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 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 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.

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.