Papers by Toshimitsu Masuzawa
We consider wait-free linearizable implementations of shared objects which tolerate crash faults ... more We consider wait-free linearizable implementations of shared objects which tolerate crash faults of any number of processes on a distributed message-passing system. We consider the system where each process has a local clock that runs at the same speed as real-time clock and an message delays are in the range $
A fault-tolerant and self-stabilizing protocol for the topology problem
2013 9th International Wireless Communications and Mobile Computing Conference (IWCMC), 2013
The energy is a critical resource in Wireless Sensor Networks that impacts on networks lifetime. ... more The energy is a critical resource in Wireless Sensor Networks that impacts on networks lifetime. In this paper, we propose a distributed self-stabilizing algorithm of topology control to preserve energy in case of communications by broadcast. The topology control is achieved by the reduction of the transmission power of the nodes in the network. The self-stabilizing property is a very desirable property in Wireless Sensor Networks that guarantees to reach a correct behavior in a finite number of steps, regardless of its initial state. Our solution is validated by extensive simulations. The obtained results show the efficiency of our solution in case of communication by broadcast.
IEICE Transactions on Information and Systems, 2009
A self-stabilizing protocol is a protocol that achieves its intended behavior regardless of the i... more A self-stabilizing protocol is a protocol that achieves its intended behavior regardless of the initial configuration (i.e., global state). Thus, a self-stabilizing protocol is adaptive to any number and any type of topology changes of networks: after the last topology change occurs, the protocol starts to converge to its intended behavior. This advantage makes self-stabilizing protocols extremely attractive for designing highly dependable distributed systems on dynamic networks. While conventional self-stabilizing protocols require that the networks remain static during convergence to the intended behaviors, some recent works undertook the challenge of realizing self-stabilization in dynamic networks with frequent topology changes. This paper introduces some of the challenges as a new direction of research in self-stabilization.
Communication-efficient Self-stabilizing Protocols for Spanning-Tree Construction
In the population protocol model Angluin et al. proposed in 2004, there exists no self-stabilizin... more In the population protocol model Angluin et al. proposed in 2004, there exists no self-stabilizing leader election protocol for complete graphs, arbitrary graphs, trees, lines, degree-bounded graphs and so on unless the protocol knows the exact number of nodes. To circumvent the impossibility, we introduced the concept of loose-stabilization in 2009, which relaxes the closure requirement of self-stabilization. A loosely-stabilizing protocol guarantees that starting from any initial configuration a system reaches a safe configuration, and after that, the system keeps its specification (e.g. the unique leader) not forever, but for a sufficiently long time (e.g. exponentially large time with respect to the number of nodes). Our previous works presented two loosely-stabilizing leader election protocols for arbitrary graphs; One uses agent identifiers and the other uses random numbers to elect a unique leader. In this paper, we present a loosely-stabilizing protocol that solves leader el...
HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci-entific ... more HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et a ̀ la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
IEEE Transactions on Parallel and Distributed Systems, 2021
In the population protocol model, many problems cannot be solved in a self-stabilizing manner. Ho... more In the population protocol model, many problems cannot be solved in a self-stabilizing manner. However, global knowledge, such as the number of nodes in a network, sometimes enables the design of a self-stabilizing protocol for such problems. For example, it is known that we can solve the self-stabilizing leader election in complete graphs if and only if every node knows the exact number of nodes. In this article, we investigate the effect of global knowledge on the possibility of self-stabilizing population protocols in arbitrary graphs. Specifically, we clarify the solvability of the leader election problem, the ranking problem, the degree recognition problem, and the neighbor recognition problem by self-stabilizing population protocols with knowledge of the number of nodes and/or the number of edges in a network.
We give a silent self-stabilizing protocol for computing a maximum matching in an anonymous netwo... more We give a silent self-stabilizing protocol for computing a maximum matching in an anonymous network with a tree topology. The round complexity of our protocol is O(diam), where diam is the diameter of the network, and the step complexity is O(n*diam), where n is the number of processes in the network. The working space complexity is O(1) per process, although the output necessarily takes O(log(delta)) space per process, where delta is the degree of that process. To implement parent pointers in constant space, regardless of degree, we use the cyclic Abelian group Z_7.
