR selected from a node must have a symmetric or bi

35

directional link to minimize the problems of packet transmissions over asymmetric or

unidirectional links. Basically in classical link state routing, only two modifications /

optimizations are made to make optimized link state routing protocol [26]. The concept of

MPR set of nodes that are responsible of broadcasting topology control messages. And 2ndly

contents of topology control message are reduced.

2.9.1 Multipoint Relay Concept:

The vital role of minimizing routing overhead in optimized link state routing protocol goes to

the multipoint relaying concept. [23] This idea was generated to reduce the routing overhead

by minimizing the retransmissions of the same packet in the same region. This concept limits

the number of retransmissions by limiting the number of re-transmitters. It is achieved by

selecting some nodes that belongs to one hop neighbor-hood of a node instead of all neighbor

36

nodes of that node. The neighboring nodes that are selected as multipoint relay set of a node

are permitted to rebroadcast the packet they receive while rest of the nodes which are not

selected as multipoint relays will only receive the packets but wont forward them. [RFC

OLSR] Only nodes that have maximum coverage to 2 hop symmetric neighbors of the node

and by self they are one hop symmetric neighbors of that node can be selected as Multipoint

relays of said node. In order to achieve this, link state information is a must in between the

nodes. This Link State information is provided using periodic Hello Message.

2.9.2 Route Discovery and Maintenance of OLSR:

According to RFC 3626, OLSR’s functionality is divided into two aspects, i.e. the core

functionality and the Auxiliary functionality.

RFC 3626 specifies the core functionality of OLSR as: packet forwarding, packet formatting,

periodic hello messages, link sensing, neighbor detection, topology discovery, calculating

routing table and node configurations.

In Auxiliary functionality, the protocol deals with: non OLSR interfaces, notifications form

layer 2, redundant MPR flooding etc.

There are 4 types of messages utilized in OLSR.

1. Hello messages:

i. Used for neighborhood detection

ii. Selection of MPR set

iii. Link Sensing

2. Topology control Messages(TC)

i. Route Calculation

3. Multiple interface Declaration messages(MID)

37

i. An OLSR running node having more than one interface, than relation between main address and other OLSR interface addresses is exchange via MID messages.

4. Host and Network Association messages(HNA)

i. Allows external routing information in OLSR underlying network.

When a network initiates, Periodic Hello messages are broadcasted for the purposes of

neighbor detection. Once the neighbors are detected, MPR selection initiates. For this purpose

MPR selectors are made that selects the MPR set of nodes of a specified node. When MPR set

of nodes is selected by MPR selectors, The Topology control messages are broadcasted to

entire network. These messages actually calculate the route and spread this route calculation to

every node of the network. Only selected MPRs will flood the TC messages hence saving lots

of network resources. If the number of MPRs in a network is low, the routing overhead will

also be lower. Once the route information is distributed amongst all the nodes, there is another

feature of OLSR. It offers multiple interfaces to a node. These interfaces may be OLSR

interfaces or interfaces for other protocols. One on these OLSR interfaces is termed as main

address of the node on which major transactions will happen. But at times, other OLSR

interfaces may also be utilized. To exchange the relation between main address and OLSR

other interface addresses, MID messages are spread. As discussed earlier, that OLSR also

provide interfaces to other networks as well. And for that purpose, HNA messages are

broadcasted periodically.

38

Chapter 3

Analytical Modeling:

Reactive & Proactive

39

3.1 Reactive Modeling

Unlike proactive routing protocols, where all the routes are formulated whenever the network

initializes, in reactive approach, routes are queried only when needed by a node. A route

request is flooded in the entire network and when a route is established, data is to be sent.

Route Discovery and route maintenance are the two major aspects of routing overhead of a

reactive routing protocol.

3.1.1 Route Discovery:

When a node wants to transmit some data to another node, and there is no valid route

stored in its routing table, it will flood the RREQ packet. An RREQ packet comprises of many

fields, most prominent ones are Source identifier field to identify the route requesting node,

Destination identifier field to identity the destination node and TTL field to limit the flooding

or other purposes that can be defined according to need of the protocol. This uniquely

identified RREQ is flooded amongst all the nodes of network until it reaches destination node

via different paths/ routes. Via RREQ packet which has reached destination node, destination

node will keep the route back to source and send an RREP packet to all those routes from

which RREQ has reached it. On every node, where packet reaches, hop count / TTL is

incremented / decremented and route table entries are updated. [30]

3.1.2 Route Maintenance:

Whenever a route is established via RREQ and RREP messages, link sensing initiates with the

help of periodic messages [29] a link can be deteriorate due to noise or topology change. This

is the main reason that link is being monitored periodically. In either case when a node finds

no link to next hop, it issues an RERR packet informing the un-reachability of destination

40

node that is transmitted back to main source node. On receiving a RERR packet, the main

source node initiates new route request for broken link. [31]

In this work, we are concerned only with the basic architecture of route discovery and link

monitoring phase of reactive routing protocols. Generally following are the steps for Route

Discovery and Route Maintenance involved in almost all of the proposed reactive routing

protocols. These two phases of a routing protocol gives the routing overhead of that protocol.

3.1.3 Steps involved in Route Discovery and Route Maintenance:

1. Flooding RREQ packet (route request packet)

2. Receiving RREP packet (route reply packet) when destination node is found by RREQ

3. Link is established and now link monitoring starts by periodic messages.

4. When the link is found broken, different methods apply to rectify this problem.

5. New route discovery / local repair/ wait for time out happen for the link that has broken.

Form the above mentioned 5 steps of Route Discovery and Route maintenance; we have

analytically modeled first three steps of main architecture of Reactive Routing protocols.

