E-mail System for Delay Tolerant Network

E-mail System for Delay Tolerant Network Emir Husni, Agus Wibowo School of Electrical Engineering & Informatics, Institut Teknologi Bandung Jl. Ganesha no. 10 Bandung, Indonesia [email protected] Abstract— DTN protocol can overcome network problems such as intermittent connectivity, long or variable delay, asymmetric data rates, and high error rates. TCP/IP protocol, a common network protocol currently used for the internet, cannot handle these problems. By using postfix and DTN2, we can build a DTN-based e-mail server that is capable of sending and receiving e-mails even the server is not continuously connected to a network. This also requires a new method to send and receive e-mails. Postfix is used for managing and processing e-mail users. DTN2 is used for processing e-mails into bundles and bundles into e-mails based on DTN protocol. This requires programs that integrate the postfix e-mail system with DTN2, implemented using bash shell and awk, for sending and receiving e-mail. The email system has been tested in the real condition using trains. The results show that the DTN based email system is working properly. Keywords— e-mail; delay tolerant network; train; e-mail server; store and forward.

I. INTRODUCTION

remote areas may be passed through by a train on one trip, this can make DTN-based Internet services proposed having low costs and appropriate for remote areas. In this research, e-mail servers that do not always connect to the network was built. E-mail server postfix is used on DTN based networks. Postfix used is version 2.5.5 which already exists on Linux 5.0.3 Debian "Lenny" and DTN-2.6.0. A. Delay Tolerant Network (DTN)

Existing Internet protocols (e.g., TCP/IP) are not well-suited for Internet services in highly stressed networking environments because they were designed under very different assumptions, both in terms of service requirements and technology constraints. TCP model is based on the end-to-end principle, which must be continuous connection in end-to-end, low delay paths between sources and destinations with low error rates and relatively symmetric bidirectional data rates [1-4]. DTN overcomes the problems associated with intermittent connectivity, long or variable delay, asymmetric data rates, and high error rates by using store-and-forward message switching. The key idea is to facilitate opportunistic transport on a hop-byhop basis rather than end-to-end streaming of data as in TCP/IP. Every node in DTN has a storage and every packet is stored from one node to the next node if the connection is available until all packets are sent from the source to the the destination, as illustrated by Fig. 1.

E-mail is one of the four major Internet applications since 1970. However not all people have enjoyed the e-mail service, i.e. the village community. Many villages do not have Internet access. This is due to the lack of adequate Internet infrastructure network. A network architecture and protocol technique called Delay Tolerant Network (DTN) is used in this research to approaching the digital divide problem. By implementing DTN, communications can be provided in an extreme environment with intermittent connectivity, large and/or variable delays, and high bit error rate, which are common characteristics of remote areas. The DTN-based network for delivering Internet services can be built by utilizing the available store store store store NODE NODE NODE NODE facilities and infrastructures around the area and A B C D adding some sets of supporting equipment. One of forward forward forward facilities and infrastructures that can be used for building a DTN-based network is Public Fig. 1 Store-and-forward mechanism Transportation System. In this research, a train system was chosen to be infrastructures as DTN The DTN architecture implements store-androuters using Wi-Fi. Tens/hundreds/thousands of forward message switching by overlaying a new

protocol layer, called the bundle layer, on top of heterogeneous region-specific lower layers, as shown in Fig. 2 [1]. Bundles are also called messages. 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. Application Bundle Transport Network Link Physical Fig. 2 DTN’s bundle layer [1]

The DTN protocol has been implemented for various applications. In addition to the spacecraft, researchers have proposed or using DTN to support schools in rural areas in developing countries [5], tracking zebras in Africa[6], water quality in lakes of Ireland [7], a social network in northern Scandinavia [8], and even monitoring of cane toad invasion that took place in Australia [9]. II. E-MAIL SYSTEM FOR DTN

Here, an e-mail system for DTN was built and tested in the real condition. The detail explaination is given below. B. DTN-2.6.0 Software

