A. Elsts, S. Duquennoy, X. Fafoutis, G. Oikonomou, R. Piechocki, I. Craddock, "Microsecond-accuracy time synchronization using the IEEE 802.15.4 TSCH Protocol", in Proc. IEEE SenseApp, 2017
Time-Slotted Channel Hopping from the IEEE 802.15.4-2015 standard requires that network nodes are tightly time-synchronized. Existing implementations of TSCH on embedded hardware are characterized by tens-of-microseconds large synchronization errors; higher synchronization accuracy would enable reduction of idle listening time on receivers, in this way decreasing the energy required to run TSCH. For some applications, it would also allow to replace dedicated time synchronization mechanisms with TSCH. We show that time synchronization errors in the existing TSCH implementations on embedded hardware are caused primarily by imprecise clock drift estimations, rather than by real unpredictable drift variance. By estimating clock drift more precisely and by applying adaptive time compensation on each node in the network, we achieve microsecond accuracy time synchronization on point-to-point links and a <2 microsecond end-to-end error in a 7-node line topology. Our solution is implemented in the Contiki operating system and tested on Texas Instruments CC2650-based nodes, equipped with common off-the-shelf hardware clock sources (20 ppm drift). Our implementation uses only standard TSCH control messages and is able to keep radio duty cycle below 1%.
A. Elsts, X. Fafoutis, J. Pope, G. Oikonomou, R. Piechocki, I. Craddock, "Scheduling high-rate unpredictable traffic in IEEE 802.15.4 TSCH networks", in Proc. IEEE DCOSS 2017, 2017 (accepted, to appear)
The upcoming Internet of Things (IoT) applications include real-time human activity monitoring with wearable sensors. Compared to the traditional environmental sensing with low-power wireless nodes, these new applications generate a constant stream of a much higher rate. Nevertheless, the wearable devices remain battery powered and therefore restricted to low-power wireless standards such as IEEE 802.15.4 or Bluetooth Low Energy (BLE). Our work tackles the problem of building a reliable autonomous schedule for forwarding this kind of dynamic data in IEEE 802.15.4 TSCH networks. Due to the a priori unpredictability of these data source locations, the quality of the wireless links, and the routing topology of the forwarding network, it is wasteful to reserve the number of slots required for the worst-case scenario; under conditions of high expected datarate, it is downright impossible. The solution we propose is a hybrid approach where dedicated TSCH cells and shared TSCH slots coexist in the same schedule. We show that under realistic assumptions of wireless link diversity, adding shared slots to a TSCH schedule increases the overall packet delivery rate and the fairness of the system.
S. Duquennoy, A. Elsts, B. Nahas, G. Oikonomou, "TSCH and 6TiSCH for Contiki: challenges, design and evaluation", in Proc. IEEE DCOSS 2017, 2017 (accepted, to appear)
Synchronized communication has recently emerged as a prime option for low-power critical applications. Solutions such as Glossy or Time Slotted Channel Hopping (TSCH) have demonstrated end-to-end reliability upwards of 99.99%. In this context, the IETF Working Group 6TiSCH is currently standardizing the mechanisms to use TSCH in low-power IPv6 scenarios. This paper identifies a number of challenges when it comes to implementing the 6TiSCH stack. It shows how these challenges can be addressed with practical solutions for locking, queuing, scheduling and other aspects. With this implementation as an enabler, we present an experimental validation and comparison with state-of-the-art MAC protocols. We conduct fine-grained energy profiling, showing the impact of link-layer security on packet transmission. We evaluate distributed time synchronization in a 340-node testbed, and demonstrate that tight synchronization (hundreds of microseconds) can be achieved at very low cost (0.3% duty cycle, 0.008% channel utilization). We finally compare TSCH against traditional MAC layers: low-power listening (LPL) and CSMA, in terms of reliability, latency and energy. We show that with proper scheduling, TSCH achieves by far the highest reliability, and outperforms LPL in both energy and latency.
A. Elsts, G. Oikonomou, X. Fafoutis, R. Piechocki, "Internet of things for smart homes: lessons learned from the SPHERE case study", in Proc. Global Internet of Things Summit, 2017 (accepted, to appear)
Building large-scale low-power Internet of Things (IoT) systems remains a challenge, as these systems have to meet the requirements of reliability, robustness, and energy- efficiency while running on resource-restricted microcontrollers without memory protection. In this paper we present the case study of IoT in SPHERE (Sensor Platform for HEalthcare in a Residential Environment), a project with the objective to develop a multipurpose, multi-modal sensor platform for monitoring people’s health inside their homes. Atypically for academic projects, in 2017 the SPHERE software is going to be deployed in a 100-home study in volunteer homes, therefore it has to satisfy many real-world requirements. We discuss the requirements for IoT networking in this project, the IoT architecture (built on top of Contiki OS), software engineering challenges and lessons learned, as well as some of the general aspects that still make embedded low-power IoT software development difficult.
P. Woznowski, A. Burrows, T. Diethe, X. Fafoutis, J. Hall, S. Hannuna, M. Camplani, N. Twomey, M. Kozlowski, B. Tan, N. Zhu, A. Elsts, A. Vafeas, A. Paiement, L. Tao, M. Mirmehdi, T. Burghardt, D. Damen, P. Flach, R. Piechocki, I. Craddock, G. Oikonomou, "SPHERE: A sensor platform for healthcare in a residential environment", in Designing, Developing, and Facilitating Smart Cities, Springer, pp. 315-333, 2017
It can be tempting to think about smart homes like one thinks about smart cities. On the surface, smart homes and smart cities comprise coherent systems enabled by similar sensing and interactive technologies. It can also be argued that both are broadly underpinned by shared goals of sustainable development, inclusive user engagement and improved service delivery. However, the home possesses unique characteristics that must be considered in order to develop effective smart home systems that are adopted in the real world.
X. Fafoutis, A. Elsts, A. Vafeas, G. Oikonomou, R. Piechocki, "Demo: SPES-2 – A Sensing Platform for Maintenance-Free Residential Monitoring", in Proc. EWSN 2017, 2017
SPES-2 is a sensing board for room-level monitoring in a home environment. It constitutes a vital modality of the SPHERE architecture: a multi-modal sensing platform for healthcare in a residential environment. SPES-2 uses an optimised implementation of the IEEE 802.15.4-2015 TSCH (Time-Slotted Channel Hopping) standard to operate efficiently and reliably in unknown environments for more than one year without battery replacement, providing continuous information about the ambient characteristics of the room (such as temperature, humidity and light levels), as well as presence information captured through a motion sensor.
P. Cooper, K. Maraslis, T. Tryfonas, G. Oikonomou, "An intelligent hot-desking model harnessing the power of occupancy sensing", Journal of Facilities, Emerald Group Publishing Limited, 2017 (in press)
In this paper a model is developed to harness the power of occupancy sensing in an Intelligent Hot-Desking system utilizing experimental data from a commercial office in central London. To achieve that, the model uses that data as an input in order to undertake the task of allocating the office desks to the employees in a way that will maximise their productivity based on the type of project that each employee is working on each time. In this way, and by taking into account other parameters that are involved as well, the synergy that this situation can create, can increase productivity significantly compared to the situation where employees have their desks fixed under any circumstances and also allow for expenses cut since the desks can now be less than the employees. Not only is this approach able to optimize desk utilization based on quality occupancy data, but also speculates how and by how much overall productivity increases, while proving that its benefits outweigh the costs of adopting such a system. Furthermore, this paper explores the barriers towards Intelligent Hot-Desking, including how an increase in occupancy data collection in the private sector could have key advantages for the business as an organization and the city as a whole. Ultimately, it provides a valuable and feasible use case for the use of occupancy data in smart buildings, a dataset that is perceived to be valuable yet underexplored.
A. Elsts, S. Duquennoy, X. Fafoutis, G. Oikonomou, R. Piechocki, I. Craddock, "Microsecond-Accuracy Time Synchronization Using the IEEE 802.15.4 TSCH Protocol", in Proc. International Workshop on Practical Issues in Building Sensor Network Applications (IEEE SenseApp 2016), 2016
Time-Slotted Channel Hopping from the IEEE 802.15.4-2015 standard requires that network nodes are tightly time-synchronized. Existing implementations of TSCH on embedded hardware are characterized by tens-of-microseconds large synchronization errors; higher synchronization accuracy would enable reduction of idle listening time on receivers, in this way decreasing the energy required to run TSCH. For some applications, it would also allow to replace dedicated time synchronization mechanisms with TSCH. We show that time synchronization errors in the existing TSCH implementations on embedded hardware are caused primarily by imprecise clock drift estimations, rather than by real unpredictable drift variance. By estimating clock drift more precisely and by applying adaptive time compensation on each node in the network, we achieve microsecond accuracy time synchronization on point-to-point links and a <2 microsecond end-to-end error in a 7-node line topology. Our solution is implemented in the Contiki operating system and tested on Texas Instruments CC2650-based nodes, equipped with common off-the-shelf hardware clock sources (20 ppm drift). Our implementation uses only standard TSCH control messages and is able to keep radio duty cycle below 1\%.