In this work, we have analyzed two types of scenarios i.e. the one where there is only one link

active in the network and a source node S wants to create a link to its destination node D

during network life time T. And in other case we have tested the limits of a network of n

nodes where every node is eager to send its data during network life time “T”.

3.1.4 Routing overhead for a single Route:

Routing over head of a single link is the sum of broadcasting of Route request (RREQ)

packets to all the nodes of network and the Route Reply (RREP) packets received by the

source node

41

(We considered that a single link between a source node S and destination node D can have

multiple routes.)

It can be written as

𝑅𝑂(𝑖) = 𝑅𝑂[𝑅𝐷𝑖] + 𝑅𝑂[𝐿𝑀𝑖]

Or in some detail

𝑅𝑂(𝑖) = [𝑅𝑅𝐸𝑄𝑖] + [𝑅𝑅𝐸𝑃𝑖] + 𝑅𝑂[𝐿𝑀𝑖]

Where

RO(i) = Routing over head of one link

RO[RDi] = Routing overhead of Route discovery phase of one link

RO[LMi]= Routing overhead of Link monitoring of one route

[RREQi] = Expected route requests for one link

[RREPi] = Expected route Replies for one destination to one source

T = Route Life Time

t = periodic update interval

3.1.5 Overhead due to Route Request packets:

Assumptions:

n= number of nodes in a network

A= area of network = (X x Y) sq. m.

42

r= Communication range of node= 𝝅r2

Considering the above suppositions, we can say that if a node floods a packet than, that packet

will reach (n-1) nodes of the network. As discussed in [27] the any node in the network must

has some neighbors. Average number of neighbors in network for any node can be defined as

Navg = (𝑛 − 1) 𝜋𝑟2/𝐴………………………………………………………………………....1

Navg is the average number of neighbors of any node.

The Route Request packet when flooded, than routing overhead due to RREQ packet at 1st hop

would be equal to number of neighbors of packet initiating node. Hence it can be written as

[𝑅𝑅𝐸𝑄1𝑠𝑡 ℎ𝑜𝑝 ] = (𝑛 − 1) 𝜋𝑟2/𝐴

The number of route request packets for one route can be calculated as

43

[𝑅𝑅𝐸𝑄𝑖] = ∑ (𝑛 − 1) 𝜋𝑟2/𝐴𝑖𝑘=1 ……………………………………………………….………2

3.1.6 Overhead Due to Route Reply:

When a route request packet (RREQ) reaches its destination, destination will generate Route

Reply Packet (RREP). This packet has to reach the main source node in order to establish a

route. In RREQ packet header, there is a field of hop count that stores the number of hops this

RREQ packet has passed to reach destination. Now the destination knows that how many hops

are there in between destination node and source node.

Mover over according to Route replies packets follow the reverse path and there may be a

number of routes that are found from one destination. Considering these all aspects, we can

conclude that overhead due to Route Reply packets for one route can be expressed as:

[𝑅𝑅𝐸𝑃𝑖] = ∑ 𝐻 (𝑛 − 1) 𝜋𝑟2/𝐴𝑙𝑘=1 …………………………………………………….………3

Where

44

l = number of routes discovered by RREQ packet for a single destination

H= number of hops of one route.

Route Discovery overhead can be expressed as

𝑅𝑂[𝑅𝐷𝑖] = [𝑅𝑅𝐸𝑄𝑖] + [𝑅𝑅𝐸𝑃𝑖]

𝑅𝑂[𝑅𝐷𝑖] = ∑ (𝑛 − 1) 𝜋𝑟2/𝐴𝑖𝑘=1 + ∑ 𝐻 (𝑛 − 1) 𝜋𝑟2/𝐴𝑙

𝑘=1 ......................................................4

3.1.7 Monitoring over head of one link:

When the route is established, link sensing or monitoring starts. According to [29] when link

is established periodic hello messages are used for continues link monitoring. As discussed

earlier the route life time is” T” whereas periodic update interval time is “t”. Than number of

periodic messages propagated during the network life time would be “T/t”.

Suppose that there are “m” nodes in a route. Hence m nodes will broadcast hello messages for

link sensing. Average number of neighbors of any node is discussed in eq. 1 than, routing

overhead due to link monitoring of one route:

𝑅𝑂[𝐿𝑀𝑖] = 𝑇𝑡∑ ((𝑛 − 1) 𝜋𝑟

2

𝐴𝑚𝑘=1 )……………………………………………………………..5

45

Over all routing overhead due to route discovery and route monitoring (for one route) can be

expressed as:

𝑅𝑂(𝑖) = ∑ (𝑛 − 1) 𝜋𝑟2/𝐴𝑖𝑘=1 + ∑ 𝐻 (𝑛 − 1) 𝜋𝑟

2

𝐴+ 𝑇

𝑡∑ (𝑛 − 1) 𝜋𝑟

2

𝐴𝑚𝑘=1

𝑙𝑘=1 …………………6

3.1.8 Routing overhead for n Routes:

Routing over head for n routes can be calculated as

𝑅𝑂(𝑛) = ∑ [𝑅𝑅𝐸𝑄𝑖]𝑛𝑖=1 + ∑ [𝑅𝑅𝐸𝑃𝑖]𝑛

𝑖=1 + ∑ [𝐿𝑀𝑖]𝑛𝑖=1 ………………………………….7

Placing values:

