Research On Dynamic Trust Model For MANETs

Mobile Ad-hoc Networks (MANETs) are the multi-hop temporary communicationnetworks of mobile nodes equipped with wireless transmitters and receivers without theaid of any fixed network infrastructure. MANETs have their fundamental characteristics,such as open medium, dynamic topology, distributed cooperation, and constrainedcapability. Due to the anonymous and self-organization nature of mobile nodes in thenetwork, intermediate nodes on a communication path are expected to forward packetsof other nodes so that nodes can communicate beyond their wireless transmission range.Because mobile nodes are usually constrained by limited energy, bandwidth andcomputational power, a node may be unwilling to spend its resources in forwardingpackets which are not of its direct interest, even though it expects other nodes toforward its packets to the destination. At the same time, nodes have to manage the riskinvolved with the transactions without prior knowledge about each other's trust. Eachmobile node in MANETs may even be attacked directly or indirectly by maliciousnodes. With increasing applications of MANETs, it is a crisis issue to guaranteenetwork security.To solve above topics, the dissertation focuses on researching on dynamic trustmodel for MANETs. It concludes and analyses the present status and future challengesof security issues in MANETs. Based on the traditional network security and theinherence characteristics of MANETs, some novel research on guaranteeing networksecurity for MANETs are explored without adding the additional hardware. Somerelated trust models and a trusted routing discovery algorithm in frequency-domain areproposed based on game theory, fuzzy theory and certainty-factor for MANETs in thepaper.Related efforts result in following major innovative achievements:(1)Selfish nodes in MANETs do not forward packets to save battery or otherresources, which leads to make against realizing trust routing between nodes andforwarding data. In this paper, game theory is used to study nodes' behaviors whennodes receive service based on their reputations. Reputation is employed as a mechanism to incentives nodes to share resource and forward packets for other nodes.The model thinks synchronously over that there is not any central authority and acentralized solution to stimulate cooperation is not suitable for MANETs.Theoretical analysis and experimental results show the proposed trust model cansuccessfully identify selfish nodes and build trust among trust nodes to improve theefficiency of the network.(2)Based on that fuzzy logic provides a natural framework to deal with uncertaintyand the tolerance of imprecise data inputs for the subjective tasks of trust evaluation,packet-forwarding review and credibility adjustment, a trust model based on fuzzyrecommendation is proposed to quantify and evaluate the recommendationtrustworthiness of a node, which includes five types of fuzzy trust recommendationrelationships based on the fuzzy relation theory and a mathematical description forMANETs. The model aims at preventing the synergistic effect of selfish nodes. Theglobal trust value of a node is a global view of the whole network on the node bysummarizing the recommendations of nodes. Evaluation is not made only through someof "acquaintances" of selfish nodes. It simultaneity avoids the phenomenon that selfishnodes mutually forge recommendations to "flatter" each other in order to obtain themendacious and high trust values.Theoretical analysis and experimental results show that it is still robust under moregeneral conditions where selfish nodes cooperate in an attempt to deliberately subvertthe system, end-to-end packet delivery ratio more quickly, and decreases the averageenergy consumes more effectively compared with some traditional trust models. Theeffect of node rating data's sparsity can be greatly reduced and show the excellentperformance on typical data set.(3)The sample space of evidence may be not integrative or reliable because of thechange of network topology or the occurrence of wireless collision, so the existing trustevaluation model can not be applied. In this paper, a trust model based oncertainty-factor is proposed to quantify and to evaluate the trustworthiness of nodes,which includes a mathematical description and an implementation. The certainty-factorhas been used to model the issues of trust management. The evaluation of trust model isdiscussed, the derivation rules of recommendation trust relationships in MANETs arepresented and a trust model is provided. Theoretical analyses and experimental results show the model is more effectivelycomparing with the trust model based on evidence-evaluation. The trust model providesa new valuable way for MANETs.(4)In this paper, a trusted routing selection algorithm based on multi-objectives infrequency-domain for MANETs is proposed. It is distinctly different with most ofrouting algorithms that select routing based on a single-objective in the time-domain.Our proposed algorithm tries to analyze the secure and trusted routing based onprobability theory to reduce the computation complex with the mutual transformation ofprobability functions between time-domain and frequency-domain. It solves thequestion of finding secure and trusted routing for MANETs in the ease of the lack ofphysical security, untrustworthy scenario and low trust levels among nodes in MANETsand malicious nodes colluding with one another to disrupt the network operation.Extensive analysis has been carried out to evaluate the design of our algorithm.