This document summarizes research on Delay Tolerant Networks (DTNs). It discusses DTNs' characteristics including long latency, unstable topology, and lack of end-to-end paths. It also examines challenges like privacy concerns when humans are involved. The document reviews data forwarding techniques in DTNs like store-and-forward and epidemic routing. Potential applications are also discussed, such as providing rural internet access through projects like DakNet that use transportation infrastructure. The document concludes by encouraging further research on DTNs and their applications.

1. NOTRE DAME UNIVERSITY
Faculty of Science
Computer Science Department
Data Communication and Computer Networks
Formal Report
Delay Tolerant Network - DTN
Submitted by:
Michel Chamat
Michel Azzi

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Table Of Content
Abstract ………………………………………………………………………………………….. 3
Introduction and Problem Definition ……………………………………………………………. 4
Background Documented Research ……………………………………………………………... 5
Conclusion ………………………………………………………………………………………. 9
List of Reference ………………. ……………………………………………………………….10

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I. Abstract
This research is based on the Delay Tolerant Network. Main aspects and characteristics of
DTN are subject of this report, taking into considerationthe technical problems this network
may encounter while applying them in real life. The report contains a documented research
about the actual applications that can be applied, data forwarding process and privacy
protectionforusers inthis kind of network. Furthermore,future possible worksinthis domain,
in addition to possible applications, are included to encourage the research in this subject.

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II. Introduction and Problem Definition
Delay Tolerant Network, based on network architecture, is made to ensure continuous
network connectivity between heterogeneous networks operating on different transmission
media. Also, thecommunicationdoesn’tonlydepend ontheInternet.Such network isdesigned
to operate effectivelyover extreme distances, as those encounteredinspace communications.
In this environment, long latency is inevitable. However, similar problems canalso occur over
small distances, where interference is high or network resources are overloaded.
When it comes to application, Delay Tolerant Network has many problems which
directly affects the efficiency of the network, especially with the involvement of human
interaction. It features long latency and unstable network topology, where delay is enormous
and routing paths may not exist. Traditional routing protocols for mobile networks are
thereforeunsuitableforDTNs. In addition, the networkusesstoreand forwardtechniqueswith
no fixed connectionavailable between the users, allowing the increase in transmissiondelay.
Finally, privacy of real social life may be subject to potential attacks as data is being forward
in public places through public devices.
Despite these problems, DTN is the solutionfor challenging networks, such as space
communicationand military operations, as its characteristics are perfect match in these kind
of networks.

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III. Background Documented Research
Most routing protocols for traditional networks need to set up a complete end-to-end
route, with at least one available end-to-endpath between the source and destination, before
packet transferring in the traditional mobile network. It is assumed that in DTNs, any link
between two nodes is duplex and the latency of the network is not an issue. Therefore, the
DTN doesn’tneedto setupthe paths forcommunications.Regardlessbeingoneofits problem,
the Delay Tolerant Network can be very useful in very complex networks, such as space
communication. Hereafter, data processing, privacy protection in addition to the applications
of the DTN are to be discussed.
Concerning data forwarding, DTN typically uses store and forward technique: if no
connection is available at a particular time in this technique, the source node storesandcarries
the message until the next available node is encountered andform a candidature set. Although
this technique is being applied, the comparisonand selectionof the most suitable forwarding
targets are topics for more advanced researches in DTN. On the other hand, when mobile
devices in DTN are associatedwithhuman beings, such as a Bluetoothenabledmobile phone,
they demonstrate certain social aspects associated with human-to-human communications.
More specifically, the human’s social behavior has a big role in these kinds of delay tolerant
networks. Also, the locationwhere a DTN is locatedmight have severe consequences onthe
efficiency comparedto humaninteraction, as geographic topologyinaDTN is unstable, while
socialcharacteristics ofmobilenodesarerelativelystableforafixedperiodoftime.Therefore,
the influence of human contribution can be very supportive and more important than
geographic informationin routing. The main problem with human interactions is that social
activities are limitedto specific hours, and therefore the data forwarding in such DTN will be
very time-dependent. For example, after midnight, the communication will barely exist and
the communicationwillbe very slowtounavailable, while inthe middle ofthe day it will reach
its peak. Moreover, a faster way for forwarding data in DTN is by using vehicles. Vehicular
DTN (VDTN) has many advantages as it expands connectivity, despite any lack of
infrastructure. It also simplifies the networkarchitecture by settingmobile routers, stationary