𝑅𝑂(𝑛) = ∑ ∑ (𝑛 − 1) 𝜋𝑟2/𝐴𝑖𝑘=1

𝑛𝑖=1 + ∑ ∑ 𝐻 (𝑛 − 1) 𝜋𝑟2/𝐴𝑙

𝑘=1𝑛𝑖=1 + ∑ 𝑇

𝑡∑ (𝑛 −𝑚𝑘=1

𝑛𝑖=1

1) 𝜋𝑟2

𝐴…………………………………………………………………………………….….8

46

Now we have two optimum functions with respect to route discovery and route monitoring

mechanism of reactive routing i.e. f(x) and f (y). f(x) represents the routing overhead of route

discovery and route monitoring of a route while f(y) represents route discovery and route

monitoring of n routes. If we want to analyze the routing protocol behavior with respect to

changes in range of a node, route life time, area of network and periodic update interval times,

we have the optimum function x(r, A, T, t). Taking partial derivatives of f(x) and we get

δx/δr = ∑ (𝑛 − 1) 2𝜋𝑟/𝐴𝑖𝑘=1 + ∑ 𝐻 (𝑛 − 1) 2𝜋𝑟

𝐴+ 𝑇

𝑡∑ (𝑛 − 1) 2𝜋𝑟

𝐴𝑚𝑘=1

𝑙𝑘=1 ………………9

rate of change of size of network will effect as equation 10

δxδA

= ∑ (𝑛 − 1) 𝜋𝑟2

−𝐴2𝑖𝑘=1 + ∑ 𝐻 (𝑛 − 1) 𝜋𝑟2

−𝐴2+ 𝑇

𝑡∑ (𝑛 − 1) 𝜋𝑟2

−𝐴2𝑚𝑘=1

𝑙𝑘=1 ………..…10

Partial derivative of T will be:

δx/δT = 1𝑡∑ ((𝑛 − 1) 𝜋𝑟

2

𝐴𝑚𝑘=1 ) ……………………………………………………………….11

if we want to analyze overhead on increased the periodic update interval, we will get the

following equation

δx/δt = 𝑇−𝑡2

∑ ((𝑛 − 1) 𝜋𝑟2

𝐴𝑚𝑘=1 ) ……………………………………………………..………12

Equation 9 validates that if the communication range of nodes increases; there would be a

decrease in routing over head.

Equation 10 expresses that increasing the Area of network will also increase in routing

overhead as number of hops and number of neighbors are nonlinearly concerned with the area

of network.

47

Equation 11 shows that if we increase the route life time, overhead will increase.

Equation 12 shows that increase in the periodic interval time will result in decrease of routing

overhead.

3.2 Proactive Routing:

As we know that in proactive approach, whenever a network initializes, all the routes are

created immediately using flooding mechanism. Further onwards, that complete routing table

is updated periodically with the help of periodic messages. If any change occurs between two

periodic messages, a trigger message is broadcasted as described in DSDV [6] (a proactive

routing protocol) instead of waiting for next periodic update message. In a dynamic network,

there may be loss of packets due to broken links which are not updated at that moment. Hence

if we consider routing over head of a proactive routing protocol, than we can say that it is the

sum of number of packets failed due to link breakage, periodic messages that are broadcasted

after every specified instance of time and triggered update messages due to change in topology

in between periodic updates.

𝑅𝑂 = 𝑃𝐹 + 𝑃𝑅 + 𝑇𝑅

Where

RO= Total routing over head of protocol

PF= packets failed to reach node due to link breakage

PR= Periodic update messages

TR= Triggered update messages

48

Normally there are two types of errors that lead to packet failure as discussed in detail in [32]

one error is this that, a node knows that it has a neighbor X where as node is unable to

communicate it where as the other error is this that a node don’t know that there is a neighbor

X from which it can communicate. In either case, the probability of packet loss is increased.

3.2.1 Route failure impact on routing Over head:

During periodic update time span (Tpr), number of packets encountering route failure is

defined in [33]

𝑂𝐻(𝑃𝐹) = � � �Qrl (Tpr)Na(TPR)�L1

𝑟=0𝑃𝑖∊𝑃𝐴……………………………………………13

Where

OH(PF) = Overhead of packet failures due to link breakage.

Qrl (Tpr) = probability that during first r hopes, the uplink state will not change its state

to down link.

Na (Tpr) = Number of Data packets arriving at time Tpr

Tpr = Periodic route update time

Li = length of Pi (ith Path)

PA = set of all paths in the network

3.2.2 Periodic Message Overhead:

Periodic message over head in proactive routing protocols can be stated as size of routing table

per periodic route update time. While routing table size is equivalent to the size of network.

49

Combining it with the complexity of routing over head we get the periodic message update as

discussed in [33]

𝑂𝐻(𝑃𝑟) = 𝐾𝑛3

B∗Tpr…………………………………………………………………………..14

Where

OH(Pr)= over head due to periodic updates

B = Bandwidth

n = Number of nodes in a network

K = used to adjust routing protocol impulse factor

3.2.3 Trigger Overhead

Coming to the third important aspect of overall routing over head, the triggered messages, we

have to understand when and how actually a trigger message is updated.

Consider that there is a node in a network that moves in such a way that it changes its

topology in between two periodic messages i.e. in between Tpr and Tpr +1 say at T time. The

routing protocol will not wait for next periodic message to update this change in topology

instead; it immediately broad cast a triggered message. The following illustration will help in

clearing the concept of triggered message.

50

Analytically we can express this illustration as

Tpr<T<Tpr+1

As discussed in [34] this notation can be expressed as:

Tr(a) = ⌈T\Tpr⌉𝑇/𝑇𝑝𝑟

…………………………………………………………………………15

Where ⌈ ⌉ in mathematics, is the ceiling operator and it should be solved by taking the highest

possible values. In a network where only one node a moves within a time span of Tpr and

Tpr+1 , the above equation qualifies but considering a highly mobile environment where all

the nodes of network are mobile, the maximum over head due to triggered update during Tpr

and Tpr+1 will be:

OH(Tr) = ∑ ⌈T\Tpr⌉𝑇𝑇𝑝𝑟

ni=1 ……………………………………………………………………..16

51

Where

OH(TR) = Trigger message over head

T = triggered update

3.2.4 Routing Overhead of Proactive Routing Protocol:

Placing the respective values of Eq.2, Eq.3 and Eq. 5 in Eq. 1 we get the analytical equation

expressing the total routing overhead of the network.

