Volume
LIPIcs, Volume 324
28th International Conference on Principles of Distributed Systems (OPODIS 2024)
Event
OPODIS 2024, December 11-13, 2024, Lucca, ItalyEditors
Publication Details
- published at: 2025-01-08
- Publisher: Schloss Dagstuhl – Leibniz-Zentrum für Informatik
- ISBN: 978-3-95977-360-7
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Complete Volume
LIPIcs, Volume 324, OPODIS 2024, Complete Volume
Abstract
LIPIcs, Volume 324, OPODIS 2024, Complete Volume
Cite as
28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 1-772, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@Proceedings{bonomi_et_al:LIPIcs.OPODIS.2024,
title = {{LIPIcs, Volume 324, OPODIS 2024, Complete Volume}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {1--772},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024},
URN = {urn:nbn:de:0030-drops-227373},
doi = {10.4230/LIPIcs.OPODIS.2024},
annote = {Keywords: LIPIcs, Volume 324, OPODIS 2024, Complete Volume}
}
Document
Front Matter
Front Matter, Table of Contents, Preface, Conference Organization
Abstract
Front Matter, Table of Contents, Preface, Conference Organization
Cite as
28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 0:i-0:xvi, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{bonomi_et_al:LIPIcs.OPODIS.2024.0,
author = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
title = {{Front Matter, Table of Contents, Preface, Conference Organization}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {0:i--0:xvi},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.0},
URN = {urn:nbn:de:0030-drops-227360},
doi = {10.4230/LIPIcs.OPODIS.2024.0},
annote = {Keywords: Front Matter, Table of Contents, Preface, Conference Organization}
}
Document
Invited Talk
The Power of Simplicity on Dependable Distributed Systems (Invited Talk)
Abstract
Contrary to a (somewhat) common belief, the most important property of a practical distributed algorithm is not its efficiency or performance but its simplicity. This fact is even more evident when considering dependable distributed systems. In this talk, I will present some cases in which simple protocols and elegant abstractions - which were not the most efficient for the problem at hand - enabled the deployment of dependable solutions that changed the practice of distributed computing. I will also discuss how the quest for simplicity influenced my work on BFT and multi-cloud storage. Ultimately, I aim to convince the audience that "simplicity is the ultimate sophistication" in distributed computing.
Cite as
Alysson Bessani. The Power of Simplicity on Dependable Distributed Systems (Invited Talk). In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, p. 1:1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{bessani:LIPIcs.OPODIS.2024.1,
author = {Bessani, Alysson},
title = {{The Power of Simplicity on Dependable Distributed Systems}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {1:1--1:1},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.1},
URN = {urn:nbn:de:0030-drops-225372},
doi = {10.4230/LIPIcs.OPODIS.2024.1},
annote = {Keywords: Abstractions, Simplicity, Byzantine Fault Tolerance, Cloud Storage}
}
Document
Invited Talk
Distributed Computing by Mobile Robots: Expanding the Horizon (Invited Talk)
Abstract
Extensive research focus within distributed computing has been spent on the computational and complexity issues arising in systems of mobile computational entities (called robots) operating in the Euclidean space in Look-Compute-Move cycles. In the classical OBLOT model, the robots are homogeneous, having no distinguishing features and running the same algorithm. Moreover, they are silent, having no explicit means of communication, and oblivious, meaning that, whenever activated, they forget everything they have seen and done in previous cycles.
The research focus has been in determining the impact that internal capabilities (e.g., memory, communication) and external conditions (e.g. synchrony, type of the activation scheduler) have on the computability power of these robots (e.g., see [P. Flocchini et al., ed., 2019] and chapters therein). Over the years, various enhancement of the basic model have been studied in regards to memory and communication under the different activation schedules (e.g., [K. Buchin et al., 2021; K. Buchin et al., 2022; S. Das et al., 2016; P. Flocchini et al., 2023; P. Flocchini et al., 2016]). At the same time, the computational landscape has been broadened by examining aspects typically explored in other areas of distributed computing that have not yet been investigated in these systems. One such aspect is the concept of robots possessing identifiers (which need not be identical), diverging from the usual assumption of homogeneity (e.g., [Y. Asahiro and M. Yamashita, 2023; S. Bhagat et al., 2020; P. Flocchini et al., 2024a; P. Flocchini et al., 2024b; H. Seike and Y. Yamauchi, 2023]).
In this talk, I will first discuss some of the recent results shaping the overall computational landscape. I will then describe some recent explorations on the impact of introducing non-homogeneity of the robots.
Cite as
Paola Flocchini. Distributed Computing by Mobile Robots: Expanding the Horizon (Invited Talk). In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 2:1-2:2, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{flocchini:LIPIcs.OPODIS.2024.2,
author = {Flocchini, Paola},
title = {{Distributed Computing by Mobile Robots: Expanding the Horizon}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {2:1--2:2},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.2},
URN = {urn:nbn:de:0030-drops-225381},
doi = {10.4230/LIPIcs.OPODIS.2024.2},
annote = {Keywords: Mobile Robots, Look-Compute-Move, Computability, Moving and Computing}
}
Document
Invited Talk
BFT Consensus: From Academic Paper to Mainnet (Invited Talk)
Abstract
This talk shares our journey in bringing Byzantine Fault Tolerant (BFT) consensus from academic papers to operational blockchain networks. It begins in 2019 with our initial effort as researchers and engineers at Facebook to deploy the HotStuff consensus protocol [Yin et al., 2019] at the heart of the Libra blockchain [Facebook, 2022]. We present how this journey led to modifications from the original theoretical design [Rati Gelashvili et al., 2021] and the eventual migration to DAG-based systems [George Danezis et al., 2022; Alexander Spiegelman et al., 2022], now implemented in the Sui blockchain [The Sui team, 2023] and gaining traction across the blockchain space [Arun et al., 2024; Kushal Babel et al., 2024; Shrestha et al., 2024; Malkhi et al., 2023]. We outline the numerous research and engineering challenges we faced at every step of this journey, describe how we addressed some of these challenges [Bano et al., 2020; Giuliari et al., 2024], and point out which ones remain open questions and require further research. This talk aims to offer a different perspective on BFT consensus, focusing on the needs of real-world blockchains and offering insights that may not be visible from research papers alone.
Cite as
Alberto Sonnino. BFT Consensus: From Academic Paper to Mainnet (Invited Talk). In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, p. 3:1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{sonnino:LIPIcs.OPODIS.2024.3,
author = {Sonnino, Alberto},
title = {{BFT Consensus: From Academic Paper to Mainnet}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {3:1--3:1},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.3},
URN = {urn:nbn:de:0030-drops-225396},
doi = {10.4230/LIPIcs.OPODIS.2024.3},
annote = {Keywords: BFT Consensus, Blockchain, Real-World}
}
Document
AMECOS: A Modular Event-Based Framework for Concurrent Object Specification
Abstract
In this work, we introduce a modular framework for specifying distributed systems that we call AMECOS. Specifically, our framework departs from the traditional use of sequential specification, which presents limitations both on the specification expressiveness and implementation efficiency of inherently concurrent objects, as documented by Castañeda, Rajsbaum and Raynal in CACM 2023. Our framework focuses on the interactions between the various system components, specified as concurrent objects. Interactions are described with sequences of object events. This provides a modular way of specifying distributed systems and separates legality (object semantics) from other issues, such as consistency. We demonstrate the usability of our framework by (i) specifying various well-known concurrent objects, such as registers, shared memory, message-passing, reliable broadcast, and consensus, (ii) providing hierarchies of ordering semantics (namely, consistency hierarchy, memory hierarchy, and reliable broadcast hierarchy), and (iii) presenting a novel axiomatic proof of the impossibility of the well-known Consensus problem.
Cite as
Timothé Albouy, Antonio Fernández Anta, Chryssis Georgiou, Mathieu Gestin, Nicolas Nicolaou, and Junlang Wang. AMECOS: A Modular Event-Based Framework for Concurrent Object Specification. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 4:1-4:29, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{albouy_et_al:LIPIcs.OPODIS.2024.4,
author = {Albouy, Timoth\'{e} and Fern\'{a}ndez Anta, Antonio and Georgiou, Chryssis and Gestin, Mathieu and Nicolaou, Nicolas and Wang, Junlang},
title = {{AMECOS: A Modular Event-Based Framework for Concurrent Object Specification}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {4:1--4:29},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.4},
URN = {urn:nbn:de:0030-drops-225409},
doi = {10.4230/LIPIcs.OPODIS.2024.4},
annote = {Keywords: Concurrency, Object specification, Consistency conditions, Consensus impossibility}
}
Document
RMR-Efficient Detectable Objects for Persistent Memory and Their Applications
Abstract
We describe a novel construction of arbitrary read-modify-write (RMW) primitives in a persistent shared memory model with process failures. Our construction uses blocking synchronization, in the form of recoverable mutual exclusion (RME), and is optimal in terms of the widely studied remote memory reference (RMR) complexity measure. The implemented objects tolerate either system-wide or independent process crashes, depending on the RME lock used, and also provide detectability for resolving the outcome of operations interrupted by failures. We prove that our construction is RMR-optimal using a reduction back to the RME problem. Our proof technique introduces a novel algorithmic style that enables solving challenging synchronization problems using a common execution path for both the system-wide and independent failure models, which previously required separate analyses, and relies only on a suitable implementation of the detectable base objects in each model to achieve RMR efficiency. Experiments demonstrate that our construction outperforms prior wait-free and lock-free algorithms on a multiprocessor with Intel Optane persistent memory.
