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.
@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} }
Feedback for Dagstuhl Publishing