P. Woznowski, D. Kaleshi, G. Oikonomou, I. Craddock, "Classification and Suitability of Sensing Technologies for Activity Recognition", Computer Communications, 89-90, pp. 34-50, 2016
Wider availability of sensors and sensing systems has pushed research in the direction of automatic activity recognition (AR) either for medical or other personal benefits e.g. wellness or fitness monitoring. Researchers apply different AR techniques/algorithms and use a wide range of sensors to discover home activities. However, it seems that the AR algorithms are purely technology-driven rather than informing studies on the type and quality of input required. There is an expectation to over-instrument the environment or the subjects and then develop AR algorithms, where instead the problem should be approached from a different angle i.e. what sensors (type, quality and quantity) a given algorithm requires to infer particular activities with a certain confidence? This paper introduces the concept of activity recognition, its taxonomy and familiarises the reader with sub-classes of sensor-based AR. Furthermore, it presents an overview of existing health services Telecare and Telehealth solutions, and introduces the hierarchical taxonomy of human behaviour analysis tasks. This work is a result of a systematic literature review and it presents the reader with a comprehensive set of home-based activities of daily living (ADL) and sensors proven to recognise these activities. Apart from reviewing usefulness of various sensing technologies for home-based AR algorithms, it highlights the problem of technology-driven cycle of development in this area.
P. Andriotis, G. Oikonomou, T. Tryfonas, S. Li, "Highlighting Relationships of a Smartphone’s Social Ecosystem in Potentially Large Investigations", IEEE Transactions on Cybernetics, IEEE, 46(9), pp. 1974-1985, 2016
Social media networks are becoming increasingly popular because they can satisfy diverse needs of individuals (both personal and professional). Modern mobile devices are empowered with increased capabilities, taking advantage of the technological progress that makes them smarter than their predecessors. Thus, a smartphone user is not only the phone owner, but also an entity that may have different facets and roles in various social media networks. We believe that these roles can be aggregated in a single social ecosystem, which can be derived by the smartphone. In this paper, we present our concept of the social ecosystem in contemporary devices and we attempt to distinguish the different communities that occur from the integration of social networking in our lives. In addition, we propose techniques to highlight major actors within the ecosystem. Moreover, we demonstrate our suggested visualization scheme, which illustrates the linking of entities that live in separate communities using data taken from the smartphone. Finally, we extend our concept to include various parallel ecosystems during potentially large investigations and we link influential entities in a vertical fashion. We particularly examine cases where data aggregation is performed by specific applications, producing volumes of textual data that can be analyzed with text mining methods. Our analysis demonstrates the risks of the rising ``bring your own device'' trend in enterprise environments.
A. Mavromatis, G. Papadopoulos, X. Fafoutis, A. Elsts, G. Oikonomou, T. Tryfonas, "Impact of Guard Time Length on IEEE 802.15.4e TSCH Energy Consumption", in Proc. IEEE International Conference on Sensing, Communication and Networking (SECON), 2016
The IEEE 802.15.4-2015 standard defines a number of Medium Access Control (MAC) layer protocols for low- power wireless communications in the IoT. Originally defined in the IEEE 802.15.4e amendment, TSCH (Time Slotted Channel Hopping) is among the proposed mechanisms. TSCH is a scheme aiming to guarantee network reliability by keeping nodes time-synchronised at the MAC layer. In order to ensure successful communication between a sender and a receiver, the latter starts listening shortly before the expected time of a MAC layer frame’s arrival. The offset between the time a node starts listening and the estimated time of frame arrival is called guard time and it aims to reduce the probability of missed frames due to clock drift. In this poster, we investigate the effect of the guard time duration on energy consumption. We identify that, when using the 6tisch minimal schedule, the most significant cause of energy consumption is idle listening during guard time. Therefore, the energy-efficiency of TSCH can be significantly improved by guard time optimisation. Our performance evaluation results, conducted using the Contiki operating system, show that an efficient configuration of guard time may reduce energy consumption by up to 30%, without compromising network reliability.
G. Papadopoulos, V. Kotsiou, A. Gallais, G. Oikonomou, P. Chatzimisios, T. Tryfonas, T. Noël, "A Mobility-Supporting MAC Scheme for Bursty Traffic in IoT and WSNs", in Proc. IEEE GLOBECOM, 2016
Recent boom of mobile applications has become an essential class of mobile Internet of Things (IoT), whereby large amounts of sensed data are collected and shared by mobile sensing devices for observing phenomena such as traffic or the environmental. However, most of the existing Medium Access Control (MAC) protocols mainly focus on static networks. Thus, mobile sensor nodes may pose many communication challenges during the design and development of a MAC protocol. These difficulties first require an efficient connection establishment between a mobile and static node, and then an effective data packet transmissions. In this study, we propose MobIQ, a MAC scheme that allows an advanced mobility-handling scheme for low-power MAC protocols, which allows for efficient neighbour(hood) discovery and low-delay communication. Our thorough performance evaluation, conducted on top of Contiki OS, shows that MobIQ outperforms state-of-the-art solutions such as MoX-MAC, MOBINET and ME-ContikiMAC, in terms of reducing both delay, contention to the medium and energy consumption.
G. Papadopoulos, A. Mavromatis, X. Fafoutis, N. Montavont, R. Piechocki, T. Tryfonas, G. Oikonomou, "Guard Time Optimisation and Adaptation for Energy Efficient Multi-hop TSCH Networks", in Proc. IEEE World Forum on Internet of Things (WF-IoT), 2016
In the IEEE 802.15.4-2015 standard, Time Slotted Channel Hopping (TSCH) aims to guarantee high-level network reliability by keeping nodes time-synchronised. In order to ensure successful communication between a sender and a receiver, the latter starts listening shortly before the expected time of a MAC layer frame’s arrival. The offset between the time a node starts listening and the estimated time of frame arrival is called guard time and it aims to reduce the probability of missed frames due to clock drift. In this paper, we investigate the impact of the guard time on network performance. We identify that, when using the 6tisch minimal schedule, the most significant cause of energy consumption is idle listening during guard time. Therefore, we first perform mathematical modelling on a TSCH link to identify the guard time that maximises the energy-efficiency of the TSCH network in single hop topology. We then continue in multi-hop network, where we empirically adapt the guard time locally at each node depending its distance, in terms of hops, from the sink. Our performance evaluation results, conducted using the Contiki OS, demonstrate that the proposed decentralised guard time adaptation can reduce the energy consumption by up to 40\%, without compromising network reliability.
G. Papadopoulos, A. Georgallides, T. Tryfonas, G. Oikonomou, "BMFA: Bi-Directional Multicast Forwarding Algorithm for RPL-based 6LoWPANs", in 2nd EAI International Conference on Interoperability in IoT, ser. LNICST, 190, pp. 18-25, 2016
In scenarios involving point-to-multipoint network traffic, transmitting to each destination individually with unicast may lead to poor utilisation of network bandwidth, excessive energy consumption caused by the high number of packets and suffers from low scalability as the number of destinations increases. An alternative approach, would be to use network-layer multicast, where packets are transmitted to multiple destinations simultaneously. In doing so, applications adopting a one-to-many communication paradigm may improve their energy efficiency and bandwidth utilisation. In this paper, we present Bi-directional Multicast Forwarding Algorithm (BMFA), a novel RPL-based multicast forwarding mechanism. BMFA improves its pre-predecessor SMRF in that it allows multicast traffic to travel both upwards as well as downwards in an RPL tree. At the same time, it retains SMRF’s low latency and very low energy consumption characteristics. Our performance evaluation results, conducted using the Contiki operating system, show that BMFA outperforms its rival Trickle Multicast / Multicast Protocol for Low power and Lossy Networks (TM / MPL), in terms of reducing both delay and energy consumption.
G. Papadopoulos, A. Mavromatis, X. Fafoutis, R. Piechocki, T. Tryfonas, G. Oikonomou, "Guard Time Optimisation for Energy Efficiency in IEEE 802.15.4-2015 TSCH Links", in 2nd EAI International Conference on Interoperability in IoT, ser. LNICST, pp. 56-63, 2016
Time Slotted Channel Hopping (TSCH) is among the Medium Access Control (MAC) schemes defined in the IEEE 802.15.4-2015 standard. TSCH aims to guarantee high-level network reliability by keeping nodes time-synchronised. In order to ensure successful communication between a sender and a receiver, the latter starts listening shortly before the expected time of a MAC layer frame’s arrival. The offset between the time a node starts listening and the estimated time of frame arrival is called guard time and it aims to reduce the probability of missed frames due to clock drift. In this paper, we investigate the impact of the guard time length on network performance. We identify that, when using the 6TiSCH minimal schedule, the most significant cause of energy consumption is idle listening during guard time. Therefore, we perform empirical optimisations on the guard time to maximise the energy-efficiency of a TSCH link. Our experiments, conducted using the Contiki OS, show that optimal guard time configuration can reduce energy consumption by up to 40\%, without compromising network reliability.
G. Margelis, X. Fafoutis, R. Piechocki, G. Oikonomou, T. Tryfonas, P. Thomas, "Practical Limits of the Secret Key-Capacity for IoT Physical Layer Security", in Proc. IEEE World Forum on Internet of Things (WF-IoT), 2016
The confidentiality of communications in the Internet of Things (IoT) is critical, with cryptography being currently the most widely employed method to achieve it. Establishing cryptographically secure communication links between two transceivers requires the pre-agreement on some key, unknown to an external attacker. In recent years there has been growing interest for techniques that generate a shared random key through observation of the channel and its effects on the exchanged messages. The maximum length of that key is characterised by the Mutual Information (MI) between the observations of the two radios. In this work we examine the practical limits of the MI of off-the-shelf transceivers communicating through the IEEE 802.15.4 specification in an indoor office environment, and calculate the secret-key capacity, that is, the maximum length of an extracted secret-key in the presence of an eavesdropper. Furthermore, we study how using groups of observations can affect the MI and both analytically and experimentally prove that grouping observations leads to better results and an increased key-capacity.
