Delay Tolerant Network Based Internet Services for Remote Areas Using Train Systems

Emir Husni School of Electrical Engineering & Informatics

Institut Teknologi Bandung Bandung, Indonesia

ehusni@lskk.ee.itb.ac.id

Abstract— A Delay Tolerant Network (DTN) technique is used in this research for approaching the digital divide problem in Indonesia. In this research, a train system was chosen as infrastructures as DTN routers using Wi-Fi. Tens/hundreds/ thousands of remote areas are passed through by a train, this makes Internet services proposed having low costs and appropriate for remote areas. The complete Internet services system was successfully designed and implemented.

Keywords-component; delay tolerant network; remote area; train system; Internet services

I. INTRODUCTION Right now, Internet plays important role on people’s life.

So many applications can run on Internet, such as e-mail, chatting, social networking, news service, tele-medicine, tele-education and e-commerce. Therefore, Internet is believed in having big impact to economy growth. Right now, Indonesia is still having a digital divide problem, especially in remote areas because Indonesia has a huge area with thousands of islands. Geographical conditions, installation cost, and subscriber fee are becoming major constraints in building Internet infrastructures at remote areas.

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 facilities and infrastructures around the area and adding some sets of supporting equipment. One of facilities and infrastructures that can be used for building a DTN-based network is Public Transportation System. In this research, a train system was chosen to be infrastructures as DTN routers using Wi-Fi. Tens/hundreds/thousands of 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.

The idea in this research is to design a communication network by utilizing a train system as a DTN router to connect

remote areas to global Internet network through a server in a city so the users at remote areas can take benefits of the Internet services. The primary Internet services will be news broadcasting, email services and file transfer/digital courier.

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 [1-2].

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-by-hop 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. DTN routers need persistent storage for one or more following reasons:

• Communication link availability to the next hop is low. • One node in a communicating pair may send or receive

data faster or slower than the other node. • Data transmission may need to be retransmitted if an

error occurs while the data was being transmitted to the destination or the destination declines the forwarded data.

Figure 1. Store-and-forward mechanism.

The DTN architecture implements store-and-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

47978-1-4577-1826-7/11/$26.00 ©2011 IEEE ICON 2011

(or bundle fragments) between nodes. A single bundle-layer protocol is used across all networks that make up a DTN.

Figure 2. DTN’s bundle layer. [1]

II. INTERNET SERVICES SYSTEM FOR REMOTE AREAS The objective of this research is to build an Internet services

system by utilizing train system as a DTN router to connect remote areas to the global Internet network through a server in a city so the users at a remote area can take benefits of the internet services, in this case, email services, news portal and file transfer/digital courier. The network architecture of the proposed Internet services system is shown in Fig. 3.

INTERNET

Main Server

wi-ficlient

Email services

Wi-fi link1

News Site

VillageServer

wi-fiAP

VILLAGE

router

Users at Village

hub

VillageServer

wi-fiAP

VILLAGE

router

Users at Village

hub

modem

StationServer

wi-fiAP

router

TRAIN STATION

modem

StationServer

wi-fiAP

router

TRAIN STATION

ISP

Wi-fi link4

Wi-fi link2 Wi-fi link3

TRAIN

Router Server

ISP

other DTN-basedNetwork

other DTN-basedNetwork

Figure 3. Network architecture of Internet services system for remote areas.

The network architecture of Internet services system for remote areas consists of primary elements as follows:

• Main Server, functions as a central data processing unit and main storage connected to the global Internet network.

• Train Station Server, functions as a middleware for transmitting data between main server and the DTN

router at the train. The station server connects to the DTN router using Wi-Fi.

• Train, functions as a DTN router. The train is equipped with a router server along with wireless outdoor customer premise equipment (CPE) set as wi-fi client. Router server is placed at the locomotive engineers’ cabin or other location which has a power source outlet.

• Village Server, functions as a village central data processing at a remote area. Village server is equipped with a wireless outdoor CPE set as Wi-Fi access point (Wi-Fi access point) to connecting the village server to the router server at the train. Hub/switch and router are used for connecting the users’ workstations to the Village Server.

• Wi-Fi Network, as an intermediate network between station server and train’s router server and also between train’s train server and village server.

• Other DTN-based network is a network which has a similar architecture and services system as this DTN network and sharing the same Main Server.

