Standard network QoS analysis usually accounts for the infrastructure performance/availability on... more Standard network QoS analysis usually accounts for the infrastructure performance/availability only, with scarce consideration of the user perspective. With reference to the General Packet Radio Service (GPRS), this paper addresses the problem of how to evaluate the impact of system unavailability periods on QoS measures, explicitly accounting for user characteristics. In fact, the ultimate goal of a service provider is user satisfaction, therefore it is extremely important to introduce the peculiarities of the user population when performing system analysis in such critical system conditions as during outages. The lack of service during outages is aggravated by the collision phenomenon determined by accumulated users requests, which (negatively) impacts on the QoS provided by the system for some time after its restart. Then, depending on the specific behavior exhibited by the variety of users, such QoS degradation due to outages may be perceived differently by different user categories. We follow a compositional modeling approach, based on the GPRS and user models; the focus is on the GPRS random access procedure on one side, and different classes of users behavior on the other side. Quantitative analysis, performed using a simulation approach, is carried out, showing the impact of outages on a relevant QoS indicator, in relation with the considered user characteristics and network load.
This workshop summary gives a brief overview of the workshop on "Architecting Dependable Systems"... more This workshop summary gives a brief overview of the workshop on "Architecting Dependable Systems" held in conjunction with DSN 2007. The main aim of this workshop is to promote cross-fertilization between the software architecture and dependability communities. We believe that both of them will benefit from clarifying approaches that have been previously tested and have succeeded as well as those that have been tried but have not yet been shown to be successful.
In this chapter we present approaches for analysis and monitoring of dependability and performanc... more In this chapter we present approaches for analysis and monitoring of dependability and performance of connected systems, and their combined usage. These approaches need to account for dynamicity and evolvability of connected systems. In particular, the chapter covers the quantitative assessment of dependability and performance properties through a stochastic model-based approach: first an overview of dependability-related measurements and stochastic model-based approaches provides the necessary background. Then, our proposal in connect of an automated and modular dependability analysis framework for dynamically connected systems is described. This framework can be used off-line for system design (specifically, in connect, for connector synthesis), and on-line, to continuously assess system behaviour and detect possible issues arising at run-time. For the latter purpose, a generic, flexible and modular monitoring infrastructure has been developed. Monitoring is at the core of the connect vision, in order to ensure run-time observation of specified quantitative properties and possibly trigger adequate reactions. We focus here on the interaction chain between monitoring and analysis, to allow for on-line continuous validation of specified dependability and performance properties. Illustrative examples of applications of analysis and monitoring are provided with reference to the connect Terrorist Alert scenario.
Over the last few years wireless local area networking (WLAN) has become a very important technol... more Over the last few years wireless local area networking (WLAN) has become a very important technology that offers high-speed communication services to mobile users in indoor environments. WLAN technology offers some very attractive characteristics such as high data rates, increased QoS capabilities, and low installation costs which has made many professionals claim that it will be the main opponent of IMT-2000, despite the enormous effort needed for the specification and implementation of 3G systems. However, WLANs also present many important constraints related mainly to their restricted coverage capabilities. On the other hand, 3G systems are deployed gradually and carefully since their business prospects have not been validated yet and it is expected that 2G and 2G+ cellular systems will continue to play an important role for at least five more years. Thus, today's wireless networking environment is in fact a conglomeration of all these technologies for which there is a strong need for cooperation. In this article we describe a heterogeneous wireless networking environment together with its features and user requirements. We explain the importance of the existence of WLANs and describe a framework and system architecture that supports seamless integration of WLAN in heterogeneous cellular networking environments, focusing on support for efficient resource provision and management.
Gracefully degradable algorithm for Byzantine agreement. FD Giandomenico, ML Guidotti, F Grandoni... more Gracefully degradable algorithm for Byzantine agreement. FD Giandomenico, ML Guidotti, F Grandoni, L Simoncini COMP. SYST. SCI. ENG. 3:11, 32-40, 1988. An algorithm for Byzantine agreement without authentication in ...
Gracefully degradable algorithm for Byzantine agreement. FD Giandomenico, ML Guidotti, F Grandoni... more Gracefully degradable algorithm for Byzantine agreement. FD Giandomenico, ML Guidotti, F Grandoni, L Simoncini COMP. SYST. SCI. ENG. 3:11, 32-40, 1988. An algorithm for Byzantine agreement without authentication in ...
Electric power systems are critical infrastructures that provide vital services for the human act... more Electric power systems are critical infrastructures that provide vital services for the human activities; assessing their dependability is thus an high priority task. This paper presents an ad-hoc simulator for the evaluation of dependability and performability measures in electrical power system (EPS). Our stochastic model is composed by separated and simple submodels of the dynamics of the two subsystems composing EPS: the electrical infrastructure and the computer-based control system. By providing explicit modeling of the interdependencies between the main subsystems, the impact on the dependability and performability of the cascading or escalating failures can be analyzed. Some preliminary analysis on a case study are also shown.
