469 research outputs found
Verification and Synthesis of Symmetric Uni-Rings for Leads-To Properties
This paper investigates the verification and synthesis of parameterized
protocols that satisfy leadsto properties on symmetric
unidirectional rings (a.k.a. uni-rings) of deterministic and constant-space
processes under no fairness and interleaving semantics, where and are
global state predicates. First, we show that verifying for
parameterized protocols on symmetric uni-rings is undecidable, even for
deterministic and constant-space processes, and conjunctive state predicates.
Then, we show that surprisingly synthesizing symmetric uni-ring protocols that
satisfy is actually decidable. We identify necessary and
sufficient conditions for the decidability of synthesis based on which we
devise a sound and complete polynomial-time algorithm that takes the predicates
and , and automatically generates a parameterized protocol that
satisfies for unbounded (but finite) ring sizes. Moreover, we
present some decidability results for cases where leadsto is required from
multiple distinct predicates to different predicates. To demonstrate
the practicality of our synthesis method, we synthesize some parameterized
protocols, including agreement and parity protocols
Self-Stabilization in the Distributed Systems of Finite State Machines
The notion of self-stabilization was first proposed by Dijkstra in 1974 in his classic paper. The paper defines a system as self-stabilizing if, starting at any, possibly illegitimate, state the system can automatically adjust itself to eventually converge to a legitimate state in finite amount of time and once in a legitimate state it will remain so unless it incurs a subsequent transient fault. Dijkstra limited his attention to a ring of finite-state machines and provided its solution for self-stabilization. In the years following his introduction, very few papers were published in this area. Once his proposal was recognized as a milestone in work on fault tolerance, the notion propagated among the researchers rapidly and many researchers in the distributed systems diverted their attention to it. The investigation and use of self-stabilization as an approach to fault-tolerant behavior under a model of transient failures for distributed systems is now undergoing a renaissance. A good number of works pertaining to self-stabilization in the distributed systems were proposed in the yesteryears most of which are very recent. This report surveys all previous works available in the literature of self-stabilizing systems
A Systematic Approach to Constructing Families of Incremental Topology Control Algorithms Using Graph Transformation
In the communication systems domain, constructing and maintaining network
topologies via topology control (TC) algorithms is an important cross-cutting
research area. Network topologies are usually modeled using attributed graphs
whose nodes and edges represent the network nodes and their interconnecting
links. A key requirement of TC algorithms is to fulfill certain consistency and
optimization properties to ensure a high quality of service. Still, few
attempts have been made to constructively integrate these properties into the
development process of TC algorithms. Furthermore, even though many TC
algorithms share substantial parts (such as structural patterns or tie-breaking
strategies), few works constructively leverage these commonalities and
differences of TC algorithms systematically. In previous work, we addressed the
constructive integration of consistency properties into the development
process. We outlined a constructive, model-driven methodology for designing
individual TC algorithms. Valid and high-quality topologies are characterized
using declarative graph constraints; TC algorithms are specified using
programmed graph transformation. We applied a well-known static analysis
technique to refine a given TC algorithm in a way that the resulting algorithm
preserves the specified graph constraints.
In this paper, we extend our constructive methodology by generalizing it to
support the specification of families of TC algorithms. To show the feasibility
of our approach, we reneging six existing TC algorithms and develop e-kTC, a
novel energy-efficient variant of the TC algorithm kTC. Finally, we evaluate a
subset of the specified TC algorithms using a new tool integration of the graph
transformation tool eMoflon and the Simonstrator network simulation framework.Comment: Corresponds to the accepted manuscrip
On the Limits and Practice of Automatically Designing Self-Stabilization
A protocol is said to be self-stabilizing when the distributed system executing it is guaranteed to recover from any fault that does not cause permanent damage. Designing such protocols is hard since they must recover from all possible states, therefore we investigate how feasible it is to synthesize them automatically. We show that synthesizing stabilization on a fixed topology is NP-complete in the number of system states. When a solution is found, we further show that verifying its correctness on a general topology (with any number of processes) is undecidable, even for very simple unidirectional rings. Despite these negative results, we develop an algorithm to synthesize a self-stabilizing protocol given its desired topology, legitimate states, and behavior. By analogy to shadow puppetry, where a puppeteer may design a complex puppet to cast a desired shadow, a protocol may need to be designed in a complex way that does not even resemble its specification. Our shadow/puppet synthesis algorithm addresses this concern and, using a complete backtracking search, has automatically designed 4 new self-stabilizing protocols with minimal process space requirements: 2-state maximal matching on bidirectional rings, 5-state token passing on unidirectional rings, 3-state token passing on bidirectional chains, and 4-state orientation on daisy chains
Stochastic Activity Networks Templates: Supporting Variability in Performability Models
Model-based evaluation is extensively used to estimate performance and
reliability of dependable systems. Traditionally, those systems were small and
self-contained, and the main challenge for model-based evaluation has been the
efficiency of the solution process. Recently, the problem of specifying and
maintaining complex models has increasingly gained attention, as modern systems
are characterized by many components and complex interactions. Components share
similarities, but also exhibit variations in their behavior due to different
configurations or roles in the system. From the modeling perspective,
variations lead to replicating and altering a small set of base models multiple
times. Variability is taken into account only informally, by defining a sample
model and explaining its possible variations. In this paper we address the
problem of including variability in performability models, focusing on
Stochastic Activity Networks (SANs). We introduce the formal definition of
Stochastic Activity Networks Templates (SAN-T), a formalism based on SANs with
the addition of variability aspects. Differently from other approaches,
parameters can also affect the structure of the model, like the number of cases
of activities. We apply the SAN-T formalism to the modeling of the backbone
network of an environmental monitoring infrastructure. In particular, we show
how existing SAN models from the literature can be generalized using the newly
introduced formalism
Analysing Coloured Petri Nets by the Occurrence Graph Method
This paper provides an overview og the work done for the author's PhD thesis. The research area of Coloured Petri Nets is introduced, and the available analysis methods are presented. The occurrence graph method, which is the main subject of this thesis, is described in more detail. Summaries of the six papers which, together with this overview, comprise the thesis are given, and the contributions are discussed.A large portion of this overview is dedicated to a description of related work. The aim is twofold: First, to survey pertinent results within the research areas of -- in increasing generality -- Coloured Petri Nets, High-level Petri Nets, and formalisms for modelling and analysis of parallel and distributed systems. Second, to put the results obtained in this thesis in a wider perspective by comparing them with important related work
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