Cite as
Sahil Dhoked, Ahmed Fahmy, Wojciech Golab, and Neeraj Mittal. RMR-Efficient Detectable Objects for Persistent Memory and Their Applications. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 5:1-5:26, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{dhoked_et_al:LIPIcs.OPODIS.2024.5,
author = {Dhoked, Sahil and Fahmy, Ahmed and Golab, Wojciech and Mittal, Neeraj},
title = {{RMR-Efficient Detectable Objects for Persistent Memory and Their Applications}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {5:1--5:26},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.5},
URN = {urn:nbn:de:0030-drops-225417},
doi = {10.4230/LIPIcs.OPODIS.2024.5},
annote = {Keywords: persistent memory, synchronization, recoverability, fault tolerance, detectability, scalability, RMR complexity, theory, mutual exclusion}
}
Document
DULL: A Fast Scalable Detectable Unrolled Lock-Based Linked List
Abstract
Persistent memory (PM) has emerged as a promising technology that enables data structures to preserve their consistent state after recovering from system failures. Detectable data structures have been proposed to detect the response of the last operation of a crashed process. Various lock-free detectable and recoverable concurrent data structures have been developed in the literature. However, designing detectable lock-based structures is challenging due to the need to preserve the correctness properties of the underlying locks, such as mutual exclusion and deadlock-freedom, across failures. Therefore, lock-based detectable and persistent data structures are not as common as lock-free structures. In this work, we introduce DULL: a fast, scalable and Detectable Unrolled Lock-based Linked list. This paper presents the design and implementation of DULL, along with an evaluation of its recoverability and scalability. Experimental Results show that DULL is several-fold faster than the competition in all workloads that involve updates. Moreover, as opposed to some of the previous works, our algorithm is scalable when the multiprocessor is oversubscribed. DULL is a demonstration of the feasibility of using lock-based data structures with detectability in PM environments. We believe that DULL opens up new research directions for designing and analyzing detectable lock-based data structures.
Cite as
Ahmed Fahmy and Wojciech Golab. DULL: A Fast Scalable Detectable Unrolled Lock-Based Linked List. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 6:1-6:25, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{fahmy_et_al:LIPIcs.OPODIS.2024.6,
author = {Fahmy, Ahmed and Golab, Wojciech},
title = {{DULL: A Fast Scalable Detectable Unrolled Lock-Based Linked List}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {6:1--6:25},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.6},
URN = {urn:nbn:de:0030-drops-225429},
doi = {10.4230/LIPIcs.OPODIS.2024.6},
annote = {Keywords: detectability, lock-based, mutual exclusion, linked list, fault-tolerance, persistent memory, concurrency}
}
Document
Incentive Compatibility of Ethereum’s PoS Consensus Protocol
Abstract
This paper investigates whether following the fork-choice rule in the Ethereum PoS consensus protocol constitutes a Nash equilibrium - i.e., whether the protocol that maintains the canonical chain in Ethereum is incentive-compatible. Specifically, we explore whether selfish participants may attempt to manipulate the fork-choice rule by forking out previous blocks and capturing the rewards associated with those blocks. Our analysis considers two strategies for participants: the obedient strategy, which adheres to the prescribed protocol, and the cunning strategy, which attempts to manipulate the fork-choice rule to gain more rewards. We evaluate the conditions under which selfish participants might deviate from the obedient strategy. We found that, in a synchronous system, following the prescribed fork-choice rule is incentive-compatible. However, in an eventually synchronous system, the protocol is eventually incentive-compatible - that is, only a limited number of proposers will find it profitable to fork the chain during the synchronous period. After this sequence of cunning proposers, subsequent proposers will find it more profitable to follow the protocol.
Cite as
Ulysse Pavloff, Yackolley Amoussou-Guenou, and Sara Tucci-Piergiovanni. Incentive Compatibility of Ethereum’s PoS Consensus Protocol. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 7:1-7:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{pavloff_et_al:LIPIcs.OPODIS.2024.7,
author = {Pavloff, Ulysse and Amoussou-Guenou, Yackolley and Tucci-Piergiovanni, Sara},
title = {{Incentive Compatibility of Ethereum’s PoS Consensus Protocol}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {7:1--7:23},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.7},
URN = {urn:nbn:de:0030-drops-225431},
doi = {10.4230/LIPIcs.OPODIS.2024.7},
annote = {Keywords: Ethereum PoS, Game Theory, Block Reward}
}
Document
Optimal Multilevel Slashing for Blockchains
Abstract
We present the notion of multilevel slashing, where proof-of-stake blockchain validators can obtain gradual levels of assurance that a certain block is bound to be finalized in a global consensus procedure, unless an increasing and optimally large number of Byzantine processes have their staked assets slashed - that is, deducted - due to provably incorrect behavior. Our construction is a highly parameterized generalization of combinatorial intersection systems based on finite projective spaces, with asymptotic high availability and optimal slashing properties. Even under weak conditions, we show that our construction has asymptotically optimal slashing properties with respect to message complexity and validator load; this result also illustrates a fundamental trade off between message complexity, load, and slashing. In addition, we show that any intersection system whose ground elements are disjoint subsets of nodes (e.g. "committees" in committee-based consensus protocols) has asymptotic high availability under similarly weak conditions. Finally, our multilevel construction gives the flexibility to blockchain validators to decide how many "levels" of finalization assurance they wish to obtain. This functionality can be seen either as (i) a form of an early, slashing-based block finalization; or (ii) a service to support reorg tolerance.
Cite as
Kenan Wood, Hammurabi Mendes, and Jonad Pulaj. Optimal Multilevel Slashing for Blockchains. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 8:1-8:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{wood_et_al:LIPIcs.OPODIS.2024.8,
author = {Wood, Kenan and Mendes, Hammurabi and Pulaj, Jonad},
title = {{Optimal Multilevel Slashing for Blockchains}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {8:1--8:18},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.8},
URN = {urn:nbn:de:0030-drops-225445},
doi = {10.4230/LIPIcs.OPODIS.2024.8},
annote = {Keywords: Blockchains, Finality, Slashablility, Committees, Availability}
}
Document
Crash-Tolerant Exploration of Trees by Energy-Sharing Mobile Agents
Abstract
We consider the problem of graph exploration by energy sharing mobile agents that are subject to crash faults. More precisely, we consider a team of two agents where at most one of them may fail unpredictably, and the considered topology is that of connected acyclic graphs (i.e. trees). We consider both the asynchronous and the synchronous settings, and we provide necessary and sufficient conditions about the energy.
Cite as
Quentin Bramas, Toshimitsu Masuzawa, and Sébastien Tixeuil. Crash-Tolerant Exploration of Trees by Energy-Sharing Mobile Agents. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 9:1-9:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{bramas_et_al:LIPIcs.OPODIS.2024.9,
author = {Bramas, Quentin and Masuzawa, Toshimitsu and Tixeuil, S\'{e}bastien},
title = {{Crash-Tolerant Exploration of Trees by Energy-Sharing Mobile Agents}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {9:1--9:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.9},
URN = {urn:nbn:de:0030-drops-225452},
doi = {10.4230/LIPIcs.OPODIS.2024.9},
annote = {Keywords: Mobile Agents, Distributed Algorithms, Energy sharing}
}
Document
Universal Finite-State and Self-Stabilizing Computation in Anonymous Dynamic Networks
Abstract
A communication network is said to be anonymous if its agents are indistinguishable from each other; it is dynamic if its communication links may appear or disappear unpredictably over time. Assuming that an anonymous dynamic network is always connected and each of its n agents is initially given an input, it takes 2n communication rounds for the agents to compute an arbitrary (frequency-based) function of such inputs (Di Luna-Viglietta, DISC 2023).
It is known that, without making additional assumptions on the network and without knowing the number of agents n, it is impossible to compute most functions and explicitly terminate. In fact, current state-of-the-art algorithms only achieve stabilization, i.e., allow each agent to return an output after every communication round; outputs can be changed, and are guaranteed to be all correct after 2n rounds. Such algorithms rely on the incremental construction of a data structure called history tree, which is augmented at every round. Thus, they end up consuming an unlimited amount memory, and are also prone to errors in case of memory loss or corruption.
In this paper, we provide a general self-stabilizing algorithm for anonymous dynamic networks that stabilizes in max{4n-2h, 2h} rounds (where h measures the amount of corrupted data initially present in the memory of each agent), as well as a general finite-state algorithm that stabilizes in 3n² rounds. Our work improves upon previously known methods that only apply to static networks (Boldi-Vigna, Dist. Comp. 2002). In addition, we develop new fundamental techniques and operations involving history trees, which are of independent interest.