ABSTRACT Analysis of interdependencies in Electric Power Systems (EPS) has been recognized as a c... more ABSTRACT Analysis of interdependencies in Electric Power Systems (EPS) has been recognized as a crucial and challenging issue to improve their trustworthiness. The recent liberalization process in energy markets has promoted the entry of a variety of operators in the electricity industry. The resulting new organization contributed to increase in complexity, heterogeneity and interconnection. This paper proposes a framework for analyzing EPS organized as a set of interconnected regions, both from the point of view of the electric power grid and of the cyber control infrastructure. The emphasis is on interdependencies and in assessing their impact on indicators representative of the QoS perceived by users. Taking a reference power grid as test case, the effects of failures on selected measures are shown, both in case the grid is partitioned in a number of regions and in case of a single region, to illustrate the behavior of different grid and control configurations.
Efforts have been significantly invested in the last years on analysis of interdependencies in cr... more Efforts have been significantly invested in the last years on analysis of interdependencies in critical infrastructures, including Electric Power Systems (EPS). Among other studies, a modeling and analysis framework has been proposed, able to account for the impact of interdependencies in EPS organized as a set of interconnected regions, both from the point of view of the electric power grid and of the cyber control infrastructure. Indicators representative of the quality of service (QoS) perceived by users have been defined and assessed on reference test cases under homogeneous conditions of the network parameters and of the cost associated to power losses and to power generation. This paper advances such previous studies by extending the developed framework considering loads of different criticality (from the point of view of consequences of power loss) and different failure rates for the power lines. The proposed extensions address relevant aspects of non-homogeneity of real EPS infrastructures, which need to be taken into account in assessment studies to get accurate results, to be exploited as useful guidelines to appropriate configuration and reconfiguration policies.
this paper planned conversations (inwhich a set of communicating processes are rolled back togeth... more this paper planned conversations (inwhich a set of communicating processes are rolled back together), which also allow therecomputation after roll-back to use different code from the first computation, so that errorscaused by software design faults may not be repeated at the new execution [Randell 1975], andatomic transactions (in which a sequence of changes on a set of data items are
Standard network QoS analysis usually accounts for the infrastructure performance/availability on... more Standard network QoS analysis usually accounts for the infrastructure performance/availability only, with scarce consideration of the user perspective. With reference to the General Packet Radio Service (GPRS), this paper addresses the problem of how to evaluate the impact of system unavailability periods on QoS measures, explicitly accounting for user characteristics. In fact, the ultimate goal of a service provider is user satisfaction, therefore it is extremely important to introduce the peculiarities of the user population when performing system analysis in such critical system conditions as during outages. The lack of service during outages is aggravated by the collision phenomenon determined by accumulated users requests, which (negatively) impacts on the QoS provided by the system for some time after its restart. Then, depending on the specific behavior exhibited by the variety of users, such QoS degradation due to outages may be perceived differently by different user categories. We follow a compositional modeling approach, based on the GPRS and user models; the focus is on the GPRS random access procedure on one side, and different classes of users behavior on the other side. Quantitative analysis, performed using a simulation approach, is carried out, showing the impact of outages on a relevant QoS indicator, in relation with the considered user characteristics and network load.
This workshop summary gives a brief overview of the workshop on "Architecting Dependable Systems"... more This workshop summary gives a brief overview of the workshop on "Architecting Dependable Systems" held in conjunction with DSN 2007. The main aim of this workshop is to promote cross-fertilization between the software architecture and dependability communities. We believe that both of them will benefit from clarifying approaches that have been previously tested and have succeeded as well as those that have been tried but have not yet been shown to be successful.
In this chapter we present approaches for analysis and monitoring of dependability and performanc... more In this chapter we present approaches for analysis and monitoring of dependability and performance of connected systems, and their combined usage. These approaches need to account for dynamicity and evolvability of connected systems. In particular, the chapter covers the quantitative assessment of dependability and performance properties through a stochastic model-based approach: first an overview of dependability-related measurements and stochastic model-based approaches provides the necessary background. Then, our proposal in connect of an automated and modular dependability analysis framework for dynamically connected systems is described. This framework can be used off-line for system design (specifically, in connect, for connector synthesis), and on-line, to continuously assess system behaviour and detect possible issues arising at run-time. For the latter purpose, a generic, flexible and modular monitoring infrastructure has been developed. Monitoring is at the core of the connect vision, in order to ensure run-time observation of specified quantitative properties and possibly trigger adequate reactions. We focus here on the interaction chain between monitoring and analysis, to allow for on-line continuous validation of specified dependability and performance properties. Illustrative examples of applications of analysis and monitoring are provided with reference to the connect Terrorist Alert scenario.