• Email services are global and web-based email services providers, such as Gmail or Yahoo Mail, or email services of an Internet service provider.

• News site is a site providing web-based news services, such as www.detik.com and www.okezone.com.

Railway transportation system or train is used as the DTN-routers with consideration that railway network has railroads whose its routes are passing through remote areas thus, there is no need to building infrastructures specially for providing the Internet services to the remote areas. Wi-Fi is used as the intermediate network because of its availability, flexible deployment and minimal wiring problems, along with reason that there is no subscribing fee as in satellite communication or cellular network services.

Internet service delivery mechanism, shown in Fig. 4, is as follows:

1) Main Server downloads any recent news from various news sites at the Internet and receives any emails that addressed to users at the villages.

2) Station Server downloads the news and emails addressed to the users at villages passed through by its trains, from the Main Server.

3) Train’s Router Server downloads the news and emails from the Station Server, addressed to users at villages will be passed through.

4) While passing through a village and within range of the village’s Wi-Fi network, train’s router server transmit news, emails, and other data addressed to users at the village, to the village server.

5) While the train passing through the village, emails and other data from users at the village are transmitted from the village server to the train’s router server. Emails which addressed to users at other villages will be immediately transmitted by the train’s router server

Application

Bundle

Transport

Network

Link

Physical

48

to the designated village server as soon as the public transportation passes through the designated village.

6) 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 email will be downloaded by other train’s router server which has a travelling route to the designated villages. Emails from the users at villages addressed to other users at public email server are also forwarded to the station server.

7) Station server uploads the emails from the users at villages addressed to other users at the global Internet, to the Main Server.

8) Emails from the users at villages addressed to other users at the global Internet will be forwarded by the main server to the global Internet cloud.

8

1

8

88

Village

2a

Village

Main Server

7

4a 5a4b5b

6b

4a 5a4b5b

2b

INTERNET

7b

2

7a

3a

6a

3aTrain

Station

Train Station

Train

Train

Email Services

Station Server

Station Server

Router Server

Router Server

OtherDTN-based

Network

OtherDTN-based

Network1

1 1

1

News Site

8

Village Server Village Server

Figure 4. Internet service delivery mechanism.

Some applications used for building Internet services system for remote areas using train are as follows:

• DTN2 Application functions as the core network application for processing all data transmission using DTN protocol. DTN2 is responsible for transmitting all the data from the source as bundles and converts the bundles back to its original form at the destination. DTN2 is also responsible for managing the data transmission in accordance with connections availability.

• Email Server Application functions to regulate the transmission and reception of emails and managing the user’s email account. Postfix is used as the Mail Transfer Agent (MTA) along with dovecot-imapd for supporting the Internet Message Access Protocol

(IMAP). A Python application is used for integrating Postfix with DTN. For regulating transmission and reception of emails with DTN, some applications are specifically designed using shellbash and AWK [3].

• News Server Application is a group of applications specifically designed using shellbash and PHP, for downloading news data from various news sites at the global Internet and then sending the news to the users [4].

• Email Client Application is a user’s application for writing, sending, and reading emails. Mutt and Evolution are used as Mail User Agent (MUA) for the Email Client Application.

• News Client Application is a user’s application for accessing the news services provided. Web browser Ice Weasel is used as the News Client Application.

III. FIELD TESTS 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:

• 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 emails delivery through the train station. • Diesel train, Baraya Geulis, as the DTN-router.

Devices used for conducting the tests are as follows:

• 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

49

as wi-fi access point for Station Server at Bandung Station.

Kind of tests performed are as follows:

• Download some news data from www.okezone.com then sent them to the users at Village_11 and Village_12.

• Sending emails from Gmail to the users at Village_11 and Village_12

• Sending emails between Village_11 and Village_12. • Sending email from Village_11 and Village_12 to

Gmail at the global Internet.

Baraya Geulis diesel train which was carrying router server did two routes, called Trip1 and Trip2. Trip1 route was starting from Bandung station and 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 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.

Tests’ scenario conducted at PT KA Daop 2 Bandung, illustrated in Fig. 5, are as follows.

1) Main Server downloaded and saved news form www.okezone.com as well as received and saved emails sent from Gmail (mail.google.com).

