an admission control method for ieee 802.11e …2.10 data frame format in ieee 802.11e 27 2.11...

AN ADMISSION CONTROL METHOD FOR IEEE 802.11e CONTENTION

ACCESS MECHANISM

CHEN WENG CHEOW

UNIVERSITI TEKNOLOGI MALAYSIA

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AN ADMISSION CONTROL METHOD FOR IEEE 802.11e CONTENTION

ACCESS MECHANISM

CHEN WENG CHEOW

A thesis submitted in fulfilment of the

requirements for the award of the degree of

Master of Engineering (Electrical)

Faculty of Electrical Engineering

Universiti Teknologi Malaysia

OCTOBER 2005

iii

To my parents, siblings and Angeline

for their love and support to make the journey

iv

ACKNOWLEDGEMENT

I am deeply indebted to my supervisors, Assoc. Prof. Dr. Sulaiman bin Mohd

Nor and En. Alias bin Mohd. for their patience in guiding me. Their distinctive

supervision and mentorship were a great source of help throughout the course of my

research.

I wish to express my gratitude to my parents and siblings for their continuous

support throughout the research. Nothing would have ever been achieved without

their continuous support and encouragement. I want to thank my coursemates,

especially Lai Chen (Jolyn), Hock Lai, and Ker Chea for their companionship in

these two years.

Last but not least, thanks to all the people who have contributed to the

success of this research directly and indirectly.

v

ABSTRACT

IEEE 802.11 Wireless Local Area Network (WLAN) is a shared medium

communication network that transmits information over wireless links for all 802.11

stations in its transmission range. With the applications over 802.11 WLAN increasing,

customers demand more and more new features and functions. The support of audio,

video, real-time voice over IP and other multimedia applications over 802.11 WLAN

with Quality of Service (QoS) requirements is the key for 802.11 WLAN to be

successful in multimedia home networking and future wireless communications.

Recently, the IEEE 802.11 task group e specified a distributed access approach, called

Enhanced Distributed Channel Access (EDCA), which supports service differentiation

in the Medium Access Control (MAC) layer. It ensures the packets sent by each mobile

station can be differentiated by assigning different access parameters. However, no

assurance can be given to higher priority traffic in terms of throughput and delay

performance. The problem is especially apparent when the wireless channel is

overloaded causing the bandwidth share of each flow to diminish. Admission control is

the solution for the problem addressed above. In this research, a simple measurement

based admission control method is proposed to enhance the QoS of EDCA network

when it is heavily loaded. The proposed method can control the number of allowed

wireless stations in the WLAN network without degrading the QoS (medium access

delay and throughput) of the existing flows under a high load condition. Several QoS

parameters such as delay and throughput are analyzed to investigate the performance of

the proposed method. The simulation is done using Network Simulator ns-2 to study the

QoS. The results have shown that the proposed method can protect the QoS of high

priority applications and at the same time sacrificing the QoS of low priority flow at a

moderate level.

vi

ABSTRAK

Rangkaian Setempat Wayerles (WLAN) IEEE 802.11 merupakan satu

rangkaian komunikasi dengan perkongsian medium yang menghantar maklumat

melalui laluan wayerles di antara semua stesen IEEE 802.11 yang berada dalam jarak

penghantaran dan penerimaan. Keupayaan untuk menyokong aplikasi audio, video,

suara melalui IP (VoIP) dan aplikasi multimedia lain yang memerlukan jaminan

kualiti perkhidmatan (QoS) adalah kriteria penting untuk mempopularkan Rangkaian

Setempat Wayerles IEEE 802.11. Kumpulan Tugas e di bawah IEEE 802.11

menyediakan piawaian untuk meningkatkan kualiti perkhidmatan (QoS) dalam

Rangkaian Setempat Wayerles. Salah satu kaedah yang diperkenalkan dalam

piawaian itu ialah Saluran Capaian Teragih (EDCA), yang mampu menyokong

pengkelasan aplikasi di lapisan Kawalan Capaian Media (MAC). Ia memastikan

paket yang dihantar oleh setiap stesen bergerak mendapat layanan yang berbeza

berdasarkan tahap kepentingan aplikasi tersebut. Namun, tiada kepastian mutlak

yang dapat dijanjikan kepada aplikasi berkepentingan tinggi dalam pencapaian truput

