Seminar ReportOn

A MPR BASED SOLUTION FOR FLOODINGOF BROADCAST MESSAGES IN OLSR

ADHOC NETWORK

Submitted in partial fulfillment of the requirementsfor the degree of

Master of Technology(CSE)

by

Suvendra MishraRegd. No :1361025003

Under the guidance of

Mr. Prabhat Kumar Sahu

Department of Computer Science & EngineeringInstitute of Technical Education and Research

Siksha ’O’ Anusandhan University

2014

Certificate

This is to certify that the seminar work entitled "A MPR BASED SOLU-TION FOR FLOODING OF BROADCAST MESSAGES IN OLSRADHOC NETWORK" carried out by Suvendra Mishra bearing Regd.No:1361025003, a student of 3rd semester M.Tech having specialization in Com-puter Science and Informatics from Institute of Technical Education and Re-search, Bhubaneswar, under my guidance has been completed by him andworthy of acceptance for the degree of Master of Technology in Computer Sci-ence and Informatics, under Siksha O Anusandhan University, Bhubaneswar,Odisha.

Submitted BySuvendra MishraRegd No.1361025003M. Tech(CSI)

Guided ByMr. Prabhat Kumar SahuAsst. ProfessorDept. of Comp. Sc. & Engg.

Acknowledgment

I owe deep gratitude to the ones who have contributed greatly in preparingthe seminar.

Foremost, I would like to express my sincere gratitude to HOD, ComputerScience and Informatics for his esteemed motivations and support. MoreoverI am thankful to my guide for his suggestions, motivations, cooperation andsustained support throughout the seminar work to make it out a success.

I express my thanks and love to all my friends to stand by my side and fortheir timely suggestions and encouragements.

Suvendra MishraRegd No: 1361025003

ABSTRACT

In an Optimized Link State Routing (OLSR)-based mobile wireless network,optimizing the flooding of broadcast messages is a challenging task due tonodeŠs mobility and bandwidth resource consumption. To complement ex-isting solutions to this problem, the Multi-Point Relays (MPR) selection hasrecently been advocated as a promising technique that has an additional fea-ture of reducing the number of redundant re-transmission occurring in thenetwork. Here in this paper, continuous on the investigation of an existingMPR-based solution, arguing that by considering a cost factor as an addi-tional decision parameter in selecting the MPR nodes, the enhanced MPRselection algorithm leads to less packet loss in the network. Simulation exper-iments are presented to validate the stated goal, using the average packet lossratio as the performance metric.

Guided ByMr. Prabhat Kumar SahuAsst. Prof.Dept of Comp. Sc. & Engg.

Submitted BySuvendra Mishra

Regd No:1361025003M.Tech(CSI)

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Contents

1 INTRODUCTION 61.1 Mobile Ad-hoc Network (MANET) . . . . . . . . . . . . . . . . 61.2 Routing in Ad-hoc Network . . . . . . . . . . . . . . . . . . . . 6

1.2.1 Proactive Protocols . . . . . . . . . . . . . . . . . . . . . 71.2.2 Reactive Protocols . . . . . . . . . . . . . . . . . . . . . 71.2.3 Hybrid Protocols . . . . . . . . . . . . . . . . . . . . . . 8

2 Optimized Link State Routing (OLSR) Protocol 9

3 Multi Point Relay (MPR) 113.1 MPR Selection Algorithm . . . . . . . . . . . . . . . . . . . . . 123.2 Future Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4 Conclusion 14

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List of Figures

1.1 Types of Routing Protocols in Ad-hoc Network . . . . . . . . . 7

2.1 General Flooding . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.1 Multi Point Relay Flooding . . . . . . . . . . . . . . . . . . . . 113.2 Step - 1 of MPR Selection Algorithm . . . . . . . . . . . . . . . 123.3 Step - 2 of MPR Selection Algorithm . . . . . . . . . . . . . . . 12

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Chapter 1

INTRODUCTION

1.1 Mobile Ad-hoc Network (MANET)A mobile ad hoc network (MANET) is a collection of mobile devices whichare connected by wireless links without the use of any fixed infrastructuresor centralized access points. In MANET, each node acts not only as a hostbut also as a router to forward messages for other nodes that are not withinthe same direct wireless transmission range. Each device in a MANET is freeto move independently in any direction, and will therefore change its links toother devices frequently.

MANETs are much more vulnerable and are susceptible to various kinds ofsecurity attacks because of its cooperating environment. In the absence of afixed infrastructure that establishes a line of defense by identifying and isolat-ing non-trusted nodes, it is possible that the control messages generated by therouting protocols are corrupted or compromised thus affecting the performanceof the network.

