Cloud computing relies on the sharing of resources between users of the same physical machine, to reduce costs through optimizing and increasing utilization. However, sharing these resources may be with malicious users, which could lead to confidentiality violations through co-residency attacks. These attacks may exploit the sharing of resources such as cache memory to reveal a legitimate user’s recent activities. Multiple techniques and factors can be exploited to perform side-channel attacks and other microarchitectural attacks successfully. Therefore, despite all its benefits, multi-tenancy remains a risk factor in cloud computing. Without appropriate mitigation, this security risk could become the primary concern hindering cloud adoption. This doctoral paper proposes the integrated use of three approaches to provide the necessary protection for shared virtualized systems. These approaches provide self-protection for the virtual machine (VM) on which they are used by monitoring activities within shared virtualized systems, determining the threat level of suspicious VMs, and providing periodic scanning of the virtualized system against microarchitectural attacks and viruses.

Unmanned aerial vehicles (UAVs) are a rapidly evolving technology, and being highly mobile, UAV systems are able to cooperate with each other to accomplish a wide range of different tasks. UAVs can be used in commercial applications, such as goods delivery, as well as in military surveillance. They can also operate in civil domains like search-and-rescue missions, that require multiple UAVs to collect location data as well as transmit video streams. However, the malicious use of UAVs began to emerge in recent years. The frequency of such attacks has been significantly increasing and their impact can have devastating effects. Hence, the relevant industries and standardisation bodies are exploring possibilities for securing UAV systems and networks. Our survey focuses on UAV security and privacy issues whilst establishing flying ad-hoc networks (FANETs) as well as on threats to the Internet of drones (IoD) infrastructure used to provide control and access over the Internet between UAVs and users. The goal of this survey is to categorise the versatile aspects of the UAV threat landscape and develop a classification approach based on different types of connections and nodes in FANETs and IoD. In particular, we categorise security and privacy threats on connections between UAVs, ground control stations, and personal pilot devices. All the most relevant threats and their corresponding defence mechanisms are classified using characteristics of the first four layers of the OSI model. We then analyse the conventional and novel UAV routing protocols, indicating their advantages and disadvantages from the cyber security perspective. To provide a deeper insight, the reviewed defence mechanisms have undergone a thorough examination of their security requirements and objectives such as availability, authentication, authorisation, confidentiality, integrity, privacy, and non-repudiation. Finally, we discuss the open research challenges, the limitations of current UAV standards, and provide possible future directions for research.

The authors consider a low earth orbit (LEO) mobile satellite system (MSS) that accepts new and handover calls of multirate service‐classes. New calls arrive in the system as batches, following the batched Poisson process. A batch has a generally distributed number of calls. Each call is treated separately from the others and its acceptance is decided according to the availability of the requested number of channels. Handover calls follow also a batched Poisson process. All calls compete for the available channels under the complete sharing policy. By considering the LEO‐MSS as a multirate loss system with ‘satellite‐fixed’ cells, it can be analysed via a multi‐dimensional Markov chain, which yields to a product form solution (PFS) for the steady‐state distribution. Based on the PFS, they propose a recursive and yet efficient formula for the determination of the channel occupancy distribution, and consequently, for the calculation of various performance measures including call blocking and handover failure probabilities. The latter are much higher compared to the corresponding probabilities in the case of the classical (and less bursty) Poisson process. Simulation results verify the accuracy of the proposed formulas. Furthermore, they discuss the applicability of the proposed model in software‐defined LEO‐MSS.

