PERFORMANCE EVALUATION OF A FAST HANDOFF BY …

PERFORMANCE EVALUATION OF A FAST HANDOFF

SCHEME FOR CAPWAP CENTRALIZED WLAN

BY

MOHAMMED ABOBAKR AHMED BALFAQIH

A dissertation submitted in fulfilment of the requirement for

the degree of Master of Science of Communication

Engineering

Kulliyah of Engineering

International Islamic University Malaysia

FEBRUARY 2014

ii

ABSTRACT

The growing demand to provide secure wireless connectivity, especially in hot spot

areas such as conference halls and events, introduced centralized Wireless Local Area

Network (WLAN). The centralized WLAN utilizes Access Controller (AC) to

simplify configuration, management and control of Wireless Termination Points

(WTPs) in a large-scale deployment of wireless network. To manage the connection

between these two entities, Control and Provisioning of Wireless Access Point

(CAPWAP) Working Group has defined standard interoperable protocol. Currently,

deployment of a CAPWAP centralized WLAN poses a challenge for real-time

applications that are sensitive to network latencies such as gaming, audio and Voice

over Internet Protocol (VoIP). In order to roam the mobile clients between the WTPs,

scanning and authentication phases are performed, which are considered as the main

handoff latency components. This excessive latency in turn will cause disruption on

the ongoing session, which is unsuitable for real-time applications. The scanning

phase produces highest latency with more than 90% of the total handoff latency in

CAPWAP centralized WLAN (Behcet S., 2006). This dissertation aims to propose a

fast handoff scheme for CAPWAP Centralized WLAN by determining the next WTP

before initiating the MAC layer handoff process. The setup phase latency of network

entities and the handoff process in CAPWAP centralized WLAN are, firstly, evaluated

using CAPWAP centralized WLAN simulator developed by Visual Basic.NET

(VB.NET). This is to evaluate the association latency of the CAPWAP protocol to

ensure that the CAPWAP can effectively be used in network management and validate

the developed simulator. Then, the proposed scheme is evaluated and benchmarked

with the standard Active Scan Method (IEEE Std. 802.11, 2012) and Fast Handoff

Mechanism in WLANs Based on Neighbor Graph Information (Sarddar D., 2010).

The obtained results show that pre-configuring the IP address of the AC in the WTPs

could bring down the setup latency to 84ms, regardless of the number of WTPs per

AC. The case of the setup process with considering failure states showed that error

during negotiation, in the worst case scenario, increases the setup latency by almost 12

times. On the other hand, during the handoff process, the results show that the

scanning latency is the main contributor of the handoff latency. The scanning latency

represents around 87% (in active scan) and around 96% (in passive scan) of the total

handoff latency. Moreover, the results show that the proposed Fast Handoff scheme

reduces 85.5% of the handoff latency using active scan method. The handoff latency

is around 41.12 ms compared to 134.63 ms using the benchmark work. The signaling

cost is also decreased using the proposed scheme to around 87.26% compared to the

active scan method.

iii

خلاصة البحث

ما ايجاد أدّى الى مثل قاعات المؤتمرات( HotSpot)الحاجة المتزايدة للاتصال اللاسلكي الآمن خصوصاً في النقاط الساخنة ( AC)متحكم الوصول تستخدم هذه الشبكة . ( Centralized WLAN) يعُرف بالشبكة المحلية اللاسلكية المركزية

في الشبكات اللاسلكية واسعة ( WTPs)الإدارة و التحكم بمجموعة من نقاط نهايات الوصول اللاسلكي الترتيب و لتسهيل قدمت مجموعة عمل السيطرة والتزويد لنقاط الوصول اللاسلكية الاتصال بين هذبن الجهازين،دارة لإ. النطاق

(CAPWAP )جنة الخاصة لنظام الانترنت لالتابعة لل(IETF ) يُسمى معياري قابل للاستخدام المتبادلميثاق اتصالات(CAPWAP) .،استخدام شبكة يعُد في الوقت الحاليCAPWAP ًبالنسبة لتطبيقات المحلية اللاسلكية المركزية تحديا

( VoIP)مثل الألعاب والصوتيات و الصوت عبر ميثاق الانترنت ( Real-Time Applications)الزمن الحقيقي المستخدم المتحرك بين نقاط نهايات الوصول اللاسلكي يتم انتقالل .في الشبكةالزمني تأخير بال والتي تتأثر بشكل كبير

