Routing in « Delay Tolerant Networks » (DTN) Improved Routing With Prophet and the Model of “Transfer by Delegation” (Custody Transfer)

El Mastapha Sammou & Abdelmounaim Abdali
International Journal of Computer Networks (IJCN), Volume (4): Issue (6) 240
Routing in « Delay Tolerant Networks » (DTN)
Improved Routing With Prophet and the Model of “Transfer by
Delegation” (Custody Transfer)
El Mastapha Sammou sammouelmastapha@yahoo.fr
Department of Computer Science,
Faculty of Science and Technology,
University Cadi Ayyad,
Marrakech, 40000, Morocco
Abdelmounaim Abdali aabdali5@ gmail.fr
Department of Computer Science,
Faculty of Science and Technology,
University Cadi Ayyad,
Marrakech, 40000, Morocco
Abstract
In this paper, we address the problem of routing in “delay tolerant networks”
(DTN). In such networks there is no guarantee of finding a complete
communication path connecting the source and the destination at any time,
especially when the destination is not in the same region of the source, what
makes the traditional routing protocols inefficient in that transmission of the
messages between nodes. We propose to combine the routing protocol Prophet
and the model of "transfer by delegation" (custody transfer) to improve the
routing in DTN network and to exploit the nodes as a common carriers of
messages between the network partitioned.
To implement this approach and assess those improvements and changes we
developed a DTN simulator.
Simulation examples are illustrated in the article.
Keywords: Routing, Delay Tolerant Networks, DTN, Intermittent network connectivity, Simulator.
1. INTRODUCTION
Delay tolerant networks or networks with intermittent connectivity networks are wireless mobile ad
hoc often where a communication path between a source node and destination node does not
exist, either directly or through established routes by intermediate nodes. This situation occurs if
the network is sparse and partitioned into several areas due to high mobility, low density nodes or
when the network extends over long distances; In these cases, the traditional routing protocols
have been developed for mobile ad hoc networks proved to be insufficient because they require
the existence of a dense and connected in order to route the packets, To resolve this problem of
routing in DTN networks, researchers have proposed the use of routing approaches based on the
Principe "Store-Carry-and-forward [8], such as:
The epidemic routing protocol [9]: Messages propagate through the network like an outbreak of
disease. This approach ensures that the message reaches its destination as much as possible,
but it also wastes a lot of resources by unnecessary transfers of messages.

The Prophet routing protocol [1] is one of the routing algorithms that have been proposed to use
these resources properly. Prophet introduced a metric called Delivery Predectability , P (A, B) ∈
[0, 1]. This metric is calculated by each node A of the DTN network and for each known
destination B and will be used to decide which messages to be exchanged whenever two nodes
meet.
The model of "transfer by delegation"(custody transfer) [2] [3] [8]: In this model by assigning
responsibility for a message to a single node at any time. This model has the advantage of being
economical in terms of resources, since a message is the responsibility of a node at any time
during its delivery. However it now risk losing the message if the wearer goes down or destroyed.
Our approach is to combine the two approaches to routing, Prophet [1] and the model of
"transfer by delegation" (custody transfer) [2] [3] [8] to overcome the problems of routing in DTN
networks.
2. OUR APPROACH TO ROUTING
Normally, one of the most fundamental requirements is to find a communication path between
nodes in a sparse network and partitioned into several zones, in this case, communication
between areas of the network depends only on the displacement of certain nodes between areas
(as shown in Figure 1) As the delivery of messages depends on the mobility of nodes, it is very
difficult to obtain global information and routing becomes an important issue.
With the aim to maximize the chances that a message reaches its destination and to minimize the
resources consumed in the network such as bandwidth, capacity of storage devices and the
energy of the different nodes in an environment characterized by disconnections that often occur
because of the low density of nodes, node mobility and energy failure.
Our approach is to combine the routing protocol Prophet [1] and the model of "transfer by
delegation"(custody transfer) [2] [3] [8] to exploit the nodes as carriers of messages between
the network partitioned . The combination of these two approaches (Prophet and The model of
"transfer by delegation") combines two kinds of routing technique based on the degree of the
knowledge that the node has about its future contacts with other nodes in the network [4]:
• Technique of controlled routing.
• Technical routing predicted.
The key issues resolved by our approach:
• The choice of nodes that can act as carriers of messages (delegates) between the network
partitioned.
• Nodes incorporating elements of knowledge and contextual elements.
• Increases the chances that a message reaches its destination while minimizing the time from
End to End.
• Economic from the point of view of the network resources consumed.
FIGURE 1: Illustrating the transport of messages by a mobile
node moving between two areas, each consisting of a few nodes