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nodes and relaynodes placedat intersections, for example. Whenit comes to dataforwarding,
time varying social contact topology model is proposed to combine social attributes, time
patterns and geographic information. This model analyses the social similarityof nodes along
with the geographic information bounded with time factors to generate an overall delivery
probabilityforeachnode to the destination.Basedonthisdeliveryprobability, a multicastdata
forwarding algorithm is deployed to efficiently deliver packets.
To apply the store and forwardtechnique in the delay tolerant network, routing implies
and concerns itself with the ability to deliver data from a source to a destination which is
essential in any network. Despite DTN’s lack of connectivity and instantaneous end-to-end
paths, data is incrementally moved and stored throughout the network in hopes that it will
eventually reach its destination when the correct nodes are found. Epidemic router is the
technicusedto increasetheprobabilityofa packet being successfullytransferredistoreplicate
many copies of the packet in hopes that one will reaches its correct destination.
As thedata forwarding issuebecomesincreasinglyimportantinhuman involved DTNs,
lots of researchers use real social trace files to study the characteristics of mobile nodes.
However, thesedatasetsaresensitive,with potentialattacksusing the providedsocialattributes
to retrieve the subject identification, and thereforethe publisher may not want to release these
datasets. Privacy protectionis important for researchers andin most cases, researchers use the
data anonymous method to pre-processdata identifiers and attributes to make sure attackers
do not disclosethe dataset withthe released data. K-anonymityand Generalizations.These are
typical anonymous methods, which decrease the data utilityto protect attribute semanticsand
thereforeprevent the privacy disclosure issue. Attribute semantics shouldbe reservedinsome
scenarios, such as data mining or information retrieval. However, it is not necessary in a
scenario of DTNs. As the informationrequiredfor the routing decisionmaking process is the
corresponding relationships amongattributes, the attributes themselves canbe anonymized. If
both node’s identification and their associated attributes are anonymous, privacy disclosure
canbe prevented. In addition, an Entropybasedanonymous data detectionmodel wasproposed
to measure how important each attribute and their overall relationships were. Based on these
relationships and their importance, each attribute was assigned a weight factor to identify its

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positionin this anonymous dataset. Furthermore, a social aware K-core (S-kcore)algorithm
was designedto combine these generatedweight factors to detect the keynode. Although this
key node may not be physically locatedin the neighbor area of the source node, the S-kcore
algorithm was based on social attributes and their associatedweight factor where it is not be
affectedby the physical movement of nodes. Another advantage of the proposedmodel is the
unicast forwarding model. As the network topology of human associated delay tolerant
networks is unpredictable, the concurrent most popular node is selectedby using the S-kcore
algorithm to conduct unicast forwarding to reduce those duplicated copies.
Typical applications of DTN techniques stratify four aspects: digital communication
forruralareas, personal/wildlifecommunications,battlefieldcommunications,disasterrescues
and environmental monitoring communications.
When it comes to rural areas, many prototypes were designed and applied to provide
connectionto the biggest number of users. Such prototypes are calledDakNet, TrainNet and
KioskNet, and they share the same basic principles of sharing facilities to provide
communication for the users. DakNet, for example, provides an asynchronous digital
connectionon the infrastructure of ad hoc networks. DakNet uses existing communications
and transport infrastructure to form a DTN, where it combines physical transportationwith a
wireless data transferal functionto extendInternet connectivityto acentral hub, such as a post
office. It transmits data over short point-to-point links between kiosks and portable storage
devices called mobile access points (MAPs). The point-to-point data transfers use high
bandwidth with low-cost WiFi radio transceivers. The same concept is applied to TrainNet,
using the already working trains in any location, and to KioskNet, using the available kiosks
in smaller cities to provide public networks.
Other applications for this network are personal/wildlife, battlefield, disaster rescues
and environmental monitoringcommunications and they all have the same fundamentals for
their DTNs. Free space optical communications (FSOC) is used in these kinds of missions,
where bandwidth and communicationsignals might be affectedbythe geographical area: lack
of infrastructure, uncovered zone… DTN serves efficientlyas it helps to move information
closer to its destination on each of the transactions by considering the topology control

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requirement from FSOC. Therefore, units communicate internallywithno significant noise or
interruptions throughinterconnect devices, and a mobile router connectedto the base through
FSOC is available to communicate with the base to gather additional information, when
necessary. Delay tolerant networks are very useful in these kinds of mission as the main
problem any team could face in these uncovered places is the lack of connection, which the
DTN solves efficiently.
Finally, one of the most important application is space communication. Using DTN,
the communication between devices on different planets is provided by the space base.
Connectedto earth, to provide internet, and the remaining hosts, this DTN provide the basic
elements to exchange data and keep the connection going without using the necessity of
internet.

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IV. Conclusion
To conclude, delay tolerant networks are the best solutionfor very complexnetworks,
due togeographical orinfrastructureproblems.Basedonthestoreandforwardtechnique,these
networks offer high bandwidth with low cost despite the unavailability of connectionat many
times. DTNs use the available basic resources to spread the network for the users in the
location, with DakNet and TrainNet as examples. In addition, privacy in public areas is
protectedusinganonymous addresses to protect the datasets of mobile routers. Finally, many
applicationsarenow being usedtoensurebasicconnectionsindifficultconditionslikeinspace
or battlefields, inadditionto future works that couldimprove these networks like Multicasting
efficiency in VDTN and Multi-Layer Survivability.

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V. List of References
Delay Tolerant Networks, L. Gao, S. Yu & T. Luan, 2015
http://searchnetworking.techtarget.com/definition/delay-tolerant-network
https://en.wikipedia.org/wiki/Routing_in_delay-tolerant_networking
https://en.wikipedia.org/wiki/Delay-tolerant_networking