dan lengahan walaupun EDCA telah digunakan. Kualiti perkhidmatan tetap akan

menurun apabila tahap beban dalam medium wayerles sudah melebihi kapasiti yang

boleh ditampung. Kawalan kemasukan adalah kaedah untuk menangai masalah yang

disebut di atas. Dalam tesis ini, satu kaedah kawalan kemasukan yang menggunakan

pengukuran tahap beban dalam medium wayerles telah dicadangkan. Kaedah yang

dicadangkan dapat mengawal bilangan stesen wayerles tanpa menurunkan kualiti

perkhidmatan aliran sedia ada semasa keadaan beban tinggi. Lengahan dan truput

telah dianalisis untuk mengkaji prestasi kaedah ini. Simulasi ini telah dijalankan

dengan menggunakan perisian simulasi rangkaian ns-2 untuk mengkaji kualiti

perkhidmatannya. Keputusan penyelidikan telah menunjukkan kaedah yang

dicadangkan dapat melindungi kualiti perkhidmatan untuk aplikasi keutamaan tinggi

dan pada masa yang sama mengorbankan kualiti perkhidmatan aplikasi keutamaan

rendah pada tahap yang tidak keterlaluan.

vii

TABLE OF CONTENTS

CHAPTER TITLE PAGE

TITLE PAGE i

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES xii

LIST OF FIGURES xiii

LIST OF SYMBOLS xvii

LIST OF APPENDICES xix

1 INTRODUCTION 1

1.1 Overview 1

1.2 Research Background and Motivation 1

1.3 Problem Statement 5

1.4 Research Objectives 6

1.5 Scope of Work 7

1.6 Research Contributions 8

1.7 Thesis Organization 8

2 BACKGROUND OF WIRELESS LOCAL AREA

NETWORK (WLAN) 10

viii

2.1 Overview 10

2.2 WLAN Overview 10

2.3 IEEE 802.11 Standard 12

2.3.1 Distributed Coordination Function

(DCF) 15

2.3.2 Virtual Carrier Sense 16

2.4 QoS in IEEE 802.11 MAC 18

2.4.1 QoS Limitation of DCF 19

2.4.2 QoS Resource Allocation Schemes for

IEEE 802.11 21

2.4.2.1 Blackburst Scheme 21

2.4.2.2 Deng and Chang’s Scheme 23

2.4.2.3 Distributed Weighted Fair

Queuing (DWFQ) 24

2.4.2.4 Distributed Fair Scheduling

(DFS) 24

2.4.2.5 Distributed Deficit Round

Robin (DDRR) 25

2.4.2.6 Upcoming IEEE 802.11e QoS

Enhancement Standard 26

2.4.2.6.1 EDCA 27

2.4.3 Admission Control Schemes for

IEEE 802.11 30

2.4.3.1 Measurement-Based Admission

Control Method for IEEE 802.11

WLAN (Gu’s Method) 31

2.4.3.2 Flow Reservation and

Admission Control (Ming Li’s

Method) 32

2.4.3.3 Call Admission Control for

IEEE 802.11 Contention

Access Mechanism

(Dennis’s Method) 33

2.4.3.4 An Admission Control Strategy

ix

for Differentiated Services in

IEEE 802.11 (Kuo’s Method) 34

2.5 Network Simulator ns-2 35

2.5.1 Mobile Networking in ns-2 37

2.5.2 Contributed Modules 38

2.5.2.1 NOAH Module 38

2.6 Summary 38

3 ARCHITECTURE AND IMPLEMENTATION

OF THE PROPOSED ADMISSION CONTROL

METHOD 42

3.1 Overview 42

3.2 Proposed Admission Control Method (ACM) 42

3.2.1 ACM Operation 46

3.2.1.1 ACM Operation (At AP) 49

3.2.1.1.1 New Uplink Flow 52

3.2.1.1.2 Existing Uplink

Flow 54

3.2.1.1.3 New Downlink

Flow 55

3.2.1.1.4 Existing Downlink

Flow 56

3.2.1.2 Changes in Mobile Station 56

3.2.2 ACM Implementation in ns-2 58

3.2.2.1 IEEE 802.11e MAC in ns-2 62

3.2.2.2 IEEE 802.11e MAC for Mobile

Node with ACM in ns-2 65

3.2.2.3 IEEE 802.11e MAC for Access

Point with ACM in ns-2 66

3.3 ns-2 Simulation 68

3.3.1 Simulation Traffic 68

3.3.2 Simulation Parameter 69

3.3.3 Simulation Topology 70

x

3.3.4 Simulation Metrics 71

3.3.5 Assumptions in Simulation 73

3.3.6 QoS Issue in Downlink Voice Flows 73

3.3.7 The Validation of NUC Value 76

3.4 Test Scenarios 77

3.4.1 Test Scenario 1 78




4 RESULTS AND DISCUSSION 86

4.1 Overview 86

4.2 Performance Comparison 86

4.2.1 Waiting Time Performance in EDCA MAC

with and without ACM when the medium

is heavily loaded 87

4.2.2 Throughput Performance in EDCA MAC

with and without ACM 93

4.2.3 Average Throughput Comparison with

Increasing Number of Voice Sessions 97

4.2.4 Average Waiting Time Comparison with

Increasing Number of Voice Sessions 101

4.2.5 The Impact of NUC_Threshold to the QoS

Performance 105

4.3 Summary 105

5 CONCLUSION AND RECOMMENDATION 107

5.1 Overview 107

5.2 Conclusion 107

5.3 Recommendation 108

xi

REFERENCES 110

Appendices A – D 116 – 184

A Installation of MAC 802.11e EDCF-Code 116

B ACM Source Codes 118

C Tcl Scripts 171

D Post Process Program 180

xii

LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Deng and Chang’s scheme priority classes 23

