Ioannis Stavrakakis

National and Kapodistrian University of Athens | uoa · Faculty of Informatics and Telecommunications

Edge computing has emerged as the next big thing in distributed computing, by extending the cloud paradigm and offering efficient ways to engage with latency-intolerant applications, such as Virtual Reality (VR) multiplayer games. In edge computing, the service providers can benefit from existing cellular infrastructure to deploy services on edge s...

This work studies the decentralized and uncoordinated energy source selection problem for smart-grid consumers with heterogeneous energy profiles and risk attitudes, which compete for a limited amount of renewable energy sources. We model this problem as a non-cooperative game and study the existence of mixed-strategy Nash equilibria under the prop...

Probabilistic flooding is an efficient information dissemination policy capable of spreading information to the network nodes by sending information messages according to a fixed forwarding probability in a per-hop manner starting from an initiator node. It is a suitable approach, especially in topologies where the number of information messages se...

Distributed Complex Event Processing (DCEP) is a commonly used paradigm to detect and act on situational changes of many applications, including the Internet of Things (IoT). DCEP achieves this using a simple specification of analytical tasks on data streams called operators and their distributed execution on a set of infrastructure. The adaptivity...

Distributed Complex Event Processing (DCEP) is a commonly used paradigm to detect and act on situational changes of many applications, including the Internet of Things (IoT). DCEP achieves this using a simple specification of analytical tasks on data streams called operators and their distributed execution on a set of infrastructure. The adaptivity...

In order to support location-based services, vehicles share their location with a server to receive relevant data. Revealing a vehicle’s location compromises its privacy. One way to reduce this problem is obfuscating the vehicle’s location by adding artificial noise. However, this increases the area where the true location of the vehicle may be. He...

Fog-assisted cloud computing advances have paved the way for new solutions in online gaming, by integrating all rendering resources directly into the edges of the cloud. However, despite the numerous benefits, these systems still remain prone to network delays, ergo, the discovery of an optimal rendering service placement in the fog layer, that eff...

The aim of a mobile recharger operating in a wireless sensor network (WSN) is to keep the network’s average consumed energy and covered distance low. As shown in the literature, the covered distance is minimized when the mobile recharger’s base is located as per the solution of a median problem, while the network’s average energy consumption is m...

Single-task UAVs are increasingly being employed to carry out surveillance, parcel delivery, communication support, and other specific tasks. When the geographical area of operation of single-task missions is common, e.g., in post-disaster recovery scenarios, it is more efficient to have multiple tasks carried out as part of a single UAV mission. I...

Single-task UAVs are increasingly being employed to carry out surveillance, parcel delivery, communication support, and other specific tasks. When the geographical area of operation of single-task missions is common, e.g., in post-disaster recovery scenarios, it is more efficient to have multiple tasks carried out as part of a single UAV mission. I...

Cloudification of heterogeneous networks along with the virtualization of gaming resources, allow the game providers to move into the cloud gaming era. Cloud gaming offloads computation-intensive tasks to the cloud in order to alleviate the computational burden of end-users' devices, but introduces delay which deteriorates their Quality of Experien...

The recent technological evolution of drones along with the constantly growing maturity of its commercialization, has led to the emergence of novel drone-based applications within the field of wireless sensor networks for information collection purposes. In such settings, especially when deployed in outdoor environments with limited external contro...

As current network technologies evolve towards 5G supporting increased throughput and low time delays, a need emerges for supporting time constraint applications at the wireless end user level. The network formed due to the dynamicity of the Internet of Things (IoT), can be seen as a wireless ad hoc environment where certain time constraints need t...

To support location-based services, vehicles must share their location with a server to receive relevant data, compromising their (location) privacy. To alleviate this privacy compromise, the vehicle's location can be obfuscated by adding artificial noise. Under limited available bandwidth, and since the area including the vehicle's location increa...

To capture the dynamics of context-aware decision making for network functions in Mobile Ad Hoc Networks (MANETs), the paper introduces the concept of Decision-Related Event Occurrence Times (DREOTs). By considering a generic scenario, the paper develops a broadly applicable analysis methodology, which produces upper and lower bounds for the tail p...