𝑅𝑂 = � � �Qrl (Tpr)Na(TPR)� + kn3

𝐵∗𝑇𝑝𝑟

L1

𝑟=0𝑃𝑖∊𝑃𝐴

+ ∑ ⌈T\Tpr⌉𝑇𝑇𝑝𝑟

ni=1 ……………………17

Let RO be the optimized function y (µk, Tpr, T, n, λ).Hence Eq.6 can be written as:

𝑦(µk, Tpr, T, n, λ) = � � �Qrl (Tpr) λ(Tpr)� + kn3

𝐵∗𝑇𝑝𝑟

L1

𝑟=0𝑃𝑖∊𝑃𝐴

+ ∑ ⌈T\Tpr⌉𝑇𝑇𝑝𝑟

ni=1 ……..….18

As discussed in [35]:

Qrl (Tpr)𝑒𝑥 = 1 − 𝑒−𝑟𝑇𝑝𝑟/µ𝑘………………………………………………………………….19

And we can say that λ is the average number of packets arrived successfully at node, µk is the

uplink time, T is triggered update messages and n stands for number of nodes in a network.

Substituting the value from Eq.8 to Eq.7, we get our Eq. 9

𝑦(µk, Tpr, T, n, λ) = (PNavg)� �(1 − 𝑒−𝑟𝑇𝑝𝑟/µ𝑘) λ(Tpr)� + kn3

𝐵∗𝑇𝑝𝑟

L1

𝑟=0+ ∑ ⌈T / Tpr⌉

𝑇𝑇𝑝𝑟

ni=1 ..20

52

To analyze the variation in these parameters, we take the partial derivative of function y and

we get:

𝛿𝑦𝛿𝑇𝑝𝑟

= (C)� ��1 − 𝑒−𝑟𝑇𝑝𝑟

µ𝑘 � + � r∗Tprµk

� 𝑒−𝑟𝑇𝑝𝑟

µ𝑘 � − kn3

𝐵∗Tpr2

Lavg

𝑟=0

+ ∑ �−T\Tpr2�+T\Tpr2

𝑇2/𝑇𝑝𝑟2ni=1 …21

Take PNavg* λ= C the partial derivative with respect to the rate of packet arrival will be

expressed as eq 11

𝛿𝑦𝛿𝜆

= (PNavg)� �Tpr �1 − 𝑒−𝑟𝑇𝑝𝑟

µ𝑘 ��Lavg

𝑟=0

…………………………………………………22

Similarly if we take partial derivative with respect to T, we will get the eq 12.

𝛿𝑦𝛿𝑇

= ∑ �1\Tpr2�−1\Tpr2

𝑇2/𝑇𝑝𝑟2ni=1 ……………………………………………………………………23

If we want to analyze the rate of change of link arrival time in the same scenario we will get

eq 13.

𝛿𝑦𝛿µ𝑘

= (PNavg ∗ λ ∗ Tpr)� �−rTprµk2

�𝑒−𝑟𝑇𝑝𝑟

µ𝑘 ��Lavg

𝑟=0

………………………………………24

and obviously number of nodes of a network plays a vital role in routing over head. We can

calculate the impact of change in number of nodes of a network we can do so via eq 14.

𝛿𝑦𝛿𝑛

= 3𝑘𝑛2

𝐵∗𝑇𝑝𝑟…………………………………………………………………………………...25

53

3.2.5 Calculations and Results:

Considering the Eq.14, that is partial derivative w.r.t. “ n”, we can infer that as number of

nodes of a network increases, its routing overhead increases but, if number of nodes decreases

than 3 nodes, the over head of the network will reduce.

Keeping in view Eq. 10 and Eq. 12 are the partial derivatives with respect to Tpr and T i.e.

periodic update interval and triggered updates. Considering all the aspects of network in

mobility and scalability remain constant, than we can say that these two variables are

dependent on each other. As the periodic message exceeds in its interval, there would be more

triggered messages than before. In the same sense if we reduce the periodic update interval

time, triggered updates will be lowered but only and only if all other parameters mainly

mobility and number of nodes in a network remain same. To further analyze this change, we

take total derivative of Tpr and T variables of function y.

𝑑𝑦𝑑𝑇𝑝𝑟

=𝛿𝑦𝛿𝑇𝑝𝑟

+𝛿𝑦𝛿𝑇

�dT

dTpr�

𝑑𝑦 =𝛿𝑦𝛿𝑇𝑝𝑟

(𝑑𝑇𝑝𝑟) +𝛿𝑦𝛿𝑇

(dT)

𝑑𝑦 =

(C)� ��1 − 𝑒−𝑟𝑇𝑝𝑟

µ𝑘 � + � r∗Tprµk

� 𝑒−𝑟𝑇𝑝𝑟

µ𝑘 � − kn3

𝐵∗Tpr2

Lavg

𝑟=0

+ ∑ �−T\Tpr2�+T\Tpr2

𝑇2

𝑇𝑝𝑟2

ni=1 (𝑑𝑇𝑝𝑟) +

∑ �1\Tpr2�−1\Tpr2

𝑇2

𝑇𝑝𝑟2

ni=1 (dT)…………………………………………………………26

54

In static environment, longer Tpr might not affect the performance of routing protocol and

favor reducing routing over head but if in mobile environments, if longer Tpr is used, it will

result in high rate of triggered messages. Eq. 15 shows that Tpr and T are two variables which

are tied with nonlinear relationship with one another. Simulation results will clearly validate

this mathematical statement.