2) Station Server downloaded the news and emails data from the Main Server which were addressed to the users at Village_11 and Village_12.

3) Router Server downloaded the news and emails data from the Station Server which were addressed to the users at Village_11 and Village_12.

4) While Baraya Geulis diesel train was passing through Village_11 (without stopping) on Trip1 and within range of Village_11 Wi-Fi network, Router Server was transmiting news data and emails addressed to the user at Village_11, to Village_11 Server.

5) 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 emails from users at Village_11 addressed to users at Village_12 and Gmail users, to the Router Server.

6) While Baraya Geulis diesel train was passing through Village_12 (without stopping) on Trip1 and within range of Village_12 Wi-Fi network, Router Server was transmiting news data, emails from Gmail users, and emails from users at Village_11, to Village_12 Server.

7) 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 emails from users at Village_12 addressed to users at Village_11 and Gmail users, to the Router Server.

8) When Village_12 Server sent emails to Router Server on Trip1 which were addressed to users at Village_11, the train had already passed through Village_11. Those emails were hold by the Router Server until the train

arrived at Cicalengka Station. At Cicalengka Station, Router Server was transmiting the emails to Station Server and the Station Server will forwards those emails back to Router Server to delivering those emails to Village_11 when Baraya Geulis diesel train did Trip2 route.

9) Station Server forwarded the emails 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.

10) 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 emails from users at Village_12 addressed to users at Village_11 and Gmail users, to the Router Server.

11) While Baraya Geulis diesel train was passing through Village_11 (without stopping) on Trip2 and within range of Village_11 Wi-Fi network, Router Server was transmiting emails addressed to user at Village_11 which were sent from Village_12 on Trip1 and Trip2.

12) 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 emails from users at Village_11 addressed to users at Village_12 and Gmail users, to the Router Server.

13) Router Server forwarded emails data sent from users at Village_11 and Village_12 to the Station Server. Station Server sorted them out those according to their destination. Emails addressed to Gmail users were uploaded to the Main Server. Emails 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 emails.

14) Station Server uploaded emails addressed to Gmail users to Main Server.

15) Main Server received the emails uploaded by Station Server and then forwarded them to Gmail.

Figure 5. Tests’ scenario at PT KAI Daop 2 Bandung.

50

A. Results Summary of the tests’ results conducted at PT KA Daop 2

Bandung are shown in Table 1, Table 2, and Table 3.

TABLE I. EMAIL DELIVERY TEST’S RESULT

Tests’ Location Amount of Email Sent

Total Data Sent

(Mbps) Cimekar Sation (Village_11) to Router Server on Trip1 300 8.2 to Router Server on Trip2 400 10.9 Haurpugur Station (Village_12) to Router Server on Trip1 274 7.5 to Router Server on Trip2 274 7.5 Baraya Geulis Diesel Train (Router)

to Cimekar Station on Trip2 246 6.7 to Haurpugur Station on Trip1 157 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 1 minutes 52 seconds 11.7277

to Router Server on Trip2 2 minutes 34 seconds 27.9866

Haurpugur Station (Village_12)

to Router Server on Trip1 1 minutes 52 seconds 30.1049

to Router Server on Trip2 2 minutes 43 seconds 32.6166

Baraya Geulis Diesel Train (Router)

to Cimekar Station on Trip2 2 minutes 44 seconds 14.3104

to Haurpugur Station on Trip1 2 minutes 2 seconds 52.0230

TABLE III. MEAN THROUGHPUT TEST’S RESULT

Tests’ Location Mean Throughput (Mbps)

Cimekar Sation (Village_11) to Router Server on Trip1 5.5981 to Router Server on Trip2 3.1280 Haurpugur Station (Village_12) to Router Server on Trip1 1.9919 to Router Server on Trip2 1.8385 Baraya Geulis Diesel Train (Router) to Cimekar Station on Trip2 3,7674

to Haurpugur Station on Trip1 0,6674 Fig. 6 and 7 show transmission time and throughput

graphics whose data were taken from one of the test’s results in PT KAI Daop 2 Bandung.