Over the last few years wireless local area networking (WLAN) has become a very important technol... more Over the last few years wireless local area networking (WLAN) has become a very important technology that offers high-speed communication services to mobile users in indoor environments. WLAN technology offers some very attractive characteristics such as high data rates, increased QoS capabilities, and low installation costs which has made many professionals claim that it will be the main opponent of IMT-2000, despite the enormous effort needed for the specification and implementation of 3G systems. However, WLANs also present many important constraints related mainly to their restricted coverage capabilities. On the other hand, 3G systems are deployed gradually and carefully since their business prospects have not been validated yet and it is expected that 2G and 2G+ cellular systems will continue to play an important role for at least five more years. Thus, today's wireless networking environment is in fact a conglomeration of all these technologies for which there is a strong need for cooperation. In this article we describe a heterogeneous wireless networking environment together with its features and user requirements. We explain the importance of the existence of WLANs and describe a framework and system architecture that supports seamless integration of WLAN in heterogeneous cellular networking environments, focusing on support for efficient resource provision and management.
Gracefully degradable algorithm for Byzantine agreement. FD Giandomenico, ML Guidotti, F Grandoni... more Gracefully degradable algorithm for Byzantine agreement. FD Giandomenico, ML Guidotti, F Grandoni, L Simoncini COMP. SYST. SCI. ENG. 3:11, 32-40, 1988. An algorithm for Byzantine agreement without authentication in ...
Gracefully degradable algorithm for Byzantine agreement. FD Giandomenico, ML Guidotti, F Grandoni... more Gracefully degradable algorithm for Byzantine agreement. FD Giandomenico, ML Guidotti, F Grandoni, L Simoncini COMP. SYST. SCI. ENG. 3:11, 32-40, 1988. An algorithm for Byzantine agreement without authentication in ...
Electric power systems are critical infrastructures that provide vital services for the human act... more Electric power systems are critical infrastructures that provide vital services for the human activities; assessing their dependability is thus an high priority task. This paper presents an ad-hoc simulator for the evaluation of dependability and performability measures in electrical power system (EPS). Our stochastic model is composed by separated and simple submodels of the dynamics of the two subsystems composing EPS: the electrical infrastructure and the computer-based control system. By providing explicit modeling of the interdependencies between the main subsystems, the impact on the dependability and performability of the cascading or escalating failures can be analyzed. Some preliminary analysis on a case study are also shown.
ABSTRACT Analysis of interdependencies in Electric Power Systems (EPS) has been recognized as a c... more ABSTRACT Analysis of interdependencies in Electric Power Systems (EPS) has been recognized as a crucial and challenging issue to improve their trustworthiness. The recent liberalization process in energy markets has promoted the entry of a variety of operators in the electricity industry. The resulting new organization contributed to increase in complexity, heterogeneity and interconnection. This paper proposes a framework for analyzing EPS organized as a set of interconnected regions, both from the point of view of the electric power grid and of the cyber control infrastructure. The emphasis is on interdependencies and in assessing their impact on indicators representative of the QoS perceived by users. Taking a reference power grid as test case, the effects of failures on selected measures are shown, both in case the grid is partitioned in a number of regions and in case of a single region, to illustrate the behavior of different grid and control configurations.
Efforts have been significantly invested in the last years on analysis of interdependencies in cr... more Efforts have been significantly invested in the last years on analysis of interdependencies in critical infrastructures, including Electric Power Systems (EPS). Among other studies, a modeling and analysis framework has been proposed, able to account for the impact of interdependencies in EPS organized as a set of interconnected regions, both from the point of view of the electric power grid and of the cyber control infrastructure. Indicators representative of the quality of service (QoS) perceived by users have been defined and assessed on reference test cases under homogeneous conditions of the network parameters and of the cost associated to power losses and to power generation. This paper advances such previous studies by extending the developed framework considering loads of different criticality (from the point of view of consequences of power loss) and different failure rates for the power lines. The proposed extensions address relevant aspects of non-homogeneity of real EPS infrastructures, which need to be taken into account in assessment studies to get accurate results, to be exploited as useful guidelines to appropriate configuration and reconfiguration policies.
this paper planned conversations (inwhich a set of communicating processes are rolled back togeth... more this paper planned conversations (inwhich a set of communicating processes are rolled back together), which also allow therecomputation after roll-back to use different code from the first computation, so that errorscaused by software design faults may not be repeated at the new execution [Randell 1975], andatomic transactions (in which a sequence of changes on a set of data items are
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Papers by Felicita Di Giandomenico