DEVELOPMENT OF DH-AODV ROUTING

PROTOCOL FOR WIRELESS MESH NETWORKS

BY

ZAINAB SENAN MAHMOD

A dissertation submitted in partial fulfilment of the

requirement for the degree of Master of Science (Computer

and Information Engineering)

Kulliyyah of Engineering

International Islamic University Malaysia

AUGUST 2010

ii

ABSTRACT

Wireless mesh networks (WMNs) have emerged as a key technology for next-

generation wireless networking. Although WMNs can be built up based on existing

technologies, field trials and experiments with existing WMNs prove that the

performance of WMNs is still far below expectations. Therefore, several challenging

research issues need to be resolved. One of the most effective factors to improve the

performance of WMNs is the routing protocol used. There are many performance

issues need to be improved such as robustness, QoS, security, power consumption,

and scalability which is the most critical issue in WMNs. Current researches are trying

to develop new protocols or enhance some of the Ad-hoc protocol to be adapted to

WMNs. This research aims to design and implement a routing protocol that improves

the scalability of the WMNs. To achieve this, a Directional Hierarchical Ad-hoc On

Demand Vector (DH-AODV) routing protocol is proposed. The DH-AODV is taking

advantage of the existing fields in the AODV's control packets in order to reduce the

load on the network's bandwidth and to quickly detect route breakage. The proposed

protocol is designed, implemented and evaluated using Qualnet Simulator. The Ad-

hoc on Demand Distance Vector (AODV) is selected as a benchmark. Simulation

results indicate that this enhanced routing protocol can 47% reduce the end-to-end

delay of data packets, improve the throughput by 11.2%, and decrease the packet loss

rate 20% less than the standard AODV.

iii

ملخص البحث

الشبكات نالت الشبكات اللاسكية المعشقة اهتماماً واسعاً من قبل الباحثين لقدرا على قيادة الجيل القادم من

وعلى الرغم من إمكانية بناء هذا النوع من الشبكات على أسس من شبكات أخرى متواجدة حالياً، إلا . اللاسلكية

أن التجارب المختبرية والاختبارات الميدانية ذات الصلة بالشبكات اللاسلكية المعشقة أثبتت أن الفاعلية الحالية لهذه

السبب فإن الباحثين في هذا اال يواجهون الكثير من التحديات والعقبات ولهذا . الشبكات ما زالت تحت المتوقع

ومن أهم العوامل المؤثرة في أداء الشبكات اللاسلكية المعشقة هي بروتوكولات توجيه الشبكات . التي تحتاج حلولاً

إمكانية التوسع وهي من أكثر وهناك العديد من الأمور التي تحتاج تطويراً منها جودة الخدمات والحماية و . المعشقة

هذا البحث يهدف لتصميم وبناء بروتوكول موجه يمكنه معالجة نقطة .النقاط تعقيداً في هذه البروتوكولات الموجهة

). AODV(توسع الشبكة اللاسلكية المعشقة، ولهذا تم عرض إصدار هرمي محدد الاتجاه من بروتوكول التوجيه

يستغل بعض الحقول الموجودة حالياً في حزم السيطرة في تقليل الضغط على ) DH-AODV(البروتوكول المطور

وقد تم تصميم وإنشاء واختبار البروتوكول المطور باستخدام . عرض الحزمة ولتسريع عملية ترميم المسارات المعطوبة

-DH(صدار المعدل و الإ) AODV(حيث تم عمل مقارنة بين البروتوكول الأصلي . QualNet برنامج المحاكاة

AODV .( ر وصول الحزمل لبروتوكول التوجيه بإمكانه التقليل من تأخإن نتائج المحاكاة تؤكد أن الإصدار المعد

كما أن نتائج . مقارنة بالبروتوكول الأصلي% 20، وكذلك التقليل من نسبة الحزم المفقودة بنسبة %47بنسبة

.ءدافي الأ %11,2الاختبار تشير إلى تحسن

iv

APPROVAL PAGE

I certify that I have supervised and read this study and that in my opinion, it conforms

to acceptable standards of scholarly presentation and is fully adequate, in scope and

quality, as a dissertation for the degree of Master of Science (Computer and

Information Engineering).

…………………………………………

Aisha Hassan Abdalla

Supervisor

I certify that I have read this study and that in my opinion, it conforms to acceptable

standards of scholarly presentation and is fully adequate, in scope and quality, as a

dissertation for the degree of Master of Science (Computer and Information

Engineering).

………………………………………...