Considering Eq.11 and Eq. 13, it is obvious that if there is always an uplink for whole of the

network / for the entire life of the network, or there is no periodic interval i.e ifµk tends to

infinity and Tpr is zero, both partial derivatives with respect to λ and µk will be zero. [33]

Assuming 𝛿y / 𝛿Tpr = 0, we get:

(C)� ��1 − 𝑒−𝑟𝑇𝑝𝑟

µ𝑘 � + � r∗Tprµk

� 𝑒−𝑟𝑇𝑝𝑟

µ𝑘 �Lavg

𝑟=0

= kn3

𝐵∗Tpr2− ∑ �−T\Tpr2�+T\Tpr2

𝑇2/𝑇𝑝𝑟2ni=1 ………27

The ratio between periodic update time and uplink time can be termed as update coefficient

[33]. Let us denote that update coefficient as “h”= Tpr/ µk or Tpr= µk*h.

Placing the values in Eq. 14 will give us optimized network analytical model.

(C)� {(1 − 𝑒−𝑟ℎ) + (r ∗ h)𝑒−𝑟ℎ}Lavg𝑟=0 = kn3

𝐵∗(µ𝑘∗ℎ)2− ∑ �−T\(µ𝑘∗ℎ)2�+T(µ𝑘∗ℎ)2

𝑇2/(µ𝑘∗ℎ)2ni=1 ………….28

Eq. 17 shows that if average link uptime increases, “h” or update coefficient will also increase

but this increase don’t linearly affect the periodic interval time. As depicted before, here again

this equation shows the same, as number of nodes increases, the routing overhead will also

nonlinearly increase.

This is the generalized routing over head analytical model for proactive routing protocols. In

this model we have taken care of DSDV by injecting trigger message which were not

discussed in [33] and [35], where as in many other papers including [34], periodic messages

55

and triggered messages are taken into consideration leaving the overhead due to failure of

packets in reaching at destination. In our model, we consider all these three vital factors

influencing routing overhead.

If we consider OLSR routing protocol, than we will come to know that it is actually an

optimization of LSR with the use of MPR concept. MPR set is a subset of set of all the nodes

of network. As small the MPR set will be, as much over head or retransmissions will be

reduced.

According to RFC 3626 [36], there are 4 periodic messages in OLSR. Hello, Topology

control, MID and HNA. Mostly only hello message and TC messages are taken into

considerations. If we look into theme of OLSR routing protocol, we will come to know that

hello messages are used to gain the neighborhood knowledge and to select MPR set (MPR set

is the only set which is allowed to retransmit or broadcast the receiving message). once,

neighborhood is known and MPR set is established, TC message is broadcasted by that

selected MPR set for topology information. Hence Hello message as given in RFC3626, is of

1 sec while TC message interval is 2 sec. in other words, authors of RFC 3626 proposed that

hello message interval should be taken as half of the TC message interval.

Placing the values of hello message and TC message in composed analytical model, we get the

equation:

𝑅𝑂𝑂𝐿𝑆𝑅 = (PNavg)� �(1 − 𝑒−𝑟𝑇𝑝𝑟/µ𝑘) λ(Tpr)�+ kn3

𝐵∗𝐻

L1

𝑟=0+ kn3

𝐵∗2𝐻+ ∑ ⌈T/H+2H⌉

𝑇𝐻+2𝐻

ni=1 ……..29

Where

H = Hello message interval

56

2H = TC message interval, twice the

To analyze the rate of change in hello and TC interval, we partially derivate equation 18 with

respect to “h” and we get:

𝛿𝑦𝛿𝐻

= − 𝑘𝑛3

𝐵∗𝐻2 −𝑘𝑛3

𝐵∗2𝐻2 + ∑ �−T/(H+2H)2�+T\(H+2H)2

𝑇2/(H+2H)2ni=1 ………………………………………30

With the help of same model, we can also calculate our desired over head, whether to find

over head due to hello message emissions or topology control messaging over head or the

overhead due to lost packets.

3.3 Future works:

`Considering the step 4 of initially described steps in RD and RM phases of reactive routing, a

reactive routing protocol may choose the following three options [28] i.e.

1. Wait for TIME OUT time and than new route discovery

2. RERR packet to main source node via reverse path and new route discovery

3. Local repair

We will find the overhead considering all the three phases one by one. Especially the case 3 is

the requirement of the time.

57

Chapter 4

Experiments, Results and Discussions

58

4.1 Simulations

AODV [38], DSR [40], DSDV [39] are used as default ones that come with NS2. AODV

coding used was developed by CMU/MONARCH group while it was optimized by Samir Das

and Mahesh Marina (University of Cincinnati). DYMOUM by MASIMUM [41] is used for

DYMO. We used NS-2.34 for simulating AODV and DSR while, DYMOUM was simulated

in NS 2.29. Sven JAAP [42] gives us FSR implementation while MASIMUM produced UM-

OLSR [41] which we utilized here. Simulations of DSDV and OLSR are made on NS-2.34

while FSR was already available on NS-2.30. We pin points on mobility and Scalability

factors of Ad Hoc networks in this work. Hence all the simulations are done taking these

aspects into account.

4.2 Parameters for Experiments:

We have considered a network of 50 nodes where nodes are randomly located and mobile.

These nodes are privileged with the bandwidth of 2 Mbps. Speed by which a data packet

travels is set at 8m/s. Packet size is defined as 512 bytes while simulation setup runs on

Continues bit rate traffic sources. The size of network is defined as 1000 square meter.

For every experiment, any particular scenario with same parameters and pause timings is

executed for 5 times. The mean value of these 5 times is used to plot the graphs which are

presented underneath.

