AN OFFLINE EMAIL IMPLEMENTATION BASED ON DELAY TOLERANT NETWORK

(DTN)

MOHD KHAIRUN NASIR BIN SA‟ADI

A thesis submitted

In fulfillment of the requirements for the Master of Advanced Information Technology

Faculty of Computer Science and Information Technology

UNIVERSITI MALAYSIA SARAWAK

2013

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DEDICATION

“This thesis is dedicated to my mom and dad, who was giving the infinite support

and also to my wife, brothers and sisters who always giving encouragement”

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ACKNOWLEDGEMENTS

Firstly, thanks to the project supervisor, Dr. Kartinah Zen for the guidance on matters

related to Offline Email based on Delay Tolerant Network project and her encouragement to

complete this project.

Advice and support from families also help in the completion of this thesis as well as help

from friends who incessantly give guidance and knowledge to me.

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ABSTRACT

This thesis focuses on extending offline email system in a local area network environment to the

internet connected email system in online environment based on delay tolerant network. This

offline email system will allow the rural users to have an access to the internet connected email

system. It allows the user to read, write and send email in an offline local network environment.

This offline email system will be able to connect to online email system via infomediary device

based on delay tolerant network concept. Even though in an offline environment, user also able to

read, write and send email as if he or she is in an online environment. This offline email system

will allow the email flow through the offline environment to the online environment and vice

versa. The most important part of this offline email system is an implementation of email

database synchronization between offline mail server and infomediary device and between online

mail server and infomediary device. Another part is an implementation of offline and online

email system consist of mail server and mail client for both sides. This offline email system will

be using operating system Windows XP 32bit, wireless local area network, and internet

connection 1MB/s TMnet Streamyx Dynamic IP with the conjunction of Uniform Server for

personal home server. This offline email system consists of offline mail client, offline mail

server, database synchronization at offline server, infomediary device, online mail client, online

mail server and database synchronization at online server.

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ABSTRAK

Tesis ini memberi tumpuan ke atas melanjutkan sistem emel luar talian dalam persekitaran

rangkaian kawasan tempatan ke sistem emel bersambungan internet dalam persekitaran dalam

talian berdasarkan rangkaian toleransi kelewatan. Sistem emel luar talian ini akan membolehkan

pengguna luar bandar untuk mempunyai akses kepada sistem emel yang bersambungan internet.

Ia membolehkan pengguna untuk membaca, menulis dan menghantar emel dalam persekitaran

rangkaian kawasan tempatan luar talian. Sistem emel luar talian ini akan boleh menyambung ke

sistem emel dalam talian melalui alat informediari berdasarkan konsep rangkaian toleransi

kelewatan. Walaupun dalam persekitaran luar talian, pengguna juga boleh membaca, menulis dan

menghantar emel seolah-olah dia berada dalam persekitaran dalam talian. Sistem emel luar talian

ini akan membolehkan aliran emel melalui persekitaran luar talian ke persekitaran dalam talian

dan sebaliknya. Bahagian yang paling penting dalam sistem emel ini adalah perlaksanaan

penyegerakan pangkalan data emel antara pelayan mel luar talian dan alat informediari dan antara

pelayan mel dalam talian dan alat informediari. Sebahagian yang lain adalah perlaksanaan sistem

emel luar talian dan dalam talian yang terdiri daripada pelayan mel dan klien mel untuk kedua-

dua pihak. Sistem emel luar talian ini akan menggunakan sistem operasi Windows XP 32 bit,

rangkaian kawasan tempatan tanpa wayar dan sambungan internet 1MB/s TMNet Streamyx IP

Dinamik bersama dengan Uniform Server untuk pelayan rumah peribadi. Sistem emel luar talian

ini terdiri daripada klien mel luar talian, pelayan mel luar talian, penyegerakan pangkalan data di

pelayan luar talian, alat informediari, klien mel dalam talian, pelayan mel dalam talian dan

penyegerakan pangkalan data di pelayan dalam talian.

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TABLE OF CONTENTS

1. INTRODUCTION ................................................................................................................... 1

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

1.2 Problem Statement ............................................................................................................. 4

1.3 Objective ............................................................................................................................ 5

1.4 The Proposed System ........................................................................................................ 6

1.5 System Implications ........................................................................................................... 8

1.6 System Advantages ............................................................................................................ 9

1.7 Summary of chapters ....................................................................................................... 11

2. LITERATURE REVIEW ...................................................................................................... 13

2.1 Transmission Control Protocol and Internet Protocol (TCP/IP) ...................................... 13

2.1.1 Detailed explanation in each TCP/IP Layers ........................................................... 14

2.1.2 Internet Addressing .................................................................................................. 20

2.1.3 TCP/IP Operation ..................................................................................................... 22

2.2 Delay Tolerant Network (DTN) ...................................................................................... 24

2.2.1 Reason to use DTN ................................................................................................... 24

2.2.2 Architecture of DTN ................................................................................................ 26

2.3 Comparison of TCP/IP and DTN .................................................................................... 32

2.3.1 DTN vs. TCI/IP: Protocol Architecture ................................................................... 32

2.3.2 DTN Router vs. TCP/IP Router ............................................................................... 36

2.3.3 Naming and addressing mechanism: Endpoint IDs ................................................. 38

2.4 Network Architecture: Emails ......................................................................................... 40

2.5 Similar Works .................................................................................................................. 43

2.5.1 Bytewalla 5 ............................................................................................................... 43

2.5.2 Offline Gmail ........................................................................................................... 44

2.6 Summary .......................................................................................................................... 45

3. METHODOLOGY ................................................................................................................ 46

4. OFFLINE EMAIL SYSTEM DESIGN ARCHITECTURE ................................................. 49

4.1 TCP/IP Mail System works as a DTN Mail System........................................................ 49

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4.2 Idea and Concept Analysis .............................................................................................. 52

4.3 Abstraction of TCP/IP Mail System based on DTN ........................................................ 53

4.4 Application and Network Topology ................................................................................ 59

4.5 Network Protocol Design ................................................................................................ 61

4.6 Offline Email System Detail Design ............................................................................... 63

4.7 Database Synchronization ............................................................................................... 66

4.8 Summary .......................................................................................................................... 67

5. SYSTEM IMPLEMENTATION ........................................................................................... 69

5.1 System Platform and Environment .................................................................................. 69

5.2 Implementation Issues ..................................................................................................... 70

5.3 Requirements ................................................................................................................... 72

5.4 Implementation Details .................................................................................................... 75

5.4.1 Server Computer ....................................................................................................... 75

5.4.2 Web server Application ............................................................................................ 76

5.4.3 External IP Address .................................................................................................. 78

5.4.4 Mail Server ............................................................................................................... 82

5.4.5 Mail Client ................................................................................................................ 83

5.4.6 Process of Database Synchronization ....................................................................... 87

5.4.7 Related Data for Synchronization ............................................................................ 88

5.4.8 Database Synchronization Application .................................................................... 89

5.4.9 System Control Graphical User Interface (GUI) ...................................................... 96

5.5 Summary ........................................................................................................................ 100

6. SYSTEM TEST ................................................................................................................... 101

6.1 New Account Registration Test ..................................................................................... 101

6.1.1 Test Design ............................................................................................................. 101

6.1.2 Expected Outcome ................................................................................................. 102

6.1.3 Test result ............................................................................................................... 102

6.2 Connectivity Test ........................................................................................................... 104

6.2.1 Test Design ............................................................................................................. 104

6.2.2 Expected Outcome ................................................................................................. 105

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6.2.3 Test Result .............................................................................................................. 106

6.3 Delay Test ...................................................................................................................... 108

6.3.1 Test Design ............................................................................................................. 108

6.3.2 Expected Outcome ................................................................................................. 109

6.3.3 Test Result .............................................................................................................. 109

6.4 Limitation of Infomediary Device Pass by Movement Speed ....................................... 110

6.4.1 Test Design ............................................................................................................. 110

6.4.2 Expected Outcome ................................................................................................. 110

6.4.3 Test Result .............................................................................................................. 111

6.5 Size of Data Test ............................................................................................................ 113

6.5.1 Test Design ............................................................................................................. 113

6.5.2 Expected Outcome ................................................................................................. 114

6.5.3 Test Result .............................................................................................................. 114

6.6 Types of Data Test ......................................................................................................... 115

6.6.1 Test Design ............................................................................................................. 115

6.6.2 Expected Outcome ................................................................................................. 116

6.6.3 Test Result .............................................................................................................. 116

6.7 Multiple of Senders and Receivers Test ........................................................................ 117

6.7.1 Test Design ............................................................................................................. 117

6.7.2 Expected Outcome ................................................................................................. 117

6.7.3 Test Result .............................................................................................................. 118

6.8 Multiple of Communications Test ................................................................................. 118

6.8.1 Test Design ............................................................................................................. 118

6.8.2 Expected Outcome ................................................................................................. 119

6.8.3 Test Result .............................................................................................................. 120

6.9 Discussion of Results ..................................................................................................... 122

6.10 Summary .................................................................................................................... 123

7. CONCLUSION .................................................................................................................... 124

7.1 Future Work ................................................................................................................... 124

7.2 Conclusion ..................................................................................................................... 125

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REFERENCES ............................................................................................................................ 127

APPENDIX ................................................................................................................................. 129

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LIST OF FIGURES

Figure 1.1: Offline email system overview ...................................................................................... 4

Figure 1.2: Offline email system components .................................................................................. 7

Figure 2.1: TCP/IP Protocol Architecture ...................................................................................... 14

Figure 2.2: TCP/IP Layer ............................................................................................................... 15

Figure 2.3: Hypertext Transfer Protocol (HTTP) ........................................................................... 15

Figure 2.4: Simple Mail Transfer Protocol (SMTP) ...................................................................... 16

Figure 2.5: Address Classes [5] ...................................................................................................... 21

Figure 2.6: Subnet Address ............................................................................................................ 22

Figure 2.7: TCP/IP operation of accessing a website ..................................................................... 23

Figure 2.8: Store and forward delivery .......................................................................................... 26

Figure 2.9: Bundles ........................................................................................................................ 27

Figure 2.10: Bundle Space ............................................................................................................. 28

Figure 2.11: Bundle Overlay .......................................................................................................... 30

Figure 2.12: Bundle Routing .......................................................................................................... 31

Figure 2.13: Bundle Authentication Block (BAB) ......................................................................... 31

Figure 2.14: Comparison Internet Protocol Layers with DTN Protocol Layers ............................ 33

Figure 2.15: Bundle Encapsulation [9] ........................................................................................... 34

Figure 2.16: Minimal conversational lower layer protocols [9] ..................................................... 35

Figure 2.17: Class of Bundle Service [9] ....................................................................................... 36

Figure 2.18: Internet Router [9] ..................................................................................................... 37

Figure 2.19: DTN Router [9] .......................................................................................................... 37

Figure 2.20: DTN Naming and addressing mechanism [9] ............................................................ 40

Figure 2.21: Internet Mail .............................................................................................................. 41

Figure 2.22: DTN Mail ................................................................................................................... 42

Figure 3.1: Iterative Approach ....................................................................................................... 46

Figure 4.1: IMAP vs POP............................................................................................................... 50

Figure 4.2: Offline Email System Architecture .............................................................................. 60

Figure 4.3: Networking Protocol flow ........................................................................................... 62

Figure 4.4: Store and Forward ........................................................................................................ 63

Figure 4.5: Offline Email System Network Protocol layout .......................................................... 64

Figure 4.6: Online Email System Network Protocol layout ........................................................... 66

Figure 5.1: Uniform Server Binary Codes ..................................................................................... 80

Figure 5.2: TMnet SMTP relayer ................................................................................................... 83

Figure 5.3: Process of database synchronization ............................................................................ 88

Figure 5.4: Database Synchronization Path ................................................................................... 91

Figure 5.5: Realtime Synchronize Setting ...................................................................................... 93

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Figure 5.6: Samba File sharing application configuration ............................................................. 95

Figure 5.7: Pemail system control Graphical User Interface (GUI) ............................................... 97

Figure 5.8: Uniform Server Core Control ...................................................................................... 98

Figure 6.1: New Email User Registration .................................................................................... 101

Figure 6.2: New account registration test result ........................................................................... 103

Figure 6.3: Test sample ................................................................................................................ 105

Figure 6.4: Range and speed for mail data synchronization ........................................................ 113

Figure 6.5: Multiple communication ............................................................................................ 119

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LIST OF TABLES

Table 1.1: Estimated Cost for Offline Email System based on DTN ............................................. 10

Table 1.2: Cost for DANAWA Wi-Fi Hotspot implementation .................................................... 11

Table 2.1: Private addressing ......................................................................................................... 21

Table 2.2: Reserved and available IP addresses [5] ....................................................................... 22

Table 2.3: TCP/IP Endpoint ID ...................................................................................................... 38

Table 2.4: DTN Endpoint ID .......................................................................................................... 39

Table 4.1: Store, Carry and Forward Scenario ............................................................................... 50

Table 4.2: Comparison of DTN Email ........................................................................................... 55

Table 4.3: Comparison of Web server ............................................................................................ 56

Table 4.4: Comparison of Mail Server software ............................................................................ 57

Table 4.5: Comparison of Mail Client ............................................................................................ 57

Table 4.6: Comparison of File Synchronize software .................................................................... 58

Table 4.7: Comparison of Infomediary Device .............................................................................. 59

Table 5.1: D-Link DWL-2100AP indoors and outdoors coverage range ...................................... 70

Table 5.2: Hardware Requirements ................................................................................................ 73

Table 5.3: Software Requirements ................................................................................................. 75

Table 5.4: Enable Web server External Access Script ................................................................... 76

Table 5.5: Enable Cron ................................................................................................................... 80

Table 5.6: Enable Cron automatic update on Uniserver ................................................................ 81

Table 5.7: Apache. MySQL and Cron startup script configuration ............................................... 81

Table 5.8: Enable Mail Client External Access Script ................................................................... 85

Table 5.9: Enable New User Registration Page Script ................................................................... 86

Table 5.10: hMailServer SQL Database driver name setting ......................................................... 86

Table 5.11: Domain name setting ................................................................................................... 86

Table 5.12: Infomediary Device Data Synchronization Folder ..................................................... 91

Table 5.13: Mail Server Data Synchronization Folder ................................................................... 91

Table 5.14: StartFFS.bat Script ...................................................................................................... 94

Table 5.15: Offline Server Computer Start script (Start_Server.bat) ............................................. 98

Table 5.16: Offline Server Computer Stop script (Stop_Server.bat) ............................................. 99

Table 5.17: Mail Server Start and Stop script .............................................................................. 100

Table 6.1: Send and receive email test result on each node ......................................................... 107

Table 6.2: Delay Period Test Result ............................................................................................. 109

Table 6.3 Transfer rate, read speed and write speed comparisons ............................................... 112

Table 6.4: Testing email data size ................................................................................................ 115

Table 6.5: Testing types of data attachment ................................................................................. 116

Table 6.6: Multiple sender and receiver test result ...................................................................... 118

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Table 6.7: Multiple communication test result ............................................................................. 121

LIST OF EQUATIONS

Equation 6.1 Infomediary device movement speed ..................................................................... 112

1

1. INTRODUCTION

1.1 Overview

Email application has been commonly used as one of the communication tools

which are cheap and easy to use as long as the person has internet connection. Email

application is tolerant to delay and the email sender and recipient not required to be online

at the same time. Email is suitable especially for those who not in urgency and delay in

sending and receiving is acceptable. For those who live in the rural area without the

Internet connection, even the application such as an email application is impossible. Rural

area such as Bario has a telecentre which is built with the Internet facilities only offer the

Internet connection in four kilometers diameter around the telecentre [1]. Therefore, the

best approach to provide email services for users who has no internet connection at other

areas is by introducing an offline email system. This offline email system using

Transmission Control Protocol and Internet Protocol (TCP/IP) with the database

synchronization application as a data mule where it works as a network bridge by bringing

the pending emails from offline server computer to the online server computer.

TCP/IP has been used widely in the email application as well as in World Wide

Web (WWW), File Transfer Protocol (FTP) and Voice-over-IP (VoIP). TCP/IP

fundamental assumption is, there is always end-to-end communication between sender

and receiver. End-to-end communication means that the network provides a reliable

transport layer with immediate data transmission to the receiver and to provide data

integrity, delivery guarantees, delivery acknowledgement, duplicate message suppression,

per packet encryption and transaction management [2]. However, end-to-end

communications cannot be applied in this offline email system because of the rural area is

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lack of continuous connection from sender to receiver. TCP/IP drops the packets if the

next connection cannot be found immediately. Delay tolerant network (DTN) protocol is

used in this thesis to solve this problem. DTN used store and forward operation and

introduced a bundle protocol in between the application layer and the transport layer.

Delay tolerant network (DTN) is an approach to computer network to overcome

the lack of end-to-end network connectivity. DTN tolerates delay and disruption with

acceptable performance in high loss and delay error environments. DTN tries to solve

some of the issues by relaxing some of the TCP/IP end-to-end communication

assumptions by introducing bundle protocol. The bundle protocol defines a series of data

blocks as a bundle. Bundles are routed in Store and Forward operation from source node

to the destination node. Store and Forward operation is a DTN fundamentals where it is

designed to use storage within the network and perform incremental progress before

proceeding to another path.