(WTPs) في طبقة الـ(MAC)، بطوري البحث على المستخدم أن يقوم(Scanning ) والتوثيق(Authentication ) واللذان يعُتبران المكونان الرئيسان للتأخر في عملية الانتقال(Handoff .)الزمني المررطيرالتأخ

في شبكة يعُتبر طور البحث . تطبيقات الزمن الحقيقيناسب يُ والذي لا جلسة الاتصال القائمة بدوره يُسبب اختلال في CAPWAP من اجمالي % 09بما نسبته الانتقال في عمليةللتأخير الزمني سبب الأكبر الالمحلية اللاسلكية المركزية

المحلية CAPWAPفي شبكة ع بتهدف هذه الأطروحة لتقديم طريقة انتقال سر لهذا، . (Behcet S., 2006)تأخيرالأولًا، تم تقييم التأخير في طور التنصيب . نقطة نهاية الوصول التالية قبل بدء عملية الانتقالبتحديد اللاسلكية المركزية وذلك

CAPWAP)المحلية اللاسلكية المركزية باستخدام برنامج المحاكاة CAPWAPلأجهزة الشبكة وعملية الانتقال في شبكة centralized WLAN simulator ) ه بلغة والذي تم تطوير(VB.NET .) بعد ذلك، تم تقييم الطريقة المقترحة و

Fast Handoff Mechanism in WLANs Based)و (Active Scan Method)مقارنتها بطريقتي formationon Neighbor Graph In .) عملية التنصيب المهيأة مسبقاً حيث أظهرت النتائج أنه خلال(-pre

configuring) بتخصيص نقطة نهاية الوصول اللاسلكي مع عنوان الـ(IP ) لمتحكم الوصول، يقلل تأخير التنصيب إلىفي حالة عملية التنصيب . ميللي ثانية، بغض النظر عن عدد نقاط نهايات الوصول اللاسلكية لكل متحكم وصول 48حوالي

من ناحية . اً ضعر 21إلى حوالي تضاعف التأخيريأن التأخبر –في أسوأ الحالات -الإخراق أظهرت النتائج مراحلمع اعتبار ير خلال عملية البحث هو المسبب الرئيسي للتأخير في عملية الإنتقال في أخرى، دللت نتائج تقييم عملية الإنتقال أن التأخ

و ( في حالة البحث الرعال% )48حوالي التأخير في عملية البحثيمثل . المحلية اللاسلكية المركزية CAPWAPشبكة تائج أن طريقة البحث علاوة على ذلك، دللت الن. من إجمالي تأخير عملية الإنتقال( في حالة البحث غير الرعال% )06

كان تأخير . حث الرعالبمن التأخير في عملية الإنتقال باستخدام طريقة ال% 45.5السريع المقترحة قللت التأخير إلى حوالي كما أن كلرة نقل .ميللي ثانية باستخدام الطريقة المقارنة 134.63ميللي ثانية مقارنة بـ 81.21عملية الإنتقال حوالي

.مقارنة بطريقة البحث الرعال% 48.16المقترحة إلى حوالي قلّت باستخدام الطريقةالإشارات

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 in Communication

Engineering.

………………………..

Aisha Abdalla Hashim

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 in Communication Engineering.

………………………..

Suhaimi Abd Latif

Internal Examiner

………………………..

Mohd. Dani B.Baba

External Examiner

This dissertation was submitted to the Department of Electrical and Computer

Engineering and is accepted as fulfilment of the requirement for the degree of Master

of Science in Communication Engineering.

………………………..

Othman O. Khalifa

Head, Department of

Computer and

Electrical Engineering

This Dissertation was submitted to the Kulliya of Engineering and is accepted as a

fulfillment of the requirement for the degree of Master of Science in Communication

Engineering.

………………………..

Md. Noor B. Salleh

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.

Mohammed Abobakr Ahmed Balfaqih

Signature………………………………… Date…………………………………

vi

INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIA

DECLERATION OF COPYRIGHT AND AFFIRMATION

OF FAIR USE OF UNPUBLICATISHED RESEARCH

Copyright © 2014 by International Islamic University Malaysia. All right reserved.