2.2 Mapping between user priority and access category 28

2.3 The four default access categories specified in

IEEE 802.11e 29

2.4 Comparison of service differentiation Schemes using

DCF enhancement 40

2.5 Comparison of the previous admission control methods 41

3.1 Valid Type and Subtype Combination 48

3.2 Simulation traffic 69

3.3 The four default ACs specified in IEEE 802.11e 69

3.4 Simulation Parameter Values 70

3.5 s value chosen in the simulation 77

3.6 Trace File’s Fields 79

3.7 FAR/FAG exchange when the NUC_Threshold is

not exceeded 80

3.8 FAR/FAG exchange when the NUC_Threshold is

Exceeded 82

3.9 Flow setup for downlink flow when

the NUC_Threshold is not exceeded 83

3.10 Flow setup for downlink flow when the

NUC_Threshold is exceeded 85

4.1 Number of Admitted traffic flows in different

NUC_Threshold 105

xiii

LIST OF FIGURES

FIGURE NO. TITLE PAGE

1.1 Protocol Layers in Wireless Local Area Network 2

1.2 Background of QoS Issue in WLAN 5

2.1 Ad-hoc topology 13

2.2 Infrastructure topology 13

2.3 Snapshot of IEEE 802.11 PHY and MAC Standard 14

2.4 DCF basic access method 16

2.5 Data/ACK exchange process 16

2.6 RTS/CTS access method 17

2.7 QoS Mechanisms in WLAN 20

2.8 Timing Diagram of Blackburst method 22

2.9 The DDRR mechanism 26

2.10 Data Frame Format in IEEE 802.11e 27

2.11 Internal contentions of different access categories 29

2.12 EDCA channel access method 29

2.13 Previous admission control methods in IEEE 802.11e 30

2.14 The occupation of wireless medium 31

2.15 ns-2 features classified according to TCP/IP layers 36

2.16 Schematic of a mobilenode in ns-2 37

3.1 FAR Frame Format 47

3.2 FAG Frame Format 47

3.3 Frame Control Field 47

3.4 Classifications of Wireless Traffic Flows 50

3.5 Flow Chart of ACM at Access Point 51

3.6 Congestion control for bandwidth management 52

3.7 FAR/FAG/DATA/ACK and NAV setting 54

xiv

3.8 Flow Chart of the MAC in Mobile Node 57

3.9 Flow Chart of ACM Implementation using ns-2 59

3.10 Class Hierarchy in ns-2 60

3.11 Functional Diagram of IEEE 802.11 MAC Layer

in ns-2 61

3.12 The files in ns-2 framework that is edited and added 62

3.13 Finite State Machine for IEEE 802.11e MAC in ns-2 64

3.14 Finite State Machine of IEEE 802.11e MAC for mobile

Station in ns-2 65

3.16 Simulation topology 71

3.17 Snapshot of Network Animator (NAM) 72

for simulation topology

3.18 Waiting Time for Downlink Voice 74

3.19 Voice waiting time for uplink and downlink 75

3.20 The scenario of voice queue in contention of medium 76

3.21 NUC comparisons for real and estimated value 77

3.22 Sequence of Packet Exchange for Uplink New Flow

when the Air-link is Not Overloaded 78

3.23 Sequence of Packet Exchange for Uplink New Flow

when the Air-link is heavily loaded 81

3.24 Sequence of Packet Exchange for Downlink New

Flow when the Air-link is not Overloaded 82

3.25 Sequence of Packet Exchange for Downlink

New Flow when the Air-link is Overloaded 84

4.1 Waiting time for uplink voice in EDCA MAC with ACM 87

4.2 Waiting time for uplink voice in EDCA MAC without

ACM 88

4.3 Waiting time comparison for uplink voice in EDCA

MAC with and without ACM 88

4.4 Waiting time for downlink voice in EDCA MAC

with ACM 89

4.5 Waiting time for downlink voice in EDCA MAC

without ACM 90

4.6 Waiting time comparison for downlink voice in EDCA

xv

MAC with and without ACM 90