“cbrgen” located in directory/ nsallinone-nn/ns-nn/indep-utils/cmu-scen-gen is used in making

the random source to destined node interconnections . The traffic we used under such scenario

is CBR i.e. constant bit rate.

Given these parameters, we have confined our experiments only for the three metrics.

59

1. Throughput

2. End - End Delay

3. Normalized routing Load.

4.3 Reactive Experimentations:

4.3.1 Through put of Reactive Routing:

a) With respect to mobility

In general sense, throughput refers to the amount of data that has successfully reached its

destination. Mathematically it can be stated as

𝑇ℎ𝑟𝑜𝑢𝑔𝑝𝑢𝑡 =(𝑆𝑢𝑐𝑐𝑒𝑠𝑠𝑓𝑢𝑙𝑙𝑦 𝑑𝑒𝑙𝑖𝑣𝑒𝑟𝑒𝑑 𝑑𝑎𝑡𝑎 𝑝𝑎𝑐𝑘𝑒𝑡𝑠)

𝑇𝑖𝑚𝑒

Represented as B/s

Considering simulation results for throughput, we can state that when mobility factor in a

network is high, DSR enjoys the maximum throughput with respect to AODV and DYMO

subjected to FCM not at 0, 100, 200 pause times. If FCM is at 0 or 100 or 200 pause times,

AODV gives better throughput than DYMO and DSR. If mobility factor is further increased,

DSR will face trouble in route caching (as no mechanism is defined to erase stale routes hence

it fails to converge at high mobility). If we consider AODV, than it surely have a TIME_OUT

factor involved. AODV waits for a specified time and than the route is termed invalid finally

erased from routing table. “Hello messages” in AODV also works very well for high mobile

environment. Leaving highly mobility factor, DSR performs most stable throughput as no

unnecessary packets are generated by this routing protocol. In DSR, in link breakages, it also

have multiple routes for the same source and destined station while, in AODV, the routing

table keeps only one the best chosen path between the nodes. Hence the environment where

links are immune to break due to noise or other factors, DSR again supersedes AODV and

DYMO. DYMO proves itself the worst amongst the other two protocols.

60

Throu

ghpu

t (Kbp

s)

Pause Time

Fig. 4.1 Throughput (AODV, DSR, DYMO)

Throu

ghpu

t (Kbp

s)

No. of Nodes

b) With respect to scalability:

According to our experiments, AODV converged almost all data rates with all

scalabilities, While DSR proves itself to be scalable but during high data traffic, it

couldn’t converge the network. DYMO perfoms worst among these studied routing

protocols. As the number of nodes increases or data traffic increases, its performance

degrades dramatically. According to [18] a network of multiple thousands of nodes

with different traffic loads can be handled by AODV. The reason that AODV

supersedes DSR and DYMO is lower packet loss ratio and propagating of information

regarding distant vector which practically consume minimum bandwidth. This feature

gives AODV the room for scalability and traffic loads across the number of routes. In

AODV, routing packet contains only one hop information while in DSR; packet size is

61

larger as it keeps the information of whole route. This is another reason that AODV

outperforms DSR.

4.3.2 End - End Delay of Reactive Routing:

a) With respect to mobility

The time a packet takes in reaching destined node from the originator node can be termed as

End - End delay. Mathematically we can express End - End delay as

𝐸𝐷 =𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝𝑎𝑐𝑘𝑒𝑡𝑠 𝑡𝑟𝑎𝑛𝑠𝑚𝑖𝑡𝑡𝑒𝑑(𝑅𝑜𝑢𝑛𝑑 𝑡𝑟𝑖𝑝 𝑡𝑖𝑚𝑒)

𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑠𝑢𝑐𝑐𝑒𝑠𝑠𝑓𝑢𝑙𝑙𝑦 𝑑𝑒𝑙𝑖𝑣𝑒𝑟𝑑 𝑝𝑎𝑐𝑘𝑒𝑡𝑠

End - End delay is calculated in time scale i.e. seconds.

As shown in the graph, AODV produces lowest performance as link breakages due to mobility

factor may lead to longer routes. DYMO though works worst in throughput case but here it

works best amongst DSR and AODV. It is so because, DYMO don’t check the routes in

memory as DSR looks into route cache and AODV in to its routing table, instead DYMO

starts expanding ring search algorithm whenever a route is required.

b) With respect to scalability:

The concept of grat. RREP is used both in DSR and AODV while this is the reason that

DYMO enjoyes lowest End - End delay irrelevant of number of nodes in the network. Grat.

Route replies though results in lower delay at normal traffic rates but DSR checks the route

cache before using expanding ring search algorithm in the same way as AODV searches the

route in its routing table before starting a route request using expanding ring search algorithm.

DYMO don’t use such stored information rather it simply initiates ERS. AODV also have a

link repair feature that makes it bear the highest End - End delay with respect to any

scalability among DYMO and DSR.