Rashid Abdelhaleem Saeed

Internal Examiner

…………………………………………

Mahamod bin Ismail

External Examiner

This dissertation was submitted to the Department of Manufacturing and Materials

Engineering and is accepted as partial fulfilment of the requirements for the degree of

Master of Science (Computer and Information Engineering).

…..……………..…………..………….

Othman O. Khalifa

Head, Department of Electrical and

Computer Engineering

This dissertation was submitted to the Kulliyyah of Engineering and is accepted as

partial fulfilment of the requirements for the degree of Master of Science (Computer

and Information Engineering).

……..….……………....…….............

Amir Akramin Shafie

Dean, Kulliyyah of Engineering

v

DECLARATION

I hereby declare that this dissertation is the result of my own investigations, except

where otherwise stated. I also declare that it has not been previously or concurrently

submitted as a whole for any other degrees at IIUM or other institutions.

Zainab Senan Mahmod

Signature:……………………………....… Date:……………………….

vi

INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIA

DECLARATION OF COPYRIGHT AND

AFFIRMATION OF FAIR USE OF UNPUBLISHED

RESEARCH

Copyright © 2010 by Zainab Senan Mahmod. All rights reserved.

DEVELOPMENT OF DH-AODV ROUTING PROTOCOL FOR WIRELESS

MESH NETWORKS

No part of this unpublished research may be reproduced, stored in a retrieval

system, or transmitted, in any form or by any means, electronics, mechanical,

photocopying, recording or otherwise without prior written permission of the

copyright holder except as provided below.

1. Any material contained in or derived from this unpublished research

may only be used by others in their writing with due acknowledgement.

2. IIUM or its library will have the right to make and transmit copies

(print or electronic) for institutional and academic purposes.

3. The IIUM library will have the right to make, store in a retrieval system

and supply copies of this unpublished research if requested by other

universities and research libraries.

Affirmed by Zainab Senan Mahmod

……………..………….. …………..…….…….

Signature Date

vii

ACKNOWLEDGEMENTS

Alhamdulillah, praise to Allah s.w.t for the completion of this project. It is with His

blessings and guidance that I am able to complete my work.

I also would like to express my sincere gratitude to my respective supervisor

Dr. Aisha Hassan Abdalla for her valuable guidance, enthusiastic encourage and

support in every stage of my research. Without her close supervision, guidance and

teaching this research would not be where it is.

I would like to thank my family and friends for their unending encouragement

and support.