We consider a reference cell of fixed capacity in a wireless cellular network while concentrating on next-generation network architectures. The cell accommodates new and handover calls from different service-classes. Arriving calls follow a random or quasi-random process and compete for service in the cell under two bandwidth sharing policies: 1) a probabilistic threshold (PrTH) policy or 2) the multiple fractional channel reservation (MFCR) policy. In the PrTH policy, if the number of in-service calls (new or handover) of a service-class exceeds a threshold (difference between new and handover calls), then an arriving call of the same service-class is accepted in the cell with a predefined state-dependent probability. In the MFCR policy, a real number of channels is reserved to benefit calls of certain service-classes; thus, a service priority is introduced. The cell is modeled as a multirate loss system. Under the PrTH policy, call-level performance measures are determined via accurate convolution algorithms, while under the MFCR policy, via approximate but efficient models. Furthermore, we discuss the applicability of the proposed models in 4G/5G networks. The accuracy of the proposed models is verified through simulation. Comparison against other models reveals the necessity of the new models and policies.

In the recent years, mobile cellular networks are undergoing fundamental changes and many established concepts are being revisited. New emerging paradigms, such as Software-Defined Networking (SDN), Mobile Cloud Computing (MCC), Network Function Virtualization (NFV), Internet of Things (IoT), and Mobile Social Networking (MSN), bring challenges in the design of cellular networks architectures. Current Long-Term Evolution (LTE) networks are not able to accommodate these new trends in a scalable and efficient way. In this paper, first we discuss the limitations of the current LTE architecture. Second, driven by the new communication needs and by the advances in aforementioned areas, we propose a new architecture for next-generation cellular networks. Some of its characteristics include support for distributed content routing, Heterogeneous Networks (HetNets) and multiple Radio Access Technologies (RATs). Finally, we present simulation results which show that significant backhaul traffic savings can be achieved by implementing caching and routing functions at the network edge.

Line Speed Publish/Subscribe Inter-networking (LIPSIN) is one of the proposed forwarding mechanisms in Information Centric Networking (ICN). It is a stateless source-routing approach based on Bloom filters. However, it has been shown that LIPSIN is vulnerable to brute-force attacks which may lead to distributed denial-of-service (DDoS) attacks and unsolicited messages. In this work, we propose a new forwarding approach that maintains the advantages of Bloom filter based forwarding while allowing forwarding nodes to statelessly verify if packets have been previously authorized, thus preventing attacks on the forwarding mechanism. Analysis of the probability of attack, derived analytically, demonstrates that the technique is highly-resistant to brute-force attacks.

In this paper, we propose a multirate teletraffic loss model of a single link with certain bandwidth capacity that accommodates Poisson arriving calls, which can tolerate bandwidth compression (elastic traffic), under the threshold policy. When compression occurs, the service time of new and in-service calls increases. The threshold policy provides different QoS among service-classes by limiting the number of calls of a service-class up to a predefined threshold, which can be different for each service-class. Due to the bandwidth compression mechanism, the steady state probabilities in the proposed model do not have a product form solution. However, we approximate the model by a reversible Markov chain, and prove recursive formulas for the calculation of call blocking probabilities and link utilization. The accuracy of the proposed formulas is verified through simulation and found to be very satisfactory.

Software-defined networking (SDN) has gained a tremendous attention in the recent years, both in academia and industry. This revolutionary networking paradigm is an attempt to bring the advances in computer science and software engineering into the information and communications technology (ICT) domain. The aim of these efforts is to pave the way for completely programmable networks and control-data plane separation. Recent studies on feasibility and applicability of SDN concepts in cellular networks show very promising results and this trend will most likely continue in near future. In this work, we study the benefits of SDN on the radio resource management (RRM) of future-generation cellular networks. Our considered cellular network architecture is in line with the recently proposed Long-Term Evolution (LTE) Release 12 concepts, such as control-data plane split, heterogeneous networks (HetNets) environment, and network densification through deployment of small cells. In particular, the aim of our RRM scheme is to enable the macro base station (BS) to efficiently allocate radio resources for small cell BSs in order to assure quality-of-service (QoS) of moving users/vehicles during handoffs. We develop an approximate, but very time- and space-efficient algorithm for radio resource allocation within a HetNet. Experiments on commodity hardware show algorithm running times in the order of a few seconds, thus making it suitable even in cases of fast moving users/vehicles. We also confirm a good accuracy of our proposed algorithm by means of computer simulations.

