1. Cooperation in DTN-Based Network Architectures
Authors:
Vasco N. G. J. Soares1,2, Joel J. P. C. Rodrigues1
1 Instituto de Telecomunicações, University of Beira Interior, Covilhã, Portugal
2 Superior School of Technology, Polytechnic Institute of Castelo Branco, Portugal
Editors:
Mohammad S. Obaidat1, Sudip Misra2
1 Monmouth University, USA
2 Ryerson University, Toronto, Canada

2. Outline Delay-Tolerant Network Vehicular Delay-Tolerant Network
Cooperation in DTN-Based Networks
Study of the Impact of Cooperation in a VDTN
4/23/2017

3. Delay-Tolerant Network (DTN)
Overlays a protocol layer, called bundle layer, that it is meant to provide internetworking on heterogeneous networks operating on different transmission media
Store-carry-and-forward paradigm
These networks experience any combination of the following:
Sparse connectivity
Long or variable delay
Intermittent connectivity
Asymmetric data rate
High latency
High error rates
No end-to-end connectivity
4/23/2017

4. Delay-Tolerant Network (DTN)
Application Domains
Interplanetary networks
Underwater networks
Wildlife tracking networks
Data MULEs
Transient networks
Disaster recovery networks
People networks
Military tactical networks
Vehicular networks
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5. Vehicular Delay-Tolerant Network (VDTN)
VDTN architecture appears as a network architecture proposal based on the DTN architecture, that aims to provide innovative solutions for challenged vehicular communications
VDTN applications
Urban Scenario
Disseminate information advertisements
Disseminate safety related information
Distribute multimedia content
Monitoring networks to collect data …
Rural Connectivity
Provide data communications to undeveloped remote areas
Disaster recovery networks
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6. VDTN Layered Architecture
Based on the principle of asynchronous, bundle-oriented communication from the DTN architecture
Store-carry-and-forward paradigm
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7. VDTN Layered Architecture
However, the design of the VDTN network architecture, and its protocol layering, presents unique characteristics:
IP over VDTN approach
Control plane and data plane decoupling
Out-of-band signaling
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8. VDTN Layered Architecture
Control plane and data plane separation
Control plane functions
Signaling messages exchange, node localization, resources reservation (at the data plane) and routing, among others
Data plane functions
Buffer management and scheduling, traffic classification, data aggregation/de-aggregation, and forwarding, among others
Distinct planes suggests that they can operate independently using their own layers and protocols
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9. VDTN Layered Architecture
Out-of-band signaling
Control plane
Uses a separate, dedicated, low-power, low bandwidth, and long-range link to exchange signaling information
Data plane
Uses a high-power, high bandwidth, and short- range link to exchange data bundles
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10. Cooperation in DTN-Based Networks
Cooperation is a key issue to the success of data communication in DTNs
In a cooperative environment, network nodes collaborate with each other, storing and distributing bundles not only in their own interest, but also in the interest of other nodes
This increases the number of possible transmission paths, improving the robustness to failure of individual nodes
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11. Cooperation in DTN-Based Networks
In a non-cooperative environment, network nodes exhibit a selfish behavior
This behavior can be caused by several reasons, such as, resource limitations (e.g. storage, energy) or rogue operation (malicious behavior)
This leads to degradation of the network performance
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12. Cooperation in DTN-Based Networks
Although cooperation is highly important to improve the limited capability of network nodes and, consequently, in increasing the overall network performance, to the best our knowledge, little research has been done in this field
This chapter surveys recent advances related with the field of cooperation on delay tolerant networks
Furthermore, it presents a study that evaluates the impact of cooperative behavior on the performance of a VDTN

13. Cooperation in DTN-Based Networks
Previous works (1)
Panagakis et al., “On the Effects of Cooperation in DTNs”, COMSWARE 2007
State that the literature related to the performance of DTN routing protocols usually assumes fully cooperative environments, which can be an unrealistic assumption
Define cooperation as the probability of a node to forward message copies or dropped them on their arrival, and evaluate its effect in terms of delivery delay and transmission overhead on Epidemic, Two-Hop and Binary Spray and Wait routing
Buttyán et al., “Barter-Based Cooperation in Delay-Tolerant Personal Wireless Networks”, WOWMOM 2007
Study the problem of selfish node behavior in DTNs used for personal wireless communications
Propose a mechanism to discourage selfish node behavior during message exchange based on the principles of barter. This barter-based approach is analyzed with a game- theoretic model

14. Cooperation in DTN-Based Networks
Previous works (2)
Shevade et al., “Incentive-Aware Routing in DTNs”, ICNP 2008
Also demonstrate the degradation of a DTN network performance due to selfish node behavior
Propose an incentive-aware DTN routing scheme to stimulate cooperation, which is based on the use of pair-wise tit-for-tat (TFT) incentive mechanism
Resta et al., “The Effects of Node Cooperation Level on Routing Performance in Delay Tolerant Networks”, SECON 2009
Present a theoretical framework for evaluating the effects of different degrees of node cooperation on the performance of DTN routing protocols (Epidemic, Two-Hop, and Binary Spray and Wait)
The observed results show that Binary Spray and Wait has the better resilience to lower node cooperation, while presenting the best compromise between packet delivery ratio and message overhead