viii

TABLE OF CONTENTS

Abstract …………………………………………………………………………… ii

Abstract in Arabic ………………………………………………….……………… iii

Approval Page ..………………………………………………………....………… iv

Declaration Page …..………………………………………………….....………… v

Copyright page ….………………………………………………………………… vi

Acknowledgments ………………………………………………………………… vii

List of Tables…………………………………………………………….………… x

List of Figures ………...…………………………………………...………….…… xi

List of Abbreviation ….…………………………………………...………………. xiii

CHAPTER 1: INTRODUCTION …………………………………..…………… 1

1.1 Overview …………………………….………….…………….…........ 1

1.2 Background ….………………………………….………….……….... 1

1.3 Problem Statement …………………………………..……….………. 5

1.4 Objectives …………………………………..………….…….……….. 5

1.5 Methodology..…………………………………..………….……….… 6

1.6 Research Scope ……………………………………..……..………….. 6

1.7 Thesis Organization ……………………………………………..….… 7

CHAPTER 2: LITERATURE REVIEW ……………………………….……… 8

2.1 Overview……………………………………………………………… 8

2.2 Technical Background ……………………………………….………. 8

2.2.1 IEEE 802.11 MAC Protocol ……………………………………. 10

2.2.2 Hybrid Wireless Mesh Protocol …………………….............….. 13

2.3 Related Works ………………………………………………….…….. 15

2.3.1 AODV Protocol Specifications …………………………...……. 30

2.4 Chapter Summary ………………………………………….…………. 34

CHAPTER 3: PROPOSED DESIGN ………………………………...…..…...… 35

3.1 Overview……………………………………………………………… 35

3.2 Design Considerations ………………………………………..………. 35

3.2.1 The AODV's Drawbacks in Hybrid WMNs ……………..…..…. 37

3.3 The Design of the Proposed Routing Protocol …………………….…. 38

3.4 Simulation Tool …………………………..…………………………... 44

3.5 Chapter Summary …………………………………………….…….… 46

CHAPTER 4: RESULTS ANALYSIS AND DISCUSSION ……..…………… 47

4.1 Overview………………………………………………………………. 47

4.2 Simulation Scenario ………………………………………………...… 47

4.3 Simulation Parameters ………………………………………………... 49

4.3.1 Packet Loss Rate ………..……………………………………… 49

ix

4.3.2 Average End-to-End Delay of Data Packets ………….………... 50

4.3.3 Average Throughput………………………………….…………. 50

4.3.4 Average Jitter………………………………………………….... 51

4.4 Result Analysis for DH-AODV ………………………………….…... 52

4.4.1 Average Throughput……………………………………………. 54

4.4.2 Average End-to-End Delay …………………………………….. 55

4.4.3 Packet Loss Rate………………………………………………… 56

4.4.4 Average Jitter……………………………………………………. 58

4.5 Result Discussion……………………………………..……………….. 59

4.6 Summary ………………………………………….…………………... 60

CHAPTER 5: CONCLUSION AND RECOMMENDATION ………………… 61

5.1 Conclusion…………………………………………….…………….… 61

5.2 Contribution..……………………………………….……………….… 62

5.3 Future Work……………………………………….…………………... 62

.

BIBLIOGRAPHY ………………………………………………..……………… 63

PUBLICATION………………………………………………………………….. 67

APPENDIX I ………………………..…………………….……………………… 68

APPENDIX II ……………………………………………….…………………….. 74

APPENDIX III……………………………………………………………………. 85

x

LIST OF TABLES

Table No. Page No.

2.1 Differences between Ad-hoc and mesh networks 12

2.2 Main Routing Metrics Characteristics 19

2.3 Comparison of AODV variants 26

3.1 Comparison between Routing Protocols 36

4.1 Simulation environment 49

A1.1 Minimum System Requirements for QualNet 87

xi

LIST OF FIGURES

Figure No. Page No.