This thesis focuses on an offline email system implementation in a rural area with

some modification to the protocol because it is designed as such the email needs to be

transferred to another different device before it can be transmitted. This offline email

system is designed for rural users with no internet connection to allow them to access their

email account and compose new messages or check the last reply as shown in Figure 1.1.

Village A and Village B are located very far from the telecentre, from three kilometers to

40 kilometers. Rural villagers send their emails using their laptop or handphone and send

it to the nearby offline mail server. From this offline mail server, the appointed person

with infomediary device will collect all the emails from the offline mail server by

positioning his infomediary device close to the offline mail server so that the transmission

3

takes place wirelessly based on wireless local area network (WLAN) based on IEEE

802.11 standards. Conventionally, there is a need of a more internet hotspot datacenter at

each village to stay connected which will require a higher cost.

Email application is asynchronous in nature and do not need end-to-end

connectivity. Therefore, DTN store and forward fundamental is suitable for use to

implement an offline email system in a rural area. In this thesis work, the store and

forward process implemented by using file synchronization method. Store and forward

process is a technique in which data is sent to an intermediate station and kept temporarily

before sent to the final destination or to another intermediate station [3]. The file

synchronization process is critical because the offline email on the offline mail server

should capable to synchronize its database with the intermediate device and the online

mail server. The intermediate device, known as an infomediary device is a temporary

storage for the email database. This device collects the emails from the offline

environment and brings them to the online environment.

4

Figure 1.1: Offline email system overview

This offline email system is working in two different environments which is an

offline local area network (LAN) environment and online internet environment. Both

offline and online mail server running on operating system Windows XP 32bit.

Smartphone android 2.3.5 conjunction with Samba File sharing application working as an

infomediary device to allow receiving and sending files between both mail servers. Only

one online mail server is connected to regular Streamyx ISP (Dynamic IP) internet

connection instead of the need of a more internet hotspot datacenter at each village.

1.2 Problem Statement

TCP/IP does not fully support this offline email system because it requires

immediate end-to-end path between sender and receiver. This means the connection must

5

exist at the same time sender send the email because the email packets will travel through

the transport layer and finally to the destination. The email client is disconnected from

email server if there is no end-to-end path and the user cannot access their email account.

However, if the Gmail offline application is used, the user has to bring their device to the

connected area. In rural area, this seems not practical. Delay tolerant network (DTN) is

designed to overcome this limitation by implementing store and forward message

switching by overlaying a new protocol layer called the bundle layer. DTN use storage

within the network to support the store and forward operation over networking paths. The

problem arises when the emails have to be collected into another device before it is

brought physically to the connected area. The store and forward process of DTN is

integrated using the file synchronization method because it involves the third device and

the third person to bring the emails to the connected area.

1.3 Objective

The objective of this thesis is to provide an offline email system at rural area that

has no internet connection. There are three research questions in this thesis as below:

1) Implementation: How the user registration page should be implemented and

how the store and forward process in delay tolerant network (DTN) supports

the offline email system in terms of email connectivity from the offline

environment network to online environment network?

2) Functionality: Can the email data maintain in the mail server for a very long

time delay until it synchronized with infomediary device? What is the

limitation size of email data which include email content and file attachment?

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What are the types of data supported when uploading an attachment? Can the

email data synchronization process avoid conflict when the email sent and

replied from multiple sender and receiver or when the email sent and replied

through multiple communications?

3) Performance: What is the limitation movement speed of an infomediary device

when moving through a mail server and performing a database

synchronization?

1.4 The Proposed System

An offline mail server in the rural area local area network (LAN) is where rural

users can read, send and receive email locally in the LAN. Meanwhile the external email

content to be sent online will be stored temporarily until it is transferred to infomediary

device. The database synchronization system in the offline server computer will transfer

and receive new database from the infomediary device as shown in Figure 1.2.

Infomediary device working as a temporary storage and can be accessible via Wi-Fi or

wireless local area network (WLAN). Then the database synchronization system in the

online server computer will transfer and receive new email data from this infomediary

device. Online mail server has all the features as offline mail server where the user in that

area can use the offline email system locally through LAN. Online mail server is

connected to the internet. This offline email system can be access from the internet

through the online mail server. The external email content to be sent offline will be stored

temporarily until it is being transferred to infomediary device and then to the offline mail

server at rural area.

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Figure 1.2: Offline email system components

Store and forward process between mail server and infomediary device provide the

ability of connection between offline email system and online email system. This will

enable the email content to flow through the offline environment to the internet

environment and vice versa. It is critical to develop a suitable subsystem that can fulfill

the need of this offline email system because there is a challenge in the email database

synchronization. This synchronization system should have the ability to synchronize the

database between the offline mail server and the infomediary device. It is also responsible

to synchronize the database in the online mail server and database in the infomediary

device. Infomediary device is a temporary storage for the email database operates

wirelessly to collect the email data between the offline environment and the online

8

environment. It should be portable, secured and has a long life battery. There are two

different environments for this offline email system which is offline and online. Both

sides consist of mail server and mail client for their respective environment. At the online

side, the online mail system is connected to the internet using a personal home server.

This mail server is running on Streamyx dynamic IP conjunction with Uniform Server.

The Uniform Server is a Windows Apache, MySQL and PHP, Perl or Python (WAMP)

package that allows the user to run a server on any Microsoft Windows Operating System

based computer.

1.5 System Implications

At offline mail server, users have a local mail access. They can manage, read, send

or receive email locally to another person in the local area network. Infomediary device

allows email data to be sent from offline network to online network and vice versa. This

extends the offline email system network by allowing user to read, send and receive email

in an offline environment or in an online environment. At the online mail server, users

also have a local mail access. Since the online mail server is connected to the internet,

users able to send and receive email from other Internet Mail such as Gmail and Hotmail

directly. With the help of infomediary device, online users can receive or send email to

the rural users at the offline mail server. This offline email system is not using native

DTN protocol but applies a DTN store and forward fundamentals in TCP/IP by using a

database synchronization process.

9

1.6 System Advantages

There is only one mail server required to be connected to the internet and rural

mail server can be extended to more than one. This offline email system is based on DTN

fundamentals, store and forward operation by using TCP/IP. It is easy for implementation

and system requirement is easy for maintenance. Finding of hardware malfunction

replacement can be done easily. This system offers simplicity usage with a less

complicated system and fulfills the typical user experience. User only need a web browser

application to access the offline email system either from their personal computer, tablet

PC or Smartphone. By using a windows based system, awkward environment can be

avoided especially for inexperienced user and hence there is no need for special training if

it was using Mac OS, Linux or other Unix system. There is no needs for the rural users to

travel very far to the internet connected area to have the opportunity as equal as the people

who live near to the internet connection. Only one user is moving instead of all users

moving to the internet connected area. The system is affordable where there are no

complicated requirements needed. There is the hardware cost needed for this offline email

system implementation. Related software required is a free and open source. Estimated

cost for this offline email system is RM6034.00 as shown in Table 1.1. This total cost

consists of one offline mail server, one informediary device, one online mail server and

one month internet subscription cost. The additional cost will be needed to support

another rural area by providing another offline mail server which will cost RM2304 for

offline mail server computer and wireless access point. Compared to other Wireless

Service Provider such as Danawa Wireless Solution Provider, the cost is very high as

shown in Table 1.2. Appendix A shows the details of the Danawa service. To use Danawa

10

service, multiple Wi-Fi internet hotspots required for each rural area. And each Wi-Fi

internet hotspot for 1 MBps which is one megabytes per second price is RM3000 monthly

subscription and RM1000 for one time installation. By using DTN method, only one Wi-

Fi internet hotspot required and can be extended to another rural area by providing offline

mail server at each area where each area connected by infomediary device.

Items Cost (RM)

Offline mail server (Laptop Lenovo Z460) 2099.00

Offline side wireless access point (D-Link DWL-2100AP) 205.00

Infomediary device(LG Optimus 3D P920) 2000.00

Online server computer (Desktop Computer) 1500.00

Online side wireless ADSL Modem (Riger DB 108-WL

Wireless ADSL Modem 2/2+)

120.00

TM Streamyx Dynamic 1 MBps Internet Service Provider (ISP)

(Monthly Subscriptions)

110.00

Total Cost: 6034.00

Table 1.1: Estimated Cost for Offline Email System based on DTN

The user interface is based on webmail where it can be accessed from a desktop

computer, laptop or a mobile phone. The user can interact with the email application as it

is a standard email and most users are familiar with it. It also uses the standard email

address as an example: test1@pemail.suroot.com and webmail address as example for

offline webmail http://192.168.1.7/pemail and for online webmail

http://pemail.suroot.com. File transfer was executed automatically from each mail server

11

to infomediary device whenever they are connected. The disadvantage of using native

DTN is due to the complexity of the system while offline email system offers simplicity

and every part of the offline email system is easy to implement and maintain. It is much

convenient for the users and the email system administrator.

Table 1.2: Cost for DANAWA Wi-Fi Hotspot implementation

Some of DTN email such as Bytewalla 5 did not offer email registration at user side

where it only can be done on administrator side. While this offline email system enables

user to register a new email account from online mail server side.

1.7 Summary of chapters

This chapter gives a brief introduction to the topic and objectives of this thesis.

TCP/IP, the concept of delay-tolerant networking and its architecture discussed in more

details in the next chapter. There is discussion of TCP/IP and DTN comparison along with

how TCP/IP may work as DTN from the standpoint of an email system. In Chapter 3, the

methodology being used is discussed. In chapter 4, the offline email system architecture

12

was designed based on the input from chapter 2 and the approach proposed from chapter

3. In chapter 5, the design concepts from earlier chapters are implemented. The system

test and the result discussed in chapter 6. Final chapter summarizes the thesis by

reviewing what was done and pointing out potential directions for future development.

13

2. LITERATURE REVIEW

In this chapter, the background to Transmission Control Protocol and Internet Protocol

(TCP/IP) and delay and disruption tolerant networking (DTN) presented. The details begin by

describing the TCP/IP layers, internet addressing and how TCP/IP works. Then continue by

describing the basic problem when using internet protocols and outline the reason to use

DTN. After that architecture of DTN is discussed and then the TCP/IP and DTN is compared.

2.1 Transmission Control Protocol and Internet Protocol (TCP/IP)

The Transmission Control Protocol and Internet Protocol (TCP/IP) enable

communications across a vast and heterogeneous collection of networks. Transmission

Control Protocol (TCP) is a reliable data delivery and connection service protocol. TCP

making sure the packet delivery is acknowledged and transmitted as needed.

The TCP/IP offers two basic communication services that operate on top of IP

which is Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). There

are five main layers in TCP/IP which is Application Layer, Host-to-Host Transport Layer,

Network/Internet Layer, Data link/Network Access Layer and Physical Layer [4]. Figure

2.1 shows a TCP/IP Architecture Layers compare against Open Systems Interconnection

(OSI) Model Layers. In this comparison, the TCP/IP application layer includes the OSI

application layer, presentation layer and session layer. Its Host-to-Host transport layer

includes the some part of the OSI session layer and OSI transport layer. The

Network/Internet Layer is a subset of the OSI network layer. The Data link/Network

Access layer includes the OSI Data link Layer. Physical Layers in TCP/IP and OSI Model

14

is on the same level. Mostly TCP/IP Physical Layer is included in Data link/Network

Access layer and also called Network Interface Layer.

Figure 2.1: TCP/IP Protocol Architecture

2.1.1 Detailed explanation in each TCP/IP Layers

Figure 2.2 shows details of TCP/IP Layers. Each layer stacks on top of each other

to form the basic TCP/IP structure and functionality.

15

Figure 2.2: TCP/IP Layer

A) Application Layer

The top layer is an Application Layer. It is used by most applications for network

communication such as Telnet, Hypertext Transfer Protocol (HTTP), File Transfer

Protocol (FTP), Simple Mail Transfer Protocol (SMTP), Domain Name System (DNS),

Routing Information Protocol (RIP) and Simple Network Management Protocol (SNMP).

Figure 2.3 shows the interaction between user and HTTP Server. HTTP is used for

viewing pages on the internet.

Figure 2.3: Hypertext Transfer Protocol (HTTP)

16

Figure 2.4 shows the outbound mail and inbound mail through SMTP. SMTP is

used for mail transfer from a mail server to a client computer.

Figure 2.4: Simple Mail Transfer Protocol (SMTP)

DNS is a naming system for a computer that is connected to the internet. It finds

the nearest DNS server and requests the IP address of the website before it is able to

connect into that website. As an example; facebook.com turns into 69.63.189.11. This

naming system used because facebook.com is far easier to remember than 69.63.189.11.

RIP is used by router to exchange routing information with each other. This gives

computers network information as to where to route the packets through. This gives a

simple easy path for the data to go through, instead of the computer sending the packet to

every other computer on the internet. SNMP enables user to manage server remotely from

other devices in a network.

17

B) Transport Layer

The second layer is Host-to-Host Transport layer. Application layer will inform this

layer that it has some data to be sent. There are two protocols which are Transmission

Control Protocol (TCP) and User Datagram Protocol (UDP). TCP is a reliable one-to-one

connection service. This connection oriented protocol ensures data transmitted accurately.

This layer also manages errors such as packet loss, sequencing and acknowledgement of

how many packets were sent. It negotiates and maintains a connection between two hosts.

It uses the connection to ensure the receiver is ready to receive a packet. It acknowledges

sender that it accepts the packet and retransmit a packet that is not acknowledged by the

receiver. UDP is a one-to-one or one-to-many communication service. It is very unreliable

and connectionless because UDP cannot guarantee delivery of packet data. UDP is used

when the data want to be sent is very small (one packet) and do not a TCP connection or

when the applications provide reliable delivery. It does not check if the receiver is ready

when it sends a packet to a host. When it receives a packet, it does not acknowledge the

delivery because it does not send a large number of messages. UDP required much less

bandwidth than TCP. UDP is used by application layer protocol such as DNS to transmit

short messages such as name query and response. UDP reject corrupted packet as much as

TCP did. Streaming media also use UDP because it is low overhead. The media player

will buffered enough of arriving data to be able to request a new copy of a bad packet

from the sender and receive it before it was needed.

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C) Network layer

The third layer is Network Layer or Internet Layer. This layer is accountable to handle

addressing, packaging and routing functions. This layer has many protocols such as

Internet Protocol (IP), Address Resolution Protocol (ARP), Internet Control Message

Protocol (ICMP) and Internet Group Management Protocol (IGMP). IP is a main protocol

of the Internet Layer. This is an unreliable, connectionless protocol for routing between

hosts. This protocol makes its best effort to get the data to receiving host. If a piece of

data does not get through, this protocol does not attempt to recover that piece of data. It

manages the movement of packet between sending and receiving host. It was responsible

for routing packet to their destination. Dividing them into a size that would fit through the

router among their route and addressing packet. An IP address is a series of number that is

assigned to the physical hardware address of the host. ARP resolves the Media Access

Control (MAC) address which is a unique number given to every network capable device.

It helps to deliver the packets to the receiving host by giving the packets a path to go

through. It looks up physical address that link to an IP address. ICMP is the protocol that

makes sure that all of the packets go through the network. If a packet is not delivered, or

is lost during transmission, this protocol sends another request to send the packet. It

carries error messages and provides the simple diagnostic capability. IGMP is used by

router to track group membership on the subnet and manages groups of hosts such as

computers, routers etc.

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D) Data Link Layer

The fourth layer is the Data Link Layer or Network Access layer. This layer handles

packet transmission. This is designed to give the layers that stack on top of this to be able

to function normally across any network medium such as Ethernet or wireless LAN. The

data link layer is divided into two sub layers which is logical link control (LLC) and

media access control (MAC). LLC is a function required to establish and control of

logical links between local devices on a network to allow different technologies to work

seamlessly with the higher layers. MAC is a procedure to control device access to the

network medium. Usually networks sharing a medium such as a single network cable or a

series of cables that are electrically connected into a single virtual medium. Rules are

needed for managing the medium to avoid conflicts. Example of a MAC is ethernet uses

the CSMA/CD method while Token Ring uses token passing. Data Link Layer also

responsible for Data Framing, Addressing and Error Detection and Handling.

E) Physical Layer

The bottom layer is Physical Layer. The physical layer of the network involves of

hardware elements such as network interface cards, cables and repeaters. Ethernet is the

most common protocol used at the physical layer. Ethernet network such as 10BaseT or

100BaseTX specifies the configuration of the hardware elements such as type of cables

that can be used, the optimal topology such as star topology, bus topology etc. and the

maximum length of cables.

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2.1.2 Internet Addressing

There are 32-bit number IP address known as Internet Protocol Version 4 (IPv4)

and a new 128-bit number IP address known as Internet Protocol Version 6 (IPv6). An

Internet Protocol Version 4 (IPv4) is used in this thesis project and will be discussed. An

IP address is divided into two parts which is network part and host part. The part of a

public IP address that identifies the network is internationally controlled by the Network

Information Center (NIC) located in the Stanford Research Institute in California. The

part that identifies the host is controlled locally at a network level. An Internet Address is

four octets long. The first few bits in the network part of the address help to interpret the

address. These bits indicate the class of the address. A system need to have a public

address when it wants to communicate over the internet. There are five Internet Address

classes which are Class A/B/C/D/E [5].

