Chen et al. [20] proposes a scheme where a node is rewarded
each time it cooperates with another one. By given them this
incentive it was shown that n odes follow rigorously the
established routing protocol. In order to preserve the best
interests of each node this scheme considers storage space
limitations. This scheme is based on coalitional game theory.
Vehicle Ad-Hoc Network Reputation System (VARS) [21]
was proposed to enforce cooperation in VANETs. This system
is based on the concepts opinion generation and confidence of
the decision. With this system, each time a message is ex-
changed between two nodes, the receptor generates an opinion
on the trustworthiness of this message. This opinion is calcu-
lated considering three different approaches. It can be calcu-
lated using other nodes partial opinions that are attached to the
message, using indirect trust (if the sender is known), or a
combination of both. Calculated the node opinion, this is
attached to the message the next type it is forwarded. The
confidence decision is calculated by verifying the constraints
based on the node reputation levels.
In order to stimulate the cooperation between VANET
nodes, in [22], authors propose a new scheme. This scheme
rewards all the intermediary no des that participate in the
forwarding process of a specific message. In order to accom-
plish it, each time a message reaches its destination, all the
participant nodes should report its contribution to the source
node. By reporting nodes participation to the source node
allows source node to calculate the final contribution of each
node. This contribution is calculated through the sum of the
partial contribution given by each node in the forwarding tree.
Each intermediate node will receive a percentage as a reward
for forwarding the message.
Wang et al. [23] propose a dynamic trust-token (DDT) based
on cooperation enhancement mechanism. With this scheme,
selfish nodes are detected and marked as uncooperative nodes
in order to notify other nodes. This approach ensures data
packet integrity during the delivery process. Data packets are
forwarded with a token attached in order to evaluate their
correctness. To accept a packet, nodes will evaluate this token
in order to prove their corresponding. During the network
operation a reputation system of each node is set up.
In [24] authors propose a new protocol called Network
Coding-based Medium Access Control for VANETs. This
protocol takes advantages of cooperative Automatic Repeat
reQuest (ARQ) techniques in order to minimize the number of
total transmissions needed to deliver messages to their final
destination. This is achieved by coordinate the channel access
among a set of relays capable of using network coding.
The performance of DTNs is affected by several constraints
such as limited network bandwidth, limited storage capacity,
node density, or even disruption [25, 26]. To overcome these
issues and improve the overall network performance, cooper-
ation between nodes must be considered. The store-carry-and-
forward paradigm of DTN architecture assumes that nodes
cooperate between them. DTN nodes are capable to store and
forward bundles, not only in their own interest, but also in the
interest of other nodes. Using this approach, the number of
contacts opportunities increase, which result in a considerable
improvement of the network performance.
Panagakis et al. [27] state that DTN routing protocols must
assume a fully cooperative environment in order to improve
the overall network performance. This is not a correct and
consistent assumption because network nodes may adopt a
selfish behavior due to resource constraints or strategy. How-
ever, this work studies the impact of cooperation in the fol-
lowing three well-known routing protocols: Epidemic [28],
Two-hop [29], and Spray-and-Wait [30]. It was shown that
coopera tive algorithms perform better than uncooperative
ones. In this work authors also include simple cooperation
mechanism, which proved to improve the overall network
performance. Authors of [31] propose a game-theory mecha-
nism to stimulate cooperation between nodes. Performance
experiments show that, individually, the most beneficial be-
havior leads to an improved social optimum system.
C-ARQ [32] is a cooperative scheme to stimulate coopera-
tion between nodes in DTNs. The main goal of this scheme is to
reduce packet losses during transmissions between vehicles and
fixed access points. Cooperation is used to enable communica-
tions in places where an access point is not available. The same
authors proposed a variant of C-ARQcalledDC-ARQ(Delayed
Cooperative ARQ) [33]. In this variant, cooperation between
vehicles is active until they are out of range of the access point.
Taking into account the work presented in [33], Trullols-
Cruces et al. [34] create a fra mework that considers two
cooperation mechanisms. This framework tries to reduce the
number of packet losses during vehicle communications. To
accomplish this goal this framework calculates and predicts
nodes trajectory. This feature combined with the DTN store-
carry-and-forward paradigm improves the overall network
performance.
Resta et al. [35] studied and evaluated the impact of differ-
ent levels of cooperation in three DTN routing protocols. This
study is conducted through a theoretical framework. In a first
moment, Epidemic and Two-Hop schemes were studied as-
suming a fully cooperative environment. In this case, Epidem-
ic overcomes the performance of Two-Hop. Thus, different
layers of cooperation are enforced into Epidemic. To conclude
this study, authors enforce the same cooperation layers into the
binary version of Spray-and-Wait. Between all the conducted
studies, binary version of the Spray-and-Wait routing protocol
was the one who got the best results. In [36]theTwo-Hop
routing protocol was used to study the impact of node coop-
eration in DTNs. To stimulate nodes to cooperate, a game
theory scheme was used. To compare a cooperative with an
uncooperative scenario several balanced policies were used.
Solis et al. [37] present the “resource hog” concept. In this
concept, nodes try to send more of their own data and less peer
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