K. Maraslis, P. Cooper, T. Tryfonas, G. Oikonomou, "An intelligent hot-desking model based on occupancy sensor data and its potential for social impact", in Proc. HICSS, ser. Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), 9860, pp. 142-158, 2016
In this paper we develop a model that utilises occupancy sensor data in a commercial Hot-Desking environment. Hot-Desking (or ‘office-hoteling’) is a method of office resource management that emerged in the nineties hoping to reduce the real estate costs of workplaces, by allowing offices to be used interchangeably among employees. We show that sensor data can be used to facilitate office resources management, in our case desk allocation in a Hot-Desking environment, with results that outweigh the costs of occupancy detection. We are able to optimise desk utilisation based on quality occupancy data and also demonstrate the effectiveness of the model by comparing it to a theoretically ideal, but impractical in real life, model. We then explain how a generalisation of the model that includes input from human sensors (e.g. social media) besides the presence sensing and pre-declared personal preferences, can be used, with potential impact on wider community scale.
V. Kumar, G. Oikonomou, T. Tryfonas, "Traffic Forensics for IPv6-Based Wireless Sensor Networks and the Internet of Things", in Proc. IEEE World Forum on Internet of Things (WF-IoT), 2016
Research and standardisation efforts in the fields of Wireless Sensor Networks (WSNs) and the Internet of Things (IoT) are leading towards the adoption of TCP/IP for deployments of networks of severely constrained smart embedded objects. As a result, wireless sensors can now be uniquely identified by an IPv6 address and thus be directly connected to and reachable from the internet. This has a series of advantages but also exposes sensor deployments to new security vulnerabilities. Should a deployment be compromised, post-incident analysis can provide information about the nature of the attack by inspecting the network’s state and traffic during the time period prior, during and after the attack. In this paper we adopt traffic forensic techniques in order to achieve post-hoc detection of attacks against availability in IPv6-based Low-Power Wireless Personal Area Networks. To this end, we first implement an attack which exploits inherent vulnerabilities of the IPv6 Routing Protocol for Low-Power and Lossy Networks (RPL). Subsequently, we present an automated method to detect and analyse this attack by examining network packet captures.
A. Fragkiadakis, G. Oikonomou, H. Pöhls, E. Tragos, M. Wojcik, T. Tryfonas, "Securing Communications Among Severely Constrained, Wireless Embedded Devices", in Engineering Secure IoT Systems, IET, 2016
The goal of this chapter is to present the ideas and concepts of the EU-FP7 SMARTCITIES project “RERUM” with regards to improving the communication security in IoT-based smart city applications. The chapter tries to identify the gaps in previous IoT frameworks with regards to security and privacy and shows the advances that RERUM brings to the IoT community with its significant focus on embedded device functionalities. The goal of the RERUM secure communications framework is to provide light-weight solutions so that they can be applied even in the very constrained IoT devices. Solutions for lightweight encryption (based on the relatively new theory of Compressive Sensing), on transport-layer security (based on DTLS) and on integrity verification of data (using on-device signatures) are presented in detail, discussing their applicability and the benefits they bring to IoT.
X. Fafoutis, L. Marchegiani, G. Papadopoulos, R. Piechocki, T. Tryfonas, G. Oikonomou, "Privacy Leakage of Physical Activity Levels in Wireless Embedded Wearable Systems", Signal Processing Letters, IEEE, 24(2), pp. 136-140, 2016
With the ubiquity of sensing technologies in our personal spaces, the protection of our privacy and the confidentiality of sensitive data becomes a major concern. In this paper, we focus on wearable embedded systems that communicate data periodically over the wireless medium. In this context, we demonstrate that private information about the physical activity levels of the wearer can leak to an eavesdropper through the physical layer. Indeed, we show that the physical activity levels strongly correlate with changes in the wireless channel that can be captured by measuring the signal strength of the eavesdropped frames. We practically validate this correlation in several scenarios in a real residential environment, using data collected by our prototype wearable accelerometer-based sensor. Lastly, we propose a privacy enhancement algorithm that
mitigates the leakage of this private information.
P. Andriotis, G. Oikonomou, A. Mylonas, T. Tryfonas, "A Study on Usability and Security Features of the Android Pattern Lock Screen", Information and Computer Security, Emerald, 24(1), pp. 53-72, 2016
The Android pattern lock screen (or graphical password) is a popular user authentication method that relies on the advantages provided by the visual representation of a password, which enhance its memorability. Graphical passwords are vulnerable to attacks (e.g. shoulder surfing); thus, the need for more complex passwords becomes apparent. This paper aims to focus on the features that constitute a usable and secure pattern and investigate the existence of heuristic and physical rules that possibly dictate the formation of a pattern.
P. Cooper, T. Crick, T. Tryfonas, G. Oikonomou, "Whole-Life Environmental Impacts of ICT Use", in Proc. 2015 IEEE Globecom Workshops (GC Wkshps), 2015
In this paper we apply a whole-life assessment approach to estimate the environmental impact of the use of ICT of an individual within the UK over a one-year period. By estimating the energy and data consumption of an average user's use of a typical device, and estimating the associated energy usage (and thus CO2 produced) of each stage in the data chain, we are able to calculate the summed CO2 value for embodied carbon of an average device. Overall, device energy is seen to dominate; within device, desktops dominate, both due to their high energy use for a given task, but also their high standby power, which is the most significant point of behaviour-driven waste. Geographical, behavioural and chronological factors are all evaluated to be highly significant to the impact of a user's ICT use, along with a number of secondary factors. Finally, we present policy recommendations to further the understanding of the factors affecting the environmental impact of ICT, particularly focusing on sustainability, resource efficiency and the social implications of ICT in a low-carbon transformation.
M. Haghighi, K. Maraslis, T. Tryfonas, G. Oikonomou, A. Burrows, P. Woznowski, "Game Theoretic Approach Towards Optimal Multi-tasking and Data-distribution in IoT", in Proc. IEEE World Forum on Internet of Things (WF-IoT), pp. 406-411, 2015
Current applications of Internet of Things (IoT) often require nodes to implement logical decision-making on aggregated data, which involves more processing and wider interactions amongst network peers, resulting in higher energy consumption and shorter node lifetime. This paper presents a game theoretic approach used in Sensomax, an agent-based WSN middleware that facilitates seamless integration of mathematical functions in large-scale wireless sensor networks. In this context, we investigate game theoretic and auction-based techniques to optimise task distribution and energy consumption in IoT networks of multiple concurrent WSNs. We also demonstrate how our proposed game theoretic approach affects the performance of WSN applications with different operational paradigms.
L. Suzuki, P. Cooper, T. Tryfonas, G. Oikonomou, "Hidden Presence: Sensing Occupancy and Extracting Value from Occupancy Data", in Design, User Experience, and Usability: Interactive Experience Design, ser. Lecture Notes in Computer Science, 9188, pp. 412-424, 2015
In this paper we review various technical architectures for sensing occupancy in commercial real estate spaces and discuss the potential benefits of applications that could be built upon the collected data. The technical capabilities reviewed range from simple presence detection to identifying individual workers and relating those semantically to jobs, teams, processes or other elements of the business. The volume and richness of accumulated data varies accordingly allowing the development of a range of occupancy monitoring applications that could bring multiple benefits to an organization. We find that overall occupancy-based applications are underappreciated in the Smart Buildings mantra due to occupancy’s inability to align to traditional building engineering silos, a lack of common view between stakeholders with respect to what is ‘value’ and the current client assessment tendencies which use predominantly demonstrator-based logic rather than a combination of practical demonstrators and theoretical value. We demonstrate that in commercial office buildings, occupancy-based Smart Building concepts have the potential to deliver benefits that can be orders of magnitude greater than current practice associated with silos such as energy and lighting. The directness of value in these is far more variable however, and the barriers and enablers to its realization are non-trivial. We identify and discuss these factors (including privacy, perceived additional capital expenditure, retrofitting requirements etc.) in more detail and relate them to stages of design and delivery of the built environment. We conclude that, on the presumption costs of development and implementation are relatively similar, the value streams of occupancy-based systems, while requiring more careful and bespoke design in the short term, could produce greater lifetime value in commercial office scenarios than leading smart building technologies.
T. Spyridopoulos, K. Maraslis, A. Mylonas, T. Tryfonas, G. Oikonomou, "A Game Theoretical Method for Cost-Benefit Analysis of Malware Dissemination Prevention", Information Security Journal: A Global Perspective, Taylor & Francis, 24(4-6), pp. 164-176, 2015
Literature in malware proliferation focuses on modeling and analyzing its spread dynamics. Epidemiology models, which are inspired by the characteristics of biological disease spread in human populations, have been used against this threat to analyze the way malware spreads in a network. This work presents a modified version of the commonly used epidemiology models Susceptible Infected Recovered (SIR) and Susceptible Infected Susceptible (SIS), which incorporates the ability to capture the relationships between nodes within a network, along with their effect on malware dissemination process. Drawing upon a model that illustrates the network’s behavior based on the attacker’s and the defender’s choices, we use game theory to compute optimal strategies for the defender to minimize the effect of malware spread, at the same time minimizing the security cost. We consider three defense mechanisms: patch, removal, and patch and removal, which correspond to the defender’s strategy and use probabilistically with a certain rate. The attacker chooses the type of attack according to its effectiveness and cost. Through the interaction between the two opponents we infer the optimal strategy for both players, known as Nash Equilibrium, evaluating the related payoffs. Hence, our model provides a cost-benefit risk management framework for managing malware spread in computer networks.