4.7 Waiting time for video in EDCA MAC with ACM 91

4.8 Waiting time for video in EDCA MAC without ACM 92

4.9 Waiting time comparison for video in EDCA MAC with

and without ACM 92

4.10 Total transmitted packet for downlink voice 93

4.11 Throughput for web traffic in EDCA MAC with ACM 94

4.12 Throughput for web traffic in EDCA MAC without ACM 94

4.13 Throughput comparisons for web traffic in EDCA MAC


4.14 Throughput for FTP in EDCA MAC with ACM 96

4.15 Throughput for FTP in EDCA MAC without ACM 96

4.16 Throughput comparisons for FTP in EDCA MAC


4.17 Average Throughput Comparison when the number

of voice flow increases 98

4.18 Average throughput comparison for voice 99

4.19 Average throughput comparison for video when the

number of voice session increases 99

4.20 Average throughput comparison for web traffic when

the number of voice session increases 100

4.21 Average throughput comparison for FTP traffic when

the number of voice session increases 100

4.22 Average waiting time comparison for all traffic

with and without ACM when the number of voice

session increases 102

4.23 Average waiting time comparison for voice with and

without ACM 103

4.24 Average waiting time comparison for video



4.25 Average waiting time comparison for web traffic



xvi

4.26 Average waiting time comparison for FTP with and

without ACM when the number of voice session increases 104

xvii

LIST OF ABBREVIATIONS

AC - Access Category

ACK - Acknowledge

ACM - Admission Control Method

AIFS - Arbitrary Inter Frame Space

AP - Access Point

ARP - Automatic Rate Fallback

BER - Bit Error Rate

BSS - Basic Service Set

CSMA/CA - Carrier Sense Multiple Access with Collision Avoidance

CSMA/CD - Carrier Sense Multiple Access with Collision Detection

CTS - Clear to Send

CW - Contention Windows

DCF - Distributed Coordination Function

DDRR - Distributed Deficit Round Robin

DFS - Distributed Fair Scheduling

DIFS - DCF Inter Frame Space

DSDV - Destination-Sequenced Distance Vector

DSR - Dynamic Source Routing

DSSS - Direct Sequence Spread Spectrum

EDCA - Enhanced Distributed Channel Access

EDCF - Enhanced Distributed Coordination Function

ETSI - European Telecommunications Standards Institute

FHSS - Frequency Hopping Spread Spectrum

HCF - Hybrid Coordination Function

HIPERLAN - High Performance Local Area Network

IEEE - Institute of Electrical and Electronics Engineers

xviii

IFS - InterFrame Space

IP - Internet Protocol

IR - Infrared

LAN - Local Area Network

LLC - Logical Link Control

MAC - Medium Access Control

MS - Mobile Station

NAV - Network Allocation Vector

NOAH - Non Ad-Hoc

ns-2 - network simulator 2

NUC - Network Utilization Characteristic

OFDM - Orthogonal Frequency Division Multiplexing

OSI - Open System Interconnection

PCF - Point Coordination Function

PHY - Physical Layer

PIFS - PCF Inter Frame Space

QoS - Quality of Service

RTS - Ready to Send

SIFS - Short Inter Frame Space

STA - Station

TCP - Transport Control Protocol

UDP - User Datagram Protocol

VoIP - Voice over Internet Protocol

Wi-Fi - Wireless Fidelity

WLAN - Wireless Local Area Network

xix

LIST OF APPENDICES

APPENDIX TITLE PAGE

A Installation of MAC 802.11e EDCF-Code 116

B ACM Source Codes 118

C Tcl Scripts 171

D Post Process Program 180

CHAPTER 1

INTRODUCTION

1.1 Overview

This chapter provides an overview of this thesis. Section 1.1 briefly discusses