The emerging new paradigm under the upcom-ing 5G communication paradigm is expected to support the multitudes of low-cost devices and an all-increasing number of new applications. Considering time-constrained applications (e.g., safety applications in vehicular networks) TDMA-based medium access control (MAC) policies, like those independent of the...

The emerging new paradigm under the upcom-ing 5G communication paradigm is expected to support the multitudes of low-cost devices and an all-increasing number of new applications. Considering time-constrained applications (e.g., safety applications in vehicular networks) TDMA-based medium access control (MAC) policies, like those independent of the...

Drones are currently the focus of increased interest for various purposes related to actual applications and communication systems. Although their autonomous capabilities allow them to operate as a distinct network themselves, it is common to use them in combination with traditional communication networks, such as Wireless Sensor Networks (WSN), th...

Cloud gaming architectures have emerged in efforts to provide efficient execution of computer video games in computer machines and mobile devices with low processing/rendering capabilities. Such approaches are prone to network delays since the rendering process is offloaded to the cloud, hence, increasing cloud's computational needs and decreasing...

Routing in wireless sensor networks is a challenging task due to the energy hole problem, which negatively affects the network’s operation. Taking into account path impotence, i.e., a metric based on the transmission distance and the energy left at the nodes’ batteries, an adjustable routing policy is proposed here that allows nodes to choose diffe...

The multiple random walkers mechanism is revisited in this paper for service discovery purposes considering modern dynamic network environments like the Internet of Things (IoT), where there is a need for certain services (e.g., virtual network functions) to be available to the end users through fog computing devices. Network coverage is analytical...

In this special issue, we have collected and presented recent works on innovative approaches and emerged technologies for coping with dynamicity, heterogeneity, and the scale, which have been central to (or even enablers of) recent advances in communications and networking technologies. At a time of an ever-increasing demand for networking resource...

Time synchronization is a challenging problem for wireless sensor networks, as clocks deviate and sensor measurements need to be associated with the reference clock time they took place. In Internet of Things (IoT) environments, crucial factors like energy, robustness, limited capabilities and extreme ambient conditions (e.g., when nodes are deploy...

Connected vehicles can nowadays be equipped with multiple network interfaces to access the Internet via a number of networks. To achieve an efficient transmission within this environment, a strategic time-network selection for connected vehicles has been developed, which plans ahead delay-tolerant transmissions. Under perfect prediction (knowledge)...

Cloud or Centralized Radio Access Networks (C-RANs) are expected to be widely deployed under 5G in order to support the anticipated increased traffic demands and reduce costs. Under C-RAN, the radio elements (e.g., eNB or gNB in 5G) are split into a basic radio part (Distributed Unit, DU), and a pool-able base band processing part (Central Unit, CU...

The proliferation of wireless sensor networks supports nowadays numerous areas of everyday life and activities. Each sensor node senses some data of interest (e.g., humidity, temperature) and the corresponding measurements need to be tagged with the reference time (usually sink node's time) they took place, in order to be further analyzed. Given th...

The multiple random walkers mechanism is revisited in this paper for service discovery purposes considering modern dynamic network environments like fog computing, where there is a need for certain services (e.g., virtual network functions) to be available to the end users. Network coverage is analytically investigated here considering multiple ran...

Medium access control (MAC) is a challenging problem in vehicular environments due to a constantly changing topology due to vehicle's mobility and stringent delay requirements, especially for safety-related applications (e.g., for vehicular-to-vehicular communication). Consequently, topology-independent TDMA MAC policies that guarantee a number of...

Efficient energy consumption is a challenging problem in wireless sensor networks especially close to the sink node, known as the energy hole problem. Various policies for recharging battery exhausted nodes have been proposed using special recharging vehicles. The focus in this paper is on a simple recharging policy that permits a recharging vehicl...

