Download Chapter 7

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
[email protected], [email protected]
Editors:
Mohammad S. Obaidat1, Sudip Misra2
1
Monmouth University, USA
2 Ryerson University, Toronto, Canada
[email protected], [email protected]
Outline
• Delay-Tolerant Network
• Vehicular Delay-Tolerant Network
• Cooperation in DTN-Based Networks
• Study of the Impact of Cooperation in a VDTN
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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:
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Sparse connectivity
Long or variable delay
Intermittent connectivity
Asymmetric data rate
High latency
High error rates
No end-to-end connectivity
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Delay-Tolerant Network (DTN)
• Application Domains
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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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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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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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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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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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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 shortrange link to exchange
data bundles
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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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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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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
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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 gametheoretic model
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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
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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 “wellbehaved” 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
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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
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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
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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
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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
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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
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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%
Effect of node cooperation
percentage on the delivery delay
• This behavior was expected since similar
delivery probabilities are observed in these
cases
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Conclusions
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Delay tolerant networking (DTN) is a timely topic that addresses communication in
challenged network environments
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DTN-based networks like vehicular delay-tolerant networks (VDTNs) rely on
cooperation behavior to help deliver bundles across sporadically connected nodes
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Non-cooperative behaviors adversely affect the network operation and
performance
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This study addressed the research problem of node cooperation in DTN-based
network architectures
• The related literature about this topic was surveyed
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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
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