the background and motivation for this research. Section 1.2 formulates statement of

problems to be solved in this research. Section 1.3 lists research objectives. Section

1.4 defines scope of work. Section 1.5 discusses the contributions of this research.

Finally, Section 1.6 describes the organization of this thesis.

1.2 Research Background and Motivation

Nowadays, Wireless Local Area Network (WLAN) is becoming more

important because users want the connectivity of a wired LAN, coupled with the

mobility of a wireless link. With WLAN being developed to achieve data rates

comparable to those of wired LANs, more and more interests have been taken in

developing these systems. The IEEE 802.11 Working Group developed an

International Standard so that inexpensive, interoperable equipment could be

designed by different manufacturers and used to build a wireless infrastructure. The

IEEE 802.11 Standard [1] defines the Medium Access Control (MAC) sublayer,

MAC Management protocols and services, and three Physical Layers (PHY). The

IEEE 802.11a [2] and IEEE 802.11b [3] define the other Physical Layers. Currently,

the IEEE 802.11a and IEEE 802.11g [4] Physical Layer can support a maximum

2

transmission speed of 54Mbps. The medium access controller provides the interface

between a host computer bus and the Physical Layer radio. The MAC is common for

802.11 Standard and its extensions. The PHY provides information to the MAC

about the status of the channel (idle, busy). These layers are shown in Figure 1.1.

mobile terminal

Access point

server

fixed terminal

Infrastructure network

application

TCP

802.11 PHY

802.11 MAC

IP

802.3 MAC

802.3 PHY

application

TCP

802.3 PHY

802.3 MAC

IP

802.11 MAC

802.11 PHY

LLC LLC LLC

Figure 1.1 Protocol Layers in Wireless Local Area Network

In wired networks, the network can have a very high bandwidth by increasing

the number of links or link capacity. However, in wireless networks, there is only

one medium that is shared by all the nodes (as shown in Figure 1.1) that are in the

same radio communications range, and the radio frequency bandwidth is limited.

Hence, packet collisions are unavoidable due to the fact that traffic arrivals are

random and there is non-zero propagation time between transmitters and receivers.

Therefore, MAC schemes are used to coordinate access to the single channel in the

network.

With the provisioning of high-speed Wireless LAN (WLAN) environments, it

is possible to offer high-speed data services to the users. Hence, traffic classes (e.g.,

VoIP or Video Conference) with different QoS requirements will be provided in

3

future WLANs. Supporting QoS requirements of different applications has become

the key challenge for IEEE 802.11 WLAN to be successful in future wireless

communications.

Since these traffic classes require distinct specific features, such as delay

sensitivity or guaranteed bandwidth requirement, it is desired to provide a service

differentiation mechanism in the IEEE 802.11 Standard. The existing standard of

IEEE 802.11 does not support service differentiation because it was initially created

for the data communications. Many research [5] [6] [7] [8] [9] [10] [11] [12] [13]

have been carried out to propose a suitable and robust service differentiation or QoS

mechanism for WLAN.

