arXiv subjects

Philippe Quéinnec

Publications and source records attributed to Philippe Quéinnec.

3 recordsLinked to original sources

arXiv2026

A Distributed Computing Framework for Satellite Swarms

The rise of large satellite constellations and Distributed Space Systems (DSS) demands generalized frameworks that enable fault-tolerant, autonomous distributed space applications. Conventional ground-centric command and control does not scale to systems of tens or hundreds of satellites, motivating the adoption of distributed computing. This paper introduces a conceptual distributed computing framework for satellite swarms, covering distributed state, command and control, and scientific mission. As a first validation step, a strongly eventually consistent distributed state service is designed and implemented using Conflict-free Replicated Data Types (CRDT), specifically a Last-Write-Wins Register-based key-value store. The service is evaluated in the context of Space Situational Awareness catalog dissemination across a simulated 66-satellite constellation emulated with GoNetEm. Results show that the CRDT-based approach reduces ground-to-satellite communication from 66 messages to a single uplink per update, with tree traversal matching the total message count of direct uplink. Under concurrent updates, sub-linear inter-satellite message growth is observed as nodes discard outdated versions, further reducing network overhead. These results demonstrate the viability of a CRDT-based distributed state as a scalable and fault-tolerant foundation for satellite swarm applications.

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arXiv2019

Tasks in Modular Proofs of Concurrent Algorithms

Proving correctness of distributed or concurrent algorithms is a mind-challenging and complex process. Slight errors in the reasoning are difficult to find, calling for computer-checked proof systems. In order to build computer-checked proofs with usual tools, such as Coq or TLA+, having sequential specifications of all base objects that are used as building blocks in a given algorithm is a requisite to provide a modular proof built by composition. Alas, many concurrent objects do not have a sequential specification. This article describes a systematic method to transform any task, a specification method that captures concurrent one-shot distributed problems, into a sequential specification involving two calls, Set and Get. This transformation allows system designers to compose proofs, thus providing a framework for modular computer-checked proofs of algorithms designed using tasks and sequential objects as building blocks. The Moir&Anderson implementation of renaming using splitters is an iconic example of such algorithms designed by composition.

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arXiv2018

Characterizing Asynchronous Message-Passing Models Through Rounds

Message-passing models of distributed computing vary along numerous dimensions: degree of synchrony, kind of faults, number of faults... Unfortunately, the sheer number of models and their subtle distinctions hinder our ability to design a general theory of message-passing models. One way out of this conundrum restricts communication to proceed by round. A great variety of message-passing models can then be captured in the Heard-Of model, through predicates on the messages sent in a round and received during or before this round. Then, the issue is to find the most accurate Heard-Of predicate to capture a given model. This is straightforward in synchronous models, because waiting for the upper bound on communication delay ensures that all available messages are received, while not waiting forever. On the other hand, asynchrony allows unbounded message delays. Is there nonetheless a meaningful characterization of asynchronous models by a Heard-Of predicate? We formalize this characterization by introducing Delivered collections: the collections of all messages delivered at each round, whether late or not. Predicates on Delivered collections capture message-passing models. The question is to determine which Heard-Of predicates can be generated by a given Delivered predicate. We answer this by formalizing strategies for when to change round. Thanks to a partial order on these strategies, we also find the "best" strategy for multiple models, where "best" intuitively means it waits for as many messages as possible while not waiting forever. Finally, a strategy for changing round that never blocks a process forever implements a Heard-Of predicate. This allows us to translate the order on strategies into an order on Heard-Of predicates. The characterizing predicate for a model is then the greatest element for that order, if it exists.

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