PERFORMANCE EVALUATION OF A FAST HANDOFF

SCHEME FOR CAPWAP CENTRALIZED WLAN

I hereby affirm that the international Islamic University Malaysia (IIUM) holds all

rights in the copyright of this work and henceforth any reproduction or use in any

form or by means whatsoever is prohibited without the written consent of IIUM. No

part of this unpublished research may be reproduced, stored in a retrieval system, or

transmitted, in any form or by means, electronic, mechanical, photocopying, recording

or otherwise without prior written permission of the copyright holder.

Affirmed by Mohammed Abobakr Ahmed Balfaqih

………………………………….. …………………………………..

Signature Date

vii

ACKNOWLEDGMENTS

I would like to thank all of those who have helped to finish this dissertation, including

my supervisors, my family and my friends who have provided extraordinary efforts to

assist me throughout my research.

viii

TABLE OF CONTENT

CHAPTER 1: INTRODUCTION

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

1.2 Research Motivation ......................................................................................... 3

1.3 Problem Statement ............................................................................................ 4

1.4 Research Objectives .......................................................................................... 5

1.5 Research Methodology ..................................................................................... 5

1.6 Research Scope ................................................................................................. 7

1.7 Dissertation Organization ................................................................................. 8

CHAPTER 2: BACKGROUND AND LITERATURE REVIEW

2.1 Introduction ....................................................................................................... 9

2.2 Wireless Local Area Network Architectures .................................................... 9

2.2.1 Autonomous WLAN Architecture ............................................................ 10

2.2.2 Distributed WLAN Architecture ............................................................... 11

2.2.3 Centralized WLAN Architecture ............................................................... 11

2.3 CAPWAP Centralized Architecture ................................................................. 12

2.3.1 CAPWAP Protocol .................................................................................... 13

2.3.2 Local MAC WTP Architecture ................................................................. 16

2.3.3 Split MAC WTP Architecture ................................................................... 17

2.4 IEEE 802.11 Scanning Methods ....................................................................... 18

2.4.1 Passive Scan Method ................................................................................. 19

2.4.1.1 Beacon Frame .................................................................................... 20

2.4.2 Active Scan Method .................................................................................. 20

2.4.2.1 Probe Request Message ..................................................................... 22

2.4.2.2 Probe Response Message ................................................................... 23

2.5 IEEE 802.11 Authentication Methods .............................................................. 23

2.5.1 IEEE 802.1x .............................................................................................. 26

2.5.2 Four-Way Handshake ................................................................................ 28

2.6 Client Association Procedure in CAPWAP Protocol ....................................... 29

2.7 MAC Layer Handoff Process in CAPWAP Protocol ....................................... 32

2.8 Related Work .................................................................................................... 35

2.8.1 An Evaluation Works of Setup Latency in Centralized WLAN ............... 37

Abstract .............................................................................................................................. ii

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

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

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

Copyright Page ................................................................................................................... vi

Acknowledgment ............................................................................................................... vii

List of Tables ...................................................................................................................... xi

List of Figures .................................................................................................................... xiii

List of Abbreviations .......................................................................................................... xvi

List of Symbols .................................................................................................................. xvii

ix

2.8.2 An Evaluation Works of Client Association and Re-

association in Centralized WLAN .............................................................

37

2.8.3 Reducing Scanning Latency Methods ....................................................... 39

2.9 Summary ........................................................................................................... 46

CHAPTER 3: DESIGN OF THE PROPOSED SCHEME

3.1 Introduction ....................................................................................................... 47

3.2 Overview of the Proposed Fast Handoff Scheme ............................................. 47

3.2.1 IEEE 802.11 Info Frame ........................................................................... 48

3.2.2 Client’s Moving Weight ............................................................................ 49

3.2.3 Centralized Neighbor Graph ..................................................................... 50

3.3 Handover Procedure .......................................................................................... 52

3.3.1 The Proposed Fast Handoff Scheme Operation ........................................ 52

3.3.2 The Proposed Fast Handoff Scheme Messages Flow ............................... 56

3.3.3 The proposed Fast Handoff Scheme Packet Format ................................. 57

3.3.3.1 CAPWAP Packet Format ................................................................... 57

3.3.3.2 IEEE 802.11 Packet Format ............................................................... 60

3.3.4 The Proposed Fast Handoff Scheme Messages ......................................... 63

3.3.4.1 CAPWAP Messages .......................................................................... 63

3.3.4.1.1 Neighbor WTPs Message ........................................................... 63

3.3.4.1.2 Client’s Signal Strength Message .............................................. 64

3.3.4.1.3 Next WTP’s Address Message ................................................... 64

3.3.4.2 IEEE 802.11 Messages ...................................................................... 64

3.3.4.2.1 Neighbor WTPs Message ........................................................... 64

3.3.4.2.2 Fast Probe Request Message ...................................................... 65

3.3.4.2.3 Next WTP’s Address Message ................................................... 65

3.4 Summary ........................................................................................................... 65