Cite as
Giuseppe A. Di Luna and Giovanni Viglietta. Universal Finite-State and Self-Stabilizing Computation in Anonymous Dynamic Networks. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 10:1-10:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{diluna_et_al:LIPIcs.OPODIS.2024.10,
author = {Di Luna, Giuseppe A. and Viglietta, Giovanni},
title = {{Universal Finite-State and Self-Stabilizing Computation in Anonymous Dynamic Networks}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {10:1--10:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.10},
URN = {urn:nbn:de:0030-drops-225464},
doi = {10.4230/LIPIcs.OPODIS.2024.10},
annote = {Keywords: anonymous dynamic network, history tree, self-stabilization, finite-state stabilization}
}
Document
Gathering Teams of Deterministic Finite Automata on a Line
Abstract
Several mobile agents, modelled as deterministic finite automata, navigate in an infinite line in synchronous rounds. All agents start in the same round. In each round, an agent can move to one of the two neighboring nodes, or stay idle. Agents have distinct labels which are integers from the set {1,…,L}. They start in teams, each of which consists of x agents, for some fixed integer x. Agents in a team have the same starting node. The adversary decides the compositions of teams, and their starting nodes. Whenever an agent enters a node, it sees the entry port number and the states of all collocated agents; this information forms the input of the agent on the basis of which it transits to the next state and decides the current action. The aim is for all agents to gather at the same node and stop. Gathering is feasible, if this task can be accomplished for any decisions of the adversary, and its time is the worst-case number of rounds from the start till gathering.
We consider the feasibility and time complexity of gathering teams of agents, and give a complete solution of this problem. It turns out that both feasibility and complexity of gathering depend on the crucial parameter x which is the size of teams. For the oriented line, gathering is impossible if x = 1, and it can be accomplished in time O(D), for x > 1, where D is the distance between the starting nodes of the most distant teams. This complexity is of course optimal. For the unoriented line, the situation is different. For x = 1, gathering is also impossible, but for x = 2, the optimal time of gathering is Θ(Dlog L), and for x ≥ 3 the optimal time of gathering is Θ(D).
Solving the gathering problem for agents that are finite automata navigating in an infinite environment requires new methodological tools. Traditional gathering techniques in graphs are count driven: agents make decisions based on counting steps. Since distances between agents may be unbounded, agents have to count unbounded numbers of steps. When agents are finite automata, counting unbounded numbers of steps is impossible, hence we must use different methods. In all our gathering algorithms, changes of the agents' behavior are triggered not by counting steps but by events which are meetings between agents during which they interact. Hence our new technique is event driven. Designing the behavior of the agents based on meeting events, so as to guarantee gathering regardless of the adversary’s decisions is our main methodological contribution.
Cite as
Younan Gao and Andrzej Pelc. Gathering Teams of Deterministic Finite Automata on a Line. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 11:1-11:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{gao_et_al:LIPIcs.OPODIS.2024.11,
author = {Gao, Younan and Pelc, Andrzej},
title = {{Gathering Teams of Deterministic Finite Automata on a Line}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {11:1--11:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.11},
URN = {urn:nbn:de:0030-drops-225478},
doi = {10.4230/LIPIcs.OPODIS.2024.11},
annote = {Keywords: Gathering, deterministic finite automaton, mobile agent, team of agents, line, time}
}
Document
Crash-Tolerant Perpetual Exploration with Myopic Luminous Robots on Rings
Abstract
We investigate crash-tolerant perpetual exploration algorithms by myopic luminous robots on ring networks. Myopic robots mean that they can observe nodes only within a certain fixed distance ϕ, and luminous robots mean that they have light devices that can emit a color from a set of colors. The goal of perpetual exploration is to ensure that robots, starting from specific initial positions and colors, move in such a way that every node is visited by at least one robot infinitely often. As a main contribution, we clarify the tight necessary and sufficient number of robots to realize perpetual exploration when at most f robots crash. In the fully synchronous model, we prove that f+2 robots are necessary and sufficient for any ϕ ≥ 1. In the semi-synchronous and asynchronous models, we prove that 3f+3 (resp., 2f+2) robots are necessary and sufficient if ϕ = 1 (resp., ϕ ≥ 2).
Cite as
Fukuhito Ooshita, Naoki Kitamura, Ryota Eguchi, Michiko Inoue, Hirotsugu Kakugawa, Sayaka Kamei, Masahiro Shibata, and Yuichi Sudo. Crash-Tolerant Perpetual Exploration with Myopic Luminous Robots on Rings. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 12:1-12:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{ooshita_et_al:LIPIcs.OPODIS.2024.12,
author = {Ooshita, Fukuhito and Kitamura, Naoki and Eguchi, Ryota and Inoue, Michiko and Kakugawa, Hirotsugu and Kamei, Sayaka and Shibata, Masahiro and Sudo, Yuichi},
title = {{Crash-Tolerant Perpetual Exploration with Myopic Luminous Robots on Rings}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {12:1--12:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.12},
URN = {urn:nbn:de:0030-drops-225486},
doi = {10.4230/LIPIcs.OPODIS.2024.12},
annote = {Keywords: mobile robots, crash faults, LCM model, exploration}
}
Document
Symmetry Preservation in Swarms of Oblivious Robots with Limited Visibility
Abstract
In the general pattern formation (GPF) problem, a swarm of simple autonomous, disoriented robots must form a given pattern. The robots' simplicity imply a strong limitation: When the initial configuration is rotationally symmetric, only patterns with a similar symmetry can be formed [Masafumi Yamashita and Ichiro Suzuki, 2010]. The only known algorithm to form large patterns with limited visibility and without memory requires the robots to start in a near-gathering (a swarm of constant diameter) [Christopher Hahn et al., 2024]. However, not only do we not know any near-gathering algorithm guaranteed to preserve symmetry but most natural gathering strategies trivially increase symmetries [Jannik Castenow et al., 2022].
Thus, we study near-gathering without changing the swarm’s rotational symmetry for disoriented, oblivious robots with limited visibility (the OBLOT-model, see [Paola Flocchini et al., 2019]). We introduce a technique based on the theory of dynamical systems to analyze how a given algorithm affects symmetry and provide sufficient conditions for symmetry preservation. Until now, it was unknown whether the considered OBLOT-model allows for any non-trivial algorithm that always preserves symmetry. Our first result shows that a variant of Go-To-The-Average always preserves symmetry but may sometimes lead to multiple, unconnected near-gathering clusters. Our second result is a symmetry-preserving near-gathering algorithm that works on swarms with a convex boundary (the outer boundary of the unit disc graph) and without "holes" (circles of diameter 1 inside the boundary without any robots).
Cite as
Raphael Gerlach, Sören von der Gracht, Christopher Hahn, Jonas Harbig, and Peter Kling. Symmetry Preservation in Swarms of Oblivious Robots with Limited Visibility. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 13:1-13:28, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{gerlach_et_al:LIPIcs.OPODIS.2024.13,
author = {Gerlach, Raphael and von der Gracht, S\"{o}ren and Hahn, Christopher and Harbig, Jonas and Kling, Peter},
title = {{Symmetry Preservation in Swarms of Oblivious Robots with Limited Visibility}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {13:1--13:28},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.13},
URN = {urn:nbn:de:0030-drops-225490},
doi = {10.4230/LIPIcs.OPODIS.2024.13},
annote = {Keywords: Swarm Algorithm, Swarm Robots, Distributed Algorithm, Pattern Formation, Limited Visibility, Oblivious}
}
Document
Near-Optimal Communication Byzantine Reliable Broadcast Under a Message Adversary
Abstract
We address the problem of Reliable Broadcast in asynchronous message-passing systems with n nodes, of which up to t are malicious (faulty), in addition to a message adversary that can drop some of the messages sent by correct (non-faulty) nodes. We present a Message-Adversary-Tolerant Byzantine Reliable Broadcast (MBRB) algorithm that communicates O(|m|+nκ) bits per node, where |m| represents the length of the application message and κ = Ω(log n) is a security parameter. This communication complexity is optimal up to the parameter κ. This significantly improves upon the state-of-the-art MBRB solution (Albouy, Frey, Raynal, and Taïani, TCS 2023), which incurs communication of O(n|m|+n²κ) bits per node. Our solution sends at most 4n² messages overall, which is asymptotically optimal. Reduced communication is achieved by employing coding techniques that replace the need for all nodes to (re-)broadcast the entire application message m. Instead, nodes forward authenticated fragments of the encoding of m using an erasure-correcting code. Under the cryptographic assumptions of threshold signatures and vector commitments, and assuming n > 3t+2d, where the adversary drops at most d messages per broadcast, our algorithm allows at least 𝓁 = n - t - (1 + ε)d (for any arbitrarily low ε > 0) correct nodes to reconstruct m, despite missing fragments caused by the malicious nodes and the message adversary.
Cite as
Timothé Albouy, Davide Frey, Ran Gelles, Carmit Hazay, Michel Raynal, Elad Michael Schiller, François Taïani, and Vassilis Zikas. Near-Optimal Communication Byzantine Reliable Broadcast Under a Message Adversary. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 14:1-14:29, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{albouy_et_al:LIPIcs.OPODIS.2024.14,
author = {Albouy, Timoth\'{e} and Frey, Davide and Gelles, Ran and Hazay, Carmit and Raynal, Michel and Schiller, Elad Michael and Ta\"{i}ani, Fran\c{c}ois and Zikas, Vassilis},
title = {{Near-Optimal Communication Byzantine Reliable Broadcast Under a Message Adversary}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {14:1--14:29},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.14},
URN = {urn:nbn:de:0030-drops-225503},
doi = {10.4230/LIPIcs.OPODIS.2024.14},
annote = {Keywords: Asynchronous message-passing, Byzantine fault-tolerance, Message adversary, Reliable broadcast, Erasure-correction codes, \{Threshold\} signatures, \{Vector commitments\}}
}
Document
Quit-Resistant Reliable Broadcast and Efficient Terminating Gather
Abstract
Termination is a central property in distributed computing. A party terminates a protocol once it stops accepting and sending messages. We discover that byzantine reliable broadcast is sometimes used in a manner which leads to non-terminating protocols. We consider an asynchronous network of n parties up to t of which are byzantine, and show that if each party is to broadcast its value and terminate upon obtaining n - t values, then composing n parallel reliable broadcast instances leads to non-termination. The issue is that a party must quit t broadcast instances early in order to terminate, a behaviour not supported by ordinary reliable broadcast. So, we modify Bracha’s protocol into a quit-resistant reliable broadcast (QBRB) protocol which lets the parties quit early. This protocol retains its termination guarantees as long as no party quits before some party terminates.
