A Modest Approach to Checking Probabilistic Timed Automata

Abstract

Probabilistic timed automata (PTA) combine discrete probabilistic choice, real time and nondeterminism. This paper presents a fully automatic tool for model checking PTA with respect to probabilistic and expected reachability properties. PTA are specified in Modest, a high-level compositional modelling language that includes features such as exception handling, dynamic parallelism and recursion, and thus enables model specification in a convenient fashion. For model checking, we use an integral semantics of time, representing clocks with bounded integer variables. This makes it possible to use the probabilistic model checker PRISM as analysis backend. We describe details of the approach and its implementation, and report results obtained for three different case studies.

A Comparison of Time- and Reward-Bounded Probabilistic Model Checking Techniques

“…probability of any host seizing the line while all hosts enter backoff ≤ b times. -BRP [9]: The PTA model of the bounded retransmission protocol with N ∈ { 32, 64 } frames to transmit, retransmission bound MAX ∈ { 6, 12 } and transmission delay TD ∈ { 2, 4 } time units. We compute the max.…”

“…4 for N ∈ { 4, 6 } parallel processes and constant K ∈ { 2, 4, 8 }. -CSMA [9]: PTA model of a communication protocol using CSMA/CD, with max. backoff counter BCMAX ∈ { 1, .…”

mctau: Bridging the Gap between Modest and UPPAAL

“…mctau is able to analyse (the nondeterministic overapproximations of) the three original mcpta PTA case studies [12], models unchanged. In all cases where mctau Table 1.…”

“…In all cases where mctau Table 1. Results of mctau and mcpta for the probabilistic BRP model (16, 2, 1) [12]). This shows how mctau can be of great help in debugging and sanity checking of probabilistic models.…”

“…Started in 2008, the Modest Toolset constitutes the second generation [6] of tools with this philosophy and currently consists of (i) mcpta [11,12], which enables model checking of networks of PTA using the Prism [16] [4,11], a discrete-event simulator that primarily targets GSMP models but in fact is enhanced to handle certain nondeterministic models in a sound way, and (iii) mime as a graphical user interface that seamlessly integrates the analysis tools into a Modest source code editor with syntax and error highlighting. The tools are usable and robust.…”