CHAPTER 4: PERFORMANCE EVALUATION AND DISCUSSION

4.1 Introduction ....................................................................................................... 66

4.2 CAPWAP Centralized WLAN Simulator ......................................................... 67

4.2.1 Mathematical Models ................................................................................ 70

4.2.2 Simulation Setup ....................................................................................... 73

4.2.2.1 CAPWAP Setup Phase Latency ........................................................ 73

4.2.2.2 Mobility Evaluation ........................................................................... 75

4.2.3 Performance Metrics ................................................................................. 77

4.3 Simulation Results and Analysis ...................................................................... 78

4.3.1 The Setup Latency in Centralized WLAN Results ................................... 79

4.3.1.1 The Setup Latency Without Considering Error ................................ 79

4.3.1.2 The Setup Latency With considering Error ...................................... 84

4.3.1.3 Pre-Configured WTP Setup Latency ................................................ 90

4.3.2 IEEE 802.11 MAC Layer Handoff Latency in CAPWAP

Centralized WLAN Results .......................................................................

91

4.3.2.1 IEEE 802.11 MAC Layer Handoff Latency in Local

MAC WTP ........................................................................................ 92

4.3.2.2 IEEE 802.11 MAC Layer Handoff Latency in Split MAC

WTP .................................................................................................. 101

4.3.3 IEEE 802.11 MAC Layer Handoff Latency using Fast

Handoff Scheme Results ........................................................................... 109

x

4.4 Summary ........................................................................................................... 111

CHAPTER 5: CONCLUSION AND FUTURE WORK

5.1 Conclusion ........................................................................................................ 112

5.2 Contribution ...................................................................................................... 114

5.3 Future Works .................................................................................................... 114

REFERENCES ................................................................................................................. 115

PUPLICATIONS .............................................................................................................. 119

APPENDIX A: Part of Access Controller Class ................................................................ 120

APPENDIX B: Part of Wireless Termination Point Class ................................................. 128

APPENDIX C: Part of Mobile Client Class ...................................................................... 135

xi

LIST OF TABLES

Table No. Page No.

2.1 Mapping of 802.11 Functions for Split MAC and Local

MAC Architectures

18

2.2 Security Standards and Authentication Methods

25

2.3 Summary of Relate Work in Reducing Authentication

Latency

45

3.1 A Sample NG List Stored in AC

52

3.2 The Employed Message Elements

59

3.3 Category Values in Action Frame

61

3.4 Message Type Values

63

4.1 Simulation Configuration Parameters for CAPWAP Setup

latency Evaluation

74

4.2 Simulation Configuration Parameters for Mobility

Evaluation

75

4.3 Simulation Configuration Parameters for Handoff Process in

CAPWPA Centralized Network Evaluation

76

4.4 Simulation Configuration Parameters for Handoff Process

using Proposed Fast Handoff Scheme Evaluation

77

4.5 The Average Handoff Latency of a Mobile Client with

Human Walking Speed and Local MAC WTP with 20MHz

bandwidth Using Different Scanning and Authentication

Methods

94


Human Walking Speed and Local MAC WTP with 40MHz


Methods

100


Human Running Speed and Local MAC WTP with 20MHz


Methods

101

xii


Human Running Speed and Local MAC WTP with 40MHz


Methods

101


Human Walking Speed and Split MAC WTP with 20MHz


Methods

102


Human Walking Speed and Split MAC WTP with 40MHz


Methods

107


Human Running Speed and Split MAC WTP with 20MHz


Methods

108


Human Running Speed and Split MAC WTP with 40MHz


Methods

108

4.13 Summary of the handoff latency evaluation in CAPWAP

centralized WLAN

109

xiii

LIST OF FIGURES

Figure No. Page No.