Then, we turn our attention to Gather, an all-to-all broadcast primitive which guarantees that the parties obtain n - t common values. Existing error-free deterministic Gather protocols either run forever, or fail to terminate since the parties quit reliable broadcast instances. We design an error-free, deterministic, terminating (and binding) Gather protocol for 𝓁-bit inputs with the communication complexity 𝒪(𝓁 n² + n³log n). This matches the state-of-the-art for non-terminating Gather.
Finally, inspired by our QBRB protocol, we design a reliable broadcast protocol which retains its termination guarantees no matter when any party quits. To achieve this, we give each party the option to output ⊥ if more than q parties quit before some party terminates. The protocol requires 4t + q < n, which is optimal, and it lets parties quit after they have suffered transient crash failures so that they can help the remaining parties terminate.
Cite as
Mose Mizrahi Erbes and Roger Wattenhofer. Quit-Resistant Reliable Broadcast and Efficient Terminating Gather. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 15:1-15:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{mizrahierbes_et_al:LIPIcs.OPODIS.2024.15,
author = {Mizrahi Erbes, Mose and Wattenhofer, Roger},
title = {{Quit-Resistant Reliable Broadcast and Efficient Terminating Gather}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {15:1--15:22},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.15},
URN = {urn:nbn:de:0030-drops-225519},
doi = {10.4230/LIPIcs.OPODIS.2024.15},
annote = {Keywords: Asynchronous networks, byzantine fault tolerance, protocol termination, reliable broadcast, all-to-all broadcast, gather}
}
Document
Byzantine Reliable Broadcast with Low Communication and Time Complexity
Abstract
Byzantine reliable broadcast is a fundamental problem in distributed computing, which has been studied extensively over the past decades. State-of-the-art algorithms are predominantly based on the approach to share encoded fragments of the broadcast message, yielding an asymptotically optimal communication complexity when the message size exceeds the network size, a condition frequently encountered in practice. However, algorithms following the standard coding approach incur an overhead factor of at least 3, which can already be a burden for bandwidth-constrained applications. Minimizing this overhead is an important objective with immediate benefits to protocols that use a reliable broadcast routine as a building block.
This paper introduces a novel mechanism to lower the communication and computational complexity. Two algorithms are presented that employ this mechanism to reliably broadcast messages in an asynchronous network where less than a third of all nodes are Byzantine. The first algorithm reduces the overhead factor to 2 and has a time complexity of 3 if the sender is honest, whereas the second algorithm attains an optimal time complexity of 2 with the same overhead factor in the absence of equivocation. Moreover, an optimization is proposed that reduces the overhead factor to 3/2 under normal operation in practice. Lastly, a lower bound is proved that an overhead factor lower than 3/2 cannot be achieved for a relevant class of reliable broadcast algorithms.
Cite as
Thomas Locher. Byzantine Reliable Broadcast with Low Communication and Time Complexity. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 16:1-16:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{locher:LIPIcs.OPODIS.2024.16,
author = {Locher, Thomas},
title = {{Byzantine Reliable Broadcast with Low Communication and Time Complexity}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {16:1--16:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.16},
URN = {urn:nbn:de:0030-drops-225524},
doi = {10.4230/LIPIcs.OPODIS.2024.16},
annote = {Keywords: Asynchronous Networks, Reliable Broadcast, Communication Complexity}
}
Document
Perpetual Exploration of a Ring in Presence of Byzantine Black Hole
Abstract
Perpetual exploration stands as a fundamental problem in the domain of distributed mobile agent algorithms, where the objective is to ensure that each node within a graph is visited by at least one agent infinitely often. While this issue has received significant attention, particularly concerning ring topologies, the presence of malicious nodes, referred to as black holes, adds more complexity. A black hole can destroy any incoming agent without leaving any trace of its existence.
In [Bampas et al., 2015; Královič and Miklík, 2010], the authors have considered this problem in the context of periodic data retrieval. They introduced a variant of a black hole called gray hole (where the adversary chooses whether to destroy an agent or let it pass) among other variants, and showed that 4 asynchronous and co-located agents are necessary and sufficient to solve the periodic data retrieval problem (hence perpetual exploration) in the presence of such a gray hole if each of the nodes of the ring has a whiteboard.
This paper investigates the exploration of a ring by introducing a realistic variant of a gray hole, called a "Byzantine black hole". In addition to the usual capabilities of a gray hole, the adversary can also choose whether to erase any previously stored information on that node.
Note that in [Bampas et al., 2015; Královič and Miklík, 2010], this problem was considered with only one particular initial scenario (i.e., agents are initially co-located) and one specific communication model (i.e., whiteboard). Now, there can be many other initial scenarios where all agents might not be co-located (i.e., they may be scattered). Also, there are many weaker communications models such as Face-to-Face and Pebble, where this perpetual exploration problem is yet to be investigated in the presence of a Byzantine black hole.
The main results of our paper focus on minimizing the number of agents while guaranteeing that they perform the perpetual exploration on a ring even in the presence of a Byzantine black hole under different communication models and for different starting scenarios. On the positive side, as a byproduct of our work, we achieved a better upper and lower bound result (i.e., 3 agents) for perpetual exploration in the presence of a Byzantine black hole (which is a more generalized version of a gray hole), by trading-off the scheduler capability, when the agents are initially co-located, and each node contains a whiteboard.
Cite as
Pritam Goswami, Adri Bhattacharya, Raja Das, and Partha Sarathi Mandal. Perpetual Exploration of a Ring in Presence of Byzantine Black Hole. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 17:1-17:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{goswami_et_al:LIPIcs.OPODIS.2024.17,
author = {Goswami, Pritam and Bhattacharya, Adri and Das, Raja and Mandal, Partha Sarathi},
title = {{Perpetual Exploration of a Ring in Presence of Byzantine Black Hole}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {17:1--17:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.17},
URN = {urn:nbn:de:0030-drops-225532},
doi = {10.4230/LIPIcs.OPODIS.2024.17},
annote = {Keywords: Mobile Agents, Exploration, Ring, Black Hole, Malicious host, Byzantine Fault}
}
Document
Stabilizing Consensus Is Impossible in Lossy Iterated Immediate Snapshot Models
Abstract
A substantial portion of distributed computing research is dedicated to terminating problems like consensus and similar agreement problems. However, non-terminating problems have been intensively studied in the context of self-stabilizing distributed algorithms, where processes may start from arbitrary initial states and can tolerate arbitrary transient faults. In between lie stabilizing problems, where the processes start from a well-defined initial state, but do not need to decide irrevocably and are allowed to change their decision finitely often until a stable decision is eventually reached.
Stabilizing consensus has been studied within the context of synchronous message adversaries. In particular, Charron-Bost and Moran showed that a necessary condition for stabilizing consensus is the existence of at least one process that reaches all others infinitely often (a perpetual broadcaster). However, it was left open whether this is also a sufficient condition for solving stabilizing consensus.
In this paper, we introduce the novel Delayed Lossy-Link (DLL) model, and the Lossy Iterated Immediate Snapshot Model (LIIS), for which we show stabilizing consensus to be impossible. The DLL model is introduced as a variant of the well-known Lossy-Link model, which admits silence periods of arbitrary but finite length. The LIIS model is a variant of the Iterated Immediate Snapshot (IIS), model which admits finite length periods of at most f omission faults per layer. In particular, we show that stabilizing consensus is impossible even when f = 1.
Our results show that even in a model with very strong connectivity, namely, the Iterated Immediate Snapshot (IIS) model, a single omission fault per layer effectively disables stabilizing consensus. Furthermore, since the DLL model always has a perpetual broadcaster, the mere existence of a perpetual broadcaster, even in a crash-free setting, is not sufficient for solving stabilizing consensus, negatively answering the open question posed by Charron-Bost and Moran.
Cite as
Stephan Felber and Hugo Rincon Galeana. Stabilizing Consensus Is Impossible in Lossy Iterated Immediate Snapshot Models. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 18:1-18:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{felber_et_al:LIPIcs.OPODIS.2024.18,
author = {Felber, Stephan and Rincon Galeana, Hugo},
title = {{Stabilizing Consensus Is Impossible in Lossy Iterated Immediate Snapshot Models}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {18:1--18:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.18},
URN = {urn:nbn:de:0030-drops-225544},
doi = {10.4230/LIPIcs.OPODIS.2024.18},
annote = {Keywords: distributed systems, dynamic networks, dynamic graphs, message adversaries, stabilizing consensus, asynchronous message passing}
}
Document
A General Class of Reductions and Extension-Based Proofs
Abstract
The concept of extension-based proofs models the idea of a valency argument which is widely used in distributed computing. Extension-based proofs have been shown to be limited in power: there is no extension-based proof of the impossibility of a wait-free protocol for (n,k)-set agreement among n > k ≥ 2 processes.
