Mário M. Freire

Security issues in cloud environments: a survey

In the last few years, the appealing features of cloud computing have been fueling the integration of cloud environments in the industry, which has been consequently motivating the research on related technologies by both the industry and the academia. The possibility of paying-as-you-go mixed with an on-demand elastic operation is changing the enterprise computing model, shifting on-premises infrastructures to off-premises data centers, accessed over the Internet and managed by cloud hosting providers. Regardless of its advantages, the transition to this computing paradigm raises security concerns, which are the subject of several studies. Besides of the issues derived from Web technologies and the Internet, clouds introduce new issues that should be cleared out first in order to further allow the number of cloud deployments to increase. This paper surveys the works on cloud security issues, making a comprehensive review of the literature on the subject. It addresses several key topics, namely vulnerabilities, threats, and attacks, proposing a taxonomy for their classification. It also contains a thorough review of the main concepts concerning the security state of cloud environments and discusses several open research topics.

High-Speed Networks and Multimedia Communications

Various Internet applications involve multiple parties and usually adopt a one-to-many communication paradigm (multicast). The presence of multiple receivers in a multicast session rises the problem of inter-receiver fairness. Transmitting with a rate which matches the slowest receiver will limit the throughput of other receivers and thus their satisfaction. A multi-rate mechanism where the receivers are distributed into subgroups with similar capacities, can improve the inter-receiver fairness for multicast sessions. In this paper, we deal with the problem of receivers partitioning and propose a simple algorithm based on the receivers RTT variations where an explicit estimation of the receivers capacities is avoided. Our partitioning algorithm, although simple, performs an on-the-fly partitioning depending on the receivers’ feedback. We show that our partitioning algorithm approximates and in many cases, achieves the optimal solution with a minimum computation effort.

Detection and classification of peer-to-peer traffic: A survey

The emergence of new Internet paradigms has changed the common properties of network data, increasing the bandwidth consumption and balancing traffic in both directions. These facts raise important challenges, making it necessary to devise effective solutions for managing network traffic. Since traditional methods are rather ineffective and easily bypassed, particular attention has been paid to the development of new approaches for traffic classification. This article surveys the studies on peer-to-peer traffic detection and classification, making an extended review of the literature. Furthermore, it provides a comprehensive analysis of the concepts and strategies for network monitoring.

On EPON security issues

We discuss in detail all major security-related issues inherently present in PON systems. Ethernet PON (EPON) type networks have very specific requirements for data- and system-level security, due to combining - for the first time using Ethernet links ¿ residential and business customers with different security awareness levels and protection demands. Various types of potential network structure targeted attacks are elaborated, starting from simple passive monitoring, through flavors of denial of service (DoS), towards masquerading and theft of service (ToS), presenting a complete and detailed image of security threats in EPONs. Authentication and security mechanisms, as well as their shortcomings, are also briefly examined.

Enhanced Just-in-Time: A New Resource Reservation Protocol for Optical Burst Switching Networks

This paper proposes a new resource reservation protocol for optical burst switching networks, called enhanced just-in-time (E-JIT). E-JIT intends to improve and optimize the traditional JIT protocol, keeping all the advantages of its simplicity in terms of implementation. E-JIT aims to improve data channel scheduling, reducing the period of time in which the data channel remains in reserved status, optimizing channel utilization and reducing the burst loss probability. A performance assessment of E-JIT is presented for mesh optical burst switching networks with 16 nodes. It is shown that E-JIT may lead to a better performance than JIT for small burst loss probabilities.

Object-oriented modeling and simulation of optical burst switching networks

Optical burst switching (OBS) is becoming an interesting technology for the optical Internet, since it does not need optical buffers like optical packet switching (OPS), and is capable of a better performance than optical circuit switching (OCS). Although OBS has been recently an object of intense research, it still raises a number of important questions. Due to the high costs of an OBS network infrastructure, simulators are a good choice for predicting the behavior of this kind of networks. In this paper, we describe the proposal, implementation and validation of a simulator for OBS networks. The simulator, named OBSim, mimics the behavior of OBS networks in an object-oriented approach.

