120 research outputs found
Distributed Consensus, Revisited
We provide a novel model to formalize a well-known algorithm, by Chandra and Toueg, that solves Consensus among asynchronous distributed processes in the presence of a particular class of failure detectors (Diamond S or, equivalently, Omega), under the hypothesis that only a minority of processes may crash. The model is defined as a global transition system that is unambigously generated by local transition rules. The model is syntax-free in that it does not refer to any form of programming language or pseudo code. We use our model to formally prove that the algorithm is correct
Controller synthesis for parameterized discrete event systems
Les systĂšmes Ă Ă©vĂ©nements discrets sont des systĂšmes dynamiques particuliers. Ils changent dâĂ©tat de fažcon discrĂšte et le terme Ă©vĂ©nement est utilisĂ© afin de reprĂ©senter lâoccurrence de changements discontinus. Ces systĂšmes sont principalement construits par lâhomme et on les retrouve surtout dans les secteurs manufacturier, de la circu- lation automobile, des bases de donnĂ©es et des protocoles de communication. Cette thĂšse sâintĂ©resse au contrĂŽle des systĂšmes paramĂ©trĂ©s Ă Ă©vĂ©nements discrets oĂč les spĂ©cifications sont exprimĂ©es Ă lâaide de prĂ©dicats et satisfont une condition de similaritĂ©. Des conditions sont donnĂ©es afin de dĂ©duire des propriĂ©tĂ©s, en observation partielle ou totale, pour un systĂšme composĂ© de n processus similaires Ă partir dâun systĂšme com- posĂ© de n0 processus, avec n â„ n0. De plus, il est montrĂ© comment infĂ©rer des politiques de contrĂŽle en prĂ©sence de relations dâinterconnexion entre les processus. Cette Ă©tude est principalement motivĂ©e par la faiblesse des mĂ©thodes actuelles de synthĂšse pour le traitement des problĂšmes industriels de taille rĂ©elle.Discrete event systems are a special type of dynamic systems. The state of these systems changes only at discrete instants of time and the term event is used to represent the occurrence of discontinuous changes. These systems are mostly man-made and arise in the domains of manufacturing systems, traffic systems, database management systems and communication protocols. This thesis investigates the control of parameterized discrete event systems when specifications are given in terms of predicates and satisfy a similarity assumption. For systems consisting of similar processes under total or partial observation, conditions are given to deduce properties of a system of n processes from properties of a system of n0 processes, with n â„ n0. Furthermore, it is shown how to infer a control policy for the former from the latterâs, while taking into account interconnections between processes. This study is motivated by a weakness in current synthesis methods that do not scale well to huge systems
Parameterized verification and repair of concurrent systems
In this thesis, we present novel approaches for model checking, repair and synthesis of systems that may be parameterized in their number of components. The parameterized model checking problem (PMCP) is in general undecidable, and therefore the focus is on restricted classes of parameterized concurrent systems where the problem is decidable. Under certain conditions, the problem is decidable for guarded protocols, and for systems that communicate via a token, a pairwise, or a broadcast synchronization. In this thesis we improve existing results for guarded protocols and we show that the PMCP of guarded protocols and token passing systems is decidable for specifications that add a quantitative aspect to LTL, called Prompt-LTL. Furthermore, we present, to our knowledge, the first parameterized repair algorithm. The parameterized repair problem is to find a refinement of a process implementation p such that the concurrent system with an arbitrary number of instances of p is correct. We show how this algorithm can be used on classes of systems that can be represented as well structured transition systems (WSTS). Additionally we present two safety synthesis algorithms that utilize a lazy approach. Given a faulty system, the algorithms first symbolically model check the system, then the obtained error traces are analyzed to synthesize a candidate that has no such traces. Experimental