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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
3.4.2 Test Scenario 2 80
3.4.3 Test Scenario 3 82
3.4.4 Test Scenario 4 84
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
with and without ACM 95
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
with and without ACM 97
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
with and without ACM when the number of voice
session increases 103
4.25 Average waiting time comparison for web traffic
with and without ACM when the number of voice
session increases 104
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
[3] IEEE. Part 11: Wireless LAN Medium Access Control (MAC) and Physical
Layer (PHY) specifications: High Speed Physical Layer Extension in the
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