1.1 Wireless Mesh Network 3

2.1 A Flat Architecture for WMN 13

2.2 An Hierarchical Architecture for WMN 14

2.3 Hybrid Architecture for WMN 15

2.4 Elements Affecting the Design of a Routing Protocol for WMN 17

2.5 The performance of AODV, DSR and OLSR protocols 21

2.6 Comparisons between the performance of TORA and DSDV 22

2.7 The packet delivery ratio for HEAT, OLSR, and AODV 23

2.8 Throughput vs. number of sources for D-AODV 25

2.9 The performance of DDSR, DAODV, DSR and AODV 30

2.10 RREQ message and the table of neighbors 31

2.11 Route Reply message 32

2.12 Sequence Number and updating the Routing List 33

3.1 Hop count setting at the network's nodes 38

3.2 A Flowchart of RREQ packet process in any node 40

3.3 The Broadcasted and Discarded RREQ Packets 41

3.4 A Flowchart of Route Discovery Procedure of DH-AODV 43

3.5 Flowchart of DH-AODV operations 44

4.1 Network topology as displayed in QualNet 48

4.2 Hybrid WMP RREQs received 52

4.3 RERRs Received by each Node 53

xii

4.4 Route Error Messages Forwarded by each Node 54

4.5 A Comparison between the Average Throughput of AODV and 55

DH-AODV

4.6 Comparison between the End-to-End Delay of Data Packets in 56

AODV and DH-AODV

4.7 The Number of Packets to CBR server's application layer for 57

both AODV and DH-AODV

4.8 The Average Jitter for both AODV and DH-AODV 58

A1.1 QualNet Protocol Stack 84

A1.2 A Screenshot of QualNet Simulator 87

xiii

LIST OF ABBREVIATION

AODV Ad-hoc On Demand Vector

AODV-HM Ad-hoc On Demand Vector – Hybrid Mesh

AODV-MR Ad-hoc On Demand Vector – Multiple Radios

AODV-PA Ad-hoc On Demand Vector- Path Accumulation

AODV-ST Ad-hoc On Demand Vector- Spanning Tree

BSS Basic Service Set

CBR Constant Bit Rate

D-AODV Dimensional Ad-hoc On Demand Vector

DH-AODV Directional Hierarchical Ad-hoc On Demand Vector

DSDV Highly Dynamic Destination-Sequenced Distance-Vector

DSR Dynamic Source Routing

ENT Effective Number of Transmission

ETT Expected Transmission Time

ETX Expected Transmission Count

HWMP Hybrid Wireless Mesh Protocol

iAWARE Interference Aware

IBSS Independent Basic Service Set

IH-AODV Improved Hierarchical Ad-hoc On Demand Vector

IP Internet Protocol

ISP Internet Service Provider

LAN Local Area Network

LQ-AODV Link Quality aware Ad-hoc On Demand Vector

MAC Media Access Control

MAN Metropolitan Area Network

MIC Metric of Interference and Channel-switching

MAP Mesh Access Point

ML Minimum Loss

MP Mesh Point

MPP Mesh Portal Point

NS-2 Network Simulator version 2

OLSR Optimized Link State Routing

PAN Personal Area Network

PHY Physical Layer

QoS Quality of Service

RERR Route Error

RREQ Route Request

RREP Route Reply

SAODV Secure Ad-hoc On Demand Vector

SNR Signal to Noise Ratio

SNT Scalable Network Technologies

TAP Transient Access Point

TBRPF Topology Broadcast Based on Reverse-Path Forwarding

TORA Temporally Ordered Routing Algorithm

WAN Wide Area Network

xiv

WCETT Weighted Cumulative Expected Transmission Time

WMN Wireless Mesh Network

1

CHAPTER ONE

INTRODUCTION

1.1 OVERVIEW

This thesis investigates recent protocols proposed to enhance the performance of the

WMN, considering the routing protocols used in these networks as one of the most

important factors. It aims to enhance the performance of the routing protocol that's

chosen as a bench mark.

The first chapter of the thesis is introducing the main points of the research.

Firstly, it has a background about the research area and its importance. Followed by

the problem statement highlighting the critical issues need to be resolved. According

to it, the objectives of this research are derived. The methodology used to achieve the

objectives is declared. Then, the scope of this research is mentioned. Lastly, the

organization of the whole thesis is pointed out.

1.2 BACKGROUND

Over the previous years, wireless Internet used widely all over the world. Even mobile

users in cars, trains and so on require constantly network connectivity. However,

Internet access is still below the expectations especially for mobile devices using

wireless communication. Today most of wireless Internet access is using cellular

networks or networks based on wireless local area networks (LAN) or wireless

metropolitan area networks (WiMAX). But these technologies are not proper choices

for the city-wide networks either because of the expensive costs or the shortage of

communication coverage range.

2

One of the current solutions is using a multihop system in which devices assist

each other in transmitting packets through the network, especially in adverse

conditions. These networks can be dropped into place with minimal preparation, and

they provide a reliable, flexible system that can be extended to thousands of devices.

A wireless mesh network (WMN) is a mesh network implemented over a

wireless network system (Riggio, 2006). The wireless mesh network topology, shown

in Figure 1.1, is a point-to-point-to-point, or peer-to-peer, system. A node can send

and receive messages, and also functions as a router and relay messages for its

neighbors. Through the relaying process, a packet of wireless data will find its way to

its destination, passing through intermediate nodes with reliable communication links.

Like the Internet and other peer-to-peer router-based networks, a mesh

network offers multiple redundant communications paths throughout the network. If

one link fails for any reason, the network automatically routes messages through

alternate paths. (Akyildiz, 2005)

Such networks are characterized by dynamic self-organization, self-

configuration and self-healing. These are enable flexible integration, quick

deployment, easy maintenance, low cost, high scalability and reliable services.

Furthermore, it enhanced the network capacity, connectivity and throughput in multi-

hop ad-hoc networks, wireless personal area networks (PAN), wireless local area

networks (LAN), wireless metropolitan area networks (MAN) and wireless wide area

networks (WAN). (Bruno, 2005)

3

Figure 1.1 Wireless Mesh Network

A wireless mesh network delivers scalable performance because it can be

expanded easily and incrementally. Such expansion does require, of course, sufficient

interfaces in the form of gateway connections to other network segments or services.

The aggregate bandwidth from edge-to-edge depends on the topology and the nature

of the traffic. In theory, more nodes lead to better overall performance and reliability

of the mesh. To maximize performance and reliability, each node should have at least

two neighbors. For these and other reasons, a wireless mesh networks affords

unparalleled flexibility and simplicity.

Wireless mesh networks (WMNs) are dynamically self-organized and self-

configured, with the nodes in the network automatically establishing an ad-hoc

network and maintaining the mesh connectivity. WMNs are comprised of two types of

nodes: mesh routers and mesh clients. Other than the routing capability for

gateway/bridge functions as in a conventional wireless router, a mesh router contains

additional routing functions to support mesh networking. Through multi-hop

communications, the same coverage can be achieved by a mesh router with much

4

lower transmission power. To further improve the flexibility of mesh networking, a

mesh router is usually set with multiple wireless interfaces built on either the same or

different wireless access technologies.