Address Class summariesshown in Figure 2.5. A host ID that contains all 1s is

meant to broadcast the packet to all hosts specified by the network. If the network ID also

contains all 1s the packet is broadcast on the local network. A host ID that contains all 0s

refers to the network specified by the network ID. A source may send all 0s in the source

address while trying to find out the correct IP address. The machine is then identified by

its MAC address.

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Figure 2.5: Address Classes [5]

There are an IP address ranges reserved for private networks within organizations

as shown in Table 2.1. These addresses will not be allocated by NIC as public IP

addresses for the internet. When a packet goes outside the organization, the local IP

address gets translated into the public IP address purchased by the organization to avoid

clash problems [5].

Class A: 10.0.0.0 to 10.255.255.255 --------- 1 Class A network

Class B: 172.16.0.0 to 172.31.255.255 ------ 16 contiguous Class B networks

Class C: 192.168.0.0 to 192.168.255.255 --- 255 contiguous Class C networks

Table 2.1: Private addressing

Details of reserved IP address and available IP address shown in Table 2.2.

22

Class Address or Range Status

A 0.0.0.0

1.0.0.0 through 126.0.0.0

127.0.0.0

Reserved

Available

Reserved

B 128.0.0.0

128.1.0.0 through 191.254.0.0

191.255.0.0

Reserved

Available

Reserved

C 192.0.0.0

192.0.1.0 through 223.255.254

223.255.255.0

Reserved

Available

Reserved

D 224.0.0.0 through

239.255.255.255

Multicast group

address

E 240.0.0.0 through

255.255.255.254

255.255.255.255

Reserved

Broadcast

Table 2.2: Reserved and available IP addresses [5]

Figure 2.6 shows the Subnet Address. Subnet Addressing is to add another

hierarchical level called the subnet. The advantage of the subnet addressing is to allow

each organization to have its own internet connection within the internet [6].

Figure 2.6: Subnet Address

2.1.3 TCP/IP Operation

Figure 2.7 shows TCP/IP operation of accessing a website. After a user click on

the website link, the application uses DNS client software to request DNS Server to send

an IP address of the destination host. The DNS client software uses UDP and IP to build a

DNS name query message to request the IP address of the host that the user wants to

connect to. Link layer builds an ethernet frame and pass it to the network operating

23

system to be sent to the DNS Server. DNS Server sends back the DNS name query

response message and a target host IP address. It comes in link layer, goes through IP

layer where the address information is stripped off and goes back through UDP where the

packet integrity is checked. Then it goes up to the DNS client software and passes the IP

address to the application.

Figure 2.7: TCP/IP operation of accessing a website

The application then instructs TCP to create a connection. After a TCP connection

is established, the application requests a file from the target host. The target host uses TCP

to segment the file user wanted into packet and send it to the client. Each packet comes

through link layer, through IP and passes it up to TCP which verify the segment integrity

and hold until all files segments had arrived. It also acknowledges receiving of the packet

to the sender. This cycle repeated until the whole files had been reassembled.

24

If the packet arrive does not pass the integrity check, TCP discarded it and not

send acknowledgement to the sender. If the last packet was not acknowledged within a lot

of time, the sender retransmit it. When the last packet arrives, the files are reassembled

and acknowledged to the sender. The client then closed TCP connection. The completed

files passed to the application where users can access it.

2.2 Delay Tolerant Network (DTN)

Delay and disruption tolerant networking (DTN) approach is to overcome the

network connection problem when there is no end-to-end connectivity in Internet

Transport Protocols. DTN is an approach to computer network architecture that seeks to

address the technical issues in heterogeneous network that may lack continuous network

connectivity. The DTN application must tolerate delay and disruption with acceptable

performance in high loss or delay error environments.

2.2.1 Reason to use DTN

Internet Protocols (IP) required end-to-end connectivity. It operates poorly in an

environment with a very long delay path and frequent network partitions which causes by

severe power or memory constraints by end nodes which make the network infrastructure

lacking „always-on‟ environment. Delay and disruption can be caused by long distance

and time. There are some fundamental assumptions in the internet architecture that can

cause a break in the network under long delays and intermittent connectivity such as [7]

[3]:

i. There is always an end-to-end path between source and destination exists.

25

ii. Need to establish at least one round-trip or transmission and response

before any application data can flow. This means that there is a

requirement of the sender and receiver negotiate a connection to regulate

the flow of data.

iii. Retransmissions from the source are good way to provide reliable

communication.

iv. End-to-end loss is relatively small.

v. Endpoint-based security is sufficient to meet most security concerns.

DTN is used to tolerate long delays and intermittent connectivity which is a weakness in

Internet Protocols. DTN is able to enable a connection when there is no end-to-end path

between the source and destination, the round-trip is not needed to regulate the flow of

data, retransmission from data receivers is not in use for repairing errors because there is

no end-to-end path and unlike IP, DTN is ignoring the end-to-end dependency such as in

IP fundamental assumptions (iv) and (v). There are environments that exhibiting some of

these characteristics which are:

i. Space communications where there are high latencies, intermittent

connectivity due to antenna schedule.

ii. Sensor networks when nodes need to power down to conserve energy.

iii. Line of sight radios especially for urban area with wooded/hill

environments.

iv. Mobile networks

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2.2.2 Architecture of DTN

The DTN architecture implements store and forward message switching by

overlaying the bundle layer on top of heterogeneous regional networks. Bundles also

called messages (message switched). The bundle layer stores and forward bundle

fragments between nodes. A single bundle layer protocol is used in all regional networks

and make up a DTN.

DTN designed to use storage within the network to support the store and forward

operation over a networking path as shown in Figure 2.8. IP end to end communication in

between the source and destination must wait for complete path while DTN store and

forward delivery did not need to wait for a complete path. DTN store and forward

delivery will perform incremental progress without end to end path.

Figure 2.8: Store and forward delivery

Application Data Units (ADUs) are a DTN-enabled application that sends

messages of arbitrary length. The bundle layer transformed the ADUs into "bundles"

which is a one or more protocol data unit. Bundles are forwarded by DTN nodes and have

two or more "blocks" of data as shown in Figure 2.9.

27

Figure 2.9: Bundles

Application data or other information in each block used to deliver the containing

bundle to its destinations. Blocks used to hold information in the header or payload

portion of protocol data units in other protocol architectures. It is called "block" instead

of "header" because blocks may not appear at the beginning of a bundle due to particular

processing requirements [8].

Bundle layer as shown in Figure 2.10 support end to end transfer across

heterogeneous network protocol stacks. An essential element of the bundle-based style of

forwarding is that bundles have a place to wait in a queue until a communication contact

is available. Size of storage used in this operation is depending on the system

requirement. The assumptions for this operation as follows:

i. Storage is available and well-distributed throughout the network.

ii. Storage is sufficiently persistent and robust to store bundles until

forwarding can occur.

iii. This "store-and-forward" model is a better choice than attempting to effect

continuous connectivity or other alternatives.

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Figure 2.10: Bundle Space

Bundle Protocol nodes and endpoints are identified by name. Bundle Protocol

names are used Uniform Resource Identifier (URI). Each URI begins with a scheme name

followed by a series of characters where the syntax is defined by the scheme. This is

examples of Bundle Protocol name:

i. dtn://thismachine/ping

ii. dtn:pop:mailto:myemail@gmail.com

The bundle protocol is designed with a Primary Bundle Block, payload block

which contains the ADU data itself and a set of other blocks. The following fields are all

present in the primary bundle block [3]:

i. Creation Timestamp - a concatenation of the bundle is creation time and a

monotonically increasing sequence number such that the creation timestamp is

guaranteed to be unique for each ADU originating from the same source. The

creation timestamp is based on the time-of-day an application requested an

ADU to be sent (not when the corresponding bundle(s) are sent into the

29

network). DTN nodes are assumed to have a basic time synchronization

capability.

ii. Lifespan - the time-of-day at which the message is no longer useful. If a

bundle is stored in the network (including the source is DTN node) when its

lifespan is reached, it may be discarded. The lifespan of a bundle is expressed

as an offset relative to its creation time.

iii. Class of Service Flags - indicates the delivery options and priority class for the

bundle.

iv. Source EID - EID of the source.

v. Destination EID - EID of the destination.

vi. Report-To Endpoint ID - an EID identifying where should be sent. This may

or may not identify the same endpoint as the Source EID.

vii. Custodian EID - EID of the current custodian of a bundle.

The lifespan field is very useful in an attempt to keep the email data in this offline email

system for a longer period of time until it transferred to another device. Another block

such as metadata block is used to identify the content. It could be used to implement

„network as a database‟ and can be encrypted separately from the payload. The payload

block indicates information about the contained payload and the payload itself.

Binding interprets an endpoint identifier (EID) to select the next hop or next

region specific layer the bundle can be forwarded toward its destination. Figure 2.11

shows the bundle layer through every region specific layer. Late binding means that the

binding of a bundle is a destination to a particular set of destination identifiers or

30

addresses does not necessarily happen at the bundle source. Binding might occur at the

source, during transit or at the destination. DTN nodes use some form of persistence

storage and stored bundles can maintain even if the system restarts. Persistence assumes

that storage is available, distributed well through the network and store bundles

sufficiently until forwarding can occur [9].

Figure 2.11: Bundle Overlay

DTN can store bundles at intermediate nodes. It can still route even there is a

waiting time. Primarily the route will be forwarded to the nodes that will have

connectivity later on. In Figure 2.12, data can be transferred directly between user

computer A (PC A) and user computer B (PC B) when both are connected. When the PC

B is disconnected, DTN routes data to Temporary Data Storage and deliver it later to the

PC B. When the PC B is reconnected, data stored in the Temporary Data Storage is

delivered even if PC A is disconnected.

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Figure 2.12: Bundle Routing

Security also can be provided to protect against unauthorized use. Bundle

Authentication Block (BAB) as shown in Figure 2.13 [7], provides hop-by-hop

authentication and integrity protection for the bundle between adjacent bundle nodes.

Unauthorized resource utilization can be prevented by enabling modified bundles to be

detected and discarded at the first node at the destination receiver.

Figure 2.13: Bundle Authentication Block (BAB)

32

2.3 Comparison of TCP/IP and DTN

2.3.1 DTN vs. TCI/IP: Protocol Architecture

Internet layers and DTN layers are identical except that DTN architecture

implements store and forward message switching by overlaying a new protocol layer

called bundle layer. It is placed on top of Transport layers. The bundle layer ties together

the Transport layers and below with application programs to communicate across multiple

regions. Bundles are also called messages switched. The bundle layer stores and forwards

entire bundles or bundle fragments between nodes. A single bundle layer protocol is used

across all networks that make up a DTN. By contrast, the layers below the bundle layer

which is transport layer and below are chosen for their appropriateness to the

communication environment of each region.

Figure 2.14 shows the DTN layer compares to the Internet layer [9]. Bundle

consists of a source-application user data, Control Information provided by source

application and destination application which describes how to process, store, dispose and

handle user data and a Bundle header. Bundles extend the hierarchy of data-object

encapsulation performed by the Internet protocols.

33

Figure 2.14: Comparison Internet Protocol Layers with DTN Protocol Layers

Figure 2.15 shows how bundle-layer encapsulation works in the context of TCP/IP

protocols. A bundle layer may break whole bundles or messages into fragments as an IP

layer may break a whole datagram into fragments. If bundles are fragmented, the bundle

layer at the final destination reassembles them.

34

Figure 2.15: Bundle Encapsulation [9]

On intermittently connected links with long delays, conversational protocols such

as TCP/IP that involves many end to end round trips may take impractical amounts of

times or connectivity failure. To overcome this problem, DTN bundle layers communicate

between themselves using simple sessions with minimal or no round trips as shown in

Figure 2.16. Acknowledgement from the receiving node is depending on the class of

service selected as shown in Figure 2.17. The lower layer protocols that support bundle

layer exchange may of course follow the existing TCP. But on intermittently connected

links with long delays, minimal conversational lower layer protocols can be implemented

[9].

35

Figure 2.16: Minimal conversational lower layer protocols [9]

The bundle layer provides six classes of Bundle Services:

i. Custody Transfer: Responsible of data retransmission to an accepting node. The

sending node can recover its retransmission resources. The accepting node returns

a custodial acceptance acknowledgement to the previous custodian.

ii. Return Receipt: Confirmation to the source. It is a reply to the sender application

that the bundle has been received by the destination application.

iii. Custody Transfer Notification: Notify the source when a node accepts a custody

transfer of the bundle.

iv. Bundle Forwarding Notification: Notify the source when a bundle is forwarded to

another node.

v. Priority of Delivery

vi. Authentication: Verify sender identity and message integrity.

36

In this thesis, the bundle service class (i), (v) and (vi) is used to form a store and forward

overlay network and provide the key capabilities of bundle protocol which is custody

based retransmission and able to cope with intermittent connectivity [10].

Figure 2.17: Class of Bundle Service [9]

2.3.2 DTN Router vs. TCP/IP Router

Internet layer used TCP and IP protocols through the network. TCP operates at

each end point of the path and manages end to end delivery of message segments. IP

operates on all nodes on the path and routes message datagram. Internet routers as shown

in Figure 2.18 do not need a transport layer for routing. They only implemented for

maintenance purposes.

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Figure 2.18: Internet Router [9]

In a DTN, the protocol stacks of all nodes include both bundle and transport

layers. DTN gateways have the same double stack layers as DTN routers as shown in

Figure 2.19. DTN gateways can run different lower layer protocols on each side of their

double stack. This allows DTN gateway to span two regions that use different lower layer

protocols.

Figure 2.19: DTN Router [9]

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2.3.3 Naming and addressing mechanism: Endpoint IDs

Internet address for TCP/IP identifies a node on the internet. Internet address is a

name or IP of a Web site Uniform Resource Locator (URL). Abbreviation of Uniform

Resource Locator (URL) it is the global address of documents and other resources on the

World Wide Web. The first part of the address is called a protocol identifier and it

indicates what protocol to use and the second part is called a resource name and it

specifies the IP address or the domain name where the resource is located. IP addresses

are binary numbers, but they are usually stored in text files and displayed in human-

readable notations, such as 172.16.254.1 (for IPv4), and 2001:db8:0:1234:0:567:8:1 (for

IPv6). The protocol identifier and the resource name are separated by a colon and two

forward slashes. Table 2.3 shows the two URLs below point to two different files at the

domain website.com. The first specifies a file that should be fetched using the FTP

protocol while the second specifies a Web page that should be fetched using the HTTP

protocol.

ftp://www.website.com/file.exe

http://www.website.com/index.html

Table 2.3: TCP/IP Endpoint ID

A URL is one type of Uniform Resource Identifier (URI). URI is the generic term for all

types of names and addresses that refer to objects on the World Wide Web.

39

In a DTN, Bundle Protocol endpoints are identified by name. Bundle Protocol

names are Uniform Resource Identifier (URI). Table 2.4 shows examples of Bundle

Protocol name.

dtn://thismachine/ping

dtn:pop:mailto:myemail@mymail.com

Table 2.4: DTN Endpoint ID

In URI terminology, each URI begins with a scheme name followed by a series of

characters where the syntax is defined by the scheme. Each DTN node has a two part

name consist of a region ID and entity ID as shown in Figure 2.20. Routing between

regions is based only on region IDs, which are bound to their corresponding addresses

throughout the DTN. Routing within regions is based only on entity IDs which are bound

to their corresponding address only within that region. Thus each region uses a different

mapping of entity IDs to address and no bandwidth is needed to copy name address

mappings between regions. Gateways belong to two or more regions and move bundles

between regions. It has multiple region IDs. Region IDs use the same namespace syntax

as the internet DNS [9].

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Figure 2.20: DTN Naming and addressing mechanism [9]

2.4 Network Architecture: Emails

TCP/IP is an end-to-end network. Figure 2.21 shows TCP/IP Mail system

architecture where user A can read, write, send and receive an email directly from internet

mail server to the user B and vice versa. Both computers of user A and user B connected

from its Network Interface Card through the internet router to the internet. The data flow

from each email client to the email server is the same as TCP/IP operation in Chapter

2.1.3.

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Figure 2.21: Internet Mail

Figure 2.22 shows DTN Mail system architecture where there is a separate

networking environment which is an offline local area network and internet connected

network. There are mail servers on both sides which act as a storage for email system. The

storage in between that used to forward the data is called infomediary device.

42

Figure 2.22: DTN Mail

The DTN architecture aims to provide interconnection between several networks which

may have a network disruption because of distance or time delay in data transmission.

DTN user communicates through a DTN network to the internet user, while TCP/IP had

the direct connection to the internet. Each network station requires one DTN mail server

for temporary storage while TCP/IP does not need a local server and had a direct

connection to various internet mail servers. A DTN network requires an infomediary

43

device to transfer and receive data between network stations while TCP/IP does not need

it.