1,0967001,251720

1,751340

2,330690

0,969870

2,1146502,212720

0,000000

0,500000

1,000000

1,500000

2,000000

2,500000

354.942 628.492 901.821 1.176.982 1.448.102 1.722.636 1.973.615

13 23 33 43 53 63 72

Data Size (Bytes) compare to amount of BundleTr

ansm

isio

n T

ime

(sec

onds

)

Figure 6. Transmission time Vs Data Size of transmission from Village_11 Server to Router Server on Trip1.

11,9447

4,03994,1195

2,5892

4,0168

7,13556,5170

0,0000

2,0000

4,0000

6,0000

8,0000

10,0000

12,0000

14,0000

354.942 628.492 901.821 1.176.982 1.448.102 1.722.636 1.973.615

Data Size (Bytes)

Thr

ough

put (

Mbp

s)

Figure 7. Throughput Vs data size of transmission from Village_11 Server

to Router Server on Trip1.

B. Analysis In the field tests conducted at PT KAI Daop 2 Bandung:

• the processes of sending and receiving data including emails 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 emails from Gmail users and news from www.okezone.com were successfully received by users at Village_11 and Village_12.

• All emails addressed to Gmail, sent from Village_11 and Village_12 Servers, were successfully received by Gmail users.

51

• 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 emails delivered was 400 emails 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.

Emails from Gmail users and news from www.okezone.com, received and downloaded by the Main Server, were forwarded to Station Server, and then successfully delivered to Village Server through the 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.

IV. CONCLUSION In this research, Internet services system using train for

remote areas based on DTN proposed has been designed, implemented and tested in actual conditions. It was shown in the tests that email, news, and file transfer services were successfully delivered. This showed that by using DTN, data transmission can be done using the hop-by-hop principle without having the end-to-end connection between the source and the destination. Thus by using DTN techniques, users in remote areas are able to communicate to global Internet network even they do not have direct access to the global Internet network.

Other important tests’ results were: the highest mean throughput was 5.5981 Mbps, and the highest amount of emails delivered was 400 emails with a total data size of 10.94284 Mbytes in 27.9866 seconds time.

In improving the Internet services for remote areas based on DTN, it is suggested to design the Internet services system for remote areas based on DTN utilizing other public transportation systems (such as: bus, boat, airplane). Therefore, not only remote areas covered by train can take benefit of this system, but also remote areas located far away from railway.

REFERENCES [1] Demmer M., Brewer E., Fall K., Jain S., Ho M. and Patra

R., “Implementing Delay Tolerant Networking,” Intel Research Technical Report IRB-TR-04-020, Dec. 2004.

[2] Lijun D, Hongbo L, Yanyong Z, Paul S, Raychaudhuri. On the Cache-and-Forward Network Architecture. Proceeding of International Conference on Communications 2009 (ICC’09), 2009. 1-5.

[3] Agus U. Pengembangan Sistem Email untuk Delay Tolerant Network. Master Thesis. Bandung: Institut Teknologi Bandung; 2010.

[4] Aswin S. Sistem Telemedis Dan Layanan Berita Untuk Masyarakat Daerah Terpencil Dengan Memanfaatkan Transportasi Publik dan DTN (Delay Tolerant Network). Master Thesis. Bandung: Institut Teknologi Bandung; 2010.

[5] Ari R. Sistem Layanan Internet Berbasis Delay Tolerant Network dengan Memanfaatkan Kereta Api Sebagai Router. Master Thesis. Bandung: Institut Teknologi Bandung; 2010.

[6] Pentland, R. Fletcher, and A. Hasson, “DakNet: Rethinking Connectivity in Developing Nations,” IEEE Computer, vol. 37, No. 1, pp. 78–83, Jan. 2004.

[7] Vania C, Jeremie L, Timur F., “Fixed Point Opportunistic Routing in Delay Tolerant Networks,” IEEE Journal on Selected Areas in Communications, Vol. 26, No. 5, pp. 773 – 782, 2008.

[8] Laurent F, Felipe G., “Using Delay Tolerant Networks for Car2Car Communications,” Proceedings of the 2007 IEEE International Symposium on Industrial Electronics, 2007, pp. 2573 – 2578.

[9] Farid F, Ankitkumar N, Patel, Jason P, Jue, Vasco S, Joel R., “Vehicular Wireless Burst Switching Network: Enhancing Rural Connectivity,” Proceedings of the 2008 IEEE GLOBECOM Workshops, 2008, pp . 1 – 7.

52