Context: Modern automated source code analysis techniques can be very successful in detecting a priori de- fined defect patterns and security vulnerabilities. Yet, they cannot detect flaws that manifest due to erroneous translation of the software’s functional requirements into the source code. The automated detection of logical errors that are attributed to a faulty implementation of applications’ functionality, is a relatively uncharted territory. In previous research, we proposed a combination of automated analyses for logical error detection. In this paper, we develop a novel business-logic oriented method able to filter mathematical depictions of software logic in order to augment logical error detection, eliminate previous limitations in analysis and provide a formal tested logical error detection classification without subjective discrepancies. As a proof of concept, our method has been implemented in a prototype tool called PLATO that can detect various types of logical errors. Potential logical errors are thus detected that are ranked using a fuzzy logic system with two scales characterizing their impact: (i) a Severity scale, based on the execution paths’ characteristics and Information Gain, (ii) a Reliability scale, based on the measured program’s Computational Density. The method’s effectiveness is shown using diverse experiments. Albeit not without restrictions, the proposed automated analysis seems able to detect a wide variety of logical errors, while at the same time limiting the false positives.

Large, reliable and efficient storage systems are becoming increasingly important in enterprise environments. Our research in storage system design is oriented towards the exploitation of commodity hardware for building a high performance, resilient and scalable storage system. We present the design and implementation of DHTbd, a general purpose decentralized storage system where storage nodes support a distributed hash table based interface and clients are implemented as in-kernel device drivers. DHTbd, unlike most storage systems proposed to date, is implemented at the block device level of the I/O stack, a simple yet efficient design. The experimental evaluation of the proposed system demonstrates its very good I/O performance, its ability to scale to large clusters, as well as its robustness, even when massive failures occur.

The aim of this paper is proposing a flexible and component-oriented XML-based e-learning services management framework taking into account several parameters concerning the educational process, the network infrastructure, the QoS requirements, the available educational content, etc. Within this framework, a session profile is dynamically created for each request for e-learning service according to current context.

We propose a configurable architecture for implementing e-learning service management, taking into account several diverse aspects concerning not only the educational process, but also network infrastructure, the QoS requirements, the types of educational content, etc. We present a flexible, parametrical and component-oriented management scheme, which dynamically creates a session profile for each request for e-learning service according to current context that depends on all diverse aspects that an e-learning service comprises. Continuously, we analyse the components comprising the management scheme and the management information bases that they maintain.

This paper proposes a CORBA-based framework for managing the network state evolution over time. This framework is based on the concept of CORBA temporal agents, capable of managing the past and current behavior of network resources. Managed objects use specific time attributes for representing how their values are evolving in time. Moreover, specially designed operations (services) enable users to exploit the temporal dimension of management information in order to understand the past, control the present, and thus even predict the future of managed objects. The management environment is designed in order to provide coexistence and interoperability with existing management platforms.

Due to unexpected network interconnection growth, the security of technological and information infrastructures is becoming difficult to be managed and controlled. In addition, security is becoming more and more crucial for an organisation's information systems operation. The management of an organisation has to establish rules and regulations in order to face the threats that its information systems face. The network manager is obliged to enforce the regulations that senior management addresses. We propose a framework that a network manager could use in order to effectively enforce security policies. In addition, we present a scalable security management architecture suitable for TCP/IP networks. The communication of systems' logical components is based on the use of the SNMP protocol. Finally, the system includes facilities for collecting and efficiently storing raw and aggregate historical security management information in a temporal database for off-line analysis.

We address the problem of accounting management for communication networks. Our approach is based on the general framework of network management. The goal of this work is to determine an open accounting technology framework. We propose the general architecture of an accounting system. Our perspective is based on a temporal management information base for accounting management which is implemented at the switch level.

We propose an information model and a number of services for managing the security of TCP/IP networks. More precisely, we identify a number of managed objects included in SNMP management information base (MIBs) that are important for security management and we propose a temporal network management model for the historical representation of the security management information. This model incorporates the temporal dimension in the management information model proposed by the Internet Engineering Task Force. Moreover, we define a number of services for the monitoring, storage, capitalisation and analysis of the historical security management information.

This paper presents a prototype for management services which enables the performance monitoring and control of resources in a TCP/IP network. A time reference information model required to accomplish the different needs of performance management functions, is also described. This temporal model can be used not only to provide a diachronic view of the management information, but also to define a set of measures needed to observe the performance of network elements. The performance management application is implemented using a distributed architecture. It provides facilities to dynamically create aggregate managed objects, to collect the management information and to store the collected data in a database. The database schema is designed to follow the proposed time reference information model and also the structure of the MIB. Finally, the architecture of the prototype and the supported facilities are also illustrated in this paper.

Algorithms for the control of the retransmission procedure in random multiple access schemes are needed to ensure stability of the system operation under high traffic conditions. Optimal retransmission control policies cannot be applied in practice since they are based on global information about the system state. In the case of the most well-known implementation of the CSMA/CD protocol, ANSI/IEEE Std 802.3-1985, a heuristic approach, known as the "truncated binary exponential backoff" algorithm, is employed. Such schemes are not amenable to theoretical analysis because of the state space. explosion problem of the underlying Markovian model. In this paper, a new retransmission control algorithm, suitable for CSMA/CD protocols, based on information acquired by monitoring the channel transmissions is proposed. A Markovian model is presented and the algorithm is analyzed in detail. The performance of the algorithm is evaluated, several numerical and simulation results are presented and comparisons to other protocols are made.

In this paper, we propose a new queueing model appropriate for the analysis of a buffered CSMA/CD protocol. We assume that each user has a finite buffer capacity. The system, in general, can be modeled as a multidimensional semi-Markov chain. The enormous state space for the complete description is reduced by appropriate exploitation of the features of the system, e.g., fairness towards all users, dependence of the probability of successful transmission only on the total number of busy users, etc. Using a further assumption we construct a two-dimensional semi-Markov chain, examining the state of the system immediately after the successful transmission of packets. The obtained solution is extremely accurate and exhibits excellent agreement with simulation results, which corroborates the correctness of our method.