In building this system, DTN2 needed to handle the bundle that is sent from one computer and received by another computer. So that one computer to another computer does not have to always be connected because the e-mail that has been converted into the bundle does not have to be accepted by the destination computer on the spot. C. E-mail System

MTA, using SMTP protocol. Then the local MTA determines the recipient's address provided by the SMTP protocol instead of an e-mail header. Internet e-mail address has the form of name@domain. Part before the @ sign is the local part of the address is usually the recipient's name and the part after the @ sign is the domain name or fully qualified domain name (FQDN). Now we know the address of the recipient, the local MTA asked the server DNS to find the MTA which is responsible to the recipient domain and send an email to the recipient MTA using SMTP protocol. Then, the Local MTA asks the DNS server the IP address of the corresponding e-mail domain or the FQDN. DNS server was the one who can map a domain name or FQDN to the IP address and vice versa. Following a request from the local MTA, DNS server will look for mail exchange record (MX) for that domain. E-mail messages are travelling from the sender’s computer to the sender's e-mail server, and finally arrive at the recipient domain. Depending on the network configuration, e-mail messages may be passed to several MTAs before arrive at the receiver. Finally, an MTA at the receiver will be responsible for the e-mail messages arrived and sending them to the recipients. The receiver’s MTA submits every e-mail to MDA. In essence, an MDA is responsible for storing e-mail to the disk. Some MDA also do something else, such as selecting an e-mail or send to a subfolder. The MDA saves every e-mail to the recipient’s server. To check the e-mail messages, recipient run the MUA and MUA asking e-mail server using one of the standard protocols: IMAP or post office protocol (POP). If the authentication of the recipient is success, the e-mail server will send all e-mail messages from a storage place to the recipient’s MUA. So now the recipient can read your e-mail. D. E-mail Server

Here, Postfix program which is as a well known Here, MUA is used as an e-mail editor. Examples as exim4-* is used as the MTA with SMTP. Postfix of MUA are the Mozilla Thunderbird and Microsoft program is known as the complete, fast, simple, and Outlook Express. Whatever MUA is used, an e-mail safe software. has been created and e-mail is sent to the local

Here, MUA used is the evolution which is Xbased program GUI, text-based mutt, MS Outlook Express on Windows, and the Simple Mail which is one of the add-ons in Mozilla Firefox. E. Program Incorporation Postfix Into DTN2

Village 12, Village 21, and the Village 22. The other parts are Internet service providers (ISP) and public e-mail services (yahoo and gmail). They are illustrated in Fig. 3. The specifications of parts of the system are as follows.

In this research postfix program must be 1. A computer/server that has a public IP address and a incorporated into DTN2. This merger program will domain name that is known on the global Internet. The computer/server Utama processes e-mails from the global convert e-mail file to the bundle at sender’s e-mail Internet, from computer Utama’s user, and from server, and convert the bundle to the e-mail file at computers/servers at the station. Here, a DNS server is set receiver’s e-mail server. Some programs needed to to help the e-mail server. build the merger program are as follows. 2. Two station computers/servers with private IP address are 1. 2.

3. 4. 5.

dp_main.py a main routine interface postfix into DTN2. dp_dtn.py Three interface threads are arranged in this program: dtn_send_interface to set the bundle sent on the dtnd interface, dtn_recv_interface to set the bundle received on the interface dtnd, and the thread used to handle the delivery report received. dp_pfmailin.py an interface to handle e-mail to be sent to postfix after received from dtnd. dp_pfmailout.py an interface to handle e-mail sent from postfix which will be forwarded by using dtnd. dtn_pymail_log.conf Contains parameters to handle the log file.

3.