In [5], the author analytically studied the performance of the IEEE 802.11

protocol with a dynamically tuned backoff based on the estimation of the network

status. The author in [6] proposed a simple and efficient method to modify the

CSMA/CA protocol such that station priorities can be supported in IEEE 802.11

MAC. In [7], Imad and Castelluccia presented three service differentiation schemes

for IEEE 802.11. The first one is based on scaling the contention window according

to the priority of each flow or user. The second one assigns different inter frame

spacing to different users. Finally, the last one uses different maximum frame lengths

for different users. The author of [8] proposed a priority-based fair medium access

control (PMAC) protocol by modifying the Distributed Coordination Function (DCF)

of the IEEE 802.11 MAC. The author in [9] proposed a distributed multiple access

procedure to transport rel-time traffic over IEEE 802.11 WLAN. Vaidya et. al. [10]

in the other hand presented a fully distributed algorithm for fair scheduling in

WLAN. The algorithm can be implemented without using a centralized coordinator

to arbitrate medium access. Simulation results showed that the proposal algorithm is

able to schedule transmissions such that the bandwidth allocated to different flows is

proportional to their weights. Qiang Ni et. al. [11] proposed an approach, called

Adaptive Enhanced Distributed Coordination Function (AEDCF), which is derived

from the new EDCF introduced in the upcoming IEEE 802.11e standard. The scheme

aimed to share the transmission channel efficiently. Relative priorities are

provisioned by adjusting the size of the Contention Window (CW) of each traffic

class taking into account both applications requirements and network conditions.

4

Results showed that AEDCF outperformed the basic EDCF, especially at high traffic

load conditions. In [12], Banchs and Perez proposed an extension of the DCF

function of IEEE 802.11 to provide weighted fair queuing in Wireless LAN.

Simulation results showed that the proposed scheme is able to provide the desired

bandwidth distribution independent of the flows aggressiveness and their willingness

to transmit. Wasan et. al. [13] proposed a novel fair bandwidth allocation

mechanism based on deficit round robin scheduling. Service differentiation is

provided by translating the user throughput requirements into the 802.11 MAC Inter

frame space parameter. Simulation results showed that the proposed mechanism

provided low variability of throughput and delay and has the advantage of low

complexity.

Recently, the IEEE 802.11 task group e [14] is specifying a distributed access

approach, called Enhanced Distributed Channel Access (EDCA), which supports

service differentiation in the MAC layer. It ensures the packets sent by each mobile

station can be differentiated by assigning different access parameters. However,

supporting service differentiation in the MAC protocol does not guarantee that the

QoS requirement of the each traffic class to be fully satisfied. Since each mobile

station may transmit packets egotistically in a distributed environment, network load

might be led to an unacceptable level. An admission control strategy could mitigate

the effect of egotistic transmission. It could ensure that the acceptance of a new

traffic stream will not cause the QoS of any ongoing sessions below an unacceptable

level.

From the issues mentioned above, we have decided to explore the QoS issue

of IEEE 802.11 WLAN and address the QoS problem when the network is heavily

loaded. The details of the research will be explained in the succeeding sections.

Figure 1.2 summarizes the research background and the motivation of the research.

5

Figure 1.2 Background of QoS Issue in WLAN

1.3 Problem Statement

Based on the reviews done, two questions arise and need to be answered.

From the literature findings, it is found that there are so many QoS method proposed

for resource allocation in IEEE 802.11 to support high priority flows in future.

Dajiang and Charles [15] found out that under heavy loaded condition, the QoS of

wireless traffic will still degrade even though there is a good service differentiation

implemented in the MAC Layer of the mobile station. From literature findings, not

many works have been dealing with the solution to maintain QoS when the wireless

medium is heavily loaded. Therefore, it triggers the first question of this research as

follows:

• How can an admission control method be implemented in EDCA MAC layer

of the WLAN access point?

When the WLAN is heavily loaded, admission control is needed to ensure the

QoS of the existing flows do not degrade. Several admission control methods have

been proposed in the IEEE 802.11 wireless network [16][17][18][19][20]. Sachin

and Kappes proposed a concept of measurement based admission control method in

their publication [21]. The method was proposed for IEEE 802.11 MAC which does

6

not have any QoS mechanism in it. There were no results provided in the proposed

method. Based on the concept proposed by Sachin and Kappes, the next question to

ask is:

• How good is the proposed admission control in maintaining the QoS of the

existing flows under heavy load condition?