H. Read, K. Xynos, I. Sutherland, F. Roarson, P. Andriotis, G. Oikonomou, "An Extensible Platform for the Forensic Analysis of Social Media Data", in Human Aspects of Information Security, Privacy, and Trust - HAS 2015, ser. Lecture Notes in Computer Science, 9190, pp. 404-414, 2015
Visualising data is an important part of the forensic analysis process. Many cell phone forensic tools have specialised visualisation components, but are as of yet able to tackle questions concerning the broad spectrum of social media communication sources. Visualisation tools tend to be stove-piped, it is difficult to take information seen in one visualisation tool and obtain a different perspective in another tool. If an interesting relationship is observed, needing to be explored in more depth, the process has to be reiterated by manually generating a subset of the data, converting it into the correct format, and invoking the new application. This paper describes a cloud-based data storage architecture and a set of interactive visualisation tools developed to allow for a more straightforward exploratory analysis. This approach developed in this tool suite is demonstrated using a case study consisting of social media data extracted from two mobile devices.
K. Maraslis, T. Spyridopoulos, G. Oikonomou, T. Tryfonas, M. Haghighi, "Application of a Game Theoretic Approach in Smart Sensor Data Trustworthiness Problems", in Proc. 30th IFIP TC 11 International Conference (SEC), ser. IFIP Advances in Information and Communication Technology, 455, pp. 601-615, 2015
In this work we present an Intrusion Detection (ID) and an Intrusion Prevention (IP) model for Wireless Sensor Networks (WSNs). The attacker’s goal is to compromise the deployment by causing nodes to report faulty sensory information. The defender, who is the WSN’s operator, aims to detect the presence of faulty sensor measurements (ID) and to subsequently recover compromised nodes (IP). In order to address the conflicting interests involved, we adopt a Game Theoretic approach that takes into consideration the strategies of both players and we attempt to identify the presence of Nash Equilibria in the two games. The results are then verified in two simulation contexts: Firstly, we evaluate the model in a middleware-based WSN which uses clustering over a bespoke network stack. Subsequently, we test the model in a simulated IPv6-based sensor deployment. According to the findings, the results of both simulation models confirm the results of the theoretic one.
M. Haghighi, K. Maraslis, G. Oikonomou, T. Tryfonas, "Game Theoretic Approach Towards Energy - Efficient Task Distribution in Multitasking Wireless Sensor Networks", in Proc. IEEE Sensors 2015, 2015
WSNs have a wide variety of applications, and their usability for remote monitoring of various parameters of interest is growing dramatically. Conventional applications mostly involved a single WSN for collecting raw parameters with limited aggregation on the node side, whereby more sophisticated data mining was implemented by the end-users. Recent applications however, often require more intelligent functions, in which nodes are expected to implement logical decision-makings on the aggregated data. Implementing such functions often involves more processing, and wider interactions amongst network peers, hence resulting in higher energy consumption and shorter node lifetime. Sensomax is an agent-based WSN middleware, which facilitates seamless integration of mathematical functions in large-scale wireless sensor networks. In this paper, we will investigate game theoretic and auction-based techniques in order to optimise task distribution and energy consumption in WSNs.
B. Chen, Z. Fan, F. Cao, G. Oikonomou, T. Tryfonas, "Class Based Overall Priority Scheduling for M2M Communications over LTE Networks", in Proc. 81st Vehicular Technology Conference (VTC2015-Spring), 2015
The rapidly increasing demand of M2M (Machine to Machine) communications poses great challenges to the capacity of cellular networks. This paper proposes a new M2M scheduling algorithm, namely, Class Based Overall Priority (CBOP) scheduling, which is designed particularly to improve uplink scheduling for a massive number of MTCDs (Machine Type Communication Devices) in LTE networks. We compare the proposed algorithm with several existing scheduling algorithms via simulations and discuss its advantages and limitations.
P. Andriotis, G. Oikonomou, "Messaging Activity Reconstruction with Sentiment Polarity Identification", in Human Aspects of Information Security, Privacy, and Trust - HAS 2015, ser. Lecture Notes in Computer Science, 9190, pp. 475-486, 2015
Sentiment Analysis aims to extract information related to the emotional state of the person that produced a text document and also describe the sentiment polarity of the short or long message. This kind of information might be useful to a forensic analyst because it provides indications about the psychological state of the person under investigation at a given time. In this paper we use machine-learning algorithms to classify short texts (SMS), which could be found in the internal memory of a smartphone and extract the mood of the person that sent them. The basic goal of our method is to achieve low False Positive Rates. Moreover, we present two visualization schemes with the intention to provide the ability to digital forensic analysts to see graphical representations of the messaging activity of their suspects and therefore focus on specific areas of interest reducing their workload.
P. Andriotis, T. Tryfonas, G. Oikonomou, I. King, "A framework to describe multimedia circulation in the smartphone ecosystem", in Advances in Digital Forensics XI, ser. IFIP Advances in Information and Communication Technology, 462, pp. 251-267, 2015
Contemporary mobile devices allow almost unrestricted sharing of multimedia and other types of files. But as smartphones and tablets can easily access the Internet or exchange files wirelessly, they've also transformed to useful tools for criminals, aiming at performing illegal activities such as sharing contraband or distributing child abuse images. Thus, the need to investigate the source and destination of a multimedia file that resides in the internal memory of a smartphone becomes apparent. In this paper we present a framework that illustrates and visualizes the flow of digital images as evidence obtained from the artefacts retrieved from Android smartphones during a forensic investigation. Our approach uses `big data' concepts to facilitate the processing of diverse (semi-structured) evidence derived from mobile devices and extends the idea of Digital Evidence Bags (DEB). We obtained our data after running an experiment that included image exchanging through numerous channels such as Bluetooth, Internet and cloud services. Our study presents information about the locations where evidence resides and uses graph databases to store metadata and therefore, visualize the relationships that connect images with apps and events.
V. Kumar, G. Oikonomou, T. Tryfonas, D. Page, I. Phillips, "Digital Investigations for IPv6-Based Wireless Sensor Networks", Digital Investigation, Elsevier, 11, Supplement 2(0), pp. S66-S75, 2014 (Fourteenth Annual DFRWS Conference)
Developments in the field of Wireless Sensor Networks (WSNs) and the Internet of Things (IoT) mean that sensor devices can now be uniquely identified using an IPv6 address and, if suitably connected, can be directly reached from the Internet. This has a series of advantages but also introduces new security vulnerabilities and exposes sensor deployments to attack. A compromised Internet host can send malicious information to the system and trigger incorrect actions. Should an attack take place, post-incident analysis can reveal information about the state of the network at the time of the attack and ultimately provide clues about the tools used to implement it, or about the attacker's identity. In this paper we critically assess and analyse information retrieved from a device used for IoT networking, in order to identify the factors which may have contributed to a security breach. To achieve this, we present an approach for the extraction of RAM and flash contents from a sensor node. Subsequently, we analyse extracted network connectivity information and we investigate the possibility of correlating information gathered from multiple devices in order to reconstruct the network topology. Further, we discuss experiments and analyse how much information can be retrieved in different scenarios. Our major contribution is a mechanism for the extraction, analysis and correlation of forensic data for IPv6-based WSN deployments, accompanied by a tool which can analyse RAM dumps from devices running the Contiki Operating System (OS) and powered by 8051-based, 8-bit micro-controllers.
P. Andriotis, T. Tryfonas, G. Oikonomou, "Complexity metrics and user strength perceptions of the pattern-lock graphical authentication method", in Proc. 16th International Conference on Human-Computer Interaction (HCI 2014), ser. Lecture Notes in Computer Science, 8533, pp. 115-126, 2014 (invited)
One of the most popular contemporary graphical password approaches is the Pattern-Lock authentication mechanism that comes integrated with the Android mobile operating system. In this paper we investigate the impact of password strength meters on the selection of a perceivably secure pattern. We first define a suitable metric to measure pattern strength, taking into account the constraints imposed by the Pattern-Lock mechanism's design. We then implement an app via which we conduct a survey for Android users, retaining demographic information of responders and their perceptions on what constitutes a pattern complex enough to be secure. Subsequently, we display a pattern strength meter to the participant and investigate whether this additional prompt influences the user to change their pattern to a more effective and complex one. We also investigate potential correlations between our findings and results of a previous pilot study in order to detect any significant biases on setting a Pattern-Lock.
H. Pöhls, V. Angelakis, S. Suppan, K. Fischer, G. Oikonomou, E. Tragos, R. Rodriguez, T. Mouroutis, "RERUM: Building a Reliable IoT upon Privacy- and Security- enabled Smart Objects", in Proc. Workshop on IoT Communications and Technologies (WCNC 2014), Istanbul, Turkey, 2014
The Internet of Things (IoT) provides a platform for the interconnection of a plethora of smart objects. It has been widely accepted for providing Information and Communication Technologies (ICT) applications in many ``smart'' environments, such as cities, buildings, metering, and even agriculture. For several reasons though such applications have yet to achieve wide adoption; a major hurdle is the lack of user trust in the IoT and its role in everyday activities. RERUM, a recently started FP7 European Union project. aims to develop a framework which will allow IoT applications to consider security and privacy mechanisms early in their design phase, ensuring a configurable balance between reliability (requiring secure, trustworthy and precise data) and privacy (requiring data minimization for private information, like location). The RERUM framework will comprise an architecture, built upon novel network protocols and interfaces as well as the design of smart objects hardware. To highlight the challenges and evaluate the framework, RERUM will employ several Smart City application scenarios, which will be deployed and evaluated in real-world testbeds in two Smart Cities participating in the project. Here we detail the key technologies RERUM will investigate over the coming three years to reach its vision for IoT security, privacy and trust.
