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19
A processalgebraic language for probabilistic I/O automata
 IN PROC. OF THE 14TH INT. CONF. ON CONCURRENCY THEORY (CONCUR 2003), LNCS
, 2003
"... We present a processalgebraic language for Probabilistic I/O Automata (PIOA). To ensure that PIOA specifications given in our language satisfy the “inputenabled” property, which requires that all input actions be enabled in every state of a PIOA, we augment the language with a set of type inferenc ..."
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Cited by 15 (2 self)
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We present a processalgebraic language for Probabilistic I/O Automata (PIOA). To ensure that PIOA specifications given in our language satisfy the “inputenabled” property, which requires that all input actions be enabled in every state of a PIOA, we augment the language with a set of type inference rules. We also equip our language with a formal operational semantics defined by a set of transition rules. We present a number of results whose thrust is to establish that the typing and transition rules are sensible and interact properly. The central connection between types and transition systems is that if a term is welltyped, then in fact the associated transition system is inputenabled. We also consider two notions of equivalence for our language, weighted bisimulation equivalence and PIOA behavioral equivalence. We show that both equivalences are substitutive with respect to the operators of the language, and note that weighted bisimulation equivalence is a strict refinement of behavioral equivalence.
Analysing randomized distributed algorithms
 Validation of Stochastic Systems
, 2004
"... Abstract. Randomization is of paramount importance in practical applications and randomized algorithms are used widely, for example in coordinating distributed computer networks, message routing and cache management. The appeal of randomized algorithms is their simplicity and elegance. However, thi ..."
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Cited by 13 (2 self)
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Abstract. Randomization is of paramount importance in practical applications and randomized algorithms are used widely, for example in coordinating distributed computer networks, message routing and cache management. The appeal of randomized algorithms is their simplicity and elegance. However, this comes at a cost: the analysis of such systems become very complex, particularly in the context of distributed computation. This arises through the interplay between probability and nondeterminism. To prove a randomized distributed algorithm correct one usually involves two levels: classical, assertionbased reasoning, and a probabilistic analysis based on a suitable probability space on computations. In this paper we describe a number of approaches which allows us to verify the correctness of randomized distributed algorithms. 1
Implementation of a Compositional Performance Analysis Algorithm for Probabilistic I/O Automata
 IN PROCEEDINGS OF 1999 WORKSHOP ON PROCESS ALGEBRA AND PERFORMANCE MODELING (PAPM99). PRENSAS UNIVERSITARIAS DE
, 1999
"... In previous papers, we defined the probabilistic I/O automata model for specification and modeling of probabilistic concurrent systems, and we showed how certain performance measures for such systems could be computed compositionally, one component at a time, without the need for explicit constr ..."
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Cited by 12 (5 self)
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In previous papers, we defined the probabilistic I/O automata model for specification and modeling of probabilistic concurrent systems, and we showed how certain performance measures for such systems could be computed compositionally, one component at a time, without the need for explicit construction of the full global state space. In this paper, we report on our experiences in constructing and testing a computer implemention of these compositional analysis algorithms. Our implementation, which is coded in the functional programming language Standard ML, uses exact rational arithmetic to calculate performance measures, and it is also capable of producing symbolic rational function expressions that describe the dependence of performance measures on a system parameter.
The Integrated CWBNC/PIOATool for Functional Verification and Performance Analysis of Concurrent Systems
 PROCEEDINGS TACAS ’03, NUMBER 2619 IN LECTURE NOTES IN COMPUTER SCIENCE
, 2003
"... This paper reports on an effort to integrate two verification tools, the Concurrency Workbench of the New Century (CWBNC) and PIOATool. Our aim is to build a single tool that combines the "functional" analysis capabilities of the CWBNC with the compositional performanceanalysis featu ..."
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Cited by 7 (0 self)
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This paper reports on an effort to integrate two verification tools, the Concurrency Workbench of the New Century (CWBNC) and PIOATool. Our aim is to build a single tool that combines the "functional" analysis capabilities of the CWBNC with the compositional performanceanalysis features of PIOATool. We discuss some of the issues involved in the integration, highlighting a particular integration paradigm in which one tool becomes a subshell of the other.
On the verification of probabilistic I/O automata with unspecified rates
 In SAC ’09: Proceedings of the 2009 ACM symposium on Applied Computing
, 2009
"... We consider the Probabilistic I/O Automata framework, for which we address the verification of reachability properties in case the rates (also called delay parameters) are unspecified. We show that the problem of finding (or even approximating) the supremum probability that a set of states is reac ..."
