A given Boolean function has its input distributed among many parties. The aim is to determine which parties to tMk to and what information to exchange with each of them in order to evaluate the function while minimizing the total communication. This paper shows that it is possible to obtain the Boolean answer deterministically with only a polynomial increase in communication with respect to the information lower bound given by the nondeterministic communication complexity of the function.

Several probabilistic simulation relations for probabilistic systems are defined and evaluated according to two criteria: compositionality and preservation of "interesting" properties. Here, the interesting properties of a system are identified with those that are expressible in an untimed version of the Timed Probabilistic concurrent Computation Tree Logic (TPCTL) of Hansson. The definitions are made, and the evaluations carried out, in terms of a general labeled transition system model for concurrent probabilistic computation. The results cover weak simulations, which abstract from internal computation, as well as strong simulations, which do not.

The problem of resolving conflicts between processes in distributed systems is of practical importance. A conflict between a set of processes must be resolved in favor of some (usually one) process and against the others: a favored process must have some property that distinguishes it from others. To guarantee fairness, the distinguishing property must be such that the process selected for favorable treatment is not always the same. A distributed implementation of an acyclic precedence graph, in which the depth of a process (the longest chain of predecessors) is a distinguishing property, is presented. A simple conflict resolution rule coupled with the acyclic graph ensures fair resolution of all conflicts. To make the problem concrete, two paradigms are presented: the well-known distributed dining philosophers problem and a generalization of it, the distributed drinking philosophers problem.

We study the problem of perfectly secure communication in a general network in which processors and communication lines may be faulty. Lower bounds are obtained on the connectivity required for success-ful secure communication. Efficient algorithms are obtained that operate with this connectivity and rely on no complexity theoretic assumptions. These are the first algorithms for secure communication in a general network to simultaneously achieve the three goals of perfect secrecy, perfect resiliency, and worst case time linear in the diameter of the network.

In this tutorial we give an overview of the process algebra EMPA, a calculus devised in order to model and analyze features of real-world concurrent systems such as nondeterminism, priorities, probabilities and time, with a particular emphasis on performance evaluation. The purpose of this tutorial is to explain the design choices behind the development of EMPA and how the four features above interact, and to show that a reasonable trade off between the expressive power of the calculus and the complexity of its underlying theory has been achieved.

Virtually all research in scheduling theory has been concerned with clairvoyant scheduling where it is assumed that the characteristics of a job (in particular, its execution time, release time and dependence on other jobs) are known a priori. This assumption is invalid for scheduling problems that arise in time-sharing operating systems where the scheduler must provide fast turnaround for processes being generated by the users without any knowledge of the future behavior of these processes. We study preemptive, non-clairvoyant scheduling schemes where the scheduler has no knowledge of the jobs' characteristics. We develop a model for evaluating scheduling strategies for single and multi-processor systems. This model compares the non-clairvoyant scheduler against the optimal clairvoyant scheduler, and it takes into account various issues such as release times, execution time, preemption cost, and the inter-dependence between jobs. Within this model we study some standard sc...

The -calculus with synchronous output and mixed-guarded choices is strictly more expressive than the -calculus with asynchronous output and no choice. As a corollary, Palamidessi recently proved that there is no fully compositional encoding from the former into the latter that preserves divergence-freedom and symmetries. This paper shows

. EMPA enhances the expressiveness of classical process algebras by integrating functional and performance descriptions of concurrent systems. This is achieved by offering, besides passive actions (useful for pure nondeterminism), actions whose duration is exponentially distributed as well as immediate actions (useful for performance abstraction), parametrized by priority levels (hence prioritized choices) and weights (hence probabilistic choices). In order to analyze an EMPA term, from its integrated semantic model (a transition system labeled on both action types and action durations) we derive a functional semantic model (a transition system labeled on action types only) and a performance semantic model (a Markov chain). We show that an integrated analysis, i.e. a notion of equivalence on the integrated semantic model, is not only convenient but also necessary to achieve compositionality. 1 Introduction The need of integrating the performance modeling and analysis of a concurrent s...

A method of analyzing time bounds for randomized distributed algorithms is presented, in the context of a new and general framework for describing and reasoning about randomized algorithms. The method consists of proving auxiliary statements of the form U , which means that whenever the algorithm begins in a state in set U , with probability p, it will reach a state in set U within time t.

We survey results from distributed computing that show tasks to be impossible, either outright or within given resource bounds, in various models. The parameters of the models considered include synchrony, fault-tolerance, different communication media, and randomization. The resource bounds refer to time, space and message complexity. These results are useful in understanding the inherent difficulty of individual problems and in studying the power of different models of distributed computing.