Future mobile applications will increasingly rely on direct communication among devices or with the environment—e.g., sensors—to provide interactive experiences to their users. The resulting communication characteristics are highly dynamic due to mobility and social behavior of humans, requiring applications to continuously adapt to the prevailing...

Wireless sensor networks suffer from increased energy consumption close to the sink node, known as the energy hole problem. Various policies for recharging battery exhausted nodes have been proposed using special recharging vehicles. The focus in this paper is on a simple recharging policy that permits a recharging vehicle, stationed at the sink no...

This book constitutes the proceedings of the Third International Conference on Internet Science held in Florence, Italy, in September 2016. The 25 papers presented were carefully reviewed and selected for inclusion in this volume. They were organized in topical sections named: collective awareness and crowdsourcing platforms¸ collaboration, privacy...

Locally aware routing protocols base their next-hop selection on information about their immediate neighborhood, gathered by means of a beaconing mechanism. In general, beacons may be proactively broadcasted from nodes to their neighbors (‘receiver-initiated’ beaconing) or may be solicited by the node carrying the routed message (‘on-demand’ beacon...

Internet vulnerability studies typically consider highly central nodes as favorable targets of intelligent (malicious) attacks. Heuristics that use redundancy adding k extra links in the topology are a common class of countermeasures seeking to enhance Internet robustness. To identify the nodes to be linked most previous works propose very simple c...

Advances in Information and Communication Technologies have dramatically changed the role of users and resulted in unprecedented amounts of information that enrich users' awareness about their environment and its resources. While this broad awareness for (low-priced) limited resources can bring benefits, it also intensifies competition phenomena in...

The tremendous growth of urbanization calls for several interventions for the efficient and environmentally sustainable management of various urban processes, including the road traffic management. Indeed, transportation engineers need to be able to understand how drivers decide their route to effectively address the plethora of challenges for alle...

Acquiring the full global information is impractical, if feasible at all, in many networks with distributed operation and self-organization features. To meet scalability requirements practical protocol implementations could use local information instead, drawn from the nodes' ego-networks, the Social Network Analysis (SNA) counterpart of centered g...

The position of the nodes within a network topology largely determines the level of their involvement in various net-working functions. Yet numerous node centrality indices, proposed to quantify how central individual nodes are in this respect, yield very different views of their relative significance. Our first contribution is then an exhaustive s...

Collective awareness platforms (CAPs) are internet and mobile tools for collaboration, sustainability and social innovation that can allows drastic improvement of our lifestyle, beyond the standard economic model. However, their development is often driven (and motivated) by technology, while their adoption and usage characteristics are determined...

The proliferation of mobile computing devices has enabled the utilization of infrastructure-less networking as commercial solutions. However, the distributed and cooperative nature of routing in such networks makes them vulnerable to a variety of attacks. This paper proposes a host-based monitoring mechanism, called SIDE that safeguards the operati...

Opportunistic networking leverages the volume, heterogeneity and mobility of end user nodes to foster the dissemination of information in the absence of network infrastructure. Nevertheless, in competitive settings (where the possession of information itself is an asset) user nodes often face a strategic dilemma: cooperate, to realize the network a...

The optimal placement of service facilities largely determines the capability of a data network to efficiently support its users' service demands. As centralized solutions over large-scale distributed environments are extremely expensive, inefficient or even infeasible, distributed approaches that rely on partial topology and demand information are...

The effectiveness of service provisioning in large-scale networks is highly dependent on the number and location of service facilities deployed at various hosts. The classical, centralized approach to determining the latter would amount to formulating and solving the uncapacitated k-median (UKM) problem (if the requested number of facilities is fix...

Our paper investigates normative abstractions for the way drivers pursue parking space and respond to pricing policies about public and private parking facilities. The drivers are viewed as strategic agents who make rational decisions while attempting to minimize the cost of the acquired parking spots. We propose auction-based systems for realizing...

This paper seeks to systematically explore the efficiency of the uncoordinated information-assisted parking search in urban environments with two types of parking resource facilities: inexpensive but limited facilities (public) and expensive yet unlimited ones (private); an additional cruising cost is incurred when deciding for a public facility bu...

