Time synchronization is an important issue in multihop ad hoc wireless networks such as sensor networks. Many applications of sensor networks need local clocks of sensor nodes to be synchronized, requiring various degrees of precision. Some intrinsic properties of sensor networks, such as limited resources of energy, storage, computation, and bandwidth, combined with potentially high density of nodes make traditional synchronization methods unsuitable for these networks. Hence, there has been an increasing research focus on designing synchronization algorithms specifically for sensor networks. This article reviews the time synchronization problem and the need for synchronization in sensor networks, then presents in detail the basic synchronization methods explicitly designed and proposed for sensor networks.

Information and communication technologies (ICTs) have a profound impact on the current state and envisioned future of automobiles. This paper presents an overview of research on ICT-based support and assistance services for the safety of future connected vehicles. A general classification and a brief description of the focus areas for research and development in this direction are given under the titles of vehicle detection, road detection, lane detection, pedestrian detection, drowsiness detection, and collision avoidance. Following an overview and taxonomy of the reviewed research articles, a categorized literature survey of safety critical applications is presented in detail. Future research directions are also highlighted.

Attack graphs show possible paths that an attacker can use to intrude into a target network and gain privileges through series of vulnerability exploits. The computation of attack graphs suffers from the state explosion problem occurring most notably when the number of vulnerabilities in the target network grows large. Parallel computation of attack graphs can be utilized to attenuate this problem. When employed in online network security evaluation, the computation of attack graphs can be triggered with the correlated intrusion alerts received from sensors scattered throughout the target network. In such cases, distributed computation of attack graphs becomes valuable. This article introduces a parallel and distributed memory-based algorithm that builds vulnerability-based attack graphs on a distributed multi-agent platform. A virtual shared memory abstraction is proposed to be used over such a platform, whose memory pages are initialized by partitioning the network reachability information. We demonstrate the feasibility of parallel distributed computation of attack graphs and show that even a small degree of parallelism can effectively speed up the generation process as the problem size grows. We also introduce a rich attack template and network model in order to form chains of vulnerability exploits in attack graphs more precisely.

Smart cities generally aim at efficiently organizing and managing city resources through a digital layer on top of the legacy infrastructure. As the digitalization trend goes on with an increasing pace and with the involvement of a diverse set of actors, proper management of this digital layer as well as the services deployed over it becomes ever more crucial. This paper presents our methodology of transforming the complex smart city concept and its digital layer into a structured model for creating a dynamic and adaptive service ecosystem in the digital cities of the future. An overview of the smart city concept and the three-tier architecture that emerges through the digitalization of cities is presented first, together with the main challenges in attaining coherent smart city service environments that can avoid fragmentation, ensure scalability, and allow reuse. The three major enablers that are identified in this direction are 1) a semantic functional description of city objects, representing physical devices or abstract services; 2) a distributed service directory that embodies available city services for service lookup and discovery; and 3) planning tools for selecting and chaining basic services to compose new complex services. For each of these, a high-level overview of the available tools and results from the research literature are provided as well as the relevant standards. This overview is complemented with our own approach and design choices in project ISCO (Internet of smart city objects). Through the implementation of two distinct use cases, this paper illustrates how ISCO components can jointly enrich service creation and consumption of various stakeholders in smart cities.

In this paper we define a new metric for quantifying the degree of anonymity collectively afforded to users of an anonymous communication system. We show how our metric, based on the permanent of a matrix, can be useful in evaluating the amount of information needed by an observer to reveal the communication pattern as a whole. We also show how our model can be extended to include probabilistic information learned by an attacker about possible sender-recipient relationships. Our work is intended to serve as a complementary tool to existing information-theoretic metrics, which typically consider the anonymity of the system from the perspective of a single user or message.