1,720,973 research outputs found
Real-time networks and protocols for industrial automation
Full text linkNowadays, networks are fundamental elements for developing factory automation systems. In this thesis, we focus industrial communication networks (ICNs) employed at the device level, for the fast data exchange between controller and sensors/actuators, that are required to satisfy tight reliability and real-time requirements. In this context, the scenario is rapidly evolving. Indeed on the one hand, high performance and low costs are required to cope with more and more demanding requirements, while, on the other hand, real-time characteristics are needed in an increasing number of industrial automation applications. In the last years, two new types of ICNs have been introduced for device-level industrial communication. Besides fieldbuses, traditionally employed, both real-time Ethernet (RTE) networks, based on IEEE 802.3 standard, and wireless networks have become available.
In this thesis we focus on Ethernet Powerlink, a popular RTE network. Firstly, we refer to the Ethernet Powerlink specifications and provide a description of the network and, in particular, of the data link layer protocol real-time features. We propose a modification to the protocol that allow the network to better manage real-time acyclic traffic and provide results of a relevant both theoretical and a simulative analysis.
Subsequently we investigate possible wireless extensions of Ethernet Powerlink based on the IEEE 802.11 wlan and present results of both a theoretical and a simulative analysis relevant to two specific solutions. Finally we practically realize one of the two solutions and provide results of extensive measurements on the real system. We particularly focus on the comparison between theoretical, simulative and experimental results and on the influence of real components behavior on the overall performance of the system.Le reti di comunicazione sono diventate un elemento fondamentale dei sistemi di automazione industriale. In questa tesi si considerano, in particolare le reti di comunicazione impiegate per la comunicazione di livello dispositivo, per il veloce scambio di dati tra contollori e sensori/attuatori, e alle quali è solitamente richiesto un elevato grado di affidabilità e determinismo. Lo scenario della comunicazione industriale si sta rapidamente evolvendo. Infatti da una parte prestazioni sempre più elevate e costi contenuti devono sempre più conciliarsi con la soddisfazione di aspettative crescenti in termini di real-time, dall'altra sempre più applicazioni di automazione industriale richiedono uno scambio di dati preciso e veloce.
Negli ultimi anni, in particolare, due nuovi tipi di reti di comunicazione industriale sono apparse sul mercato e si sono iniziate ad utilizzare nei sistemi di automazione. Oltra alle reti di comunicazione di campo, tradizionalmente utilizzate, reti real-time Ethernet, che si basano sullo standard 802.3, e reti wireless si sono cominciate ad diffondere negli ambienti industriali.
In questa tesi ci focalizziamo su Ethernet Powerlink, una diffusa rete real-time Ethernet. Inizialmente descriviamo la rete e in particolare le caratteristiche di real-time del protocollo di livello data-link da essa definito. Proponiamo, quindi una modifica al protocollo che consentirebbe alla rete di gestire in modo più efficiente il traffico real-time aciclico e presentiamo alcuni risultati, ottenuti sia analiticamente che per mezzo di simulazioni. In seguito, analizziamo possibili estensioni wireless di Ethernet Powerlink mediante la rete 802.11 e presentiamo risultati ottenuti per via teorica e simulativa relativi a due particolari soluzioni. Infine implementiamo praticamente una delle due soluzioni e presentiamo i risultati di una serie di misure effettuate sul sistema reale. In particolare, mettiamo in evidenza differenze tra l'analisi teorica, simulativa e sperimentale e l'influenza del comportamento di componenti reali sulle prestazioni fornite dal sistema nel suo complesso
A comprehensive approach to the automatic refinement and verification of access control policies
Full text linkAbstract: Access control is one of the building blocks of network security and is often managed by network administrators through the definition of sets of high-level policies meant to regulate network behavior (policy-based management). In this scenario, policy refinement and verification are important processes that have to be dealt with carefully, possibly relaying on computer-aided automated software tools. This paper presents a comprehensive approach for access control policy refinement, verification and, in case errors are detected in the policy implementation, their fixing. The proposed methodology is based on a twofold model able to describe both policies and system configurations and allows, by suitably processing the model, to either propose a system configuration that correctly enforces the policies, or determine whether a specific implementation matches the policy specification also providing hints on how possible anomalies can be fixed. Results on the average complexity of the solution confirm its feasibility in terms of computation time, even for complex networked systems consisting of several hundred nodes
On the Rate Adaptation Techniques of IEEE 802.11 Networks for Industrial Applications
No full textThe performance of the IEEE 802.11 WLAN are influenced by the wireless channel characteristics that reflect on the Signal-to-Noise Ratio (SNR), particularly in industrial communication systems, that often operate in harsh environments.
In order to cope with SNR reductions, the IEEE 802.11 WLAN specification suggests to adapt (reduce) the transmission rate, since the modulation techniques employed at the lower rates are more robust. However, the standard does not define any Rate Adaptation (RA) technique, leaving the actual implementation to the device manufacturers choice. In this paper we focus on RA techniques for industrial communication systems that are typically subjected to tight reliability and timing requirements. In detail, we compare the performance figures of a general purpose widespread technique, namely the Automatic Rate Fallback (ARF), with those of the RA techniques actually implemented on two commercially available IEEE 802.11 devices via a set of practical experiments. The obtained results show that these techniques are characterized by a relevant number of packet retransmissions that may introduce a considerable randomness on the service time, possibly leading to performance degradation.
Consequently, we propose two new techniques and evaluate their behavior by means of numerical simulations carried out for typical industrial traffic profiles. The outcomes are encouraging since the proposed RA techniques show in most cases better performance than ARF
Experimental evaluation of the service time for industrial hybrid (wired/wireless) networks under non-ideal environmental conditions
No full textInfluence of real components behavior on the performance of wireless industrial communication systems
No full text
Automated Fixing of Access Policy Implementation in Industrial Networked Systems
Full text linkAccess control (AC) is the core of every architectural solution for information security. Indeed, no effective protection scheme can abstract from the careful design of access control policies, and infrastructures underlying modern Industrial Networked Systems (INSs) are not exceptions from this point of view. This paper presents a comprehensive framework for INS access control. The proposed approach enables the description of both positive and negative AC policies, by applying the Role Based Access Control (RBAC) paradigm to typical INS implementations, while taking into account different levels of abstraction. Suitable techniques are adopted to check whether or not policies are correctly implemented in the system (verification). When conflicts are detected, possible (re)assignments of credentials to the system users are automatically computed, that can be adopted to correct anomalies (conflict resolution)
Estimation and analysis of communication service time in a real-time wireless industrial network
Full text linkWireless communication systems for industrial applications should cope with the demanding performance figures of real–time wired networks, providing high reliability and satisfying tight timeliness constraints. The implementation of a scheduling framework may represent a relevant method to deploy real–time behavior in distributed measurement, process control and supervision networks. A schedulability analysis, based on task parameters, determines if the network will be able to provide the guarantees required by the specified application. Nonetheless, this strategy and the related error recovery mechanism are often implemented at a high level protocol layer, without carefully considering the behavior of physical/data–link layers of the network. An effective characterization of the service time for packet delivery, as seen by the data link–layer, is instead required for a fine tuning of the scheduling algorithms.
We analyzed the case of an IEEE 802.11g based network, where a central scheduler manages the traffic. We derived a model for the transmission times, in particular accounting for retransmissions due to channel impairment and interference. An improved model for the service time is then proposed, based on a cross–layer analysis. This allows to reshape the statistical knowledge of the metric, hence improving the network performance and admission test outcomes. The provided case- study enables the reader to understand the effectiveness of the proposed method, which provide a reliable soft real–time data acquisition system
- …