It is just not sufficient to propose an admission control method but as well to

study how the admission control method performs especially under heavy loaded

conditions.

1.4 Research Objectives

In order to solve the problem posed in the preceding sections, the research

objectives are set out as follows: -

1. To propose and simulate a measurement-based admission control method in

the Medium Access Control (MAC) layer of the access point in the IEEE

802.11e network that can control the amount of traffic contending for the

wireless medium.

2. To investigate the performance of the admission control method (ACM) on

the delay and throughput of the multimedia flows under heavy load condition.

The proposed ACM should protect the QoS of high priority flows while not

starving the low priority flows seriously.

7

1.5 Scope of Work

Considering the restricted resources and time frame allocated, the scope of

this research work is defined as follows:

1. The entire work only involves simulation because it is difficult to conduct

experiments with real equipments and large number of nodes. The

research simulates a proposed measurement based admission control

method in the MAC layer of the base station in the WLAN using ns-2

network simulator.

2. In the research, it is decided not to look at the mobility and handover

issue, since that would increase the workload and the complexity of the

research. Hence, the simulation only involves one cell which comprises of

one base station and a number of mobile stations.

3. The EDCA module contributed by [37] in ns-2 is used in the research.

The admission control method is added in the EDCA module. Several

QoS metrics such as delay, variation of delay, and throughput are

analyzed. Comparison is only made between WLAN with admission

control implemented and the WLAN with no admission control admitted.

4. Most of the 802.11b commercial network cards support some kind of

Automatic Rate Fallback (ARP) mechanisms which will adjust the data

rate to a lower one when there are a lot of packet errors. However, ns-2

does not support multirate functionality. Therefore, in the simulation, all

mobile stations transmit with the data rate 11Mbps.

5. In the wireless channel model of the current version of ns-2, the received

power of the packet only depends on the distance of the sender and the

receiver. But in real life, there are a lot of other factors influencing the

received power of a packet. In our research, our main concern is on MAC

layer. Therefore, we assume the limitation of the physical layer

implementation in ns-2 will not affect the findings of our research.

8

6. Other physical factors such as radio interference, noises are not

considered in this research. Thus the channel is assumed to be error free.

1.6 Research Contributions

The following are the contributions of this research:

1. A proposal and implementation of a measurement based admission control

method in the IEEE 802.11e EDCA MAC.

2. A performance study on admission control method proposed in this research.

1.7 Thesis Organization

This thesis is organized into five chapters. The first chapter serves as an

introductory chapter which covers research background and motivation, problem

statements, objectives, scope of work, and research contributions.

Chapter 2 outlines the background of the Wireless Local Area Network

(WLAN). The chapter will cover the basics of WLAN, including IEEE 802.11, QoS

in IEEE 802.11 and the previous contributed works in QoS of IEEE 802.11. Besides,

the last part of the chapter will also focus on the fundamental of ns-2 network

simulator.

Chapter 3 will introduce the architecture and implementation of the proposed

admission control method. The method will be explained using diagrams and finite

state machines. The ACM is implemented in ns-2 network simulator.

9

Chapter 4 presents the performance evaluation of the ACM. The simulation

results are obtained from simulation in EDCA with ACM and EDCA without ACM.

The results are presented in graphs and analyzed.

Finally, chapter 5 wraps up the thesis with the conclusion and some

recommendations for future research.

REFERENCES

[1] IEEE. Wireless LAN Medium Access Control (MAC) and Physical Layer

(PHY) Specification. USA, IEEE 802.11. 1999

[2] IEEE. Part 11: Wireless LAN Medium Access Control (MAC) and Physical

Layer (PHY) specifications: High Speed Physical Layer in the 5GHz Band.

USA, IEEE 802.11a. 1999


Layer (PHY) specifications: High Speed Physical Layer Extension in the

2.4GHz Band. USA, IEEE 802.11b. 1999


Layer (PHY) specifications: Further High Data Rate Extension in the 2.4GHz

Band. USA, IEEE 802.11g. 2003

[5] Cali, F., Conti, M., and Gregori, E.. IEEE 802.11 Protocol: Design and

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