Security and Energy Efficiency in Resource-Constrained Wireless Multi-hop Networks

In recent decades, there has been a huge improvement and interest from the research community in wireless multi-hop networks. Such networks have widespread applications in civil, commercial and military applications. Paradigms of this type of networks that are critical for many aspects of human lives are mobile ad-hoc networks, sensor networks, which are used for monitoring buildings and large agricultural areas, and vehicular networks with applications in traffic monitoring and regulation. Internet of Things (IoT) is also envisioned as a multi-hop network consisting of small interconnected devices, called ``things", such as smart meters, smart traffic lights, thermostats etc. Wireless multi-hop networks suffer from resource constraints, because all the devices have limited battery, computational power and memory. Battery level of these devices should be preserved in order to ensure reliability and communication across the network. In addition, these devices are not a priori designed to defend against sophisticated adversaries, which may be deployed across the network in order to disrupt network operation. In addition, the distributed nature of this type of networks introduces another limitation to protocol performance in the presence of adversaries. Hence, the inherit nature of this type of networks poses severe limitations on designing and optimizing protocols and network operations. In this dissertation, we focus on proposing novel techniques for designing more resilient protocols to attackers and more energy efficient protocols. In the first part of the dissertation, we investigate the scenario of multiple adversaries deployed across the network, which reduce significantly the network performance. We adopt a component-based and a cross-layer view of network protocols to make protocols secure and resilient to attacks and to utilize our techniques across existing network protocols. We use the notion of trust between network entities to propose lightweight defense mechanisms, which also satisfy performance requirements. Using cryptographic primitives in our network scenario can introduce significant computational overhead. In addition, behavioral aspects of entities are not captured by cryptographic primitives. Hence, trust metrics provide an efficient security metric in these scenarios, which can be utilized to introduce lightweight defense mechanisms applicable to deployed network protocols. In the second part of the dissertation, we focus on energy efficiency considerations in this type of networks. Our motivation for this work is to extend network lifetime, but at the same time maintain critical performance requirements. We propose a distributed sleep management framework for heterogeneous machine-to-machine networks and two novel energy efficient metrics. This framework and the routing metrics are integrated into existing routing protocols for machine-to-machine networks. We demonstrate the efficiency of our approach in terms of increasing network lifetime and maintaining packet delivery ratio. Furthermore, we propose a novel multi-metric energy efficient routing protocol for dynamic networks (i.e. mobile ad-hoc networks) and illustrate its performance in terms of network lifetime. Finally, we investigate the energy-aware sensor coverage problem and we propose a novel game theoretic approach to capture the tradeoff between sensor coverage efficiency and energy consumption

On the dynamics of linear functional differential equations with asymptotically constant solutions

We discuss the dynamics of general linear functional differential equations with solutions that exhibit asymptotic constancy. We apply fixed point theory methods to study the stability of these solutions and we provide sufficient conditions of asymptotic stability with emphasis on the rate of convergence. Several examples are provided to illustrate the claim that the derived results generalize, unify and in some cases improve the existing ones

Accountable Storage

We introduce Accountable Storage, a framework allowing a client with small local space to outsource n file blocks to an untrusted server and be able (at any point in time after outsourcing) to provably compute how many bits have been discarded by the server. Such protocols offer ``provable storage insurance to a client: In case of a data loss, the client can be compensated with a dollar amount proportional to the damage that has occurred, forcing the server to be more ``accountable for his behavior. The insurance can be captured in the SLA between the client and the server. Although applying existing techniques (e.g., proof-of-storage protocols) could address the problem, the related costs of such approaches are prohibitive. Instead, our protocols can provably compute the damage that has occurred through an efficient recovery process of the lost or corrupted file blocks, which requires only sublinear $O(\delta\log n)$ communication, computation and local space, where $\delta$ is the maximum number of corrupted file blocks that can be tolerated. Our technique is based on an extension of invertible Bloom filters, a data structure used to quickly compute the distance between two sets. Finally, we show how our protocol can be integrated with Bitcoin, to support automatic compensations proportional to the number of corrupted bits at the server. We also build and evaluate our protocols showing that they perform well in practice

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Stability by Fixed Point Theory in Consensus Dynamics

We study the stability of linear time invariant distributed consensus dynamics in the presence of multiple propagation and processing delays. We employ fixed point theory (FPT) methods and derive sufficient conditions for asymptotic convergence to a common value while the emphasis is given in estimating the rate of convergence. We argue that this approach is novel in the field of networked dynamics as it is also flexible and thus capable of analyzing a wide variety of consensus based algorithms for which conventional Lyapunov methods are either too restrictive or unsuccessful