15. Cooperation in DTN-Based Networks
Previous works (3)
Altman, “Competition and Cooperation Between Nodes in Delay Tolerant Networks with Two Hop Routing”, Lecture Notes in Computer Science, Network Control and Optimization
Analyzes competitive and cooperative operation in DTNs considering a Two-Hop routing strategy
The effect of competition between network nodes is studied in a game theoretical setting
Solis et al., “Controlling Resource Hogs in Mobile Delay-Tolerant Networks”, Computer Communications, Elsevier
Introduce the concept of “resource hog” as a network node that attempts to send more of its own data and possibly forward less peer data than a typical well-behaved node
A performance evaluation through simulation reveals that the delivery ratio of “well- behaved” nodes decreases significantly in the presence of a reduced number of nodes acting as “resource hogs”
The work also proposes and evaluates resource management solutions to deal with the “resource hogs” problem

16. Study of the Impact of Cooperation in a VDTN
Simulation Settings (network setup)
Modified version of the Opportunistic Network Environment (ONE) Simulator
New modules added (VDTN architecture model, buffer management scheme, scheduling and drop policies for evaluating the impact of node cooperation)
Simulation time of a 12-hour period (e.g., from 8:00 to 20:00)
100 Mobile Nodes (e.g. vehicles)
Random pause times between 5 and 15 m
Speed of 30 km/h
Buffer size varies between 25, 50, 75 and 100 Megabytes across the simulations
5 Stationary Relay Nodes
500 Mbytes message buffer size
Placed at selected crossroads
Helsinki simulation scenario

17. Study of the Impact of Cooperation in a VDTN
Simulation Settings (network setup)
Data Bundles
Size is uniformly distributed in the range of [250 K, 2 M] Bytes
Inter-bundle creation interval in the range [15, 30] seconds
Random source and destination vehicles
Time-to-live (TTL) of 180 minutes
Data bundles transmitted through a link with a data rate of 6 Mbps and an omni-directional transmission range of 30 meters
Epidemic and Binary Spray and Wait are used as the underlying routing schemes
Performance metrics: bundle delivery probability; bundle delivery delay
We analyze different performance results when mobile nodes employ 10, 20, 30, 40, or 50 percent of their buffer capacity and bandwidth resources to cooperate in bundle relay

18. Study of the Impact of Cooperation in a VDTN
Epidemic routing (1)
Delivery Probability
20 % of cooperation percentage means that:
20% of a node’s buffer capacity is used to store bundles relayed by other nodes, while the remaining 80% are available to store its bundles
In addition, at a contact opportunity, only 20% of the transmission link bandwidth will be used to relay the other nodes bundles
When network nodes use a 25 MB buffer, increasing the cooperation percentage from 10% to 20%, results in improving the overall delivery ratio in 13%
A better delivery ratio can be obtained using a 25 MB buffer size and a 30% cooperation percentage, instead of a 100 MB buffer with a 10% cooperation percentage
Effect of node cooperation percentage on the delivery probability

19. Study of the Impact of Cooperation in a VDTN
Epidemic routing (2)
Delivery Delay
Increasing the mobile nodes buffer size, contributes to increase the delivery ratio, but also increases the average delivery delay
This effect is reinforced by the increase of the nodes’ cooperation percentage that also contributes to increase the average time that bundles spend in buffers before being delivered
Using a 25 MB buffer, when cooperation percentage is lower than 20%, the storage space available for cooperating in the bundle relay process is very close to the average bundle size, which results in a very low number of cooperative bundles stored, and leads to frequent drops of such bundles
Effect of node cooperation percentage on the delivery delay

20. Study of the Impact of Cooperation in a VDTN
Binary spray and wait routing (1)
Delivery Probability
The effect of cooperation, as an effective strategy to increase the overall network bundle delivery, is even more pronounced in this routing protocol
When mobile nodes have a 25 MB buffer size, changing the cooperation percentage from 10% to 50%, increases the bundles delivery ratio in approximately 19%, 12%, 8%, and 7%, respectively
Employing a 100 MB buffer with a 10% cooperation percentage results in a similar delivery probability to a 25 MB buffer with a 40% cooperation percentage
Effect of node cooperation percentage on the delivery probability

21. Study of the Impact of Cooperation in a VDTN
Binary spray and wait routing (2)
Delivery Delay
Spray and Wait routing not only registers better delivery ratios, but also achieves better delivery delays than Epidemic flooding-based routing
However, cooperation does not have a significant effect on the average delay registered in this routing protocol
Furthermore, similar average delays are registered for buffer sizes greater than 25 MB, and cooperation percentages greater than 20%
This behavior was expected since similar delivery probabilities are observed in these cases
Effect of node cooperation percentage on the delivery delay

22. Conclusions
Delay tolerant networking (DTN) is a timely topic that addresses communication in challenged network environments
DTN-based networks like vehicular delay-tolerant networks (VDTNs) rely on cooperation behavior to help deliver bundles across sporadically connected nodes
Non-cooperative behaviors adversely affect the network operation and performance
This study addressed the research problem of node cooperation in DTN-based network architectures
The related literature about this topic was surveyed
A study to evaluate the impact of cooperation on the performance of VDTNs using two routing protocols was driven
Results demonstrate the importance of cooperation to improve the bundle delivery ratio