4.

located at Zone 1 and Zone 2. The station computer/server processes e-mails from computer/server Utama and the computers/servers on the train. One computer/server on each train with private IP address at Region 1 and Region 2. The train computer/server processes e-mails from computers/servers at the station and in the village. One computer/server in every village with private IP address at Region 1 and Region 2. Here, the e-mail server is needed with a DNS server. Domain name owned by computers/servers in the village is not known on the global Internet. The computer/server in the village process e-mails from the computer/server on the train and from computer users in the village.

Server and IP Address 192.168.10.5

III. SYSTEM IMPLEMENTATION

Utama 110.232.72.13

Station 2

192.168.21.5

Basically the system is divided into two parts, namely a system that uses DTN2 and systems that do not use DTN2. Systems that use DTN2 utilize basic program that uses DTN protocols. The basic program is available when installing DTN2. While the system does not use DTN2 use TCP-based file transfer program and the use of security techniques key pair private/public. Domains that are used in this study is kampoeng.net. Parts of the system that use DTN2 are computers/servers in the village, train, and station. While the part of the system that do not use DTN2 is computer/server Utama (Main). The Computer/server in the station functions as a gateway between a system using DTN2 and a Fig. 3 DTN system using train system not using DTN2. In this research, parts of the DTN system using train implemented are as follows. There are nine Data flow diagram (DFD) of the computer/server computers/servers needed, namely: Utama (Main), in the village, trains, stations, and the Utama are Station 1, Station 2, Train 1, Train 2, Village 11, given in Fig. 4-7. ISP

Village 21

yahoo

Train 2 192.168.x.128

Internet

192.168.22.5

gmail

ISP

Village 22

Region 2

Station 2 192.168.10.5

192.168.10.5

ISP

ISP

Station 1 192.168.10.5

Station 1

Village 11 192.168.11.5

Train 1 192.168.x.128

Region 1

Village 12 192.168.12.5

5.

6. Fig. 4 DFD of the computer/serve in the village

7. Fig. 5 DFD of the computer/server on the train

8.

While the train passing through the village, e-mails from users at the village are transmitted from the village server to the train’s router server. E-mails which addressed to users at other villages will be immediately transmitted by the train’s router server to the designated village server as soon as the public transportation passes through the designated village. If the designated villages have already passed through by the train or do not listed in the route of the train, the emails will be hold by the router server at the tain and forwarded to the station server as the train arrives at the final station. The e-mail will be downloaded by other train’s router server which has a travelling route to the designated villages. E-mails from the users at villages addressed to other users at public e-mail server are also forwarded to the station server. Station server uploads the e-mails from the users at villages addressed to other users at the global Internet, to the server Utama. E-mails from the users at villages addressed to other users at the global Internet will be forwarded by the server Utama to the global Internet cloud.

IV. FIELD TESTS

Fig. 6 DFD of computer/server at the station

Field tests were conducted by implementing Internet services system for remote areas based on DTN at PT Kereta Api Indonesia (PT KAI) Daop 2 Bandung. The objective of these tests was seeing the overall performances of the system and analysing the possibility for implementing this system on the actual conditions. PT KAI’s facilities and locations used for conducting the experiment are as follows: •

Fig. 7 DFD of the computer/server Utama

• • •

Bandung Train Station as the Train Station which has a direct connection to the Internet. Cimekar Train Station as Village_11. Haurpugur Train Station as Village_12. Cicalengka Train Station as the transit station for managing e-mails delivery through the train station. Diesel train, Baraya Geulis, as the DTN-router.

In each computer/server, several programs that use the bash shell and awk needed to assist postfix • program incorporated into DTN2. Devices used for conducting the tests are as E-mail service delivery mechanism is as follows: follows: 1. The server Utama receives any e-mails that addressed to 2. 3. 4.

users at the villages. Station Server downloads the e-mails addressed to the users at villages passed through by its trains, from the server Utama. Train’s Router Server downloads the e-mails from the Station Server, addressed to users at villages will be passed through. While passing through a village and within range of the village’s Wi-Fi network, train’s router server transmit emails addressed to users at the village, to the village server.