1.1 CAPWAP Centralized Architecture 2

1.2 Research Methodology and Activity 7

2.1 802.11 MAC functions mapping between AC and

WTP in (a) Local MAC (b) Split MAC

13

2.2 CAPWAP Finite State Machine 15

2.3 CAPWAP Protocol Exchange Messages 16

2.4 Passive Scanning Method Process 19

2.5 The Format of MAC Header with Beacon Frame 20

2.6 Active Scanning Method Process 21

2.7 The Format of MAC Header with Probe Request Frame 22

2.8 The Format of MAC Header with Probe Response

Frame

23

2.9 WPA2-Enterprise Authentication Process in Centralized

WLAN Architecture Using Local MAC WTP

26

2.10 Messages Flow of Client First Time Association in

Local MAC WTP

30

2.11 Messages Flow of Client First Time Association in Split

MAC WTP

32

2.12 Messages Flow of Client Handoff Process in Local

MAC WTP

34

2.13 Messages Flow of Handoff process in Split MAC WTP 35

3.1 IEEE 802.11 Frame Info Format 49

3.2 A Simple Indoor Scenario with the Potential Path of

Motion for 4 WTPs

51

3.3 The Flowchart of the Proposed Scheme Operation on

Network Side

53

xiv

3.4 The Flowchart of the Proposed Scheme Operation on a

Client Side

55

3.5 The Messages Flow of the Proposed Fast Handoff

Scheme

56

3.6 CAPWAP Control Packet (DTLS Security Required) 58

3.7 CAPWAP Control Header Format 58

3.8 Message Element Format 59

3.9 WTP Addresses Message Element Format 60

3.10 Client’s RSSI Message Element Format 60

3.11 The Format of MAC Header and Control Field Frames 61

3.12 The Format of MAC Header and Control Field Frames 61

3.13 The format of WTP Addresses Action Frame 62

3.14 The Format of Fast Probe Request Action Frame 62

4.1 The Main Interface of CAPWAP Centralized WLAN

Simulator

68

4.2 Some Windows in CAPWAP Centralized WLAN

Simulator a) Simulation Configuration Window. b)

Simulation Control Window

69

4.3 CAPWAP Finite State Machine 74

4.4 The setup process latency of 1 AC with different number

of WTP in 50 experiments and its average

80

4.5 The relation between setup latency and increasing

number of WTP with 1 AC

83

4.6 The Average Setup Latency of Using Different Number

of AC and WTP in a Network and The Average Setup

Latency of 1 AC with 1 WTP

84

4.7 Figure 4-7: Comparing the average setup latency with

considering errors in each phase individually and

combined with other phases with the normal setup

latency

86

xv

4.8 The Latency of Setup Process with Error in Discovery,

DTLS Establishment and Join Phases Comparing to The

Normal Setup Process

90

4.9 The Average Setup Latency of using Pre-configured

WTP Setup Process

91


Human Walking Speed and Local MAC WTP with

20MHz bandwidth using Different Scanning and

Authentication Methods

92

4.11 The Handoff Latency Components in Different

Environment using Active Scan Method

95


Environment using Passive Scan Method

97


Human Walking Speed and Split MAC WTP with

20MHz bandwidth Using Different Scanning and

Authentication Methods

102


Environment using Active Scan Method

103


Environment using Passive Scan Method

105

4.16 The Handoff Latency of a Mobile Client Using Proposed

Handoff Scheme Comparing to Active Scan Method and

The Benchmark Work.