Previous work used a restricted class of reductions to show that there are no extension-based proofs of the impossibility of wait-free protocols for some other distributed computing problems. It is known that for a restricted class of reductions, if a task 𝒯 reduces to 𝒮 and 𝒯 has an augmented extension-based proof that it is impossible to solve in the NIS model, then so does 𝒮. We introduce multiple-instance extension-based proofs and show that, if 𝒯 reduces to multiple instances of 𝒮, instead of just one instance and 𝒯 has an augmented extension-based proof, then 𝒮 has a multiple-instance extension-based proof that it is impossible to solve in the NIIS model. We introduce a new version of extension-based proofs that can further our understanding of extension-based proofs and their limitations.
Cite as
Yusong Shi and Weidong Liu. A General Class of Reductions and Extension-Based Proofs. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 19:1-19:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{shi_et_al:LIPIcs.OPODIS.2024.19,
author = {Shi, Yusong and Liu, Weidong},
title = {{A General Class of Reductions and Extension-Based Proofs}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {19:1--19:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.19},
URN = {urn:nbn:de:0030-drops-225559},
doi = {10.4230/LIPIcs.OPODIS.2024.19},
annote = {Keywords: Reductions, Impossibility proofs, Extension-based proof}
}
Document
How Robust Are Synchronous Consensus Protocols?
Abstract
Synchronous Byzantine fault-tolerant (BFT) protocols have long been a reality in an academic setting, yet their practicality remains debated. The main concern of skeptics of synchronous systems is that the correctness of these protocols depends on the timely delivery of all messages within a predefined synchronous bound, Δ. This dependency creates a challenging tradeoff between protocol correctness and performance, as Δ directly impacts both. In this paper, we examine this tradeoff in detail. Specifically, we introduce BoundBFT, a new synchronous BFT consensus protocol. We analyze how BoundBFT’s correctness can be compromised and use this analysis to design and implement the most effective attack strategies that malicious processes could employ. Furthermore, we experimentally determine the synchronous bound Δ that provides sufficient confidence in maintaining protocol correctness even in the presence of malicious replicas. Finally, we apply this discovered bound to BoundBFT, evaluate its performance, and compare it to state-of-the-art synchronous and partially synchronous protocols.
Cite as
Nenad Milošević, Daniel Cason, Zarko Milošević, and Fernando Pedone. How Robust Are Synchronous Consensus Protocols?. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 20:1-20:25, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{milosevic_et_al:LIPIcs.OPODIS.2024.20,
author = {Milo\v{s}evi\'{c}, Nenad and Cason, Daniel and Milo\v{s}evi\'{c}, Zarko and Pedone, Fernando},
title = {{How Robust Are Synchronous Consensus Protocols?}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {20:1--20:25},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.20},
URN = {urn:nbn:de:0030-drops-225560},
doi = {10.4230/LIPIcs.OPODIS.2024.20},
annote = {Keywords: Synchronous Consensus, Byzantine Failures, Blockchain}
}
Document
No Symmetric Broadcast Abstraction Characterizes k-Set-Agreement in Message-Passing Systems
Abstract
This paper explores the relationship between broadcast abstractions and the k-set agreement (k-SA) problem in crash-prone asynchronous distributed systems. It specifically investigates whether any broadcast abstraction is computationally equivalent to k-SA in message-passing systems.
A key contribution of the paper is the delineation of the realm of "meaningful" broadcast abstractions, through the introduction of two new symmetry properties: compositionality and content-neutrality, inspired by the principle of network neutrality. Such preciseness in definition is essential for this paper’s scope, as our aim is not to characterize the computing power of a specific broadcast abstraction, but rather to explore the domain of broadcast abstractions as a whole, in search of a broadcast abstraction with certain characteristics. The paper’s main contribution is the proof that no broadcast abstraction, which is both content-neutral and compositional, is computationally equivalent to k-set agreement when 1 < k < n, in the crash-prone asynchronous message-passing model. To the best of our knowledge, this result represents the first instance of showing that a coordination problem cannot be expressed by an equivalent broadcast abstraction. It does not establish the absence of an implementation, but rather the absence of a specification that possesses certain properties.
Cite as
Sylvain Gay, Achour Mostéfaoui, and Matthieu Perrin. No Symmetric Broadcast Abstraction Characterizes k-Set-Agreement in Message-Passing Systems. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 21:1-21:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{gay_et_al:LIPIcs.OPODIS.2024.21,
author = {Gay, Sylvain and Most\'{e}faoui, Achour and Perrin, Matthieu},
title = {{No Symmetric Broadcast Abstraction Characterizes k-Set-Agreement in Message-Passing Systems}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {21:1--21:20},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.21},
URN = {urn:nbn:de:0030-drops-225573},
doi = {10.4230/LIPIcs.OPODIS.2024.21},
annote = {Keywords: Agreement problem, Asynchronous system, Broadcast abstraction, Communication abstraction, Compositionality, Message-passing system, Network neutrality, Process crash, k-Set agreement, Wait-free model, Total order broadcast}
}
Document
FaaSLoad: Fine-Grained Performance and Resource Measurement for Function-As-a-Service
Abstract
Cloud computing relies on a deep stack of system layers: virtual machine, operating system, distributed middleware and language runtime. However, those numerous, distributed, virtual layers prevent any low-level understanding of the properties of FaaS applications, considered as programs running on real hardware. As a result, most research analyses only consider coarse-grained properties such as global performance of an application, and existing datasets include only sparse data.
FaaSLoad is a tool to gather fine-grained data about performance and resource usage of the programs that run on Function-as-a-Service cloud platforms. It considers individual instances of functions to collect hardware and operating-system performance information, by monitoring them while injecting a workload. FaaSLoad helps building a dataset of function executions to train machine learning models, studying at fine grain the behavior of function runtimes, and replaying real workload traces for in situ observations.
This research software project aims at being useful to cloud system researchers with features such as guaranteeing reproducibility and correctness, and keeping up with realistic FaaS workloads. Our evaluations show that FaaSLoad helps us understanding the properties of FaaS applications, and studying the latter under real conditions.
Cite as
Mathieu Bacou. FaaSLoad: Fine-Grained Performance and Resource Measurement for Function-As-a-Service. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 22:1-22:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{bacou:LIPIcs.OPODIS.2024.22,
author = {Bacou, Mathieu},
title = {{FaaSLoad: Fine-Grained Performance and Resource Measurement for Function-As-a-Service}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {22:1--22:21},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.22},
URN = {urn:nbn:de:0030-drops-225581},
doi = {10.4230/LIPIcs.OPODIS.2024.22},
annote = {Keywords: cloud, serverless, Function-as-a-Service, measurement, performance, resource utilization, dataset generation, workload injection}
}
Document
Distributed Recoverable Sketches
Abstract
Sketches are commonly used in computer systems and network monitoring tools to provide efficient query executions while maintaining a compact data representation. Switches and routers maintain sketches to track statistical characteristics of the network traffic. The availability of such data is essential for the network analysis as a whole. Consequently, being able to recover sketches is critical following a switch crash.
In this paper, we explore how nodes in a network environment can cooperate to recover sketch data whenever any of them crashes. In particular, we focus on frequency estimation linear sketches, such as the Count-Min Sketch. We consider various approaches to ensure data reliability and explore the trade-offs between space consumption, runtime overheads, and traffic during recovery, which we point out as design guidelines. Besides different aspects of efficacy, we design a modular system for ease of maintenance and further scaling.
A key aspect we examine is how nodes update each other about their sketch content as it evolves over time. In particular, we compare between periodic full updates vs. incremental updates. We also examine several data structures to economically represent and encode a batch of latest changes. Our framework is generic, and other data structures can be plugged-in via an abstract API as long as they implement the corresponding API methods.
Cite as
Diana Cohen, Roy Friedman, and Rana Shahout. Distributed Recoverable Sketches. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 23:1-23:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{cohen_et_al:LIPIcs.OPODIS.2024.23,
author = {Cohen, Diana and Friedman, Roy and Shahout, Rana},
title = {{Distributed Recoverable Sketches}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {23:1--23:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.23},
URN = {urn:nbn:de:0030-drops-225594},
doi = {10.4230/LIPIcs.OPODIS.2024.23},
annote = {Keywords: Sketches, Stream Processing, Distributed Recovery, Incremental Updates, Sketch Partitioning}
}
Document
Hash & Adjust: Competitive Demand-Aware Consistent Hashing
Abstract
Distributed systems often serve dynamic workloads and resource demands evolve over time. Such a temporal behavior stands in contrast to the static and demand-oblivious nature of most data structures used by these systems. In this paper, we are particularly interested in consistent hashing, a fundamental building block in many large distributed systems. Our work is motivated by the hypothesis that a more adaptive approach to consistent hashing can leverage structure in the demand, and hence improve storage utilization and reduce access time.
We initiate the study of demand-aware consistent hashing. Our main contribution is H&A, a constant-competitive online algorithm (i.e., it comes with provable performance guarantees over time). H&A is demand-aware and optimizes its internal structure to enable faster access times, while offering a high utilization of storage. We further evaluate H&A empirically.