Self-stabilizing and silent distributed algorithms for token distribution in rooted tree networks... more Self-stabilizing and silent distributed algorithms for token distribution in rooted tree networks are given. Initially, each process of a graph holds at most ` tokens. Our goal is to distribute the tokens in the whole network so that every process holds exactly k tokens. In the initial configuration, the total number of tokens in the network may not be equal to nk where n is the number of processes in the network. The root process is given the ability to create a new token or remove a token from the network. We aim to minimize the convergence time, the number of token moves, and the space complexity. A self-stabilizing token distribution algorithm that converges within O(n`) asynchronous rounds and needs Θ(nh ) redundant (or unnecessary) token moves is given, where = min(k, `− k) and h is the height of the tree network. Two novel ideas to reduce the number of redundant token moves are presented. One reduces the number of redundant token moves to O(nh) without any additional costs wh...
Theoretical Computer Science, 2019
A loosely-stabilizing leader election protocol with polylogarithmic convergence time in the popul... more A loosely-stabilizing leader election protocol with polylogarithmic convergence time in the population protocol model is presented in this paper. In the population protocol model, which is a common abstract model of mobile sensor networks, it is known to be impossible to design a self-stabilizing leader election protocol. Thus, in our prior work, we introduced the concept of loose-stabilization, which is weaker than self-stabilization but has similar advantage as selfstabilization in practice. Following this work, several loosely-stabilizing leader election protocols are presented. The loosely-stabilizing leader election guarantees that, starting from an arbitrary configuration, the system reaches a safe configuration with a single leader within a relatively short time, and keeps the unique leader for an sufficiently long time thereafter. The convergence times of all the existing loosely-stabilizing protocols, i.e., the expected time to reach a safe configuration, are polynomial in n where n is the number of nodes (while the holding times to keep the unique leader are exponential in n). In this paper, a loosely-stabilizing protocol with polylogarithmic convergence time is presented. Its holding time is not exponential, but arbitrarily large polynomial in n.
IEICE Transactions on Information and Systems, 2019
In this paper, we consider the partial gathering problem of mobile agents in arbitrary networks. ... more In this paper, we consider the partial gathering problem of mobile agents in arbitrary networks. The partial gathering problem is a generalization of the (well-investigated) total gathering problem, which requires that all the agents meet at the same node. The partial gathering problem requires, for a given positive integer g, that each agent should move to a node and terminate so that at least g agents should meet at each of the nodes they terminate at. The requirement for the partial gathering problem is no stronger than that for the total gathering problem, and thus, we clarify the difference on the move complexity between them. First, we show that agents require Ω(gn + m) total moves to solve the partial gathering problem, where n is the number of nodes and m is the number of communication links. Next, we propose a deterministic algorithm to solve the partial gathering problem in O(gn + m) total moves, which is asymptotically optimal in terms of total moves. Note that, it is known that agents require Ω(kn+ m) total moves to solve the total gathering problem in arbitrary networks, where k is the number of agents. Thus, our result shows that the partial gathering problem is solvable with strictly fewer total moves compared to the total gathering problem in arbitrary networks.
The K-node connectivity augmentation problem for directed binary trees
Systems Computers Controls, 1984
Le probleme de determiner l'ensemble de bords minimum devant etre ajoute a un graphe pour sat... more Le probleme de determiner l'ensemble de bords minimum devant etre ajoute a un graphe pour satisfaire une certaine condition est appele le probleme d'augmentation. On considere ici le probleme d'augmentation pour une connectivite de K nœuds (K≥2), ou le graphe est un arbre binaire oriente et tous les poids des bords sont egaux
Systems and Computers in Japan, 1986
Given a graph and a positive integer k , in the k-node-connectivity augmentation problem (k-NCAP)... more Given a graph and a positive integer k , in the k-node-connectivity augmentation problem (k-NCAP), a set of edges is determined to be added to convert the graph into a knode-connected graph with the minimum sum of the added edge-weights. It is known that 1-NCAP, for the directed acyclic graph where the weight is restricted to 1 and 2, is NPcomplete. It is also known that when the weight of the edges are all equal, 1-NCAP for any directed graph can be solved in O((V (+ I E I) time, and when the graph is restricted to the directed binary tree, k-NCAP (k h 2) is solved in O (k l V () time. In the preceding, 1V1 and IEl are the number of nodes and the number of edges of the given graph, respectively. This paper discusses k-NCAP (k 2 2) for the directed graph, where all edge weights are equal. for the family of graphs properly containing the directed ternary trees. It is shown that the problem can be solved in (k 2 3) time O (k l V 1) for the directed ternary tree, which is the optimal-time algorithm within a constant factor. In this paper, a new family of regular and k-node-connected graphs called a k-bouquet is defined. The solution for k-NCAP is obtained by constructing a k-bouquet by adding edges to the given graph. A solution for k-NCAP is shown *C is called a monotonically increasing property, if the following condition is 1 c ' g (n) holds for any n t n o '. I f f (n) = O(g(n)) and f(n) = Q(g(n)), it is written that f (n > = e (g (n)) .