The position of the nodes within a network topology largely determines the level of their involvement in various networking functions. Yet numerous node centrality indices, proposed to quantify how central individual nodes are in this respect, yield very different views of their relative significance. Our first contribution in this paper is then an...

This paper systematically explores the efficiency of uncoordinated parking space allocation in urban environments with two types of parking facilities. Drivers decide whether to go for inexpensive but limited on-street parking spots or for expensive yet overdimensioned parking lots, incurring an additional cruising cost when they decide for on-stre...

With the emergence of mobile communication devices and social networking applications, new opportunities arise for various mobile networking applications. In this paper, we seek to experimentally study some fundamental properties of vehicular social applications that have been deployed to assist in the parking search process. The awareness and ince...

In many networks with distributed operation and self-organization features, acquiring their global topological information is impractical, if feasible at all. Internet protocols drawing on node centrality indices may instead approximate them with their egocentric counterparts, computed out over the nodes’ ego-networks. Surprisingly, however, in rou...

This paper explores how the degree of similarity within a social group can dictate the behavior of the individual nodes, so as to best tradeoff the individual with the social benefit. More specifically, we investigate the impact of social similarity on the effectiveness of content placement and dissemination. We consider three schemes that represen...

In this paper we explore the interplay of node density, mobility and cooperation in routing decisions for mobile networks. Specifically, routing is based on a novel metric that jointly accounts for all three aforementioned attributes and helps identify the most promising venue available for getting the message closer/faster to the destination, even...

In competitive autonomic networking environments, user nodes face a strategic dilemma: on the one hand, they need to cooperate to support the networking infrastructure and information flow; on the other hand they are tempted not to do so, e.g., in order to conserve own system resources or create an advantage for themselves. In this paper we investi...

The need to efficiently accommodate over the Internet the ever exploding (user-generated) content and services, calls for the development of service placement schemes that are distributed and of low complexity. As the derivation of the optimal placement in such environments is prohibitive due to the global topology and demand requirement and the la...

Our paper approaches the parking assistance service in urban environments as an instance of service provision in non-cooperative network environments. We propose normative abstractions for the way drivers pursue parking space and the way they respond to partial or complete information for parking demand and supply as well as specific pricing polici...

Recently, a set of problems have been solved analytically, in order to improve various aspects of the authentication procedure in mobile networks. In these problems, an analytical model is derived, which is used to draw guidelines on the selection of the appropriate value of various system parameters. We observe that all these problems can be solve...

In this paper, we explore the way the discovery of service can be facilitated or not by utilizing service location information that is opportunistically disseminated primarily by the service consumers themselves. We apply our study to the real-world case of parking service in busy city areas. As the vehicles drive around the area, they opportunisti...

We examine a network where autonomous nodes participate in content exchange or delivery, and define a replication group as a set of nodes that cooperate in order to effectively retrieve information objects from a distant server. Each node locally replicates a subset of the server objects and can access objects stored by other nodes in the group at...

This article proposes a performance model of the IEEE 802.11 MAC layer that employs the notion of Effective Capacity. In particular, the paper establishes that an IEEE 802.11 mobile station can be regarded as a Semi-Markovian bursty server of the On/Off type, with known distributions for the On and Off periods, and subsequently applies known result...

Specification-based detection engines share the advantages of signature-based and anomaly-based detection, since they can detect unknown attacks, without the side effects of high rates of false positives. However, such solutions for MANETs have seen limited use. This paper introduces a specification-based detection engine that is built upon the fun...

Micro-blogging services have recently been experiencing increasing success among Web users. Differ-ent to traditional online social applications, micro-blogs are lightweight, require small cognitive effort and help share real-time information about personal activities and interests. In this article we explore scalable pushing protocols that are par...

Authentication in 3G encompasses a mechanism, which ensures that the authentication vectors (AVs) are used only once. To achieve this, the employed mechanism maintains counters at both sides (mobile station and network) and verifies that the provided AVs are among the last α generated. However, there are many cases in which the mobile station recei...