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Cited by 7 (7 self)
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We consider the Probabilistic I/O Automata framework, for which we address the verification of reachability properties in case the rates (also called delay parameters) are unspecified. We show that the problem of finding (or even approximating) the supremum probability that a set of states is reached is undecidable. However, we give an algorithm to obtain a nontrivial overestimation of this value. We explain why this overestimation may result useful for many systems. Finally, in order to compare our approach against Markov Decision Processes, we study a simple protocol for anonymous fair service. In this case, the overestimation computed over the PIOA gives a more realistic result than the exact computation over the MDP.
On Behavior Equivalence for Probabilistic I/O Automata and its Relationship to Probabilistic Bisimulation
 Journal of Automata, Languages, and Combinatorics
, 2003
"... Previous work of the author has developed probabilistic input /output automata (PIOA) as a formalism for modeling systems that exhibit concurrent and probabilistic behavior. Central to that work was the notion of the "behavior map" associated with a state of a PIOA. The present paper p ..."
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Cited by 7 (1 self)
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Previous work of the author has developed probabilistic input /output automata (PIOA) as a formalism for modeling systems that exhibit concurrent and probabilistic behavior. Central to that work was the notion of the "behavior map" associated with a state of a PIOA. The present paper presents a new, simpler definition for PIOA behavior maps, investigates the induced "same behavior map" equivalence relation, and compares it with the standard notion of probabilistic bisimulation equivalence.
Decidability Results for Parametric Probabilistic Transition Systems with an Application to Security
 In Proc. of SEFM’04, IEEE
, 2004
"... We develop a model of Parametric Probabilistic Transition Systems. In this model probabilities associated with transitions may be parameters, and we show how to find instances of parameters that satisfy a given property and instances that either maximize or minimize the probability of reaching a giv ..."
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Cited by 5 (4 self)
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We develop a model of Parametric Probabilistic Transition Systems. In this model probabilities associated with transitions may be parameters, and we show how to find instances of parameters that satisfy a given property and instances that either maximize or minimize the probability of reaching a given state. We show, as an application, the model of a probabilistic non repudiation protocol. The theory we develop, allows us to find instances that maximize the probability that the protocol ends in a fair state (no participant has an advantage over the others).
INTERCONNECTION OF PROBABILISTIC SYSTEMS
, 2000
"... There is a growing interest in models for probabilistic systems. This fact is motivated by engineering applications, namely in problems concerning the evaluation of the performance of systems. It is of ..."
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Cited by 3 (3 self)
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There is a growing interest in models for probabilistic systems. This fact is motivated by engineering applications, namely in problems concerning the evaluation of the performance of systems. It is of
Compositional Performance Analysis using Probabilistic I/O Automata
 In CONCUR 2000
, 2000
"... ible" collection of I/O automata can be combined into a single, larger automaton. The notion of composition depends in an essential way on a distinction made in the I/O automata model between input actions, which are stimuli applied to an automaton by its environment, output actions, which are ..."
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Cited by 2 (1 self)
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ible" collection of I/O automata can be combined into a single, larger automaton. The notion of composition depends in an essential way on a distinction made in the I/O automata model between input actions, which are stimuli applied to an automaton by its environment, output actions, which are responses made by an automaton to its environment, and internal actions, which represent internal steps in which the automaton does not interact with its environment. Output and internal actions are called locally controlled, because their occurrence is under the control of the automaton, whereas input actions are under the control of the environment, with the automaton unable to exert any influence over their occurrence. The PIOA model integrates probability and timing into the I/O automata model, while carrying over in a natural way its essential features of asynchrony and compositionality. To the original I/O automata model, two
Practical Considerations in Protocol Verification: The E2C Case Study
, 1999
"... We report on our efforts to formally specify and verify a new protocol of the E2C Hawkeye Early Warning Aircraft. The protocol, which is currently in test at Northrop Grumman, supports communication between a Mission Computer (MC) and three or more Tactical Workstations (TWSs), connected by a singl ..."
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We report on our efforts to formally specify and verify a new protocol of the E2C Hawkeye Early Warning Aircraft. The protocol, which is currently in test at Northrop Grumman, supports communication between a Mission Computer (MC) and three or more Tactical Workstations (TWSs), connected by a singlesegment LAN. We modeled the protocol in the PROMELA specification language of the SPIN verification tool, and used SPIN to analyze a number of properties of the protocol. Our investigation revealed a race condition that can lead to a disconnect of an MC/TWS connection when there is one lost UDP datagram and significant timing delays. Such delays are virtually impossible under normal E2C operating conditions, but could be due to noise on the MC/TWS LAN. A simple modification was proposed that avoids the disconnect in many situations. Practical considerations, however, mandated that the protocol be left as is: shutting down a noisy connection and reinitializing the TWS, with minimal delay and loss of information to the operator, was deemed preferable to operating in degraded mode. 1.