Delay tolerant networks (DTNs) are characterized by high end-to-end latency, frequent disconnection, and opportunistic communication over unreliable wireless links. In this paper, we design and validate a dynamic trust management protocol for secure routing optimization in DTN environments in the presence of well-behaved, selfish and malicious nodes. We develop a novel model-based methodology for the analysis of our trust protocol and validate it via extensive simulation. Moreover, we address dynamic trust management, i.e., determining and applying the best operational settings at runtime in response to dynamically changing network conditions to minimize trust bias and to maximize the routing application performance. We perform a comparative analysis of our proposed routing protocol against Bayesian trust-based and non-trust based (PROPHET and epidemic) routing protocols. The results demonstrate that our protocol is able to deal with selfish behaviors and is resilient against trust-related attacks. Furthermore, our trust-based routing protocol can effectively trade off message overhead and message delay for a significant gain in delivery ratio. Our trust-based routing protocol operating under identified best settings outperforms Bayesian trust-based routing and PROPHET, and approaches the ideal performance of epidemic routing in delivery ratio and message delay without incurring high message or protocol maintenance overhead.

We propose a highly scalable cluster-based hierarchical trust management protocol for wireless sensor networks (WSNs) to effectively deal with selfish or malicious nodes. Unlike prior work, we consider multidimensional trust attributes derived from communication and social networks to evaluate the overall trust of a sensor node. By means of a novel probability model, we describe a heterogeneous WSN comprising a large number of sensor nodes with vastly different social and quality of service (QoS) behaviors with the objective to yield "ground truth" node status. This serves as a basis for validating our protocol design by comparing subjective trust generated as a result of protocol execution at runtime against objective trust obtained from actual node status. To demonstrate the utility of our hierarchical trust management protocol, we apply it to trust-based geographic routing and trust-based intrusion detection. For each application, we identify the best trust composition and formation to maximize application performance. Our results indicate that trust-based geographic routing approaches the ideal performance level achievable by flooding-based routing in message delivery ratio and message delay without incurring substantial message overhead. For trust-based intrusion detection, we discover that there exists an optimal trust threshold for minimizing false positives and false negatives. Furthermore, trust-based intrusion detection outperforms traditional anomaly-based intrusion detection approaches in both the detection probability and the false positive probability.

We propose a trust-based intrusion detection scheme utilizing a highly scalable hierarchical trust management protocol for clustered wireless sensor networks. Unlike existing work, we consider a trust metric considering both quality of service (QoS) trust and social trust for detecting malicious nodes. By statistically analyzing peer-to-peer trust evaluation results collected from sensor nodes, each cluster head applies trust-based intrusion detection to assess the trustworthiness and maliciousness of sensor nodes in its cluster. Cluster heads themselves are evaluated by the base station. We develop an analytical model based on stochastic Petri nets for performance evaluation of the proposed trust-based intrusion detection scheme, as well as a statistical method for calculating the false alarm probability. We analyze the sensitivity of false alarms with respect to the minimum trust threshold below which a node is considered malicious. Our results show that there exists an optimal trust threshold for minimizing false positives and false negatives. Further, the optimal trust threshold differs depending on the anticipated wireless sensor network lifetime.

We propose and analyze a class of trust management protocols for encounter-based routing in delay tolerant networks (DTNs). The underlying idea is to incorporate trust evaluation in the routing protocol, considering not only quality-of-service (QoS) trust properties (connectivity) but also social trust properties (honesty and unselfishness) to evaluate other nodes encountered. Two versions of trust management protocols are considered: an equal-weight QoS and social trust management protocol (called trust-based routing) and a QoS only trust management protocol (called connectivity-based routing). By utilizing a stochastic Petri net model describing a DTN behavior, we analyze the performance characteristics of these two routing protocols in terms of message delivery ratio, latency, and message overhead. We also perform a comparative performance analysis with epidemic routing for a DTN consisting of heterogeneous mobile nodes with vastly different social and networking behaviors. The results indicate that trust-based routing approaches the ideal performance of epidemic routing in delivery ratio, while connectivity-based routing approaches the ideal performance in message delay of epidemic routing, especially as the percentage of selfish and malicious nodes present in the DTN system increases. By properly selecting weights associated with QoS and social trust metrics for trust evaluation, our trust management protocols can approximate the ideal performance obtainable by epidemic routing in delivery ratio and message delay without incurring high message overhead.

With the advance of various wireless access technologies, the demand for a mobile user equipped with multiple air interfaces simultaneously executing diverse applications emerged. In such network environment, per- application mobility management is a key to allow each application of an end user device to dynamically and fully take advantage of the most suitable access technology. In this paper, we devised a comprehensive architectural platform with cross- layer techniques to realize this disruptive technology, i.e., per- application mobility management. Four core functional modules composing the proposed platform for end user devices are defined: Monitoring Agents, Profile Database, Decision Engine, and IP Agent. We show through simulations that the presented platform provides an improved QoS as it selectively utilizes the best available networks depending on different QoS constraints of different applications.

In this paper, we propose a wireless network domain structure which deploys a special cell, called a gray cell. The boundaries of wireless network regions are surrounded by the gray cells, and the gray cells are supposed to belong to all of its neighboring regions. Based on this wireless domain structure, we propose a mechanism which completely removes the waste of redundant resource reservation in the wireless network domain while greatly reducing the risk of reservation disruption caused by inter-region handovers. Using simulation, it is shown that the proposed mechanism can deal with inter-region handover as effectively as it does with intra-region handover. It is also shown that the proposed mechanism outperforms existing mechanisms with respect to reservation disruption time and packet losses caused by handovers.

In order to provide continuous QoS guarantees to a mobile user, it is required to deploy a mechanism which reserves resources in advance at the locations to which the mobile user is expected to move. An important issue with regards to these mechanisms is to minimize the waste of resources caused by redundant reservations while keeping up the QoS services to the user. In this paper, we propose a wireless network domain structure which deploys a special cell, called a gray cell. The boundaries of wireless network regions are surrounded by the gray cells, and the gray cells are supposed to belong to all of their neighboring regions. Based on this structure, we propose a mechanism which completely removes the waste of redundant resource reservation while greatly reducing the risk of reservation disruption caused by inter-region handovers. Using simulation, it is shown that the proposed mechanism can deal with inter-region handover as effectively as it does with intra-region handover. It is also presented that the proposed mechanism outperforms existing mechanisms with respect to reservation disruption time and packet losses caused by handovers.