By exploiting the unattended nature of the wireless sensor networks, an attacker can physically capture and compromise sensor nodes and then launch a variety of attacks. He can additionally create many replicas of a few compromised nodes and spread these ...

The exploitation of social context for routing data in oppor-tunistic networks is a relatively recent trend. Node central-ity metrics, such as the betweenness centrality, quantify the relaying utility of network nodes and inform routing deci-sions, resulting in better performance than more naive rout-ing approaches. Nevertheless, centrality-based r...

We summarize undertaken and ongoing work on the direct and exclusive use of mobile phone traces for assessing the performance of different opportunistic forwarding schemes. Our methods draw on graph-expansion techniques and circumvent the need for more custom simulation software packages. They address a wide range of opportunistic dissemination sch...

As social networking sites provide increasingly richer context, user-centric service development is expected to explode following the example of User-Generated Content. A major challenge for this emerging paradigm is how to make these exploding in numbers, yet individually of vanishing demand, services available in a cost-effective manner; central...

Mobile Ad Hoc Networks are susceptible to a variety of attacks that threaten their operation and the provided services. Intrusion Detection Systems may act as defensive mechanisms, since they monitor network activities in order to detect malicious actions performed by intruders. Anomaly-based detection engines are a topic of ongoing interest in the...

Many network applications rely on stochastic QoS guarantees. With respect to loss-related performance, the effective bandwidth/capacity theory has proved useful for calculating loss probabilities in queues with complex input and server processes and for formulating simple admission control tests to ensure associated QoS guarantees. This success has...

form only given. Social metrics have recently been considered to capture the degree of similarity in interests of the nodes as well as their “standing” within a community or network. In this talk some recent works-examples are briefly presented showing the potential benefits from incorporating social metrics in content replication, forwarding and p...

This paper proposes a framework for node clustering in computerized social networks according to common interests. Communities in such networks are mainly formed by user selection, which may be based on various factors such as acquaintance, social status, educational background. However, such selection may result in groups that have a low degree of...

This paper presents a rigorous analytic study of gossip-based message dissemination schemes that can be employed for content/service dissemination or discovery in unstructured and distributed networks. When using random gossiping, communication with multiple peers in one gossiping round is allowed. The algorithms studied in this paper are considere...

Mobile Ad Hoc Networks (MANETs) are susceptible to a variety of attacks that threaten their operation and the provided services. Intrusion Detection Systems (IDSs) may act as defensive mechanisms, since they monitor network activities in order to detect malicious actions performed by intruders, and then initiate the appropriate countermeasures. IDS...

— Our work draws on a concrete parking space search application to explore fundamental tradeoffs of wireless networking solutions to the provision of real-life services. In particular, we consider a city area, wherein each vehicle (mobile user) moves towards a chosen destination and seeks vacant parking space in its vicinity. Three main approaches...

This paper proposes a routing protocol that jointly exploits location and motion information in a dynamically adjusted way, towards self-adaptability in different combinations of mobility and node density conditions. The protocol employs a metric of the rate at which a packet approaches its destination over a multihop path, as an effect of both the...

Several peer-to-peer (P2P) streaming systems have proved by now their ability to deliver live video streams to hundreds of users. However the inherent instability of the distribution environment poses several obstacles for these systems to manage to deliver a high quality experience to the end users. In this paper we explore node churn which indepe...

This paper proposes a novel Intrusion Detection System (IDS) for Mobile Ad Hoc Networks (MANETs) that aims at overcoming the limitations and weaknesses of the existing IDSs. The proposed IDS incorporates a novel random walk-based IDS architecture as well as a multi-layer, specification-based detection engine. The proposed solution does not belong t...

With social networking sites providing increasingly richer context, User-Centric Service (UCS) creation is expected to explode following a similar success path to User-Generated Content. One of the major challenges in this emerging highly user-centric networking paradigm is how to make these exploding in numbers yet, individually, of vanishing dema...