2.5 Similar Works

2.5.1 Bytewalla 5

Bytewalla 5 is a delay tolerant network on Android phones. This project uses

android phones with delay-tolerant networking to connect African rural villages. The idea

is that the android mobile phone will store and carry data from villages to cities. In the

village, the data will be downloaded to android mobile phone from a Wi-Fi access point

for example in a telecentre with no internet connectivity. When in the city, the Android

phone will connect to another Wi-Fi access point and upload the data. This "data mule"

operation will enable emails downloaded at the village to be delivered in the city.

The Bytewalla 5 approaches are the same as this thesis project, the difference is the

data transfer in Bytewalla 5 being done by the DTN application on android phone while

this thesis project data transfer being done by file synchronization application on a server

computer. The details comparison is discussed in chapter 4.4 and illustrated in Table 4.2.

Bytewalla 5 and this thesis project similarly use android phone as a data mule. This data

mule has no Bundle Protocol layer implemented since Bytewalla 5 and this thesis project

only use android phone as Bundle Protocol carriers. The bundle data for Bytewalla 5 is

stored in one single file while this thesis project bundle data is the exact copy of data from

the server with no alteration. Bytewalla 5 uses Ubuntu 8.04 for its DTN Server and this

thesis project use Windows XP for its DTN Server. Bytewalla 5 follows very closely the

design of DTN2, the DTN reference implementation written in C++ by the DTNRG while

44

this thesis project only follows the concept of store and forward in DTN and applied it in

TCP/IP using a suitable application for its email application.

2.5.2 Offline Gmail

Offline Gmail is an email system by Google which is separated from Gmail itself.

It is designed for accessing, managing and sending email while user disconnected from

the web. Offline Gmail originally build based off the tablet version which designed to

function with or without internet access. It contains all the features needed while offline

including organizing, starring, labeling, archiving reading and responding to email. When

sending email offline, the email will be stored in the Outbox. The stored email will

automatically sent when connected to the internet.

Offline Gmail data were updated only on mail client and every user needs to bring

their mail client from offline to online environment. Therefore, it does not need any

database synchronization. Comparison of Offline Gmail and this thesis work is also

discussed in chapter 4.4 and illustrated in Table 4.2. Offline Gmail only available in

Chrome Browser while others such as Firefox needed Google Gears installed. Google

Gears adding new features to the web browser to allow some online files to be used

offline. Unfortunately Google Gears was discontinued on 19 February 2010. The ordinary

mail client being used in this thesis which mean any web browser can be used to access

this offline email system. A third party mail client such as Mozilla Thunderbird and

Microsoft Outlook can be used.

45

2.6 Summary

The DTN architecture aims to provide interconnection between several networks

which may have a poor performance characteristic because of distance or time delay in

data transmission. There are differences in TCP/IP compare to delay tolerant network

protocol. But for some application such as email, there is some similarity in term of

operation where email is a delay tolerant application and no need for end-to-end

connectivity. This makes it possible to implement a TCP/IP email system to work as a

delay tolerant network (DTN) with some additional method to establish a connection

between separate terminal locations by using data mule. In the next chapter, methodology

is discussed.

46

3. METHODOLOGY

This offline email system development is using an iterative approach as illustrated in

Figure 3.1.

Figure 3.1: Iterative Approach

In step 1, the information from various sources was gathered to define the problem and

understand how to actually make the email based on delay tolerant networking. Major

findings are listed below:

i) RFC5050 is a standard for delay networking define by the DTN Research Group

(DTNRG).

ii) CafNet is a Carry and Forward delay tolerant network. It implements a delay-

tolerant network stack that allows applications to send messages to other network

nodes when no end-to-end connectivity is present. CafNet delay-tolerant network

stack consists of a CafNet Transport Layer, CafNet Network Layer and one or

more Mule Adaptation Layers. Each node connected through link mechanisms

47

where the data is physically carried on a USB key. CafNet prioritizes messages

such that data with a higher priority is sent during short bursts of connectivity.

iii) The Architecture of Email [11] and protocols such as TCP/IP, delay tolerant

network (DTN) [10], simple mail transfer protocol (SMTP) [12] and internet

message access protocol (IMAP) [13].

In step 2, the development approach of this offline email system is selected and related

information is identified. CafNet concept is used in this offline email system where the data is

physically carried on a USB Key. The difference is this system data is carried and transferred

automatically when it reaches the terminal location through a wireless local area network and

database synchronization. The standard for delay networking defines by DTN Research

Group (DTNRG) concept applied on data mule and data bundling for its store and forward

operation. There are several possible ways to implement the systems including:

i) Implementation from scratch by following the native DTN protocol

ii) Implementation from scratch by using TCP/IP mail system works as a DTN

mail system

iii) Implementation using existing application to fulfill requirement of TCP/IP

mail system working as a DTN mail system.

The third approach is selected because of the design effort is fairly follows the TCP/IP

thus adding some new design to make it working as DTN, a free and open source software is

used and adaptation of standard email usage to the end user.

In step 3, the system is designed closely as standard TCP/IP email architecture except for

the infomediary device and emails data synchronization implemented to make a connection

48

between separate terminal locations. Step 4, step 5 and step 6 which is implementation,

system testing and result analysis progressed simultaneously starting from setting up a local

server computer, home server accessible to the internet implementation, mail server, mail

client and infomediary device which includes the database synchronization. This is to ensure

every part of the implementation is working accordingly and produced the expected result.

Finally in step 7, documentations were recorded including the system requirement, design,

implementation, testing and result. The documentation progress simultaneously from the

beginning of the project until completed and then finalize at the end. In the next chapter

system design architecture is discussed.

49

4. OFFLINE EMAIL SYSTEM DESIGN ARCHITECTURE

In this chapter the network architecture of the TCP/IP email system and DTN email

system briefly presented. The approach of using a TCP/IP on a DTN email system discussed

by presenting the idea of using TCP/IP mail system as a DTN mail system, analysis of the

idea and abstraction of the TCP/IP mail system based on DTN. Then the application and

network topology being used for this offline email system discussed. After that, network

protocol and details of the design for this offline email system is discussed and then go on to a

design solution for database synchronization.

4.1 TCP/IP Mail System works as a DTN Mail System

Email is a method of exchanging digital messages from a sender to one or more

recipients. Email system commonly operates across the internet and is based on a store

and forward operation. Users on both sides are not required to be online at the same time.

User only needs to connect to mail server briefly for them to read, write or send messages.

Unique of email system is it tolerant to delay and disruption. Email applications are

asynchronous in nature. No need for "always on" connectivity. It does not communicate

most of the time and does not require end-to-end connectivity. Since email system briefly

is a DTN system, TCP/IP email system can be implemented as a DTN email system [14].

Table 4.1 shows a Store, Carry and Forward Scenario for Internet (TCP/IP), Email and

DTN.

50

Scenario Data Delivery Paradigm

Internet

(TCP/IP)

Independently handled packets with immediate forward

or discard

Email

(RFC 5322)

Unitary Transfer of complete emails with Store and

Forward at each intermediate hop

DTN

(RFC 5050)

Unitary Transfer of „Bundles‟ with Store, Carry and

Forward at each intermediate hop node; nodes may be

mobile.

Table 4.1: Store, Carry and Forward Scenario

There are two current internet standard protocols for email retrieval which are Post

Office Protocol (POP) and Internet Message Application Protocol (IMAP). There is a

difference in a way of IMAP and POP control the email Inbox. When using IMAP to

access email Inbox, IMAP actually does not move messages into the computer even

though the message appears on the computer. The message still remains in the mail

server. When using POP to access email Inbox, POP checks the server for new messages

and download them to the computer and then deletes the messages from the mail server.

Figure 4.1 shows the difference between IMAP and POP. In this thesis, IMAP is used to

ensure the message remains on the mail server for data synchronization between

infomediary device and both side mail servers.

Figure 4.1: IMAP vs POP

51

There are several commercials and free mail server available such as hMailServer,

AtMail etc. HMailServer is a free mail server for Microsoft Windows. It supports the

common email protocols such as IMAP, SMTP and POP3. ) HMailServer can easily be

integrated with many existing webmail systems. It has a flexible score-based spam

protection using Bayesian spam filtering which is an email filtering based on statistical

technique. This technique classified collection of words to identify spam email. It also can

attach email to the virus scanner to scan all incoming and outgoing email [15]. AtMail is a

webmail client written in PHP. It provides an elegant Ajax webmail client for existing

IMAP mail servers, with less bloat and a focus on an intuitive, simple user interface.

Atmail supports a variety of platforms. It offers a web interface feature [16]. In this thesis

work, hMailServer is used for a mail server since it is easy to use, open source, free and

Windows based application.

There are also several commercials and free mail client available such as

SquirrelMail, Rmail, roundcube. SquirrelMail is a standards-based webmail package

written in PHP. It includes built-in pure PHP support for the IMAP and SMTP protocols,

and all pages render in pure HTML 4.0 (with no JavaScript required) for maximum

compatibility across browsers. It has very few requirements and is very easy to configure

and install. SquirrelMail has all the functionality as an email client, including strong

MIME support, address books, and folder manipulation. Rmail is a Java[TM] library for

sending and receiving e-mail messages with Mime extensions (attachments, html), SMTP

(sending) and POP3 (receiving) protocols [17].

52

Roundcube webmail is a browser-based multilingual IMAP client with an application-like

user interface. It provides full functionality as an e-mail client, including MIME support,

address book, folder management, message searching and spell checking. Roundcube

webmail is written in PHP and requires the MySQL, PostgreSQL or SQLite database. Its

plugin API is easily extendable and the user interface is fully customizable using skins

which are pure XHTML and CSS 2.Roundcube webmail is used in this thesis work since

it supports IMAP and browser based which mean of portability [18].

4.2 Idea and Concept Analysis

The email system is based on store and forward operation. This operation is

matched with the DTN system operation where it needs storage to store a data from the

sender before it forwarded to a receiver. The native DTN protocol is much complicated

for the average user. The DTN system is mostly Linux based. Average user mostly not

familiar with command line and DTN Endpoint ID. TCP/IP email implementation based

on DTN concept is much convenient for the average user. The usage is much familiar

since it uses native TCP/IP approach for the system. Average users mostly familiar with

Windows operating system and this approach maintain the TCP/IP Endpoint ID.

Offline Gmail provides the ability for the user to read and manage their email in an

offline environment. But, it is still required each user to move their device to the internet

connected area for the pending email being sent, receive and synchronize. The advantage

for this thesis work is there is only one device need to move in between terminal location

to establish a network. The user can read, send and manage their account normally at each

terminal location. The updated data such as new email will be pending in the local mail

53

server until that data is collected by the infomediary device and transferred to the internet

connected mail server.

4.3 Abstraction of TCP/IP Mail System based on DTN

There are several of the DTN Email system exists such as Bytewalla 5, DTNmailex

and offline Gmail. Mail client for this thesis offline email system, Bytewalla 5 and offline

Gmail is a web based. User can use a web browser to access the webmail. There are two

mail servers for the offline email system which is an offline local mail server and an

online local mail server. Bytewalla 5 also has two mail servers which are offline DTN

mail server and online DTN mail server while there is only internet mail server available

for offline Gmail.

DTN implementation of this offline email system is based on TCP/IP. The

advantage of this approach is the user can use the offline email system as it was a normal

email system and may not even noticed it was a DTN email system. The Bytewalla 5 uses

a native DTN implementation designed by Delay Tolerant Networking Research Group

(DTNRG) while offline Gmail uses Google Gears.

This offline email system use Windows operating system for its web server, mail

server application and database synchronization application. Bytewalla 5 uses Ubuntu

8.04 LTS a Linux operating system for its DTN mail server and offline Gmail is browser

based where it use Google mail server.

Data mule for being used is an android phone where it acts as an infomediary

device. The Samba File sharing application is used to enable a network storage

connection with a mail server where it receives an email data from database

54

synchronization software to be sent to the destination mail server. Bytewalla 5 also use

android phone as a data mule. It has three main applications running which is DTNService

for handling DTN communication, DTN Manager to configure, monitor and manage

DTNService and DTNApps (DTNSend for sending messages and DTNReceive for

receiving messages). Offline Gmail use Web Browser with Google Gears to store some

online files to be used offline.

Temporary storage location for a pending email data in this offline email system

and Bytewalla 5 is stored in email server computer while offline Gmail storage is in the

mail client computer. Endpoint ID for this offline email system and offline Gmail is a

standard email address where there is a local part, @ sign, and domain part. As an

example: test1@email.com. [19]. Table 4.2 shows a comparison of this thesis project

offline email system with Bytewalla 5 and offline Gmail.

55

DTN Email

Features

Offline Email

based on Delay

Tolerant

Network (DTN)

Bytewalla 5 Offline Gmail

Mail Client Web based Web based Web based

Mail Server -Offline local

mail server

-Online local mail

server

-Offline DTN mail server

-Online DTN mail server

Internet mail

server

DTN

implementation

TCP/IP based Native DTN Google Gears

Operating

System

Windows Linux (Ubuntu 8.04 LTS) Browser based

Data mule Android phone

running Samba

File sharing

-Android phone running

DTNService for handling DTN

communication, DTN Manager

to configure, monitor and

manage DTNService, DTNApps

(DTNSend for sending

messages and DTNReceive for

receiving messages)

Web Browser

with Google

Gears

Temporary

Storage

location

Email server

computer

Email server computer Email computer

client

Endpoint ID test1@email.com dtn:pop:mailto:test1@email.com test1@email.com

Table 4.2: Comparison of DTN Email

Table 4.3 shows the comparison of selected free web server Uniserver 7.1.4 and

XAMPP 1.8.1. Both web servers offer the same feature for a setting up a Windows home

server. Uniserver has been selected because it has a Cron feature which can be used with

56

DtDNS service. Cron is a job scheduler allowing scripts to be run automatically at a

certain time or date. It is used to update the external IP address of the server computer to

the DtDNS service.

Web server

Features

Uniserver 7.1.4 XAMPP 1.8.1

Size (MB) 14.5 99.0

License Berkeley Software

Distribution (BSD)

GNU General Public License

(GPL)

Apache HTTP Server 2.2.19 2.4.3

PHP 5.4.8 5.4.7

MySQL 5.5.15 5.5.27

phpMyAdmin 3.4.3.2 3.5.2.2

OpenSSL 1.0.1c 1.0.1c

Portable application Yes + Multi server Yes

Cron Yes No

Table 4.3: Comparison of Web server

Table 4.4 shows the comparison of mail server software for hMailServer, AtMail

and citadel. HMailServer is selected since it is free, open source and Windows based

application.

57

Mail Server

Features

hMailServer AtMail Citadel

Operating System Windows Linux Linux

SMTP Yes Yes Yes

POP3 Yes Yes Yes

IMAP Yes Yes Yes

Webmail Yes Yes Yes

Database Yes Yes Yes

License GNU General Public

License (GPL)

Commercial GNU General Public

License (GPL)

Table 4.4: Comparison of Mail Server software

Table 4.5 shows a comparison of free mail client for Roundcube and SquirrelMail.

Both Mail Clients offer the same features. Either one can be used. Roundcube is selected

for this thesis work.

Mail Client

Features

Roundcube SquirrelMail

Operating System Cross platform Cross platform

License GNU General Public

License (GPL)

GNU General Public

License (GPL)

User Interface Web Web

New user registration Yes by using a plugin Yes by using a plugin

Table 4.5: Comparison of Mail Client

58

Table 4.6 shows comparison of File Synchronize software for FreeFilesync,

Synchronize It and rsync. FreeFilesync is selected for this thesis project because of it a

free Open Source for Windows and support for batch file for automated file

synchronization.

File Synchronize

Features

FreeFilesync Synchronize It rsync

Operating System Windows/Linux Windows Linux/Windows

License GNU General Public

License (GPL)

Commercial GNU General Public

License (GPL)

Portable Yes Yes Yes

Detect conflict Yes No No

Detect rename Yes No No

Detect move Yes No No

Scheduling Yes Yes No

Table 4.6: Comparison of File Synchronize software

Table 4.7 shows the comparison of the suggested infomediary device. Android

phone is used in this thesis work because of its size, weight and battery life.

59

Infomediary Device

Features

Android phone

(LG Optimus 3D P920)

Laptop

(Lenovo Z460)

Battery Li-Ion 1500 mAh 6-Cell Li-ion5200 mAh

Battery Life Standby up to 450 h Standby 56Wh

Size 4.3” 14”

Weight 168g 2.24 Kg

Storage 8GB storage + 32GB

MicroSD

500GB HDD

WLAN Wi-Fi 802.11 b/g/n Wi-Fi 802.11b/g/n

Table 4.7: Comparison of Infomediary Device

4.4 Application and Network Topology

Figure 4.2 shows the offline email system architecture. Each Wi-Fi access point

uses a star topology. Each node connected by using a mobility device which is called

infomediary device. There is only one online mail server needed and offline mail server

can be more than one for each rural village. Offline mail server and online mail server have

the same required software installed which is Uniform Server, hMailServer, roundcube and

FreeFilesync. Infomediary device has Samba File sharing installed to enable the data

transfer from each node. Online mail server configured to be able to connect to the internet

and accessible from the internet. This is the transit point for this offline email system to be

able to send or receive email from internet email such as Gmail, Hotmail etc.

