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. ThisÃƒâ€šÃ‚Â cooperation is a cost-intensive activity and some nodes can refuse to cooperate, leading to a selfish node behaviour. Thus, the overallÃƒâ€šÃ‚Â network performance could be seriously affected. The use of watchdogs is a well-known mechanism to detect selfish nodes. However,Ãƒâ€šÃ‚Â the detection process performed by watchdogs can fail, generating false positives and false negatives that can induce to wrongÃƒâ€šÃ‚Â operations. Moreover, relying on local watchdogs alone can lead to poor performance when detecting selfish nodes, in term ofÃƒâ€šÃ‚Â precision and speed. This is specially important on networks with sporadic contacts, such as delay tolerant networks (DTNs), whereÃƒâ€šÃ‚Â sometimes watchdogs lack of enough time or information to detect the selfish nodes. Thus, we propose collaborative contact-basedÃƒâ€šÃ‚Â watchdog (CoCoWa) as a collaborative approach based on the diffusion of local selfish nodes awareness when a contact occurs, soÃƒâ€šÃ‚Â that information about selfish nodes is quickly propagated. As shown in the paper, this collaborative approach reduces the time andÃƒâ€šÃ‚Â 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.