• • •

• •

Virtual Private Server (VPS) as Main Server, with public IP 110.232.72.13. One unit AMD Turion™ X2 Dual-Core RM-70 notebook as Station Server, with IP 192.168.10.5. Two unit AMD Duron 256 MB PC, each as Village_11 Server with IP 192.168.11.5 and Village_12 Server with IP 192.168.12.5. One unit Intel® Core 2 Duo Processor T5870 notebook as Router Server at Baraya Geulis diesel train. Two sets 2.4 GHz Wireless Outdoor CPE TL-WA5210g, each set as wi-fi access point for Village_11 Server at

•

•

Cimekar Station and Village_12 Server at Haurpugur Station. One unit 2.4 GHz Outdoor Nano Station 2 CPE with a 400mw 802.11b/g radio and a dual polarity 10dbi antenna as wi-fi client for Router Server at Baraya Geulis diesel train. One unit 3G/HSDPA Wireless Router 2.4 GHz b/g/n Fonera 2.0n along with a HSDPA modem E160E set as wi-fi access point for Station Server at Bandung Station.

7.

8.

Kind of tests performed are as follows: • • •

Sending e-mails from Gmail to the users at Village_11 and Village_12 Sending e-mails between Village_11 and Village_12. Sending e-mail from Village_11 and Village_12 to Gmail at the global Internet.

9.

Baraya Geulis diesel train which was carrying router server did two routes, called Trip1 and Trip2. Trip1 route was starting from Bandung station and 10. then passing through Cimekar and Haurpugur Station and finally arriving at the Cicalengka Station. Trip2 route was starting from Cicalengka Station then passing through the Haupugur and 11. Cimekar Station and finally arriving at the Bandung station. Router server is placed in locomotive engineers’ cabin at Baraya Geulis diesel train because of power outlet facility availability. 12. Tests’ scenario conducted at PT KA Daop 2 Bandung, illustrated in Fig. 8, are as follows. 1. 2. 3. 4.

5.

6.

Server Utama received and saved e-mails sent from Gmail (mail.google.com). Station Server downloaded the e-mails data from the Main Server which were addressed to the users at Village_11 and Village_12. Train’s Router Server downloaded the e-mails data from the Station Server which were addressed to the users at Village_11 and Village_12. While Baraya Geulis diesel train was passing through Village_11 (without stopping) on Trip1 and within range of Village_11 Wi-Fi network, Train’s Router Server was transmiting e-mails addressed to the user at Village_11, to Village_11 Server. While Baraya Geulis diesel train was passing through Village_11 (without stopping) on Trip1 and within range of Village_11 Wi-Fi network, Village_11 Server will transmits e-mails from users at Village_11 addressed to users at Village_12 and Gmail users, to the Train’s Router Server. While Baraya Geulis diesel train was passing through Village_12 (without stopping) on Trip1 and within range of Village_12 Wi-Fi network, Train’s Router Server was transmiting e-mails from Gmail users, and e-mails from users at Village_11, to Village_12 Server.

13.

14. 15.

