Introduction to Delay Tolerant Networks Tzu-Chieh Tsai Department of Computer Science, National Cheng Chi University

Outline  Introduction  How does it works?  Key Properties of DTNs  Potential Applications  Summary

Future Wireless Internet Slide from “DTNs and Sensor Networks”, Myung-Ki Shin at Future Internet Camp, August 2007.

Introduction  Core function of communication network  Routing  Find a path from a source to some destinations  Traditional routing solutions  Assume that there exists an end-to-end path between communicating nodes  Delay/disruption tolerant networks  Communication is possible even if end-to-end connectivity is never achievable  Exploiting node’s mobility  Using store-carry-forward fashion

D S Data Traditional Routing How does it work?

D S R Store Carry Forward Store Forward Data How does it work? Carry

Bagel = Source Ants = Relay

 Fact 1: Wireless is everywhere !

 Fact 2: We need mobility!

 Fact 1: Wireless is everywhere !  Fact 2: We need mobility!  Fact 3: Storage is cheap and vast!

Opportunistic Networks

Opportunistic Networks vs Internet

Key Properties of DTNs  High Latency  Any two nodes may never meet each other.  Low Data Rate  Due to the long latency of data delivery.  Disconnection  It is hard to find an end-to-end path.  Long Queuing Delay  Because of the disconnection.  Short Range Contact  Only one-hop communication is guaranteed.  Dynamic Network Topology  Different types of user behavior will result in dramatically different network conditions.

Outline  Introduction  How does it works?  Key Properties of DTNs  Potential Applications  Summary

Potential Applications  Telemedicine for Developing Regions  DTN-based Social Network Service  Communication in the Presence of Oppressive Governments  File Sharing and Bulk Data Transfer  Share Air Minutes

Telemedicine for Developing Regions  Store-Carry-forward Voice-over-IP telemedicine system  Improve the possibility for doctors to give correct diagnose and prescribe treatment from remote location  Benefit  Can be used by those who lack computer skills.  Open source software is relatively cheap.  Can be deployed without fixed infrastructure  Challenge  Long delay would causes some disruption in voice quality. M. Chetty, W. Tucker, and E. Blake. Developing locally relevant applications for rural areas: A south african example. In SAICSIT, 2004.

DTN-based Social Network Service  DTN-based Short Message Service  Example: A farmer can send a advertisement message to his friends, and the friends can help to propagate the message through the social network.  Benefit  A more convenient way to find and exchange information than traditional face-to-face communication  Challenge  Need to find incentive mechanisms to convince end user to use the system B. E. Kolko, E. J. Rose, and E. J. Johnson. Communication as information-seeking: the case for mobile social software for developing regions. In Proc. of WWW ’07, 2007.

Communication in the Presence of Oppressive Governments  Anonymous Delay Tolerant Networks  Opportunistic forwarding message between people  Much more difficult for government agencies to track the communication.  Benefit  Using mobility and delay of transmission to increase anonymity.  Challenge  How to avoid rogue agents injecting fake acknowledgements to purge messages from the network? R. Dingledine, N. Mathewson, and P. Syverson. Tor: The second-generation onion router. In Proceedings of the 13th USENIX Security Symposium, August 2004.

File Sharing and Bulk Data Transfer  Use the cellular network to transmit the request for some content, and then use delay tolerant techniques to deliver the data to the mobile device.  It’s more beneficial if the data access patterns are somehow localized such that users in a certain area are more likely to request a certain data item.  Benefit  File data would rapidly be shared between a large part of population with less resource usage.  Challenge  Copyright and DRM issues N. Laoutaris, G. Smaragdakis, R. Sundaram, and P. Rodriguez. Delay-Tolerant Bulk Data Transfer on the Internet. In Proceedings of ACM SIGMETRICS 2009, Seattle, WA, June 2009.

Share Air Minutes  Allowing the contract users to share their excess air minutes to the prepaid card users.  The shared phone acting as the server then diverts the voice traffic to the cellular network via the phone’s cellular link.  Benefit  Contract users sell their unused minutes  Pre-pay users could still use the calling service  Operators can gain the value of the resold minutes.  Challenge  How to deal with the micro-payments? P. Hui, R. Mortier, K. Xu, J. Crowcroft, and V. O. Li. Sharing airtime with shair avoids wasting time and money. In Proc. of HotMobile 2009, February 2009.

Outline  Introduction  How does it works?  Key Properties of DTNs  Research Issues  Mobility Pattern Analysis  Routing Protocol Design  Potential Applications  Summary

Summary  Characteristics of DTN  No end-to-end path  Intermittent connectivity  Dynamic topology  Long delay  DTN routing  Flooding-based: redundancy  Forwarding-based: require topology information  Potential Application  Urban area: DTN-based Social Network Service  Developing region: Low cost communication solutions