In this work we have developed a DTN simulator written in Java which is based on our approach to
evaluate the different routing parameters.
3. SCENARIO OF OUR APPROACH
The probability of delivery are calculated locally in each area according to the approach of
Prophet [1] and the nodes move according to the two mobility models: Model Random Waypoint
and model Restricted Random Waypoint [10] [11] [12] as shown in Figure 2:
N0 node wants to send a message to N1. This can not be done because there is no path
between the two areas. The message is sent to N4 that has a better probability of delivery and a
planned movement and stores it. As shown in Figure 3:
After a certain period of time, N4 moves to another area (as shown in Figure 4). The message
reached its intended recipient using the routing protocol Prophet.
FIGURE 2: Illustrates the calculation of probability
according to Prophet in each zone.
FIGURE 4: Illustrates the node N4 in the second zone so
that the message is delivered to its intended recipient
.
FIGURE 3: Illustrates the transport of messages by a
mobile node moving between two areas.

4. STRATEGY FOR TRANSMISSION OF OUR APPROACH
When the source and destination are in two different areas [1] [2] [3] [6] [7] [8]
1. Nodes that can act as carriers are the nodes that have:
• A high probability of delivery.
• The planned movements between zones.
• A sufficient transmission energy.
2. In the case of a network where there are nodes that have random movements, the best
carriers are the nodes that have:
• A high probability of delivery.
3. In the case of a network where there are nodes that have random movements and nodes
which have planned movements, the best carriers are the nodes that have:
• A planned and controlled movement between areas.
4. When the nodes which have planned and controlled movements between zones are nodes
that have better features in terms of energy and storage capacity as the case of buses,
planes, trains … We may use them :
• On the one hand as the best carriers (delegates) of the message.
• Secondly as fixed relay " mobile "with a periodic occurrence in both areas, these relays
can be exploited on the one hand to describe the movements and mobility of nodes [5] in
each zone, based on the frequency of visits to these relays [6], secondly to increase the
number of contacts between nodes.
The principle of communication in the same area [1] [2] [3] [6] [7] [8]
• When a node encounters another node with the greatest probability of delivery, it sends
the message to that node and still keep the message for transmission to other nodes in
the future.
• When a node encounters another node that has a planned movement and a low
probability of delivery, it sends this message to the node even if the probability of delivery
is low, then it deletes the copy of the message, then it frees up the space at its storage
unit.
• When a node encounters another node that has a planned movement and a high
probability of delivery, it sends the message to this node, then it deletes the copy of the
message, then it releases the space at its storage unit.
Mechanisms of acquittals
The acknowledgment mechanism between nodes is done according to the acknowledgment
mechanism used by the model of "transfer by delegation"(custody transfer) [2] [3] [8].
Cases where the nodes are not allowed to transmit messages
• When a node encounters another node that has a high probability of delivery and has not
enough energy.
• When a node encounters another node that has a planned movement and controlled and
not enough energy.
• When a node encounters another node that has a planned and controlled movement and
a high probability of delivery and has not enough energy.
5. SIMULATION AND TEST
The simulator is written in Java. JAVA is an object-oriented programming language, allows one
hand to develop real applications and the other hand the object-oriented approach considers a
program as consisting of a set of objects which adapts our approach. Figure 5 shows the general
design of the application and Figure 6 shows the main interface of the application.