E. Tragos, V. Angelakis, A. Fragkiadakis, D. Gundlegård, C. Nechifor, G. Oikonomou, H. Pöhls, A. Gavras, "Enabling Reliable and Secure IoT-based Smart City Applications", in Proc. IEEE International Conference on Pervasive Computing and Communications Workshops (PERCOM Workshops), Budapest, Hungary, 2014
Smart Cities are considered recently as a promising solution for providing efficient services to citizens with the use of Information and Communication Technologies. With the latest advances on the Internet of Things, a new era has emerged in the Smart City domain, opening new opportunities for the development of efficient and low-cost applications that aim to improve the Quality of Life in cities. Although there is much research in this area, which has resulted in the development of many commercial products, significant parameters like reliability, security and privacy have not been considered as very important up until now. The newly launched FP7-SmartCities-2013 project RERUM aims to build upon the advances in the area of Internet of Things in Smart Cities and develop a framework to enhance reliability and security of smart city applications, with the citizen at the center of attention. This work presents four applications that will be developed within RERUM, gives a general description of the open reliability and security issues that have to be taken into account and gives an overall view of the solutions that RERUM will develop to address these issues.
T. Spyridopoulos, K. Maraslis, T. Tryfonas, G. Oikonomou, S. Li, "Managing Cyber Security Risks in Industrial Control Systems with Game Theory and Viable System Modelling", in Proc. 9th IEEE International System of Systems Engineering Conference (SOSE 2014), 2014
Cyber security risk management in Industrial Control Systems has been a challenging problem for both practitioners and the research community. Their proprietary nature along with the complexity of those systems renders traditional approaches rather insufficient and creating the need for the adoption of a holistic point of view. This paper draws upon the principles of the Viable System Model and Game Theory in order to present a novel systemic approach towards cyber security management in this field, taking into account the complex inter-dependencies and providing cost-efficient defence solutions.
V. Michopoulos, G. Oikonomou, I. Phillips, L. Guan, "CADC: Congestion Aware Duty Cycle Mechanism A Simulation Evaluation", in Proc. 19th International Workshop on Computer Aided Modeling and Design of Communication Links and Networks (CAMAD), 2014
In WSNs idle listening is a major source of energy consumption. Devices can maximise battery, and hence network, lifetime by keeping their radio transceivers off when not needed. We propose CADC, a new Congestion Aware Duty Cycle (DC) MAC protocol, for 6LoWPANs. This protocol uses a new mechanism for the adaptation of the Radio Duty Cycle (RDC), that reacts quickly to changing traffic loads and pat- terns. CADC is independent of network topology, operating protocols and applications and does not require any clock synchronisation between the nodes. Through simulation, we highlight that in static duty cycle MACs there is always a trade-off between energy-efficiency and performance leading to increased energy consumption and low throughput in certain networks. Additionally, it is shown that dynamic protocols can overcome the constraints observed in static DC MACs. CADC outperforms other previously proposed static and dynamic duty cycle protocols in terms of energy consumption, packet loss and goodput while it achieves competitive delay times
S. Li, G. Oikonomou, T. Tryfonas, T. Chen, L. Xu, "A distributed consensus algorithm for decision-making in service-oriented Internet of Things", Transactions on Industrial Informatics, IEEE, 10(2), pp. 1461-1468, 2014
In a service-oriented Internet of Things (IoT) deployment, it is difficult to make consensus decisions for services at different IoT edge nodes, where available information might be insufficient or overloaded. Existing statistical methods attempt to resolve the inconsistency, which requires adequate information to make decisions. Distributed Consensus Decision Making (CDM) methods can provide an efficient and reliable means of synthesizing information by using a wider range of information than existing statistical methods. In this paper, we firstly discuss service composition for the IoT, by minimizing the multi-parameter dependent matching value. Subsequently, a cluster-based distributed algorithm is proposed, whereby consensuses are first calculated locally and subsequently combined in an iterative fashion to reach global consensus. The distributed consensus method improves the robustness and trustiness of the decision process.
P. Andriotis, T. Tryfonas, G. Oikonomou, S. Li, Z. Tzermias, K. Xynos, H. Read, V. Prevelakis, "On the Development of Automated Forensic Analysis Methods for Mobile Devices", in Proc. 7th International Conference on Trust & Trustworthy Computing (TRUST 2014), ser. Lecture Notes in Computer Science, 8564, pp. 212-213, 2014
T. Spyridopoulos, G. Karanikas, T. Tryfonas, G. Oikonomou, "A Game Theoretic Defence Framework Against DoS/DDoS Cyber Attacks", Computers & Security, Elsevier, 38, pp. 39-50, 2013
Game-theoretic approaches have been previously employed in the research area of network security in order to explore the interaction between an attacker and a defender during a Distributed Denial of Service (DDoS) attack scenario. Existing literature investigates payoffs and optimal strategies for both parties, in order to provide the defender with an optimal defence strategy. In this paper, we model a DDoS attack as a one-shot, non-cooperative, zero-sum game. We extend previous work by incorporating in our model a richer set of options available to the attacker compared to what has been previously achieved. We investigate multiple permutations in terms of the cost to perform an attack, the number of attacking nodes, malicious traffic probability distributions and their parameters. We analytically demonstrate that there exists a single optimal strategy available to the defender. By adopting it, the defender sets an upper boundary to attacker payoff, which can only be achieved if the attacker is a rational player. For all other attack strategies (those adopted by irrational attackers), attacker payoff will be lower than this boundary. We preliminary validate this model via simulations with the ns2 network simulator. The simulated environment replicates the analytical model's parameters and the results confirm our model's accuracy.
T. Butt, I. Phillips, L. Guan, G. Oikonomou, "Adaptive and Context-aware Service Discovery for the Internet of Things", in Proc. 6th conference on Internet of Things and Smart Spaces (ruSMART 2013), St.Petersburg, Russia, pp. 36-47, 2013
The Internet of Things (IoT) vision foresees a future Internet encompassing the realm of smart physical objects, which offer hosted functionality as services. The role of service discovery is crucial when providing application-level, end-to-end integration. In this paper, we propose trendy: a RESTful web services based Service Discovery protocol to tackle the challenges posed by constrained domains while offering the required interoperability. It provides a service selection technique to offer the appropriate service to the user application depending on the available context information of user and services. Furthermore, it employs a demand-based adaptive timer and caching mechanism to reduce the communication overhead and to decrease the service invocation delay. trendy’s grouping technique creates location-based teams of nodes to offer service composition. Our simulation results show that the employed techniques reduce the control packet overhead, service invocation delay and energy consumption. In addition, the grouping technique provides the foundation for group-based service mash-ups and localises control traffic to improve scalability.
T. Spyridopoulos, G. Oikonomou, T. Tryfonas, M. Ge, "Game Theoretic Approach for Cost-Benefit Analysis of Malware Proliferation Prevention", in Proc. 28th IFIP TC-11 SEC 2013 International Information Security and Privacy Conference, pp. 28-41, 2013
Many existing research efforts in the field of malware proliferation aim at modelling and analysing its spread dynamics. Many malware dissemination models are based on the characteristics of biological disease spread in human populations. In this work, we utilise game theory in order to extend two very commonly used malware spread models (SIS and SIR) by incorporating defence strategies against malware proliferation. We consider three different security mechanisms, ``patch'', ``removal'' and ``patch and removal'' on which our model is based. We also propose a cost-benefit model that describes optimal strategies the defender could follow when cost is taken into account. Lastly, as a way of illustration, we apply our models on the well studied Code-Red worm.
P. Ilia, G. Oikonomou, T. Tryfonas, "Cryptographic Key Exchange in IPv6-Based Low Power, Lossy Networks", in Proc. Workshop in Information Theory and Practice (WISTP 2013), ser. Lecture Notes in Computer Science, 7886, pp. 34-49, 2013
The IEEE 802.15.4 standard for low-power radio communications defines techniques for the encryption of layer 2 network frames but does not discuss methods for the establishment of encryption keys. The constrained nature of wireless sensor devices poses many challenges to the process of key establishment. In this paper, we investigate whether any of the existing key exchange techniques developed for traditional, application-centric wireless sensor networks (WSN) are applicable and viable for IPv6 over Low power Wireless Personal Area Networks (6LoWPANs). We use Elliptic Curve Cryptography (ECC) to implement and apply the Elliptic Curve Diffie Hellman (ECDH) key exchange algorithm and we build a mechanism for generating, storing and managing secret keys. The mechanism has been implemented for the Contiki open source embedded operating system. We use the Cooja simulator to investigate a simple network consisting of two sensor nodes in order to identify the characteristics of the ECDH technique. We also simulate a larger network to examine the solution's performance and scalability. Based on those results, we draw our conclusions, highlight open issues and suggest further work.