62

No. Of Nodes

End t

o End

Delay

(ms)

Pause Time

Fig. 4.2 End to End Delay (AODV, DSR, DYMO)

End t

o End

Delay

(ms)

4.3.3 Normalized Routing Load of Reactive Routing:

a) With Respect to Mobility:

When a single data packet is to be sent from one node to another within an ad hoc network, a

number of routing packets are involved in sending this data packet . The number of these

routing packets which are sent just to transfer one data packet are termed as normalized

routing load. Mathematically we can state it as

𝑁𝑜𝑟𝑚𝑎𝑙𝑖𝑧𝑒𝑑 𝑅𝑜𝑢𝑡𝑖𝑛𝑔 𝐿𝑂𝐴𝐷 = 𝑇𝑜𝑡𝑎𝑙 𝑅𝑜𝑢𝑡𝑖𝑛𝑔 𝐿𝑜𝑎𝑑 − 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑑𝑎𝑡𝑎 𝑝𝑎𝑐𝑘𝑒𝑡𝑠 𝑠𝑒𝑛𝑡

AODV and DSR use the concept of gratuitous route replies. i.e. when a route request reaches

any node that has a valid route stored in its route cache or routing table, it generates a route

reply by its self to the main source node. This route reply contains the full information upto

the destined node and overhead of finding route beyond that node limits. DYMO don’t use

this grat. RREP. And that’s the reason; DYMO suffers from greater routing overhead with

respect to the other two protocols. AODV also works well in the context of normalized routing

overhead but, there is a concept of local link repair and above all the use of hello message for

63

link monitoring makes it perform lowers then DSR. A node with underlying DSR protocol use

promiscuous mode and this is the reason that it bears lowest over head.

A common observation with respect to increase in mobility of nodes in network, all the three

routing protocols bear gradually higher overhead. The reason is propagations of route error

packets. As the mobility increases, the chances of link breakages also increase in the same

proportion. Hence routing overhead must be increased.

No. of Nodes

Norm

alized

Routin

g Loa

d

Pause Time

Fig 4.3 Normalized Routing Loead (AODV, DSR, DYMO)

Norm

alized

Routin

g Loa

d

b) With respect to scalability:

In normal conditions of network populations or even at high population, routing overhead of

DYMO is lower than that of AODV and DSR where as AODV bears high routing overhead in

dense networks. Periodic link sensing, packets involved in local link repair mechanism and

grat. RREP results in high routing overhead. Whereas promiscuous mode utilized by DSR

reduces the routing overhead in no so dense environment.

.

64

4.4 Proactive Experimentations:

4.4.1 Throughput of Proactive Routing:

a) With respect to mobility:

When we simulated proactive routing protocols for throughput prospective, DSDV proves

itself to be the most efficient protocol among other two i.e. FSR and OLSR. Main reason of

this result is the basic functioning of DSDV protocol. As stated in chapter 3 as well that a

packet is sent only on the best possible route and this route search may get a bit of delay as

DSDV delays the route advertisements that have higher probability to be changed earlier.

Moreover, un-stabilized routes that have the same sequence number in DSDV routing protocol

are also advertised with delay. These features of DSDV results in accurate routing hence

increased throughput. On other hand, taking OLSR into account, its ability to converge

declines as the mobility increases, thus lower throughput is the result. Though, in static

environment, due to MPR concept in OLSR, it gives better throughput than FSR and DSDV.

Whenever a link breaks, there is a concept of triggered messages in DSDV routing protocol

that also increase the route accuracy where as in FSR and OLSR there is no availability of

triggered updates.

b) With respect to scalability:

FSR is better under fluctuating traffic patterns while OLSR works well with dense

environment among proactive routing protocols. Throughput of FSR also increases as it used

multi level fisheye scope. This technique results in lower overhead, and less consumption of

bandwidth which is a major plus point for the throughput. DSDV use NPDUs for lower

overhead but triggered messages create routing overhead consuming bandwidth and resulting

in lower throughput. OLSR uses MPR for lowering the routing overhead but periodic

messages used to calculate and compute a MPR set for a node take more bandwidth. Though

65

its throughput is more than that of DSDV but lower than FSR. FSR, is highly scalable as it use

different frequencies for different scopes i.e. at different time intervals. OLSR is also highly

scalable but network convergence is issue in very dense environment where traffic load is

high. Hence OLSR is a highly scalable protocol but if data traffic rates are not that high. Th

rough

put

No. of Nodes

Pause time

Fig 4.4 Troughput (FSR, DSDV, OLSR)

Throu

ghpu

t

4.4.2 End - End Delay of Proactive Routing:

a) With respect to mobility:

According to the general behavior of proactive routing it can be observed that End - End delay

will be higher with respect to reactive routing protocols when we emphasis on mobility of

nodes within the network. The reason is spreading the topology and routing information to

each and every participant node of the network. Whenever any change occurs, it is notified to

entire network. DSDV proved to be the best for throughput but when considering delay, it

bears the worst conditions with respect to FSR and OLSR. DSDV, don’t sends the data packet

66

until a fair enough time for creating and choosing the best possible route. Moreover the

delayed advertisements of unstable routes results in overall End - End delay. In DSDV, this is

done to reduce the routing overhead and provide route accuracy but it compromises on delay.

OLSR performs better than DSDV. FSR owns the highest End - End delay among the studied

protocols. As in the basic theme of FSR, when the mobility increases, the accuracy of far away

destined nodes fades. However as the packet gets closer to destined node, the routing info gets

accurate.

No. Of Nodes

Pause Time

End t

o End

Dela

y (ms

)

Fig 4.5 End to End Delay (DSDV, FSR, OLSR)

End t

o End

Dela

y (ms

)

b) With respect to scalability:

As the environment get dense, the End - End delay of all three routing protocols i.e. FSR,

DSDV and OLSR will increase. FSR shares routing updates with its neighbors in small

intervals while the information’s shared at far away nodes has some larger interval in them. As

the network become more scalable, End - End delay will increase in FSR. In DSDV, End -

End delay is due to the two procedures, i.e. finding some routes, choosing the best one route.

As the network gets denser, the routing of End - End time will also increase. As in proactive

67

nature, the information is spread in whole network. OLSR use MPRs and during low traffic

rates, End - End delay using OLSR will be lower. This is because of MPR concept that

presents weel organized flooding control instead of flooding the packet on whole network.