110

4.17 The Scanning Latency of a Mobile Client Using

Proposed Handoff Scheme Comparing to Active Scan

Method and The Benchmark Work

111

xvi

LIST OF ABBREVIATIONS

IEEE Institute of Electrical and Electronics Engineers

WLAN Wireless Local Area Network

AP Access Point

CAPWAP Control and Provisioning of Wireless Access Point

WTP Wireless Termination Points

AC Access Controller

BSS Basic Service Set

ESS Extended Service Set

SSID Service Set Identifier

MSDU MAC Service Data Unit

LLC Logic Link Control

DS Distribution System

RF Radio Frequency

IETF Internet Engineering Task Force

MAC Medium Access Control

UDP User Datagram Protocol

DTLS Datagram Transport Layer Security

AAA Authentication, Authorization and accounting

EAP Extensible Authentication Protocol

RSNA Robust Security Network Association

RSSI Received Signal Strength Indicator

FHSS Frequency Hopping Spread Spectrum

DSSS Direct Sequence Spread Spectrum

xvii

PSK Pre-Shared Key

TIKP Temporal Integrity Key Protocol

WPS Wi-Fi Protected Setup

WPA Wi-Fi Protected Access

AES-CCMP AES-Counter Mode CBC-MAC Protocol

TLS Transport Layer Security

PMK Pairwise Master Key

PTK Pairwise Transient Key

Anonce Authenticator nonce

Snonce Supplicant nonce

MIC Message Integrity Code

GTK Group Temporal Key

HOKEY Handover Keying protocol

GER Generic Routing Encapsulation

NG Neighbor Graph

GPS Global Positioning System

UL Update Location

HI Handover initiate

BU Binding Update

HA Home Agent

DCS Data Collection Server

PS Power Saving

NBL Neighbor List

IAPP Inter Access Point Protocol

BMP Behaviour based Mobility Prediction

CNG Centralized Neighbor Graph

xviii

LIST OF SYMBOLS

Scan latency

The needed time to switch from current channel to next channel

Probing Time

the waiting time for a channel to probe response

the probability a channel to be empty

the probability a channel to be non-empty

The transmission latency between a client and a WTP

The communication latency between WTP and AC

y The dependent variable

X The explanatory variable

C an intersection points of the least square line with y axis

M The slope

N The total number of variables

The measured RSS at time

Θ The slope of the least square line

The defined threshold where the AC transfers the Neighbor WTPs’

address to the client.

The defined threshold where the AC transfers the next WTP’s address

to the client.

The handoff threshold

The certain time that the client probes the Neighbor WTPs

The average of collected client’s RSS for Neighbor WTPs

1

CHAPTER ONE

INTRODUCTION

1.1 OVERVIEW

Nowadays, the need of a high data transmission rate with easy deployment is the

demand of many electronic devices, including laptop computers, PDAs and smart

phones. Therefore, deploying Institute of Electrical and Electronics Engineers (IEEE)

802.11 Wireless Local Area Network (WLAN) is the most widely accepted broadband

wireless network technology. IEEE 802.11 technology is, primarily, designed for

indoor environments with limited data rates - only 1 and 2 Mbps -. The success of

IEEE 802.11 to increase the available data rate, removes significant factor holding

back the adoption of IEEE 802.11 in large scale deployments. However, the high

numbers of Access Points (APs), called Wireless Termination Point (WTP) in the

centralized WLAN, in a large scale network have introduced several burdens such as

control, management and monitoring. In addition, the challenges of distributing and

maintaining a consistent configuration with considering security issues are more

severe in large deployments and new architectures. These issues forced many network

vendors such as Aruba, Cisco and Meraki to offer proprietary centralized solutions.

The common characteristic of the proposed solutions is splitting the functionality of

APs and adding more centralized operation functions for configuring, managing and

monitoring purposes.

However, since that proposed solutions do not provide interoperability, Control

and Provisioning of Wireless Access Point (CAPWAP) Working Group have defined

standard interoperable protocol to address the aforementioned problems (RFC 3990,

2

2005). This interoperable protocol will allow the network operators to control and

extend the manageability of their wireless network infrastructure (RFC 5415, 2009).

The CAPWAP is a standard protocol that enables Access Controllers (ACs) to

centrally manage Wireless Termination Points (WTPs) and provide compatibility

between different vendors in large scale networks. AC is a network entity that

provides access to a WTP to the network infrastructure where the WTP exchanges

clients’ traffic with it (see Figure 1.1). CAPWAP protocol supports two types of

architectures; local MAC WTP architecture and split MAC WTP architecture (RFC

5416, 2009).

Figure 1.1: CAPWAP Centralized Architecture

Since WTPs have limited transmission range and clients are able to roam

freely, usually, the client hand-offs among the WTPs. However, the handoff process in

3

CAPWAP specification (RFC 5415, 2009) is unsuitable for real-time applications

such as gaming, video and VoIP. In order to seamlessly provide real time application,

handoff latency must be limited within 150 ms (ITU-TG.114, 2003), (Seitz N., 2003).

Therefore, the MAC layer handoff latency components must be reduced to support

real time applications.

In general, this dissertation deals with reducing MAC layer handoff latency for

CAPWAP centralized WLAN. To achieve fast handover and delivery of real-time

traffic in mobile environment, a fast handoff scheme is developed for CAPWAP

centralized WLAN. The fast handoff according to (RFC 3753, 2004) is the handoff

process that aims to eliminate the number of required round-trips during the handoff

without any explicit interest in packet loss. This introductory chapter introduces the

research motivation, the problem statement, objective, the methodology, the scope of

the research work and finally the dissertation organization.