QoS provisioning is one of the key challenges facing current as well as future Internet architectures. Its dependency on content recognition does not allow a straightforward support of QoS in the IP, host-centric, model. In contrast, Information-Centric Networking (ICN) offers native content identification in the network, which can be exploited to develop a common, elegant, framework for supporting QoS-based delivery. Therefore, ICN may naturally overcome many of the cumbersome fixes and limitations of today's solutions. In this work, we exploit the flexibility in semantic representation offered by ICN to present a flexible and scalable ICN-based QoS model. Our model defines QoS requirements as information items that can be linked to the content at various aggregation levels, independent of the communication approach. Therefore, it can be applied uniformly to various network types and hierarchies. Furthermore, our model offers enhanced traffic treatment as well as resource utilization while significantly reducing the overhead on the network.

We present a new model, named Wireless Finite Connection-Dependent Threshold Model, for the call-level analysis of W-CDMA networks that support both elastic and stream traffic. Calls generated by service-classes of finite source population (quasi-random call arrival process) compete for their acceptance to a W-CDMA cell, under the complete sharing policy. An arriving call can be accepted with one of several contingency Quality-of-Service (QoS) requirements, depending on the resource availability in the cell; the latter is indicated by thresholds. We present an approximate but recurrent formula for the efficient calculation of the system state probabilities; consequently, the call blocking (time congestion) probabilities and other performance metrics in the uplink direction are provided. The model's accuracy is verified by simulation and found to be quite satisfactory. Moreover, the proposed model performs much better than the corresponding model of infinite number of sources.

The call-level performance modelling and evaluation of 3G cellular networks is important for the proper network dimensioning and efficient use of the network resources, such as bandwidth and power. In the case of the wideband code division multiple access (W-CDMA) cellular networks, this task is complicated, not only because of the so called soft blocking, the multiple access interference (MAI) and the heterogeneous traffic, but also due to the handoff process. In this paper, we propose a new teletraffic model for the call-level analysis of handoff traffic in the uplink of W-CDMA networks where multiple services with finite number of traffic sources are accommodated. Parameters related to the soft blocking and MAI are included into the model. The proposed model is described by a discrete time Markov chain. An efficient recurrent formula for the calculation of the system state probabilities is derived. Based on this formula, blocking probabilities of both new and handoff calls are determined. The accuracy of the proposed model is evaluated through simulation and is found to be very satisfactory. Moreover, we show the necessity of distinguishing the handoff traffic from the new traffic, in respect of blocking probabilities.

We propose a new teletrafflc model for the calculation of link occupancy distribution and determine the call blocking probabilities and link utilization in a single-link multi-rate loss system. We considerKdifferent service-classes, either of elastic or of adaptive type, that compete for the available link bandwidth under the complete sharing policy. Calls arrive to the link with several contingency bandwidth requirements that depend on thresholds, which indicate the total link occupied bandwidth. It is possible for a call, while in service with a certain bandwidth to reduce it, in order for new calls to be accepted in the link. The accuracy of the new model is verified by simulation results. Moreover, the proposed model performs much better than the existing model for elastic and adaptive traffic.

We propose a new teletraffic model, named Wireless Engset Multi-rate Loss Model (W-EnMLM) for the call-level analysis of W-CDMA networks, supporting heterogeneous service-classes of finite population of traffic sources. Quasi- random arriving calls (generated by mobile users), compete for their admission to a W-CDMA cell under the Complete bandwidth Sharing (CS) policy. We present an approximate but recurrent formula for the efficient calculation of the system state probabilities and the call blocking probabilities in the uplink direction. The accuracy of the proposed model is verified by simulation results and found to be completely satisfactory. Moreover, the proposed model performs much better than the corresponding model of infinite number of traffic sources.