P. Andriotis, T. Tryfonas, G. Oikonomou, T. Spyridopoulos, A. Zaharis, A. Martini, I. Askoxylakis, "On Two Different Methods for Steganography Detection in JPEG Images with Benford's Law", in Proc. 7th Scientific NATO Conference in Security and Protection of Information (SPI 2013), Brno, Czech Republic, pp. 3-14, 2013
The practice of steganography, which in a computer context usually means manipulating multimedia content to embed hidden messages, may be used by criminals worldwide to facilitate their communication instead of, or complementary to, encryption. There is even speculation that global terrorist groups have been using steganography to communicate in covert ways. This paper will introduce steganography and discuss practical aspects of its detection. It will also discuss two recently proposed methods for detecting whether hidden messages exist in JPEG images using Benford's Law. The Law describes the logarithmic distribution of leading digits in sets of naturally set numbers and has been used with success in detecting financial fraud and election rigging in the past. The first approach examines the lead digit distribution of the raw contents of the bytes of a suspect image, whilst the second examines the distribution of lead digits of quantised discrete cosine transform (DCT) coefficients of the JPEG encoding. Both methods produce fast and credible results and are supported by open source toolkits that can be used by law enforcement and investigative authorities worldwide.
P. Andriotis, G. Oikonomou, T. Tryfonas, "JPEG Steganography Detection with Benford's Law", Digital Investigation, Elsevier, 9(3-4), pp. 246-257, 2013
In this paper we present a novel approach to the problem of steganography detection in JPEG images by applying a statistical attack. The method is based on the empirical Benford's Law and, more specifically, on its generalised form. We prove and extend the validity of the logarithmic rule in colour images and introduce a blind steganographic method which can flag a file as a suspicious stego-carrier. The proposed method achieves very high accuracy and speed and is based on the distributions of the first digits of the quantised Discrete Cosine Transform coefficients present in JPEGs. In order to validate and evaluate our algorithm, we developed steganographic tools which are able to analyse image files and we subsequently applied them on the popular Uncompressed Colour Image Database. Furthermore, we demonstrate that not only can our method detect steganography but, if certain criteria are met, it can also reveal which steganographic algorithm was used to embed data in a JPEG file.
P. Andriotis, Z. Tzermias, A. Mparmpaki, S. Ioannidis, G. Oikonomou, "Multilevel Visualization Using Enhanced Social Network Analysis with Smartphone Data", International Journal of Digital Crime and Forensics, IGI Global, 5(4), pp. 34-54, 2013
While technology matures and becomes more productive, mobile devices can be affordable and, consequently, fully integrated in people's lives. After their unexpected bloom and acceptance, Online Social Networks are now sources of valuable information. We therefore use them for tasks varying from direct marketing to forensic analysis. We have already seen Social Network Forensics techniques focused on particular networks implementing methods that collect data from user accounts. During the forensic analysis it is common to aggregate information from different sources but, usually, this procedure causes correlation problems. Here, we present our method to correlate data gathered from various social networks in combination with smartphones creating a new form of social map of the user under investigation. In addition, we introduce a multi level graph that utilises the correlated information from the smartphone and the social networks and demonstrates in three dimensions the relevance of each contact with the suspect.
G. Oikonomou, I. Phillips, T. Tryfonas, "IPv6 Multicast Forwarding in RPL-Based Wireless Sensor Networks", Wireless Personal Communications, Springer US, 73(3), pp. 1089-1116, 2013
Abstract In wireless sensor deployments, network layer multicast can be used to improve the bandwidth and energy efficiency for a variety of applications, such as service discovery or network management. However, despite efforts to adopt IPv6 in networks of constrained devices, multicast has been somewhat overlooked. The Multicast Forwarding Using Trickle (Trickle Multicast) internet draft is one of the most noteworthy efforts. The specification of the IPv6 Routing Protocol for Low power and Lossy Networks (RPL) also attempts to address the area but leaves many questions unanswered. In this paper we highlight our concerns about both these approaches. Subsequently, we present our alternative mechanism, called Stateless Multicast RPL Forwarding algorithm (SMRF), which addresses the aforementioned drawbacks. Having extended the TCP/IP engine of the Contiki embedded operating system to support both Trickle Multicast (TM) and SMRF, we present an in-depth comparison, backed by simulated evaluation as well as by experiments conducted on a multi-hop hardware testbed. Results demonstrate that SMRF achieves significant delay and energy efficiency improvements at the cost of a small increase in packet loss. The outcome of our hardware experiments show that simulation results were realistic. Lastly, we evaluate both algorithms in terms of code size and memory requirements, highlighting SMRF’s low implementation complexity. Both implementations have been made available to the community for adoption.
P. Andriotis, T. Tryfonas, G. Oikonomou, C. Yildiz, "A Pilot Study on the Security of Pattern Screen-Lock Methods and Soft Side Channel Attacks", in Proc. 6th ACM Conference on Security and Privacy in Wireless and Mobile Networks (WiSec 13), pp. 1-6, 2013
Graphical passwords that allow a user to unlock a smartphone's screen are one of the Android operating system's features and many users prefer them instead of traditional text-based codes. A variety of attacks has been proposed against this mechanism, of which notable are methods that recover the lock patterns using the oily residues left on screens when people move their fingers to reproduce the unlock code. In this paper we present a pilot study on user habits when setting a pattern lock and on their perceptions regarding what constitutes a secure pattern. We use our survey's results to establish a scheme, which combines a behaviour-based attack and a physical attack on graphical lock screen methods, aiming to reduce the search space of possible combinations forming a pattern, to make it partially or fully retrievable.
A. Jamil, D. Parish, I. Phillips, R. Phan, J. Whitley, G. Oikonomou, "Maximise Unsafe Path Routing Protocol for Forest Fire Monitoring System using Wireless Sensor Networks", in Proc. 3rd IEEE International Conference on Networked Embedded Systems for Every Application (NESEA 2012), Liverpool, UK, 2012
Wireless Sensor Networks are an emerging technology with wide potential to be used in many applications. One such application is the detection and prevention of disasters in scenarios such as forest fires, floods and earthquakes. In these disaster situations, the events being monitored have the potential to destroy the sensing devices, for example, they can be burnt in a fire, sunk in a flood, melted in volcano lava, short-circuited in harmful chemicals, etc. In this paper, a novel energy-efficient routing protocol called Maximise Unsafe Path (MUP) Routing using IPv6 over Low power Wireless Personal Area Networks (6LoWPAN) is presented. The protocol aims to extend network lifetime by adapting the routes accordingly based on node destruction threat. MUP uses a routing technique that maximises the energy utilisation of nodes that are going to fail sooner, in order to save the energy of the other nodes. MUP is implemented as an extension to the RPL protocol for IPv6-based WSNs. The performance of the presented routing is evaluated with simulations and compared with the standard RPL in the same scenarios.
P. Andriotis, G. Oikonomou, T. Tryfonas, "Forensic Analysis of Wireless Networking Evidence of Android Smartphones", in Proc. IEEE International Workshop on Information Forensics and Security (WIFS 12), Tenerife, Spain, pp. 109 - 114, 2012
This paper introduces a method for acquiring forensic-grade evidence from Android smartphones using open source tools. We investigate in particular cases where the suspect has made use of the smartphone's Wi-Fi or Bluetooth interfaces. We discuss the forensic analysis of four case studies, which revealed traces that were left in the inner structure of three mobile Android devices and also indicated security vulnerabilities. Subsequently, we propose a detailed plan for forensic examiners to follow when dealing with investigations of potential crimes committed using the wireless facilities of a suspect Android smartphone. This method can be followed to perform physical acquisition of data without using commercial tools and then to examine them safely in order to discover any activity associated with wireless communications. We evaluate our method using the Association of Chief Police Officers' (ACPO) guidelines of good practice for computer-based, electronic evidence and demonstrate that it is made up of an acceptable host of procedures for mobile forensic analysis, focused specifically on the device's Bluetooth and Wi-Fi facilities.
T. Butt, I. Phillips, L. Guan, G. Oikonomou, "TRENDY: An Adaptive and Context-Aware Service Discovery Protocol for 6LoWPANs", in Proc. Third International Workshop on the Web of Things (WoT 2012), Newcastle, UK, pp. 2:1-2:6, 2012
We propose, TRENDY, a new registry-based Service Discovery protocol with context awareness. It uses CoAP-based RESTful web services to provide a standard interoperable interface which can be easily translated from HTTP. In addition, TRENDY introduces an adaptive timer and grouping mechanism to minimise control overhead and energy consumption. TRENDY's grouping is based on location tags to localise status maintenance traffic and to compose and offer new group based services. Our simulation results show that TRENDY techniques reduce the control traffic considerably and also reduce the energy consumption, while offering the optimal service selection.
W. Rukpakavong, I. Phillips, L. Guan, G. Oikonomou, "RPL Router Discovery for Supporting Energy-Efficient Transmission in Single-hop 6LoWPAN", in Proc. 3rd Workshop On Energy Efficiency in Wireless Networks and Wireless Networks for Energy Efficiency (E2Nets), Ottawa, Canada, pp. 7264-7268, 2012
In Wireless Sensor Networks (WSNs), controlling transmission power is a commonly used technique to extend battery life. This paper describes a novel mechanism using measured RSS (Received Signal Strength) to calculate optimal transmission power. This technique works in multipath environments and with nodes with differing transmission capability. Our technique achieves automatic configuration employing modifications to RPL (Routing Protocol for Low-power and lossy networks) router discovery without requiring extra steps or messages. Consequently, each node can send packets with ideal transmission power, which will usually be lower than maximum power and will help to prolong its lifetime. We evaluate the effectiveness of the proposed scheme, using performance metrics such as energy consumption and packet loss, on an WSN testbed. Several factors that impact the RSS, such as antenna, multipath environment, output power and the node's capabilities are also investigated. Moreover, two RSS estimation techniques are evaluated and compared to the average measured RSS. The experimental results show that energy consumption is reduced by using the proposed technique.
