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Probabilistic quorum systems can tolerate a larger fraction of faults than can traditional (strict) quorum systems, while guaranteeing consistency with an arbitrarily high probability for a system with enough replicas. However, the masking and opaque types of probabilistic quorum systems are hampered in that their optimal load—a best-case measure of the work done by the busiest replica, and an indicator...
Consensus is a fundamental building block used to solve many practical problems that appear on reliable distributed systems. In spite of the fact that consensus is being widely studied in the context of classical networks, few studies have been conducted in order to solve it in the context of dynamic and self-organizing systems characterized by unknown networks. While in a classical network the set...
We consider asynchronous distributed systems with message losses and process crashes. We study the impact of finite process memory on the solution to consensus, repeated consensus and reliable broadcast. With finite process memory, we show that in some sense consensus is easier to solve than reliable broadcast, and that reliable broadcast is as difficult to solve as repeated consensus: More precisely,...
We study the group renaming task, which is a natural generalization of the renaming task. An instance of this task consists of n processors, partitioned into m groups, each of at most g processors. Each processor knows the name of its group, which is in { 1, ..., M }. The task of each processor is to choose a new name for its group such that processors from different groups choose different new names...
Consider the problem of scheduling real-time tasks on a multiprocessor with the goal of meeting deadlines. Tasks arrive sporadically and have implicit deadlines, that is, the deadline of a task is equal to its minimum inter-arrival time. Consider this problem to be solved with global static-priority scheduling. We present a priority-assignment scheme with the property that if at most 38% of the processing...
The scheduling of sporadic task systems upon uniform multiprocessor platforms using global Deadline Monotonic algorithm is studied. A sufficient schedulability test is presented and proved correct. It is shown that this test offers non-trivial quantitative guarantees, in the form of a processor speedup bound.
This paper presents a performance comparison of three multiprocessor real-time locking protocols: the multiprocessor priority ceiling protocol (M-PCP), the distributed priority ceiling protocol (D-PCP), and the flexible multiprocessor locking protocol (FMLP). In the FMLP, blocking is implemented via either suspending or spinning, while in the M-PCP and D-PCP, all blocking is by suspending. The presented...
We propose a self-stabilizing marching algorithm for a group of oblivious robots in an obstacle-free workplace. To this end, we develop a distributed algorithm for a group of robots to transport a polygonal object, where each robot holds the object at a corner, and observe that each robot can simulate the algorithm, even after we replace the object by an imaginary one; we thus can use the algorithm...
This paper studies the flocking problem, where mobile robots group to form a desired pattern and move together while maintaining that formation. Unlike previous studies of the problem, we consider a system of mobile robots in which a number of them may possibly fail by crashing. Our algorithm ensures that the crash of faulty robots does not bring the formation to a permanent stop, and that the correct...
In this paper we study the impact of the speed of movement of nodes on the solvability of deterministic reliable geocast in mobile ad-hoc networks, where nodes move in a continuous manner with bounded maximum speed. Nodes do not know their position, nor the speed or direction of their movements. Nodes communicate over a radio network, so links may appear and disappear as nodes move in and out of the...
Most peer-to-peer (P2P) networks proposed until now have either logarithmic degree and logarithmic dilation or constant degree and logarithmic dilation. In the latter case (which is optimal up to constant factors), the constant degree is achieved either in expectation or with high probability. We propose the first overlay network, called SkewCCC, with a maximum degree of 3 (minimum possible) and logarithmic...
We consider wait-free implementations of a regular read/ write register for unauthenticated data using a collection of 3t + k base objects, t of which can be subject to Byzantine failures. We focus on amnesic algorithms that store only a limited number of values in the base objects. In contrast, non-amnesic algorithms store an unbounded number of values, which can eventually lead to problems of space...
Kleinberg [17] proposed in 2000 the first random graph model achieving to reproduce small world navigability, i.e. the ability to greedily discover polylogarithmic routes between any pair of nodes in a graph, with only a partial knowledge of distances. Following this seminal work, a major challenge was to extend this model to larger classes of graphs than regular meshes, introducing the concept of...
The aim of a software transactional memory (STM) system is to facilitate the delicate problem of low-level concurrency management, i.e. the design of programs made up of processes/threads that concurrently access shared objects. To that end, a STM system allows a programmer to write transactions accessing shared objects, without having to take care of the fact that these objects are concurrently accessed:...
Interesting tasks are scarce. Yet, they are essential as an investigation material, if we are to understand the structure of the tasks world. We propose a new collection of families of tasks called 0-1 Exclusion tasks, and show that families in this collection are interesting. A 0-1 Exclusion task on n processors is specified by a sequence of n − 1 bits b(1),b(2),...,b(n − 1). For participating...
Causality tracking mechanisms, such as vector clocks and version vectors, rely on mappings from globally unique identifiers to integer counters. In a system with a well known set of entities these ids can be preconfigured and given distinct positions in a vector or distinct names in a mapping. Id management is more problematic in dynamic systems, with large and highly variable number of entities,...
It has been widely suggested that memory transactions should behave as if they acquired and released a single global lock. Unfortunately, this behavior can be expensive to achieve, particularly when—as in the natural publication/privatization idiom—the same data are accessed both transactionally and nontransactionally. To avoid overhead, we propose selective strict serializability (SSS) semantics,...
Due to the heterogenous power-saving requirement in wireless sensor networks, we propose the Cyclic Quorum System Pair (CQS-Pair) which can guarantee that two asynchronous nodes adopt different cyclic quorum systems can hear each other at least once in bounded time intervals. To quickly assemble a CQS-Pair, we present a fast construction scheme, which is based on the Multiplier Theorem and the ...
We consider asynchronous deterministic broadcasting in radio networks. An execution of a broadcasting protocol is a series of events, each of which consists of simultaneous transmitting or delivering of messages. The aim is to transmit the source message to all nodes of the network. If two messages are delivered simultaneously to a node, a collision occurs and this node does not hear anything. An...
We consider the following model of cellular networks. Each base station has a given finite capacity, and each client has some demand and profit. A client can be covered by a specific subset of the base stations, and its profit is obtained only if its demand is provided in full. The goal is to assign clients to base stations, so that the overall profit is maximized subject to base station capacity...
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