While Baraya Geulis diesel train was passing through Village_12 (without stopping) on Trip1 and within range of Village_12 Wi-Fi network, Village_12 Server was transmits e-mails from users at Village_12 addressed to users at Village_11 and Gmail users, to the Router Server. When Village_12 Server sent e-mails to Train’s Router Server on Trip1 which were addressed to users at Village_11, the train had already passed through Village_11. Those e-mails were hold by the Train’s Router Server until the train arrived at Cicalengka Station. At Cicalengka Station, Train’s Router Server was transmiting the e-mails to Station Server and the Station Server will forwards those e-mails back to Router Server to delivering those e-mails to Village_11 when Baraya Geulis diesel train did Trip2 route. Station Server forwarded the e-mails which were addressed to users at Village_11, back to Router Server to delivering them to Village_11 when Baraya Geulis diesel train did Trip2 route. While Baraya Geulis diesel train was passing through Village_12 (without stopping) on Trip2 and within range of Village_12 Wi-Fi network, Village_12 Server was transmiting e-mails from users at Village_12 addressed to users at Village_11 and Gmail users, to the Router Server. While Baraya Geulis diesel train was passing through Village_11 (without stopping) on Trip2 and within range of Village_11 Wi-Fi network, Train’s Router Server was transmiting e-mails addressed to user at Village_11 which were sent from Village_12 on Trip1 and Trip2. While Baraya Geulis diesel train was passing through Village_11 (without stopping) on Trip2 and within range of Village_11 Wi-Fi network, Village_11 Server was transmiting e-mails from users at Village_11 addressed to users at Village_12 and Gmail users, to the Train’s Router Server. Train’s Router Server forwarded e-mails data sent from users at Village_11 and Village_12 to the Station Server. Station Server sorted them out those according to their destination. E-mails addressed to Gmail users were uploaded to the Server Utama. E-mails sent from Village_11 which addressed to Village_12 were hold by Station Server until another Router Server at different train, which did the next route, downloaded those e-mails. Station Server uploaded e-mails addressed to Gmail users to Server Utama. Server Utama received the e-mails uploaded by Station Server and then forwarded them to Gmail.

Main Server 110.232.72.13

Cicalengka St. 9

1

15 2

TABLE III MEAN THROUGHPUT TEST’S RESULT.

8

14

Station Server 192.168.10.5

Gmail

15 1

INTERNET

mail.google.com

Tests’ Location

1

OkeZone

www.okezone.com 2

Cimekar Sation (Village_11) to Router Server on Trip1 to Router Server on Trip2 Haurpugur Station (Village_12) to Router Server on Trip1 to Router Server on Trip2 Baraya Geulis Diesel Train (Router) to Cimekar Station on Trip2 to Haurpugur Station on Trip1

Haurpugur St. (Village_12)

14

10

Bandung St.

Station Server

Cimekar St. (Village_11)

Village_11 Server

192.168.10.5

192.168.11.5

3

Village_12 Server

7 6

192.168.12.5

4 5 13

11 12

Baraya Geulis DT Router Server 192.168.x.5

Mean Throughput (Mbps) 5.5981 3.1280 1.9919 1.8385 3,7674 0,6674

Fig. 8 Tests’ scenario at PT KAI Daop 2 Bandung

B. Analysis

In the field tests conducted at PT KAI Daop 2 Summary of the tests’ results conducted at PT Bandung: • the processes of sending and receiving data including eKA Daop 2 Bandung are shown in Table I, II, III. A. Results

TABLE I E-MAIL DELIVERY TEST’S RESULT

Tests’ Location Cimekar Sation (Village_11) to Router Server on Trip1 to Router Server on Trip2 Haurpugur Station (Village_12) to Router Server on Trip1 to Router Server on Trip2 Baraya Geulis Diesel Train (Router) to Cimekar Station on Trip2 to Haurpugur Station on Trip1

Amount of E-mail Sent

Total Data Sent (Mbps)

300 400

8.2 10.9

•

274 274

7.5 7.5

•

246 157

6.7 4.3

•

•

TABLE II TRANSMISSION AND CONNECTION TIME TEST’S RESULT

Tests’ Location

Connection Time

Transmission Time (sec)

Cimekar Sation (Village_11) to Router Server on Trip1 to Router Server on Trip2

1 minutes 52 seconds 2 minutes 34 seconds

11.7277 27.9866

Haurpugur Station (Village_12) to Router Server on Trip1 to Router Server on Trip2

1 minutes 52 seconds 2 minutes 43 seconds

30.1049 32.6166

Baraya Geulis Diesel Train (Router) to Cimekar Station on Trip2 to Haurpugur Station on Trip1