Cite as
Arash Pourdamghani, Chen Avin, Robert Sama, Maryam Shiran, and Stefan Schmid. Hash & Adjust: Competitive Demand-Aware Consistent Hashing. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 24:1-24:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{pourdamghani_et_al:LIPIcs.OPODIS.2024.24,
author = {Pourdamghani, Arash and Avin, Chen and Sama, Robert and Shiran, Maryam and Schmid, Stefan},
title = {{Hash \& Adjust: Competitive Demand-Aware Consistent Hashing}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {24:1--24:23},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.24},
URN = {urn:nbn:de:0030-drops-225607},
doi = {10.4230/LIPIcs.OPODIS.2024.24},
annote = {Keywords: Consistent hashing, demand-awareness, online algorithms}
}
Document
Reliable Communication in Hybrid Authentication and Trust Models
Abstract
Reliable communication is a fundamental distributed communication abstraction that allows any two nodes within a network to communicate with each other. It is necessary for more powerful communication primitives, such as broadcast and consensus. Using different authentication models, two classical protocols implement reliable communication in unknown and sufficiently connected networks. In the former, network links are authenticated, and processes rely on dissemination paths to authenticate messages. In the latter, processes generate digital signatures that are flooded throughout the network. This work considers the hybrid system model that combines authenticated links and authenticated processes. Additionally, we aim to leverage the possible presence of trusted nodes (e.g., network gateways) and trusted components (e.g., Intel SGX enclaves). We first extend the two classical reliable communication protocols to leverage trusted nodes. Then we propose DualRC, our most generic algorithm that considers the hybrid authentication model by manipulating dissemination paths and digital signatures, and leverages the possible presence of trusted nodes and trusted components. We describe and prove methods that establish whether our algorithms implement reliable communication on a given network.
Cite as
Rowdy Chotkan, Bart Cox, Vincent Rahli, and Jérémie Decouchant. Reliable Communication in Hybrid Authentication and Trust Models. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 25:1-25:26, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{chotkan_et_al:LIPIcs.OPODIS.2024.25,
author = {Chotkan, Rowdy and Cox, Bart and Rahli, Vincent and Decouchant, J\'{e}r\'{e}mie},
title = {{Reliable Communication in Hybrid Authentication and Trust Models}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {25:1--25:26},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.25},
URN = {urn:nbn:de:0030-drops-225611},
doi = {10.4230/LIPIcs.OPODIS.2024.25},
annote = {Keywords: Reliable communication, Byzantine, Authentication models, Trust}
}
Document
The Singular Optimality of Distributed Computation in LOCAL
Abstract
It has been shown that one can design distributed algorithms that are (nearly) singularly optimal, meaning they simultaneously achieve optimal time and message complexity (within polylogarithmic factors), for several fundamental global problems such as broadcast, leader election, and spanning tree construction, under the KT₀ assumption. With this assumption, nodes have initial knowledge only of themselves, not their neighbors. In this case the time and message lower bounds are Ω(D) and Ω(m), respectively, where D is the diameter of the network and m is the number of edges, and there exist (even) deterministic algorithms that simultaneously match these bounds.
On the other hand, under the KT₁ assumption, whereby each node has initial knowledge of itself and the identifiers of its neighbors, the situation is not clear. For the KT₁ CONGEST model (where messages are of small size), King, Kutten, and Thorup (KKT) showed that one can solve several fundamental global problems (with the notable exception of BFS tree construction) such as broadcast, leader election, and spanning tree construction with Õ(n) message complexity (n is the network size), which can be significantly smaller than m. Randomization is crucial in obtaining this result. While the message complexity of the KKT result is near-optimal, its time complexity is Õ(n) rounds, which is far from the standard lower bound of Ω(D). An important open question is whether one can achieve singular optimality for the above problems in the KT₁ CONGEST model, i.e., whether there exists an algorithm running in Õ(D) rounds and Õ(n) messages. Another important and related question is whether the fundamental BFS tree construction can be solved with Õ(n) messages (regardless of the number of rounds as long as it is polynomial in n) in KT₁.
In this paper, we show that in the KT₁ LOCAL model (where message sizes are not restricted), singular optimality is achievable. Our main result is that all global problems, including BFS tree construction, can be solved in Õ(D) rounds and Õ(n) messages, where both bounds are optimal up to polylogarithmic factors. Moreover, we show that this can be achieved deterministically.
Cite as
Fabien Dufoulon, Gopal Pandurangan, Peter Robinson, and Michele Scquizzato. The Singular Optimality of Distributed Computation in LOCAL. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 26:1-26:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{dufoulon_et_al:LIPIcs.OPODIS.2024.26,
author = {Dufoulon, Fabien and Pandurangan, Gopal and Robinson, Peter and Scquizzato, Michele},
title = {{The Singular Optimality of Distributed Computation in LOCAL}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {26:1--26:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.26},
URN = {urn:nbn:de:0030-drops-225629},
doi = {10.4230/LIPIcs.OPODIS.2024.26},
annote = {Keywords: Distributed algorithms, round and message complexity, BFS tree construction, leader election}
}
Document
Local Problems in Trees Across a Wide Range of Distributed Models
Abstract
The randomized online-LOCAL model captures a number of models of computing; it is at least as strong as all of these models:
- the classical LOCAL model of distributed graph algorithms,
- the quantum version of the LOCAL model,
- finitely dependent distributions [e.g. Holroyd 2016],
- any model that does not violate physical causality [Gavoille, Kosowski, Markiewicz, DISC 2009],
- the SLOCAL model [Ghaffari, Kuhn, Maus, STOC 2017], and
- the dynamic-LOCAL and online-LOCAL models [Akbari et al., ICALP 2023]. In general, the online-LOCAL model can be much stronger than the LOCAL model. For example, there are locally checkable labeling problems (LCLs) that can be solved with logarithmic locality in the online-LOCAL model but that require polynomial locality in the LOCAL model.
However, in this work we show that in trees, many classes of LCL problems have the same locality in deterministic LOCAL and randomized online-LOCAL (and as a corollary across all the above-mentioned models). In particular, these classes of problems do not admit any distributed quantum advantage.
We present a near-complete classification for the case of rooted regular trees. We also fully classify the super-logarithmic region in unrooted regular trees. Finally, we show that in general trees (rooted or unrooted, possibly irregular, possibly with input labels) problems that are global in deterministic LOCAL remain global also in the randomized online-LOCAL model.
Cite as
Anubhav Dhar, Eli Kujawa, Henrik Lievonen, Augusto Modanese, Mikail Muftuoglu, Jan Studený, and Jukka Suomela. Local Problems in Trees Across a Wide Range of Distributed Models. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 27:1-27:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{dhar_et_al:LIPIcs.OPODIS.2024.27,
author = {Dhar, Anubhav and Kujawa, Eli and Lievonen, Henrik and Modanese, Augusto and Muftuoglu, Mikail and Studen\'{y}, Jan and Suomela, Jukka},
title = {{Local Problems in Trees Across a Wide Range of Distributed Models}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {27:1--27:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.27},
URN = {urn:nbn:de:0030-drops-225633},
doi = {10.4230/LIPIcs.OPODIS.2024.27},
annote = {Keywords: Distributed algorithms, quantum-LOCAL model, randomized online-LOCAL model, locally checkable labeling problems, trees}
}
Document
How Local Constraints Influence Network Diameter and Applications to LCL Generalizations
Abstract
In this paper, we investigate how local rules enforced at every node can influence the topology of a network. More precisely, we establish several results on the diameter of trees as a function of the number of nodes, as listed below. These results have important consequences on the landscape of locally checkable labelings (LCL) on unbounded degree graphs, a case in which our lack of knowledge is in striking contrast with that of bounded degree graphs, that has been intensively studied recently.
First, we show that the diameter of a tree can be controlled very precisely by a local checker (that is, a distributed decision algorithm that accepts a graph iff all nodes accept locally), granted that its checkability radius is at least 2 (and that the target diameter is not too close to n). As a corollary, we prove that the gaps in the landscape of LCLs (in bounded-degree graphs) basically disappear in unbounded degree graphs.
Second, we prove that for checkers at distance 1, the maximum diameter can only be trivial (constant or linear), while the minimum diameter can in addition be Θ(log n) and Θ(n^(1/k)) for k ∈ ℕ. These functions interestingly coincide with the known regimes for LCLs.
Third, we explore computational restrictions of local checkers. In particular, we introduce a class of checkers, that we call degree-myopic, that cannot distinguish perfectly the degrees of their neighbors. With these checkers, we show that the maximum diameter can only be O(1), Θ(√n), Θ((log n)/(log log n)), Θ(log n), or Ω(n). Since gaps do appear in the maximum diameter, one can hope that an interesting LCL landscape exists for restricted local checkers.
In addition to the LCL motivation, we hope that our distributed lenses can help give a new point of view on how global structures, such as living beings, can be maintained by local phenomena; understanding the trade-off between the power of the checking and the possible resulting shapes.
Cite as
Nicolas Bousquet, Laurent Feuilloley, and Théo Pierron. How Local Constraints Influence Network Diameter and Applications to LCL Generalizations. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 28:1-28:28, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{bousquet_et_al:LIPIcs.OPODIS.2024.28,
author = {Bousquet, Nicolas and Feuilloley, Laurent and Pierron, Th\'{e}o},
title = {{How Local Constraints Influence Network Diameter and Applications to LCL Generalizations}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {28:1--28:28},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.28},
URN = {urn:nbn:de:0030-drops-225643},
doi = {10.4230/LIPIcs.OPODIS.2024.28},
annote = {Keywords: Locally checkable labelings, network diameter, local checkers, LOCAL model}
}
Document
On Reliability of the Extrema Propagation Technique in Random Environment
Abstract
We study the reliability of the following simple mechanism for spreading information in a communication network in the presence of random message loss. Initially, some nodes have information that they want to distribute throughout the network. Each node that has received the information tries to broadcast it to all its neighbors. However, due to interference or communication failures, each transmission between two nodes is broken independently with some fixed probability.