Lecture Notes in Computer Science, 2014
In this paper, we consider the partial gathering problem of mobile agents in asynchronous tree ne... more In this paper, we consider the partial gathering problem of mobile agents in asynchronous tree networks. The partial gathering problem is a generalization of the classical gathering problem, which requires that all the agents meet at the same node. The partial gathering problem requires, for a given positive integer g, that each agent should move to a node and terminate so that at least g agents should meet at each of the nodes they terminate at. The requirement for the partial gathering problem is weaker than that for the (well-investigated) classical gathering problem, and thus, we clarify the difference on the move complexity between them. We consider two multiplicity detection models: weak multiplicity detection and strong multiplicity detection models. In the weak multiplicity detection model, each agent can detect whether another agent exists at the current node or not but cannot count the exact number of the agents. In the strong multiplicity detection model, each agent can count the number of agents at the current node. In addition, we consider two token models: non-token model and removable token model. In the nontoken model, agents cannot mark the nodes or the edges in any way. In the removabletoken model, each agent initially leaves a token on its initial node, and agents can remove the tokens. Our contribution is as follows. First, we show that for the non-token model agents require (kn) total moves to solve the partial gathering problem, where n is the number of nodes and k is the number of agents. Second, we consider the weak multiplicity detection and non-token model. In this model, for asymmetric trees, by a previous result agents can achieve the partial gathering in O (kn) total moves, which is asymptotically optimal in terms of total moves. In addition, for symmetric trees we show that there exist no algorithms to solve the partial gathering problem. Third, we consider the strong multiplicity detection and non-token model. In this model, for any trees we propose an algorithm to achieve the partial gathering in O (kn) total moves, which is asymptotically optimal in terms of total moves. At last, we consider the weak multiplicity detection and removable-token model. In this model, we propose an algorithm to achieve the partial gathering in O (gn) total moves. Note that in this model, agents require (gn) total moves ✩ The conference version of this paper is published in the proceedings of 21th International Colloquium on Structural Information and Communication Complexity (SIROCCO 2014).
Lecture Notes in Computer Science, 2012
In this paper, we consider the partial gathering problem of mobile agents in asynchronous unidire... more In this paper, we consider the partial gathering problem of mobile agents in asynchronous unidirectional rings equipped with whiteboards on nodes. The partial gathering problem is a new generalization of the total gathering problem. The partial gathering problem requires, for a given integer g, that each agent should move to a node and terminate so that at least g agents should meet at the same node. The requirement for the partial gathering problem is weaker than that for the (well-investigated) total gathering problem, and thus, we have interests in clarifying the difference on the move complexity between them. We propose three algorithms to solve the partial gathering problem. The first algorithm is deterministic but requires unique ID of each agent. This algorithm achieves the partial gathering in O(gn) total moves, where n is the number of nodes. The second algorithm is randomized and requires no unique ID of each agent (i.e., anonymous). This algorithm achieves the partial gathering in expected O(gn) total moves. The third algorithm is deterministic and requires no unique ID of each agent. For this case, we show that there exist initial configurations in which no algo-✩ The conference version of this paper is published in the proceedings of 16th International Conference on Principles of Distributed Systems (OPODIS 2012).
A Self-stabilizing Link-Coloring Protocol Resilient to Byzantine Faults in Tree Networks
Lecture Notes in Computer Science, 2005
ABSTRACT Self-stabilizing protocols can tolerate any type and any number of transient faults. But... more ABSTRACT Self-stabilizing protocols can tolerate any type and any number of transient faults. But self-stabilizing protocols have no guarantee of their behavior against permanent faults. Thus, investigation concerning self-stabilizing protocols resilient to permanent faults is important. This paper proposes a self-stabilizing link-coloring protocol resilient to (permanent) Byzantine faults in tree networks. The protocol assumes the central daemon, and uses Δ + 1 colors where Δ is the maximum degree in the network. This protocol guarantees that, for any nonfaulty process v, if the distance from v to any Byzantine ancestor of v is greater than two, v reaches its desired states within three rounds and never changes its states after that. Thus, it achieves fault containment with radius of two. Moreover, we prove that the containment radius becomes Ω(log n) when we use only Δ colors, and prove that the containment radius becomes Ω(n) under the distributed daemon. These lower bound results prove necessity of Δ + 1 colors and the central daemon to achieve fault containment with a constant radius.