60

Figure 4.2: Offline Email System Architecture

61

This offline email system is using TM Streamyx Dynamic 1 MBps Internet

Service Provider (ISP) with conjunction with DtDNS service. Dynamic IP is used by

Internet Service Provider (ISP) so that one external IP address can be assigned to several

users. ISP's use Sticky Dynamic IP Addressing and do not change the external IP address

very often and only change the external IP address as ISP deem it necessary. DtDNS

service used to enable the system to be accessible from the internet without worrying about

frequently change of external IP address.

4.5 Network Protocol Design

Figure 4.3 shows the flow of the email in the networking protocol. This email

queue delay period was set by the email system administrator. It can be set to minimum

value 0 and maximum value is 2147483647 due to maximum value for a 32-bit signed

integer (int32) supported by a SQL database. This means that the email data can be kept in

temporary storage for a maximum period of 2147483647 minutes equal to 4083 years.

The user at the offline server will write and send an email at application stage where the

email data will be stored in the offline mail server for a maximum period of 4083 years

before it being discarded. If the offline or online email server computer was shutdown or

restart, the pending email remains in the database and will eventually discard when the

time delay exceeded. Once the offline mail server connected to infomediary device, the

pending email data will move through TCP in Transport layer where the application use

NetBIOS over TCP/IP (NBT) to request NetBIOS name server to send an IP address of

the destination NetBIOS at infomediary device [20]. Link layer builds an ethernet frame

and pass it to the network operating system to be sent to the NetBIOS name server. The

62

NetBIOS name server sends back the NetBIOS name. After the TCP connection is

established, the application transfers the file to the target host which is infomediary

device.

Figure 4.3: Networking Protocol flow

On the other side, when infomediary device establishes a connection with an online mail

server computer, the email data is transferred to the mail server database. The data are

transferred packet by packet and when the last packet arrives, the files are reassembled

and completed files passed to the application layer. Figure 4.4 shows the Store and

forward operation between mail server A, infomediary device and mail server B. Each

node contains storage to store the email data.

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Figure 4.4: Store and Forward

4.6 Offline Email System Detail Design

Figure 4.5 shows offline email system network protocol layout. When email is

sent, a message was sent from the sender mail server Mail Transport Agent (MTA). Both

MTA side communicates using Simple Mail Transfer Protocol (SMTP) Server. The

recipient MTA delivers the email to the Mail Delivery Agent (MDA) which stores the

email as it wait for the user to accept it. Internet Message Access Protocol (IMAP) used

for retrieving email on MDA.

64

Figure 4.5: Offline Email System Network Protocol layout

MDA is protected by login system where it needs a username and password. Email

is retrieved by using Mail User Agent (MUA) where it is called an email client on the user

device. Webmail is used for this thesis work. If the email destination is not in the local

network, the email delivery is pending and the data remain in the mail server storage until

it is transferred to the infomediary device. This operation matches the bundle protocol

(BP) where the data being stored temporarily and later forwarded to next destination.

When the infomediary device establishes a network connection with the offline mail

server, the mail database synchronization application will transfer the email data from

offline mail server to infomediary device and retrieve new email data from infomediary

device to the offline mail server. The new email data from infomediary device which is

65

received from online mail server will be in the new pending email delivery where it is

being sent immediately since the destination was in the network until it reaches the user to

accept it. The Dynamic Host Configuration Protocol (DHCP) is a network protocol used

to configure devices that are connected to a network. The SSID and security codes for the

access points are chosen by the administrators. This offline email system used static IP

addresses. Both the online and offline server computers are configured as DHCP servers.

This enables the servers to allocate IP addresses to any DHCP client.

Figure 4.6 shows online email system network protocol layout. The process is the

same as when the infomediary device establishes a network connection with online mail

server, the mail database synchronization application will retrieve email data from

infomediary device to online mail server and transfer the new email data from online mail

server to the infomediary device to be sent to the offline mail server. The email data from

infomediary device which is received from the offline mail server will be in pending

delivery where the delivery is executed immediately because of the destination is

available in the network until it reaches the user to accept it.

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Figure 4.6: Online Email System Network Protocol layout

4.7 Database Synchronization

Data synchronization is important in the DTN email system. This part of the

system is to ensure the email data can be transferred from the email storage to the

infomediary device and reach the destination storage. Data synchronization operates in the

email server computer on both sides. When the email server computer receives an

available connection of infomediary device, the data synchronization will begin where the

mail server will grab the new data from infomediary device and transfer a new data from

mail server to infomediary device at the same time. There are several options available for

this purpose which is FreeFilesync, Synchronize It, Beyond Compare 3, rsync etc.

67

FreeFilesync is a free Open Source software for Windows and able to compare and

synchronize files and synchronize folders. It supports filters, file sizes greater than 4GB

and creation of batch files for automated synchronization. Synchronize It is a commercial

folders comparison and data synchronize for Windows. It also supports command line

switches for unattended synchronization. Beyond Compare 3 is the commercial folders

comparison and data synchronization for Windows. Rsync is a batch of folders and file

synchronization tools for UNIX systems. Rsync can copy or display directory contents

optionally using compression and recursion. FreeFilesync is suitable for this thesis project

being it is a free Open Source for Windows and support for batch file for automated file

synchronization.

Infomediary device is working as a data mule. It carries data storage between data

communication link. It is able to automatically load and unload the data when arrives at

its terminal location. In this thesis, infomediary device requires to establish network

connection at the terminal location which is a mail server and Storage to store the email

data. A laptop, Tablet PC or a Smartphone can be used for this purpose. An Android

Smartphone is used in this thesis project because of its less power consumption and

prolongs battery life. An Android Smartphone is smaller and easy to move in between

terminal location and able to establish a connection through Wi-Fi. Samba File Sharing is

used to provide network storage for the Terminal Location for data synchronization.

4.8 Summary

This system main requirement consists of a two mail servers, mail client at each

mail server and an infomediary device. This offline email system architecture depends on

68

data synchronization among DTN nodes for four primary purposes which are bundled and

fragment identification, routing with scheduled and bundle expiration time computations.

This design architecture can enable the email to be sent locally in an offline environment

or online environment and a delay network connection between this two environment

created by infomediary device. This system offers an advantage compare to conventional

Wi-Fi Hotspot and native DTN implementation in term of simplicity, user experience and

affordability. System implementation is discussed in the next chapter.

69

5. SYSTEM IMPLEMENTATION

This chapter started by explaining the system platform and environment. Then the issues

arise during implementation and system requirement is discussed. This offline email system is

implemented by using suitable existing application to fulfill requirement of TCP/IP mail

system working as a DTN mail system. The details of this offline email system

implementation are discussed starting from the server computer, web server application,

external IP address solution, mail server, mail client, explanation of the database

synchronization process, related data for synchronization, database synchronization

application and System Control Graphical User Interface (GUI).

5.1 System Platform and Environment

Operating system for server computer is Windows XP 32bit because of convenient

development and maintenance. Infomediary device runs on android 2.3.5 to support

interoperability with Windows XP 32bit. User can use any standard web browser from

any platform such as Linux or MAC to access this offline email system. There are two

types of networking environment involve in this offline email system which is offline

networking and online networking. Offline networking is a local area network with no

internet connectivity while online networking is a local area network with internet

connectivity. Offline mail client, offline mail server and offline server computer are

running on offline networking. Online mail client, online mail server and online server

computer are running on online networking. Infomediary device is working in both offline

and online networking environment.

70

5.2 Implementation Issues

There are some implementation issues that limiting the design and operation of the

offline email system as per below:

i) The offline email system accessibility is limited by the wireless local area network

(WLAN) coverage range. The D-Link DWL-2100AP was used as a Wi-Fi access

point at the offline mail server. Table 5.1 shows the effective range of D-Link

DWL-2100AP. Details of D-Link DWL-2100AP shown in Appendix C. Riger DB

108-WL Wireless ADSL Modem 2/2+was used as a Wireless ADSL Modem at

the online mail server with the same effective range of D-Link DWL-2100AP as

shown in Table 5.1.

Indoors Outdoors

Transfer Rate Effective Range Transfer Rate Effective Range

54 Mbps 30 Meters 54 Mbps 95 Meters

48 Mbps 32 Meters 11 Mbps 290 Meters

36 Mbps 37 Meters 6 Mbps 420 Meters

24 Mbps 45 Meters

18 Mbps 60 Meters

12 Mbps 68 Meters

9 Mbps 77 Meters

6 Mbps 90 Meters

Table 5.1: D-Link DWL-2100AP indoors and outdoors coverage range

71

ii) The speed of database synchronization process limited by the network data

transfer rate of the Wi-Fi access point at each server computers. The D-Link

DWL-2100AP used as a Wi-Fi access point at the offline mail server has network

data transfer rate up to 54 Mbps which is 54 megabits per second for Standards

IEEE 802.11b/g. Riger DB 108-WL Wireless ADSL Modem 2/2+was used as a

Wireless ADSL Modem at the online mail server. The network data transfer rate is

up to 54 Mbps for Standards IEEE 802.11b/g. It is the same as shown in Table 5.1

for D-Link DWL-2100AP. The ADSL, ADSL2 and ADSL2+ network data

transfer rate are up to 24 Mbps.

iii) Infomediary device battery life is important to ensure the data can be moved from

both offline and online side without interruption. LG Optimus 3D (P920) can offer

up to 250 hours in standby mode as shown in Appendix D.

iv) User only can register a new email account at online mail server side. This offline

email system did not enable email registration page on the offline mail server

because of conflict may occur with online mail server registration database or

several other offline mail server registration databases. Since an offline mail server

can be more than one and only one online mail server required, registration system

only implemented on online mail server to avoid database conflict. Data conflict

most likely happen when same username registered on several mail servers. This

will cause database synchronization cannot be done when either data might be

deleted or both.

72

5.3 Requirements

Table 5.2 shows the hardware requirements for this system which is consist of one

offline server computer, offline side wireless access point, android phone as an

infomediary device, one online server computer and online side Wireless ADSL Modem.

No Items Details

1.

Offline server computer

(Details in Appendix B)

Laptop Lenovo Z460Intel Core i5-460M 2.53GHz

RAM: 4GB RAM

Storage: 500GB HD

OS: Windows XP SP3

NIC: Realtek Semiconductor RTL8101 PCIe Fast

Ethernet Adapter

2.

Online server computer

Desktop PC Intel i3 2.93GHz

RAM: 4GB RAM

Storage: 700GB HD Samsung HD754JJ

OS: Windows XP SP3

NIC: Realtek Semiconductor RTL8101 PCIe Fast

Ethernet Adapter

73

3.

Offline side Wireless

Access Point

(Details in Appendix C)

D-Link DWL-2100AP

Data Transfer Rate: 54 Mbps

Data Link Protocol: IEEE 802.11b, 802.11 Super G,

IEEE 802.11g

Interfaces: 1 x Network - Ethernet 10Base-T/100Base-

TX - RJ-45

4.

Infomediary device

(Details in Appendix D)

LG Optimus 3D P920

OS: Android 2.3.5

Storage: 8GB internal storage + 32GB MicroSD

WLAN: Wi-Fi 802.11 b/g/n

5.

Online side Wireless

ADSL Modem

(Details in Appendix E)

Riger DB 108-WL Wireless ADSL Modem 2/2+

Data Transfer Rate: 54 Mbps

Support IEEE 802.11b/g, ANSI T1.413 Issue 2, ITU

G.992.1 (G.dmt) Annex A,C, ITU G.992.2 (G.lite),

ITU G.992.3 ADSL2 (G.dmt.bis), ITU G.992.4 ADSL

(G.lite.bis), ITU G.992.5, ADSL2+, Extended

Reach(READSL2)

Table 5.2: Hardware Requirements

74

Table 5.3 shows the software needed for this system which is Uniform Server

7.1.4, hMailServer 4.4.4, Roundcubemail 0.7.2, FreeFilesync 4.6 and Samba File sharing

build 111107m.

No. Items Details

1. Uniform Server

7.1.4

Uniform Server is a WAMP package used to run a server on any MS

Windows OS based computer. It is small and mobile to download or move

around and can also be used or setup as a production or live server [21].

2. hMailServer

4.4.4

HMailServer is a free mail server for Microsoft Windows. It supports the

common e-mail protocols (IMAP, SMTP and POP3) and can easily be

integrated with many existing web mail systems. It has a flexible score-

based spam protection and can attach to virus scanner to scan all incoming

and outgoing email [15].

3. Roundcubemail

0.7.2

Roundcube webmail is a browser-based multilingual IMAP client with an

application-like user interface. It provides full functionality of an e-mail

client, including MIME support, address book, folder manipulation,

message searching and spell checking [18].

4. FreeFilesync

4.6

FreeFilesync is a free and open source folder and file synchronization

program that features a beautiful, two pane user interface and a host of

powerful options. It can compare files by their content or by file size and

date, synchronize files and subfolders, process multiple pairs of folders at

once, load/save folder comparison sessions, create batch jobs that can be

run from the command line, and can handle cloned. It also offers UniCode

75

and Network support and also a portable [22].

5. Samba File

sharing build

111107m

Enable access of android device storage over Wi-Fi as a Windows shared

folder [23].

Table 5.3: Software Requirements

There are two additional requirements for this thesis which are TM Streamyx

Dynamic 1 MBps Internet Service Provider (ISP) and DtDNS. 1 MBps internet

connection provided by TMnet Internet Service Provider is sufficient for this offline email

system. DtDNS service is a DNS hosting and DNS management services with a focus on

dynamic DNS and dynamic IP address management [24]. DtDNS was used to solve the

dynamic IP limitation of the internet connection to ensure accessibility of the system from

the Internet.

5.4 Implementation Details

This offline email system consists of the server computer to run a mail server for

both offline and online side, web server application to deliver web access to the user, mail

server, mail client, synchronization database application on the server computer,

infomediary device as a data mule and a system control graphical user interface.

5.4.1 Server Computer

The offline server computer is connected to a wireless access point using ethernet

cable CAT5. The IP address configured to 192.168.1.7, subnet mask to 255.255.255.0,

default gateway to 192.168.1.1 and DNS Server to 192.168.1.1. While, the online server

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computer is connected to Wireless ADSL Modem using ethernet cable and the IP address

also configured with the same address as the offline server computer. This similar

configuration is needed for a success database synchronization process at both server

computers.

5.4.2 Web server Application

Web server application running on the server computer to deliver webmail page

access to the client. Web server application for this system is Uniserver 7.1.4. Web server

application file extracted to respective location which is C:\PEmailOffline\UniServer for

offline environment server computer. Starting Uniserver will open a Server Administrator

page in a default Web Browser. The Server Administrator page only accessible by the

server computer admin. Admin of the server computer used this page to configure the

username and password for the admin panel configuration, private server configuration

and private secure server configuration (SSL) and MySQL server configuration. MySQL

is a relational database management system (RDBMS) used by the web server application.

Files C:\PEmailOffline\UniServer\www\.htaccess edited with text editor and next four

lines commented by adding “#” to allow external access as per Table 5.4 below:

#Order Deny,Allow

#Deny from all

#Allow from 127.0.0.1

#Allow from ::1

Table 5.4: Enable Web server External Access Script

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This will disable server security limitation access from localhost only and enable access

using the server IP address. The PHP value for maximum message size located in “.

htaccess” file in "...UniServer\www\pemail" and “php.ini” file in

"...UniServer\usr\local\php" also configured to upload maximum file size is 10MB, post

maximum size is 50MB and memory limit is 64MB. This value is to give a size limit of

attachment file.

This offline email system uses MIME standards and do not specify any file size

limits for maximum upload size to be allowed [25]. Limits for maximum upload size can

be configured in web server setting file “php.ini”, where the maximum attachment size is

2147483647 MB which is a maximum value for a 32-bit signed integer supported by a

SQL database. The maximum message size is unlimited by setting the value to zero. The

maximum disk space that the account may use is limited to the server computer hard disk

storage available space. If the hard disk is full, the limit is reached and the account will

not be able to receive any more email. If a maximum message size is specified, the mail

server will reject messages larger than that size. It is recommended to set a maximum

message size limit to prevent the server from any types of attack. As an example, attackers

could send a big size message and fills the server hard disk which will cause a problem to

the server computer.

This offline email system maximum message size is set to 50MB. The mail server

will reject messages larger than this size. Email content size is small and usually 1MB or

less. This offline email system maximum message size is set to 10MB. Limiting

maximum attachment size default value 10MB is acceptable to ensure the mail server

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network performance is not dropping when multiple users uploading a very big file at the

same time to the mail server. Limiting the size of email attachments to 10MB is also a

safe setting for the maximum size of an email since other email services commonly used

10MB as a maximum size of an email attachment. If the maximum size of an email

attachment is 30MB or greater than 10MB and this offline email system is successfully

send the email to the receiver, there is no guarantee that the receiver can receive the email

since there is a different maximum size limitation of email attachment on every email

service. Gmail limiting the size of email attachments to 25MB with no specified limit to

the number of attachment as long the total size is 25MB [26]. Yahoo Mail allows user to

upload up to 50 files to an email message as long as the total message size remains under

25MB [27].

Every email account has total allocated maximum size storage. If an email is sent

to this account when the quota has been used, the mail server will deliver a notification to

the sender containing the information that the quota for the recipient had been reached.