Routing protocols in MANET can be classified into two categories: reac-tive protocol and proactive protocol. In proactive routing protocols, all nodesneed to maintain a consistent view of the network topology. When a networktopology changes, respective updates must be propagated throughout the net-work to notify the change. In reactive routing protocols for mobile ad hocnetworks, which are also called "on-demand" routing protocols, routing pathsare searched for, when needed. Even though many research works had beencarried out for routing attacks in MANET, most of it concentrated mainlyon re- active routing protocols. Optimized link state routing (OLSR) routingprotocol which is a proactive routing protocol offers promising performancein terms of bandwidth and traffic overhead but it does not incorporate anysecurity measures.

1.2 Routing in Ad-hoc NetworkThe ad hoc routing protocols are divided into three groups:

1. Proactive Protocols

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2. Reactive Protocols

3. Hybrid Protocols

Figure 1.1: Types of Routing Protocols in Ad-hoc Network

1.2.1 Proactive Protocols

Proactive or table-driven protocols are similar to the ones used in the wirednetworks. Routes to all destinations are updated periodically. The family ofproactive protocols includes basically Destination Sequenced Distance VectorRouting (DSDV), Optimized Link State Routing Protocol (OLSR), TopologyBroadcast Based on Reverse Path Forwarding (TBRPF), DSDV is based on aDistance Vector approach. It associates to each route entry a sequence numberindicating its freshness. Routes for each destination are preferred if they have:1. A newer sequence number, or 2. A best cost metric, in the case that tworoutes have the same sequence number.

1.2.2 Reactive Protocols

In contrast, reactive (On-demand) protocols determine the route to a destina-tion only when it is required. Thus, a node floods the network with a routerequest and waits for the route reply message to establish a route to the des-tination node. This reduces the routing load as compared to the proactive

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protocols. This technique does not require constant broadcast messages, butcauses additional delay since the routes are not usually available. Ad hoc Ondemand Distance Vector Protocol (AODV) and Distributed Source RoutingProtocol (DSR) are the two most popular reactive routing protocols for Adhoc networks. AODV and DSR include the same two routing phases (routediscovery and route maintenance).

1.2.3 Hybrid Protocols

The limits and disadvantages of both Proactive and Reactive Routing Proto-cols have lead to the design of Hybrid Routing Protocols. Hybrid is a combi-nation of both. The types are Zone Routing Protocols (ZRP), Fisheye StateRouting (FSR), Landmark Routing (LANMAR)

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Chapter 2

Optimized Link State Routing(OLSR) Protocol

OLSR is a proactive routing protocol for mobile ad hoc networks. The protocolinherits the stability of a link state algorithm and has the advantage of havingroutes immediately available when needed due to its proactive nature. OLSRis an optimization over the classical link state protocol, tailored for mobile adhoc networks.

OLSR minimizes the overhead from flooding of control traffic by using onlyselected nodes, called MPRs, to retransmit control messages. This techniquesignificantly reduces the number of retransmissions required to flood a messageto all nodes in the network. Secondly, OLSR requires only partial link stateto be flooded in order to provide shortest path routes. The minimal set oflink state information required is, that all nodes, selected as MPRs, MUSTdeclare the links to their MPR selectors. Additional topological information,if present, MAY be utilized e.g., for redundancy purposes.

OLSR may optimize the reactivity to topological changes by reducing themaximum time interval for periodic control message transmission. Further-more, as OLSR continuously maintains routes to all destinations in the net-work, the protocol is beneficial for traffic patterns where a large subset of nodesare communicating with another large subset of nodes, and where the [source,destination] pairs are changing over time. The protocol is particularly suitedfor large and dense networks, as the optimization done using MPRs works wellin this context. The larger and more dense a network, the more optimizationcan be achieved as compared to the classic link state algorithm.

OLSR is designed to work in a completely distributed manner and doesnot depend on any central entity. The protocol does NOT REQUIRE reliabletransmission of control messages: each node sends control messages periodi-cally, and can therefore sustain a reasonable loss of some such messages. Suchlosses occur frequently in radio networks due to collisions or other transmissionproblems.

Also, OLSR does not require sequenced delivery of messages. Each controlmessage contains a sequence number which is incremented for each message.Thus the recipient of a control message can, if required, easily identify which

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information is more recent - even if messages have been re-ordered while intransmission.

Furthermore, OLSR provides support for protocol extensions such as sleepmode operation, multicast-routing etc. Such extensions may be introducedas additions to the protocol without breaking backwards compatibility withearlier versions.