Loosely-Stabilizing Leader Election in Population Protocol Model
Structural Information and Communication Complexity, 2010
A self-stabilizing protocol guarantees that starting from an arbitrary initial configuration, a s... more A self-stabilizing protocol guarantees that starting from an arbitrary initial configuration, a system eventually comes to satisfy its specification and keeps the specification forever. Although self-stabilizing protocols show excellent fault-tolerance against any transient faults (e.g. memory crash), designing self-stabilizing protocols is difficult and, what is worse, might be impossible due to the severe requirements. To circumvent the difficulty and impossibility, we introduce a novel notion of loose-stabilization, that relaxes the closure requirement of self-stabilization; starting from an arbitrary configuration, a system comes to satisfy its specification in a relatively short time, and it keeps the specification for a long time, though not forever. To show effectiveness and feasibility of this new concept, we present a probabilistic loosely-stabilizing leader election protocol in the Probabilistic Population Protocol (PPP) model of complete networks. Starting from any configuration, the protocol elects a unique leader within O(nNlogn) expected steps and keeps the unique leader for Ω(Ne N ) expected steps, where n is the network size (not known to the protocol) and N is a known upper bound of n. This result proves that introduction of the loose-stabilization circumvents the already-known impossibility result; the self-stabilizing leader election problem in the PPP model of complete networks cannot be solved without the knowledge of the exact network size.
Proceedings of the 30th annual ACM SIGACT-SIGOPS symposium on Principles of distributed computing - PODC '11, 2011
This paper demonstrates the usefulness of distributed local verification of proofs, as a tool for... more This paper demonstrates the usefulness of distributed local verification of proofs, as a tool for the design of self-stabilizing algorithms. In particular, it introduces a somewhat generalized notion of distributed local proofs, and utilizes it for improving the time complexity significantly, while maintaining space optimality. As a result, we show that optimizing the memory size carries at most a small cost in terms of time, in the context of Minimum Spanning Tree (MST). That is, we present algorithms that are both time and space efficient for both constructing an MST and for verifying it. This involves several parts that may be considered contributions in themselves. First, we generalize the notion of local proofs, trading off the time complexity for memory efficiency. This adds a dimension to the study of distributed local proofs, which has been gaining attention recently. Specifically, we design a (self-stabilizing) proof labeling scheme which is memory optimal (i.e., O(log n) bits per node), and whose time complexity is O(log 2 n) in synchronous networks, or O(∆ log 3 n) time in asynchronous ones, where ∆ is the maximum degree of nodes. This answers an open problem posed by Awerbuch and Varghese (FOCS 1991). We also show that Ω(log n) time is necessary, even in synchronous networks. Another property is that if f faults occurred, then, within the required detection time above, they are detected by some node in the O(f log n) locality of each of the faults. Second, we show how to enhance a known transformer that makes input/output algorithms self-stabilizing. It now takes as input an efficient construction algorithm and an efficient self-stabilizing proof labeling scheme, and produces an efficient self-stabilizing algorithm. When used for MST, the transformer produces a memory optimal self-stabilizing algorithm, whose time complexity, namely, O(n), is significantly better even than that of previous algorithms. (The time complexity of previous MST algorithms that used Ω(log 2 n) memory bits per node was O(n 2), and the time for optimal space algorithms was O(n|E|).) Inherited from our proof labelling scheme, our self-stabilising MST construction algorithm also has the following two properties: (1) if faults occur after the construction ended, then they are detected by some nodes within O(log 2 n) time in synchronous networks, or within O(∆ log 3 n) time in asynchronous ones, and (2) if f faults occurred, then, within the required detection time above, they are detected within the O(f log n) locality of each of the faults. We also show how to improve the above two properties, at the expense of some increase in the memory.
Lecture Notes in Computer Science, 2011
Checkpoint-rollback recovery, which is a universal method for restoring distributed systems after... more Checkpoint-rollback recovery, which is a universal method for restoring distributed systems after faults, requires a sophisticated snapshot algorithm especially if the systems are large-scale, since repeatedly taking global snapshots of the whole system requires unacceptable communication cost. As a sophisticated snapshot algorithm, a partial snapshot algorithm has been introduced that takes a snapshot of a subsystem consisting only of the nodes that are communication-related to the initiator instead of a global snapshot of the whole system. In this paper, we modify the previous partial snapshot algorithm to create a new one that can take a partial snapshot more efficiently, especially when multiple nodes concurrently initiate the algorithm. Experiments show that the proposed algorithm greatly reduces the amount of communication needed for taking partial snapshots.
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Papers by Toshimitsu Masuzawa