After that, the email message will be dropped. Each email in this offline email system

allocated size is set to 250MB.

5.4.3 External IP Address

The Uniform Server setup for online web server is the same as for offline server.

The IP address used is 192.168.1.7. The difference is that the online server is connected to

the internet. The Internet Service Provider being used in this research is TM Streamyx

Dynamic 1 MBps. This ISP provides an internet with dynamic IP address connection. The

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external IP address will change periodically depending on the ISP. This leads to an access

problem to existing setup to act as a server. To solve that problem, DtDNS service is used.

DtDNS is a complete provider of DNS hosting and DNS management services with a

focus on dynamic DNS and dynamic IP address management. There is a free domain

name provided and tracking software to automatically update IP address as it changes.

This free service enables a dynamic IP address to host a service just as it had a static IP

address. The DtDNS service hostname details for this offline email system configured

where the hostname is pemail and domain is suroot.com.

Cron is used to integrate DtDNS with Uniform Server. Cron originated from a

UNIX environment. It is a job scheduler allowing scripts to be run automatically at a

certain time or date. Cron has been integrated into Uniform Server 7.1.4. The script has

been pre-configured to run the three scripts which are Drupal Cron, Moodle Cron and

DtDNS automatic IP updater. Only script for DtDNS automatic IP updater used for this

offline email system. Cron automatic update default period is every ten minutes. DtDNS

automatic IP updater has been pre-configured, but it is disabled by default on Uniserver.

To enable DtDNS automatic IP updater, Cron configuration file in

C:\PEmailOffline\UniServer\unicon\main\run_cron.php edited by changing lines in the

section list of scripts to be run as shown in Table 5.5 (A). Then those lines uncomment as

shown in Table 5.5 (B).

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A

// $cmd = 'start ..\..\usr\local\php\php-win.exe

..\..\plugins\dtdns_updater\dtdns_updater.php';

// pclose(popen($cmd,'r')); // Start detatched process

B

$cmd = 'start ..\..\usr\local\php\php-win.exe

..\..\plugins\dtdns_updater\dtdns_updater.php';

pclose(popen($cmd,'r')); // Start detatched process

Table 5.5: Enable Cron

DtDNS account details where the hostname is pemail.suroot.com and password

configured in a Cron script configuration file located in:

“C:\PEmailOnline\UniServer\plugins\dtdns_updater\dtdns.ini”

Uniserver uses binary code 1 which means perform the function while 0 means ignore and

do nothing. Default value "7" is a total of 1+2+4 which will run the Apache, MySQL and

Index page processes. Cron Binary code is "16".Total binary code value for Apache,

MySQL and Cron is 19. Figure 5.1 shows the binary codes have been assigned.

Figure 5.1: Uniform Server Binary Codes

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To enable automatic Cron on Uniserver, file in

“C:\PEmailOffline\UniServer\unicon\main\includes\config.inc.php” edited as shown in

Table 5.6. This binary code value will enable the Apache, MySQL, Index page processes

and Cron run when the Uniserver program started.

$server_standard = 19;

$server_service = 19;

Table 5.6: Enable Cron automatic update on Uniserver

Apache, MySQL and Cron need to be configured to start up all at once. Cron can

be configured to run automatically when the servers are started by editing file in

C:\PEmailOnline\UniServer\unicon\tray_menu\UniTray1.ini. Under “LEFT MENU”

there are lines to control Server Start and Stop. Programs or batch files that run either of

the control scripts start_servers.php or stop_servers.php must include a single binary

coded parameter. If this parameter is missing defaults value 7 are used. A parameter

overrides any default settings this allows independent control of a particular function.

Then, default binary code should be changed from 7 to 19 for these lines "%PHP%\php.exe";

Parameters: " -n %ServerConMain%\start_servers.php 19"; as per Table 5.7 below:

;=== LEFT MENU ============

[Menu.Left]

Type: item; Caption: "Start UniServer (Apache MySQL)"; Action: shellexecute; FileName:

"%PHP%\php.exe"; Parameters: " -n %ServerConMain%\start_servers.php 19"; ShowCmd: hidden; Glyph: 9

Type: item; Caption: "Stop UniServer (Apache MySQL)"; Action: shellexecute; FileName:

"%PHP%\php.exe"; Parameters: " -n %ServerConMain%\stop_servers.php 19";ShowCmd: hidden; Glyph: 11

Table 5.7: Apache. MySQL and Cron startup script configuration

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5.4.4 Mail Server

Offline mail server and online mail server should use the same configuration. This

is to enable mail data synchronization where both mail servers should share the same

content and configuration for data synchronization purposes. HMailServer version 4.4.4

being used as mail server application. HMailServer installed to respective location as

“Full installation” with Server and Administrative tool component included. A database

server is an external database which is a new hMailServer database created on MySQL

Server and running on Uniserver. The database server address is “localhost” and TCP Port

is 3306. The database name for this offline email system is “pemail” and should be the

same for both offline server computer and online server computer. HMailServer security

password configured accordingly. The created database location is:

“C:\PEmailOffline\UniServer\usr\local\mysql\data\pemail”

The domain name for this offline email system is pemail.suroot.com which can be

configured accordingly at hMailServer Administrator welcome pages. A public host name

also configured as “mail.pemail.suroot.com” under Settings -> Protocols -> SMTP,

Delivery of e-mail tab. SMTP relayer setting depends on ISP either port 25 is open or not.

If port 25 is open, a free SMTP relayer can be used such as “mail.hmailserver.com 25”.

Since 03 November 2008, TM Streamyx was blocking outgoing port 25 [28]. TM had

suggested using the configuration for SMTP relayer as “smtp-proxy.tm.net.my”.

The port can be tested by running the command: telnet smtp-proxy.tm.net.my 25

and the result should a success connection as in Figure 5.2. The offline mail server is not

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needed to use suggested SMTP relayer setting, but it is recommended to use the same

configuration since whenever the offline mail server connected to the internet, the offline

email system can communicate directly without the need of infomediary device.

Figure 5.2: TMnet SMTP relayer

5.4.5 Mail Client

Roundcubemail version 0.7.2 served as Mail Client application for an offline mail

client and an online mail client. Mail Client is a mail user agent (MUA). It is a web

application used to access and manage the email. The application file extracted into

respective location and the folder renamed into “pemail”. In this thesis work, the location

is:

“C:\PEmailOffline\UniServer\www\pemail.”

Mail Client installation performed by entering the URL: http://localhost/pemail/installer

into the web browser. The configuration for both offline mail client and online mail client

should be the same for the database synchronization purpose where the product_name,

syslog_id and the database name is pemail, the database server is localhost and the

database username and password configured accordingly for administrator access. IMAP

Settings for offline mail client configured where the IP address of the offline server

computer which is 192.168.1.7 was used as a default host address. This IP address is

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accessible only in LAN. IMAP common port which is 143 was set for default port with

username domain is “pemail.suroot.com” which is used for email address. SMTP settings

for offline mail client configured where the IP address of the offline server computer also

used for the SMTP Server address. SMTP common port is 25. The current IMAP

username and password was used for SMTP authentication. This option can be configured

under SMTP settings.

SMTP settings for online mail client configured where the domain name of the

online server computer which is “pemail.suroot.com” was used for the SMTP Server

address. This domain is accessible through internet. SMTP common port is 25. The

current IMAP username and password also used for SMTP authentication and configured

under SMTP settings.

When the configuration is completely configured, this mail client configuration is

saved through “create config” button where it will create two configuration files which are

“main.inc.php” and “db.inc.php”. This configuration files transferred into a mail client

application folder such as:

“C:\PEmailOffline\UniServer\www\pemail\config”

The configuration can be tested through “Test config” button. The configuration is correct

and working when everything was remark with “OK”. Then the “installer” folder can be

removed from mail client application folder.

The files “.htaccess” in temp, logs and config folder which located in mail client

folder “C:\PEmailOffline\UniServer\www\pemail” need to be configured to enable access

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of this Mail Client. This can be done by commenting next two lines in “. htaccess” files as

shown in Table 5.8 by adding “#”.

#Order allow,deny

#Deny from all

Table 5.8: Enable Mail Client External Access Script

New user registration page only required on online mail server to avoid database

synchronization conflict between offline mail system and online mail system.

Configuration for online mail client is the same as for the offline mail client except that

online mail client includes the “new user registration” page. Plugins “roundcube-0.7.2-

bundle-v.1.0” required for enabling “new user registration” page. The plugins can be

found at http://code.google.com/p/myroundcube/downloads/list. The required plugin files

which are bundle register, taskbar and captcha plugins were transferred into email plugins

folder which is located at “C:\PEmailOnline\UniServer\www\pemail\plugins”. New

plugins were enabled in an active plugins configuration file at

“C:\PEmailOnline\UniServer\www\pemail\config” by editing “/config/main.inc.php” file

and append new plugin names into configuration directive as shown in Table 5.9.

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// ----------------------------------

// PLUGINS

// ----------------------------------

// List of active plugins (in plugins/ directory)

$rcmail_config['plugins'] = array('taskbar','register','captcha');

Table 5.9: Enable New User Registration Page Script

Then, taskbar plugin “/plugins/taskbar/config.inc.php.dist” file can be activated by

renaming into “/plugins/taskbar/config.inc.php”, captcha plugin

“/plugins/captcha/config.inc.php.dist” file can be activated by renaming into

“/plugins/captcha/config.inc.php” and register plugin

“/plugins/register/config.inc.php.dist” file can be activated by renaming into

“/plugins/register/config.inc.php”. HMailServer SQL database driver name to be used in

registering new users is “'hmail_sql_db_4402” and need to be set by editing file

“/plugins/register/config.inc.php” as shown in Table 5.10.

/* driver */

$rcmail_config['register_driver'] = 'hmail_sql_db_4402';

Table 5.10: hMailServer SQL Database driver name setting

Default domain name and other domains are “pemail.suroot.com” and set up as shown in

Table 5.11.

$rcmail_config['webadddoms']['default'][] = "pemail.suroot.com";

Table 5.11: Domain name setting

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5.4.6 Process of Database Synchronization

The related email data that need to be synchronized located in offline server

computer, online server computer and infomediary device. The database synchronization

performed by comparing the email data reside in server computer and infomediary device.

Database synchronization application on server computer will check if the email data path

on the server computer and email data path on infomediary device availability. When

infomediary device connected in the server computer local network, the networking path

of the email data on infomediary device will be discovered by database synchronization

application. Database synchronization application will start comparing the email data

between server computer and infomediary device. If there is no change of email data

between server computer and infomediary device, the synchronization process is finished.

When there is new email data found, the database synchronization application will start

retrieve the new email data from infomediary device and transfer new email data to the

infomediary device. Figure 5.3 shows the flowchart of the database synchronization.

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Figure 5.3: Process of database synchronization

5.4.7 Related Data for Synchronization

Related data that need to be synchronized is mail server data and web server data.

Mail server data contain the pending email data that need to be synchronized. This email

data consists of a folder named with the email domain name, folders named based on

email username and email messages in a ".eml" format. This email message contains the

full message headers, DomainKeys Identified Mail (DKIM) Signature and full

Multipurpose Internet Mail Extensions (MIME) encoded message content. Email message

consists of three main components which is message envelope, message header and the

message body. Full message headers formed by message envelope header and message

header. The message envelope header contains a delivery parameter such as sender and

receiver email address. This data used by SMTP for transporting email messages.

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Message header structured into fields such as From, To, CC, Subject, Date, and other

information about the email [19]. DomainKeys Identified Mail (DKIM) Signature

provides a method for validating a domain name identity that is associated with a message

through cryptographic authentication [29]. Message body uses a MIME version 1.0

format. MIME redefines the format of messages to allow textual message bodies in

character sets other than US-ASCII, an extensible set of different formats for non-textual

message bodies, multi-part message bodies and textual header information in character

sets other than US-ASCII [25].

Web server data contain the webmail client MySQL database. This MySQL

database stores the user login details, email messages and email settings. Whenever new

user was registered, the new complete transaction of email messages and new updated

email settings will be stored in this MySQL database.

5.4.8 Database Synchronization Application

There are two database storage devices involve in each synchronization process

which are between server computer and infomediary device. The process of the database

synchronization is the same on both offline server computer and online server computer.

Infomediary device acted as a data mule where later on, the database storage being

synchronized with the server computer. Both side synchronization performed by the

database synchronization application. FreeFilesync version 4.6 used as a database

synchronization application and running on a server computer. Samba File sharing

application bridged the data flow between server computers and infomediary device.

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Server computer synchronization discussed in Part A and infomediary device discussed in

Part B.

Part A: Server Computer Synchronization

Offline server computer and online server computer configured identically for the

database synchronization purpose. FreeFilesync installed as “Portable” to respective

location such as “C:\PEmailOffline\FreeFileSync” to enable the application mobility

features where it can be transfer and use on other machine. These options remove

dependencies on a dedicated computer and enable the portable database synchronization.

Following the configuration in Part B, infomediary device can be accessed by

opening “Windows Explorer” and entering location path such as “\\data mule”. Accessing

this path for the first time will require the username and password as per configuration on

infomediary device. Windows XP automatically store logon information for network

locations. This stored username and password can be edited later from the user accounts

menu in windows control panel. When infomediary device is connected to the server

computer network, the server computer automatically have access to the infomediary

device network sharing path. New folders to stored email data for database

synchronization created in infomediary device network sharing path such as “\\data

mule\share2\”. Two email data path for storing mail server data and web server data

which are required for database synchronization created in infomediary device storage as

the example shown in Table 5.12.

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\\data mule\share2\pemailsync\UniServer\pemail

\\data mule\share2\pemailsync\hMailServer\Data

Table 5.12: Infomediary Device Data Synchronization Folder

Mail data will be stored in this location in infomediary device each time database

synchronization process occurs. Email data path for storing mail server data and web

server data which are required for database synchronization at the server computer

configured in the FreeFilesync application as the example shown in Table 5.13.

C:\PEmailOffline\UniServer\usr\local\mysql\data\pemail

C:\PEmailOffline\hMailServer\Data

Table 5.13: Mail Server Data Synchronization Folder

Email data paths in the server computer configured in the left side of FreeFilesync

while email data path for the infomediary device configured in the right side of

FreeFilesync as shown in Figure 5.4.

Figure 5.4: Database Synchronization Path

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Comparison settings for “compare” is configured to “File Content” and

“synchronize” is configured to “Automatic”. File data comparisons can be performed

manually by using the “Compare” button and file data synchronization can be performed

manually by using the “Synchronize…” and “Start” button. Both files data comparison

and synchronization function can be executed with a particular setting by using a batch

job. A batch job is a set of programs processed with a sequence of commands to be

executed listed in a file which often called a batch file. This sequence of commands

executes as a single unit job. A batch job is useful for automatic file synchronization.

Batch job created with the same configuration where the “Compare” configured to “File

Content” and “Synchronize…” configured to “Automatic”. Batch Settings configured

with “Show progress log” enable and “Error handling” configured to “Ignore errors”.

Batch job saved as “SyncJobOffline.ffs_batch” in C:\PEmailOffline\FreeFileSync.

Mail server data and web server data paths that need to be monitor configured in

RealtimeSync as the example shown in Figure 5.5.

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Figure 5.5: Realtime Synchronize Setting

“StartFFS.bat” configured in “command line” section. The program will run when “Start”

button clicked, and remain idle in the system tray. Whenever any changes made on these

respective paths or when all paths are available will trigger data synchronization process

command line script, “StartFFS.bat”. Table 5.14 shows the batch script for

“StartFFS.bat”. "FreeFileSync.exe SyncJobOffline.ffs_batch" line will execute File

Synchronization application, FreeFileSync with a batch job setting

"SyncJobOffline.ffs_batch".

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"start C:\PEmailOffline\hMailServer\DataDirectorySynchronizer.exe" will execute

hMailServer Data Directory Synchronizer. This tool checks all message files in the data

folder and search files with extension .eml. HMailServer will insert the message into user

account if any .eml file found in the user directory and the message will be inserted into

the delivery queue if the .eml file found in the Data root directory [30].

“C:\PEmailOffline\UniServer\unicon\program\unidelay.exe 20" line gives a twenty

second delay to allow text to be read. Both hmailserver and Uniserver need to be restarted

for the mail database synchronization update. "start

C:\PEmailOffline\hMailServer\Bin\stop_hmailserver.bat" line will stop the hmailserver

service and "start C:\PEmailOffline\UniServer\Stop_Server.bat" line will stop Uniserver

service. "start C:\PEmailOffline\UniServer\Start_Server.bat" line and "start

C:\PEmailOffline\hMailServer\Bin\start_hmailserver.bat" line will start the hmailserver

service and Uniserver service.

FreeFileSync.exe SyncJobOffline.ffs_batch

start C:\PEmailOffline\hMailServer\DataDirectorySynchronizer.exe

C:\PEmailOffline\UniServer\unicon\program\unidelay.exe 20

start C:\PEmailOffline\hMailServer\Bin\stop_hmailserver.bat

start C:\PEmailOffline\UniServer\Stop_Server.bat

C:\PEmailOffline\UniServer\unicon\program\unidelay.exe 10

start C:\PEmailOffline\UniServer\Start_Server.bat

start C:\PEmailOffline\hMailServer\Bin\start_hmailserver.bat

Table 5.14: StartFFS.bat Script

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Part B: Infomediary Device

Samba File sharing used for data receiving applications from the server computer.