Models for resource description and management in wireless testbeds

207 σ.Η ανάπτυξη και χρήση πειραματικών πλατφορμών διευκολύνει την ανάπτυξη νέων αρχιτεκτονικών και πρωτοκόλλων για το Διαδίκτυο του μέλλοντος, αφού παρέχουν τους απαιτούμενους πόρους για διεξαγωγή πειραμάτων υπο πραγματικές συνθήκες. Για τη διαχείριση μιας πειραματικής πλατφόρμας απαιτείται ένας κοινός τρόπος περιγραφής των πόρων, ο οποίος θα είναι ανεξάρτητος της εκάστοτε υλοποίησης τόσο σε υλικό όσο και σε λογισμικό. Στη διπλωματική εργασία δημιουργήσαμε μια επέκταση στη δομή δεδομένων Resource Specification (version 2), η οποία αποτελεί ένα μηχανισμό δημοσίευσης διαθέσιμων πόρων, περιγραφής αιτήσεων χρηστών για συγκεκριμένους πόρους και περιγραφή των πόρων οι οποίοι έχουν δεσμευθεί και χρησιμοποιούνται απο τους ερευνητές, και ο οποίος αναπτύχθηκε απο το ProtoGENI (www.protogeni.net). Η επέκταση χρησιμοποιήθηκε για την κατάλληλη περιγραφή των ασύρματων πόρων της πειραματικής πλατφόρμας του εργαστηρίου Διαχείρισης και Βέλτιστου Σχεδιασμού Δικτύων Τηλεματικής. Στο δεύτερο μέρος της διπλωματικής εργασίας σχεδιάσαμε ένα σύστημα διαχείρισης για την πειραματική πλατφόρμα ασύρματων πόρων του εργαστηρίου Διαχείρισης και Βέλτιστου Σχεδιασμού Δικτύων Τηλεματικής, το οποίο κάνει χρήση της εκτεταμένης δομής RSpec v.2. Συγκεκριμένα το σύστημα αυτό επιτρέπει στους ερευνητές να δημιουργήσουν, να δεσμεύσουν και να διαχειριστούν τις φέτες (slices) πόρων τους. Με την έννοια φέτα πόρων (slice) εννοούμε ένα υποσύνολο των πόρων της εργαστηριακής πλατφόρμας τους οποίους δεσμεύει ο ερευνητής για τα πειράματα του. Η λειτουργία του συστήματος βασίζεται στο σχεδιασμό κατάλληλων υπηρεσιών διαδικτύου που περιέχουν τις απαιτούμενες λειτουργίες για δημιουργία, δέσμευση και διαχείριση των φετών. Παράλληλα αναπτύξαμε ένα χρονοπρογραμματιστή δέσμευσης πόρων ώστε οι ερευνητές να μπορούν να δεσμεύσουν μόνο τους διαθέσιμους πόρους σε κάποιο συγκεκριμένο χρονικό διάστημα. Τέλος σχεδιάσαμε ένα γραφικό περιβάλλον χρήστη για να μπορούν οι δίαφοροι ερευνητές να χρησιμοποιήσουν τις παραπάνω υπηρεσίες διαδικτύου και να διαχειριστούν τα slices που έχουν δημιουργήσει.The development and wide use of experimental testbeds facilitates the development of new innovating architectures and protocols for the Internet of the future, as well as providing the necessary resources to conduct experiments under real conditions. Management of the testbed’s resources requires a common way to describe these resources, which will be independent of each hardware and software implentation. In this diploma thesis we created an extension to the Resource Specification (version 2) mechanism for advertising, requesting and describing the resources used by experimenters developed by ProtoGENI (www.protogeni.net). The extension was made to describe properly wireless resources at the testbed of NEtwork Management and Optimal Design Laboratory. In the second part of this diploma thesis we designed a system for managing wireless resources at the testbed of NEtwork Management and Optimal Design Laboratory, based on this extended RSpec v.2 format. Specifically, the proposed system enables researchers to create, reserve and manage their slices. A slice is a subset of the testbed’s resources, which a researcher reserves in order to conduct his experiment. The system is based on the design of appropriate web services that contain the operations required for the creation, reservation and management of slices. In parallel we developed a time-based slice scheduler in order for researchers to be able to reserve only available resources at the requested timeframe. Finally we designed a Graphical User Interface to allow different researchers to use these Web Services and manage their slices.Ευριπίδης Χ. Παρασκευά

An educational intervention to optimize use of proton pump inhibitors in a Greek university hospital

Background Misuse of proton pump inhibitors (PPIs) is an alarming issue for patients and healthcare systems. Methods We conducted a 3-phase interventional, prospective study in a Greek university hospital. During Phase I, we collected data from patients’ records to evaluate the appropriate use of PPIs. During Phase II, educational seminars about the proper use of PPIs were offered to the medical staff. In Phase III we collected data from the records of patients admitted to the hospital department with the highest rate of inappropriate PPI administration during Phase I, to evaluate the efficacy of the intervention. Inappropriate use was defined as either PPI administration without indication, or lack of use despite adequate indication. Appropriateness of PPI use was measured at admission, during hospitalization and at discharge. Results The rate of inappropriate PPI use was higher (51.7% and 48.6%) during hospitalization than at admission (34.9% and 21.9%), but at discharge was similar to pre-hospitalization levels (26.9% and 23.6%), in Phases I and III, respectively. At discharge during Phase I, the inappropriate use of PPIs was significantly higher (odds ratio 3.79, 95% confidence interval 1.98-7.19) for internal medicine patients than for surgical patients. The educational intervention failed to reduce the inappropriate use of PPIs during hospitalization (51.7% vs. 48.6%, P=0.478) or at discharge (26.9% vs. 23.6%, P=0.391) in the internal medicine patients. Conclusions The rate of inappropriate PPI use is almost double during hospitalization compared to the rates at admission and at discharge. Implementation of an educational intervention failed to reduce the inappropriate use of PPIs in internal medicine patients