2 minutes 44 seconds 2 minutes 2 seconds

•

14.3104 52.0230

mails between villages, namely Cimekar Station as Village_11 and Haurpugur Station as Village_12 with Baraya Geulis Diesel Train as a DTN-router, were all successfully carried out. All e-mails from Gmail users were successfully received by users at Village_11 and Village_12. All e-mails addressed to Gmail, sent from Village_11 and Village_12 Servers, were successfully received by Gmail users. The highest mean throughput was 5.5981 Mbps. It was on the transmission from Village_11 Server to Router Server on Trip1. The lowest throughput was 0.6674 Mbps. It was on the transmission from Router Server to Village_12 Server on Trip1. The highest amount of e-mails delivered was 400 e-mails with a total data size of 10.94284 Mbytes in 27.9866 seconds time. It was sent from Village_11 Server to Router Server on Trip2.

E-mails from Gmail users, received and downloaded by the Server Utama, were forwarded to Station Server, and then successfully delivered to Village Server through the Train’s Router Server. This showed that by using DTN, data transmission can be done by the hop-by-hop principle without having the end-to-end connection between the source and the destination. Also, the tests showed that DTN can be used to provide global Internet services to remote areas that does not have direct access to the global Internet network.

remote areas covered by train can take benefit of In this research, E-mail service system using train this system, but also remote areas located far away for remote areas based on DTN proposed has been from railway. designed, implemented and tested in actual conditions. It was shown in the tests that e-mail REFERENCES transfer services were successfully delivered. This [1] Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst, R., Scott, K., Fall, K., and Weiss, H., “Delay-Tolerant Network Architecture,” showed that by using DTN, data transmission can RFC4838, 2007. be done using the hop-by-hop principle without [2] Warthman, F., “ Delay-Tolerant Networks (DTNs) A Tutorial v1.1,” Available: http://www.ipnsig.org/reports/DTN_Tutorial11. pdf., 2003. having the end-to-end connection between the [3] Fall, K. and Farrell, S., “DTN: An Architectural Retrospective,” IEEE source and the destination. Thus by using DTN Journal on Selected Areas in Communications, Vol.26 No.5, pp.828836, Nov. 2008. techniques, users in remote areas are able to [4] Farrell, S., Cahill, V., Geraghty, D., Humphreys, I., and McDonald, P., communicate to global Internet network even they “When TCP Breaks: Delay- and Disruption-Tolerant Networking,” IEEE Internet Computing, pp. 72-78, July-August 2006. do not have direct access to the global Internet [5] Azfar, A., Jiang, J., Shan, L., Marval, M.J.P., Yanggratoke, R., and network. Ahmed, S., ByteWalla: Delay Tolerant Networks on Android phones, CSD Labs, The Royal Institute of Technology, Stockholm, Final Other important tests’ results were: the highest Report, 2010. mean throughput was 5.5981 Mbps, and the highest [6] P. Juang, H. Oki, Y. Wang, et al, “Energy-Eficient Computing for Wildlife Tracking: Design Tradeos and Early Experiences with amount of e-mails delivered was 400 e-mails with a ZebraNet,” Proceedings of ASPLOS-X, Oct. 2002. total data size of 10.94284 Mbytes in 27.9866 [7] J. Keyes, F. Gibbons, Envionmental Section, Cavan County Council, “The Quality of River and Lake Water in County Cavan,” Report for seconds time. the year 2004, April 2005. In improving the Internet services for remote [8] Elwyn D., “DTN-The State of the Art Version 1.0,” Folly Consulting Ltd. Report. Availale: http://www.n4c.eu/Download/n4c-wp2-012areas based on DTN, it is suggested to design the state-of-the-art-101.pdf. Internet services system for remote areas based on [9] Pubudu N.P., Nirupama B. et.al., “Node Localization Using Mobile Robots in Delay-Tolerant Sensor Networks, “ IEEE Transactions on DTN utilizing other public transportation systems Mobile Computing, Vol.4 No.3, pp.285-296, May/June 2005. (such as: bus, boat, airplane). Therefore, not only V. CONCLUSION