.
FIGURE 5: Illustrates the general design of the application
FIGURE 6: Illustrates the main interface of the application

Assumptions and Data Analysis
1. Assumptions: We assume that Packet routing is done from the "store-carry-and-
forward" ; The volume of the queue is considered infinite; The nodes move according to
the two models of random mobility: Restricted random waypoint and Radom Waypoint
[10] [11] [12]; The speed of nodes varies between Vmin= 200 ms and Vmax = 50 ms; The
space of traveled nodes varies between 50 and 500 units of surface; The number of
nodes varies between 8 and 300 nodes; The number of packets from the source is 1000
packets; The energy level of each node is 1000 units of energy ; The probability of
delivery is calculated locally according to formulas presented by the routing protocol
prophet [1].
P (A, B) = P (A, B) old+ (1− P (A, B) old ) * Pinit
P (A,C )= P (A,C )old + (1 - P (A,C ) old) * P (A, B ) * P (B,C )*β
P (A, B) = P (A, B) *ϒk
2. Data analysis: In this simulator we have analyzed the following data: The number of
packets transmitted in the network; The number of packets not sent; The number of
packets received by the destination; The energy consumed in the network; The amount
of memory consumed in the network. This analysis is done according to the approach of
the Prophet and in our approach to compare the two approaches.
Tests and results
1. Scénario1
Both areas are dense and connected. The internal connectivity of each zone is guaranteed.
However, there is no permanent connection between the two areas.
Simulation parameters 1 Values
Number of nodes 50
Energy level of each node 1000
Radius of the focused communication 50 m
Maximum Speed 50 ms
Size of each area 300*300
Simulation time 1500 ms
Initial probability 0,75
β 0,25
ϒ 0,98
• Simulation results under the approach of Prophet.
TABLE1: Parameters of simulation 1

• Simulation results based on our approach.
2. Scénario2: The node density is low in both areas. The internal connectivity of each zone is
not guaranteed and there is no permanent connection between the two areas.
• Simulation results under the approach of Prophet.
Simulation parameters 2 Values
Number of nodes 20
Energy level of each node 1000
Radius of the focused communication 40
Maximum Speed 50 ms
Size of each area 500*500
Simulation time 1500 ms
Initial probability 0,75
β 0,25
ϒ 0,98
Figure 8: Illustrates the analytical result of our approach
Depending on the parameters of simulation 1
TABLE2: Parameters of simulation 2
FIGURE 7: Illustrates the result of analysis of the approach of the
prophet depending on the parameters of simulation 1

• Simulation results based on our approach.
6. CONCLUSION
DTN networks suffer from several shortcomings related to routing, especially when the network is
partitioned into several zones and where the destination is not in the same region of the source,
what makes traditional routing protocols ineffective to the extent of transmit messages between
nodes.
We proposed an approach that involves combining the routing protocol Prophet and the model of
"transfer by delegation" (custody transfer) to improve routing in DTN networks based on
contextual elements and the elements of knowledge a node has about its future contacts with
other nodes in the network.
According to the simulations realized, our approach has good performance in comparison to the
Prophet algorithm, but its effectiveness can be further improved.
7. REFERENCES
1. A.Lindgren, A. Doria and O. Scheln. Probabilistic routing in intermittently connected
networks. In Proceedings of ACM MobiHoc (poster session), Maryland, USA, June2003.
2. F. GUIDEC, “Deployment and implementation support services communicating in
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communicants dans les environnements d’informatique ambiante,”L’UNIVERSITÉ DE
BRETAGNE SUD, June 2008, pp. 35-65
3. Kevin Fall, Wei Hong, and Samuel Madden. Custody Transfer for Reliable Delivery in Delay
Tolerant Networks. Technical report, Intel Research Berkeley, 2003.
FIGURE 9: Illustrates the result of analysis of the approach of
Prophet depending on the parameters simulation 2
FIGURE 10: Illustrates the result of analysis of our approach
Depending on the parameters of simulation 2
.

4. M. IBRAHIM “Routing and performance evaluation of Disruption tolerant networks,”
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Mobile Networks” in Proc. WOWMOM, 2005.
8. F. Warthman, “Delay Tolerant Networks”, Delay Tolerant Networking Tutorial,2003,
http://www.ipnsig.org/reports/DTN_Tutorial11.pdf
9. A. Vahdat and D. Becker, “Epidemic routing for partially connected ad hoc networks,”
Technical Report CS-200006, Duke University, April 2000”.
10. Christian Bettstetter, Hannes Hartenstein, and Xavier Pérez-Costa, “Stochastic properties
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Modeling and Analysis of Mobile Networks, 10(5) :555–567, Sept.2004.
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Routing in « Delay Tolerant Networks » (DTN) Improved Routing With Prophet and the Model of “Transfer by Delegation” (Custody Transfer)

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