Automating the mean-field method for large dynamic gossip networks

We investigate an abstraction method, called mean- field method, for the performance evaluation of dynamic net- works with pairwise communication between nodes. It allows us to evaluate systems with very large numbers of nodes, that is, systems of a size where traditional performance evaluation methods fall short.\ud While the mean-field analysis is well-established in epidemics and for chemical reaction systems, it is rarely used for commu- nication networks because a mean-field model tends to abstract away the underlying topology.\ud To represent topological information, however, we extend the mean-field analysis with the concept of classes of states. At the abstraction level of classes we define the network topology by means of connectivity between nodes. This enables us to encode physical node positions and model dynamic networks by allowing nodes to change their class membership whenever they make a local state transition. Based on these extensions, we derive and implement algorithms for automating a mean-field based performance evaluation

Smart Sampling for Lightweight Verification of Markov Decision Processes

Markov decision processes (MDP) are useful to model optimisation problems in concurrent systems. To verify MDPs with efficient Monte Carlo techniques requires that their nondeterminism be resolved by a scheduler. Recent work has introduced the elements of lightweight techniques to sample directly from scheduler space, but finding optimal schedulers by simple sampling may be inefficient. Here we describe "smart" sampling algorithms that can make substantial improvements in performance.Comment: IEEE conference style, 11 pages, 5 algorithms, 11 figures, 1 tabl

Equational Reasonings in Wireless Network Gossip Protocols

Gossip protocols have been proposed as a robust and efficient method for disseminating information throughout large-scale networks. In this paper, we propose a compositional analysis technique to study formal probabilistic models of gossip protocols expressed in a simple probabilistic timed process calculus for wireless sensor networks. We equip the calculus with a simulation theory to compare probabilistic protocols that have similar behaviour up to a certain tolerance. The theory is used to prove a number of algebraic laws which revealed to be very effective to estimate the performances of gossip networks, with and without communication collisions, and randomised gossip networks. Our simulation theory is an asymmetric variant of the weak bisimulation metric that maintains most of the properties of the original definition. However, our asymmetric version is particularly suitable to reason on protocols in which the systems under consideration are not approximately equivalent, as in the case of gossip protocols

Modelling Interactive Experience, Function and Performance in Ubiquitous Systems

Abstract The cost of deploying a ubiquitous system to enhance a physical environment is likely to be considerable. The success of its deployment is highly dependent on its context: the physical environment and the activities that are to be carried out within it. This paper provides an initial exploration of whether stochastic process algebras (in particular PEPA with a Fluid Flow semantics) might be used to explore consequences before deployment. The focus of the exploration is to aid understanding of how a proposed system supports users within the environment. The challenge is to provide notations and techniques that will enable the analysis of potentially complex systems

Conceptual Models for Assessment & Assurance of Dependability, Security and Privacy in the Eternal CONNECTed World

This is the first deliverable of WP5, which covers Conceptual Models for Assessment & Assurance of Dependability, Security and Privacy in the Eternal CONNECTed World. As described in the project DOW, in this document we cover the following topics: • Metrics definition • Identification of limitations of current V&V approaches and exploration of extensions/refinements/ new developments • Identification of security, privacy and trust models WP5 focus is on dependability concerning the peculiar aspects of the project, i.e., the threats deriving from on-the-fly synthesis of CONNECTors. We explore appropriate means for assessing/guaranteeing that the CONNECTed System yields acceptable levels for non-functional properties, such as reliability (e.g., the CONNECTor will ensure continued communication without interruption), security and privacy (e.g., the transactions do not disclose confidential data), trust (e.g., Networked Systems are put in communication only with parties they trust). After defining a conceptual framework for metrics definition, we present the approaches to dependability in CONNECT, which cover: i) Model-based V&V, ii) Security enforcement and iii) Trust management. The approaches are centered around monitoring, to allow for on-line analysis. Monitoring is performed alongside the functionalities of the CONNECTed System and is used to detect conditions that are deemed relevant by its clients (i.e., the other CONNECT Enablers). A unified lifecycle encompassing dependability analysis, security enforcement and trust management is outlined, spanning over discovery time, synthesis time and execution time