This transmission mechanism is the basis for the extrema propagation technique, proposed and analyzed in [Carlos Baquero et al., 2012; Baquero et al., 2009; Jacek Cicho{ń} et al., 2012]. Extrema propagation is a simple but powerful method of spreading the extreme values stored by the nodes. In a fully reliable environment, only the number of rounds equal to the network diameter is required for all nodes to be informed. It was shown empirically in [Carlos Baquero et al., 2012] that it also performs well in the presence of link failures and message loss. Extrema propagation is an algorithmic framework that was adopted for designing efficient method for distributed data aggregation, such as estimation of cardinalities, sums, and averages, estimation of data distribution via histograms and random sampling (cf. [Baquero et al., 2009; Karol Gotfryd and Jacek Cichoń, 2023]).
In this paper, we propose a formal network model in which random transmission failures occur and analyze the operation time of the extrema propagation technique for any connected network graph. We provide new general probabilistic upper bounds on the number of rounds needed to spread the extreme values that depend only on the number of nodes, the diameter of the network, and the probability of successful transmission. For some special families of graphs, we also derive specific, more accurate estimates. Our theoretical and experimental results confirm the reliability and efficiency of the extrema propagation technique in faulty or noisy environments.
Cite as
Jacek Cichoń, Dawid Dworzański, and Karol Gotfryd. On Reliability of the Extrema Propagation Technique in Random Environment. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 29:1-29:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{cichon_et_al:LIPIcs.OPODIS.2024.29,
author = {Cicho\'{n}, Jacek and Dworza\'{n}ski, Dawid and Gotfryd, Karol},
title = {{On Reliability of the Extrema Propagation Technique in Random Environment}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {29:1--29:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.29},
URN = {urn:nbn:de:0030-drops-225657},
doi = {10.4230/LIPIcs.OPODIS.2024.29},
annote = {Keywords: wireless ad-hoc networks, extrema propagation, distributed data aggregation, fault tolerant aggregation, randomly evolving networks}
}
Document
Fast, Fair and Truthful Distributed Stable Matching for Common Preferences
Abstract
Stable matching is a fundamental problem studied both in economics and computer science. The task is to find a matching between two sides of agents that have preferences over who they want to be matched with. A matching is stable if no pair of agents prefer each other over their current matches. The deferred acceptance algorithm of Gale and Shapley solves this problem in polynomial time. Further, it is a mechanism: the proposing side in the algorithm is always incentivised to report their preferences truthfully.
The deferred acceptance algorithm has a natural interpretation as a distributed algorithm (and thus a distributed mechanism). However, the algorithm is slow in the worst case and it is known that the stable matching problem cannot be solved efficiently in the distributed setting. In this work we study a natural special case of the stable matching problem where all agents on one of the two sides share common preferences. We show that in this case the deferred acceptance algorithm does yield a fast and truthful distributed mechanism for finding a stable matching. We show how algorithms for sampling random colorings can be used to break ties fairly and extend the results to fractional stable matching.
Cite as
Juho Hirvonen and Sara Ranjbaran. Fast, Fair and Truthful Distributed Stable Matching for Common Preferences. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 30:1-30:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{hirvonen_et_al:LIPIcs.OPODIS.2024.30,
author = {Hirvonen, Juho and Ranjbaran, Sara},
title = {{Fast, Fair and Truthful Distributed Stable Matching for Common Preferences}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {30:1--30:20},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.30},
URN = {urn:nbn:de:0030-drops-225666},
doi = {10.4230/LIPIcs.OPODIS.2024.30},
annote = {Keywords: stable matching, deferred acceptance, local algorithm, mechanism design}
}
Document
Dynamic Probabilistic Reliable Broadcast
Abstract
Byzantine reliable broadcast is a fundamental primitive in distributed systems that allows a set of processes to agree on a message broadcast by a dedicated process, even when some of them are malicious (Byzantine). It guarantees that no two correct processes deliver different messages, and if a message is delivered by a correct process, every correct process eventually delivers one. Byzantine reliable broadcast protocols are known to scale poorly, as they require Ω(n²) message exchanges, where n is the number of system members. The quadratic cost can be explained by the inherent need for every process to relay a message to every other process.
In this paper, we explore ways to overcome this limitation by casting the problem to the probabilistic setting. We propose a solution in which every broadcast message is validated by a small set of witnesses, which allows us to maintain low latency and small communication complexity. In order to tolerate the slow adaptive adversary, we dynamically select the witnesses through a novel stream-local hash function: given a stream of inputs, it generates a stream of output hashed values that adapts to small deviations of the inputs.
Our performance analysis shows that the proposed solution exhibits significant scalability gains over state-of-the-art protocols.
Cite as
João Paulo Bezerra, Veronika Anikina, Petr Kuznetsov, Liron Schiff, and Stefan Schmid. Dynamic Probabilistic Reliable Broadcast. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 31:1-31:30, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{bezerra_et_al:LIPIcs.OPODIS.2024.31,
author = {Bezerra, Jo\~{a}o Paulo and Anikina, Veronika and Kuznetsov, Petr and Schiff, Liron and Schmid, Stefan},
title = {{Dynamic Probabilistic Reliable Broadcast}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {31:1--31:30},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.31},
URN = {urn:nbn:de:0030-drops-225679},
doi = {10.4230/LIPIcs.OPODIS.2024.31},
annote = {Keywords: Reliable broadcast, probabilistic algorithms, witness sets, stream-local hashing, cryptocurrencies, accountability}
}
Document
Distributed Agreement in the Arrovian Framework
Abstract
Preference aggregation is a fundamental problem in voting theory, in which public input rankings of a set of alternatives (called preferences) must be aggregated into a single preference that satisfies certain soundness properties. The celebrated Arrow Impossibility Theorem is equivalent to a distributed task in a synchronous fault-free system that satisfies properties such as respecting unanimous preferences, maintaining independence of irrelevant alternatives (IIA), and non-dictatorship, along with consensus since only one preference can be decided.
In this work, we study a weaker distributed task in which crash faults are introduced, IIA is not required, and the consensus property is relaxed to either k-set agreement or ε-approximate agreement using any metric on the set of preferences. In particular, we prove several novel impossibility results for both of these tasks in both synchronous and asynchronous distributed systems. We additionally show that the impossibility for our ε-approximate agreement task using the Kendall tau or Spearman footrule metrics holds under extremely weak assumptions.
Cite as
Kenan Wood, Hammurabi Mendes, and Jonad Pulaj. Distributed Agreement in the Arrovian Framework. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 32:1-32:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{wood_et_al:LIPIcs.OPODIS.2024.32,
author = {Wood, Kenan and Mendes, Hammurabi and Pulaj, Jonad},
title = {{Distributed Agreement in the Arrovian Framework}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {32:1--32:18},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.32},
URN = {urn:nbn:de:0030-drops-225686},
doi = {10.4230/LIPIcs.OPODIS.2024.32},
annote = {Keywords: Approximate Agreement, Set Agreement, Preference Aggregation, Voting Theory, Impossibility}
}
Document
Self-Stabilizing Fully Adaptive Maximal Matching
Abstract
A self-stabilizing randomized algorithm for mending maximal matching (MM) in synchronous networks is presented. Starting from a legal MM configuration and assuming that the network undergoes k faults or topology changes (that may occur in multiple batches), the algorithm is guaranteed to stabilize back to a legal MM configuration in time O(log k) in expectation and with high probability (in k), using constant size messages. The algorithm is simple to implement and is uniform in the sense that it does not assume unique identifiers, nor does it assume any global knowledge of the communication graph including its size. It relies on a generic probabilistic phase synchronization technique that may be useful for other self-stabilizing problems. The algorithm compares favorably with the existing self-stabilizing MM algorithms in terms of the dependence of its run-time on k, a.k.a. fully adaptive run-time. In fact, this dependence is asymptotically optimal for uniform algorithms that use constant size messages.
Cite as
Shimon Bitton, Yuval Emek, Taisuke Izumi, and Shay Kutten. Self-Stabilizing Fully Adaptive Maximal Matching. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 33:1-33:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{bitton_et_al:LIPIcs.OPODIS.2024.33,
author = {Bitton, Shimon and Emek, Yuval and Izumi, Taisuke and Kutten, Shay},
title = {{Self-Stabilizing Fully Adaptive Maximal Matching}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {33:1--33:21},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.33},
URN = {urn:nbn:de:0030-drops-225698},
doi = {10.4230/LIPIcs.OPODIS.2024.33},
annote = {Keywords: self-stabilization, maximal matching, fully adaptive run-time, dynamic graphs}
}
Document
Quantum Simultaneous Protocols Without Public Coins Using Modified Equality Queries
Abstract
In this paper we study a quantum version of the multiparty simultaneous message-passing (SMP) model, and we show that in some cases, quantum communication can replace public randomness, even with no entanglement between the parties. This was already known for two players, but not for more than two players, and indeed, so far all that was known was a negative result. Our main technical contribution is a compiler that takes any classical public-coin simultaneous protocol based on "modified equality queries," and converts it into a quantum simultaneous protocol without public coins with roughly the same communication complexity. We then use our compiler to derive protocols for several problems, including frequency moments, neighborhood diversity, enumeration of isolated cliques, and more.
