CoCoWa: A Collaborative Contact-Based Watchdog for Detecting Selfish Nodes

CoCoWa: A Collaborative Contact-Based Watchdog for Detecting Selfish Nodes

Mobile ad-hoc networks (MANETs) assume that mobile nodes voluntary cooperate in order to work properly. This cooperation is a cost-intensive activity and some nodes can refuse to cooperate, leading to a selfish node behaviour. Thus, the overall network performance could be seriously affected. The use of watchdogs is a well-known mechanism to detect selfish nodes. However, the detection process performed by watchdogs can fail, generating false positives and false negatives that can induce to wrong operations. Moreover, relying on local watchdogs alone can lead to poor performance when detecting selfish nodes, in term of precision and speed. This is specially important on networks with sporadic contacts, such as delay tolerant networks (DTNs), where sometimes watchdogs lack of enough time or information to detect the selfish nodes. Thus, we propose collaborative contact-based watchdog (CoCoWa) as a collaborative approach based on the diffusion of local selfish nodes awareness when a contact occurs, so that information about selfish nodes is quickly propagated. As shown in the paper, this collaborative approach reduces the time and increases the precision when detecting selfish nodes.


  • The literature provides two main strategies to deal with selfish behaviour:
    • Motivation or incentive based approaches
    • Detection and exclusion
  • The first approach, tries to motivate nodes to actively participate in the forwarding activities. These approaches are usually based on virtual currency and/or game theory models.
  • The detection and exclusion approach is a straight-forward way to cope with selfish nodes and several solutions have been presented.
  • Watchdogs are appropriate mechanisms to detect misbehaving and selfish nodes.
  • Watchdog systems overhear wireless traffic and analyse it to decide whether neighbour nodes are behaving in a selfish manner.
  • When the watchdog detects a selfish node it is marked as a positive detection (or a negative detection, if it is detected as a non selfish node).
  • Nevertheless, watchdogs can fail on this detection, generating false positives and false negatives that seriously degrade the behavior of the system.



  • Collaborative Contact-based Watchdog (CoCoWa) is proposed as a new scheme for detecting selfish nodes that combines local watchdog detections and the dissemination of this information on the network.
  • If one node has previously detected a selfish node it can transmit this information to other nodes when a contact occurs.
  • This way, nodes have second hand information about the selfish nodes in the network.
  • The goal of this approach is to reduce the detection time and to improve the precision by reducing the effect of both false negatives and false positives.

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