V. Michopoulos, L. Guan, G. Oikonomou, I. Phillips, "DCCC6: Duty Cycle-Aware Congestion Control for 6LoWPAN Networks", in Proc. 2012 IEEE International Conference on Pervasive Computing and Communications Workshops (PERCOM Workshops), Lugano, Switzerland, pp. 278-283, 2012
In Wireless Sensor Networks (WSNs), congestion can cause a number of problems including packet loss, lower throughput and poor energy efficiency. These problems can potentially result in reduced deployment lifetime and under-performing applications. This has led to several proposals for congestion control (CC) mechanisms for sensor networks. Furthermore, the WSN research community has made significant efforts towards power saving MAC protocols with Radio Duty Cycling (RDC). However, careful study of previous work reveals that RDC schemes are often neglected during the design and evaluation of CC algorithms. In this context, this paper contributes a new CC scheme for Duty Cycle and IPv6 over Low power Wireless Personal Area Networks 6LoWPAN sensor Networks - DCCC6. DCCC6 detects the presence of duty cycling and adjust its operation accordingly. We evaluate DCCC6 both with simulations and on a testbed with multi node topologies. The experimental results have shown that DCCC6 achieved higher goodput and lower packet loss than previous works. Moreover, simulations show that DCCC6 maintained low energy consumption, average delay times and achieved a high degree of fairness.
G. Oikonomou, I. Phillips, "Stateless Multicast Forwarding with RPL in 6LoWPAN Sensor Networks", in Proc. 2012 IEEE International Conference on Pervasive Computing and Communications Workshops (PERCOM Workshops), Lugano, Switzerland, pp. 272-277, 2012
Recent research efforts have resulted in efficient support for IPv6 in Low power Wireless Personal Area Networks (6LoWPAN), with the ``IPv6 Routing Protocol for Low power and Lossy Networks'' (RPL) being on the forefront as the state of the art routing approach. However, little attention has been paid to IPv6 multicast for networks of constrained devices. The ``Multicast Forwarding Using Trickle'' (Trickle Multicast) internet draft is one of the most noteworthy efforts, while RPL's specification also attempts to address the area but leaves many questions unanswered. In this paper we expose our concerns about the Trickle Multicast (TM) algorithm, backed up by thorough performance evaluation. We also introduce SMRF, an alternative multicast forwarding mechanism for RPL networks, which addresses TM's drawbacks. Simulation results demonstrate that SMRF achieves significant delay and energy efficiency improvements at the cost of a small increase in packet loss. We have extended the TCP/IP engine of the Contiki embedded Operating System to support both algorithms. Both implementations have been made available to the community.
G. Oikonomou, I. Phillips, "Experiences from Porting the Contiki Operating System to a Popular Hardware Platform", in Proc. 2011 International Conference on Distributed Computing in Sensor Systems and Workshops (DCOSS), Barcelona, Spain, pp. 54-59, 2011
In contrast to original belief, recent work has demonstrated the viability of IPv6-based Wireless Sensor Networks (WSNs). This has led to significant research and standardization efforts with outcomes such as the ``IPv6 over Low-Power Wireless Personal Area Networks'' (6LoWPAN) specification. The Contiki embedded operating system is an important open source, multi-platform effort to implement 6LoWPAN functionality for constrained devices. Alongside its RFC-compliant TCP/IP stack (uIP), it provides support for 6LoWPAN and many related standards. As part of our work, we have made considerable fixes and enhancements to one of Contiki's ports. In the process, we made significant optimizations and a thorough evaluation of Contiki's memory and code footprint characteristics, focusing on network-related functionality. In this paper we present our experiences from the porting process, we disclose our optimizations and demonstrate their significance. Lastly, we discuss a method of using Contiki to deploy an embedded Internet-to-6LoWPAN router. Our porting work has been made available to the community under the terms of the Contiki license.
V. Michopoulos, L. Guan, G. Oikonomou, I. Phillips, "A Comparative Study of Congestion Control Algorithms in IPv6 Wireless Sensor Networks", in Proc. 2011 International Conference on Distributed Computing in Sensor Systems and Workshops (DCOSS), Barcelona, Spain, pp. 1-6, 2011
In Wireless Sensor Networks (WSNs), congestion can cause a plethora of malfunctions such as packet loss, lower throughput and energy inefficiency, potentially resulting in reduced deployment lifetime and under-performing applications. This has led to several proposals describing congestion control (CC) mechanisms for sensor networks. Furthermore, the WSN research community has made significant efforts towards power saving MAC protocols with Radio Duty Cycling (RDC). However, careful study of previous work reveals that RDC schemes are often neglected during the design and evaluation of congestion control algorithms. In this paper, we argue that the presence (or lack) of RDC can drastically influence the performance of congestion detection. In addition, most WSN CC mechanisms are evaluated under traditional sensor network topologies and protocols (e.g. trickle data dissemination, tree data collection). The emerging IPv6 over Low power Wireless Personal Area Networks (6LoWPAN) and related standards pose a new requirement: we now need to investigate if previous findings regarding congestion control are still applicable. In this context, this paper contributes a comprehensive evaluation of existing congestion detection mechanisms in a simulated, multi-node 6LoWPAN sensor network. We present results from two sets of experiments, differentiated by the presence or lack of RDC.
G. Oikonomou, I. Phillips, L. Guan, A. Grigg, "ADDER: Probabilistic, Application Layer Service Discovery for MANETs and Hybrid Wired-Wireless Networks", in Proc. 9th Annual Communication Networks and Services Research Conference (CNSR 2011), Ottawa, Canada, pp. 33-40, 2011
Over the past years, Mobile ad-hoc networks (MANETs) have attracted a considerable degree of research attention, with service discovery, selection and invocation being among the topics of interest of previous efforts. In this paper we introduce ADDER, a probabilistic, hybrid, directory-less service discovery mechanism. It has been designed for military IPv6-based MANETs but will work in any hybrid wired-wireless deployment. It achieves very low service acquisition time through the exchange of a very small number of short messages. Propagation of service descriptions is based on a distance vector algorithm, achieving loop and starvation freedom through a feasibility condition, which has been adopted from established and well-tested routing protocols. This paper also presents evaluation results, obtained by actual execution of the ADDER daemon on two different test beds. The experiments aim to demonstrate that the mechanism achieves good scalability with increasing number of services and network size.
A. Jamil, D. Parish, R. Phan, J. Whitley, I. Phillips, G. Oikonomou, "Designing Environmental Aware Routing in Wireless Sensor Networks", London, UK, 2011 (non-refereed)
T. Edwan, L. Guan, G. Oikonomou, I. Phillips, "Higher Order Delay Functions for Delay-Loss Based TCP Congestion Control", in Proc. 6th Wireless Advanced, London, UK, pp. 1-6, 2010
TCP-Illinois aims to address TCP's low throughput when operating in high-speed, high-delay networks. Previous research has shown that, due to its linear increase behaviour and to its relatively long congestion epochs, TCP-Illinois exhibits sub-optimal scaling behaviour with an increasing path Bandwidth-Delay Product (BDP). This paper discloses our contributions towards improving the aggressiveness and responsiveness of loss-based TCP congestion control algorithms. We formally show that higher order versions (of power n) of the delay functions used by TCP-Illinois become more aggressive and responsive with an increasing value of n. Based on this finding, we propose three variants: i) a second order (quadratic) version of additive increase and multiplicative decrease (TCP-Q), ii) a second order multiplicative decrease only (TCP-Fq) and iii) a sub-linear multiplicative decrease only (TCP-Fs). By modifying the TCP-Illinois code in the GNU/Linux kernel, we obtained the three corresponding modules and used them for our simulations using the TCP/Linux patch for ns2. Based on standardised congestion control metrics, we conducted a comparative analysis between our variants and a number of relevant high speed TCP algorithms. Simulation results agree with our analytical findings; compared to TCP-Illinois, TCP-Q exhibits shorter congestion epochs and thus better responsiveness and convergence.
T. Edwan, L. Guan, G. Oikonomou, I. Phillips, "Understanding the Impact of Link Errors on TCP Congestion Control", in Proc. 26th UK Performance Engineering Workshop (UK PEW 2010), Coventry, UK, pp. 59-64, 2010
This paper presents a control-theoretic-like analysis of TCP congestion control mechanism. We extend previous analysis by considering two additional factors: i) wireless link errors and ii) general variable multiplicative decrease (MD). Wireless link errors are usually the cause for unnecessary TCP congestion window reductions and thus lower throughput. We also study the effects of those parameters on TCP's stability condition. In this paper, we present a modified TCP model and analyse it in the presence of delay. This is then linearised around an equilibrium point and re-analysed using a control-theoretic-like framework. The analysis verifies that non-congestive packet loss acts as a disturbance, as opposed to loss due to congestion, which is well within TCP's control.