4.4.3 Normalized Routing Load of Proactive Routing:

Norm

alized

Routin

g Load

No. Of Nodes

Pause Time

Fig 4.6 Normalized Routing Load (FSF, DSDV, OLSR)

Norm

alized

Routin

g Load

a) With Respect to Mobility:

Among the studied proactive routing protocols, OLSR bears maximum number of periodic

messages to compute MPRs. Hence as it was observed, experiments proved it as well that

OLSR bears highest routing overhead. DSDV again proves to be the normal choice amongst

FSR and OLSR in terms of routing overhead. Reason is discussed in End - End delay section

of proactive routing protocols. Considering FSR, it bears lower overhead due to control and

periodic messages in competition with OLSR. FSR’s control messages are periodic based

rather event driven based as in OLSR. This feature helps FSR in reduced routing overhead.

68

Moreover, there is limited flooding in FSR i.e. link state information is not flooded among

whole network besides, every node manage a LS table which is derieved on the basis of UP

TO DATE information received. This information is not broadcasted or flooded but is shared

amongst neighbors.

b) With respect to scalability:

Among all studied proactive routing protocols, OLSR gives the highest routing overhead due

to MPR comupational messages and topology control messages. DSDV and FSR have lower

overhead in dense environments. DSDV reduces overhead with the help of NPDUs and FSR

use Fisheye scope to limit overhead. The simulated results show that FSR stands best amongs

DSDV and OLSR in a dense and highly mobile environment in terms of overhead.

4.5 Conclusions:

In this thesis, we have initially presented the literature survey of route discovery and

maintenance phases of both reactive and proactive routing protocols for mobile Ad Hoc and

Vehicular Ad Hoc networks. We contributed generalized analytical framework representing

routing overhead due to route discovery and maintenance phases of both reactive and

proactive routing protocols. Reactive routing is based on immediate response. This can waste

network resources. Binary exponential back off algorithm and Expanding ring search

algorithms are used in AODV DSR and DYMO. Both of these algorithms are expressed in

this thesis as well. Later experiments are conducted on the six routing protocols keeping the

parameters of throughput, End - End delay and routing overhead in emphasis with respect to

mobility and scalability factors of any Ad Hoc network. Routing overhead comprises of the

overhead caused by control packets only. Data packets are not included in routing overhead.

As the routing overhead increases and or End - End delay increases, performance of the

routing protocol deteriorates. The protocol that uses minimum resources of bandwidth by its

69

control packets can provide better data flow. Hence the environments where traffic load is

very high, only those protocols that have low routing overhead will survive. If we consider

scalability, than AODV stands at top of rest of five routing protocols. It use distance vector

distribution that minimizes the network resources consumption. In proactive routing, OLSR

stands tall as it limits retransmissions due to use of MPR concept but only in dense

environments. If mobility with the number of nodes of network increases, than FSR is be a

good choice as it generates low routing overhead that leads to high data rates within the

limited bandwidth.

The experiments conducted show us that considering over all behaviors and performance of

routing protocols, reactive protocols works better than proactive routing protocols if only

mobility factor is considered. The network underlying AODV protocol, bears low routing

overhead as control packets of AODV contains a very small part of information in them

where as if we compare it with DSR, control packet of DSR carries whole routing

information in it. Hence we can say that DSR has higher routing overhead in terms of bytes

or size. If we consider number of control packets than DSR broadcast lesser number of

packets than that of AODV. AODV use periodic hello packet for link sensing and also the

local repair routing overhead. Hence if we genially compare both of these routing protocols

considering mobility and speed factors, we can conclude that both of these protocols give

almost same performance.

Concluding all the six routing protocols, our study suggest that, AODV can be selected for

denser environments where lower routing overhead is required, DSR should be used within a

network having limited number of hops. DYMO routing protocol can be used in networks

where delay is in tolerable. As like other reactive protocols, DYMO don’t look for any stored

route as DSR looks into its cache and AODV in its routing table. It initializes binary

70

exponential back off and expanding ring search algorithm immediately. In proactive routing,

OLSR also stands good for lower end to end delay due to MPRs. The following table

summarizes the basic differences and similarities between the studied six routing protocols.

AODV DSR DYMO FSR OLSR DSDV

Protocol type Distance Vector

Source routing

Source routing

Link state Link state Distance Vector

Route maintained in

Routing table Route Cache Routing table Routing table Routing table Routing table

Multiple route discovery

No yes no yes no No

Multicast Yes yes no yes yes Yes

Periodic broad cast

Yes no no Yes (with in limited range)

yes Yes

Route reconfiguration

Erase route notify source

Erase route notify source

Erase route notify source

Link state mechanism with sequence number

Link state mechanism / Control messages send in advance

Sequence number adopted

Route discovery packets

using RREQ and RREP packets

using RREQ and RREP packets

using RREQ and RREP packets

Link state messages

via control message link sensing

Via control messages

Limiting over head ,collision avoidance, network congestion

Expanding ring search algorithm using specific time period

Expanding ring search algorithm using hop count

Expanding ring search algorithm using specific time period

Fisheye procedure, broadcast limited only to transmission range.

Concept of Multipoint relays

concept of sequence number

Limiting over head , collision avoidance , network congestion

Binary exponential back off time

Binary exponential back off time

Binary exponential back off time

MAC layer protocols only

MAC layer protocols only

MAC layer protocol only

71

Update information

By RERR message

By RERR message

By RERR message

Only neighbor information

2 hop neighbor information

By control messages

Topology information

Full topology Full topology Full topology Reduced topology

Full topology Full topology

Update destination

Source source source neighbors MPR sets source

Broadcast Full Full Full Local/ limited Limited by MPR Set

full

Reuse of routing info

No Yes Yes Yes Yes yes

Route selection Only searched route

Hop count Only searched route

Shortest hop count

Hop count Shortest hop count

72

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