Cite as
François Le Gall, Oran Nadler, Harumichi Nishimura, and Rotem Oshman. Quantum Simultaneous Protocols Without Public Coins Using Modified Equality Queries. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 34:1-34:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{legall_et_al:LIPIcs.OPODIS.2024.34,
author = {Le Gall, Fran\c{c}ois and Nadler, Oran and Nishimura, Harumichi and Oshman, Rotem},
title = {{Quantum Simultaneous Protocols Without Public Coins Using Modified Equality Queries}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {34:1--34:20},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.34},
URN = {urn:nbn:de:0030-drops-225701},
doi = {10.4230/LIPIcs.OPODIS.2024.34},
annote = {Keywords: SMP model, multi-party communication, quantum distributed algorithms}
}
Document
Near-Optimal Resilient Labeling Schemes
Abstract
Labeling schemes are a prevalent paradigm in various computing settings. In such schemes, an oracle is given an input graph and produces a label for each of its nodes, enabling the labels to be used for various tasks. Fundamental examples in distributed settings include distance labeling schemes, proof labeling schemes, advice schemes, and more. This paper addresses the question of what happens in a labeling scheme if some labels are erased, e.g., due to communication loss with the oracle or hardware errors. We adapt the notion of resilient proof-labeling schemes of Fischer, Oshman, Shamir [OPODIS 2021] and consider resiliency in general labeling schemes. A resilient labeling scheme consists of two parts - a transformation of any given labeling to a new one, executed by the oracle, and a distributed algorithm in which the nodes can restore their original labels given the new ones, despite some label erasures.
Our contribution is a resilient labeling scheme that can handle F such erasures. Given a labeling of 𝓁 bits per node, it produces new labels with multiplicative and additive overheads of O(1) and O(log(F)), respectively. The running time of the distributed reconstruction algorithm is O(F+(𝓁⋅F)/log n) in the Congest model.
This improves upon what can be deduced from the work of Bick, Kol, and Oshman [SODA 2022], for non-constant values of F. It is not hard to show that the running time of our distributed algorithm is optimal, making our construction near-optimal, up to the additive overhead in the label size.
Cite as
Keren Censor-Hillel and Einav Huberman. Near-Optimal Resilient Labeling Schemes. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 35:1-35:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{censorhillel_et_al:LIPIcs.OPODIS.2024.35,
author = {Censor-Hillel, Keren and Huberman, Einav},
title = {{Near-Optimal Resilient Labeling Schemes}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {35:1--35:22},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.35},
URN = {urn:nbn:de:0030-drops-225713},
doi = {10.4230/LIPIcs.OPODIS.2024.35},
annote = {Keywords: Labeling schemes, Erasures}
}
Document
Distributed Branching Random Walks and Their Applications
Abstract
In recent years, the explosion of big data and analytics has necessitated distributed storage and processing with several compute nodes (e.g., multiple datacenters). These nodes collaboratively perform parallel computation, where the data is typically partitioned across these nodes to ensure scalability, redundancy and load-balancing. But the nodes may not always be co-located; in many cases, they are part of a larger communication network. Since those nodes only need to communicate among themselves, a key challenge is to design efficient routes catered to that subnetwork.
In this work, we initiate the study of distributed sampling and routing problems for subnetworks in any well-connected network. Given any network G = (V, E) with mixing time τ_mix, consider the canonical problem of permutation routing [Ghaffari, Kuhn and Su, PODC 2017] that aims to minimize both congestion and dilation of the routes, where the demands (i.e., set of source-terminal pairs) are such that each node sends or receives number of messages proportional to its degree. We show that the permutation routing problem, when demands are restricted to any subset S ⊆ V (i.e., subnetwork), can be solved in exp(O(√(log|S|))) ⋅ Õ(τ_mix) rounds (where Õ(⋅) hides polylogarithmic factors of |V|). This means that the running time depends subpolynomially on the subnetwork size (i.e., not on the entire network size). The ability to solve permutation routing efficiently immediately implies that a large class of parallel algorithms can be simulated efficiently on the subnetwork.
As a prerequisite to constructing efficient routes, we design and analyze distributed branching random walks that distribute tokens started by the nodes in the subnetwork. At a high-level, these algorithms operate by always moving each token according to a (lazy) simple random walk, but also branching a token into multiple tokens at some specified intervals; ultimately, if a node starts a branching walk, with its id in a token, then by the end of execution, several tokens with its id would be randomly distributed among the nodes. As these random walks can be started by many nodes, a crucial challenge is to ensure low-congestion, which is a primary focus of this paper.
Cite as
Vijeth Aradhya, Seth Gilbert, and Thorsten Götte. Distributed Branching Random Walks and Their Applications. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 36:1-36:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{aradhya_et_al:LIPIcs.OPODIS.2024.36,
author = {Aradhya, Vijeth and Gilbert, Seth and G\"{o}tte, Thorsten},
title = {{Distributed Branching Random Walks and Their Applications}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {36:1--36:20},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.36},
URN = {urn:nbn:de:0030-drops-225723},
doi = {10.4230/LIPIcs.OPODIS.2024.36},
annote = {Keywords: Distributed Graph Algorithms, Random Walks, Permutation Routing}
}
Document
Almost Time-Optimal Loosely-Stabilizing Leader Election on Arbitrary Graphs Without Identifiers in Population Protocols
Abstract
The population protocol model is a computational model for passive mobile agents. We address the leader election problem, which determines a unique leader on arbitrary communication graphs starting from any configuration. Unfortunately, self-stabilizing leader election is impossible to be solved without knowing the exact number of agents; thus, we consider loosely-stabilizing leader election, which converges to safe configurations in a relatively short time, and holds the specification (maintains a unique leader) for a relatively long time. When agents have unique identifiers, Sudo {et al. }(2019) proposed a protocol that, given an upper bound N for the number of agents n, converges in O(mNlog n) expected steps, where m is the number of edges. When unique identifiers are not required, they also proposed a protocol that, using random numbers and given N, converges in O(mN²log{N}) expected steps. Both protocols have a holding time of Ω(e^{2N}) expected steps and use O(log{N}) bits of memory. They also showed that the lower bound of the convergence time is Ω(mN) expected steps for protocols with a holding time of Ω(e^N) expected steps given N.
In this paper, we propose protocols that do not require unique identifiers. These protocols achieve convergence times close to the lower bound with increasing memory usage. Specifically, given N and an upper bound Δ for the maximum degree, we propose two protocols whose convergence times are O(mNlog n) and O(mNlog N) both in expectation and with high probability. The former protocol uses random numbers, while the latter does not require them. Both protocols utilize O(Δ log N) bits of memory and hold the specification for Ω(e^{2N}) expected steps.
Cite as
Haruki Kanaya, Ryota Eguchi, Taisho Sasada, and Michiko Inoue. Almost Time-Optimal Loosely-Stabilizing Leader Election on Arbitrary Graphs Without Identifiers in Population Protocols. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 37:1-37:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{kanaya_et_al:LIPIcs.OPODIS.2024.37,
author = {Kanaya, Haruki and Eguchi, Ryota and Sasada, Taisho and Inoue, Michiko},
title = {{Almost Time-Optimal Loosely-Stabilizing Leader Election on Arbitrary Graphs Without Identifiers in Population Protocols}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {37:1--37:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.37},
URN = {urn:nbn:de:0030-drops-225734},
doi = {10.4230/LIPIcs.OPODIS.2024.37},
annote = {Keywords: Population protocols, Leader election, Loose-stabilization, Self-stabilization}
}
Document
Efficient Algorithms for Demand-Aware Networks and a Connection to Virtual Network Embedding
Abstract
Emerging optical switching technologies enable demand-aware datacenter networks, whose topology can be flexibly optimized toward the traffic they serve. This paper revisits the bounded-degree network design problem underlying such demand-aware networks. Namely, given a distribution over communicating node pairs (represented has a demand graph), we want to design a network with bounded maximum degree (called host graph) that minimizes the expected communication distance.
We improve the understanding of this problem domain by filling several gaps in prior work. First, we present the first practical algorithm for solving this problem on arbitrary instances without violating the degree bound. Our algorithm is based on novel insights obtained from studying a new Steiner node version of the problem, and we report on an extensive empirical evaluation, using several real-world traffic traces from datacenters, finding that our approach results in improved demand-aware network designs. Second, we shed light on the complexity and hardness of the bounded-degree network design problem by formally establishing its NP-completeness for any degree. We use our techniques to improve prior upper bounds for sparse instances.
Finally, we study an intriguing connection between demand-aware network design and the virtual networking embedding problem, and show that the latter cannot be used to approximate the former: there is no universal host graph which can provide a constant approximation for our problem.
Cite as
Aleksander Figiel, Janne H. Korhonen, Neil Olver, and Stefan Schmid. Efficient Algorithms for Demand-Aware Networks and a Connection to Virtual Network Embedding. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 38:1-38:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
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@InProceedings{figiel_et_al:LIPIcs.OPODIS.2024.38,
author = {Figiel, Aleksander and Korhonen, Janne H. and Olver, Neil and Schmid, Stefan},
title = {{Efficient Algorithms for Demand-Aware Networks and a Connection to Virtual Network Embedding}},
booktitle = {28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
pages = {38:1--38:24},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-360-7},
ISSN = {1868-8969},
year = {2025},
volume = {324},
editor = {Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.38},
URN = {urn:nbn:de:0030-drops-225742},
doi = {10.4230/LIPIcs.OPODIS.2024.38},
annote = {Keywords: demand-aware networks, algorithms, virtual network embedding}
}