Infomediary device which is an android phone connected to the Wi-Fi access point of

offline server computer or online server computer to perform mail database

synchronization. When a network connection is established, Samba File sharing

application will show “network fileshare” status as “disabled-not running” for the first

time running. Samba File sharing application preference configuration for password,

username, Workgroup name, NetBIOS name configured accordingly as the example

shown in Figure 5.6. Second Shared Folder selected under “Other File share Settings”

since the database will be stored in the external SD card. External SD card is used because

it offers larger storage size up to 32GB.

Password:

Username: SDCARD

Workgroup: SDKCH (Should be the same as server computer Workgroup)

NETBIOS Name: data mule

Figure 5.6: Samba File sharing application configuration

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Samba File sharing application can be configured to stay connected mode. This

mode available under “Wake Locks” menu with the available option which is “Screen

Wake Lock”, “Wi-Fi Wake Lock” and “Multicast Lock”. This is useful to ensure the Wi-

Fi stay active and connected as soon as the respective Wi-Fi access point (AP) available

the in infomediary device networking range. New folder such as “pemailsync” created in

“\\data mule\share2\” to store mail server data and web server data.

5.4.9 System Control Graphical User Interface (GUI)

There are three main system controls identified for this thesis project offline email

system which are a server computer, mail server and database synchronize as shown in

Figure 5.7. Server computer status can be viewed through Uniform Server system tray

menu. The server computer Status button is an additional option as an alternative to view

the networking status of the server computer. Exit button is to close the System Control

Graphical User Interface and did not affect server computer, mail server and database

synchronize operation. Server computer system control was executed through a batch file.

Server computer application script configured and placed in a Uniform Server folder.

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Figure 5.7: Pemail system control Graphical User Interface (GUI)

There is a single central control architecture for Uniform Server which is located

in folder UniServer\unicon\main. All server control requests such as Unitray, batch files

and Apanel are passed to this core for processing. The advantage of this core control is to

reduce external scripts complexity. These core controls consist of four Command-line

interface (CLI) scripts. CLI is a mean of interaction in the form of lines of text (command

line) to issue a command to the program. These CLI scripts are split into two parts which

are standard program and service. Standard program part has files for start-stop while

service part has files install-uninstall service respectively. Apache and MySQL are a

tracker file controlling the interaction between standard program part and service part as

shown in Figure 5.8.

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Figure 5.8: Uniform Server Core Control

Start batch script (Start_Server.bat) implemented as shown in Table 5.15 and Stop batch

script (Stop_Server.bat) as shown in Table 5.16.

@echo off

cls

COLOR B0

mode con:cols=65 lines=20

TITLE UNIFORM SERVER - Start

rem ###################################################

rem # Name: Server_Start.bat

rem # Created By: The Uniform Server Development Team

rem # Edited Last By: Mike Gleaves (ric)

rem # V 1.0 28-6-2009

rem ###################################################

rem ### working directory current folder

pushd %~dp0

usr\local\php\php.exe -n unicon\main\start_servers.php 19

Start.exe

rem ..\unicon\program\unidelay.exe 10

rem pause

rem ### restore original working directory

popd

exit

Table 5.15: Offline Server Computer Start script (Start_Server.bat)

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Both script parameters for start_servers.php and stop_servers.php line configured

with binary code 19 which include the control server for Apache, Mysql and Cron as

reference to Uniform Server Binary Codes shown in Figure 5.1. "Start.exe" line is to start

the UniTray while "unicon\program\unidelay.exe 10" line gives a ten second delay to

allow text to be read [21].

@echo off

cls

COLOR B0

mode con:cols=65 lines=20

TITLE UNIFORM SERVER - Stop

rem ###################################################

rem # Name: Stop_Server.bat

rem # Created By: The Uniform Server Development Team

rem # Edited Last By: Mike Gleaves (ric)

rem # V 1.0 28-6-2009

rem ##################################################

rem ### working directory current folder

pushd %~dp0

usr\local\php\php.exe -n unicon\main\stop_servers.php 19

rem ..\unicon\program\unidelay.exe 10

rem pause

rem ### restore original working directory

popd

exit

Table 5.16: Offline Server Computer Stop script (Stop_Server.bat)

Mail server application script implemented as shown in Table 5.17. Both scripts which are

“start_hmailserver.bat” and “stop_hmailserver.bat” placed in a mail server folder such as

“…PEmailOffline\hMailServer\Bin”.

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CLI script Script filename

net start hmailserver

exit

start_hmailserver.bat

net stop hmailserver

exit

stop_hmailserver.bat

Table 5.17: Mail Server Start and Stop script

“Database Synchronize” start button will execute real-time synchronization application,

“RealtimeSync.exe” which is located in a database synchronization application folder

such as “…PEmailOffline\FreeFileSync”.

5.5 Summary

In this offline email system, server computer is responsible holding the mail

server, webmail client which is running on a Web server application and the database

synchronization application. External IP address access with a dynamic IP problem was

solved with DtDNS and an automatic Cron job scheduler. Database synchronization

approach is implemented to enable email data flow through infomediary device and

bridging the no end-to-end network of offline server computer and online server

computer. The GUI is implemented for an easy access and control of the respective

applications in this offline email system. System test is discussed in the next chapter.

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6. SYSTEM TEST

In this chapter, the offline email system is tested and the result is discussed. The system

test started with new account registration test, connectivity test, delay test, limitation of

infomediary device movement speed while passing by the server computer, the size of data

test, types of data test, multiple of senders and receivers test and multiple of communications

test.

6.1 New Account Registration Test

6.1.1 Test Design

New account registration test carried out at online mail server and internet. Sample

user offlineA and user offlineB new account registration performed at the local online

mail server while sample user onlineC and user onlineD new account registration

performed through the internet which is outside of the local network as shown in Figure

6.1. Then account synchronization test carried out to ensure all the account can be

accessed at the offline mail server, online mail server and through the internet.

Figure 6.1: New Email User Registration

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6.1.2 Expected Outcome

Expected outcome from this test as per below:

i) Registration page accessibility: Email account registration page can be

access from online mail server local area network and from the internet.

ii) User registration: New email account which is offlineA, offlineB

successfully created from online mail server local area network and

onlineC and onlineD successfully created from the internet.

iii) Email account access: All email accounts which are offlineA, offlineB,

onlineC and onlineD can be access from the online mail server local area

network, from the internet and from the offline mail server local area

network after database synchronization.

6.1.3 Test result

The registration page is only accessible from LAN which connected to online mail

server or through internet. Characters such as "? * | \ / < >" does not supported in creating

an email account. Figure 6.2 shows new account registration test result through internet at

webmail address which is http://pemail.suroot.com by following the register button,

filling in the anti spam security code and setup the username and password for the new

email. The same procedure also performed on the local online mail server at the local

webmail address which is http://192.168.1.7/pemail.

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Figure 6.2: New account registration test result

Database synchronization application on the online server computer is

synchronizing the mail database into infomediary device and transferring it to the offline

server computer. All the new email accounts which are created in this test such as

offlineA@pemail.suroot.com, offlineB@pemail.suroot.com, onlineC@pemail.suroot.com

and onlineD@pemail.suroot.com was tested on the offline environment network. All

emails are successfully login, working and listed in the mail server administrator pages.

Test result is produced by actual conduct test.

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6.2 Connectivity Test

6.2.1 Test Design

There are six test samples as in Figure 6.3. Test 1 involves sending and receiving

emails between user offlineA and user offlineB through offline environment LAN. Test 2

involves sending and receiving emails between user onlineC and onlineD through an

online environment LAN. Test 3 involves sending and receiving emails between user

onlineC and an internet email such as Gmail through the internet. Test 4 involves sending

and receiving emails between user offlineA and user onlineC through infomediary device

with DTN based technique. Test 5 involves sending and receiving emails between user

offlineA and Gmail through an infomediary device with a DTN based technique where the

mail data is being transitioned on the online mail server before it being sent to the Gmail.

Test 6 involves sending and receiving emails between user onlineC and Gmail from the

online environment LAN directly to the internet.

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Figure 6.3: Test sample

6.2.2 Expected Outcome

Expected outcome from all five test samples as shown in Figure 6.3 as per below:

Test 1: Connectivity test between offline users at offline mail server in Test 1

should show that user offlineA and user offlineB can successfully send and

receive email.

Test 2: Connectivity test between online users at online mail server in Test 2

should show that user onlineC and user onlineD can successfully send and

receive email.

Test 3: Connectivity test between online user at online mail server and internet

user in Test 3 should show that user onlineC and gmail user can

successfully send and receive email. This is the same result for Test 6.

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Test 4: Connectivity test between offline user at offline mail server and online user

at online mail server in Test 4 should show that user offlineA and user

onlineC can successfully send and receive email with the help of

infomediary device.

Test 5: Connectivity test between offline user at offline mail server and internet

user in Test 5 should show that user offlineA and gmail user can

successfully send and receive email with the help of infomediary device.

6.2.3 Test Result

The email system functionality result for each test 1, test 2, test3, test4, test 5 and

test 6 shown in Table 6.1. Test result is produced by actual conduct test. Test 1 is testing

send and receives of email between user offlineA and user offlineB, test 2 is testing send

and receives of email between user onlineC and user onlineD, test 3 is testing send and

receives of email between user onlineC and Gmail through internet, test 4 is testing send

and receives of email between user offlineA and user onlineC, test5 is testing send and

receives of email between user offlineA and Gmail and test 6 is testing send and receives

of email between user onlineC and Gmail from local mail server to the internet. All email

communication tests contain sample attachment files.

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Sample

Test

Sender Receiver Result

1 offlineA@pemail.suroot.com

webmail: http://192.168.1.7/pemail

Offline Mail Server

offlineB@pemail.suroot.com

webmail: http://192.168.1.7/pemail

Offline Mail Server

Success

2 onlineC@pemail.suroot.com

webmail: http://192.168.1.7/pemail

Online Mail Server

onlineD@pemail.suroot.com

webmail: http://192.168.1.7/pemail

Online Mail Server

Success

3 onlineC@pemail.suroot.com

webmail: http://pemail.suroot.com

Internet

cyclonmaster@gmail.com

webmail: https://mail.google.com

Internet

Success

4 offlineA@pemail.suroot.com

webmail: http://192.168.1.7/pemail

Offline Mail Server

onlineC@pemail.suroot.com

webmail: http://192.168.1.7/pemail

Online Mail Server

Success

5 offlineA@pemail.suroot.com

webmail: http://192.168.1.7/pemail

Offline Mail Server

cyclonmaster@gmail.com

webmail: https://mail.google.com

Internet

Success

6 onlineC@pemail.suroot.com

webmail: http://192.168.1.7/pemail

Online Mail Server

cyclonmaster@gmail.com

webmail: https://mail.google.com

Internet

Success

Table 6.1: Send and receive email test result on each node

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6.3 Delay Test

6.3.1 Test Design

Minutes between every retry setting defines how many minutes mail servers

should wait before every retry delivering emails to other servers. The default value is 60

minutes. As explained in chapter 4.2, this offline email system queue delay period was set

by the email system administrator where the email data can be kept in temporary storage

for a maximum period of 2147483647 minutes equal to 1491308 days. This offline email

system delay time was set to 30 minutes. The email data will remain and not discarded for

30 minutes until a next retry. When every email was sent successfully from the sender to

the receiver in the delay period range of time, its mean the mail data are remaining stored

in mail server and synchronization is successfully performed.

Number of retries setting defines the number of times mail server should try to

deliver an email when the deliveries failed. Email failed to deliver when the receiving

mail server such as Gmail cannot be reached or the network is not available. The default

value of number of retries setting is 4 retries. This means hMailServer will try a total of 5

times before giving up and returning an error message to the sender. The maximum value

is 2147483647 retries. This offline email system number of retries was set to maximum

2147483647. This means that the email data is kept in the database for 30 minutes until

next retries and repeated until maximum 2147483647 retries. The email data will only

discard when the maximum retries value which is 2147483647 is exceeded. Delay period

test performed for sending email with delay 60 minutes, 1440 minutes and 10080 minutes.

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6.3.2 Expected Outcome

This offline email system expected to be able to tolerate with a long period of

delay communication between offline network environment and online network

environment. The email data expected to be remain in the mail server and keep in pending

status for 60 minutes ( one hour), 1440 minutes (one day) or 10080 minutes (one week)

and successfully reach the destination after process of database synchronization

completed.

6.3.3 Test Result

This offline email system queue delay period was set to30 minutes with maximum

retries value 2147483647. The status of the queue message available in the mail server

administrator control pages. The email from user offlineA was sent to user onlineC and

found that pending email data was remaining on the Mail Server after a period of testing

time as shown in the Table 6.2. Test result is produced by actual conduct test.

Sample test Date & time

email sent

Date & time email

received Delay period

(Minutes)

Result

1 09 June 2013

0800H

09 June 2013

0900H

60 Mail data remain

2 09 June 2013

0900H

10 June 2013

0900H

1440 Mail data remain

3 09 June 2013

1000H

16 June 2013

1000H

10080 Mail data remain

Table 6.2: Delay Period Test Result

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6.4 Limitation of Infomediary Device Pass by Movement Speed

6.4.1 Test Design

The time required for database synchronization process between infomediary

device and server computer calculated to find the recommended movement speed of the

infomediary device for ensuring the database synchronization is complete. It is to find an

ideal period of time infomediary device should remain in Wi-Fi access point range of

server computer. The range of the network connection between infomediary device and

Wi-Fi access point of server computer measured. The transfer rate of Wi-Fi access point is

compared with the offline email system storage read and write speed limitation. Based on

this transfer rate, size of data and network range, the speed movement of the infomediary

device passes by server computer network connection can be calculated. This test is to

ensure the database synchronization process is performed completely successfully.

6.4.2 Expected Outcome

This test is expected to produced is the maximum recommended speed of

infomediary device movement through the Wi-Fi range of the server computer based on

identified value of:

i) Server computer effective Wi-Fi range for outdoors

ii) Size of data sample data

iii) Transfer rate based on Wi-Fi access point transfer rate, online server

computer storage read and write speed, offline server computer storage

read and write speed and infomediary device storage read and write speed.

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6.4.3 Test Result

Wi-Fi range for outdoors is 95 Meters with data rate transfer 54 Mbps which is 54

megabits per second second where when the data size to be transferred is 54MB. One byte

is equal to eight bits. This means 54 Mbps which is 54 megabits per second is equal to

6.75 MBps which is 6.75 megabytes per. The range and speed of the synchronization

operation is shown in Figure 6.4. The Wi-Fi range and data rate transfer depends on the

wireless access point specifications and the size of data being transferred. The D-Link

DWL-2100AP used as a Wi-Fi access point for this offline email system where the

effective range is shown in Table 5.1.

Online server computer storage is Samsung HD754JJ with sequential reads speed

is 89.30 MBps and writes speed is 130.3 MBps. Infomediary device storage is Kingston

Micro SD with sequential reads speed is 20.04 MBps and writes speed is 2.03 MBps.

Offline server computer storage is Western Digital WD5000BEVT with sequential reads

speed is 54.42 MBps and writes speed is 28.79 MBps. The read and write speeds of

Online server computer storage, informediary device storage and offline server computer

result is produced by CrystalDiskMark version 3.0.2. The comparison of transfer rate,

read speed and write speed is summarized in Table 6.3.

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No Device Read Speed Write Speed

1 Wi-Fi Access Point:

Offline server computer (D-Link DWL-2100AP)

Online server computer (Riger DB 108-WL

Wireless ADSL Modem 2/2+)

Outdoors operation transfer rate is

6.75 MBps with effective range 95

meters

2 Online server computer storage (Samsung

HD754JJ)

89.30 MBps 130.3 MBps

3 Infomediary device storage (Kingston Micro SD) 20.04 MBps 2.03 MBps

4 Offline server computer storage (Western Digital

WD5000BEVT)

54.42 MBps 28.79 MBps

Table 6.3 Transfer rate, read speed and write speed comparisons

The transfer rate of data during database synchronization is limited by infomediary

device storage write speed which is 2.03 MBps. This means that when the size of data to

be transferred is 54MB with the transfer rate is 2.03 MBps and range between server

computer and infomediary device is 95 meter, the speed of infomediary device movement

through the Wi-Fi range of the server computer is:

x transfer rate = x 2.03 MBps = 3.57 m/s

Equation 6.1 Infomediary device movement speed

Based on calculation, the maximum recommended speed of infomediary device

movement through the Wi-Fi range of the server computer is 3.57 m/s equal to 12.85

km/hr or less. The data synchronization is not completed if the infomediary device

movement exceeds this speed. It is also recommended if the infomediary device is staying

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for about five to ten minutes at the server computer. This will allow for database

synchronization to complete successfully.