Wireless Mesh Networks (WMNs) rely on a multihop wireless backbone for

delivering high-speed services to end-users without the need for deploying any fixed

infrastructure. With respect to conventional star-shaped access network architectures,

WMNs offer advantages in terms of enhanced robustness (in that no single points of

failure are present and redundant links are encompassed) and flexibility (without the

need for deploying cables, connectivity may be provided only where and when

needed, which is economically attractive). With respect to traditional ad-hoc

networks, WMNs differ for firstly the goal, in that they are being intended as access

architecture, not standalone systems. Secondly the heterogeneity of the devices, in that

there might be dedicated devices (with more powerful radio systems, multi-band

capabilities etc.) acting as pure wireless routers. Thirdly, Most of the traffic originates

or terminates at the gateways. (Chlamtac, 2003)

However, Most of the existing wireless mesh networks are using the same

technologies deployed for Ad-hoc networks because of their similarities. For example,

mesh routers of Firetide Networks (Firetide Networks, 2005) are based on topology

broadcast based on reverse-path forwarding (TBRPF) protocol (Ogier, 2004),

Microsoft mesh networks (Microsoft Mesh Networks, 2004) are built based on

dynamic source routing (DSR) (Johnson, 2004), and many other companies (Kiyon

Autonomous Networks, 2004) are using ad-hoc on-demand distance vector (AODV)

routing (Perkins, 2003).

5

1.3 PROBLEM STATEMENT

Since WMNs can be viewed as a special case of wireless multi-hop ad-hoc networks,

the routing protocols developed for ad-hoc networks can be applied to WMNs.

However, WMNs have a number of features that distinguish them from pure

ad-hoc networks. First, the positions of different nodes of a WMN are relatively fixed

and any change of position is limited within certain range. Second, unlike pure ad-hoc

networks, where the traffic flows between arbitrary pairs of nodes, in WMN, all traffic

is either to or from a designated gateway, which connects the wireless mesh network

to the Internet. Third, the nodes will typically have access to a power source, and so

power consumption is not a critical issue. Finally, such systems can be created within

a single domain of authority, and so many security issues present in ad-hoc networks

are no longer relevant. (Ann Lee, 2004).

Such differences imply that the routing protocols designed for ad-hoc networks

are not appropriate for WMNs. Therefore, more research efforts are needed to develop

new routing protocols or to extend the current Ad-hoc networks protocols to adapt to

WMNs.

1.4 OBJECTIVES

The main objective of this research is to improve the performance of the AODV

routing protocol in WMNs. The detailed objectives are to propose an enhanced Ad-

hoc Network for WMNs by:

a) Reduce the end-to-end delay of data packets

b) Improve the throughput

c) Reduce the packet error rate

d) Reduce the average jitter

6

1.5 METHODOLOGY

To achieve the stated objectives of this research, a comprehensive literature review

was done on the previous works in WMNs area. The current routing algorithms and

protocols were studied to see their advantages and drawbacks.

Based on the literature review and the studied protocols, the AODV routing

protocol was chosen as a bench mark and a routing protocol was designed considering

the objectives.

Then, the implementation of the proposed routing protocol was done using

QualNet Simulator which was extended to support the protocol. The performance of

the proposed protocol was evaluated based on the selected performance metrics.

Furthermore, a comparison between the proposed routing protocol and the chosen

bench mark was done to further testing of the performance.

1.6 RESEARCH SCOPE

The research had been done on the Hybrid Wireless Mesh Network where both mesh

router and mesh client nodes are supported. Other types of path selections protocols

for MAC layer are not considered since the simulator version 4.5 does not support

those types.

Also, the cross-layer interaction is not in the scope of this research. And, the

scenario does not consider many issues, like having many gateways, random topology,

or very large scales networks that have hundreds or even thousands of nodes because

of the time limitation. These cases are part of the future work.

Testing the network under a heavy load, and issues related to security are out

of the scope of the research.

7

1.7 THESIS ORGANIZATION

The thesis is organized as follows. Chapter 2 is a literature review in which a technical

background about the IEEE 802.11 technology and the hybrid architecture is given.

Also, the previous works in the area of WMNs is presented with a particular emphasis

on the different routing algorithms and protocols.

Chapter 3 is to present the design of the proposed routing protocol. Chapter 4

describes the performance metrics used to analyze the protocol and the scenario's

environment. Also, the results obtained are analyzed, discussed and compared with the

chosen bench mark. Finally, Chapter 5 presents conclusions and recommendations.