OLSR does not require any changes to the format of IP packets. Thus anyexisting IP stack can be used as is: the protocol only interacts with routingtable management.

Figure 2.1: General Flooding

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Chapter 3

Multi Point Relay (MPR)

The idea of multipoint relays is to minimize the overhead of flooding messagesin the network by reducing redundant retransmissions in the same region. Eachnode in the network selects a set of nodes in its symmetric 1-hop neighborhoodwhich may retransmit its messages. This set of selected neighbor nodes iscalled the "Multipoint Relay" (MPR) set of that node. The neighbors of nodeN which are not in its MPR set, receive and process broadcast messages butdo not retransmit broadcast messages received from node N.

Each node selects its MPR set from among its 1-hop symmetric neighbors.This set is selected such that it covers (in terms of radio range) all symmetricstrict 2-hop nodes. The MPR set of N, denoted as MPR(N), is then an ar-bitrary subset of the symmetric 1-hop neighborhood of N which satisfies thefollowing condition: every node in the symmetric strict 2-hop neighborhood ofN must have a symmetric link towards MPR(N). The smaller a MPR set, theless control traffic overhead results from the routing protocol.

Figure 3.1: Multi Point Relay Flooding

Each node maintains information about the set of neighbors that haveselected it as MPR. This set is called the "Multipoint Relay Selector set"(MPR selector set) of a node. A node obtains this information from periodicHELLO messages received from the neighbors.

A broadcast message, intended to be diffused in the whole network, comingfrom any of the MPR selectors of node N is assumed to be retransmitted bynode N, if N has not received it yet. This set can change over time (i.e., whena node selects another MPR-set) and is indicated by the selector nodes in their

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HELLO messages.

3.1 MPR Selection AlgorithmEach point u has to select its set of MPR. Goal: select in the 1-neighborhoodof u (N1(u)) a set of nodes as small as possible which covers the whole 2-neighborhood of u (N2(u)), in two steps :

Step 1: Select nodes of N1(u) which cover isolated points of N2(u). (Thatwe call MPR1(u).)

Figure 3.2: Step - 1 of MPR Selection Algorithm

Step 2: Select among the nodes of N1(u) not selected at the first step, thenode which covers the highest number of points (not already covered) of N2(u)and go on till every points of N2(u) are covered.

Figure 3.3: Step - 2 of MPR Selection Algorithm

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3.2 Future PlanWith reduced redundancy in retransmissions and reduced overhead of floodingmessages in the network, introduction of Multi Relay Points in OptimizedLink State Routing Protocol (OSLR) proved to be very successful. Likewisethe method of Multi Point Relays can also be used in other protocols to achievethe above mentioned outputs.

Out of all such protocols in MANET, Zone Based Routing Protocol (ZRP)is a hybrid Wireless Networking routing protocol that uses both proactive andreactive routing protocols when sending information over the network. ZRP isdesigned to speed up delivery and reduce processing overhead by selecting themost efficient type of protocol to use throughout the route.

Therefore, we can use Multi Point Relays in Zone Based Routing Protocolto achieve further reduced overhead and lower redundancy.

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Chapter 4

Conclusion

Introduction of MPR in OLSR thus results in:-

1. Reduced overhead of flooding messages in network.

2. Reduced redundancy in retransmissions.

There is approximately a reduction of 60 percent of redundant packetsreceived by the nodes.

OLSR favours the networking context where this all-time-kept informationis used more and more and where route requests for new destinations are veryfrequent. The protocol also goes in favour of the applications which do notallow long delays in transmitting data packets. The protocol is adapted to thenetwork which is dense, and where the communication is assumed to occurfrequently between a large numbers of nodes.

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Bibliography

[1] Ji Hyoung Ahn, Tae Jin Lee, “Multipoint relay selection for robust broad-cast in ad hoc networks”, Elsevier, Ad Hoc Networks, vol. 5, pp. 82-97, June2008 .

[2] Reza Malekian, Aleksandar Karadimce, Abdul Hanan Abdullah, “AODVand OLSR Routing Protocols in MANET” IEEE 33rd International Confer-ence on Distributed Computing Systems Workshops (ICDCSW), pp.286-289,2013.

[3] P.Jacquet, A.Laouiti, “Analysis of Mobile Ad-hoc Network Routing Proto-cols in Random Graph Models” INRIA Technical Report, RR-3835, 2012.

[4] Philippe Jacquet, Anis Laouiti, Pascale Minet, Laurent Viennot, “Perfor-mance analysis of OLSR Multipoint Relay ooding in two ad hoc wireless-network models“ INRIA Technical Report, RR-4260, 2012.

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