1.2 RESEARCH MOTIVATION

The number of mobile terminals (i.e. multiple smart phones, laptops and tablet PCs)

that are connected to the WLAN for communication needs have drastically increased

overtime. As these individuals move from one WTP to another, they expect their

applications (i.e. Facebook, Skype, E-mails, etc.) to seamlessly follow them. This can

be offered to the mobile client in CAPWAP centralized WLAN, if its handoff latency

met real-time application requirement where the delay must be less than 150 ms (ITU-

TG.114, 2003), (Seitz N., 2003). Thus, the presented scheme provides a fast handoff

solution that can meet multimedia traffic requirements.

4

1.3 PROBLEM STATEMENT

In order to deploy enterprise wide Wi-Fi networks, the Control and Provisioning of

Wireless Access Point (CAPWAP) working group have defined a standard

interoperable protocol for centralized network solution by splitting the functionality of

Wireless Termination Points (WTPs) and adding more centralized operation functions

in Access Controller (AC) for configuring, managing and monitoring purposes.

However, since the WTPs have a small coverage size and the clients have a

high mobility index, the mobile clients roam frequently from a WTP to another. These

clients expect their real-time application services to seamlessly follow them.

Unfortunately, due to the handoff latency, the disruption on the ongoing transmission

in delay-sensitive multimedia application is resulting. As shown in (Behcet S., 2006),

the main component of handoff latency, in the CAPWAP centralized network, is

scanning latency.

Fast handoff mechanism in WLANs based on neighbor graph information

(Sarddar D., 2010), and other works had been proposed to reduce scanning phase

using different proposed methods. However, the existing centralized methods that aim

to decrease scanning latency mostly required new extra entities which incurred high

cost. Moreover, other methods increase the signalling cost during the handoff process.

The high signalling cost consumes much network bandwidth to exchange the

transition messages, especially when the WLAN is scaled up. The high distributed

messages during the handoff process may severely impact the data transmission.

Therefore, a fast handoff scheme is needed to efficiently select the next WTP without

requesting new entities and with lower signalling cost to reduce scanning phase

latency. Subsequently, this will reduce MAC layer handoff latency.

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1.4 RESEARCH OBJECTIVES

The main goal of this research work is to reduce MAC layer handoff latency for a

mobile client in CAPWAP centralized architecture. The detailed objectives of this

dissertation are to:

1. Analyze the latency components of CAPWAP centralized WLAN during

the setup phase and the handoff process including scanning phase and re-

authentication phase.

2. Develop a scheme that takes a benefit of the AC that receives the client’s

traffic from the managed WTPs. This is in order to selectively scan the

WTPs and determine the next WTP centrally by the AC before the mobile

client initiating MAC layer handoff process.

3. Evaluate the proposed scheme using our developed CAPWAP centralized

network simulator and then, benchmark the results with active scan

method and fast handoff mechanism in WLANs based on neighbor graph

information (Sarddar D., 2010).

1.5 RESEARCH METHODOLOGY

In order to achieve the above state objectives, the research approach of the work will

be as follow:

Comprehensive literature review to investigate the evaluation works of the

setup phase of network’s entities latency and MAC layer handoff latency

in the CAPWAP centralized network and investigate the current methods

that reduce scanning latency during MAC layer handoff in centralized

network.

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Developing CAPWAP centralized network simulator to evaluate the

proposed fast handoff and the benchmark work.

Validating the developed CAPWAP centralized network simulator by

evaluating the setup process of CAPWAP protocol and the handoff

process in CAPWAP centralized WLAN architecture.

Determining the handoff latency components by evaluating the handoff

process in centralized WLAN using our developed CAPWAP centralized

network simulator with considering different scanning and authentication

methods in different environments.

Designing the proposed scheme to achieve the fast MAC layer handoff in

CAPWAP centralize architecture.

Evaluating the proposed method using our developed CAPWAP

centralized network simulator, taking into account handoff latency as main

performance criteria.

Benchmark the proposed scheme with MAC layer handoff in CAPWAP

protocol using active scan method and fast handoff mechanism in WLANs

based on neighbor graph information (Sarddar D., 2010).

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PERFORMANCE EVALUATION OF A FAST HANDOFF BY …