Performance Comparison of Wavelength Routing Optical Networks with Chordal Ring and Mesh-Torus Topologies

In this paper, we present a comparison of the blocking performance in wavelength routed optical networks with chordal ring and mesh-torus topologies. The comparison is focused on chordal rings with a chord length of ?N +3, being N the number of nodes, since this chord length leads to the smallest network diameter. This performance comparison revealed an important feature of chordal rings: very small blocking gains were observed, due to the increase of the node degree from 3 (chordal ring with a chord length of ?N +3) to 4 (mesh-torus). The comparison is made for networks with 100 and 1600 nodes. The influence of wavelength interchange on these small gains is also investigated: the node degree gain is very small and increases slightly as the converter density increases. Thus, if a small blocking performance degradation is allowed, the choice of a chordal ring with a chord length of ?N +3, instead of a mesh-torus, leads to a reduction in the number of network links, and hence in the total cable length, since the number of links in a N-node chordal ring is 3N, and the number of links in a N-node mesh-torus is 4N.

On the Performance of Shortest Path Routing Algorithms for Modeling and Simulation of Static Source Routed Networks -- an Extension to the Dijkstra Algorithm

Shortest path routing algorithms, such as Dijkstras algorithm present an overload problem when used to define routes for ring topologies in networks that implement source routing. This paper presents the effects of Dijkstras shortest path routing in the simulation and modeling of static source routed networks, in particular we evaluated the effect of this routing scheme in the performance of Optical Burst Switched (OBS) networks. A new static shortest path algorithm is presented and its performance compared with the standard shortest path algorithm, using two new metrics. We propose the use of this routing algorithm in network simulators instead of standard Dijkstra, as it produces more symmetric and balanced routes over the network links, thus producing results that are closer to real networks which implement a more dynamic routing.

Influence of Chord Length on the Blocking Performance of Wavelength-Routed Chordal Ring Networks

In this paper, we present an assessment of the blocking performance of wavelength routed optical networks with chordal ring topology. The performance is focused on chord lengths of 3, N/4, and \(\sqrt N + 3\), being N the number of nodes. It is shown that, in a 100-node chordal ring network, the use of the chord length of N/4 instead of 3 clearly reduces the blocking probability. A reduction of the blocking probability is also observed when the chord length of \(\sqrt N + 3\) is used, instead of N/4 or w=3. The increase of the node degree from 3 (chordal ring with 100 nodes and a chord length of \(\sqrt N + 3\)) to 4 (mesh torus with 100 nodes) has also revealed an important feature: very small blocking gains were observed due to the increase of the node degree from 3 to 4. Thus, the choice of a chordal ring with a chord length of \(\sqrt N + 3\), instead of a mesh-torus, leads to a reduction in the number of network links, and hence in the total cable length, since the number of links in a N-node chordal ring is 3N, and the number of links in a N-node mesh-torus is 4N.

3D Lacunarity in Multifractal Analysis of Breast Tumor Lesions in Dynamic Contrast-Enhanced Magnetic Resonance Imaging

Dynamic contrast-enhanced magnetic resonance (DCE-MR) of the breast is especially robust for the diagnosis of cancer in high-risk women due to its high sensitivity. Its specificity may be, however, compromised since several benign masses take up contrast agent as malignant lesions do. In this paper, we propose a novel method of 3D multifractal analysis to characterize the spatial complexity (spatial arrangement of texture) of breast tumors at multiple scales. Self-similar properties are extracted from the estimation of the multifractal scaling exponent for each clinical case, using lacunarity as the multifractal measure. These properties include several descriptors of the multifractal spectra reflecting the morphology and internal spatial structure of the enhanced lesions relatively to normal tissue. The results suggest that the combined multifractal characteristics can be effective to distinguish benign and malignant findings, judged by the performance of the support vector machine classification method evaluated by receiver operating characteristics with an area under the curve of 0.96. In addition, this paper confirms the presence of multifractality in DCE-MR volumes of the breast, whereby multiple degrees of self-similarity prevail at multiple scales. The proposed feature extraction and classification method have the potential to complement the interpretation of the radiologists and supply a computer-aided diagnosis system.