Figure 6.4: Range and speed for mail data synchronization

6.5 Size of Data Test

6.5.1 Test Design

This offline email system maximum allowed size of file attachment is 10MB and

maximum message size is set to 10MB. Attachment file with size greater than 10MB is

unable to be uploaded and if the total size of the message is greater than 10MB, the email

will be failing to send. Each email accout in this offline email system allocated size is set

to 250MB. This size depends on the server computer storage size. If the email account

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used up all 250MB quota, the email account will fail to send or receive any email.

Different size of data test performed with an attachment size of 1MB, 5MB, 9MB, 10MB,

20MB and two 10MB files.

6.5.2 Expected Outcome

This offline email system expected to allow user uploading an attachment files

with the maximum size of 10MB. The email message is expected to be send successfully

with limitation of message size is 50MB or below.

6.5.3 Test Result

Email size content limitation is depending on the hard disk available storage. This

offline email system maximum attachment size is 10MB, maximum message size is

50MB and allocated maximum size storage for each email is 250MB. A test result of

sending an email with attachment size 1MB, 5MB, 9MB, 10MB, 20MB and two 10MB

files shown in the Table 6.4. Test result is produced by actual conduct test.

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Test Attachment Size Total message size Email delivery result

1 1MB 1.4MB Upload attachment success

Send email success

2 5MB 6.9MB Upload attachment success

Send email success

3 9MB 12MB Upload attachment success

Send email success

4 9.97MB 13MB Upload attachment success

Send email success

5 20MB - Fail to upload attachment

6 2 x 9.97MB 27MB Upload attachment success

Send email success

7 6 x 9.97MB 81MB Upload attachment success

Fail to send email

Table 6.4: Testing email data size

6.6 Types of Data Test

6.6.1 Test Design

Email tested sending with file attachment. Any file format with various extensions

is supported for attachment. The administrator can block attachments with certain

extensions on the mail server. The default setting for block attachments is for files with

extension bat, cmd, com, cpl, csh, exe, inf, lnk, msi, msp, reg, scf and scr. These types of

file extensions are recommended to be blocked as to prevent any virus attack.

Types of attachment files tested for pdf, txt, office file format such as doc, docx,

xls, xlsx, ppt and pptx, compress file format such as zip, rar and 7z, image file format

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such as jpg, png, gif and bmp, video file format such as mp4, avi and mpg and audio file

format such as mp3, wma and ogg.

6.6.2 Expected Outcome

This offline email system is expected to allow user uploading any type of data

with various extensions as an email attachment except the block attachment for files with

extension bat, cmd, com, cpl, csh, exe, inf, lnk, msi, msp, reg, scf and scr.

6.6.3 Test Result

Types of data tested by uploading a file with various extensions as an email

attachment. File type attachment test result shown in the Table 6.5. Test result is produced

by actual conduct test.

Test File Types Attachment result

1 pdf, txt Upload attachment success

2 doc, docx, xls, xlsx, ppt and pptx Upload attachment success

3 zip, rar and 7z Upload attachment success

4 jpg, png, gif and bmp Upload attachment success

5 mp4, avi and mpg Upload attachment success

6 mp3, wma and ogg Upload attachment success

7 bat, cmd, com, cpl, csh, exe, inf, lnk, msi,

msp, reg, scf and scr

Fail to upload attachment

Table 6.5: Testing types of data attachment

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6.7 Multiple of Senders and Receivers Test

6.7.1 Test Design

SMTP servers may reject messages from mail server if there are too many

recipients in a single email. This is because the receiving SMTP server may think that the

email message is spam because of sending to a large number of users. The number of

recipient uses in the same delivery can be set in the mail server configuration menu. The

mail server will disconnect from the recipient server when this number has been reached,

connect again and continue with the remaining recipients. This test is to ensure this offline

email system can it differentiate different senders sending an email at the same time. This

test performed by sending an email between two senders to one receiver which is user

offlineA and user offlineB to user onlineC, three senders to one receiver which is user

offlineA, user offlineB and user onlineD to user onlineC, one sender to two receivers

which is user offlineA to user onlineC and user onlineD and one sender to three receivers

which is user offlineA to user offlineB, user onlineC and user onlineD.

6.7.2 Expected Outcome

Expected outcome from this test as per below:

Test 1: User offlineA and user offlineB successfully send email to user onlineC.

Test 2: User offlineA, user offlineB and user onlineD successfully send email to

user onlineC.

Test 3: User offlineA successfully send email to user onlineC and user onlineD.

Test 4: User offlineA successfully send email to user offlineB, user onlineC and

user onlineD.

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6.7.3 Test Result

Test result for multiple sender and receiver sending and receiving email at the

same time through infomediary device with DTN based technique shown in the Table 6.6.

Test result is produced by actual conduct test.

Test Number of sender Number of receivers Email delivery result

1 2 1 Send email success

2 3 1 Send email success

3 1 2 Send email success

4 1 3 Send email success

Table 6.6: Multiple sender and receiver test result

6.8 Multiple of Communications Test

6.8.1 Test Design

This test is to check the maximum number of simultaneous SMTP connections to

the server. An unlimited number of simultaneous connections will be allowed by

configured mail server number of connection values to zero. This value is set to zero by

default. This is to ensure no overwrite email occurs and check this offline email system

capability of handling the same sender sent an email a few times to multiple receivers.

This test performed with a two way communication. The sender sends an email to

receiver and receiver send email to sender at the same time. There are three scenarios

tested which are between two users, four users and six users as shown in Figure 6.5.

Another test is sender send multiple emails to the receiver to ensure are not overwritten in

the mail server database.

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Figure 6.5: Multiple communication

6.8.2 Expected Outcome

Expected outcome from all three test samples as shown in Figure 6.5 as per below:

Test 1: User A1 successfully sends email to user B1, while user B1 successfully

receives email from user A1 and vice versa.

Test 2: User A1 and A2 successfully sends email to user B1 and user B2, while

user B1 and user B2 successfully receive email from user A1 and user A2

and vice versa.

Test 3: User A1, user A2 and user A3 successfully send email to user B1, user B2

and user B3, while user B1, user B2 and user B3 successfully receives

email from user A1, user A2 and user A3 and vice versa.

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6.8.3 Test Result

Test 1 is to test two way communications between two users. User A1 successfully

sends email to user B1, while user B1 successfully receives email from user A1 and vice

versa. Test 2 is to test two way communications between four users. User A1 and A2

successfully sends email to user B1 and user B2, while user B1 and user B2 successfully

receive email from user A1 and user A2 and vice versa. Test 3 is to test two way

communications between six users. User A1, user A2 and user A3 successfully send email

to user B1, user B2 and user B3, while user B1, user B2 and user B3 successfully receives

email from user A1, user A2 and user A3 and vice versa. The result of multiple

communication shown in Table 6.7. Test on multiple emails send from users at offline

network environment to users at online network environment shows that the emails is

successfully send and received. Test result is produced by actual conduct test.

Test Sender Receiver Email delivery result

Sending email Receive email

1 User A1 User B1 User A1 to User B1 - success

User B1 to User A1 - success

User B1 from User A1 - success

User A1 from User B1 - success

2 User A1 User B1 User A1 to User B1 - success

User B1 to User A1 - success

User B1 from User A1 - success

User A1 from User B1 - success

User B2 User A1 to User B2 - success

User B2 to User A1 - success

User A1 from User B2 - success

User B2 from User A1 - success

User A2 User B1 User A2 to User B1 - success

User B1 to User A2 - success

User B1 from User A2 - success

User A2 from User B1 - success

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User B2 User A2 to User B2 - success

User B2 to User A2 - success

User B2 from User A2 - success

User A2 from User B2 - success

3 User A1 User B1 User A1 to User B1 - success

User B1 to User A1 - success

User B1 from User A1 - success

User A1 from User B1 - success

User B2 User A1 to User B2 - success

User B2 to User A1 - success

User B2 from User A1 - success

User A1 from User B2 - success

User B3 User A1 to User B3 - success

User B3 to User A1 - success

User B3 from User A1 - success

User A1 from User B3 - success

User A2 User B1 User A2 to User B1 - success

User B1 to User A2 - success

User B1 from User A2 - success

User A2 from User B1 - success

User B2 User A2 to User B2 - success

User B2 to User A2 - success

User B2 from User A2 - success

User A2 from User B2 - success

User B3 User A2 to User B3 - success

User B3 to User A2 - success

User B3 from User A2 - success

User A2 from User B3 - success

User A3 User B1 User A3 to User B1 - success

User B1 to User A3 - success

User B1 from User A3 - success

User A3 from User B1 - success

User B2 User A3 to User B2 - success

User B2 to User A3 - success

User B2 from User A3 - success

User A3 from User B2 - success

User B3 User A3 to User B3 - success

User B3 to User A3 - success

User B3 from User A3 - success

User A3 from User B3 - success

Table 6.7: Multiple communication test result

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6.9 Discussion of Results

The test result shows that user were able to register a new email account locally at

online mail server or through internet. Email account created at online mail server is

accessible at the offline mail server, online mail server and through internet after mail data

synchronization between infomediary device and each mail server. Email system found to

be successfully functional to send or receive email through the offline mail server, online

mail server and internet. Pending email data is tested for a period of time and found to be

able remains in the database and not discarded. Wireless LAN range between server

computer access point and infomediary device for it to establish mail data synchronization

is 95 Meters or less with a data rate transfer is 54 Mbps which is 54 megabits per second

equal to 6.75 MBps which is 6.75 megabytes per second and limited by infomediary

device storage write speed which is 2.03 Mbps. The recommended infomediary device

move speed through the Wi-Fi range of the server computer is 3.57 m/s equal to 12.85

km/h or less to ensure the mail data synchronization is completed successfully. The

maximum size of an email attachment is 10MB with total message size limit is 50MB. It

is also recommended to limit the size to lower 10MB to prevent spam attack and viruses.

Each email account size quota is set to 250MB. It is dependable on the server computer

hard drive storage size. All tested emails are successfully sent and receive within the mail

server email size limitation. This offline email system can upload any types of file and

have the ability to block attachments with certain extensions on the mail server. Number

of email connections is unlimited. It can send or receive emails multiple times without

worrying of the mail data overwritten on the mail server database.

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6.10 Summary

A brief result of the different testing approach was provided in this chapter 6. A

demonstration setup was also explained to show various application scenarios of the

offline email system. Next chapter, conclusions and future work are discussed.

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7. CONCLUSION

In this final chapter, a brief summary of the research and development work is provided. A

recommendation for future work is concluded and conclusions of the research objectives and

results are discussed.

In the beginning, an introduction and objective to the thesis work was presented. A

comparison between TCP/IP and DTN was discussed. An email architecture and overview of

similar work was given. Next, the design of TCP/IP mail system working using a DTN store and

forward fundamentals is discussed including the network protocol design followed by offline

email system detail design. The idea of using database synchronization as DTN store and forward

fundamentals is discussed. Then, the system implementation issues and implementation details of

server computer, web server application, mail server, mail client and database synchronization.

Lastly, the system test and result of the offline email system was presented.

7.1 Future Work

There is a possibility of this offline email system can support Government‟s

“Kampung Tanpa Wayar” project where it can benefit in term of cost to expand a portion

of internet access such as the email application to rural area. It is also good to improve

email security by implementing encrypt and decrypt process in data synchronization

between Mail Server and infomediary device. A proper dedicated online mail server with

a static IP internet connection is better to replace the current approach to reduce

dependency to external services such as DtDNS. This will improve reliability of the

system. Additional mail client feature can be added such as email labeling, priority email,

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send and achieve message etc. Database synchronization speed can be improved with

better hardware, especially when dealing with many mail data and bigger attachment files.

In the process of database synchronization, there is a need of checking the database path

availability continuously between server computer and infomediary device. This process

will consume much more power while in rural area there is are constrained that there is a

need to conserve power consumption since the power in rural area mostly dependable to

electric power generator. Instead of continuously checking the database path availability,

the process can be done by checking the database path availability at a set of time or only

when the infomediary device is available in the server computer network.

7.2 Conclusion

In this thesis, the TCP/IP was used on top of delay tolerant network fundamentals

where store and forward operation perform by data synchronization at each mail server.

This approach enables the email flow through the offline mail server to infomediary

device and then to the online mail server and internet. The user registration page is

implemented at online mail server and accessible from online mail server local area

network or from the internet. The email data can remain in the mail server more than one

week time delay until it synchronized with infomediary device. Limitation size of the

offline email system file attachment is 10MB and total email message is 50MB. This

limitation is depending on the size storage of the server computer. All types of data

supported for uploading an attachment and system administrator can block various file

extension such as bat, cmd, com, cpl, csh, exe, inf, lnk, msi, msp, reg, scf and scr from

being uploaded as an email attachment. Multiple sender and receiver can send and receive

126

emails simultaneously and supporting multiple communications between users

successfully. Based on calculation, the maximum recommended speed of infomediary

device movement through the Wi-Fi range of the server computer is 12.85 km/hr or less

and depend on the hardware specifications such as Wi-Fi data transfer rate and storage

read and write speed. This offline email system fulfills the objective of this thesis work

where the system can be used at the area that has no internet connection such as rural area.

This offline email system implementation based on DTN approach can be used for other

web application such as blogging.

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REFERENCES

[1] J. Tarawe and R. W. Harris, "“Stories from e-bario,” In conference of Living the

Information Society, Philippine," 2007.

[2] R. Austein Ed J. Kempf Ed, "The Rise of the Middle and the Future of End-to-End:

Reflections on the Evolution of the Internet Architecture, RFC3724," 2004.

[3] S. Burleigh, A. Hooke, L. Torgerson, R. Durst, K. Scott, K. Fall, H. Weiss V. Cerf, "Delay-

Tolerant Networking Architecture," RFC4838, pp. 4, 15, April 2007.

[4] William Stallings, Data And Computer Communications, Eight Edition.: Prentice Hall,

2007.

[5] J. Reynolds, "Assigned Numbers," RFC3232, 2002.

[6] J. Postel J. Mogul, "Internet Standard Subnetting Procedure," RFC950, 1985.

[7] Dr. Keith Scott, "Delay/Disruption Tolerant Networking," in Large Installation System

Administration Conference (LISA‟09), 2009.

[8] Alex McMahon and Stephen Farrell, "Delay and Disruption Tolerant Networking," 2009.

[9] Forrest Warthman, "Delay-Tolerant Networks (DTNs)," 2003.

[10] K. Scott and S. Burleigh, "Bundle Protocol Specification," RFC5050, 2007.

[11] Craig Partridge, "The Technical Development of Internet Email," 2008.

[12] J. Klensin, "Simple Mail Transfer Protocol," RFC5321, 2008.

[13] M. Crispin, "Internet Message Access Protocol," RFC3501, 2003.

[14] Kevin Fall, "A Delay Tolerant Network Architecture for Challenged Internets," 2003.

[15] Martin Knafve. (2011, August) hMailServer. [Online]. http://www.hmailserver.com

[16] Ben Duncan. (2011, Aug.) @mail Open: PHP Webmail client - Open Source Webmail.

[Online]. http://atmail.org/

[17] Paul Lesniewski. (2011, Aug.) SquirrelMail - Webmail for Nuts. [Online].

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http://squirrelmail.org

[18] The RoundCube Team. (2012, March) roundcube. [Online]. http://roundcube.net

[19] Ed P. Resnick and Qualcomm Incorporated, "Internet Message Format," RFC5322, 2008.

[20] Network Working Group, "Protocol standard for a NetBIOS service on a TCP/UDP

transport," RFC 1002, 1987.

[21] Uniform Server Development Team. (2011, August) Uniform Server. [Online].

http://www.uniformserver.com

[22] Zenju. (2011, December) FreeFileSync. [Online]. http://freefilesync.sourceforge.net/

[23] JimmyChingala. (2012, February) xda-developers. [Online]. http://forum.xda-

developers.com/showpost.php?p=8239139

[24] Justin Scott. (2012, January) DtDNS. [Online]. http://www.dtdns.com

[25] N. Freed, Innosoft, and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME)

Part One:Format of Internet Message Bodies," RFC2045, November 1996.

[26] Google Inc. (2013, June) Gmail. [Online].

https://support.google.com/mail/answer/6584?rd=1

[27] Yahoo Inc. (2013, June) Yahoo Mail. [Online].

http://help.yahoo.com/kb/index?page=content&y=PROD_MAIL_ML&locale=en_US&id=

SLN3408

[28] Telekom Malaysia Berhad (TM). (2008, November) Streamyx. [Online].

http://www.tm.com.my/PublishingImages/unifi/pdf/Third%20Party%20Email%20Setting.p

df

[29] Ed. D. Crocker, Ed. T. Hansen, and Ed. M. Kucherawy, "DomainKeys Identified Mail

(DKIM) Signatures," RFC6376, September 2011.

[30] Team Uniform Server. (2011, August) hMailServer. [Online].

http://www.hmailserver.com/documentation/latest/?page=userguide_dds

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APPENDIX

APPENDIX A

DANAWA Wireless Solution Provider Brochure

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131

132

APPENDIX B

Lenovo IdeaPad Z460 Specifications

133

134

135

APPENDIX C

D-Link DWL-2100AP Specifications

136

137

138

APPENDIX D

LG Optimus 3D (P920) Specifications

139

140

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APPENDIX E

Riger DB 108-WL Wireless ADSL Modem 2/2+

142