8

CHAPTER TWO

LITERATURE REVIEW

2.1 OVERVIEW

This chapter overviews the technical background of the WMNs by explaining the

IEEE 802.11 standard and the meaning of hierarchical and hybrid network. Then, the

works related to WMNs will be stated with a special emphasis on the existing routing

protocols and the extensions done to Ad-hoc protocols to be adapted to WMNs.

2.2 TECHNICAL BACKGROUND

Wireless Mesh Networking has many advantages most of them derive from its four

self-managing capabilities. First is that the mesh is self-configuring and self-

reconfiguring, that the new nodes become full members of the mesh topology

automatically as soon as a minute after booting up. Adding, moving or removing

nodes and their attached Ethernet devices (clients, servers, access points, surveillance

cameras, gateways, routers and so on) are as painless as it is immediate. Secondly,

intelligent self-reconfiguration also makes the entire mesh self-tuning end-to-end,

allowing traffic to move dynamically along optimal paths. As those paths change, so

too do the route tables that direct traffic based on the shortest, fastest, least congested

or other characteristic of each path. (Firetide Networks, 2005)

The self-configuring and self-tuning abilities help give the mesh its third

advantage as a self-healing network. The multiple redundant paths add robust

resiliency and, when properly arranged, eliminate single points of failure and potential

bottlenecks within the mesh. Should a link become congested or a node fail the mesh

9

automatically redirects traffic on an alternate route. The fourth self-managing

advantage should now be fairly apparent: wireless mesh networks are fully self-

monitoring. Most mesh vendors do provide management consoles for centralized

command and control, but it is possible to install and operate a mesh network without

one. The console does provide a “big picture” view of the mesh, which is useful for

determining the required number of nodes and the ideal placement of each one. Still,

with or without a centralized console, the wireless mesh is simply the simplest

topology to deploy and operate. (Firetide Networks, 2005)

The WMN took advantage of two areas of innovations: existing capability in

the 802.11 standard, the Ad-Hoc Mode of communications which requires less

overhead than Infrastructure Mode and makes each node a router capable of passing

traffic to other nodes. A second 802.11 capability is the implementation of multiple

spectrums; specifically in the 2.4 GHz and 5 GHz bands. Mesh networks that operate

in the 5 GHz spectrum offer high capacity and low interference and are suitable for

both indoor and outdoor applications.

WMNs have a number of features that distinguish them from pure ad-hoc

networks. First, the positions of different nodes of a WMN are relatively fixed and

any change of position is limited within certain range. The implication of this is that

routing paths can be created that are likely to be stable. This substantially reduces the

need for routing packet overhead. Indeed, such routing packets are likely only needed

at initialization and when traffic volume is sufficiently low that a node cannot be sure

that its neighbor is still present, as opposed to having crashed.

Second, unlike pure ad-hoc networks, where the traffic flows between arbitrary

pairs of nodes, in WMN, all traffic is either to or from a designated gateway, which

connects the wireless mesh network to the Internet. The relevance of this point is that

10

the traffic may be split over multiple gateways, so as to reduce the load within any

given portions of the network.

Third, the nodes will typically have access to a power source, and so power

consumption is not a critical issue. Finally, such systems can be created within a

single domain of authority, and so many security issues present in ad-hoc networks are

no longer relevant. (Lee, 2004)

Such differences imply that the routing protocols designed for ad-hoc networks

may not be appropriate for WMNs. Therefore, more research efforts are needed to

extend the current Ad-hoc networks protocols to adapt to WMNs.

First of all, new performance metrics need to be discovered and utilized to

improve the performance of routing protocols. In addition, the existing routing

protocols treat the underlying MAC protocol as a transparent layer. However, the

cross-layer interaction must be considered to improve the performance of the routing

protocols in WMNs. Moreover, existing routing protocols still have limited

scalability.

2.2.1 IEEE 802.11 MAC protocol

The IEEE 802.11 standard defines a set of medium access layer (MAC) and physical

layer (PHY) specifications for wireless LAN, also known as WiFi. The original

standard was developed in 1997. And here several modifications have been proposed

to extend 802.11 at both the MAC and physical layers to support different features

such as higher bandwidth, QoS, and security. IEEE 802.11 defines two different

architectures, Basic Service Set (BSS) and Independent Basic Service Set (IBSS). In a

BSS or Infrastructure mode, numbers of wireless stations are associated to an Access

Point that all communications take place through it. IBSS, also known as ad-hoc mode