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 MAC-Layer Communications in Wireless Systems

We present a timed process calculus for modelling wireless networks in which individual stations broadcast and receive messages; moreover the broadcasts are subject to collisions. Based on a reduction semantics for the calculus we define a contextual equivalence to compare the external behaviour of such wireless networks. Further, we construct an extensional LTS (labelled transition system) which models the activities of stations that can be directly observed by the external environment. Standard bisimulations in this LTS provide a sound proof method for proving systems contextually equivalence. We illustrate the usefulness of the proof methodology by a series of examples. Finally we show that this proof method is also complete, for a large class of systems

An Observational Theory for Mobile Ad Hoc Networks

AbstractWe propose a process calculus to study the observational theory of Mobile Ad Hoc Networks. The operational semantics of our calculus is given both in terms of a Reduction Semantics and in terms of a Labelled Transition Semantics. We prove that the two semantics coincide. The labelled transition system is then used to derive the notions of simulation and bisimulation for ad hoc networks. As a main result, we prove that the (weak) labelled bisimilarity completely characterises (weak) reduction barbed congruence, a standard, branching-time, contextually-defined program equivalence. We then use our (bi)simulation proof methods to formally prove a number of non-trivial properties of ad hoc networks

A Formal Approach to Cyber-Physical Attacks

We apply formal methods to lay and streamline theoretical foundations to reason about Cyber-Physical Systems (CPSs) and cyber-physical attacks. We focus on %a formal treatment of both integrity and DoS attacks to sensors and actuators of CPSs, and on the timing aspects of these attacks. Our contributions are threefold: (1) we define a hybrid process calculus to model both CPSs and cyber-physical attacks; (2) we define a threat model of cyber-physical attacks and provide the means to assess attack tolerance/vulnerability with respect to a given attack; (3) we formalise how to estimate the impact of a successful attack on a CPS and investigate possible quantifications of the success chances of an attack. We illustrate definitions and results by means of a non-trivial engineering application

A Process Calculus for Dynamic Networks

In this paper we propose a process calculus framework for dynamic networks in which the network topology may change as computation proceeds. The proposed calculus allows one to abstract away from neighborhood-discovery computations and it contains features for broadcasting at multiple transmission ranges and for viewing networks at different levels of abstraction. We develop a theory of confluence for the calculus and we use the machinery developed towards the verification of a leader-election algorithm for mobile ad hoc networks

Dwelling or duelling in possibilities: how (Ir)relevant are African feminisms?

In its four decades of rebirth, the world has debated (enough) the relevance of feminism, but there is, surprisingly, refreshingly emergent dimensions at the turn of the twenty-first century: feminisms from feminism flowing from Africa. The theories or models of Womanism, Stiwanism, Motherism, and Nego-feminism, with their underlying assumptions and values,were all born at various end times of the twentieth century with a common objective of seeking gender justice. This paper examines the crucial question of how relevant these models are to the global practice of woman as human. What propels their separateness, and why didn‘t they combine to make a more solid stance on the plight of the African woman? In fact, why can‘t they simply identify with the general feminism? Put differently, are they dwelling in the same terrain or are they separable and easily recognisable discourses duelling in possibilities for the woman in Africa in particular and the woman of the globe in general? More specifically, how (ir)relevant are African feminisms?In trying to answer these questions, the paper presents a critical review of the afore-mentioned theories of African feminisms with the goal of providing readers an understanding of what is new in each model, and what is similar or different between the various strands of African feminisms. The paper concludes with the author‘s analysis of the model that holds the best promise or possibilities for African feminism to achieve its seemingly elusive goal of gender equality