results show that our algorithm solves a number of benchmarks that are intractable for existing tools. Furthermore, we introduce our tool AIGEN for generating random Boolean functions and transition systems in a symbolic representation.In dieser Arbeit stellen wir neuartige Ans atze fĂŒr das Model-Checking, die Reparatur und die Synthese von Systemen vor, die in ihrer Anzahl von Komponenten parametrisiert sein können. Das Problem des parametrisierten Model-Checking (PMCP) ist im Allgemeinen unentscheidbar, und daher liegt der Fokus auf eingeschrĂ€nkten Klassen parametrisierter synchroner Systeme, bei denen das Problem entscheidbar ist. Unter bestimmten Bedingungen ist das Problem fĂŒr Guarded Protocols und fĂŒr Systeme, die ĂŒber ein Token, eine Pairwise oder eine Broadcast-Synchronisation kommunizieren, entscheidbar. In dieser Arbeit verbessern wir bestehende Ergebnisse fĂŒr Guarded Protocols und zeigen die Entscheidbarkeit des PMCP fĂŒr Guarded Protocols und Token-Passing Systeme mit Spezifikationen in der temporalen Logik Prompt-LTL, die LTL einen quantitativen Aspekt hinzufĂŒgt. DarĂŒber hinaus prĂ€sentieren wir unseres Wissens den ersten parametrisierten Reparaturalgorithmus. Das parametrisierte Reparaturproblem besteht darin, eine Verfeinerung einer Prozessimplementierung p zu finden, so dass das synchrone Systeme mit einer beliebigen Anzahl von Instanzen von p korrekt ist. Wir zeigen, wie dieser Algorithmus auf Klassen von Systemen angewendet werden kann, die als Well Structured Transition Systems (WSTS) dargestellt werden können. AuĂerdem prĂ€sentieren wir zwei Safety-Synthesis Algorithmen, die einen "lazy" Ansatz verwenden. Bei einem fehlerhaften System ĂŒberprĂŒfen die Algorithmen das System symbolisch, dann werden die erhaltenen "Gegenbeispiel" analysiert, um einen Kandidaten zu synthetisieren der keine solchen Fehlerpfade hat. Versuchsergebnisse zeigen, dass unser Algorithmus eine Reihe von Benchmarks löst, die fĂŒr bestehende Tools nicht lösbar sind. DarĂŒber hinaus stellen wir unser Tool AIGEN zur Erzeugung zufĂ€lliger Boolescher Funktionen und Transitionssysteme in einer symbolischen Darstellung vor
Network Simulation Cradle
This thesis proposes the use of real world network stacks instead of protocol
abstractions in a network simulator, bringing the actual code used in
computer systems inside the simulator and allowing for greater simulation
accuracy. Specifically, a framework called the Network Simulation
Cradle is created that supports the kernel source code from FreeBSD, OpenBSD
and Linux to make the network stacks from these systems available to the
popular network simulator ns-2.
Simulating with these real world network stacks reveals situations where the
result differs significantly from ns-2's TCP models. The simulated
network stacks are able to be directly compared to the same operating system
running on an actual machine, making validation simple. When measuring the
packet traces produced on a test network and in simulation the results are
nearly identical, a level of accuracy previously unavailable using traditional
TCP simulation models. The results of simulations run comparing ns-2 TCP
models and our framework are presented in this dissertation along with
validation studies of our framework showing how closely simulation resembles
real world computers.
Using real world stacks to simulate TCP is a complementary approach to using
the existing TCP models and provides an extra level of validation. This way of
simulating TCP and other protocols provides the network researcher or engineer
new possibilities. One example is using the framework as a protocol
development environment, which allows user-level development of protocols with
a standard set of reproducible tests, the ability to test scenarios which are
costly or impossible to build physically, and being able to trace and debug
the protocol code without affecting results
Delay Performance and Cybersecurity of Smart Grid Infrastructure
To address major challenges to conventional electric grids (e.g., generation diversification and optimal deployment of expensive assets), full visibility and pervasive control over utilities\u27 assets and services are being realized through the integratio
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