Introduction to Delay Tolerant Networks

Tzu-Chieh TsaiDepartment 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

SData

Traditional Routing

Traditional Routing

How does it work?

D

S

R

Store Carry Forward

Store Carry Forward

StoreStore

ForwardForward

Data

How does it work?

CarryCarry

Bagel = Source

Bagel = Source

Ants = Relay

Ants = Relay

Fact 1: Wireless is everywhere !

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 NetworksOpportunistic 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 issuesN. 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