G. Oikonomou, I. Phillips, L. Guan, A. Grigg, "An Emulator for the Network Stack of Integrated Modular Systems", in Proc. 5th IEEE International Conference on Systems of Systems Engineering (IEEE SoSE), Loughborough, UK, 2010
The networked integration of military systems can enable timely exploitation of intelligence and offer strategic advantages in the battlefield. Despite operating under harsh, hostile conditions, tactical networks have many similarities with typical wireless ad-hoc networks. The UK Ministry of Defence Standard 00-74 attempts to standardise an architecture for integrated avionics and includes the specification of a three layer network stack for the message exchange between applications on board a system. As part of our work, we developed an emulator for this network stack. Furthermore, we have designed and implemented a service discovery mechanism for mobile ad hoc networks. This paper focuses on disclosing the emulator's design and implementation details. We also discuss the emulator's integration with the service discovery mechanism in order to achieve scalable, reconfigurable off board communications towards IPv6 based systems of systems.
G. Oikonomou, T. Apostolopoulos, "Web-Based Management of Distributed Services", in Advances in Electrical Engineering and Computational Science, ser. Lecture Notes in Electrical Engineering, Springer Netherlands, 39, pp. 255-266, 2009 (invited)
This paper presents WebDMF, a Web-based Framework for the Management of Distributed services. It is based on the Web-based Enterprise Management (WBEM) family of standards and introduces a middleware layer of entities called "Representatives". WebDMF can be integrated with existing WBEM infrastructures and is not limited to monitoring. On the contrary, it is capable of actively modifying the run-time parameters of a managed service. Due to its abstract design, it is suitable for the management of a variety of distributed services, such as grids and content delivery networks. The paper includes a discussion on WebDMF's design, implementation and advantages. We also present experiments on an emulated network topology as an indication of the framework's viability.
G. Oikonomou, "A Web-Based Framework for the Management of Distributed Systems and Services. Case Study: Management of Content Delivery Networks", PhD thesis, Department of Informatics, Athens University of Economics and Business, Athens, Greece, 2008 (in greek)
G. Oikonomou, T. Apostolopoulos, "Web-Based Management of Content Delivery Networks", in Proc. 19th IFIP/IEEE International Workshop on Distributed Systems: Operations and Management (DSOM). Managing Large Scale Service Deployment (MANWEEK 08), Samos, Greece, pp. 42-54, 2008
Abstract overlay networks have been considered enablers of efficient management for decentralized, large scale service deployments. A Content Delivery Network (CDN) is an example of service falling within this category. The result of our research is WebDMF, a management framework for distributed services based on the Web-Based Enterprise Management (WBEM) family of specifications. Abstract design, combined with a middleware layer of entities called "Representatives", makes WebDMF suitable for the management of a variety of services. Details related to the management of each particular service are detached from the representative logic. This paper discusses how WebDMF can be used for the management of CDNs. A WBEM provider resides on each host participating in the service deployment and implements CDN-specific operations. WebDMF representatives decentralize, unify and coordinate those on a deployment scale. Preliminary measurements on an emulated network topology are also presented as an indication of the solution's viability and scalability.
G. Oikonomou, T. Apostolopoulos, "WebDMF: A Web-Based Management Framework for Distributed Services", in Proc. The 2008 International Conference of Parallel and Distributed Computing (ICPDC 08), 1, London, UK, pp. 593-598, 2008
This paper presents WebDMF, a Web-based Framework for the Management of Distributed services. It is based on the Web-based Enterprise Management (WBEM) family of standards and introduces a middleware layer of entities called "Representatives". WebDMF can be integrated with existing WBEM infrastructures and is not limited to monitoring. On the contrary, it is capable of actively modifying the run-time parameters of the managed application. Its design is abstract and suitable for a variety of distributed services, such as grids and content delivery networks. The paper includes a discussion on WebDMF's design, implementation and advantages. We also present experiments on an emulated network topology as an indication of the framework's viability.
G. Oikonomou, T. Apostolopoulos, "Using a Web-Based Framework to Manage Grid Deployments", in Proc. The 2008 International Conference on Grid Computing and Applications (GCA 08), Las Vegas, USA, pp. 10-16, 2008
WebDMF is a Web-based Framework for the Management of Distributed services. It is based on the Web-based Enterprise Management (WBEM) standards family and introduces a middleware layer of entities called "Representatives". Details related to the managed application are detached from the representative logic, making the framework suitable for a variety of services. WebDMF can be integrated with existing WBEM infrastructures and is complementary to web service-based management efforts. This paper describes how the framework can be used to manage grids without modifications to existing installations. It compares the proposed solution with other research initiatives. Experiments on an emulated network topology indicate its viability.
G. Oikonomou, T. Apostolopoulos, "A Framework for the Management of Distributed Systems Based on SNMP", in Proc. 22nd International Symposium on Computer and Information Sciences (ISCIS 07), Ankara, Turkey, pp. 1-6, 2007
The traditional task of managing and monitoring a network has never been a trivial one. With recent changes in computing and networking, the area of distributed systems management faces new challenges and increasing complexity. Research in the relevant field reveals that, while there are many research and commercial solutions available, some of them are based on proprietary standards. Others focus on monitoring, while lacking the ability to actively make modifications and fine-tuning. Some others have a narrow target group. This paper proposes a framework for the management of distributed applications. The managed hosts are treated as integral parts of the deployment and not as stand alone, isolated entities. The framework is based on SNMP and is not limited to monitoring. On the contrary, it is capable of carrying out SNMP-SET commands, actively modifying the run-time parameters of the managed application. Finally, it can perform the management of a variety of distributed systems, ranging from small clusters to larger scale deployments such as computational or data grids.
T. Apostolopoulos, G. Oikonomou, G. Parissis, "Broadband in Greece. Perspective and Challenges", Greek Computer Society Press, pp. 28-30, 2007 (in Greek)
G. Oikonomou, V. Karakoidas, T. Apostolopoulos, "Pegasus: Competitive Load Balancing Using inetd", in Proc. 5th System Administration and Network Engineering Conference (SANE 2006), Delft, The Netherlands, pp. 59-68, 2006 (refereed paper)
T. Apostolopoulos, I. Kapetanakis, G. Oikonomou, "An Architecture for the Management of Smart Cards by Mobile Devices Using Java Technologies", in Proc. 7th International IEEE Conference on E-Commerce Technology (CEC 2005), Munich, Germany, pp. 527-530, 2005 (short paper)
Smart cards are cards with memory and a processor, ideal for authentication and secure applications. Mobile devices have an extraordinary spread; people carry them along at all times. The ability to combine the features of those two devices is quite compelling. We used technologies of the Java family in order to achieve this. In our work, we designed an architecture for the management of smart cards by mobile devices. The system is built up from three components, the Java card applet, the mobile application and the Java card-mobile device gateway. For the purposes of our work and as proof of concept, we developed a sample electronic wallet application. Finally, we extended the proposed system's functionality and described a business case, where the system could be used in the future.
T. Apostolopoulos, G. Oikonomou, "Overtester: A Peer-to-Peer, Modular Toolkit for Network Performance Evaluation", in Proc. The Fourth International Symposium on Communication Systems, Networks and Digital Signal Processing (CSNDSP 04), Newcastle, UK, pp. 404-407, 2004 (short paper)
The field of network performance evaluation is of great significance for researchers and network administrators alike. This has resulted in a great number of applications designed to aid the process. These applications vary quite a bit, ranging from simple tools, such as the famous ping program all the way to complex and sophisticated ones. OverTester resides on top of other performance measurement programs, like a management console, automating and co-coordinating the process. It is Modular, while its most significant features are its Peer-to-Peer and Cross-Platform nature.
T. Apostolopoulos, G. Oikonomou, "A Scalable, Extensible Framework for Grid Management", in Proc. IASTED International Conference on Parallel and Distributed Computing and Networks (PDCN 2004), Innsbruck, Austria, 2004
The picture of global computing is rapidly changing. In the last few years, with the progress made in the area of computer networks, standalone desktop computers became largely interconnected. And then grid computing came along. Managing and monitoring a network had never been a trivial task and many efforts have been made in this direction. A variety of protocols have been proposed and standards have arisen in order to facilitate this process. Now the task has become even more complex. Not only do we have the need to monitor and manage the underlying network, but also the availability and utilisation of shared resources. From simple resources such as CPU cycles and storage space, all the way to complicated equipment used for specific purposes, such as medical or scientific instruments. Our vision is of a management framework for grid deployments, that is easy to use, scalable, secure and modular. We propose a framework that has been designed in order to satisfy the above criteria. Furthermore, it is based on open standards, which makes it easy to implement and integrate with existing management systems.
T. Apostolopoulos, G. Oikonomou, N. Chatzivasdekis, "Statistical Analysis of the Performance of IEEE 802.11 LANs", in Proc. IASTED International Conference on Communication Systems and Networks (CSN 2003), Benalmadena, Spain, pp. 151-156, 2003
Wireless LAN technology is relatively new and rapidly developing. The performance of such networks is of great importance and deep understanding is required in order to take advantage of their full potential. In our work, we installed an infrastructure IEEE 802.11b compliant Wireless LAN in the Computer and Communication Systems Laboratory, measured its performance and analyzed it, using statistical methods. Our ultimate goal was to study the impact of various operational parameters on the aforementioned performance.
G. Oikonomou, "Statistical Analysis of the Performance of IEEE 802.11 LANs", Master's thesis, Department of Informatics, Athens University of Economics and Business, Athens, Greece, 2002 (in greek)
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